Influence of postruminal supplementation of methionine and lysine, isoleucine, or all three amino acids on intake and chewing behavior, ruminal fermentation, and milk and milk component production.

Abstract

Four multiparous Holstein cows were fed a basal diet balanced with the Cornell Net Protein and Carbohydrate System (CNCPS). Diets were formulated to be co-limiting in intestinally absorbable supplies of methionine, lysine, and isoleucine. Cows were supplemented with no amino acids (control); lysine and methionine in a ruminally protected form; isoleucine by abomasal infusion; or lysine, methionine, and isoleucine in a 4x4 Latin square arrangement of treatments with 28-d periods. Performance of cows on all treatments was lower than expected due to low intake of DM that could have been caused by the high fiber level of the basal diet. This high fiber level was likely responsible for the high daily chewing times for cows fed all diets, which was consistent with the high ruminal pH values. Intake of DM and its components were not influenced by any treatment. Milk protein percentage tended to be higher when cows were fed diets supplemented with ruminally protected lysine and methionine; however, production of milk, milk fat, and milk lactose were not affected by any treatment. Cows tended to have a higher milk lactose proportion and tended to produce more milk and milk lactose when they were abomasally infused with isoleucine alone. However, when cows were supplemented with all three amino acids, milk production and composition did not differ from that of cows fed the unsupplemented diet. Use of the CNCPS to evaluate the performance of the cows fed the unsupplemented diet suggested that these cows may have been colimited by intestinally absorbable supplies of lysine, isoleucine, and methionine in addition to metabolizable protein. Evaluation of the unsupplemented diet with an alternate model, Shield, suggested that cows fed the unsupplemented diet may have been colimited by intestinally absorbable supplies of lysine, isoleucine, and arginine. Results suggest that enhanced delivery of intestinally absorbable isoleucine may stimulate milk lactose synthesis.

Effect of rumen-protected methionine, lysine or both on milk production and plasma amino acids of high-yielding dairy cows

“…Seymour et al, 1990;Kudrna et al, 1998;Robinson et al, 1999). Similarly in our study, the milk protein content and yield were significantly higher when both Met and Lys were supplemented compared to the control (P < 0.05).…”

“…Schwab et al, 1992). In contrast, Blum et al (1999) or Robinson et al (1999) did not find any effect of RP Met and Lys supplementation on the intake of dry matter and its components. a,b means in the same row followed by different superscripts differ (P < 0.05) 1 treatments were as follows: C -control; L -control + supplemental Lys (11.7 g/day); M -control + supplemental Met (18.2 g/day); ML -control + supplemental Met and Lys (18.2 and 11.7 g/day, respectively) 2 Lys determined as LysHCl…”

“…To allow dairy cows to meet their metabolic requirements for intestinally absorbable protein, it is necessary to provide postruminally delivered protein with an amino acid (AA) profile that is consistent with AA requirements (Robinson et al, 1999). Because the amounts and proportions of AA in duodenal digesta vary when different diets are fed, it is difficult to determine which AA are limiting.…”

Responses of the bovine mammary glands to absorptive supply of single amino acids

“…1b; Robinson et al 1999). Isoleucine infusion at 30 g d -1 into the abomasum of cows did not affect yields or contents of milk protein or fat, but lactose secretion, lactose percentage and overall milk yield were increased (Robinson et al 1999).…”

“…However, depending on parameters and assumptions of the mathematical model used to make the predictions of AA balance, different AA may appear to be undersupplied. For example, in an experiment in which Lys, Met and Ile were supplemented postruminally, Robinson et al (1999) found that CNCPS version 2.13A (O'Connor et al 1993) predicted those three AA were in deficient supply in the basal diet but Shield (Robinson 1998) predicted deficiencies of Arg, Ile and Lys instead. An experimental approach, which guarantees that milk composition responses will be due to improvement of AA balance, is to administer all AA postruminally as a positive control and then subtract from the mix considerable quantities of the single AA in question.…”