Effects of prepartum plane of nutrition during mid- or late gestation on beef cow BW, BCS, and preimplantation embryo recovery

Abstract Text: Objectives were to evaluate potential effects of prepartum plane of nutrition during mid- or late-gestation on BW, BCS, and preimplantation embryo recovery. Spring-calving, multiparous beef cows (n = 60; BW = 657±70 kg) were utilized in a 3 × 2 factorial arrangement that included 3 planes of nutrition formulated to provide (limit-fed diet = 52% corn silage, 24% soybean hulls, and 24% alfalfa haylage): 100% NRC energy and protein requirement (REQ), 70% NRC requirement (70%REQ) or 130% NRC requirement (130%REQ) fed during 2 stages of gestation: mid-gestation (Mid, 195±5 to 112±5 d prepartum) or late-gestation (Late, 91±4 to 8±4 d prepartum). After treatment period, cows were fed a common diet formulated to meet NRC requirements. All cows had their estrous cycles pre-synchronized with 2 injections (14 d apart) of PGF2α beginning 43±4 d postpartum. A 7 d co-sync protocol was used to synchronize cows. A 4 d regimen of Folltropin (FSH) was administered to induce superovulation and GnRH was given 12 h and 24 h prior to breeding. Cattle were flushed 84±4 d postpartum and 7 d embryos were harvested. Cyclicity was accessed by P₄ analysis at 43±4 and 57±4 d postpartum. Statistical analysis was performed using the MIXED and GLIMMIX procedures in SAS. Nutritional plane did not affect (P = 0.61) percentage of cows cycling by 57±4 d postpartum (70%REQ, 15.8%; REQ, 27.3%; 130%REQ, 21.1%). The Logistic model revealed that cows fed nutritional treatments during late-gestation had lower odds for cyclicity than cows fed nutritional treatments in mid-gestation [odds ratio (OR) = 0.18; P = 0.02]. Cows fed 130%REQ had greater (P ≤ 0.03) BW than REQ and 70%REQ cows, and cows fed 130%REQ and REQ had greater (P ≤ 0.04) BCS than cows fed 70%REQ at time of breeding. There was a plane of nutrition by stage of gestation interaction (P < 0.01) for total embryos recovered. When nutritional treatments were applied during mid-gestation, a greater number of total embryos were recovered from cows fed 70%REQ than from cows fed REQ and cows fed 130%REQ were intermediate; however, when nutritional treatments were applied during late-gestation, a greater number of total embryos were recovered from cows fed 70%REQ and REQ than cows fed 130%REQ. In conclusion, prepartum plane of nutrition during mid- or late-gestation affects cow BW, BCS, and  total embryos recovered, but did not affect cyclicity in cows prior to breeding.

Keywords: embryo, gestational nutrition, reproduction