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Dietary energy source and rumen-protected amino acids: Effects on CH4 emissions and heat production in lactating dairy cows.

Y. Zang



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Dietary energy source and rumen-protected amino acids: Effects on CH4 emissions and heat production in lactating 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 research showed that reduced dietary starch level increased CH4 energy losses and tended to decrease milk energy of dairy cows receiving MP-deficient diets. Supplementing rumen protected (RP)-fat to reduced starch diets may improve energy use efficiency in dairy cows. Therefore, our objective was to examine the effects of dietary energy source (starch vs. RP-fat) and RP Met, Lys, and His (MLH) on enteric CH4 emission and heat production (HP) in dairy cows fed MP-deficient diets. Sixteen multiparous Holsteins 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 were 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 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 to meet digestible MLH requirements. The GreenFeed system was used to measure gaseous fluxes, with HP estimated using the Bayat et al. (2019) equation: HP (MJ/d) = 0.0184 � QCO2 (L/d) + 7.50. Data were analyzed with the MIXED procedure of SAS. Dietary treatments had no effects on CH4 production (mean = 534 g/d), CH4 yield (mean = 18.5 g/kg of DMI), and CH4 intensity (mean = 11.6 g/kg of ECM). Consequently, cows fed HS and RSF diets had similar CH4 energy losses (7.03 vs. 7.12 Mcal/d). Moreover, emission of CO2 (mean = 16.2 kg/d) and HP (mean = 37.8 Mcal/d) did not differ significantly across diets. No effect of RPMLH supplementation on energy utilization was observed. In brief, our data suggest that ground corn can be partially replaced with soyhulls and RP-fat without changing energy use efficiency in lactating dairy cows.

Keywords: amino acid, dairy cow, energy source.