Abstract #M290

# M290
Circulating blood metabolites in early lactation dairy cows fed canola or soybean meals.
S. A. E. Moore*1, K. F. Kalscheur2, 1University of Wisconsin, Madison, WI, 2US Dairy Forage Research Center, USDA-ARS, Madison, WI.

A successful transition from pregnancy to lactation is imperative for dairy cows to maximize milk production potential. Altering the dietary protein source can change the availability of energy and protein to the cow. The objective of this experiment was to evaluate the effect of CP source [canola meal (CM) or soybean meal (SBM)] and CP concentration [HI (18.1%) or LO (16.2%) DM basis] on circulating blood metabolites. At calving, multiparous Holstein cows (n = 79) were enrolled into a 2 × 2 factorial arrangement of treatments in a randomized complete block design. Cows were blocked by calving date and individual cow was the experimental unit. Enzymatic colorimetry was used to evaluate circulating concentrations of glucose, nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHB), triglycerides (TG), and plasma urea nitrogen (PUN). Serum and plasma coccygeal vein samples were collected 2 × during wk 1, 2, 3, 4, 6, and 8 postpartum. Samples were pooled by wk for each cow. Data were analyzed using the MIXED procedure of SAS. BCS and BW at calving were used as covariates when appropriate. Total milk yield was greater for CM-fed than SBM-fed cows during wk 1–8 of lactation (mean ± SEM; 53.2 vs 49.2 ± 0.98 kg/d; P < 0.001), while there was no difference in DMI (P = 0.11) to support additional production. No treatment effect was observed for glucose or BHB. Circulating TG concentration was greater for cows fed CM compared with SBM-fed cows (0.125 vs 0.118 ± 0.002 mM; P = 0.02). There was an interaction of source and wk for NEFA concentration (P = 0.04). Efficiency of nitrogen utilization favored CM vs SBM-fed cows for both circulating PUN (0.37 vs 0.40 ± 0.01 mM; P = 0.02) and concentration of milk urea N (MUN; 10.7 vs 11.4 ± 0.24 mg/dL; P = 0.04). HI-fed cows were greater in PUN (0.44 vs 0.33 ± 0.01 mM; P < 0.001) and MUN concentration (9.64 vs 12.5 ± 0.24 mg/dL; P < 0.001) compared with LO-fed cows. The increase in milk yield can be attributed in part, to an increase in circulating TG and nitrogen utilization. However, further investigation into the CM vs SBM milk disparity in early lactation is needed.

Key Words: canola meal, early lactation, energy