Influence of Dietary Protein and Supplemental Niacin on Lactational Performance of Cows Fed Normal and Low Fiber Diets’ C. A. ZIMMERMANF A.

H. RAKES: T. E. DANIEL, and 8. A. HOPKINS Department of Animal Science North Carolina State University Raleigh 27695.7621

ABSTRACT

Forty-seven cows (24 primiparous) were assigned to one of four normal (20.5%) ADF diets for wk 2 to 5 postpartum. Dietary treatments in a 2 x 2 factorial design were diets of 13.8 versus 18.8% CP and 0 versus 12 gld of niacin per cow. During wk 6 to 13 postpartum, cows were fed low (11.8%) ADF diets while maintaining CP and niacin treatments. Low CP diets contained solventextracted soybean meal, rumen soybean meal with enhanced undegradable protein was used in high CP diets. High CP diets increased milk protein percentage in multiparous cows and yields of milk, 4% FCM, fat, protein, and SNF in primiparous cows during the normal fiber period. High dietary CP also increased yields of 4% F a , fat, protein, and SNF in primiparous cows fed normal fiber diets. When switched to low fiber diets, primiparous cows fed high CP diets decreased more in 4% FCM and fat yields than those fed low CP. Primiparous cows fed niacin decreased more in 4% FCM than controls. High dietary CP increased DMI in primiparous cows fed normal fiber diets, but those fed low CP diets increased more in DMI when switched to low fiber diets. Supplemental niacin appeared to interact with die-

tary CP in multiparous cows, increasing blood glucose and decreasing blood phydroxybutyrate and NEFA concentrations with the high CP, normal fiber diet. Increased dietary CP improved yields of milk and milk components in primiparous cows. (Key words: rumen undegradable protein, niacin, soybean meal, parity)

Abbreviation key: BHBA = p-hydroxybutyrate, HP = high protein without (-) or with (+) 12 d d of niacin added, LF = low fiber, LP = low protein without (-) or with (+) 12 gld of niacin added, NF = normal fiber, PUN = plasma urea N. INTRODUCTION

High protein (22 to 23% CP) diets minimized the milk fat depression associated with consumption of low fiber (LF) diets (13, 14,15) and increased milk fat percentage when normal fiber (NF) diets were fed (35). More moderate percentages of CP (18.7%) with increased proportions of rumen undegradable protein were ineffective in raising milk fat percentage (34), although intraperitoneal infusion of the AA Arg, Leu, ne, and Val alleviated milk fat depression (1 l). However, all of these protein-supplemented diets increased milk yield (13, 14, 15, 34, 35). Diets with increased proportions of rumen undegadable protein increased milk yield in other studies as well (8, 27). Niacin (nicotinic acid) is a B vitamin synReceived August 12, 1991. thesized by rumen microbes. Ruminal syntheAccepted March 2, 1992. ‘The use of trade names in this publication does not sis was thought to meet the niacin needs of imply endorsement by the North Carolina Agricultural adult ruminants (18). However, orally suppleResearch Service of the products named or criticism of mented niacin increased milk yield (9, 16,22), similar ones not mentioned. milk fat percentage (12, 16), and milk prorein 2F’resent address: Farmland IndustrieS, Inc., Kansas test (12) in some instances. Oral niacin also City MO 64116-0005. has antilipolytic effects, causing depressions in keprint requests. 1992 J Dairy Sci 751965-1978

1965

1966

ET AL..

TABLE 1. Chemical analyses of hay, concenmtes, and soybean meal. Feedstuff1

DM

8

Alfalfa hay

(45) 88.4

17.8

88.4 88.5

9.8 19.8

885 88.5 89.0 89.4

NDF

RUD+

RDP

49.1

28.0

72.0

4.1 5.0

24.4 21.4

51.4 48.0

48.6 52.0

12.5 19.2

4.2 4.5

22.5 21.0

45.2 48.2

54.8 5 1.8

53.0 52.1

7.5 7.4

15.6 15.2

29.6 45.8

71.4 54.2

ADF (k of DM) 37.1

-(% of CP) -

concentrates4

Normal fiber LP

HP Low fiber

LP HP soybean meals5 Untreated Treated

'LP = Low protein diets (0 or 12 g/d of niacin); HP = high protein diets (0 or 12 g/d of niacin). *Rumen undegradable protein. 'Ihe NRC values (18) were used for all feeds except untreated and treated soybean meals, which wece determined by ficin procedure (20). kumen degradable protein. Calculated by difference from rumen undegradable protein. 4 c ~ ~ ~ t soybean i ~ n meai : (untna~LP diets or tru~ted:HP diets), ground corn grain, dicalcium ph~sptute, limestone, magnesium oxide, sodium sulfate, potassium chloride, tracemineralized salt, and vitamins. 'Untreated soybean meal used in LP concentrates and treated soybean meal used in HP concentrates.

blood NEFA (9). These antilipolytic actions resulted in negative yield effects in cows with lower body condition (10, 16). In a previous study conducted in our laboratory (15). cows with higher body condition and increased blood NEFA concentrations did not demonstrate an alleviation of milk fat depression on LF, high protein (HP) diets. Perhaps niacin-supplemented cows with adequate body condition would respond more favorably to a high CP diet. The objectives of this study were to examine the effects of supplemental niacin and dietary CP concentration on milk yield and composition, particularly milk fat synthesis, when early lactation cows were fed NF and LF diets. Effects on various blood and rumen m e tabolites also were examined. MATERIALS AND METHODS

Twenty-three multiparous and 24 primiparous cows were fed one of four 20.5% ADF, NF diets for wk 2 to 5 postpartum. Dietary treatments were arranged in a 2 x 2 factorial design with two levels of dietary CP (13.8 or 18.8%) and two levels of supplemental niacin (0 or 12 gld) for four dietary treatments: low protein with 0 g/d (LP-) or 12 g/d of niacin (LP+) and HP with 0 s/d (HP-) 01 12 gld Of Journal of Dairy Science Vol. 75, No. 7, 1992

niacin (HP+). Following wk 5 postpartum, cows were switched to LF, 11.8% ADF diets maintaining the respective treatment combinations. The LF diets were fed from wk 6 to 13 postpartum. Alfalfa hay served as the forage source throughout the experiment, and it was chopped in a bedding chopper to 10- to 15-cm lengths. The LP diets contained regular, solventextracted soybean meal, and the H p diets contained soybean meal enhanced with rumen undegradable protein (ProtekTM,Central Soya Co., Inc., Fort Wayne, I N). The soybean meal enhanced with rumen undegradable protein was prepared by mixing 2% of packaged, powdered premix with solvent-extracted soybean meal. The treated soybean meal was mixed in 1016.05-kg (1-ton) batches. Rumen undegradability of treated and untreated soybean meal was measured with an in vitro ficin protease procedure (20). Treatment with the premix increased the rumen undegradable protein in the soybean meal by 54.5% (Table 1). Niacin was mixed with wheat bran as a carrier. The niacin and wheat bran mixture was fed at a rate of 45.4 gld per cow to cows on LP+ and HP+ diets; cows on LP- and HPdiets received 45.4 gld of wheat bran. The

1967

DIETARY PROTEIN AND NIACIN TABLE 2. Nutrient compositions of experimental diets.' met2

DM

CP

NDF

ADP

(%I

my

conccntratt

R U D ~ mp4

(% of DM)

Normal fiber

LP HP

- (% of CP) -

88.4 88.4

13.7 18.8

20.3 20.7

36.6 35 .O

49.3 49.0

50.7 51.0

36.5 39.0

63.5 61.0

88.5 88.4

13.8 18.9

11.9 11.7

28.7 27.6

23.3 22.1

76.7 77.9

40.5 44.0

59.5 56.0

Low fiber

LP HP

l ~ a ~ eond a~hlalDMI.

*LP = Low protein diets (0 or 12 g/d of niacii); HP = high protein diets (0 or 12 g/d of niacin), %men undegradable protein. The NRC values (18) were used for all feeds except untreated and treated soybean meals, which were determined by ficin procedure (20). *men degradable protein. Calculated by difference from rumen undegradable protein.

niacin and wheat bran mix was topdressed on hay and grain and fed twice daily. During the preceding dry period, all cows were fed a high energy ration to increase body condition intentionally above normal herd levels. Following calving, cows were weighed on 2 consecutive d and photographed for body condition scoring. Body condition was scored on a fivepoint scale using the method of Edmonson et al. (5). One week postpartum, cows were adjusted gradually to their respective NF diets. Hay and concentrate were fed simultaneously,but not mixed, for 5% refusal. Following wk 5 postpartum, all cows gradually were switched in five equal increments over a 5d period to their LF diets. Hay samples were taken at the beginning of the trial, and concentrates were sampled weekly and composited by 4-wk periods. Chemical analyses of hay and concentrate are listed in Table 1. Nutrient compositions of experimental diets are listed in Table 2. Throughout the study, cows were housed in a tie-stall barn and milked twice daily; milk weights were recorded at each milking. Cows received exercise on a dirt lot for 2 h daily. Cows were fed at 0800 and 1500 h, and individual intakes were recorded twice daily. Throughout the experiment, BW was recorded weekly on 2 consecutive d Milk samples were collected at a.m. and p.m. milkings four times per week during wk 4 to 5 postpartum and twice weekly during the LF period. A composite milk sample was taken from the a.m. and p.m. milk samples and analyzed for fat by the Babcock method, protein by a dye-binding assay (32), and SNF

using a Watson lactometer (A. Daiggert and Co., Richmond, CA). Jugular blood samples collected via venipuncture and rumen fluid samples collected via stomach pump were taken 5 h after the am. feeding, three times weekly during wk 4 and 5 postpamun, and once weekly during the LF period. Urine samples also were collected at this time and scored for ketone content on a scale of 0 (negative) to 160 mddl (positive), providing a crude estimate of urine acetoacetic acid concentrations (Ketostixm, Miles Inc., Elkhart, IN). Deproteinized plasma was analyzed for p-hydroxybutyrate (BHBA) using the method of Williamson et al. (33). Plasma also was analyzed for urea N using a phenol hypochlorite procedure (29) and for glucose with a YSI model 27 industrial analyzer using a membrane-immobilized glucose oxidase (Yellow Springs Instrument Co., Yellow Springs, OH). The NEFA were determined by an enzymatic-colorimetric method (WAKO Pure Chemical Industries, Ltd., Osaka, Japan). Rumen fluid supernatant was acidified with 25% metaphosphoric acid and analyzed for molar proportions of VFA by gas chromatography (31) and ammonia N using a phenol hypochlorite procedure (2). Milk fat samples were collected and prepared using the onestep methylation procedure of Sukhija and Palmquist (30) and analyzed for relative percentage of fatty acids. Fatty acid analysis was performed on a Varian 3700 gas chromatograph (Sugarland, TX). A 183cm column (2 mm x 6 mm) packed with 10% diethylene glycol succinate-packed silica Journal of Dairy Science Vol. 75. No. 7, 1992

1968

ET AL..

on 80/100 mesh (Supelco, Inc., Bellefonte, PA) was used. Temperature was prog-.ed for an initial temperature of 35'C held for 3 min with a 10'Wmin increase up to 170'C. Total run time was 32 min. Carrier N flow was 20 ml/min. Relative area under the curve from the gas chmatograph was used as the quantitative measure in lieu of a standard Data were analyzed as a randomized complete block design using the general linear models procedure of SAS (26). Parity (multiparous versus primiparous) served as the blocking factor, and protein and niacin were the main factors. The full model contained niacin, protein, and parity as the main effects. Because of significant treatment x parity interactions and previous differences in parity sponse (13,14,15,34), data in this study were analyzed separately for multiparous and primiparous cows, using a reduced model with niacin and protein as main effects. Means were calculated by period (fiber level) for each d e pendent variable using data fkom the last 2 wk of the NFperiod and the last 6 wk of the LF period. Niacin and protein main effects and the niacin x protein interaction were tested to d e termine effects on yield, blood metabolites, and rumen responses during the NF period. Main effects and the niacin x protein interaction also were tested to determine effects when cows were switched from the NF to the LF diets. The percentage of change was calculated for each dependent variable using the following equation:

MULTIPAROUS COWS A-A

w-

A-A

LP+

0-0

HP-

0-0

HP+

low fiber diets initiated

3

4

, l , , ,

,

5

8

9

6

7

i t - - i - - t (

1 0 1 1 1 2 1 3 1 4

WEEK OF LACTATION PRIMIPAROUS COWS A-A

LP-

A-A

LP+

0-0

HP-

0-0

HP+

20

=

low fiber diets initiated

10

2

I ,

;

:

;

5

4

5

I

~

6

7

~ 8

:

9

:

:

~

:

I

1 0 1 1 1 2 1 3 1 4

WEEK OF LACTATION

Figure 1. Average daily DMI for multiparous and primiparous cows by week of lactation. LP = Low protein, HP = high PrOttin;LP- = 13.8% CP,0 @d of niacin; W = 13.8% CP,12 g/d of niacin; €IF= 18.8% CP,0 @d of niacin; HP+ = 18.8% CP, 12 g/d of niacia

RESULTS AND DISCUSSION

One multiparous cow was removed from the LP+ diet because of a displaced abomasum. Two additional multiparous cows, one each on the LP- and LP+ diets, were treated for clinical ketosis during the NF period with A = ((B - C)/B) x 100 an i.v. infusion of 500 ml of glucose. Body condition scores d 2 postpartum for where A = percentage of change in dependent multiparous cows were 3.76, 3.86, 3.78, and variable, B = lwp mean for dependent variable, and C = NF mean for dependent variable. 3.58 for W-, W+, HP-, and HP+ diets, reEffects on average daily BW change were spectively. In primiparous cows, condition tested using the actual change in BW change scores were 3.58, 3.43, 3.84, and 3.61 for the between the NF and LF diets using the follow- respective treatments. condition scores were lower (P< .08)for the W diets in primiparous ing equation: cows.

A=B-C where A = actual change for dependent variable, B = LF mean for the dependent variable, and C = NF mean for the dependent variable. Effects were considered to be dif€emt based on a significant (P < .lo) F ratio. Journal of Dairy Scieacc Vol. 75, No. 7, 1992

DMI

Dry matter intakes (Table 3) wexe unaffected by dietary treatment in multiparous cows. In primiparous cows, DMI was higher far the H p diets during the NF period. Intemtingly, when cows were switched to the LF

1969

DIETARY F'ROTEIN AND NIACIN

diets, DMI increased more on the LP diets and actually equaled DMI of the HP diets in primiparous cows (Figure 1). In a previous study (34).DMI was enhanced by an LF, H p diet with high rumen undegradable protein, such as the HP diets used in this experiment. Increased DMI on HP diets is a common finding (23,24, 25), and Egan (6) has stated that DMI could be stimulated by the correction of an AA imbalance. Whatever the mechanism for increased DMI with HP diets, the effect disappeared in the LF period.

Milk Yleld and Composltlon

Milk yield and composition are in Table 4. Milk and component yields were unaffected by dietary treatment in multiparous cows. In primiparous cows during the NF period, yields of milk (Figure 2), 4% FCM, fat, protein, and SNF were higher than for the HP diets. An earlier study (34) showed similar yield increases when an HP,high rumen undegradable protein, LF diet was fed. When cows were switched to the LF diets, 4% F C M decreased

TABLE 3. Iatakes by parity and period @M basis) with contrasts to detect treatment differences daring the normal fiber period and percentage of change differences when cows were switched from normal to low fiber diets.

CP

Ilem

RUDP'

R D S

SEM Treatment effects Low fiber

LPLP+

HPHP+ SEM

NDF

DM

Wd)

Multiparous cows Normal fiber

LP-3 LP+ HPHP+

ADP

2.21 2.25 3.10 3.37 .12

.8 1 .82 1.21 1.31 .05

1.40 1.43 1.89 2.05 .08

3.27 3.34 3.42 3.71 .08

5.89 6.00 5.77 6.26 .14

16.1 16.4 16.5 17.9 .4 NS4

2.64 2.74 3.75 3.81 .12

1.07 1.11 1.65

1.57 1.63 2.10 2.13 .08

2.28 2.36 2.33 2.37 .03

5.51 5.71 5.40

19.2 19.9 19.9 20.2 .3

1.68 .06

5.49

.08

Treatment effects, 5% of change primiparous cows N o d fiber

LP-

NS

2.01 2.01 3.12 3.01 .12

LP+

HPHP+ SEM

Treatment effects CP Level Low fibex LPLP+

HPHP+ SEM Treatment effects, % of change CP Level

.73 .73 1.22 1.17 .05

1.27 1.27 1.90 1.84 .08

2.97 2.97 3.44 3.32

.07

5.34 5.34 5.80 5.59 .14

14.6 14.6 16.6 16.0 .3 .01

2.45 2.46 3.47 326 .10

.99

1.oo 1.53 1.44

.os

1.46 1.47 1.94 1.83 .07

2.11 2.11 2.16 2.03

.a

5.11 5.11 5.00 4.70

.cn

17.8 17.9 18.4 17.3

2 .01

'Rumen degradable protein. The NRC book values (18) were asad for all feeds except untreated and treated soybean meals, which were determined by ficin procedure (20). 2Rumen degradable protein. Calcalated by difference Erom mmen degradable protein. %€"Low protein, Ogldof niacin; LP+ = low proteiu, 12 gld of niacin, HP-= high protein, Ogld ofHP+ = high protein, 12 g/d of niacih.

4P >

.lo. Jomnal of Dairy Science Vol. 75. No. 7, 1992

1970

ZIMMERMAN ET AL.. MULTIPAROUS COWS &-A

U

LP-

LP+ 0-0 HP*-• HP+ ---A

35 li!

lower propoaions of rumen undegradable protein (13, 14, 15) for alleviation of milk fat depression. Rumen Fluid Measures

Y

=?

25.-

z

low fiber diets initiated

1

PRIMIPAROUS COWS a--a

-

A-A

0-0 0-•

\ 71

2

3

4

5

6

7

8

9

LPLP+ HPHP+

1 0 1 1 1 2 1 3 1 4

WEEK OF LACTATION

Rumen W A data are in Table 5. Ruminal acetate:propionate ratios were unaffected by dietary treatment in either parity group. Molar percentage of acetate was lower for the HP diets in multiparous cows during the NF period. A significant CP x niacin interaction was observed for molar percentage of butyrate in multiparous cows during the NF period. Butyrate decreased on the Lp+ diet but increased on the Hp+ diets. Butyrate was higher in primiparous cows fed HP diets during the NF period. Isobutyrate, isovalerate, and valerate concentrations were higher for NF, HP diets in both parity groups. When switched to the LF diets, CP x niacin interaction was significant in multiparous cows, and isovalerate increased for LP- and HP+ diets, and decreased for LP+ and HP- diets. Rumen valer-

Figure 2. Average daily milk yield for multiparous and primiparouscows by week of lactation. LP = Low protein; HP = high protein; LP- = 13.8% CP, 0 g/d of niacin; LP+ = 13.8% CP, 12 B/d of niacin; HP- = 18.8% 8 . 0 g/d of niacin; HP+ = 18.8% CP, 12 g/d of niacin. 4-5 --

w

4.0.-

-A

bk;z&+ *%\

A-.2

p-

A-A 0-0

LP+ HP-

*-• HPC

on the HP and on the HP+ and LP+ diets but c 4 3.5.increased for primiparous cows on the LP%%&S+ $ 3.0Y diets. Milk fat yield also was reduced more by A‘ the HP diets when primiparous cows were 2.5-low iiber diets initiated switched to the LF diets. Reduction in FCM I , , 2 . 0 , : : ; I and fat yields when cows were switched to LF diets probably were due to a nonsignificantly higher milk fat test for the HP+ diet in primipPRIMIPAROUS COWS arous cows during the NF period. Milk fat a--a LPcontent on the HP+ diet decreased below that LP+ 0-0 HPof the other three diets during the LF period, HPf resulting in lower 4% FCM and fat yields. The only significant treatment effect on milk component percentages in either parity group was an increase in milk protein percentage that was due to HP during the NF period in multiparous cows. Milk protein content can 201 ~: :1: ~ : ; i : I be increased by HP diets (7), although the 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 response is inconsistent. We hoped to alleviate WEEK OF LACTATION milk fat depression with the HP+ diet but were Figure 3. Average milk fat percentages for multipamus unsuccessful (Figure 3). In agreement with an and primipmus Holstein cows by week of lactation. LP = earlier study (34).18.7% CP diets that are high Low protein; HP = high protein; LP- = 13.8% 8 . 0 g/d of in rumen undegradable protein do not appear niacin; LP+ = 13.8% CP, 12 g/d Of niacin; HP- = 18.8% to be equivalent to 22 to 23% CP diets with CF’, 0 g/d of niaciq HP+ = 18.8% CP, 12 g/d of niacin. LL

I

.

i

:

i

i

i

i

i

i

A-A

0-0

Journal of Dairy Science Vol. 75, No. 7, 1992

1971

DIETARY F'ROTEIN AND NIACIN

ate also increased in primiparous cows fed HP diets, when cows were switched to the I 3 diets. High CP diets can increase isobutyrate and isovalerate because of rumen degmdation of Val and Leu, respectively (35). Valerate can be produced by rumen degradation of Pro, Arg, Lys, and Met (1). ~. Rumen ammonia N concentrations (Table 6) were higher for the NF, HP diets in both

parity groups. "his was expected because, despite the higher proportion of rumen undegradable protein in the HP diets, the amount of rumen degradable protein was greater in the HE' diets (Table 3). Parameters

Blood measures are in Table 6. Plasma urea N (PUN)concentrations were higher for the

TABLE 4. Milk yield and composition by parity and period with contrasts to detect treatment differences within the normal fiber period and percentage of change differences when cows were switched from normal to low fiber diets. Item

Multiparous cows Normal fiber LP-1

LP+ HPHP+ SEM Treatment effects CP Level Niacin level Low fiber Lp-

LP+

mm+ SEM Treatment effects, % of change CP Level Niacin level primiparous cows Normal fiber

LPLP+ HPHP+ SEM Treatment effects CP Level Niacin level Low fiber

LPLP+

HPHP+ SEM Treatment effects, % of change CP Level Niacin level

Milk

4% FCM

Fat

28.8 28.3 29.0 28.3 1.0

28.5 28.8 29.3 28.1 1.2

1.13 1.17 1.18 1.12 .05

NS2 NS

NS NS

NS NS

30.1 31.3 30.7 29.9 1.1

25.4 26.9 26.7 26.5

NS NS

NS NS

NS NS

21.3 22.0 26.0 25.8 .6

19.8

20.7 24.7 Z.9

.75 .79 .% 1.03

.E

.@I

1.1

.0003 .o004 NS NS 25.7 25.3 30.4 28.8 .8

21.3 20.3 24.2 23.6 .7

NS

.06

NS

.os

.E9 .% .% .97 .05

.m NS .73 68 .80 .8 1 .03

-08 NS

Protein

SNP

.91 .89 .93

.94

2.41 2.31 2.39 2.35

.03

.08

Fat

Protein

SNP

3.88 4.06 3.88 .11

3.13 3.19 3.23 3.32 .03

8.31 8.23 8.26 8.29 .04

4.22

.M

NS NS

NS NS

NS NS

NS

NS NS

.98 1.02 1.06 1.01 .03

2.53 2.60 2.63 2.51 .08

3.02 3.15 3.18 3.18 .15

3.26 3.28 3.49 3.43 .05

8.40 8.35 8.78 8.44 .13

NS NS

NS

NS NS

NS NS

NS NS

3.50 3.52 3.67

3.14 3.26 3.27 3.28

8.28 8.46 8.43 8.38 .06

.67 .72 .85 .85 .02

NS

1.77 1.E8 2.20 2.18

4.01 .ll

.06

.@I

.OOO1 NS

NS NS

NS

NS

NS

NS

NS

.85 .E4 1.04 .98 .03

2.18 2.17 2.58 2.43 .07

2.87 2.68 2.66 2.81 .08

3.33 3.34 3.42 3.42 .06

8.48 8.57 8.49 8246

NS NS

NS NS

NS NS

NS NS

NS NS

.o004

'LP- = 13.8% 8 , 0g/d of niacin; LP+ = 13.8% CP, 12 gld of niacin; HP18.8% CP, 12 gld of niacin. 2P > .lo.

E:

.05

18.8% 8, 0 g/d of niacin; Hp+ =

Journal of Dairy Science Vol. 75, No. 7, 1992

1972

ZIMMWMAN ET AI..

HP diets in both parity groups during the NF fact, the opposite result might be expected period, in agreement with other studies (14,34, because niacin is ureolytic in the rumen (21), 35). Concentrations of PUN decreased in pri- which increases PUN. Blood glucose was miparous cows fed the NF, LP+ and HP+ higher for the HP diets in multiparous cows diets. The reason for a decrease in PUN with during the NF period; however, when cows the LP+ and HP+ diets is not known, and, in were switched to LF diets, the LP diets inTABLE 5. Rumen VFA molar pcrccntagts by parity and period with contrasts to detect normal fiber treatmeat differences and percentage of differences whcn cows were switched from normal to low fiber diets.

(moVl00 mol) Multiparous COWS Normal fiber LP-3

LP+

HPHP+ SEM Treatment effects CP Level Niacin level CP x Niacin Low fiber

LPLP+ HPHP+ SEM Treatment ef€ects. % of change CP Level Niacin level 8 x Niacin Primiparous cows Normal fiber Lp-

LP+ HPHP+ SEM Treatmemt effects CP Level Niacin level Low fiber

LFLP+ HPHP+ SEM Treatment effects, % of change 8 Level Niacin level

10.47 9.77 10.45 10.88 .19

1.33 1.26 1.76 1.82 .07

1.oo 1.09 1.26 1.35 .04

.01 NS NS

NS NS

.001 NS NS

.001 NS NS

24.6 24.8 262 225 1.1

1.06 .86 1.04 1.40 .06

11.44 11.66 12.04 12.52 26

1.39 1.17 1.50 1.97 .10

1.47 1.86 2.13 1.65 .I5

NS NS NS

NS NS NS

NS NS NS

NS NS NS

NS NS .06

NS NS NS

4.38 3.95 3.91 4.04 .13

70.0 68.3 67.4 67.4

16.8 17.6 17.3 17.0

1.01 1.01 1.29 1.18

12 6

.5

.4

.M

9.86 10.49 10.94 11.38 .22

1.11 1.12 1.27 1.19 .03

NS NS

NS NS

NS NS

.03 NS

.001 NS

2.19 2.1 1 2.10 1.94 .10

57.3 57.4 55.1 55.4 .7

28.8 28.4 27.8 29.9 .9

.83 .80 1.22 1.05

10.50 1059 12.01 10.20 .33

1.19 1.39 1.66 1.48

NS NS

NS NS

NS NS

NS NS

NS NS

NS NS

4.03 4.07 3.84 3.97

68.7 69.6 67.3 675

17.2 17.4 18.1 17.2 .4

1.03 .87 1.20 1.30

.ll

.5

NS4 NS NS

.09 NS NS

NS NS NS

2.60 256 2.37 2.82 .15

60.0 59.7 57.1 60.0 1.o

NS NS NS

.06

.M NS

.M

.08

1.43 1.81 1.82 .06

.07

.M NS 1.37 1.41 2.21 2.00 .I2

.02

NS

lAcetate:pmpionate ratio. 2~engu1of VFA carbon chain. %E.-’ = 13.8% CP, 0 g/d of niacin; W = 13.8% CP, 12 gld of niacin; HP- = 18.8% 8, 0 g/d of niacin; HP+ = 18.8% CP, 12 gld of niacin. 4P > .lo.

Journal of Dajr Science VoL 75, No. 7, 1992

1973

DIETARY PROTEIN AND WCIN

were unaffected by dietary treatment during the NF pen& however, multiparous cows on the HP+ diet tended to have lower BHBA. When switched to the LF diets, multiparous cows fed LP diets decreased more in BHBA

creased in blood glucose to a greater extent. Perhaps during the NF period, when energy was more limiting, glumgenic AA availability maeased blood glucose in multiparous cows fed HP diets. Blood BHBA concentrations

TABLE 6. Rumen ammonia N, urine ketone scores, and blood n&abolites by parity and period with contrast0 to detect normal .fiber treatment differences and pnctntagt of change diffcramswhen u1w8 were switched from normal to low fiber diets. plasma

RUlllUl

NEFA

Urine aceto-acetate score

WM-1

(mg/dl)

440.3 509.4 559.6 366.3 45.4

21.8 30.5 20.8 6.9 5.7

ammonia

N

Una

Glucose

BHBAl

MuItiparous cows Normal fiber LP-2

LP+ HPHP+ SEM Treatment effects CP Level Niacin level CP x Niacii Low fiber

LPLP+ HPHP+ SEM Treatment effects, % of change CP Level Niacii level CP x Niacin Primiparous cows Normal fiber

LPLP+ HPHP+ SEM

3.37 3.12 7.42 7.34 56

8.81

6.73 15.41 16.01 .93

55.7 54.1 59.4 63.0 I2

1123 13.51 12.63 7.06 1.46

NS

NS

NS

NS

NS

NS

NS

NS

NS NS

NS

NS

NS

NS

3.11 3.06 8.20 9.98 .76

7.98 7.85 17.36 17.46 1.13

66.4 62.8 68.4

NS NS

NS NS NS

.o001 NS3

NS 3.45 2.64 8.7 1 7.08

.64

.o001

8.75 7.48 18.34 16.70 1.07

.005

68.5

12

.os

3.66 4.69 6.43 4.94 54

177.5 148.8 183.6 1575 11.5

2.7 6.3 8.9 7.1 1.7

NS

NS

.07 NS

NS NS

NS

NS

NS

NS NS

338.9 357.1 375.8 377.1 28.3

19.0 6.2 11.8 10.3 4.2

NS NS

NS NS

60.8 64.4 62.7 62.6 1.0

7.85 5.47 6.81 7.30

.90

Treatment effects CP Level Niacin level Low fiber

LP-

w HPm+

SEM Treatment effects, 46 of change 8 Level Niacin level

.o001 NS

.OOO1

.IO

3.78 3.41 9.24 8.5 1 .67

7.55 7.75 16.29 15.34

NS

NS NS

NS

.99

NS NS 69.7 69.1 71.5 69.6 .9

NS NS

NS NS 3.18 3.07 4.05 3.40 .16 NS NS

1482 137.6 186.3 152.0 9.1

NS NS

1.5

2.0 1.9 1.4

2 NS NS

lf%Hydroxybutyrate. = 13.8% CP, 0 B/d of niacin; LPt = 13.8% CP, 12 g/d of niacin; Hp- = 18.8% 8 . 0 g/d of niacin; HP+ = 18.8% CP, 12 g/d of niacin. 3P > .lo. 2J.P-

Journal of Dairy Science Vol. 75, No. 7, 1992

1974

ZIMMWMAN ET AL.

TABLE 7. Milk fatty acids and average daily B W change for multiparous cows by period with contrasts to detect normal iik treatment differences and peroentage of change differences when cows were. switched from normal to low fibex

-

diets. Item

N o d fikr LP-2 Lp+

HPHP+ SEM Treatment effects CP Level CP x Niacin Low fiber

LPLP+

HPHP+ SEM Treatment effects, % of change CP Level CP x Niacin

C4l

c6

c8

LPHPHP+ SEM Treatment effects CP Level Niacin level CP x Niacin Low fiber

LPLP+

HPHP+ SEM Treatment effects, % of change CP Level CP x Niacin

c169

c16:l

121 .05

8.31 7.67 8.46 10.47 .30

26.91 27.19 27.84 28.63 27

3.48 3.81 3.74 3.26 .10

.06 .@I .03

.03 .02

.04 .02

.01 .01

.03 NS

NS .06

1.34 1.30 1.40 1.54 .05

3.21 3.11 3.74 4.10 .15

3.75 3.64 4.60 4.98 .20

11.82 11.64 12.87 13.88 .36

28.14 28.08 29.03 2858 .46

3.11 3.20 3.11 2.71 .12

NS NS

NS

NS .03

NS3 .01

.lo

1.92 1.84 1.68 1.79

1.89 1.73 1.84 1.98 .06

NS

.97 .83

.92

.06

NS C18:l

.05

c18:2

Clk3

NS NS .10 NS smA4 mA5

Peak area (96)

Normal f i k LP+

c14

(96) 2.06 1.78 1.98 2.89 .14

1.60 1.42 1.55 1.86

.10 NS C18a

c12

1.87 1.62 1.82 2.62 .12

2.21 1.81 1.96 2.17 .06

.06

ClO

17.02 15.12 16.69 2122 .69

35.29 37.52 34.87 30.90 .74

3.14 3.03 2.93 2.78 .12

.64

NS

.01 NS .02

NS NS

NS

NS NS 10.74 9.58 9.22 11.07 .55

28.79 29.95 27.26 24.64 .86

4.48 4.97 4.41 4.00 .19

.7 1 .05

23.92 23.26 26.12 28.28 .70

NS

NS

NS

NS

NS

NS NS NS NS ~_______

NS

.06

NS NS .8 1 .95 .84

~ _ _ _ _ _ _ ~

ADG6

Wd)

13.52 12.43 13.14 12.48 .31

.90 .79 .72

NS NS

52.58 53.88 51.74 46.89 .73

.a2 NS

.001 .10 .o 1

.01

44.83 45.45 41.74 40.42 .93 NS NS

.04

-.49 -1.40

-.m .27 .23

.02 NS NS .13 .08

.44 .33 .12 NS

NS

~

'Length of fatty acid carbon chain; i.e., C4 = butyrate, four-carbon chain. 2Lp- = 13.8% CP, 0 g/d of niacin; LP+ = 13.8% CP, 12 s/d of niacin; HP- = 18.8% CP,0 g/d of niacin; HP+ = 18.8% CP, 12 g/d of niacin. 3P > .lo. 4 ~ ~ r t - c h a ifatty a acids ( ~ to 4 ~14). 5 ~ o n g - fatty c ~ acids (c18fl to ~18:3). 6Average daily BW change.

Journal of Dairy Science Vol. 75, No. 7. 1992

DIETARY PROTEIN AND NIACIN MULTIPAROUS COWS

660

540 520

&-a

w-

A-A 0-0

LP+ HP-

low fiber diets initiated :

2

: 4

3

I , ,

;

,

-

7

6

5

,

,

:

8

;

9

;

;

;

+

1 0 1 1 1 2 1 3 1 4

WEEK OF LACTATION

PRIMIPAROUS COWS LPLP+ HPHP+

&-A A-A 0-0 *-•

,--. 540 m

440

IDW flber

420 2

diets Initiated

I , ,

i

:

:

3

4

5

#

s

6

7

8

WEEK

OF

i

i

i

9

:

:

i

f

1 0 1 1 1 2 1 3 1 4

1975

species of rumen protozoa can not synthesize niacin, so these researchers (4) suggested that heating soybean meal made niacin unavailable to rumen protozoa. Perhaps our treatment of soybean meal ma& niacin unavailable to Nmen protozoa. In other reports (17, 22), niacin supplementation was more effective with soybean meal diets than with NPN diets. The HP diets contained more soybean meal, and this may have enhanced the metabolic response to niacin. The blood metabolite response to the LP+ and HP+ diets in multiparous cows was not surprising, because older cows have a higher incidence of ketosis (28), and ketosis prevention or treatment appears to be the major benefit of supplemental niacin (18). Unfortunately, these metabolic responses did not result in yield responses. The overall low milk yield of the multiparous cows was a problem in trying to elicit a niacin response. Higher yielding cows, under more stress, may have responded more favorably to niacin.

LACTATION

Figure 4. Average body weight for multiparous and primiparous cows by week of lactation.LP = Low proteiq HP = high protein; LP- = 13.8% 8 . 0 g/d of niacin; Le+ = 13.8% 8, 12 gld of niacin; HP- = 18.8% CP,0 gld of niacin; HP+ = 18.8% CP, 12 g/d of Win.

because of higher BHBA concentrations during the NF period. Blood NEFA and urine ketone scores also were not affected by dietary treatment, but, again, multiparous cows fed the HP+ diet tended to have lower NEFA and urine ketone scores. Increased small intestinal supplies of AA increased blood NEFA (19, 35), but niacin supplementation of H p diets in multiparous cows appeared to override this response and, actually, to depress adipose tissue lipolysis. Blood metabolites apparently were affected in multiparous cows fed the NF,HP+ diet. The HP+ diet increased blood glucose and tended to decrease blood NEFA and BHBA, as well as lowering urine ketone scores, which are all typical responses to niacin supplementation of early lactation cows (9). Reasons for the apparent response in blood metabolite to HP+ diets are unknown, but Dennis et al. (4) found that niacin supplementation of heated soybean meal diets increased rumen protozoal counts compared with unheated soybean meal diets. Some

Mllk Fatty Acids

Multiparous Cows. Milk fatty acid composition for multiparous cows is in Table 7. Means are peak area percentages, which are similar to weight percentages. During the NF period, HP diets increased milk c6,c8,clo, (212, C14, Cl,j.o,and total short-chain fatty acids (C4to C14).The HP diets also decreased milk c18:1 and total long-chain fatty acids (Cl8:O to c18:3). Niacin supplementation decreased total longchain fatty acids. However, there also were many significant CP x niacin interactions during the NF period. Milk c4,c6,c89 ClO, C12r c14,c161, c18:1,total short-chain fatty acids (C4 to C14), and total long-chain fatty acids (c18:O to c18:1)all exhibited significant CP x niacin interactions, primarily because of increased shortchain fatty acids and decreased long-chain fatty acids on the HP+ diet. When cows were switched to the LF diets, Clo, C12, C14, and total shortchain fatty acids all exhibited significant CP x niacin interactions; short-chain fatty acids increased more on the LP+ diets and decreased to a greater extent on the HP+ diets. Primiparous Cows. Milk fatty acid composition for primiparous cows is in Table 8. The HP diets increased c6 of milk during the NF period, and niacin supplementation Journal of Dairy Science Vol. 75, No. 7, 1992

1976

Z M M E R W W ET AL.

TABLE 8. Milk fatty acids and B W change for primipamns cows by period with contrasts to detect normal fiber treatment differences and percentage of change treatment d i f f wh ~en~cows were switched from normal to low fiber diets. Item

C4l

c6

c8

c10 c12 Peak area (46)

c14

c169

c161

1.97 2.08 2.19 2.15

1.71 1.61 1.96 1.77

1.11 1.01 123 1.15

.07

.06

.05

2.35 2.13 2.65 2.43 .12

2.60 2.45 2.93 2.69 .14

9.96 9.57 9.90 10.00 .32

2728 27.01 26.76 28.01 .32

2.83 2.93 2.86 3.03 .08

Normal fiber LP-2

LP+

HPHP+ SEM Treatment effects CP Level Niacin level

Low fiber LPLP+

HPHP+ SEM Treatment effects, % of change CP Level Niacin level

NS3 NS

NS NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

1.69 1.87 1.64 157 .05

1.80 1.71 1.84 1.71 .04

1.30 1.24 1.43 1.35 .03

3.38 3.10 3.84 3.73 .10

4.16 3.84 4.69 4.74 .14

12.85 12.15 13.01 13.62 .22

29.27 29.51 27.78 29.80 .53

2.85 2.88 2.61 2.89

NS

NS NS

NS

NS

NS

NS

NS

NS saA4

NS NS

.07

.03

NS c180

NS C18:l

c18:2

Lp+

HPHP+ SEM Treatment effects CP Level Niacin level Low fiber

LPLP+

HPHP+ SEM Treatment effects, % of change CP Level Niacin level

-A5

Peak area (46)

Normal fiber

LP-

c183

15.19 14.34 14.87 13.72 .19

31.19 32.32 30.66 31.23 .82

2.93 3.65 3.01 2.96 .14

NS

NS NS

NS NS

10.34 9.77 10.44 9.50 .38

2751 28.42 27.26 25.89 .6 1

3.87 4.49 4.56 4.33 .13

.97 1.03

NS NS

NS

NS NS

NS

.01

NS

~

.89 .89

.98 .86

.04 NS

NS

90 .88 .05

NS

.08

NS NS ADG6

Wd)

-.a4

19.70 18.85 20.86 20.19 .66

50.19 51.21 49.52 48.77 .82

NS NS

NS

NS

NS

NS

25.18 23.91 26.45 26.71 .44

42.70 43.70 43.16 40.60 .82

NS NS

NS

-28 .24

-.04 .14

.43 .34 .42 28 .06

NS

NS

NS

~~~~

'Length of fatty acid carbon chain; i.e., C4 = butyrate, four-carbon chain. 2LP- = 13.8% CP, 0 g/d of niacin; LP+ = 13.8% CP, 12 g/d of niacin; HP- = 18.8% CP, 0 g/d of niacin; HP+ = 18.8% CP. 12 g/d of niacin. 3P > .lo. 4Short-chain fatty acids (C4 to Ci4). 5~onp-chainfatty acids (c189 to ~ 1 a 3 ) . 6Average daily B W change.

Journal of Dahy Science Vol. 75, No. 7, 1992

1977

DIETARY PROTEIN AND NIACIN

sons for these differences in parity response to increased CP between our studies and others are uncertain but may result from an interaction between parity and source of added dietary CP. Because primiparous cows are both lactating and growing, the mixture of absorbed BW AA supplied by the supplemental soybean Average daily BW changes are in Tables 7 meal may be more favorable to the combinaand 8. During the NF period, on average, tion of growth and milk yield in primiparous multiparous cows fed HP diets actually gained cows. BW, whereas multiparous cows fed LP diets lost substantial BW (Figure 4). Cows fed the CONCLUSIONS Hp+ diet were the only multiparous group to Niacin supplementation of NF, HP diets gain BW during the NF period. This could explain the protein x niacin interactions ob- appeared to stimulate a blood metabolite reserved in milk fatty acids during the NF period sponse in multiparous cows by increasing in multiparous cows. Gaining rather than los- blood glucose concentrations and producing ing BW would result in decreased long-chain lower (nonsignificant) concentrations of fatty acid availability for milk fat synthesis. BHBA and NEFA. However, this metabolite These findings also are supported by the response did not result in the expected yield decreased blood NEPA in multiparous cows response. In primiparous cows, the LP+ and fed the NF, HP+ diet. Primiparous cows HP+ diets exhibited no major effects, but HP receiving the LP diets had lower BW (Figure diets increased yields of milk, fat, protein, and 4). which may partially explain their lower SNF and increased DMI during the NF period. When primiparous cows were switched to LF DMI during the NF period. diets, DMI of Lp diets equaled that of H p diets, but milk yield was still lower for the LP General Discussion decreased the proportion of c18:O in milk fat during the NF period. When cows were switched to the Lp diets, the HP diets decreased the concentrations of milk C,.

diets.

The parity responses observed in this experiment were interesting. The major response in multiparous cows was a blood metabolite response to niacin supplementation of the NF, HP diet, resulting in increased blood glucose and decreased blood NEPA and BHBA concentrations. The only yield response observed was an increase in milk protein test on the NF, HP diets. By minimizing the metabolitic signs of ketosis, we should have triggered a yield response with the HP+ diet, because ketosis decreases milk yield; however, no milk yield response was significant, In contrast, primiparous cows responded only to increased dietary protein with a strong milk yield response during the NF period. There was no response to niacin supplementation in primiparous cows and no major metabolite responses to either protein or niacin. In contrast with other reports (3, 23, 24, 25). studies conducted in our laboratory demonstrated that primiparous cows often respond more favorably than multiparous cows to increased dietary protein supply (13, 14, 24). In these studies, soybean meal has been the source for obtaining higher CP. The rea-

The yield response observed in primiparous cows agrees with our earlier findings (13, 14, 34) but contrasts with the work of others (3, 23,24,25).The response in primiparous cows may be due to differing priorities for use of nutrients in the two parity groups. Unfortunately, an 18.7% CP diet with high rumen undegradable protein in this experiment did not elicit the same response in minimizing the milk fat depression associated with feeding LF diets as noted by others with a 22 to 23% CP diet with a lower proportion of m e n undegradable protein (13, 14,15). Further work is necessary to clarify the parity response to increased total and rumen undegradable protein. ACKNOWLEDGMENTS

The authors extend their sincere appreciation to Central Soya Co.,Inc., Fort Wayne, IN for donation of the rumen undegradable protein-enhancing premix. REFERENCES 1 Andries, J. I., F. X.Buysse, D. L. De Brabrinder, and

B. G. Cottyn. 1987. Isoacids in nlminant nutrition: Journal of Dairy Science Vol. 75, No. 7. 1992

1978

ZIMMERMAN ET AL.

their role in ruminal and intermediary metabolism and possible influences on performances-a review. h i m . Feed Sci. Technol. 18:169. 2Broderick G. A., and J. H. Eung. 1980. Automated simulumeons determination of ammonia and total amino acids innrminal fluid and invitro media J. Dairy Sci. 6364. E.E. 3 Cressman, S. G., D. G. Grieve, G.K. wheeler, and L. G.Young. 1980. Influence of dietary protein concentration on milk production by dairy cattle in early lactation. J. Dairy Sci. 63:1839. 4Denuis, S. M., M. J. Arambel, E. E. Bartley. D. 0. Riddell, and A. D. Dayton. 1982. Effect of heated or unheated soybean meal with or without niacii on rumen protozoa. J. Dairy Sci. 65:1643. 5 Edmonson, A. J., I. J. Lean, L. D. Weaver, T. Farrer, and G.Webster. 1989. A body condition scoxing chart for Holstein dairy cows. J. Dairy Sci. 72:68. 6 E g q A. R. 1980. Host animal-rumen relationships. Roc. Nutr. SOC.39:79. 7 Emery, R. S. 1978. Feeding for increased milk protein. J. Dairy Sci. 61:825. 8Forster, R. J., D. G. Grieve, J. G. Buchanan-Smith, and G. K. MacLeod. 1983. Effect of dietary protein degradability on cows in early lactation. J. Dairy Sci. 66:1653. 9 Fronk, T. J., and L. H. Schultz. 1979. Oral nicotinic acid as a treatment for ketosis. J. Dairy Sci. 621804. 10 Holter, J. B., F.J. Janicb, C. A. Bartlett, H. H. Hayes, and C. G. Schwab. 1983. Niacin supplementation in early lactation. J. Dairy Sci. 78(Suppl. 1):167.(Abstr.) lIHopkins, B. A., A. H. Rakes, T. E. Daniel, C. A. 2‘ m. and W. J. Croom, Jr. 1990. Effects of intraperitoneal infusion of Gleucine, L-isoleucine, Lvaline, and L-arginine on alleviation of milk fat depression in early lactation Holstein dairy cows. J. Dairy Sci. 73(Suppl. 1):171.(Abstr.) 12 Homer, J. L., C. E. Coppock, G. T. Schelling, J. M. Labore. and D. H. Nave. 1986. Influence of niacin and whole cottonseed on intake, milk yield and composition, and systemic responses of dairy cows. J. Dairy Sci. 693087. 13 Jaquette, R D., A. H. Rakes, and W. J. Croom. Jr. 1986. Effects of dietary protein on milk, rumen, and blood parameters in dairy cattle fed low fiber diets. J. Dairy Sci. 691026. 14 Jaquette, R D., A. H. Rakes, and W. J. Croom, Jr. 1987. Effect of amount and source of dietary nitrogen on milk fat depression in early lactation dairy cows.J. Dairy Sci. 701202. 15 Jaquette, R D., A. H. Rakes, and W. J. Croom, Jr. 1988. Effects of body condition and protein on milk fat depression in early lactation dairy cows. J. Dairy Sci. 71:2123. 16 Jaster, E. H., G. F. Harmell, and M. F.Hutjens. 1983. Feeding supplemental niacin for milk production in six dairy herds. J. Dairy Sci. 66:1046. 17Kung, L.,K. Gubert, and J. T. Huber. 1980. Supple mental niacin for lactating cows fed diets of natural protein or nonprotein nitrogen. J. Dairy Sci. 63:2020. 18Natiod Research Council. 1989. Nutrient Requuements of Dairy Cattle. 6th rev. ed. Natl. Acad. Sci., J o d of Dairy Science Vol. 75, No. 7, 1992

Washington, DC. 19Orskov, E. R., D. A. Grubb, and R.N.B. Kay. 1977. Effect of poshuminalglucose or protein supplementation on milk yield and composition in Friesian cows in early lactation and negative energy balance. Br. J. Nutr. 38:397. 20Poos-Floyd, M., T. Klopfensteia, and R. A. Britton. 1985. Evaluation of laboratory techniques for predicting ruminal protein degradation. J. Dairy Sci. 68:829. 21 Riddell, D. 0..E. E. Bartley, and A. D. Dayton. 1980. Effect of nicotinic acid on rumen fermentation in vitro and in vivo. J. Dairy Sci. 63:1429. 22 Riddell, D. O., E. E. Bartley, and A. D. Dayton. 1981. Effect of nicotinic acid on microbial protein synthesis in vitro and on dairy cattle growth and milk production. J. Dairy Sci. W782. 23Roffler, R E.,L. D. Satter, A. R &die, and W. J. Tyler. 1978. Influence of dietary protein concentration on milk production by dairy cattle during early lactation. J. Dairy Sci. 61:1422. XRoffler, R. E., and D. L. Thacker. 1983. Early lactational response to supplemental protein by dairy cows fed grass-legume forage. J. Dairy Sci. 66:2100. 25 Roffler, R. E., and D. L. Tbacker. 1983. Influence of reducing dietary crude protein from 17 to 13.5% on early lactation. J. Dairy Sci. 6651. 26 SAS@User’s Guide: Statistics. 1982. SAS Inst., Inc., Cary, NC. 27 Schingoethe,D. J., D. P. Casper, C. Yang, D. J. Illg, J. L. Sommerfeldt, and C. R Mueller. 1988. Lactational response to soybean meal, heated soybean meal, and extruded soybeans with ruminally protected mthionine.. J. Dairy Sci. 71:173. 28 Schultz, L. H. 1988. Milk fever, ketosis, and the fat cow syndrome. Page 500 in The Ruminant AnimalDigestive Physiology and Nutrition. D. C. Church, ed. Prentice Hall, Englewood Cliffs, NJ. 29 Sigma Chemical Co. 1981. The colorimetric determination of urea nitrogen. Bulletin No. 640. Sigma Chemical Co., St Louis, MO. u)Sakhija, P. S., and D. L. Palmquist. 1988. Rapid method for determination of total fatty acid content and composition of feedstuffs and feces. J. Agric. Food Chem. 36:1202. 31 Supelco, Inc. 1975. GC separation of WA’s C 2 4 5 . Bulletin No. 510. Supelco. Inc., Bellefonte, PA. 32 Udy, D.C. 1956. A rapid method for estimating total protein in milk. Nature (Lond.) 178314. 33Williamson, D. H., J. Mellanby, and H. A. Krebs. 1962. Enzymatic determination of D(-)-P hydroxybutyric acid and acetoacetic acid in blood. Biochem. J. 8290. 34 Zimmerman, C. A., A. H. Rakes, T. E. Daniel, and B. A. Hopkins. 1990. Effect of rumen undegradable protein on lactational performance in cows fed low fiber diets. J. Dairy Sci. 73(Suppl. 1):169.(Abstr.) 35 Zimmerman,C. A., A. H.Rakes, R. D. Jaquette, B. A. Hopkins. and W. J. C m m , Jr. 1991. Effects of protein level and forage source on milk production and composition in early lactation dairy cows. J. Dairy Sci. 74980.