Effects of Whole Cottonseed or Niacin or Both on Casein Synthesis by Lactating Holstein Cows1

Effects of Whole Cottonseed or Niacin or Both on Casein Synthesis by L~ctating Holstein Cows1 J. K. LANHAM, C. E. COPPOCK, K. N. BROOKS,2 D. L. WILKS, and J. L. HORNER Department of Animal SCience Texas A&M University and Texas Agricultural Experiment Station College Station 77843 ABSTRACT

Forty Holstein cows in late lactation were offered diets containing niacin and whole cottonseed: 1) 0 gld, 0%; 2) 0 gld, 15%; 3) 6 gld, 0%; and 4) 6 gld, 15%, to evaluate effects on milk casein synthesis. Cows fed diet 1 had the highest DMI. The FCM (21.4 vs. 18.7 kg/d) and milk fat percentage (4.08 vs. 3.81) were higher for cows fed diet 1 than for those fed diet 4. Milk protein percentage (3.61 vs. 3.50) was higher for cows fed diet 1 than for those fed diet 2. Casein N, as a percentage of total N, was higher (71.9 vs. 68.0%) in milk from cows fed diet 1 than those fed diet 3. Insulin tended to be elevated in cows on the diets containing niacin, but glucose was not affected. Plasma niacin was elevated in cows on the diets supplemented with niacin compared with diet 1. Plasma AA were changed only slightly by treatments. The beneficial effect of niacin on milk casein synthesis, noted in our earlier work when cows were fed whole cottonseed, was not evident in this study with cows in late lactation and during hot weather. (Key words: cottonseed, niacin, casein) Abbreviation key: EP = experimental period, SP = standardization period, WCS = whole cottonseed. INTRODUCTION

The major negative effect observed with the addition of fat to the diet of lactating dairy

Received December 28, 1990. Accepted July 15, 1991. ITechnical Article 26030 by the Texas Agricultural Experiment Station 77843. 2Deceased. 1992 J Dairy Sci 75:184-192

cows is decreased milk protein percentage (6, 10). Amos (1) suggested that decreased protein production could be related to the decreased grain (starch) intake when fat is substituted for concentrate and the related decrease in propionate production in the rumen. Propionate is gluconeogenic and is estimated to provide about 70% of the total glucose synthesized in the ruminant. Glucose is required for milk lactose synthesis, and it provides glycerol for milk fat triglyceride. Propionate production may be lowered when grain is replaced with fat in the diet, resulting in a decrease in the supply of this glucose precursor. However, fats containing a high percentage of unsaturated fatty acids may offset some of the propionate loss (from starch) by altering ruminal fermentation to increase propionate production. This may require that some absorbed AA be converted to glucose (gluconeogenesis) at an increased rate, leaving fewer free AA available for milk protein synthesis. Niacin supplementation in the diets of lactating dairy cows has resulted in positive effects on milk yield and composition. In a study involving six dairy herds, Jaster et al. (16) found that milk production of niacinsupplemented cows peaked earlier, and milk production of high producing cows in first lactation was greater when they received supplemental niacin. These researchers suggested that the response to niacin is greater for fresh cows versus those in later lactation and is greater in those fed a natural protein source over those fed urea. Riddell et al. (23) observed a slight improvement in milk protein production when niacin was fed to lactating cows. Horner et al. (13) found that milk protein percentage, casein as a percentage of total N, and milk protein yield were higher with

184

185

WHOLE COTIONSEED OR NIACIN EFFECTS ON MILK CASEIN TABLE 1. Composition of concentrate mixtures and complete diets. l Diet

2 Ground com Soybean meal Defluorinated phosphate Limestone Plain salt Magnesium oxide Sodium bicarbonate Dairy fortifie? Niacin premix3 Concentrate Whole cottonseed Coastal bermudagrass bay Corn silage Total

3

4

- - - - - - - - Concentrate mixtures - - - - - - - 60.95 59.37 59.95 58.00 33.90 33.90 33.90 33.90 1.90 1.90 1.90 1.90 1.30 2.20 1.30 2.20 .35 .35 .50 .50 .50 .67 .67 .50 1.00 1.33 1.00 1.33 .10 .13 .10 .13 1.00 .00 .00 1.33 60

o

10 30 100

- - - - - - - Complete diets - - - - - - - - 60 45 45 15 o 15 10 10 10 30 30 30 100 100 100

IDry basis. 2Dairy fortifier contained 1.59% Ca, 3.15% Mg, 5.69% K, 3.05% Na, 32.05% S, 7.62% NaCI, 38,289 ppm Fe, 521 ppm Co, 15,904 ppm Cu, 55,186 ppm Mn, 52,773 ppm Zn, 795 ppm I, 10 million IU vitamin A, 4.4 million IU vitamin D, and 3.8 million IU vitamin FJkg. 3Niacin premix contained 5% niacin and 95% com.

niacin supplementation but tended to be lower feed intake, milk yield and composition, and with whole cottonseed (WCS) feeding. These arterial-venous differences of AA across the researchers suggested that milk protein depres- mammary gland of lactating Holstein cows in sion with WCS feeding was alleviated by nia- late lactation. cin because of stimulation of mammary gland casein synthesis. MATERIALS AND METHODS Broderick et al. (5) fed five concentrations Forty Holstein cows in mid to late lactation of protein, rangiIlg from 9 to 18%, to lactating dairy cows. Examination of AA concentrations and averaging 23.5 kg of FCM/d were arin jugular and mammary vein plasma of cows ranged in a randomized complete block design on all levels of protein showed that methio- with a factorial arrangement of treatments. Avnine, valine, and lysine were the most likely erage for days in milk was 256, a value exaglimiting AA for milk production. Schwab et aI. gerated by two open cows with extended lacta(26) found that lysine infusion accounted for tions (565 and 677 d). Average BW was 587 16% of the response in yield of milk protein, kg. Cows were fed complete rations, for ad but infusion of lysine plus methionine ac- libitum intake, containing 45 or 60% concencounted for 43% of the total response in yield trate, 15 or 0% WCS, 30% com silage, and of milk protein in lactating dairy cows. This 10% chopped bermudagrass hay (Table 1). suggested that lysine and methionine were Diet treatments were 1) 0 gld of niacin plus first- and second-limiting or were colimiting 0% WCS, the control; 2) 0 gld of niacin plus AA for secretion of milk protein in their study 15% WCS; 3) 6 gld of niacin plus 0% WCS; (26), but, under conditions in which a protein and 4) 6 gld of niacin plus 15% WCS. Cows supplement high in lysine and slowly degraded were assigned to 1 wk of adjustment to the was used, this generalization would not hold. barn and feeding regimen, followed by a This study is a continuation of our earlier l-wk standardization period (SP). One week of work (13) to determine the effects of niacin adjustment was used because the herd diet the and WCS, individually and in combination, on cows had been consuming was similar to diet Journal of Dairy Science Vol. 75, No. I, 1992

186

LANHAM ET AL.

2, which was fed during the adjustment week and the SP. During the SP, feed was offered for ad libitum consumption, and individual feed consumption was measured daily. At the end of the SP, cows were ranked and blocked on FCM and assigned randomly to one of the four treatments within blocks. Observations were taken during the SP to provide data for covariance adjustment of the data obtained during the experimental period (EP). The next 2 wk were used for adjustment to treatments, followed by 4 wk of EP. Cows were confined to a tie-stall bam and fed twice daily 12 h apart (4-h access ad libitum each feeding with access to water) with individual feed consumption measured daily. The remainder of the time, cows were handled as one group in a drylot with access to water and shade except for milking twice daily in a milking parlor. Composition of the concentrate mixtures and the complete rations is in Table 1. Individual feeds and complete rations were sampled three times per week during the SP and EP. Feed sam,..,les were dried at 55"C, airequilibrated for 4~ h, and composited by period before grinding through a 2-mm screen with a Wiley mill (Arthur H. Thomas, Philadelphia, PA). Feed samples were analyzed for DM at loo·C, CP by Kjeldahl, and ether extract for 16 h for feeds without WCS and 96 h for WCS and feeds that contained WCS, ADF (2), and niacin (3). Mineral profiles of feeds were characterized by the Northeast DHI Forage Testing Laboratory (21). Blood samples were taken weekly. One sample was collected from the coccygeal artery into an EDTAcoated tube. Four blood samples were collected from the subcutaneous abdominal vein, three into heparinized tubes, and one into an EDTA-coated tube. Plasma from the EDTAcoated tubes (one arterial and one venous) was used to determine differences in arterialvenous AA (4). Plasma from the heparinized tubes was used to determine glucose by glucose oxidase (27), insulin by radioimmunoassay (15), and nicotinic acid (3). Body weights were taken weekly. Milk weights and samples were obtained during six consecutive milkings per week.. Three daily composite samples were taken for total solids, protein, fat, and SCC (11); a weekly composite was taken for analysis of casein N (24). Journal of Dairy Science Vol. 75, No.1, 1992

........

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187

WHOLE COTIONSEED OR NIACIN EFFECfS ON MILK CASEIN

Data were analyzed by SAS (25) using the model

Yijk:l = m + Bi + Wj + Nk + C l

+ NCkl + Cov +

&jkh

where the variables were m, the mean; Bi> block; Wj, weeks; Nk, level of niacin; q, level of WCS; NCkl, interaction; Cov, a covariate based on values from the SP; and &jkh the error term. Significance was declared at P < .05 unless otherwise noted. RESULTS AND DISCUSSION

Nutrient contents of the diets are in Table 2. Diets were formulated to contain 17% CP, but lower CP in com silage, coastal bermudagrass hay, and WCS caused CP in the fonnulated complete rations lower than 17%. However, the CP content of the diets exceeded NRC (20) requirements for this milk production (19 kg! d), and CP intake across diets was uniform. Differences in ether extract and ADF reflect the contribution of these components from WCS. The addition of niacin to complete rations 3 and 4 is reflected in the niacin content of those diets. AIl minerals were supplied to meet or exceed NRC (20) requirements with the exception of S, which was marginal in three of the diets with .20% recommended by NRC (20), but S probably was not limiting at the milk yields in this study. Effects of diets on OM! are in Table 3. Dry matter intakes were significantly higher for diet 1 than the other three diets, regardless of the expression of consumption. High energy, relatively low fiber diets were used-despite the late stage of lactation and relatively low yield-to sustain milk yields as much as possi-

ble in hot weather and to permit restoration of body stores before drying off. Consumption of OM was lower than on previous studies (13, 14), which reflects the late stage of lactation, heat stress (July 22 through September 8, 1987), and lower milk yield of cows on our study. The average maximum daily temperature was 35.8·C. Dry matter intake was normal for cows producing 20 kg of milk (20), and these cows were in positive energy balance. Calculation of NEL balance, assuming a 25% increase in maintenance requirements from heat stress, showed positive balances across the EP of 6.71, 4.09, 2.32, and 5.28 Mcal/d, respectively. Cows gained weight consistently (data not shown) during the study. The decline in OM! that has occurred in some studies with WCS feeding (7) occurred here also (Table 3). Because WCS was substituted entirely for concentrate, diets 2 and 4 are higher in energy density and fiber than diets 1 and 3. The higher fiber may be responsible for the lower OM! of these diets. Cows fed diet 3 (0% WCS, 6 g of niacin) had the lowest OM!. Because of the late stage of lactation and low production, niacin was probably not limiting, and the supplement may have provided an excess that caused the lower OM!. Effects of treatments on milk yield and composition are in Table 4. Muller et al' (19) showed increased milk yields during the summer with supplemental niacin but no effect on milk composition. Oaily milk yields were not different in our study. This is in agreement with results of Jaster et al. (16) and Kung et al. (17) in which actual milk yields were not affected by niacin supplementation, yet contrasts with results of Dufva et al. (9) and Riddell et aI. (23) in which milk yields were increased with niacin supplementation of cows in early lactation. There were no interactions

TABLE 3. Effects of diets with or without whole cottonseed (WCS), or niacin, or both, on DM! in Holstein cows.

og

DM!, kg/d DM!, BW DM!, kg/kg BW 75

"'''Least

6 g of Niacin

of Niacin

0% WCS (Diet I)

15% WCS (Diet 2)

0% WCS (Diet 3)

15% WCS (Diet 4)

19.8a

17.4" 2.92b .14b

16.7" 2.79b .14b

17.2" 2.88 b .14b

3.27a

.16a

SE .3 .09

<.01

squares means within rows with different superscripts differ (P < .OS). Iournal of Dairy Science Vol. 75, No.1, 1992

188

LANHAM ET AL.

TABLE 4. Effects of diets with or without whole cottonseed (WCS), or niacin, or both, on milk yield and composition of Holstein cows.

og

of Niacin

0% WCS (Diet 1) Milk yield, kg/d 3.5% FCM, kg/d Fat, % Fat yield, kg/d Protein, % Protein yield, kg/d Casein N, % total N SCC (x 1000) Lactose and minerals, % Total solids, %

19.3 21.4a 4.0S a .8oa 3.61 c .70 71.9a 145 4.97b 12.88

6 g of Niacin

15% WCS (Diet 2) 19.5 21.2ab 4.02ab .76ab 3.50d .67 71.4ab 178 5Al ab 12.73

0% WCS (Diet 3)

15% WCS (Diet 4)

19.1 20.oab 3.SSab .74ab 3.52cd

IS. 1 18.7b 3.S1b .69b 3.55cd

.67 68.0b 239 5.34ab 12.71

.63 69.4ab 346 5.73a 13.13

SE .8 .8 .09 .03 .04 .03 1.2 93 .26 .25

a,buast squares means within rows with different superscripts differ (P < .05). c.dLeast squares means within rows with different superscripts differ (P < .10).

between niacin and WCS for milk yield or composition. Milk fat percentage was highest on diet 1 and significantly higher than diet 4 (Table 4). However, the cows on the control diet (diet 1) had high milk fat percentages for Holsteins, even for this late stage of lactation. There was no effect of niacin with or without WCS. Mean milk fat percentages for the diets containing 15% WCS, 0% WCS, 6 g of niacin, or 0 g of niacin were 3.92, 3.98, 3.85, and 4.05%, respectively. Previous studies [e.g., (9, 16)] showed no change in milk fat percentage with niacin supplementation, and Muller et al. (19) showed no change in milk fat percentage with supplemental niacin in summer. The most consistent benefit of feeding WCS has been an increase in milk fat percentage (6). However, the response did not occur in our study and may reflect elevated milk fat percentages associated with late lactation and ample fiber in the control diet. Milk fat yield was significantly higher for cows fed diets 1 versus 4, which was due to the higher milk fat percentage and higher (nonsignificantly) milk yield (Table 4). Homer et a!. (13) reported that diets without WCS, but supplemented with niacin, increased milk fat percentage, but their cows were in early lactation. Milk. fat percentage of diets 1 and 3 did not differ. Milk. protein percentage was significantly depressed (P < .1) for cows fed diet 2 versus 1; however, the niacin-supplemented Journal of Dairy Science Vol. 75, No. J, J992

diets with or without WCS did not differ. This supports the reported finding that WCS and other forms of supplemental fat depress milk protein percentage (8, 10). This contrasts with our previous research (13) in which supplemental niacin in a WCS-containing diet increased milk protein percentage over that in a diet containing WCS but no niacin. However, cows in that study (13) were in early lactation, and niacin may have been limiting in cor,trast to the present study. Mean milk protein percentages for the diets containing 15% WCS, 0% WCS, 6 g of niacin, or 0 g of niacin were 3.52, 3.57, 3.54, and 3.56, respectively (Table 4). Muller et al. (19) showed no increase in milk protein percentage with supplemental niacin in summer, which is in agreement with results of our study. The yield of protein was not different among diets (Table 4). Depression in milk protein percentage, often associated with WCS feeding, has been attributed to a decrease in casein synthesis (8, 28). The niacin-supplemented diet without WCS had lower percentage casein N than the one containing no WCS and no niacin; this contrasts with our earlier research (13), which showed increased casein N with niacin supplementation of diets without WCS (Table 4). Mean casein N percentages (as a percentage of total milk. N) for the diets containing 15% WCS, 0% WCS, 6 g of niacin, or 0 g of niacin were 70.4, 69.9, 68.7, and 71.6, respectively. The differences in protein percentages be-

189

WHOLE COTTONSEED OR NIACIN EFFECTS ON MILK CASEIN

TABLE 5. Effects of diets with or without whole cottonseed (WCS) or niacin on plasma metabolites in lactating Holstein cows.

og 0% WCS (Diet 1) Insulin, IU/ml Glucose, mgldl Niacin, mgldl

14.9a 59.1 l1.1 c

6 g of Niacin

of Niacin 15% WCS (Diet 2)

0% WCS (Diet 3)

S.Sb 5S.6 12.Scd

IS.6 a

15% WCS (Diet 4) ab

12.6 6O.S 13.0"

60.2 13.0c

SE 2.1 1.6 1.2

a,"Least squares means within rows with different superscripts differ (P < .05). c,dLeast squares means within rows with different superscripts differ (P

tween this study and our previous research (13) reflect late lactation cows in the present experiment. With high yielding cows, DM! will be increased, which will increase the rate of digesta passage and escape of undegraded protein from the rumen. TIlls situation, in conjunction with stimulated microbial protein synthesis, should increase the protein available to the small intestine for absorption and subsequent use by the mammary gland However, in later lactation, niacin may not have been limiting, and this may explain why no differences were observed. Niacin has been shown to be antilipolytic and has been used to treat ketosis (12). Cows in early lactation often suffer subclinical ketosis, and niacin may allow them to recover from this metabolic disorder. If ketosis is alleviated, then fewer AA would be used for gluconeogenesis, which would spare AA for protein synthesis in the mammary gland. However, if niacin is not limiting or if cows are not affected by ketosis as in late lactation, then no differences in protein synthesis may be 0bserved. Total solids and SCC were not affected by treatments (Table 4). Lactose and minerals were highest for diet 4 and were significantly higher than diet 1. TIlls is in partial agreement with the study of Horner et al. (13) in which a WCS plus niacin diet had the highest lactose plus minerals but differed significantly only from the diet with no WCS plus niacin. Plasma metabolite concentrations are shown in Table 5. The mechanisms involved in the depression of milk protein often observed with added dietary fat have not been elucidated, but glucose and insulin have been implicated (22). The plasma concentration of insulin was significantly lower for cows fed diet 2 than for those on diets 1 and 3. Plasma glucose was not

< .1).

different among treatments. Palmquist and Moser (22) observed a decrease in plasma insulin when protected tallow was fed and a 15% decrease in gluconeogenic precursors. Requirement for insulin by the bovine mammary gland has not been demonstrated, and the possible role of insulin for mammary protein synthesis has been suggested (22) but not proven. To understand this relationship, these mechanisms need to be established Jaster et al. (16) showed a significant increase of nicotinic acid from 9.3 to 13.2 ~g/ml in venous plasma for cows receiving 12 g of supplemental niacin. In our study, plasma nicotinic acid concentrations tended to be elevated in cows fed the diets containing niacin, but these were greater (P < .1) only than those for cows fed diet 1 (Table 5). This small increase in plasma niacin suggests that niacin was not limiting under the conditions in our study. Also, low DM! causes slower passage rates and increased ruminal degradation of most nutrients, which may have been true for niacin. There were no interactions between niacin and WCS for the plasma metabolites. Concentrations of essential AA in plasma are in Table 6. Differences were small for arterial and venous concentrations of the essential AA, although there was a decrease of 31 % in total essential AA. Arterial concentration of phenylalanine was highest for diet 2 and greater (P < .1) than diets 1 and 3 (Table 6). The arterial concentration of threonine was greatest for diet 1 and significantly greater (P < .1) than for diet 3. Arterial concentration of valine was highest for diet 2 and significantly higher (P < .1) than for diet 3. Venous concentration of histidine was greatest for diet 3 and was significantly greater than for diet 2. The Jonmal of Dairy Science Vol. 75, No.1, 1992

190

LANHAM ET AL.

TABLE 6. Effects of diets with or without whole cottonseed (WCS), or niacin, or both, on essential amino acid (EAA) concentrations in the coccygeal artery and the subcutaneous abdominal mammary vein UlM/dI) in lactating Holstein cows. Arterial concentrations

og

of Niacin

15% WCS WCS (Diet 1) (Diet 2)

0%

EAA

15% WCS WCS (Diet 3) (Diet 4)

SE .42 .25 .68 .98 .53 .18 25 .55 .19 1.47

3.22 22.62c

5.36 3.91 8.97 12.22 6.44 2.07 3.1~ 666d 3.23 17.99d

Total

78.18

70.04

74.30

8.oac

5.72 3.64 9.11 12.21 5.72 1.86 3.4
of Niacin

15% WCS WCS (Diet 1) (Diet 2)

0%

Arginine 5.23 4.05 Histidine Isoleucine 9.64 Leucine 13.05 Lysine 6.27 Methionine 1.91 Phenylalanine 3.25d 1breonine 7.21 ed Tryptophan 3.08 20.61 cd Valine

5.86 3.73 10.19 12.99 5.98 1.70 3.89"

Venous concentrations

og

6 g of Niacin

0%

2.74 3.45a 6.57 8.11 3.45 1.17 1.6rJ. 4.88 3.06 15.82ab 50.92

15% WCS WCS (Diet 3) (Diet 4)

2.72 2.79b

3.02 3.56a

6.62 7.63 2.59 1.28 2.22c 5.19 2.89 17.3oa 51.23

a,buast squares means within rows with different superscripts differ (P c,dLeast squares means within rows with different superscripts differ (P

concentration of venous phenylalanine was highest for diet 4, but only significantly higher (P < .1) than for diet 1. Venous histidine concentration was lowest for diet 2 and was lower than for diet 3. Only threonine showed arterial-venous differences in AA; values with diet 2 were higher (P < .1) than with diet 4 (Table 7).

6 g of Niacin 0%

5.87 7.31 3.43 1.53 1.9Icd 4.53 3.21 14.23b 48.60

SE .31 .22 .57 .76 .44 .22 .20 .48 .22 1.25

326 2.97 ab 6.47 8.11 3.35 1.03 2.23 c 5.37 3.21 17.11 ab 53.11

< .05). < .1).

The percentage extraction of a given AA represents the proportion of that AA appearing in milk protein (18). Arterial-venous differences in essential AA and essential AA expressed as a percentage of those extracted are in Table 7. Small differences were observed in the percentage of lysine and methionine extracted. These two AA have been shown by

TABLE 7. Effects of diets with or without whole cottonseed (WCS), or niacin, or both, on essential amino acid (EAA) arterial-venous differences UlM/dI) and percentage of substrate extracted in lactating Holstein cows. Arterial-venous differences

og 0%

EAA

WCS (Diet 1)

Arginine 2.50 Histidine .59 Isoleucine 3.09 4.93 Leuci"e Lysine 2.77 Methionine .76 Phenylalanine 1.59 2.3I ab Threonine Tryptophan .05 4.80 Valine Total 23.39

of Niacin

% Amino acid extracted

og

6 g of Niacin

15% WCS (Diet 2)

0%

WCS (Diet 3)

15% WCS (Diet 4)

3.12 .91 3.55 5.38 3.31 .40 1.66 2.85a .30 5.31 26.79

2.31 .38 3.09 4.92 3.02 .56 128 2.12ab .02 3.75 21.45

2.50 .69 2.66 4.09 2.51 .80 1.18 1.69b .20 3.70 20.12

of Niacin

SE

WCS (Diet 1)

15% WCS (Diet 2)

WCS (Diet 3)

15% WCS (Diet 4)

.37 24 .52 .73 .43 28 .23 .42 20 121

47.8 14.57 32.05 37.78 44.18 39.79 48.92 32.04 1.62 23.29

5324 24.4 34.84 41.42 55.35 23.53 42.67 35.63 9.32 23.47

43.1 9.72 34.45 40.26 46.89 27.05 40.13 31.83 .62 20.84

43.71 18.96 29.20 33.50 43.88 43.01 34.71 23.90 5.85 17.78

0%

a,buast squares means within rows with different superscripts differ (P < .1). Journal of Dairy Science Vol. 75, No.1, 1992

6 g of Niacin 0%

191

WHOLE COTIONSEED OR NIACIN EFFEcrs ON MILK. CASEIN

TABLE 8. Effects of diets with or withoot whole cottonseed (WCS). or niacin, or both, on DOnessential amino acid (NEAA) concentrations in the coccygeal artery and the subcutaneous abdominal mammary vein in lactating Holstein cows. V mons concentrations

Arterial concentrations

og NEAA

of Niacin

0% 15% WCS WCS (Diet 1) (Diet 2)

og

6 g of Niacin 15% 0% WCS WCS (Diet 3) (Diet 4)

of Niacin

15% 0% WCS WCS (Diet I) (Diet 2)

SE

6 g of Niacin 0% WCS (Diet 3)

15% WCS (Diet 4)

15.89 5.01 .62 3.67 1.33 18.55 27.76 3.31 7.ma 2.66

16.47 4.68 .55 3.09 1.94 16.n 26.22 3.40 6.38 b 3.05 82.50

SE

(pm/dl)

Alanine Asparagine Aspartate Cystine Glutamate Glutamine Glycine Proline Serine Tyrosine Total

a,bu:ast

15.44 6.59 .84 3.29 4.49 20.96 25.86 3.99 8.77 4.34 94.57

16.61 7.59 .73 3.14 4.85 21.99 26.02 4.01 8.78 4.40 98.12

16.30 7.48 .82 3.30 4.31 21.66 26.23 4.11 9.22 4.15 97.58

16.34 6.66

.n 3.35 4.45 20.91 26.43 3.84 8.25 4.21 95.16

.73 .55 .09 .30 .27 1.35 1.54 .29 .56 .33

14.29 4.44 .58 3.46 1.41 17.33 25.52 2.99 6.74ab 2.86 79.62

15.08 4.45 .54 3.17 1.70 16.37 24.63 3.39 6.36b 2.79 78.48

86.n

1.22 .42 .07 .35 .26 1.27 1.72 .28 .47 .24

squares means within rows with different superscripts differ (P < .05).

others (5. 26) to be limiting under some condi- were in late lactation, which may partially explain the absence of differences in arterialtions for milk protein synthesis. Nonessential AA are synthesized in the venous concentrations of AA. Blood flow is mammary gland (18). There were no differ- correlated highly with milk yield, and the upences observed in arterial concentrations of take of milk. precursors by the manunary gland nonessential AA (Table 8). Serine was signifi- is limited more by blood flow than by differcantly higher in venous blood of cows fed diet ences in extraction efficiency (18). Blood flow 3 than for those fed diets 2 and 4. Arterial- was not measured in our study. In summary, DMI was highest for the convenous differences (data not shown) in cystine were greatest in cows fed diet 4. but only trols (diet 1). Yield of FCM. milk fat and significantly greater than those fed diet 3. even protein percentages, and casein N as a percentthough cows fed diets 1, 2, and 3 had higher age of total N were highest for cows fed diet 1. venous than arterial cystine concentrations. The diets containing niacin did not increase The arterial-venous differences for serine were these expressions over those with no niacin. highest for cows fed diet 2 and were signifi- Insulin tended to be elevated on the niacincantly higher (P < .1) than those of cows fed containing diets, but glucose was not affected. diet 3 (data not shown). The percentage of the Plasma niacin was highest in cows fed diets 3 AA extracted for the nonessential AA was and 4, but only significantly different from variable. Our data did not show large changes those fed diet 1. Amino acid concentrations in in nonessential AA concentrations across the arterial and venous plasma were changed only mammary gland. regardless of treatment, slightly by treatments, but the AA that were changed were not those thought to be the most which indicates that they probably were not limiting for milk protein yield. The failure of limiting under these conditions. Small differcows to respond to niacin supplementation in ences in AA concentrations probably are not this study probably was due to their late stage biologically significant even though they may of lactation. differ statistically. The cows apparently were in positive N balance. with an excess of AA ACKNOWLEDGMENTS being available for milk protein synthesis. because of low milk yields. Milk protein percentThe authors express appreciation to the ages were high in this study because our cows Texas DInA milking testing laboratory for Journal of Daily Science Vol. 75, No.1. 1992

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milk: analyses, to student workers for help with care and feeding of the cows, to J. R. Robinson and the Lonza Company for fmancial support, and to Barbara Perkins for manuscript preparation. REFERENCES I Amos, H. E. 1984. Whole and fullfat processed oilseed for lactating dairy cows. Page II9 in Proc. Georgia Nutr. Com. Atlanta. 2 Association of Official Analytical Chemists. 1975. Official methods of analysis. 12th ed. AOAC. Washington, DC. 3 Association of Official Analytical Chemists. 1984. Official methods of analysis. 14th ed. AOAC, Washington, DC. 4Beckman Instruments, Inc. 1979. Beckman 121MB application notes. Beckman Instruments, Inc., Palo Alto, CA. 5 Broderick, G. A., L. D. Satter, and A. E. Harper. 1974. Use of plasma amino acid concentration to identify limiting amino acids for JDilk production. J. Dairy Sci. 57:1015. 6 Coppock, C. E., J. K. Lanham, and J. L. Horner. 1987. A review of the nutritive value and utilization of whole cottonseed, cottonseed meal and associated byproducts by dairy cattle. Anim. Feed Sci. Technol. 18: 89. 7 Coppock, C. E., J. W. West, 1. R. Moya, D. H. Nave, and J. M. LaBore. 1985. Effects of amount of whole cottonseed on intake, digestibility, and physiological responses of dairy cows. 1. Dairy Sci. 68:2248. 8 DePeters, E. 1., S. J. Taylor, A. A. Franke, and A. Aguirre. 1985. Effects of feeding whole cottonseed on composition of JDilk. 1. Dairy Sci. 68:897. 9Dufva, G. S., E. E. Bartley, A. D. Dayton, and D. O. Riddell. 1983. Effect of niacin supplementation on milk production and ketosis of dairy cattle. 1. Dairy Sci. 66:2329. 10 Dunkley, W. L., N. E. Smith, and A. A. Franke. 1977. Effects of feeding protected tallow on composition of milk and milk fat. 1. Dairy Sci. 60:1863. II Foss Electric. 1977. Milk-O-Scan 300.17500 NS. Foss Electric, Hille~, DK. 12 Fronk, T. 1., and L. H. Schultz. 1979. Oral nicotinic acid as a treatment for ketosis. 1. Dairy Sci. 62:1804. 13 Homer, J. L., C. E. Coppock, G. T. Schelling, J. M. LaBore, and D. H. Nave. 1986. Influence of niacin

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and whole cottonseed on intake, JDilk yield and composition, and systemic responses of dairy cows. 1.

Dairy Sci. 69:3087. 14Horner, 1. L., L. M. Wmdle, C. E. Coppock, 1. M. LaBore, 1. K. Lanham, and D. H. Nave. 1988. Effects of whole cottonseed, niacin and niacinamide on in vitro rumen fermentation and on lactating Holstein cows. J. Dairy Sci. 71:3334. 15ICN Micromedic Systems. 1987. Micromedic insulin RIA kit. ICN Micromedic Systems. Horsham, PA. 161aster, E. H., G. F. Hartnell, and M. F. Hutjens. 1983. Feeding supplemental niacin for JDilk production in six dairy herds. J. Dairy Sci. 66:1046. I7 Kung, L., Jr., K. Guher, and J. T. Huber. 1980. Supplemental niacin for lactating cows fed diets of natural protein or nonprotein nitrogen. J. Dairy Sci. 63:2020. 18 Larson, B. L. 1985. Lactation. Iowa State Univ. Press, Ames.

19 Muller, L. D., A. J. Heinrichs, J. B. Cooper, and Y. H. Atkin. 1986. Supplemental niacin for cows dnring summer feeding. J. Dairy Sci. 69:1416. 20 National Research Council. 1978. Nutrient requirements of dairy cattle. 5th rev. ed. Nat!. Acad. Sci., Washington, DC. 21 Northeast Dairy Herd Improvement Cooperative. 1983. Forage analysis report. Forage Testing Lab., Northeast DBI Coop., Ithaca, NY. 22 Palmquist, D. L., and E. A. Moser. 1981. Dietary fat effects on blood insulin, glucose utilization, and milk protein content of lactating cows. J. Dairy Sci. 64: 1664. 23 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 produclion. J. Daily Sci. 64:782. 24 Rowland, S. 1. 1938. The determination of the nitrogen distribution in milk. J. Daily Res. 9:42. 25 SAS® Users Guide, Version 5 Edition. 1985. SAS Inst., Inc., Cary, NC. 26 Schwab, C. G., L. D. Satter, and A. B. Clay. 1976. Response of lactating dairy cows to abomasal infusion of amino acids. J. Daily Sci. 59:1254. 27 Sigma Diagnostics. 1987. Glucose; quantitative, enzymatic (glucose oxidase) determination in whole blood, serum or plasma at 425-475 nm (Proc. No. 510). Sigma Diagnostics, SI. Louis, MO. 28 Smith, N. E., and L. S. Collar. 1980. Whole cottonseed and extruded soybeans for lactating cows. Page 33 in Proc. California Dairy Cattle Day, Davis.