226 INCLUSION OF BOVINE SOMATOROPIN ON MULTIPLE-OVULATION EMBRYO TRANSFER TREATMENTS FOR LOW-RESPONDING BEEF DONOR COWS

Abstract

An experiment was designed to determine if embryo production of Angus donors could be improved by including a single dose of bovine somatotropin (bST) before starting the superovulatory treatment (SPO). Thirty-three multiparous Angus cows (body condition = 4.6 ± 0.6, range = 1–8) were submitted to 2 SPO treatments at random stages of the oestrous cycle in a crossover design (60 days apart). On Day 0, cows were divided at random to receive either 500 mg of bST (n = 18; Lactotropin, Elanco Saude Animal, Brasil) or remain without bST (control, n = 15). At the same time, all cows received 2 mg of oestradiol benzoate, 50 mg of progesterone and a CIDR (Pfizer Animal Health, Uruguay). On Day 2, all cows received 200 IU of eCG (Inducel, Universal Laboratory, Uruguay) and on Day 4 were superstimulated with 425 IU of FSH (Pluset, Calier, Spain) in twice-daily decreasing doses over 4 days. On Day 6, all cows received 2 doses (a.m. and p.m.) of a PGF analogue (800 μg, Delprostenate, Glandinex, Universal Laboratory, Uruguay) and the CIDRs were removed in the morning of Day 7. Cows were injected with 10 μg of GnRH (Receptal, Intervet, the Netherlands) on Day 8 (a.m.) and were inseminated 12, 24 and 36 h later. On Day 15, ova/embryos were collected nonsurgically and evaluated in accordance to IETS guidelines. For statistical analysis, cows were categorized according to the number of transferable embryos obtained in control treatment (without bST) in terciles: low-responding cows (LR, ≤6; n = 11), middle-responding cows (7–9, n = 12), or high-responding cows (HR ≥ 10; n = 10). Data were analysed by a paired t-test. Treatment with bST increased the total ova and embryos and the number of transferable embryos in LR cows (Table 1). However, the number of transferable embryos and the percentage of transferable embryos werereduced in HR cows. The inclusion of a single bST dose 4 days before initiating SPO with FSH treatments may be a useful alternative to improve embryo production in low-responding cows. Table 1.Response of low-responding and high-responding Angus cows to superovulatory treatments with or without bST (mean ± SD)