Effects of Dietary Crude Protein, Breed, Parity, and Health Status on the Fertility of Dairy Cows¹

Abstract

A study was conducted to determine the impact of dietary CP (13% vs. 20%), parity (first vs. second lactation or later), and breed (Holstein vs. Jersey) on the reproductive efficiency of dairy cows. Sixty-four cows were blocked by parity and breed and assigned to one of two treatments. Cows were removed from treatments on d 100 or 120 depending on pregnancy status. Cows were categorized by health status based on the occurrence of postparturient disorders. Plasma urea N concentrations were influenced by diet (8.6 vs. 21 mg/dl, 13 and 20% CP, respectively), parity, and breed. Reproductive indices were not influenced by diet except that days to first estimated ovulation increased for cows fed the 20% CP diet when health status was added to the model. Days to first observed estrus, first AI service, and cumulative pregnancy rate were affected by health status. Regression analysis for survival showed an interaction of diet and health status for days open. High CP diets tended to increase days open when cows had major health problems; otherwise, a high CP diet decreased days open. The implementation of a strict reproductive management program allowed high reproductive efficiency goals to be achieved regardless of plasma urea N concentrations.