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Dietary energy source and rumen-protected amino acids: Effects on milk production and plasma amino acid concentrations in dairy cows.

Y. Zang




Dietary energy source and rumen-protected amino acids: Effects on milk production and plasma amino acid concentrations in dairy cows.
Y. Zang*1, L. H. P. Silva1, Y. Geng2, M. J. Lange3, N. Q. Dattolico1, N. L. Whitehouse1, M. Miura4, M. A. Zambom3, A. F. Brito1. 1University of New Hampshire Durham, NH, 2Chinese Academy of Agricultural Sciences Beijing, China, 3Universidade Estadual do Oeste do Paran� Marechal C�ndido Rondon, Brazil, 4Ajinomoto Co. Inc Kawasaki-shi, Japan.

Our previous study demonstrated that reduced dietary starch level limited milk and milk protein yield in dairy cows receiving MP-deficient diets. Supplementation of reduced starch diets with fat could be a feeding strategy to improve milk production. We aimed to investigate the interactions between energy source (starch vs. fat) and rumen-protected (RP) Met, Lys, and His (MLH) on performance and plasma AA in dairy cows fed MP-deficient diets. Sixteen multiparous Holstein cows (112 � 28 DIM) were used in a replicated 4 � 4 Latin square with a 2 � 2 factorial arrangement of treatments. Each period lasted 21 d with 14 d for diet adaptation and 7 d for sample collection. Treatments included high starch (HS), HS + RPMLH, reduced starch + RP-fat (RSF), and RSF + RPMLH. Basal diets consisted of (DM basis) 50% forage and 50% concentrate. The HS diet contained (DM basis) 26% ground corn, while the RSF diet had 16% ground corn replaced with 15% soyhulls and 1.5% RP-fat (i.e., palmitic acid-enriched supplement). Dietary NEL, starch, and CP averaged 1.53 Mcal/kg, 32.6% and 15.9% for HS diets, and 1.59 Mcal/kg, 21.7% and 16.8% for RSF diets, respectively. Smartamine M, Aji-Pro L, and an Ajinomoto prototype RP-His product were fed. Data were analyzed with the MIXED procedure of SAS. Dietary treatments had no effects on DMI and milk yield. However, feeding RSF diets enhanced feed efficiency (1.57 vs. 1.54) and milk fat yield (1.65 vs. 1.50 kg/d) compared with HS diets. Concentration of milk fat increased but that of milk true protein decreased with RSF vs. HS diets. Both MUN and PUN were greater and milk N efficiency (30.6 vs. 29.1%) was lower for RSF vs. HS diets. Supplemental RPMLH tended to improve milk true protein concentration. No significant interactions between RPMLH and energy source were observed for plasma AA. Additionally, RSF diets elevated plasma concentrations of Arg, Ile, Thr, and Ala but reduced Leu relative to HS diets. Plasma Met and His increased with RPMLH. In brief, substitution of ground corn with soyhulls and RP-fat improved feed efficiency and milk fat yield but appeared to reduce N utilization.

Keywords: amino acid, dairy cow, energy source.