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Postpartum Reproductive Performance in Crude Protein-Restricted Beef Cows: Return to Estrus and Conception¹

University of Idaho^,3, Moscow 83843

Abstract

A study was conducted to evaluate the effect of a deficiency in dietary crude protein intake on postpartum reproductive performance of first-calf beef cows. Forty primigravid Hereford heifers were randomly assigned to two groups that were fed isocaloric (100% NRC requirements) diets containing .96 (adequate) or .32 (deficient) kg crude protein per head daily. Animals were individually fed from 150 d prepartum to 40 d postpartum and then were group-fed until the end of the experiment at 110 d postpartum. Total nutrient intake was increased by 33% at time of parturition to meet lactation requirements. Animals were artificially inseminated between 45 and 110 d postpartum when they showed estrus. Eighty-nine percent of those fed adequate protein showed estrus, whereas only 63% of protein-restricted heifers exhibited estrus (P < .05). First-service conception (P < .05; 71 vs 25%) and overall pregnancy rates (P < .05; 74 vs 32%) were lower in protein-restricted heifers. Compared with those fed adequately, protein-restricted heifers had a tendency for longer intervals to first estrus (P < .08; 75 vs 86 d), to first service (P < .09; 76 vs 87 d) and to conception (P < .09; 81 vs 92 d). Regardless of diet, weight at first estrus, weight at first service and average daily gain to 40 d postpartum were negatively correlated (P < .01) with length of intervals from parturition to first estrus and first service. These data show that reduced protein intake increased the postpartum interval to first estrus, to first service and to conception and decreased the number of animals that showed estrus and conceived.

¹ Idaho Agric. Exp. Sta. Publ. No. 8144. This research was supported by the Idaho Agric. Exp. Sta. and USDA Animal Health Formula Funds.

² The authors wish to thank Jean Miller and William Gray for excellent technical assistance.

³ Dept. of Anim. Sci.

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