Incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition, and finishing.

Incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition, and finishing E. Castillo-Lopez, B. I. Wiese, S. Hendrick, J. J. McKinnon, T. A. McAllister, K. A. Beauchemin and G. B. Penner J ANIM SCI published online May 30, 2014

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Left Running Head: Castillo-Lopez et al. Right Running Head: Ruminal acidosis in feedlot cattle

Incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition, and finishing1 E. Castillo-Lopez,* B. I. Wiese,*† S. Hendrick,†2 J. J. McKinnon,* T. A. McAllister,‡ K. A. Beauchemin,‡ and G. B. Penner*3 *Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Canada, S7N 5A8; †Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada, S7N 5A8; and ‡Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada, T1J 4B1 1

Funding for the project was provided through the Canadian Beef Cattle Research Council and

the Natural Sciences and Engineering Research Council of Canada Collaborative Research and Development program (NSERC-CRD). The authors thank R. Kanafany-Guzman, G. Gratton, F. Joy, J. Nair, B. Schurmann, and T. Schwaiger for assistance during the study, the staff of the Beef Cattle Research and Teaching Unit at the University of Saskatchewan (Saskatoon, SK) for animal husbandry throughout the project, and Elanco Animal Health (Calgary, AB) for liver score assessment. 2

Present address: Coaldale Veterinary Clinic, 141 Broxburn Blvd, Lethbridge, Canada, AB T1J 4P4 3 Corresponding author: [email protected]

Received January 14, 2014. Accepted May 1, 2014.

Downloaded from www.journalofanimalscience.org at Oregon University Library Serials on June 15, 2014 Published Online First on May 30, 2014State as doi:10.2527/jas.2014-7599

ABSTRACT: The objective of this study was to determine the incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition, and finishing. Steers were purchased from a local auction market (n = 250; mean ± SD, 330 ± 20.0 kg initial BW) and were grouped together with 28 steers fitted with a ruminal cannula (248 ± 25.5 kg initial BW). Steers were randomly allocated to 1 of 8 pens (3 to 4 cannulated steers per pen with a total of 35 steers/pen). The feeding period (143 d) was divided into 4 phases; backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), and the first (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of finishing. The BKGD diet contained (% DM) barley silage (45.7%), barley grain (41.6%), canola meal (4.2%), and a pelleted mineral and vitamin supplement (8.5%). Steers were transitioned to a finishing diet containing (% DM) barley silage (5%), barley grain (80.9%), canola meal (4.9%), and a pelleted mineral and vitamin supplement (9.2%) using 4 transition diets. Feed was offered to achieve 5% refusals (as is basis). Ruminal pH was recorded in cannulated steers every 10 min throughout the study, and feed refusals and BW were recorded at 2 wk intervals. Mean ruminal pH (P < 0.01) was 6.4, 6.3, 6.2 and 6.0 ± 0.01 during the BKGD, TRAN, FIN1 and FIN2, respectively. The duration (P < 0.01) pH < 5.5 was 4.1, 12.1, 78.7 and 194 ± 9.4 min/d during BKGD, TRAN, FIN1, and FIN2, respectively. Using a threshold of ruminal pH < 5.5 for at least 180 min to diagnose ruminal acidosis, incidence was defined as the number of times steers experienced ruminal acidosis during each period and prevalence was defined as the percentage of steers that experienced acidosis during each period. On average, the incidence rate (P < 0.01) of ruminal acidosis was 0.1, 0.3, 6.7, and 14.8 ± 0.97 episodes during BKGD, TRAN, FIN1, and FIN2, respectively. In the same order, the prevalence (P < 0.01) was 0.7, 1.7, 15.4, and 37.8 ± 2.0%. Based on multiple regression, factors associated with prevalence of ruminal acidosis and the duration pH < 5.5 were


feeding phase (P < 0.01) and DMI (P < 0.01). Overall, the greatest incidence, prevalence and severity of ruminal acidosis were observed towards the end of the finishing phase and were associated with days on feed and DMI.

Key words: backgrounding, diet transition, feedlot cattle, finishing, prevalence, ruminal acidosis.


INTRODUCTION Beef cattle in North America are typically finished using high grain diets (> 70% grain, DM basis) to achieve maximum productivity (Vasconcelos and Galyean, 2007). A limitation to this approach is the perceived increase in the prevalence of ruminal acidosis (Penner et al., 2009; Aschenbach et al., 2011). Negative impacts of ruminal acidosis may include erosion of the ruminal epithelium (Steele et al., 2009; Penner et al., 2010) and a decrease in SCFA absorption (Harmon et al., 1985; Gaebel and Martens, 1988; Wilson et al., 2012). While ruminal acidosis is thought to be the major digestive disorder affecting finishing beef cattle, to the authors’ knowledge, no studies have comprehensively characterized the prevalence of this disorder in feedlot cattle throughout a finishing period. Of the phases of production for finishing cattle, the transition to a high grain diet has been suggested to be a time with substantial risk for ruminal acidosis (Bevans et al., 2005; Brown et al., 2006). In addition, Wierenga et al. (2010), used 16 ruminally-cannulated cattle housed with non-cannulated cattle and reported that feedlot cattle may experience sustained low ruminal pH even once adapted to their diet. However, past studies have been conducted using cattle that were individually fed (Bevans et al. 2005; Brown et al. 2006) or have used feed intake measurement systems that inherently limit bunk space availability (Wierenga et al., 2010; Holtshausen et al., 2013). While the use of feed intake measurement systems provide an opportunity to measure feed intake, restricting feed bunk space may alter feeding behavior (Proudfoot et al., 2009) and subsequently ruminal pH relative to bunk fed cattle. The objective of this study was to determine the incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition and finishing.


MATERIALS AND METHODS Animal Management and Experimental Design This experiment was conducted at the University of Saskatchewan Beef Cattle Research and Teaching Facility (Saskatoon, Saskatchewan, Canada) and was performed in accordance with the guidelines published by the Canadian Council on Animal Care (Ottawa, ON, Canada). The protocols used in this study were pre-approved by the University of Saskatchewan Animal Care and Use Committee (protocol 20100021). A total of 250 British-based crossbred steers (mean ± SD, 330 ± 20.0 kg incoming BW) were used. Steers were sourced commercially and arrived at the feedlot approximately 6 wk before the initiation of the study. In addition, 28 steers (248 ± 25.5 kg incoming BW) from the Goodale Research Farm (University of Saskatchewan, Saskatoon, SK, Canada) were fitted with a ruminal cannula (model 9C, Bar Diamond, Inc., Parma, ID) according to Bar Diamond Inc. (2011) approximately 90 d prior to the initiation of the experiment. Upon arrival, steers were implanted with Component E-S (Elanco Animal Health, Calgary AB) and given Ivomec (Merial Ltd., Duluth, GA), Ultrabac 7/Somnubac (Zoetis, Kirkland, QC), Bovashield Gold 5 (Zoetis), One Shot (Zoetis), and 32 mL of long-acting Liquamycin (Zoetis). Steers were re-implanted with component TE (Elanco Animal Health, Calgary AB) 87 d after the first implant. Steers were randomly assigned to 1 of 8 pens (3 to 4 cannulated steers and 31 to 32 non-cannulated steers/pen). The entire feeding period (143 d; from January 12, 2013 to June 3rd, 2013) was divided into 4 feeding phases; backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), the first half (FIN1; d 41 to 91), and the second half (FIN2; d 92 to 143) of the finishing phase. During BKGD, steers were fed a forage-based diet (Table 1) representative of that used


in western Canada until achieving an average pen live weight of 420 kg. Subsequently, steers were transitioned to a finishing diet over 21 d using 4 transition diets. The ingredient and chemical composition of diets are listed in Table 1. The BKGD diet was formulated to include (DM basis) barley silage (45.7%), barley grain (41.6%), canola meal (4.2%), mineral and vitamin supplement (8%), and limestone (0.5%). The finishing diet was formulated to include (DM basis) barley silage (5%), barley grain (80.9%), canola meal (4.9%), mineral and vitamin supplement (8.3%), and limestone (0.9%). Diets were formulated to supply 33 mg/kg monensin (Rumensin, Elanco Animal Health, Indianapolis, IN) and 11 mg/kg Tylosin (Tylan, Elanco Animal Health, Indianapolis, IN). Steers were fed twice daily at 0900 h and 1600 h. A constant amount of feed was offered in the morning with the amount of feed offered in the afternoon adjusted to achieve 5% refusals (as is basis). Bunks were cleaned and refusals were measured every 2 wk prior to feeding. Samples of the refusals were collected and DM was determined by drying samples in a forced air oven at 60°C for 48 h. The difference between the weight of the feed offered and that refused (DM basis) over a 2 wk interval was used to calculate DMI. At the start of the study, steer BW was recorded on 2 consecutive d and every 2 wk thereafter. The BW data were averaged by pen and the change in weight between 2 consecutive BW measurements was used to estimate ADG. Upon completion of the experiment, noncannulated and cannulated steers were slaughtered separately at 2 commercial facilities (Cargill, High River AB and Plains Processors Ltd., Carman, MB, respectively). Hot carcass weights were recorded at both facilities. Carcass quality and yield grades were measured only for noncannulated steers and were conducted according to the Canadian Beef Grading Agency (CBGA). Carcass quality grades were A (trace marbling), AA (slight marbling), AAA (small marbling), and Prime (slightly abundant marbling). Carcass yield grades were Y1 (estimated meat yield of


59% or better), Y2 (54 to 58%) or Y3 (less than 54% lean meat yield; Basarab et al., 1997). Liver scores were measured in both non-cannulated and cannulated steers according to Brown et al. (1975) with the modification that the A- and A categories were merged with 0 = no abscesses; A = 1 or 2 small abscesses or up to 2 to 4 well-developed abscesses with a diameter of < 2.5 cm and A+ = 1 or more large abscesses > 2.5 cm with inflammation of the liver tissue apparent with portions of the diaphragm adhered to the surface of the liver. Feed Sampling and Analysis Samples of barley silage were collected weekly. In addition, samples of barley grain, canola meal, and the mineral and vitamin supplement were collected every 2 wk. The DM concentration of collected feed ingredients was determined by drying samples in a forced air oven at 60°C for 48 h. The resulting DM data were used to adjust the diet to ensure proper inclusion rates for ingredients in the total mixed ration. At the end of the experiment, feed ingredient samples were ground to pass through a 1-mm screen (Wiley Mill, Arthur A. Thomas Co., Philadelphia, PA) and were composited by month, and analyzed for chemical composition by an external laboratory (Cumberland Valley Analytical Services, Hagerstown, MD). Analysis included DM (method 930.15; AOAC, 2000), N (method 990.03; Leco FP-528 Nitrogen Combustion Analyzer, Leco corp. St. Joseph, MI), NDF (Van Soest et al., 1991), starch (Hall, 2009), ether extract using diethyl ether (method 2003.05; AOAC, 2006) and ash (method 942.05; AOAC, 2000). The chemical composition of the diets (Table 1) were calculated based on the analysis of individual feed ingredients and the rate of inclusion. Ruminal pH Ruminal pH was measured according to the protocol described by Penner et al. (2009). Briefly, throughout the entire study ruminal pH was measured in cannulated steers every 10-min


using an indwelling pH measurement system (Dascor Inc., Escondido, CA). A ruminal pH measurement system was placed in the ventral sac of the rumen of each steer and was removed from the rumen every 2 wk to download the data and for standardization measurements. At the time of removal, the location of the pH system was confirmed and in all cases pH systems were retrieved from the ventral sac of the rumen. Immediately after removal from the rumen, the pH measurement systems were standardized in pH buffers 7.0 and 4.0 at 38.5°C and the corresponding mV values measured in each buffer solution were recorded before returning the pH measurement systems into the rumen. The same process was repeated after the final removal from the rumen. The mV values obtained in buffers 7.0 and 4.0 during the pre- and postmeasurement standardizations were used to derive 2 linear regression equations (beginning and ending) that were used to convert mV values obtained during in vivo measurement to ruminal pH. A linear offset was used to account for changes in the slope and intercept between the preand post-measurement standardizations such that the post-measurement standardization equation had increased weighting as the measurement period progressed. Ruminal pH data were then summarized for each steer on a daily basis. From these values the minimum, mean, and maximum pH values were determined and the time that ruminal pH < 5.5 (DUR) and the area that ruminal pH < 5.5 (AREA) were calculated. Ruminal acidosis was defined to occur in cannulated steers when ruminal pH < 5.5 for at least 180 min/d. Accordingly, the incidence of ruminal acidosis, defined as the number of times steers developed ruminal acidosis was calculated for each feeding phase and averaged by pen. The prevalence of ruminal acidosis in cannulated steers was determined by calculating the percentage of steers/pen with ruminal acidosis. Ambient Temperature Data Collection


Ambient temperature data collected during this experiment were recorded at a local weather station and data were downloaded from the Environment Canada database (http://climate.weather.gc.ca/advanceSearch/searchHistoricData_e.html#provinceTab) using the Saskatoon Airport weather station. Ambient temperature data included the minimum, mean, and maximum daily temperature. These data were then summarized on a daily basis. Statistical Analysis Feedlot Performance and Ruminal pH. Data collected for DMI, ADG, the gain-to-feed ratio (G:F) and ruminal pH were averaged by pen and were analyzed using the MIXED procedure of SAS (version 9.2, SAS Inst. Inc., Cary, NC). The model included the fixed effect of feeding phase and a repeated measures statement was used to account for the repeated observations on individual pens. Pen was considered as the experimental unit. Means are presented as least square means and the largest standard error of the mean (SEM) is reported. Statistical significance was declared at P < 0.05 and tendencies are discussed when 0.05 < P ≤ 0.10. Multiple Regression and Correlation Analysis. The Spearman correlation coefficients between production performance data, mean ambient temperature, and ruminal pH parameters were determined. In addition, data were analyzed to determine the effects of the explanatory variables as factors affecting mean ruminal pH, prevalence of ruminal acidosis, DUR, AREA, and G:F. Explanatory variables included feeding phase, ambient temperature, the change in temperature, and DMI. Models were constructed using backwards elimination process using previous knowledge of the correlation between explanatory and response variables. The backwards elimination process started with a full model of all the independent variables. Then, the most insignificant factors were manually removed (P > 0.05) one by one. Each time a


variable was removed, a 20% change in the beta coefficient of significant variables was verified. This would indicate that the removed variable was a confounding factor. The model was reduced such that the only variables remaining were those with a P < 0.05. RESULTS Steers, Ruminal pH and Ambient Temperature On d 88 of the experiment, the ruminal cannula plug of 1 steer was reported to be missing and it was replaced immediately. Therefore, measurements of ruminal pH collected from that steer on d 88 were not included in the statistical analysis. During the experiment, 5 noncannulated steers died due to reasons not related to the study. Furthermore, when aberrant data on ruminal pH were collected due to pH meter malfunction, measurements were excluded from statistical analysis. It is important to note that although pH systems were removed from steers every 2 weeks to download, verify electrode function, and for standardization, pH electrode failure during measurements ranged from 3.5 to 46.4% with an average of 22.3%. Variation in ambient temperature over the course of the experiment is reported in Fig. 1. Overall, the lowest ambient temperature values (< 0°C) were recorded during the BKGD phase. Mean ambient temperature gradually increased during TRAN and FIN1 and changed from negative to positive values at the initiation of the FIN2 feeding phase. Dry Matter Intake, Growth Performance, Carcass Yield and Quality, and Liver Abscesses Dry matter intake (Table 2) averaged 10.3 kg/d ± 0.03 and G:F averaged 0.18 ± 0.003 kg/kg. The final BW of non-cannulated steers was 668 ± 1.8 kg and ADG was 1.89 ± 0.029 kg/d, while the final BW of cannulated steers was 548 ± 6.4 kg and ADG was 1.81 ± 0.003 kg/d. Hot carcass weight averaged 376 ± 4.3 and 288 ± 15.4 kg for non-cannulated and cannulated steers, respectively (Table 3). Carcass quality grade distribution for non-cannulated steers was 1.2% B4,


0% A, 47.34% AA, 51.0% AAA and 0.41% prime. Carcass yield grade was 38.4% CBGA 1, 45.8% CBGA 2 and 15.7% CBGA 3. The prevalence for severe liver abscesses (A+) was 14.7 and 10.7% in non-cannulated and cannulated steers, respectively. Ruminal pH Mean ruminal pH (P < 0.01; Table 4 and Figure 2) was observed to be 6.44, 6.32, 6.19 and 6.03 ± 0.01 during BKGD, TRAN, FIN1 and FIN2, respectively. In the same order, the incidence (P < 0.01) of ruminal acidosis increased from BKGD (0.1 episodes/period) to FIN2 (14.9 episodes/period). The prevalence (P < 0.01; Fig. 2) of ruminal acidosis also increased from BKGD to FIN2 with a mean prevalence 37.8% during FIN2. The DUR (P < 0.01) was 4.1, 12.2, 78.8 and 194.7 ± 9.5 min/d and AREA (P < 0.01) was 0.5, 1.3, 12.3 and 38.4 ± 4.46 pH × min/d for BKGD, TRAN, FIN1, and FIN2, respectively. Correlation Coefficients Correlation analysis was conducted to investigate the association of ruminal pH with production performance, days on feed, and mean ambient temperature (Table 5). The change in ambient temperature was also evaluated but was not associated with ruminal pH, BW, or ADG and therefore, the change in temperature was excluded from further analysis. Simple regression analysis revealed a negative correlations between mean ruminal pH and BW (-0.599; P < 0.01), DMI (-0.496; P < 0.01), days on feed (-0.600; P < 0.01) and mean ambient temperature (-0.520; P < 0.01). Positive correlations were observed between the prevalence of ruminal acidosis and BW (0.534; P < 0.01), DMI (0.514; P < 0.01), days on feed (0.531; P < 0.01) and mean ambient temperature (0.474; P < 0.01). However, it should be noted that BW was correlated with days on feed (0.998; P < 0.01) and mean ambient temperature (0.832; P < 0.01). In addition, a high correlation was observed between days on feed and mean ambient temperature (0.834; P < 0.01).


Factors Associated with Ruminal pH To address limitations with simple correlation analysis, such as auto-correlation among variables, multiple regression was used to evaluate factors affecting ruminal pH and G:F (Table 6). The explanatory variables tested in the regression model were feeding phase, mean ambient temperature, and DMI. Dependent variables evaluated included mean ruminal pH, prevalence for ruminal acidosis, DUR and AREA. Factors associated with mean ruminal pH. Feeding phase and mean ambient temperature were significant explanatory variables for ruminal pH. Compared to TRAN (intercept = 6.091), mean ruminal pH was on average 0.1082 units greater during BKGD (P < 0.01) but was reduced by 0.134 units during FIN1 (P < 0.01) and 0.258 units during FIN2 (P < 0.01). In addition, for every 1-degree increase in mean ambient temperature, mean ruminal pH decreased by 0.003 units, and for every kg increase in DMI, mean ruminal pH tended to increase (P = 0.08) by 0.02 units. Factors associated with the prevalence of ruminal acidosis. Compared to TRAN (intercept = -68.344), the prevalence of ruminal acidosis was not affected during BKGD (P = 0.13) but increased by 10.84% during FIN1 (P < 0.01) and 27.89% during FIN2 (P < 0.01). Mean ambient temperature (P = 0.54) did not have an effect on the prevalence of ruminal acidosis. In addition, for every kg increase in DMI (P < 0.01) the prevalence of ruminal acidosis increased by 6.88%. Factors associated with severity for ruminal acidosis. When the response variable DUR was evaluated, compared to TRAN (intercept = -259.17), DUR was not affected during BKGD (P = 0.4) but was increased by 55.86 min/d during FIN1 (P = 0.01) and 153.16 min/d during FIN2 (P < 0.01). The effect of mean ambient temperature (P = 0.46) on DUR was not


significant. In addition, for every kg increment in DMI (P < 0.01) the DUR increased by 26.51 min/d. When the response variable AREA was evaluated, compared to TRAN (intercept = 13.753), the AREA was not affected during BKGD (P = 0.93) but was increased by 10.67 pH × min/d during FIN1 (P = 0.04) and 37.83 pH × min/d during FIN2 (P < 0.01). Mean ambient temperature (P = 0.58) and DMI (P = 0.69) did not have a significant effect on AREA. Factors Associated with the Ratio of Gain-to-feed (G:F) Results of the multiple regression analysis evaluating factors associated with G:F are listed in Table 7. The explanatory variables included were feeding phase, mean ambient temperature and mean ruminal pH. Compared to TRAN (intercept = 0.12), G:F was not affected during BKGD (P = 0.73), but was 0.01 units greater during FIN1 (P < 0.01) and decreased by 0.02 units during FIN2 (P < 0.01). Furthermore, for every 1°C increase in mean temperature (P < 0.01), G:F decreased by 0.002 units. No effect of mean ruminal pH (P = 0.11) was observed on G:F. DISCUSSION Although incidence of mortalities in feedlots associated with digestive disorders are low (Smith, 1998) when compared to mortalities from respiratory disease, losses due to digestive disorders can account for 10.4% in beef operations (USDA, 2011). Among digestive disorders, ruminal acidosis is cited as the most common (Johnson, 1991; Glock and DeGroot, 1998; Nagaraja and Lechtenberg, 2007) and has received considerable attention given the potential linkages to endotoxemia (Harmon, 1996), liver abscesses (Nagaraja et al., 1999), laminitis (Brent, 1976), and potential reductions in ADG and G:F (Stock et al., 1990). Despite the suggestion that ruminal acidosis is the most prevalent digestive disorder, there have been no


studies known by the authors that have comprehensively evaluated the prevalence or severity of ruminal acidosis in feedlot cattle during backgrounding, diet transition, and finishing. In the current study, we utilized 28 ruminally cannulated steers mixed with noncannulated cohort steers. Although we attempted to match the weight of the cannulated steers with the cohort steers when sourcing them at a local auction market, the weight of the noncannulated steers was approximately 110 kg heavier and their ADG was greater than cannulated steers. Based on this discrepancy and that it was not possible to measure DMI on an individual basis, the greater ADG and BW for the cohort steers likely also reflects greater DMI (Griffin et al., 2007; Ackerman et al., 2001). However, the proportions of unaffected and abscessed (A and A+) livers were similar between cannulated and non-cannulated steers. While liver abscesses can be caused by multiple factors (Vasconcelos en Gaylean, 2008; Nagaraja et al., 1996), ruminal lesions caused by ruminal acidosis is generally accepted as a major predisposing factor for liver abscesses (Nagaraja et al., 1998). Therefore, our assumption in this study was that despite differences in BW and ADG, the response of non-cannulated and cannulated steers in terms of liver abscesses and likely ruminal fermentation and ruminal pH were similar and thus represent a reasonable experimental model. Incidence, Prevalence, and Severity of Ruminal Acidosis Novel results from the current study indicate that the incidence and prevalence rates for ruminal acidosis were 0.1, 0.3, 6.7, and 14.9, and 0.7, 1.7, 15.4, and 37.8%, respectively. While incidence and prevalence rates have not been reported previously, past studies utilizing individually fed cattle report values for DUR between 233 and 1,251 min/d below pH 5.6 (Bevans et al., 2005; Vander Pol et al., 2009; Crawford et al., 2008) and between 340 and 601 min/d (Meyer et al., 2009; Wieranga et al., 2010) once fed finishing diets or during the last step-


up of a diet transition (Holtshausen et al., 2013). However, none of those studies incorporated long-term measurement of ruminal pH in the same cattle. In the current study, we observed that the DUR was, on average, 4.1, 12.5 78.8, and 194 min/d during BKGD, TRAN, FIN1, and FIN2 indicating that the severity of ruminal acidosis may be overestimated in short-term studies or in studies when cattle are group-housed but feeding behavior is constrained to a limited amount of feed bunk space; as is the case for studies using feed intake monitoring systems (SchwartzkopfGenswein et al., 1999; Mendes et al., 2011; Holtshausen et al., 2013). Nonetheless, these results suggest that the reduction in ruminal pH for group-fed cattle is not as severe as would have been predicted by extrapolating results from short-term studies. The greatest mean ruminal pH values were recorded during BKGD, presumably due to the higher concentration of forage in the diet compared to the diets fed thereafter. In addition, results indicate that ruminal pH gradually decreased during the diet transition and during the first half of the finishing phase, and mean pH reached its nadir towards the end of the finishing phase. Despite the decrease in mean pH during TRAN, mean pH was still above 6.2 and the DUR, on average, was only 12 min/d suggesting that steers were able to regulate ruminal pH through the dietary transition although the mechanisms behind this response cannot be determined from the current study. This differs from past studies that have suggested that the dietary transition is a time of high risk for ruminal acidosis. However, the data in previous studies were collected from cattle that were individually fed (Bevans et al. 2005; Brown et al. 2006) or used feed intake measurement systems that inherently limit bunk space availability (Holtshausen et al., 2013). Future work is needed to evaluate the feeding behavior of feedlot cattle without restricting access to bunk space and to evaluate whether cattle regulate ruminal pH by adjusting feed intake patterns in group-fed scenarios.


Factors Associated with Increased Severity or Prevalence of Ruminal Acidosis The prevalence and severity of ruminal acidosis during finishing was, on average, 15.4 and 37.8% during FIN1 and FIN2, respectively; however, peak prevalence was 63.5%. The factors associated with mean ruminal pH in this study were feeding phase, mean ambient temperature (as described above), and DMI. Specifically, the greatest risk for the development of ruminal acidosis was towards the end of the finishing phase. While there is no doubt that there is partial confounding among feeding phase, ambient temperature, and DMI; all three factors were statistically significant suggesting that the proportion of variation they account for was at least partially independent of each other. It is important to note, however, that despite the negative correlation observed between mean ambient temperature and mean ruminal pH, when prevalence and severity of ruminal acidosis were analyzed the effect of mean ambient temperature on the multiple regression model was not significant. This indicates that the greater prevalence and severity of ruminal acidosis observed towards the end of the study is likely attributed to feeding phase and DMI, rather than an increase in mean ambient temperature. In addition, although the cause for greater prevalence and severity of ruminal acidosis with advancing days on feed once fed the finishing diet is not clear; it may be possible that the severity and risk for acidosis increases once cattle experience an initial bout of ruminal acidosis (Dohme et al., 2008). Moreover, as DMI increases as cattle grow, the supply of fermentable substrate to the rumen increases and therefore, poses a greater challenge for cattle to balance acid production and acid removal from the rumen. Future studies should be conducted to evaluate how environmental conditions interact with days on feed to influence variability in DMI and the risk for ruminal acidosis for group-fed feedlot cattle. Production Performance and Liver Abscess Scores


It is often suggested that ruminal acidosis decreases performance of feedlot cattle (Fulton, 1979; Stock et al., 1990; Reinhardt et al., 1997) although quantitative proof is limited. The suggestion for acidosis negatively impacting performance is supported by studies reporting that ruminal acidosis decreases short-chain fatty acid absorption across the rumen epithelium (Gaebel and Martens, 1988; Wilson et al., 2012; Schwaiger et al., 2013) and that cattle experiencing ruminal acidosis often have variable feed intake patterns (Fulton, 1979; Holtshausen et al., 2013). However, several studies, albeit using dairy cattle, have reported that performance is greater for cows with lower ruminal pH (Kolver and de Veth, 2002; Oba and Allen 2003a,b). In the current study, ADG was positively correlated to mean ruminal pH and negatively correlated to DUR, AREA, and prevalence for ruminal acidosis. In addition, G:F was positively correlated to mean ruminal pH and negatively correlated to DUR, AREA, and prevalence for ruminal acidosis, suggesting that performance may be compromised with low pH. It should be noted that DMI, and consequently G:F, was measured on a pen basis. Given that the measurements of ruminal pH were summarized by day and ADG was only determined bi-weekly, it is difficult with the existing data set to predict pH thresholds that can be used to identify when growth performance may be compromised. That said, the observed positive association between G:F and mean ruminal pH suggests that nutrient intake or nutrient utilization decreases with increasing severity of ruminal pH depression. It is plausible that part of the response for decreased ADG and G:F with low ruminal pH may be due to decreases in SCFA absorption (Wilson et al., 2012; Schwaiger et al., 2013). In conclusion, the greatest incidence, prevalence, and severity of ruminal acidosis were observed towards the end of the finishing phase with feeding phase and DMI being major risk factors in the current study. Compared to previously reported data, the severity of ruminal


acidosis was low in the current study suggesting that direct extrapolation of data from individually fed cattle to group fed cattle may not be representative. Although, the prevalence and severity of ruminal acidosis was low in feedlot steers, the associations between low ruminal pH and reduced ADG and decreased G:F suggest that strategies to help regulate ruminal pH may have a positive impact on growth performance.


LITERATURE CITED

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Table 1. Ingredient and analyzed chemical composition of the diets fed during the backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), first half (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of the finishing phase.

BKGD BKGD

Feeding phase TRAN Step 2 Step 3 Step 4

FIN FIN1 and FIN2

Item Step1 Ingredient, % DM Barley silage 45.7 34.3 25.5 17.0 10.5 5.0 Rolled barley grain 41.6 51.3 60.8 69.3 75.7 81.2 Canola meal 4.2 5.9 5.1 5.0 5.0 4.9 1 Mineral/vitamin supplement 8.0 8.0 8.0 8.0 8.0 8.0 Limestone 0.5 0.5 0.6 0.7 0.8 0.9 2 Chemical , % DM DM 62.1 68.6 73.0 77.2 80.4 83.9 CP 13.7 14.8 14.6 14.6 14.6 13.9 NDF 32.8 27.7 25.3 23.1 21.3 21.3 Starch 34.1 38.3 41.5 44.3 46.4 48.9 Ether extract 2.5 2.5 2.4 2.4 2.3 2.1 Ash 7.0 6.6 6.1 5.7 5.4 5.5 1 Mineral and vitamin supplement containing 44.6% ground barley, 25.0% corn distillers grains with solubles, 11.8% limestone, 7.6% canola meal, 6.8% dynamate (K and Mg sulfate), 2.1% salt and 1.1% magnesium oxide, 0.91% Na, 4.53% Ca, 0.42% P, 1.18% Mg, 1.78% K, 1.81% S, 1.42% Cl, 4.6 mg/kg Co, 146.2 mg/kg Cu, 8 mg/kg I, 449.3 mg/kg Fe, 336.5 mg/kg Mn, 2.26 mg/kg Se, 313.5 mg/kg Zn, 40,000 IU/kg vitamin A, 15,000 IU/kg vitamin D3, 300 IU/kg vitamin E, 920.2 mg/kg choline, 402 mg/kg monensin (Elanco Animal Health, Indianapolis, IN) and 134 mg/kg Tylan (Elanco Animal Health, Indianapolis, IN). 2

Analyzed at Cumberland Valley Analytical Services, Inc. Hagerstown, MD.


Table 2. Dry matter intake, ADG, and the gain-to-feed (G:F) ratio for feedlot steers during the backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), first half (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of the finishing phase. Feeding phase Item BKGD TRAN FIN1 FIN2 SEM1 P-value All steers, n = 273 DMI, kg/d 9.2 10.1 10.5 11.5 0.03 < 0.001 Gain:feed, kg/kg 0.21 0.20 0.21 0.13 0.002 < 0.001 Non-cannulated, n = 245 BW Initial, kg 384 424 464 566 1.8 < 0.001 Mean, kg 402 442 514 617 2.2 < 0.001 Final, kg 422 462 564 668 1.8 < 0.001 ADG, kg/d 1.90 1.97 2.15 1.55 0.029 < 0.001 Cannulated, n = 28 BW Initial, kg 279 317 355 451 6.4 < 0.001 Mean, kg 296 334 402 500 2.4 < 0.001 Final, kg 315 353 450 548 6.4 < 0.001 ADG, kg/d 1.73 1.85 2.06 1.59 0.032 < 0.001 1 The highest standard error of the means is shown.


Table 3. Carcass weight, carcass quality, and yield grade, and the prevalence of liver abscesses from non-cannulated and cannulated steers fed a barley-based finishing diet. Steers Item Non cannulated Cannulated n 245 28 Hot carcass weight (mean ± SEM), kg 376 ± 4.3 288 ± 15.4 1 Quality grade B4, % 1.22 --A, % 0 --AA, % 47.34 --AAA, % 51.02 --Prime, % 0.41 --Yield grade2 1, % 38.42 --2, % 45.86 --3, % 15.70 --3 Liver abscesses 0, % 75.5 78.6 A, % 9.8 10.7 A+, % 14.7 10.7 1 Canada A quality grade = USDA Standard; Canada AA quality grade = USDA Select; Canada AAA quality grade = USDA Choice; Canada Prime = USDA Prime; B4 = dark cutting (Basarab et al., 1999). 2 Carcass yield grades were Y1 (estimated meat yield of 59% or better), Y2 (54 to 58%) or Y3 (less than 54% lean meat yield; Basarab et al., 1997). 3 Liver scores were measured in both non-cannulated and cannulated steers according to Brown et al. (1975) with the modification that the A- and A categories were merged with 0 = no abscesses; A = 1 or 2 small abscesses or up to 2 to 4 well-developed abscesses with a diameter of < 2.5 cm and A+ = 1 or more large abscesses > 2.5 cm with inflammation of the liver tissue apparent with portions of the diaphragm adhered to the surface of the liver.


Table 4. Mean ruminal pH, incidence, prevalence and severity of ruminal acidosis in ruminally cannulated feedlot steers during backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), and the first half (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of the finishing phase. Feeding phase Item BKGD TRAN FIN1 FIN2 SEM1 P-value2 Mean ruminal pH Initial 6.51 6.40 6.15 6.14 0.064 < 0.001 Final 6.46 6.22 6.26 5.97 0.064 < 0.001 Mean 6.44 6.32 6.19 6.03 0.015 < 0.001 Minimum ruminal pH 5.89 5.75 5.56 5.42 0.022 < 0.001 Maximum ruminal pH 6.98 6.94 6.92 6.85 0.016 < 0.001 Incidence3, no episodes/period 0.1 0.3 6.7 14.9 0.97 < 0.001 4 Prevalence , %/period 0.7 1.7 15.4 37.8 1.97 < 0.001 Minimum 0 0 0 0 ----Mean 0.7 1.8 15.5 37.8 2.32 < 0.001 Maximum 13.5 20.8 84.4 96.9 5.74 < 0.001 Ruminal pH < 5.5, min/d 4.1 12.2 78.8 194.7 9.47 < 0.001 Ruminal pH < 5.5, pH × min/d 0.5 1.3 12.3 38.4 4.46 < 0.001 1 The highest standard error of the means is shown. 2 P-values for effects of feeding phase are presented. 3 Incidence defined as the number of times steers experienced ruminal acidosis. 4 Prevalence was determined using a ruminal acidosis threshold of ruminal pH < 5.5 for at least 180 min/d.


Table 5. Correlation coefficients between ruminal pH parameters, feedlot production performance, and mean ambient temperature for steers fed during the backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), first half (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of the finishing phase. Variable Ruminal pH parameter Correlation P-value coefficient (r) BW, kg Mean ruminal pH -0.599 < 0.001 Time of ruminal pH < 5.5 0.602 < 0.001 Area of ruminal pH < 5.5 0.580 < 0.001 1 Prevalence of ruminal acidosis 0.534 < 0.001 ADG, kg/d Mean ruminal pH 0.261 < 0.001 Time of ruminal pH < 5.5 -0.249 < 0.001 Area of ruminal pH < 5.5 -0.231 < 0.001 1 Prevalence of ruminal acidosis -0.231 < 0.001 Gain:feed2, kg/kg; Mean ruminal pH 0.383 < 0.001 Time of ruminal pH < 5.5 -0.415 < 0.001 Area of ruminal pH < 5.5 -0.396 < 0.001 1 Prevalence of ruminal acidosis -0.376 < 0.001 DMI2, kg/d Mean ruminal pH -0.496 < 0.001 Time of ruminal pH < 5.5 0.568 < 0.001 Area of ruminal pH < 5.5 0.553 < 0.001 1 Prevalence of ruminal acidosis 0.514 < 0.001 DOF3 Mean ruminal pH -0.600 < 0.001 Time of ruminal pH < 5.5 0.603 < 0.001 Area of ruminal pH < 5.5 0.581 < 0.001 Prevalence of ruminal acidosis1 0.531 < 0.001 Mean ambient Mean ruminal pH -0.520 < 0.001 temperature, °C Time of ruminal pH < 5.5 0.514 < 0.001 Area of ruminal pH < 5.5 0.494 < 0.001 Prevalence of acidosis 0.474 < 0.001 Mean ruminal pH Mean ruminal pH 1 Time of ruminal pH < 5.5 -0.725 < 0.001 Area of ruminal pH < 5.5 -0.697 < 0.001 Prevalence of acidosis -0.610 < 0.001 1 Ruminal acidosis defined as pH < 5.5 for at least 180 minutes/d. 2 The ratio of G:F and DMI intake values were averaged by pen. 3 Days on feed.


Table 6. Multiple regression of feeding phase, mean ambient temperature and DMI on ruminal pH parameters in feedlot steers fed during the backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), first half (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of the finishing phase. Dependent variable Explanatory variables Intercept Regression parameter 95% CI1 P-value Mean ruminal pH 6.091 5.853, 6.328 < 0.001 Feeding phase < 0.001 BKGD 0.108 0.061, 0.155 < 0.001 TRAN 0 . … FIN1 -0.134 -0.169, -0.098 < 0.001 FIN2 -0.258 -0.313, -0.202 < 0.001 Mean ambient temperature -0.003 -0.004, -0.001 < 0.001 DMI; all steers 0.02 -0.002, 0.043 0.087 Prevalence of ruminal acidosis -68.344 -98.243, -38.444 < 0.001 Feeding phase < 0.001 BKGD 4.455 -1.456, 10.367 0.13 TRAN 0 . … FIN1 10.841 6.339, 15.342 < 0.001 FIN2 27.895 20.878, 34.911 < 0.001 Mean ambient temperature -0.067 -0.286, 0.151 0.54 DMI; all steers 6.882 3.983, 9.780 < 0.001 Time pH < 5.5 -259.170 -402.67, -115.66 < 0.001 Feeding phase < 0.001 BKGD 11.946 -16.409, 40.342 0.40 TRAN 0 . … FIN1 55.861 34.245, 77.475 < 0.001 FIN2 153.16 119.48, 186.85 < 0.001 Mean ambient temperature -0.393 -1.445, 0.659 0.46 DMI; all steers 26.509 12.596, 40.422 < 0.001 Area pH < 5.5 -13.753 -81.649, 54.143 0.69 Feeding phase < 0.001


BKGD TRAN FIN1 FIN2 Mean ambient temperature DMI, all steers 1

95% confidence interval.


-0.553 0 10.667 37.827 -0.139 1.332

-13.978, 12.872 . 0.440, 20.893 21.889, 53.764 -0.637, 0.358 -5.250, 7.914

0.93 … 0.040 < 0.001 0.58 0.69

Table 7. Multiple regression of feeding phase, mean ambient temperature and mean ruminal pH on the ratio of gain-to-feed (G:F) in feedlot steers fed during the backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), first half (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of the finishing phase. Dependent variable Explanatory variable Intercept Regression parameter 95% CI1 P-value Ratio of feed to gain, all steers

1

7.838 Feeding phase BKGD TRAN FIN1 FIN2 Mean ambient temperature Mean ruminal pH

4.443, 11.232 0.416 0.00 -0.411 1.042 0.089 -0.250

95% confidence interval.


0.014, 0.816 . -0.734, -0.088 0.576, 1.508 0.073, 0.105 -0.787, 0.286

< 0.001 < 0.001 0.042 … 0.012 < 0.001 < 0.001 0.36

Figure 1. Maximum (black line), minimum (light grey line) and mean (dark grey line) ambient temperature during the backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), first half (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of the finishing phase. The experiment was conducted from January 12, 2013 to June 03, 2013. Weather station located in Saskatoon, Saskatchewan.

Figure 2. Mean ruminal pH (black line) and prevalence (grey line) of ruminal acidosis in feedlot steers during backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), first half (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of the finishing phase. The correlation coefficient between mean ruminal pH and prevalence of ruminal acidosis was -0.610 (P < 0.01).



1 2


Ruminal acidosis in feedlot: from aetiology to prevention.

Effects of Elevated Crude Glycerin Concentrations on Feedlot Performance and Carcass Characteristics in Finishing Steers.

Dietary buffers and ruminal and blood parameters of subclinical lactic acidosis in steers.

Incidence and risk factors of linezolid-induced lactic acidosis.

The modern feedlot for finishing cattle.

Assessment of L-lactatemia as a predictor of respiratory disease recognition and severity in feedlot steers.

Performance of feedlot steers fed diets containing laidlomycin propionate or monensin plus tylosin, and effects of laidlomycin propionate concentration on intake patterns and ruminal fermentation in beef steers during adaptation to a high-concentrate diet.

Nicotinic acid supplementation in diet favored intramuscular fat deposition and lipid metabolism in finishing steers.

A comparison of supplemental calcium soap of palm fatty acids versus tallow in a corn-based finishing diet for feedlot steers.

Effect of Lipid Sources with Different Fatty Acid Profiles on Intake, Nutrient Digestion and Ruminal Fermentation of Feedlot Nellore Steers.

Influence of ruminal degradable intake protein restriction on characteristics of digestion and growth performance of feedlot cattle during the late finishing phase.

Acidosis in feedlot cattle: practical observations.

Effects of a bacterial probiotic on ruminal pH and volatile fatty acids during subacute ruminal acidosis (SARA) in cattle.

Relationship of severity of subacute ruminal acidosis to rumen fermentation, chewing activities, sorting behavior, and milk production in lactating dairy cows fed a high-grain diet.

Prevalence, incidence and risk factors for donor-specific anti-HLA antibodies in maintenance liver transplant patients.

Recombinant bovine somatotropin improves growth performance in finishing beef steers.

Dynamics of ruminal ciliated protozoa in feedlot cattle.

Ruminal changes during the onset and recovery of induced lactic acidosis in sheep.

Using a fibrolytic enzyme in barley-based diets containing wheat dried distillers grains with solubles: ruminal fermentation, digestibility, and growth performance of feedlot steers.

Risk factors: Acidosis predicts decline in EGFR.

Effects of Diets Supplemented with Ensiled Mulberry Leaves and Sun-Dried Mulberry Fruit Pomace on the Ruminal Bacterial and Archaeal Community Composition of Finishing Steers.

Shoulder injury incidence and severity through identification of risk factors in rugby union players.

Immediate and nonimmediate reactions induced by contrast media: incidence, severity and risk factors.

Induction of Subacute Ruminal Acidosis Affects the Ruminal Microbiome and Epithelium.