Effects of suckling restriction with nose plates during an 8-day progesterone, estradiol, and eCG-based synchronization protocol on reproductive performance in Bos taurus beef cows

We hypothesized that suckling restriction with nose plates (NPs) during an 8-day progesterone, estradiol, and eCG-based synchronization protocol increases fertility. On Day -9, body condition score (BCS; 1–5 scale) and the presence of corpus luteum (CL) were assessed in 502 Hereford cows (35–80 d postpartum), which were randomly assigned to the NP (n = 266) or control group (n = 236). The synchronization protocol consisted of inserting a 0.5 g progesterone intravaginal device (IVD) and administering estradiol benzoate (2.0 mg) on Day -9, followed by IVD removal and the administration of 0.5 mg estradiol cypionate and 400 IU eCG on Day -1. In the NP group, NPs were fitted to calves on Day -9 and removed on Day -1. Cows were exposed to bull mating from Day 0 to 87. On Day -9, approximately 60% of cows did not have CL or had a low BCS (< 2.75). The NP group was associated (P ≤ 0.03) with higher blood glucose and lower serum NEFA concentrations on Day -1. Suckling restriction had no effect (P > 0.1) on follicular diameter on Day -1 (control = 12.4 ± 0.4 mm and NP = 13.1 ± 0.4 mm), pregnancy rate (PR) on Day 36 (control = 50.9% and NP = 44.7%), presence of CL in cows without confirmed pregnancy on Day 36, or overall PR on Day 132 (control = 94.1% and NP = 91.7%). Eight-day NP treatment had no effect (P > 0.1) on cow BCS, CL presence on Day 36, or calf body weight at weaning. Suckling restriction before IVD removal during an 8-day synchronization protocol did not improve fertility in multiparous beef cows.