Supplemental Dietary Protein for Grazing Dairy Cows: Reproduction, Condition Loss, Plasma Metabolites, and Insulin

¹ Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803-4210
² Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Franklinton 70438, M. E. McCormick, Southeast Research Station, P. O. Drawer 567, Franklinton, LA 70438

An experiment was conducted over a 2-yr period to investigate the influence of grain crude protein (CP) and rumen undegradable protein (RUP) concentration on reproduction and energy status of dairy cows grazing annual ryegrass (Lolium multiflorum) and oats (Avena sativa). Holstein cows (n = 122) were blocked by calving group [partum (0 d postpartum) vs. postpartum (41 ± 19 d postpartum at study initiation)] and assigned to grain supplements containing high CP [22.8% of dry matter (DM)], moderate CP (16.6%), or moderate CP (16.2%)] supplemented with RUP from blood meal and corn gluten meal. Postpartum condition loss was greater and first-service pregnancy rate was lower for partum-group cows receiving high CP grain supplements compared with control cows receiving moderate CP supplements. The RUP supplements reduced grain consumption, increased days to first estrus, and reduced first-service pregnancy rate of partum-group cows. The reproduction of postpartum group cows was unaffected by protein supplements. Plasma urea nitrogen was higher for cows fed high CP diets, but plasma ammonia nitrogen, glycated hemoglobin, nonesterified fatty acids, ß-hydoxybutyrate, glucose, and insulin concentrations were similar to cows fed moderate CP. Excess postpartum condition loss, coupled with inconsistent protein supplement effects on days to first service and first-service pregnancy rate, suggest that energy deprivation may have contributed to the low fertility experienced by grazing cows in this study.

Key Words: dairy cows • dietary protein • reproduction • energy metabolites

Submitted on May 15, 2000
Accepted on November 12, 2000

This article has been cited by other articles:

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