Effect of decreasing dietary cation anion difference on feedlot performance, carcass characteristics, and beef tenderness1,2 J. P. Schoonmaker,3 K. T. Korn, K. N. Condron, C. N. Shee, M. C. Claeys, T. D. Nennich, and R. P. Lemenager
ABSTRACT: The manipulation of acid-base balance has been extensively investigated as a means of manipulating Ca homeostasis and managing milk fever in dairy cows. A low dietary cation anion difference (DCAD) increases urinary Ca, blood-ionized Ca, and responsiveness to Ca-homeostatic hormones. Very little attention has been focused on the possibility of using a low dietary DCAD to increase muscle Ca availability, calpain activity, and meat tenderness of beef cattle. Thus, 90 Angus × Simmental crossbred steers were allotted by weight (590.1 ± 2.4 kg) and breed composition (% Simmental) to 3 treatments (6 pens/treatment, 5 steers/ pen) to evaluate the effects of DCAD on beef tenderness. Treatments were initiated 2 wk before slaughter and consisted of 3 DCAD (mEq/100 g) treatments: –16, 0, and +16. Basal diets (DM basis) were 62 to 64% corn, 6 to 9% soybean meal, and 20% corn silage, and were formulated to contain similar concentrations of protein, energy (NEm; NEg), and minerals, with the exception of sodium and chlorine. A commercial chloride ion supple-
ment (PASTURChlor, West Central, Ralston, IA) was added to diets to decrease DCAD and sodium bicarbonate was added to diets to increase DCAD. Performance before initiation of the study did not differ among treatments (P > 0.22). Urine pH did not differ at the initiation of the study (P > 0.57), but did increase at a decreasing rate on d 7 (6.37, 7.69, 8.13) and d 14 (5.68, 7.66, 8.03) of the study as DCAD increased from –16 to 0 to +16, respectively (quadratic, P < 0.02). Gain and gain:feed responded quadratically to DCAD (P < 0.01), increasing from –16 to 0 DCAD and decreasing from 0 to +16 DCAD. Hot carcass weight, dressing percent, fat thickness, LM area, yield grade, marbling score, quality grade distribution, 48 h muscle pH, and Ca content of muscle did not differ among treatments (P > 0.16). In addition, DCAD did not affect Warner-Bratzler shear force among treatments after 7 and 21 d of aging (P > 0.23). Although urine pH was decreased by feeding a –16 DCAD diet, Ca influx into the LM and beef tenderness were not affected by altering the DCAD in finishing beef cattle diets.
Key words: beef cattle, calcium, DCAD, tenderness © 2013 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2013.91:5762–5768 doi:10.2527/jas2013-6525 INTRODUCTION Tenderness has been identified as the single most important factor affecting consumers’ satisfaction and perception of taste (Morgan et al., 1991). Postmortem meat tenderization occurs through myofibrillar proteolysis as a result of intracellular, Ca-dependent proteases, µ- and m-calpain (Koohmaraie et al., 1987). Injection of a Ca chloride solution into beef muscle improves 1Appreciation is extended to employees of the Purdue Beef Research and Teaching Center for help in conducting this research. 2Financial support provided by West Central, Ralston, IA. 3Corresponding author: [email protected] Received March 27, 2013. Accepted October 3, 2013.
tenderness (Wulf et al., 1996). However, the process has not been adopted by the beef packing industry because of cost. Supplementation of supranutritional levels of ≥1 million IU/d of vitamin D3 (D3) for 7 to 10 d before slaughter has been reported to increase muscle Ca, increase activation of calpains, and improve beef tenderness (Montgomery et al., 2000). However, DMI and ADG decrease, and D3 metabolites can accumulate in tissues (Montgomery et al., 2000). Thus, alternative feeding strategies are needed to improve tenderness. Lowering the dietary cation anion difference (DCAD) is an alternative to D3 and Ca chloride that could potentially increase blood Ca and responsiveness to Ca-homeostatic hormones (Block, 1994). Typical feedlot diets range from –2 to +8 mEq/100 g DCAD
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Department of Animal Science, Purdue University, West Lafayette, IN 47907
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MATERIALS AND METHODS Animals and Diets Research protocols using animals followed guidelines in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1998), and were approved by the Purdue Animal Care and Use Committee. Ninety Angus × Simmental cross steers (initial BW = 590.1 ± 2.4 kg), from the Feldun Purdue University herd, were used to determine the effect of DCAD (–16, 0, and +16 meq/100 g DCAD) on performance, carcass characteristics, and beef tenderness. Initial and final BW were determined by weighing steers on 2 consecutive days. Scales (Tru-Test XR3000; Mineral Wells, TX) weighed to the nearest 0.91 (454 kg), and were checked for accuracy at each weigh date. Steers were blocked by BW into 2 groups (heavy and light), allotted by BW and breed composition (% Simmental) to 3 treatments, and randomly assigned to pen within block (5 steers/pen; 3 heavy pens/diet, and 3 light pens/diet), and housed in curtain-sided, slatted-floor finishing barn in 6.1- × 3.3-m pens. Treatments were initiated 14 d before slaughter. Steers in the heavy block began dietary treatments 29 March 2011, and steers in the light block began dietary treatments 17 May 2011. Steers were previously vaccinated against bovine rhinotracheitis, bovine viral diarrhea, parainfluenza-3, bovine respiratory syncytial virus (Bovi-Shield GOLD FP 5; Zoetis, Florham Park, NJ), Haemophilus somnus, Pasteurella, and Clostridia (Vision-7 Somnus; Merck Animal Health, Summit, NJ), treated with an anthelmintic (Valbazen; Pfizer Animal Health) for internal and external parasites, and implanted with Revalor-XS (4 mg estradiol and 20 mg trenbolone acetate; provided courtesy of Merck Animal Health). Diets were formulated to meet or exceed NRC (1996) requirements for protein, energy, vitamins, and minerals. Before initiation of the study, all steers were
Table 1. Composition of diets fed to cattle during the last 14 d before slaughter
Ingredient, % Corn Soybean meal Corn silage Wheat middlings Vitamin/mineral premix2 Limestone Urea PasturChlor3 Magnesium oxide Sodium bicarbonate Nutrient composition4 Crude protein, % NEm, Mcal/kg5 NEg, Mcal/kg5 Calcium, % Phosphorus, % Magnesium, % Potassium, % Sodium, % Chloride, % Sulfur, % DCAD, mEq/kg
–16
DCAD1 treatment 0
+16
62.20 5.70 20.00 2.10 1.74 0.80 0.36 7.10 —– —–
64.45 8.00 20.00 2.10 1.74 0.80 0.36 2.04 0.51 —–
64.46 9.00 20.00 2.10 1.74 0.80 0.36 —– 0.72 0.82
13.24 2.03 1.31 0.92 0.30 0.57 0.64 0.10 0.99 0.14 –160.28
13.27 2.03 1.30 0.93 0.31 0.58 0.68 0.10 0.46 0.14 –0.16
13.25 2.00 1.29 0.93 0.31 0.58 0.69 0.32 0.25 0.14 160.38
1DCAD
= dietary cation anion difference ([Na + K] – [Cl + S]). premix contained (DM basis): 27.22% Ca, 0.44% Mg, 2.68% K, 0.25% S, 7.31 mg/kg Co, 658.76 mg/kg Cu, 33.36 mg/kg I, 751.09 mg/kg Fe, 0.13% Mn, 17.08 mg/kg Se, 0.19% Zn, 130 IU/g vitamin A, 18 IU/g vitamin D, 584 IU/kg vitamin E, 0.98% Rumensin (176.4 g/kg, Elanco Animal Health, Indianapolis, IN), 0.52% Tylan (88.2 g/kg, Elanco Animal Health, Greenfield, IN). 3West Central Cooperative, Ralston, IA. Contained (DM basis): 27.0% CP, 0.44% Ca, 0.33% P, 5.85% Mg, 0.48% K, 0.043% Na, 566 mg/kg Fe, 33 mg/kg Zn, 6 mg/kg Cu, 29 mg/kg Mn, 1.8 mg/kg Mo, 0.33% S, 10.47% Cl. DCAD of –3,020 mEq/kg. 4Analyzed by Sure-Tech Laboratories, Richmond, IN. 5Calculated composition (NRC, 1996). 2Vitamin/mineral
fed a common diet of 55% dry-rolled corn, 20% dry distillers grains with solubles, 20% corn silage, and 5% vitamin/mineral supplement (DM basis) for 109 (heavy block) or 158 d (light block). Treatment diets contained dry-rolled corn, soybean meal, corn silage, and vitamin/ mineral supplement (Table 1). PASTURChlor (West Central; Ralston, IA) or sodium bicarbonate was added to the basal diet to achieve the desired DCAD concentrations. Dietary cation anion difference concentrations of –16, 0, and +16 were chosen to minimize effects on DMI and were based on data of Cho et al. (2006), who reported an effect on tenderness at a –10 DCAD, and on data of Luebbe et al. (2011), who observed that a DCAD between –16 and –45 had similar effects on urine pH and that a DCAD between +16 and +40 had similar effects on urine pH. Because PASTURChlor contains Mg,
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(Luebbe et al., 2011). Negative DCAD diets can increase plasma Ca in cattle and sheep when fed for 10 to 56 d (Jackson et al., 1992; Cho et al., 2006; Las et al., 2007). When fed for 10 d, a DCAD of –10, in combination with 25-hydroxyvitmain D3,was reported to increase calpain mRNA and protein, and improve muscle tenderness in Korean beef cows (Cho et al., 2006). Very little attention has been focused on the possibility of using dietary DCAD, alone, to increase Ca availability and meat tenderness in beef cattle. Thus, our hypothesis was that feeding a negative DCAD diet 14 d before slaughter would improve beef tenderness without negatively affecting ADG or DMI. Our objective was to measure performance, carcass characteristics, including tenderness, and muscle Ca content in cattle fed a range of DCAD diets.
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Carcass Data Collection Steers were transported to a USDA-inspected facility (Tyson, Joslin, IL) for slaughter after 14 d on study. Hot carcass weights were determined immediately after evisceration and fat thickness, KPH, LM area, and USDA quality and yield grades were determined for all cattle by qualified university personnel 24 h after slaughter. Longissimus muscle samples (12th rib to third lumbar vertebra) were collected from the right and left sides of each steer. Longissimus muscle samples were transported on ice to the Purdue University Meat Laboratory where they were cut 2.54 cm thick, vacuum packaged, and aged for 7 or 21 d, before freezing at –20°C for subsequent Warner-Bratzler shear force (WBSF) determinations. Carcass side and anterior or posterior position of the steak were evenly allotted among aging treatments. An additional LM sample, aged 48 h, was collected from all steers in the light block (n = 45) and frozen at –20°C for subsequent analysis of Ca. Warner-Bratzler Shear Force Determination Warner-Bratzler shear force was determined on steaks aged 7 and 21 d, according to standards set by the American Meat Science Association (AMSA, 1995). Steaks were thawed and cooked on an electric, clamshell grill (George Foreman Indoor/Outdoor grill, model GRP99; Miramar, FL) to an internal temperature of 40°C, turned over, and removed from the heat when an internal temperature of 71°C was reached. After cooking, steaks were chilled at 2 to 5°C overnight. From each steak, six to eight 1.27-cm-diameter cores were removed parallel to the muscle fiber orientation and sheared once in the center, perpendicular to the muscle fibers. A texture
analyzer (TA.HDPlus Texture Analyzer; Stable Micro Systems Ltd., Godalming, Surrey, UK) with a WBSF attachment was used at a crosshead speed of 20 cm/min to collect WBSF measurements. Peak measurements were averaged to obtain a single WBSF value for each steak. Longissimus Muscle pH and Calcium Determination Muscle pH was determined on a 5-g subsample of the LM, according to the procedures of Bass et al. (2008). Each sample was diluted 10:1 (wt/vol), with double-distilled, deionized water, and homogenized (Model 1120 Waring Blender; Dynamics Corp., New Hartford, CT). The pH of the homogenate was determined using a pH meter (Model SB70P sympHony pH meter). Muscle Ca was determined on a 5-g subsample of the LM. Approximately 5 g of wet, ground tissue was dried overnight at 100°C. Samples were then ashed at 600°C in a muffle furnace for 16 h. Ashed samples were suspended in 25 mL of 3 N hydrochloric acid and measured in duplicate by diluting 0.5 mL of the hydrochloric acid preparation in 4.5 mL of 0.1% lanthanum chloride solution (100 mM lanthanum chloride, 50 mM HCl). Calcium concentration was determined by flame atomic absorption spectrometry (SpectrAA 220 FS Varian, Agilent Technologies, Santa Clara, CA), using a standard curve of 0, 1, 2, 3, 4, and 5 mg/kg of CaCl2. Statistical Analysis Data were analyzed using the MIXED procedures of SAS (Version 8.0; SAS Inst. Inc., Cary, NC). Pen was the experimental unit with block and pen, nested within treatment, included in the model as random effects. The model included fixed effects of DCAD concentration. Performance data, urine pH, and tenderness were analyzed as repeated measures, and 4 covariance structures were compared for each variable (compound symmetric, autoregressive order 1, heterogeneous autoregressive order 1, and unstructured). The covariance structure that yielded the smallest Bayesian information criterion was used for the results presented. The model included the fixed effects of treatment and day, as well as the appropriate treatment × day interaction. Carcass data were analyzed as a randomized complete block design. Least squares means were computed for all fixed effects and separated, using linear and quadratic coefficients of the DCAD concentration generated by PROC IML when a significant F-test (P < 0.05) was detected. RESULTS AND DISCUSSION The length of time negative DCAD diets need to be fed to induce a urine pH change and a change in Ca ho-
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Mg oxide was added to the 0 and +16 diets to maintain a similar Mg concentration among diets. Dietary cation anion difference of the diets was calculated as (Na + K) – (Cl + S) (mEq/100 g), using feed samples collected 2 wk before initiation of the study. Feed was offered once daily in the morning. Daily feed calls were adjusted to allow for ad libitum feed intake with little or no accumulation of unconsumed feed. Feed refusals were weighed, recorded, and discarded daily. Feed samples were taken every other week, dried in a forced air oven at 60°C for 48 h, and composited for analysis of DM, CP, ADF, NDF, and minerals (Ca, P, Mg, K, Na, Cl, S). Urine was collected from 2 steers/pen on d 0, 7, and 14, via pelvic stimulation into 500-mL plastic bags at ~3 h before feeding, and analyzed for pH (Model SB70P sympHony pH meter; VWR International, Radnor, PA). The pH meter was calibrated using standard solutions of pH 4, 7, and 10, at 20°C.
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meostasis in dairy cows is no more than 4 to 5 d (Goff, 2008). Anion-supplemented diets are generally fed for the last 2 to 3 wk before calving to be effective in increasing Ca in circulation and decreasing milk fever. Thus, DCAD diets in the present study were altered the last 14 d before slaughter. Urine pH for the present study is presented in Fig. 1. Urine pH decreased throughout the study for steers fed a –16 DCAD diet, whereas urine pH for steers fed 0 and +16 DCAD diets did not change throughout the duration of the study (treatment × time; P < 0.05). Urine pH did not differ on d 0 (P > 0.57). By d 7, urine pH (6.37, 7.69, and 8.13, for –16, 0, and +16, respectively) increased 1.3 units from –16 to 0 DCAD and only increased 0.44 unit from 0 to +16 DCAD (quadratic; P = 0.02). On d 14, urine pH (5.68, 7.66, and 8.03, for –16, 0, and +16, respectively) increased 1.98 units from –16 to 0 DCAD and only increased 0.37 units from 0 to +16 (quadratic; P < 0.01). Similarly, Las et al. (2007) reported a drop in urine pH, as well as blood pH, in sheep after 4 d of consuminga negative DCAD diet. McGrath et al. (2013) demonstrated that a –30 DCAD diet fed to beef steers effectively lowered urine pH after 10 d of supplementation and also observed increased urine Ca concentration in steers fed a –30 DCAD diet. Furthermore, Cho et al. (2006) successfully increased blood Ca in beef cows by feeding a negative DCAD diet 6 to 20 d before slaughter. When urine pH falls to between 6.0 and 7.0 through acidification of the diet, the animal responds to the sub-
acute metabolic acidosis by excreting H+ ions in the urine to compensate for acidosis (Jardon, 1995; Pehrson et al., 1999). Horst et al. (1997) proposed that urine pH of 5.5 to 6.2 was indicative of compensated metabolic acidosis. Ingestion of a low DCAD diet increases Ca entry into the exchangeable Ca pool by 3 main mechanisms: enhanced intestinal absorption (Lomba et al., 1978; Schonewille et al., 1994; Roche et al., 2007), increased bone resorption (Block, 1984), and decreased bone accretion (van Mosel et al., 1994), with the latter 2 mechanisms appearing to be active only in the presence of acidemia and metabolic acidosis. However, ingestion of a low DCAD diet also increases Ca exit from the exchangeable Ca pool by decreasing renal tubular Ca reabsorption (Stacy and Wilson, 1970; Fredeen et al., 1988). Performance data are presented in Table 2. Average daily gain, DMI, and gain:feed did not differ (P > 0.46) before initiation of the study. Changes in DCAD during the last 14 d did not affect final BW or DMI (P > 0.23). However, ADG and gain:feed for the 14-d trial period responded quadratically to DCAD (P < 0.01), increasing from the –16 to 0 DCAD diet and decreasing from the 0 to +16 DCAD diet. It is unclear from the present study whether decreases in ADG and DMI were due to cattle adapting to diets or a treatment effect. When hydrochloric acid-treated canola meal was used, DMI of sheep fed a –21 DCAD diet was not affected (Las et al., 2007). Similar to the current study, Las et al. (2007) used a hydrochloric
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Figure 1. Effect of feeding diets that differ in dietary cation anion difference [DCAD; (Na + K) – (Cl + S); mEq/100 g] during the last 14 d before slaughter on urine pH of beef cattle. Within days, points with different superscripts differ (P < 0.05). Treatment × time interaction (P < 0.05).
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Table 2. Effect of feeding diets that differ in dietary cation anion difference (DCAD) during the last 14 d before slaughter on performance DCAD1 treatment –16 0 +16
SEM
P-value Linear Quadratic
BW,2
588.1 597.6
589.6 606.2
592.5 602.3
2.41 3.90
0.22 0.42
0.82 0.23
1.78 0.68
1.76 1.19
1.82 0.71
0.145 0.145
0.86 0.89
0.81 0.01
958.3 140.1
988.2 149.7
978.4 141.7
90.28 89.38
0.88 0.99
0.87 0.94
10.3 10.0
10.7 10.7
10.5 10.1
0.29 0.45
0.58 0.86
0.46 0.29
0.174 0.059
0.164 0.110
0.173 0.063
0.0134 0.0134
0.95 0.84
0.58 0.01
1DCAD = dietary cation anion difference ([Na + K] – [Cl + S], mEq/100 g). 2BW were non-shrunk, taken before feed delivery.
DCAD1 treatment –16 0 +16 Hot carcass wt., kg 368.8 372.9 372.2 Dressing % 61.9 61.5 61.8 Fat thickness, cm 1.24 1.15 1.24 LM area, cm2 85.34 85.88 85.21 Kidney, pelvic, heart fat, % 2.02 1.97 2.00 Adjusted yield grade 2.99 2.89 3.01 Marbling score2 560.2 575.3 587.7 Quality grade distribution Select, % 20.0 16.7 10.8 Choice–, % 58.3 53.3 50.8 Choiceo, % 18.3 13.3 24.2 Choice+, % 3.3 16.7 10.8 Prime, % 0.0 0.0 3.3 Muscle pH 5.43 5.36 5.40 Muscle calcium, μg/g 172.2 186.4 162.4
SEM 1.87 0.28 0.075 1.143 0.01 0.11 14.55
P-value Linear Quadratic 0.22 0.33 0.80 0.41 0.94 0.33 0.94 0.67 0.42 0.03 0.92 0.42 0.20 0.94
5.0 0.22 8.0 0.52 6.1 0.51 5.7 0.37 1.9 0.24 0.03 0.47 17.50 0.61
0.84 0.90 0.31 0.19 0.49 0.16 0.68
1DCAD = dietary cation anion difference ([Na + K] – [Cl + S], mEq/100 g). 2Practically devoid = 300 to 399, slight = 400 to 499, small = 500 to 599, modest = 600 to 699, moderate = 700 to 799.
acid-treated feed (dried distillers grains, soybean meal, rice hulls). In contrast, when attempting to achieve an anionic cattle diet through feeding anionic salts, oftentimes, ADG (Ross et al., 1994a,b; Sexson et al., 2009) and DMI (Ross et al., 1994a,b; Luebbe et al., 2011) decrease over longer periods of time. Thus, a neutral DCAD diet is recommended for optimal feedlot performance (Ross et al., 1994a,b) and typical feedlot diets range from –2 to +8 mEq/100 g (Luebbe et al., 2011). However, mineral acids are more palatable than anionic salts and when used to lower DCAD in dairy cow diets, mineral acids minimize depressions in DMI compared with anionic salts (Goff et al., 1997). Carcass characteristics are presented in Table 3. Hot carcass weight, dressing percent, fat thickness, LM area, yield grade, marbling score, quality grade, and muscle pH did not differ among treatments (P > 0.16). The percentage of kidney, pelvic, and heart fat responded quadratically to DCAD (P = 0.03), decreasing from –16 to 0 DCAD and increasing from 0 to +16 DCAD. Similar to the present study, Cho et al. (2006) demonstrated that an anionic diet in combination with vitamin D did not impact carcass characteristics. Luebbe et al. (2011) reported that a –16 DCAD diet fed for 145 or 196 d did not impact hot carcass weight or fat thickness, compared with a +20 DCAD diet. However, Luebbe et al. (2011) observed that in calves fed for 196 d during winter, the LM area increased and yield grade decreased by feeding a –16 DCAD compared with feeding a +20 DCAD diet for 196 d. Luebbe et al. (2011) also reported that in yearlings fed for 145 d during summer, a –16 DCAD diet decreased marbling score compared with a +20 DCAD diet. Ross et al. (1994a) re-
ported that cationic diets increased marbling scores and did not affect any other carcass characteristics. Damir et al. (1990) reported that lambs fed a basal diet had similar protein but lower fat and energy in their carcasses, compared with lambs fed an anionic or cationic diet. In dairy cows, positive DCAD diets have been reported to increase milk fat and milk protein (Hu et al., 2007). Increases in milk fat as a result of increasing DCAD, are thought to be, in part, due to the ability of sodium bicarbonate to increase rumen pH, which increases fiber digestion and ruminal VFA production. Increased VFA then results in increased de novo synthesis of fatty acids in the mammary gland. It is possible that previous studies demonstrating an increase of marbling in steers fed positive DCAD could be a result of increased ruminal production of VFA. An increase in % KPH from 0 to +16 DCAD in the present study supports the concept that sodium bicarbonate increased production of substrates for fatty acid synthesis. However, the fact that we only observed a numerical increase in marbling with increasing DCAD indicates that 14 d is not long enough to enhance marbling deposition. Longissimus muscle pH (P > 0.16), Ca content of LM (P > 0.61), and tenderness (P > 0.34) after 7 or 14 d of aging (Fig. 2) did not differ among treatments in the current study. Ross et al. (1994a) and Cho et al. (2006) also reported that although anionic diets increased plasma Ca, anionic diets did not alter muscle Ca in beef cattle. Nonetheless, Cho et al. (2006) observed that DCAD and vitamin D increased calpain activity and improved beef tenderness. Increasing LM Ca through dietary means has
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kg Start Slaughter ADG, kg/d Pre-study Study Total DMI, kg Pre-study Study Daily DMI, kg/d Pre-study Study Gain:feed, kg/kg Pre-study Study
Table 3. Effect of feeding diets that differ in dietary cation anion difference (DCAD) during the last 14 d before slaughter on carcass characteristics, muscle pH, and muscle calcium content
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the potential to improve LM tenderness. Like DCAD diets, Ca propionate gel administration increases intestinal absorption of Ca into the bloodstream of nonlactating Holstein cows (Goff and Horst 1993). In fact, orally administering Ca propionate 3 to 6 h before slaughter has been demonstrated to increase LM Ca and calpain activity, and improve tenderness in beef aged 4 and 7 d, when compared with LM from cattle not drenched with Ca propionate (Duckett et al., 2001). The fact that LM pH and Ca were not altered by DCAD in the present study suggests that the body is very good at maintaining homeostasis in regard to tissue pH and ion concentrations. Blood pH is ultimately determined by the number of cations and anions in the blood. If more anions than cations enter the bloodstream from the digestive tract, blood and urine pH will decrease. Exhalation of carbon dioxide, lactate production by muscles, and excretion of acid or ammonium salts by the kidney tightly regulate blood pH (Harmon, 1996) to stay within a narrow range of 7.3 to 7.5, making it slightly alkaline (Swenson, 1993). Thus, urine pH is one of the most sensitive indicators of acid-base homeostasis (Constable et al., 2009). The fact that LM pH was not altered by anionic diets supports the concept that tissue homeostasis was maintained, despite differences in DCAD. Calcium homeostasis is also precisely regulated in circulation and skeletal muscle by the action of many hormones (e.g., parathyroid hormone and 1,25 dihydroxyvitamin D). The interaction between these hormones and proteins
help maintain total serum Ca levels in healthy individuals within a relatively narrow physiologic range of 10% (Peacock, 2010). Furthermore, ingestion of a low DCAD diet can increase Ca exit from the exchangeable Ca pool by decreasing renal tubular Ca reabsorption (Stacy and Wilson, 1970; Fredeen et al., 1988), potentially decreasing LM Ca. The fact that LM Ca was not altered in the present study suggests that any potential improvements in increased Ca absorption due to negative DCAD may have been ameliorated by decreased renal Ca reabsorption. Conclusions Our current study suggests that lowering DCAD to –16 mEq/100 g can decrease urine pH. However, lowering DCAD to –16 mEq/100 g may inhibit ADG and did not improve beef tenderness. It is possible that homeostatic mechanisms that maintain muscle pH and Ca content could not be altered enough to have an effect on proteolytic enzymes. Therefore, the results of this experiment suggest that decreasing DCAD negatively impacts ADG without increasing muscle Ca or enhancing beef tenderness. LITERATURE CITED AMSA. 1995. Research guidelines for cookery, sensory evaluation and instrumental measurements of fresh meat. Am. Meat Sci. Assoc. Natl. Livest. Meat Board, Chicago, IL.
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Figure 2. Effect of feeding diets that differ in dietary cation anion difference [DCAD; (Na + K) – (Cl + S); mEq/100 g] during the last 14 d before slaughter on Warner Bratzler shear force in beef steaks. No dietary treatment differences detected on d 7 (P = 0.57) or 21 (P = 0.34).
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Schoonmaker et al. Las, J. E., N. E. Odongo, M. I. Lindinger, O. AlZahal, A. K. Shoveller, J. C. Matthews, and B. W. McBride. 2007. Effects of dietary strong anion challenge on regulation of acid-base balance in sheep. J. Anim. Sci. 85:2222–2229. Lomba, F., G. Chauvaux, E. Teller, L. Lingele, and V. Bienfet. 1978. Calcium digestibility in cows as influenced by the excess of alkaline ions over stable acid ions in their diets. Br. J. Nutr. 39:425–429. Luebbe, M. K., G. E. Erickson, T. J. Klopfenstein, M. A. Greenquist, and J. R. Benton. 2011. Effect of dietary cation-anion difference on urinary pH, feedlot performance, nitrogen mass balance, and manure pH in open feedlot pens. J. Anim. Sci. 89:489–500. McGrath, J. J., D. B. Savage, J. V. Nolan, N. J. Rodgers, and R. Elliott. 2013. Anionic salts and dietary 25-hydroxyvitamin D stimulate calcium availability in steers. Animal 7:404–409. Montgomery, J. L., F. C. Parrish, Jr., D. C. Beitz, R. L. Horst, E. J. Huff-Lonergan, and A. H. Trenkle. 2000. The use of vitamin D3 to improve beef tenderness. J. Anim. Sci. 78:2615–2621. Morgan, J. B., J. W. Savell, D. S. Hale, R. K. Miller, D. B. Griffin, H. R. Cross, and S. D. Shackelford. 1991. National beef tenderness survey. J. Anim. Sci. 69:3274–3283. NRC. 1996. Nutrient requirements of beef cattle. 7th rev. ed. Natl. Acad. Press, Washington, DC. Peacock, M. 2010. Calcium metabolism in health and disease. Clin. J. Am. Soc. Nephrol. 5:S23–S30. Pehrson, B., C. Svensson, I. Gruvaeus, and M. Virkkim. 1999. The influence of acidic diets on the acid-base balance of dry cows and the effect of fertilization on the mineral content of grass. J. Dairy Sci. 82:1310–1316. Roche, J. R., D. E. Dalley, and F. P. O’Mara. 2007. Effect of a metabolically created systemic acidosis on calcium homeostasis and the diurnal variation in urine pH on the non- lactating pregnant dairy cow. J. Dairy Res. 74:34–39. Ross, J. G., J. W. Spears, and J. D. Garlich. 1994a. Dietary electrolyte balance effects on performance and metabolic characteristics in growing steers. J. Anim. Sci. 72:1842–1848. Ross, J. G., J. W. Spears, and J. D. Garlich. 1994b. Dietary electrolyte balance effects on performance and metabolism characteristics in finishing steers. J. Anim. Sci. 72:1600–1607. Schonewille, J. T., A. T. Vantklooster, A. Dirkzwager, and A. C. Beynen. 1994. Stimulatory effect of an anion (chloride)-rich ration on apparent calcium absorption in dairy cows. Livest. Prod. Sci. 40:233–240. Sexson, J. L., J. J. Wagner, T. E. Engle, and J. W. Spears. 2009. Effects of water quality and dietary potassium on performance and carcass characteristics of yearling steers. J. Anim. Sci. 88:296–305. Stacy, B. D., and B. W. Wilson. 1970. Acidosis and hypercalciuria: Renal mechanisms affecting calcium, magnesium and sodium excretion in the sheep. J. Physiol. 210:549–564. Swenson, M. J. 1993. Physiological properties and cellular and chemical constituents of blood. In: M. J. Swenson and W. O. Reece, editors, Duke’s physiology of domestic animals. 11th ed. Cornell Univ. Press, Ithaca, NY. p. 22–48. van Mosel, M., H. S. Wouterse, and A. T. Vantklooster. 1994. Effects of reducing dietary ([Na+ + K+]-[Cl- + SO4 =]) on bone in dairy cows at parturition. Res. Vet. Sci. 56:270–276. Wulf, D. M., J. B. Morgan, J. D. Tatum, and G .C. Smith. 1996. Effect of animal age, marbling score, calpastatin activity, subprimal cut, calcium injection, and degree of doneness on the palatability of steaks from limousin steers. J. Anim. Sci. 74:569–576.
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Bass, P. D., J. A. Scanga, P. L. Chapman, G. C. Smith, J. D. Tatum, and K. E. Belk. 2008. Recovering value from beef carcasses classified as dark cutters by the United States Department of Agriculture graders. J. Anim. Sci. 86:1658–1668. Block, E. 1984. Manipulating dietary anions and cations for prepartum dairy cows to reduce incidence of milk fever. J. Dairy Sci. 67:2939–2984. Block, E. 1994. Manipulation of dietary cation-anion difference on nutritionally related production diseases, productivity, and metabolic responses of dairy cows. J. Dairy Sci. 77:1437–1450. Cho, Y. M., H. Choi, I. H. Hwang, Y. K. Kim, and K. H. Myung. 2006. Effects of 25-hydroxyvitamin D3 and manipulated dietary cation-anion difference on the tenderness of beef from cull native Korean cows. J. Anim. Sci. 84:1481–1488. Constable, P. D., C. C. Gelfert, M. Furll, R. Staufenbiel, and H. Stampfli. 2009. Application of strong ion difference theory to urine and the relationship between urine pH and net acid excretion in cattle. Am. J. Vet. Res. 70:915–925. Damir, H. A., D. Scott, J. K. Thomson, J. G. Topps, W. Buchan, and K. Pennie. 1990. The effect of a change in blood acid-base status on body composition and mineral retention in growing lambs. Anim. Prod. 51:527–534. Duckett, S. K., J. G. Andrae, G. T. Pritchard, T. A. Skow, S. L. Cuvala, J. H. Thorngate, and W. K. Sanchez. 2001. Effects of pre-slaughter administration of oral calcium gel to beef cattle on tenderness. Can. J. Anim. Sci. 81:33–38. FASS. 1998. Guide for the care and use of agricultural animals in agricultural research and teaching. Fed. Anim. Sci. Soc., Champaign, IL. Fredeen, A. H., E. J. DePeters, and R. L. Baldwin. 1988. Character ization of acid-base disturbances and effects on calcium and phosphorus balances of dietary fixed ions in pregnant or lactating does. J. Anim. Sci. 66:159–173. Goff, J. P. 2008. The monitoring, prevention, and treatment of milk fever and subclinical hypocalcemia in dairy cows. Vet. J. 176:50–57. Goff, J. P., and R. L. Horst. 1993. Oral administration of calcium slats for treatment of hypocalcemia in cattle. J. Dairy Sci. 76:101–108. Goff, J. P., R. Ruiz, and R. L. Horst. 1997. Relative acidogenic activity of commonly used anionic salts—Rethinking the dietary cation-anion difference equations. J. Dairy Sci. 80(Suppl. 1):169. Harmon, D. 1996. Sudden feedlot deaths: Are pen deads due to ruminal or systemic dysfunction or a combination of both? In: Scientific update on Rumensin/Tylan/Mycotil for the professional feedlot consultant. Elanco Animal Health, Indianapolis, IN. p. L1–L6. Horst, R. L., J. P. Goff, T. A. Reinhardt, and D. R. Buxton. 1997. Strategies for preventing milk fever in dairy cattle. J. Dairy Sci. 80:1269–1280. Hu, W., M. R. Murphy, P. Constable, and E. Block. 2007. Dietary cation-anion difference effects on performance and acid-base status of dairy cows postpartum. J. Dairy Sci. 90:3367–3375. Jackson, J. A., D. M. Hopkins, Z. Xin, and R. W. Hemken. 1992. Influence of cation-anion balance on feed intake, body weight gain, and humoral response of dairy calves. J. Dairy Sci. 75:1281–1286. Jardon, P. W. 1995. Using urine pH to monitor anionic salt programs. Compend. Contin. Educ. Pract. Vet. 17:860–862. Koohmaraie, M., S. C. Seideman, J. E. Schollmeyer, T. R. Dutson, and J. D. Crouse. 1987. Effect of postmortem storage on Ca++ dependent proteases, their inhibitor and myofibril fragmentation. Meat Sci. 19:187–196.
ABSTRACT: The manipulation of acid-base balance has been extensively investigated as a means of manipulating Ca homeostasis and managing milk fever in dairy cows. A low dietary cation anion difference (DCAD) increases urinary Ca, blood-ionized Ca, and responsiveness to Ca-homeostatic hormones. Very little attention has been focused on the possibility of using a low dietary DCAD to increase muscle Ca availability, calpain activity, and meat tenderness of beef cattle. Thus, 90 Angus × Simmental crossbred steers were allotted by weight (590.1 ± 2.4 kg) and breed composition (% Simmental) to 3 treatments (6 pens/treatment, 5 steers/ pen) to evaluate the effects of DCAD on beef tenderness. Treatments were initiated 2 wk before slaughter and consisted of 3 DCAD (mEq/100 g) treatments: –16, 0, and +16. Basal diets (DM basis) were 62 to 64% corn, 6 to 9% soybean meal, and 20% corn silage, and were formulated to contain similar concentrations of protein, energy (NEm; NEg), and minerals, with the exception of sodium and chlorine. A commercial chloride ion supple-
ment (PASTURChlor, West Central, Ralston, IA) was added to diets to decrease DCAD and sodium bicarbonate was added to diets to increase DCAD. Performance before initiation of the study did not differ among treatments (P > 0.22). Urine pH did not differ at the initiation of the study (P > 0.57), but did increase at a decreasing rate on d 7 (6.37, 7.69, 8.13) and d 14 (5.68, 7.66, 8.03) of the study as DCAD increased from –16 to 0 to +16, respectively (quadratic, P < 0.02). Gain and gain:feed responded quadratically to DCAD (P < 0.01), increasing from –16 to 0 DCAD and decreasing from 0 to +16 DCAD. Hot carcass weight, dressing percent, fat thickness, LM area, yield grade, marbling score, quality grade distribution, 48 h muscle pH, and Ca content of muscle did not differ among treatments (P > 0.16). In addition, DCAD did not affect Warner-Bratzler shear force among treatments after 7 and 21 d of aging (P > 0.23). Although urine pH was decreased by feeding a –16 DCAD diet, Ca influx into the LM and beef tenderness were not affected by altering the DCAD in finishing beef cattle diets.
Key words: beef cattle, calcium, DCAD, tenderness © 2013 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2013.91:5762–5768 doi:10.2527/jas2013-6525 INTRODUCTION Tenderness has been identified as the single most important factor affecting consumers’ satisfaction and perception of taste (Morgan et al., 1991). Postmortem meat tenderization occurs through myofibrillar proteolysis as a result of intracellular, Ca-dependent proteases, µ- and m-calpain (Koohmaraie et al., 1987). Injection of a Ca chloride solution into beef muscle improves 1Appreciation is extended to employees of the Purdue Beef Research and Teaching Center for help in conducting this research. 2Financial support provided by West Central, Ralston, IA. 3Corresponding author: [email protected] Received March 27, 2013. Accepted October 3, 2013.
tenderness (Wulf et al., 1996). However, the process has not been adopted by the beef packing industry because of cost. Supplementation of supranutritional levels of ≥1 million IU/d of vitamin D3 (D3) for 7 to 10 d before slaughter has been reported to increase muscle Ca, increase activation of calpains, and improve beef tenderness (Montgomery et al., 2000). However, DMI and ADG decrease, and D3 metabolites can accumulate in tissues (Montgomery et al., 2000). Thus, alternative feeding strategies are needed to improve tenderness. Lowering the dietary cation anion difference (DCAD) is an alternative to D3 and Ca chloride that could potentially increase blood Ca and responsiveness to Ca-homeostatic hormones (Block, 1994). Typical feedlot diets range from –2 to +8 mEq/100 g DCAD
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Department of Animal Science, Purdue University, West Lafayette, IN 47907
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MATERIALS AND METHODS Animals and Diets Research protocols using animals followed guidelines in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1998), and were approved by the Purdue Animal Care and Use Committee. Ninety Angus × Simmental cross steers (initial BW = 590.1 ± 2.4 kg), from the Feldun Purdue University herd, were used to determine the effect of DCAD (–16, 0, and +16 meq/100 g DCAD) on performance, carcass characteristics, and beef tenderness. Initial and final BW were determined by weighing steers on 2 consecutive days. Scales (Tru-Test XR3000; Mineral Wells, TX) weighed to the nearest 0.91 (454 kg), and were checked for accuracy at each weigh date. Steers were blocked by BW into 2 groups (heavy and light), allotted by BW and breed composition (% Simmental) to 3 treatments, and randomly assigned to pen within block (5 steers/pen; 3 heavy pens/diet, and 3 light pens/diet), and housed in curtain-sided, slatted-floor finishing barn in 6.1- × 3.3-m pens. Treatments were initiated 14 d before slaughter. Steers in the heavy block began dietary treatments 29 March 2011, and steers in the light block began dietary treatments 17 May 2011. Steers were previously vaccinated against bovine rhinotracheitis, bovine viral diarrhea, parainfluenza-3, bovine respiratory syncytial virus (Bovi-Shield GOLD FP 5; Zoetis, Florham Park, NJ), Haemophilus somnus, Pasteurella, and Clostridia (Vision-7 Somnus; Merck Animal Health, Summit, NJ), treated with an anthelmintic (Valbazen; Pfizer Animal Health) for internal and external parasites, and implanted with Revalor-XS (4 mg estradiol and 20 mg trenbolone acetate; provided courtesy of Merck Animal Health). Diets were formulated to meet or exceed NRC (1996) requirements for protein, energy, vitamins, and minerals. Before initiation of the study, all steers were
Table 1. Composition of diets fed to cattle during the last 14 d before slaughter
Ingredient, % Corn Soybean meal Corn silage Wheat middlings Vitamin/mineral premix2 Limestone Urea PasturChlor3 Magnesium oxide Sodium bicarbonate Nutrient composition4 Crude protein, % NEm, Mcal/kg5 NEg, Mcal/kg5 Calcium, % Phosphorus, % Magnesium, % Potassium, % Sodium, % Chloride, % Sulfur, % DCAD, mEq/kg
–16
DCAD1 treatment 0
+16
62.20 5.70 20.00 2.10 1.74 0.80 0.36 7.10 —– —–
64.45 8.00 20.00 2.10 1.74 0.80 0.36 2.04 0.51 —–
64.46 9.00 20.00 2.10 1.74 0.80 0.36 —– 0.72 0.82
13.24 2.03 1.31 0.92 0.30 0.57 0.64 0.10 0.99 0.14 –160.28
13.27 2.03 1.30 0.93 0.31 0.58 0.68 0.10 0.46 0.14 –0.16
13.25 2.00 1.29 0.93 0.31 0.58 0.69 0.32 0.25 0.14 160.38
1DCAD
= dietary cation anion difference ([Na + K] – [Cl + S]). premix contained (DM basis): 27.22% Ca, 0.44% Mg, 2.68% K, 0.25% S, 7.31 mg/kg Co, 658.76 mg/kg Cu, 33.36 mg/kg I, 751.09 mg/kg Fe, 0.13% Mn, 17.08 mg/kg Se, 0.19% Zn, 130 IU/g vitamin A, 18 IU/g vitamin D, 584 IU/kg vitamin E, 0.98% Rumensin (176.4 g/kg, Elanco Animal Health, Indianapolis, IN), 0.52% Tylan (88.2 g/kg, Elanco Animal Health, Greenfield, IN). 3West Central Cooperative, Ralston, IA. Contained (DM basis): 27.0% CP, 0.44% Ca, 0.33% P, 5.85% Mg, 0.48% K, 0.043% Na, 566 mg/kg Fe, 33 mg/kg Zn, 6 mg/kg Cu, 29 mg/kg Mn, 1.8 mg/kg Mo, 0.33% S, 10.47% Cl. DCAD of –3,020 mEq/kg. 4Analyzed by Sure-Tech Laboratories, Richmond, IN. 5Calculated composition (NRC, 1996). 2Vitamin/mineral
fed a common diet of 55% dry-rolled corn, 20% dry distillers grains with solubles, 20% corn silage, and 5% vitamin/mineral supplement (DM basis) for 109 (heavy block) or 158 d (light block). Treatment diets contained dry-rolled corn, soybean meal, corn silage, and vitamin/ mineral supplement (Table 1). PASTURChlor (West Central; Ralston, IA) or sodium bicarbonate was added to the basal diet to achieve the desired DCAD concentrations. Dietary cation anion difference concentrations of –16, 0, and +16 were chosen to minimize effects on DMI and were based on data of Cho et al. (2006), who reported an effect on tenderness at a –10 DCAD, and on data of Luebbe et al. (2011), who observed that a DCAD between –16 and –45 had similar effects on urine pH and that a DCAD between +16 and +40 had similar effects on urine pH. Because PASTURChlor contains Mg,
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(Luebbe et al., 2011). Negative DCAD diets can increase plasma Ca in cattle and sheep when fed for 10 to 56 d (Jackson et al., 1992; Cho et al., 2006; Las et al., 2007). When fed for 10 d, a DCAD of –10, in combination with 25-hydroxyvitmain D3,was reported to increase calpain mRNA and protein, and improve muscle tenderness in Korean beef cows (Cho et al., 2006). Very little attention has been focused on the possibility of using dietary DCAD, alone, to increase Ca availability and meat tenderness in beef cattle. Thus, our hypothesis was that feeding a negative DCAD diet 14 d before slaughter would improve beef tenderness without negatively affecting ADG or DMI. Our objective was to measure performance, carcass characteristics, including tenderness, and muscle Ca content in cattle fed a range of DCAD diets.
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Carcass Data Collection Steers were transported to a USDA-inspected facility (Tyson, Joslin, IL) for slaughter after 14 d on study. Hot carcass weights were determined immediately after evisceration and fat thickness, KPH, LM area, and USDA quality and yield grades were determined for all cattle by qualified university personnel 24 h after slaughter. Longissimus muscle samples (12th rib to third lumbar vertebra) were collected from the right and left sides of each steer. Longissimus muscle samples were transported on ice to the Purdue University Meat Laboratory where they were cut 2.54 cm thick, vacuum packaged, and aged for 7 or 21 d, before freezing at –20°C for subsequent Warner-Bratzler shear force (WBSF) determinations. Carcass side and anterior or posterior position of the steak were evenly allotted among aging treatments. An additional LM sample, aged 48 h, was collected from all steers in the light block (n = 45) and frozen at –20°C for subsequent analysis of Ca. Warner-Bratzler Shear Force Determination Warner-Bratzler shear force was determined on steaks aged 7 and 21 d, according to standards set by the American Meat Science Association (AMSA, 1995). Steaks were thawed and cooked on an electric, clamshell grill (George Foreman Indoor/Outdoor grill, model GRP99; Miramar, FL) to an internal temperature of 40°C, turned over, and removed from the heat when an internal temperature of 71°C was reached. After cooking, steaks were chilled at 2 to 5°C overnight. From each steak, six to eight 1.27-cm-diameter cores were removed parallel to the muscle fiber orientation and sheared once in the center, perpendicular to the muscle fibers. A texture
analyzer (TA.HDPlus Texture Analyzer; Stable Micro Systems Ltd., Godalming, Surrey, UK) with a WBSF attachment was used at a crosshead speed of 20 cm/min to collect WBSF measurements. Peak measurements were averaged to obtain a single WBSF value for each steak. Longissimus Muscle pH and Calcium Determination Muscle pH was determined on a 5-g subsample of the LM, according to the procedures of Bass et al. (2008). Each sample was diluted 10:1 (wt/vol), with double-distilled, deionized water, and homogenized (Model 1120 Waring Blender; Dynamics Corp., New Hartford, CT). The pH of the homogenate was determined using a pH meter (Model SB70P sympHony pH meter). Muscle Ca was determined on a 5-g subsample of the LM. Approximately 5 g of wet, ground tissue was dried overnight at 100°C. Samples were then ashed at 600°C in a muffle furnace for 16 h. Ashed samples were suspended in 25 mL of 3 N hydrochloric acid and measured in duplicate by diluting 0.5 mL of the hydrochloric acid preparation in 4.5 mL of 0.1% lanthanum chloride solution (100 mM lanthanum chloride, 50 mM HCl). Calcium concentration was determined by flame atomic absorption spectrometry (SpectrAA 220 FS Varian, Agilent Technologies, Santa Clara, CA), using a standard curve of 0, 1, 2, 3, 4, and 5 mg/kg of CaCl2. Statistical Analysis Data were analyzed using the MIXED procedures of SAS (Version 8.0; SAS Inst. Inc., Cary, NC). Pen was the experimental unit with block and pen, nested within treatment, included in the model as random effects. The model included fixed effects of DCAD concentration. Performance data, urine pH, and tenderness were analyzed as repeated measures, and 4 covariance structures were compared for each variable (compound symmetric, autoregressive order 1, heterogeneous autoregressive order 1, and unstructured). The covariance structure that yielded the smallest Bayesian information criterion was used for the results presented. The model included the fixed effects of treatment and day, as well as the appropriate treatment × day interaction. Carcass data were analyzed as a randomized complete block design. Least squares means were computed for all fixed effects and separated, using linear and quadratic coefficients of the DCAD concentration generated by PROC IML when a significant F-test (P < 0.05) was detected. RESULTS AND DISCUSSION The length of time negative DCAD diets need to be fed to induce a urine pH change and a change in Ca ho-
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Mg oxide was added to the 0 and +16 diets to maintain a similar Mg concentration among diets. Dietary cation anion difference of the diets was calculated as (Na + K) – (Cl + S) (mEq/100 g), using feed samples collected 2 wk before initiation of the study. Feed was offered once daily in the morning. Daily feed calls were adjusted to allow for ad libitum feed intake with little or no accumulation of unconsumed feed. Feed refusals were weighed, recorded, and discarded daily. Feed samples were taken every other week, dried in a forced air oven at 60°C for 48 h, and composited for analysis of DM, CP, ADF, NDF, and minerals (Ca, P, Mg, K, Na, Cl, S). Urine was collected from 2 steers/pen on d 0, 7, and 14, via pelvic stimulation into 500-mL plastic bags at ~3 h before feeding, and analyzed for pH (Model SB70P sympHony pH meter; VWR International, Radnor, PA). The pH meter was calibrated using standard solutions of pH 4, 7, and 10, at 20°C.
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meostasis in dairy cows is no more than 4 to 5 d (Goff, 2008). Anion-supplemented diets are generally fed for the last 2 to 3 wk before calving to be effective in increasing Ca in circulation and decreasing milk fever. Thus, DCAD diets in the present study were altered the last 14 d before slaughter. Urine pH for the present study is presented in Fig. 1. Urine pH decreased throughout the study for steers fed a –16 DCAD diet, whereas urine pH for steers fed 0 and +16 DCAD diets did not change throughout the duration of the study (treatment × time; P < 0.05). Urine pH did not differ on d 0 (P > 0.57). By d 7, urine pH (6.37, 7.69, and 8.13, for –16, 0, and +16, respectively) increased 1.3 units from –16 to 0 DCAD and only increased 0.44 unit from 0 to +16 DCAD (quadratic; P = 0.02). On d 14, urine pH (5.68, 7.66, and 8.03, for –16, 0, and +16, respectively) increased 1.98 units from –16 to 0 DCAD and only increased 0.37 units from 0 to +16 (quadratic; P < 0.01). Similarly, Las et al. (2007) reported a drop in urine pH, as well as blood pH, in sheep after 4 d of consuminga negative DCAD diet. McGrath et al. (2013) demonstrated that a –30 DCAD diet fed to beef steers effectively lowered urine pH after 10 d of supplementation and also observed increased urine Ca concentration in steers fed a –30 DCAD diet. Furthermore, Cho et al. (2006) successfully increased blood Ca in beef cows by feeding a negative DCAD diet 6 to 20 d before slaughter. When urine pH falls to between 6.0 and 7.0 through acidification of the diet, the animal responds to the sub-
acute metabolic acidosis by excreting H+ ions in the urine to compensate for acidosis (Jardon, 1995; Pehrson et al., 1999). Horst et al. (1997) proposed that urine pH of 5.5 to 6.2 was indicative of compensated metabolic acidosis. Ingestion of a low DCAD diet increases Ca entry into the exchangeable Ca pool by 3 main mechanisms: enhanced intestinal absorption (Lomba et al., 1978; Schonewille et al., 1994; Roche et al., 2007), increased bone resorption (Block, 1984), and decreased bone accretion (van Mosel et al., 1994), with the latter 2 mechanisms appearing to be active only in the presence of acidemia and metabolic acidosis. However, ingestion of a low DCAD diet also increases Ca exit from the exchangeable Ca pool by decreasing renal tubular Ca reabsorption (Stacy and Wilson, 1970; Fredeen et al., 1988). Performance data are presented in Table 2. Average daily gain, DMI, and gain:feed did not differ (P > 0.46) before initiation of the study. Changes in DCAD during the last 14 d did not affect final BW or DMI (P > 0.23). However, ADG and gain:feed for the 14-d trial period responded quadratically to DCAD (P < 0.01), increasing from the –16 to 0 DCAD diet and decreasing from the 0 to +16 DCAD diet. It is unclear from the present study whether decreases in ADG and DMI were due to cattle adapting to diets or a treatment effect. When hydrochloric acid-treated canola meal was used, DMI of sheep fed a –21 DCAD diet was not affected (Las et al., 2007). Similar to the current study, Las et al. (2007) used a hydrochloric
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Figure 1. Effect of feeding diets that differ in dietary cation anion difference [DCAD; (Na + K) – (Cl + S); mEq/100 g] during the last 14 d before slaughter on urine pH of beef cattle. Within days, points with different superscripts differ (P < 0.05). Treatment × time interaction (P < 0.05).
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Table 2. Effect of feeding diets that differ in dietary cation anion difference (DCAD) during the last 14 d before slaughter on performance DCAD1 treatment –16 0 +16
SEM
P-value Linear Quadratic
BW,2
588.1 597.6
589.6 606.2
592.5 602.3
2.41 3.90
0.22 0.42
0.82 0.23
1.78 0.68
1.76 1.19
1.82 0.71
0.145 0.145
0.86 0.89
0.81 0.01
958.3 140.1
988.2 149.7
978.4 141.7
90.28 89.38
0.88 0.99
0.87 0.94
10.3 10.0
10.7 10.7
10.5 10.1
0.29 0.45
0.58 0.86
0.46 0.29
0.174 0.059
0.164 0.110
0.173 0.063
0.0134 0.0134
0.95 0.84
0.58 0.01
1DCAD = dietary cation anion difference ([Na + K] – [Cl + S], mEq/100 g). 2BW were non-shrunk, taken before feed delivery.
DCAD1 treatment –16 0 +16 Hot carcass wt., kg 368.8 372.9 372.2 Dressing % 61.9 61.5 61.8 Fat thickness, cm 1.24 1.15 1.24 LM area, cm2 85.34 85.88 85.21 Kidney, pelvic, heart fat, % 2.02 1.97 2.00 Adjusted yield grade 2.99 2.89 3.01 Marbling score2 560.2 575.3 587.7 Quality grade distribution Select, % 20.0 16.7 10.8 Choice–, % 58.3 53.3 50.8 Choiceo, % 18.3 13.3 24.2 Choice+, % 3.3 16.7 10.8 Prime, % 0.0 0.0 3.3 Muscle pH 5.43 5.36 5.40 Muscle calcium, μg/g 172.2 186.4 162.4
SEM 1.87 0.28 0.075 1.143 0.01 0.11 14.55
P-value Linear Quadratic 0.22 0.33 0.80 0.41 0.94 0.33 0.94 0.67 0.42 0.03 0.92 0.42 0.20 0.94
5.0 0.22 8.0 0.52 6.1 0.51 5.7 0.37 1.9 0.24 0.03 0.47 17.50 0.61
0.84 0.90 0.31 0.19 0.49 0.16 0.68
1DCAD = dietary cation anion difference ([Na + K] – [Cl + S], mEq/100 g). 2Practically devoid = 300 to 399, slight = 400 to 499, small = 500 to 599, modest = 600 to 699, moderate = 700 to 799.
acid-treated feed (dried distillers grains, soybean meal, rice hulls). In contrast, when attempting to achieve an anionic cattle diet through feeding anionic salts, oftentimes, ADG (Ross et al., 1994a,b; Sexson et al., 2009) and DMI (Ross et al., 1994a,b; Luebbe et al., 2011) decrease over longer periods of time. Thus, a neutral DCAD diet is recommended for optimal feedlot performance (Ross et al., 1994a,b) and typical feedlot diets range from –2 to +8 mEq/100 g (Luebbe et al., 2011). However, mineral acids are more palatable than anionic salts and when used to lower DCAD in dairy cow diets, mineral acids minimize depressions in DMI compared with anionic salts (Goff et al., 1997). Carcass characteristics are presented in Table 3. Hot carcass weight, dressing percent, fat thickness, LM area, yield grade, marbling score, quality grade, and muscle pH did not differ among treatments (P > 0.16). The percentage of kidney, pelvic, and heart fat responded quadratically to DCAD (P = 0.03), decreasing from –16 to 0 DCAD and increasing from 0 to +16 DCAD. Similar to the present study, Cho et al. (2006) demonstrated that an anionic diet in combination with vitamin D did not impact carcass characteristics. Luebbe et al. (2011) reported that a –16 DCAD diet fed for 145 or 196 d did not impact hot carcass weight or fat thickness, compared with a +20 DCAD diet. However, Luebbe et al. (2011) observed that in calves fed for 196 d during winter, the LM area increased and yield grade decreased by feeding a –16 DCAD compared with feeding a +20 DCAD diet for 196 d. Luebbe et al. (2011) also reported that in yearlings fed for 145 d during summer, a –16 DCAD diet decreased marbling score compared with a +20 DCAD diet. Ross et al. (1994a) re-
ported that cationic diets increased marbling scores and did not affect any other carcass characteristics. Damir et al. (1990) reported that lambs fed a basal diet had similar protein but lower fat and energy in their carcasses, compared with lambs fed an anionic or cationic diet. In dairy cows, positive DCAD diets have been reported to increase milk fat and milk protein (Hu et al., 2007). Increases in milk fat as a result of increasing DCAD, are thought to be, in part, due to the ability of sodium bicarbonate to increase rumen pH, which increases fiber digestion and ruminal VFA production. Increased VFA then results in increased de novo synthesis of fatty acids in the mammary gland. It is possible that previous studies demonstrating an increase of marbling in steers fed positive DCAD could be a result of increased ruminal production of VFA. An increase in % KPH from 0 to +16 DCAD in the present study supports the concept that sodium bicarbonate increased production of substrates for fatty acid synthesis. However, the fact that we only observed a numerical increase in marbling with increasing DCAD indicates that 14 d is not long enough to enhance marbling deposition. Longissimus muscle pH (P > 0.16), Ca content of LM (P > 0.61), and tenderness (P > 0.34) after 7 or 14 d of aging (Fig. 2) did not differ among treatments in the current study. Ross et al. (1994a) and Cho et al. (2006) also reported that although anionic diets increased plasma Ca, anionic diets did not alter muscle Ca in beef cattle. Nonetheless, Cho et al. (2006) observed that DCAD and vitamin D increased calpain activity and improved beef tenderness. Increasing LM Ca through dietary means has
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kg Start Slaughter ADG, kg/d Pre-study Study Total DMI, kg Pre-study Study Daily DMI, kg/d Pre-study Study Gain:feed, kg/kg Pre-study Study
Table 3. Effect of feeding diets that differ in dietary cation anion difference (DCAD) during the last 14 d before slaughter on carcass characteristics, muscle pH, and muscle calcium content
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Beef tenderness and DCAD
the potential to improve LM tenderness. Like DCAD diets, Ca propionate gel administration increases intestinal absorption of Ca into the bloodstream of nonlactating Holstein cows (Goff and Horst 1993). In fact, orally administering Ca propionate 3 to 6 h before slaughter has been demonstrated to increase LM Ca and calpain activity, and improve tenderness in beef aged 4 and 7 d, when compared with LM from cattle not drenched with Ca propionate (Duckett et al., 2001). The fact that LM pH and Ca were not altered by DCAD in the present study suggests that the body is very good at maintaining homeostasis in regard to tissue pH and ion concentrations. Blood pH is ultimately determined by the number of cations and anions in the blood. If more anions than cations enter the bloodstream from the digestive tract, blood and urine pH will decrease. Exhalation of carbon dioxide, lactate production by muscles, and excretion of acid or ammonium salts by the kidney tightly regulate blood pH (Harmon, 1996) to stay within a narrow range of 7.3 to 7.5, making it slightly alkaline (Swenson, 1993). Thus, urine pH is one of the most sensitive indicators of acid-base homeostasis (Constable et al., 2009). The fact that LM pH was not altered by anionic diets supports the concept that tissue homeostasis was maintained, despite differences in DCAD. Calcium homeostasis is also precisely regulated in circulation and skeletal muscle by the action of many hormones (e.g., parathyroid hormone and 1,25 dihydroxyvitamin D). The interaction between these hormones and proteins
help maintain total serum Ca levels in healthy individuals within a relatively narrow physiologic range of 10% (Peacock, 2010). Furthermore, ingestion of a low DCAD diet can increase Ca exit from the exchangeable Ca pool by decreasing renal tubular Ca reabsorption (Stacy and Wilson, 1970; Fredeen et al., 1988), potentially decreasing LM Ca. The fact that LM Ca was not altered in the present study suggests that any potential improvements in increased Ca absorption due to negative DCAD may have been ameliorated by decreased renal Ca reabsorption. Conclusions Our current study suggests that lowering DCAD to –16 mEq/100 g can decrease urine pH. However, lowering DCAD to –16 mEq/100 g may inhibit ADG and did not improve beef tenderness. It is possible that homeostatic mechanisms that maintain muscle pH and Ca content could not be altered enough to have an effect on proteolytic enzymes. Therefore, the results of this experiment suggest that decreasing DCAD negatively impacts ADG without increasing muscle Ca or enhancing beef tenderness. LITERATURE CITED AMSA. 1995. Research guidelines for cookery, sensory evaluation and instrumental measurements of fresh meat. Am. Meat Sci. Assoc. Natl. Livest. Meat Board, Chicago, IL.
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Figure 2. Effect of feeding diets that differ in dietary cation anion difference [DCAD; (Na + K) – (Cl + S); mEq/100 g] during the last 14 d before slaughter on Warner Bratzler shear force in beef steaks. No dietary treatment differences detected on d 7 (P = 0.57) or 21 (P = 0.34).
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