Abstract #T182

# T182
Dietary starch level 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. Ghelichkhan1, N. L. Whitehouse1, M. Miura3, A. F. Brito1, 1University of New Hampshire, Durham, NH, 2Chinese Academy of Agricultural Sciences, Beijing, China, 3Ajinomoto Co. Inc, Kawasaki-shi, Japan.

Addition of fermentable energy and rumen-protected (RP) AA to metabolizable protein (MP)-deficient diets has been shown to improve milk yield and N efficiency. However, research on the interactions between RPAA and dietary starch level on energy utilization is lacking. We aimed to investigate the impact of RP Met, Lys, and His (MLH) and dietary starch concentration on CH4 emission and heat production (HP) in dairy cows fed MP-deficient diets. Sixteen multiparous Holsteins cows (138 ± 46 DIM, 46 ± 6 kg/d milk) were used in a replicated 4 × 4 Latin square with 2 × 2 factorial arrangements 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 (RS), and RS + RPMLH. The basal diets consisted (DM basis) of 35.7% corn silage, 14.7% haylage, and 49.6% concentrate. Dietary starch level varied by replacing 30% ground corn with 20% beet pulp and 10% soyhulls. Dietary NEL, starch, and CP averaged 1.68 Mcal/kg, 34.4%, and 16.0% for HS diets, and 1.59 Mcal/kg, 12.3%, and 16.4% for RS diets, respectively. Smartamine M, Aji-Pro L, and an Ajinomoto prototype His product were fed to meet digestible MLH requirements. The GreenFeed system was used to measure gaseous fluxes, with HP estimated using the Nienaber and Maddy (1985) equation: HP (Mcal/d) = [16.18 × O2 (L/d) + 5.02 × CO2 (L/d) − 2.17 × CH4 (L/d)]/4.183/1,000. Data were analyzed with the MIXED procedure of SAS. Daily CH4 production (434 vs. 545 g/d; 605 vs. 760 L/d), yield (17.7 vs. 21.6 g/kg of DMI), and intensity (10.7 vs. 13.6 g/kg of ECM) were lower with feeding HS vs. RS diets, respectively. Consequently, cows fed HS diets had reduced CH4 energy losses than those fed RS diets (5.72 vs. 7.19 Mcal/d). Moreover, O2 consumption (mean = 8,340 L/d), CO2 emission (mean = 6,043 L/d), and HP (mean = 39.2 Mcal/d) did not differ significantly across diets. No effect of RPMLH supplementation on energy utilization was observed. Collectively, elevated energy supply by substituting fibrous byproducts with ground corn decreased energy losses as CH4 without changing HP.

Key Words: dairy cow, energy, amino acid