Abstract #M185

# M185
Effects of precision essential amino acid formulation on a metabolizable energy basis for lactating dairy cows.
P. A. LaPierre*1, M. M. McCarthy2, D. A. Ross1, M. E. Van Amburgh1, 1Cornell University, Ithaca, NY, 2Adisseo, Alpharetta, GA.

To optimize N utilization in dairy cattle, AA balancing is an approach to improve productive efficiency. Relationships between absorbed AA supply (AAS) and metabolizable energy (ME) intake have been described and can be further derived to create an essential AA (EAA) requirement relative to ME. Variation exists around the EAA to ME values, and questions involve both methodological and biological variance. The objective of the study was to evaluate differences in animal performance when grams of AAS to ME are varied around the optimum value for each EAA. Lactating Holstein cattle (n = 144; 2.9 ± 1.4 lactations, 92 ± 24 DIM) were blocked in 16 cow pens (n = 9) by DIM and parity and enrolled in a 114-d longitudinal study. Pens were fed a common diet during a 14-d covariate period and randomly assigned to 1 of 3 treatment diets (Negative [NEG], Neutral [NEU], and Positive [POS] treatments) over the 100 d treatment period. Diets were formulated to be isocaloric, varying only in the level of EAA fed and rumen N balance was positive for all diets using CNCPS v7. Cattle on NEU (14.5% crude protein [CP]) were fed according to previously calculated optimal grams of AAS to ME, whereas NEG (14% CP) and POS (16% CP) were formulated for ± 1 standard deviation relative to NEU, respectively. Results were analyzed using an ANOVA mixed model in SAS (v.9.4). Cattle fed POS made more energy corrected milk (ECM, 45.2 ± 0.5 kg) than NEG cattle (41.1 ± 0.5 kg, P < 0.01) and tended to make more than NEU cattle (43.8 ± 0.5 kg, P = 0.10). Milk true protein yield was greater in both NEU (1.26 ± 0.01 kg) and POS (1.29 ± 0.01 kg) relative to NEG (1.16 ± 0.01 kg, P < 0.01), but similar for NEU and POS (P = 0.21). Yield of milk fat was greater in POS (1.65 ± 0.03 kg) compared with NEG (1.54 ± 0.03 kg, P < 0.01) but not NEU (1.60 ± 0.03 kg, P = 0.24). Dry matter intake for POS (28.5 ± 0.2 kg) tended to be higher than NEG (27.4 ± 0.2 kg, P = 0.10), and similar to NEU (28.2 ± 0.2 kg, P = 0.68). Results indicate an increase in ECM and protein yield when cattle were fed NEU compared with NEG, and a marginal increase when fed POS compared with NEU. Results suggest a greater efficiency of nitrogen at NEU level over NEG treatment.

Key Words: Amino acid, energy, nutritional model