Effect of Rumen-Protected Methionine and Lysine on Casein in Milk When Diets High in Fat or Concentrate are Fed J. M. CHOW,1,2 E. J. DePETERS,3 and R. L. BALDWIN Department of Animal Science University of California Davis 95616 ABSTRACT
onine and lysine decreased plasma triglyceride concentrations with the 3.9% fat diet. Milk yields, DM intakes, and plasma glucose concentrations were unaffected by treatment. (Key words: dietary fat, rumen-protected amino acids, casein)
To examine the effect of supplying methionine and lysine on milk N composition, isoenergetic, isonitrogenous diets containing 50:50 with 3.9% added fat or 25:75 forage to concentrate with no added fat were fed with or without rumen-protected methionine and lysine to four primiparous and four multiparous early lactation (36 d in milk) Holstein cows in two 4 x 4 Latin squares. Diets contained 1.7 Meal NEI and were fed for ad libitum intake. Periods were 21 d. Rumen-protected methionine and lysine increased total N and casein N percentage with the 3.9% fat, but did not increase total N and casein N percentage with the diet without fat. Whey N percentage was greater with the no fat than with the 3.9% fat diet. Whey N percentage was not affected by adding amino acids. Nonprotein N percentage was greater for the diet with the 3.9% fat than with no fat. Proportions of casein N or whey N to total N were unaffected by treatments. Adding methionine and lysine to diets did not increase yields of total N and casein N. The 3.9% fat diet increased proportions of longchain (C I 8:0 and C I8 : 1) and decreased proportions of short- to medium-chain fatty acids (C8 to C16) in milk fat. Plasma nonesterified fatty acids and triglyceride concentrations were greater with the 3.9% fat as compared to the no fat diet. Methi-
INTRODUCTION
Received May 4. 1989. Accepted December II. 1989. lThis work was taken from a thesis submitted by J. M. Chow to the University of California in partial satisfaction for a Master of Science degree. 2Department of Animal Science, Cornell University, Ithaca, NY 14853. 3Reprint requests. 1990 J Dairy Sci 73:1051-1061
The growing use of milk for manufactured dairy products and the expanding adoption of component pricing have generated great interest in learning how milk composition can be modified through nutrition. In California, increasing cheese consumption is reflected in a fourfold rise in cheese production between 1977 and 1987 to a present total of 224 million kilograms (7). Casein content is critical to profitable cheese making because casein contributes its own weight plus the weight of absorbed moisture to cheese (15) and affects manufacturing properties and quality. Yet, few studies have focused on how diet ultimately affects milk casein production. Previous experiments examined effects of diet on milk fat production because it was the most important constituent influencing milk price. Most studies examining milk protein only measured total milk N and assumed it was representative of the total casein present in milk. When concentrates are substituted for forages or when additional concentrates are provided in rations, milk protein yields increase (5, 33, 42). Although some of the increase has been ascribed to increased propionate supply (33), enhancement of microbial protein synthesis may be more important. Nocek and Russell (23) indicated that microbial growth depended on carbohydrate availability. If more concentrates are fed, a greater supply of ATP will be available for microbial protein synthesis, less N is lost as ammonia, and more microbial protein will become available to the animal.
1051
1052
CHOW ET AL.
TABLE 1. Ingredient composition of !he complete mixed diets and top-dressing. 1
Composition
HF
HC
Alfalfa hay. chopped
50.3
25.2 25.2
5.0
Beet pulp
Molasses Cottonseed meal Com. cracked Fat. blended Trace-mineral salt Dicalcium phosphate Limestone Sodium bicarbonate Barley
4.2 8.5 25.7 3.9 .5 1.1 .8
4.2
Top-dressing
7.7
15.1
27.4
.5 1.1
.6 .8 92.3
IExpressed as a percentage of DM. 2HF
= High
fat and HC
= high
concentrate diet.
Dietary fat reduces milk protein concentration (4, II, 12), but the mechanism(s) by which fats alter milk protein production is still not understood. If fats are substituted for rapidly available carbohydrates, they may influence milk protein production by reducing microbial growth in the rumen and amino acid availability to the animal by affecting amino acid transport into the mammary gland (28), or by toxic effects on rumen cellulolytic and methanogenic bacteria (19). Milk protein yields are greater during infusions of methionine and lysine in combination than when either amino acid is infused individually (6, 36). Rogers et al. (32) did not observe consistent increases in milk protein yields upon addition of rumen-protected methionine and lysine, but lysine improved methionine utilization. More studies are needed to determine under which feeding conditions supplementary methionine and lysine increase milk protein production. Objectives of this study were to determine effects of rumen-protected methionine and lysine on milk casein in two isoenergetic, isonitrogenous diets which differed in their forage to concentrate ratio and fat content. MATERIALS AND METHODS
The experiment was arranged in two 4 x 4 Latin squares with primiparous cows in one square and multiparous cows in the other. Four primiparous (P) and four multiparous (M) Holstein cows were selected based on stage of lactation and milk production. Animals averJournal of Dairy Science Vol. 73.
No.4. 1990
aged 37 d in milk at initiation of the trial with average milk production of 27 and 42 kg/d for P and M cows, respectively. Cows were kept in loose housing and milked twice daily. Periods were 21 d. Diets were formulated to contain approximately equal concentrations of N. NE\, ADF, Ca, and P (Tables I and 2). The high fat (HF) diet contained 50:50 forage to concentrate ratio with 3.9% added fat (commercially purchased yellow grease) and the high concentrate (HC) diet was 25:75 and no added fat. Fatty acid composition of the fat source is presented in Table 3. Rumen-protected methionine and lysine (RPAA) were added at 0 (-RPAA) or 55.1 (+RPAA) gld to HF and HC, resulting in four dietary treatments: HF - RPAA, HF + RPAA, HC - RPAA, and HC + RPAA. Cows were individually fed complete mixed diets twice daily to ad libitum intake using Calan gates (American Calan, Inc., Northwood. NH). Half of the rumen-protected methionine and lysine was mixed into .4 kg of top-dressing (Tables I and 2) at each feeding to supply the small intestine with 6.39 g of DL-methionine and 19.99 g of L-Iysine daily (S. Pierce-Sandner, personal communication). In vivo work (29) verified that rumen-protected methionine was effective at delivering methionine postruminally, because plasma methionine was elevated in cows receiving the supplement. Sulfuric acid lignin was used as an indigestible internal marker and digestibilities (35) were calculated based on the assumption that complete mixed diets and top-dressing were consumed proportionately.
1053
MILK NITROOEN AND PROTECfED AMINO ACIDS TABLE 2. Chemical composition of the complete mixed diets and top-
.., .., t'-- -
("0")
O\.c
l,f')
«>or---.oo-..r ("')N ~ '00 . N
.;
::2 Yijklm
~
= I.L
+ SQi + Tj + Pk + AN(SQ)i\ + Eijklm.
0
c:
.~
'E
Another model was used to analyze milk yield. milk component yield. and feed intake. data:
~
'8
~
OClOON_
W
v.l
where:
Il SQi Tj Pk AN(SQ)il
= 1.2,3,4.5,6,7,8;
.~
« « c.. U :t
+
«
'0
elf
..,
Fat and total solids contents were lower for the HC than for the HF diet (P
onine and lysine decreased plasma triglyceride concentrations with the 3.9% fat diet. Milk yields, DM intakes, and plasma glucose concentrations were unaffected by treatment. (Key words: dietary fat, rumen-protected amino acids, casein)
To examine the effect of supplying methionine and lysine on milk N composition, isoenergetic, isonitrogenous diets containing 50:50 with 3.9% added fat or 25:75 forage to concentrate with no added fat were fed with or without rumen-protected methionine and lysine to four primiparous and four multiparous early lactation (36 d in milk) Holstein cows in two 4 x 4 Latin squares. Diets contained 1.7 Meal NEI and were fed for ad libitum intake. Periods were 21 d. Rumen-protected methionine and lysine increased total N and casein N percentage with the 3.9% fat, but did not increase total N and casein N percentage with the diet without fat. Whey N percentage was greater with the no fat than with the 3.9% fat diet. Whey N percentage was not affected by adding amino acids. Nonprotein N percentage was greater for the diet with the 3.9% fat than with no fat. Proportions of casein N or whey N to total N were unaffected by treatments. Adding methionine and lysine to diets did not increase yields of total N and casein N. The 3.9% fat diet increased proportions of longchain (C I 8:0 and C I8 : 1) and decreased proportions of short- to medium-chain fatty acids (C8 to C16) in milk fat. Plasma nonesterified fatty acids and triglyceride concentrations were greater with the 3.9% fat as compared to the no fat diet. Methi-
INTRODUCTION
Received May 4. 1989. Accepted December II. 1989. lThis work was taken from a thesis submitted by J. M. Chow to the University of California in partial satisfaction for a Master of Science degree. 2Department of Animal Science, Cornell University, Ithaca, NY 14853. 3Reprint requests. 1990 J Dairy Sci 73:1051-1061
The growing use of milk for manufactured dairy products and the expanding adoption of component pricing have generated great interest in learning how milk composition can be modified through nutrition. In California, increasing cheese consumption is reflected in a fourfold rise in cheese production between 1977 and 1987 to a present total of 224 million kilograms (7). Casein content is critical to profitable cheese making because casein contributes its own weight plus the weight of absorbed moisture to cheese (15) and affects manufacturing properties and quality. Yet, few studies have focused on how diet ultimately affects milk casein production. Previous experiments examined effects of diet on milk fat production because it was the most important constituent influencing milk price. Most studies examining milk protein only measured total milk N and assumed it was representative of the total casein present in milk. When concentrates are substituted for forages or when additional concentrates are provided in rations, milk protein yields increase (5, 33, 42). Although some of the increase has been ascribed to increased propionate supply (33), enhancement of microbial protein synthesis may be more important. Nocek and Russell (23) indicated that microbial growth depended on carbohydrate availability. If more concentrates are fed, a greater supply of ATP will be available for microbial protein synthesis, less N is lost as ammonia, and more microbial protein will become available to the animal.
1051
1052
CHOW ET AL.
TABLE 1. Ingredient composition of !he complete mixed diets and top-dressing. 1
Composition
HF
HC
Alfalfa hay. chopped
50.3
25.2 25.2
5.0
Beet pulp
Molasses Cottonseed meal Com. cracked Fat. blended Trace-mineral salt Dicalcium phosphate Limestone Sodium bicarbonate Barley
4.2 8.5 25.7 3.9 .5 1.1 .8
4.2
Top-dressing
7.7
15.1
27.4
.5 1.1
.6 .8 92.3
IExpressed as a percentage of DM. 2HF
= High
fat and HC
= high
concentrate diet.
Dietary fat reduces milk protein concentration (4, II, 12), but the mechanism(s) by which fats alter milk protein production is still not understood. If fats are substituted for rapidly available carbohydrates, they may influence milk protein production by reducing microbial growth in the rumen and amino acid availability to the animal by affecting amino acid transport into the mammary gland (28), or by toxic effects on rumen cellulolytic and methanogenic bacteria (19). Milk protein yields are greater during infusions of methionine and lysine in combination than when either amino acid is infused individually (6, 36). Rogers et al. (32) did not observe consistent increases in milk protein yields upon addition of rumen-protected methionine and lysine, but lysine improved methionine utilization. More studies are needed to determine under which feeding conditions supplementary methionine and lysine increase milk protein production. Objectives of this study were to determine effects of rumen-protected methionine and lysine on milk casein in two isoenergetic, isonitrogenous diets which differed in their forage to concentrate ratio and fat content. MATERIALS AND METHODS
The experiment was arranged in two 4 x 4 Latin squares with primiparous cows in one square and multiparous cows in the other. Four primiparous (P) and four multiparous (M) Holstein cows were selected based on stage of lactation and milk production. Animals averJournal of Dairy Science Vol. 73.
No.4. 1990
aged 37 d in milk at initiation of the trial with average milk production of 27 and 42 kg/d for P and M cows, respectively. Cows were kept in loose housing and milked twice daily. Periods were 21 d. Diets were formulated to contain approximately equal concentrations of N. NE\, ADF, Ca, and P (Tables I and 2). The high fat (HF) diet contained 50:50 forage to concentrate ratio with 3.9% added fat (commercially purchased yellow grease) and the high concentrate (HC) diet was 25:75 and no added fat. Fatty acid composition of the fat source is presented in Table 3. Rumen-protected methionine and lysine (RPAA) were added at 0 (-RPAA) or 55.1 (+RPAA) gld to HF and HC, resulting in four dietary treatments: HF - RPAA, HF + RPAA, HC - RPAA, and HC + RPAA. Cows were individually fed complete mixed diets twice daily to ad libitum intake using Calan gates (American Calan, Inc., Northwood. NH). Half of the rumen-protected methionine and lysine was mixed into .4 kg of top-dressing (Tables I and 2) at each feeding to supply the small intestine with 6.39 g of DL-methionine and 19.99 g of L-Iysine daily (S. Pierce-Sandner, personal communication). In vivo work (29) verified that rumen-protected methionine was effective at delivering methionine postruminally, because plasma methionine was elevated in cows receiving the supplement. Sulfuric acid lignin was used as an indigestible internal marker and digestibilities (35) were calculated based on the assumption that complete mixed diets and top-dressing were consumed proportionately.
1053
MILK NITROOEN AND PROTECfED AMINO ACIDS TABLE 2. Chemical composition of the complete mixed diets and top-
.., .., t'-- -
("0")
O\.c
l,f')
«>or---.oo-..r ("')N ~ '00 . N
.;
::2 Yijklm
~
= I.L
+ SQi + Tj + Pk + AN(SQ)i\ + Eijklm.
0
c:
.~
'E
Another model was used to analyze milk yield. milk component yield. and feed intake. data:
~
'8
~
OClOON_
W
v.l
where:
Il SQi Tj Pk AN(SQ)il
= 1.2,3,4.5,6,7,8;
.~
« « c.. U :t
+
«
'0
elf
..,
Fat and total solids contents were lower for the HC than for the HF diet (P
