title: Postpartum reproductive performance in crude protein-restricted beef cows: return to estrus and conception.
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 less than .05). First-service conception (P less than .05; 71 vs 25%) and overall pregnancy rates (P less than .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 less than .08; 75 vs 86 d), to first service (P less than .09; 76 vs 87 d) and to conception (P less than .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 less than .01) with length of intervals from parturition to first estrus and first service.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Dept. of Anim. Sci., University of Idaho, Moscow 83843.
authors.forename: R G
authors.initials: RG
authors.lastname: Sasser
authors.forename: R J
authors.initials: RJ
authors.lastname: Williams
authors.forename: R C
authors.initials: RC
authors.lastname: Bull
authors.forename: C A
authors.initials: CA
authors.lastname: Ruder
authors.forename: D G
authors.initials: DG
authors.lastname: Falk
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004971:Estrus / Q000502:physiology*; D005260:Female; D049590:Postpartum Period / Q000502:physiology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011488:Protein Deficiency / Q000503:physiopathology / Q000662:veterinary*