Supplemental dietary protein for grazing dairy cows: Reproduction, condition loss, plasma metabolites, and insulin

An experiment was conducted over a 2-yr period to investigate the influence of grain crude protein (CP) and rumen undegradable protein (RUP) concentra tion on reproduction and energy status of dairy cows grazing annual ryegras s (Lolium multiflorum) and oats (Avena sativa). Holstein cows (n = 122) wer e blocked by calving group [partum (0 d postpartum) vs. postpartum (41 +/- 19 d postpartum at study initiation)] and assigned to grain supplements con taining high CP [22.8% of dry matter (DM)], moderate CP (16.6%), or moderat e CP (16.2%)] supplemented with RUP from blood meal and corn gluten meal. P ostpartum condition loss was greater and first-service pregnancy rate was l ower for partum-group cows receiving high CP grain supplements compared wit h control cows receiving moderate CP supplements. The RUP supplements reduc ed grain consumption, increased days to first estrus, and reduced first-ser vice pregnancy rate of partum-group cows. The reproduction of postpartum gr oup cows was unaffected by protein supplements. Plasma urea nitrogen was hi gher for cows fed high CP diets, but plasma ammonia nitrogen, glycated hemo globin, nonesterified fatty acids, beta -hydoxybutyrate, glucose, and insul in concentrations were similar to cows fed moderate CP. Excess postpartum c ondition loss, coupled with inconsistent protein supplement effects on days to first service and first-service pregnancy rate, suggest that energy dep rivation may have contributed to the low fertility experienced by grazing c ows in this study.