Abstract
ABSTRACT. Mascarenhas L.M., Botteon R.C.C.M., Mello M.R.B., Botteon P.T.L. & Vargas D.F.R. [Oxytocin application during milking and reproductive efficiency of crossbred cows.] Aplicação de ocitocina durante a ordenha e eficiência reprodutiva de vacas mestiças. Revista Brasileira de Medicina Veterinária 38(Supl.2):108-112, 2016. Programa de Pós-Graduação em Medicina Veterinária, Instituto de Veterinária, Universidade Federal Rural do Rio de Janeiro, BR 465 Km 7, Seropédica, RJ 23890-000, Brazil. E-mail: mascarenhaslm@outlook.com The aim of this study was to assess the effect of exogenous oxytocin (OT) application during milking on the reproductive efficiency of crossbred cows. A total of 24 crossbred cows were evaluated (Holstein × Zebu), which were part of a fixed-time artificial insemination program [day (D)0: progesterone + estradiol benzoate (EDB) releasing intra-vaginal device (2 mg, i.m.); D8: removal of the intra-vaginal device and application of PGF2α (0,526 mg, i.m.); D9: EDB (1 mg, i.m.); D10: IA]. After ovulation, they were randomly distributed between two groups: GO (n = 12): oxytocin (25 IU: 2.5 ml, i.v. during morning and afternoon milking); GC (n = 12): without OT. The ultrasonography examinations were performed on days 10, 15, 18 and 28. A pregnancy diagnosis was performed on day 28 by transrectal ultrasonography and the pregnancy was again evaluated on days 45 and 60. An increase in the diameter of the corpus luteum (CL) was observed in the GC group between days 10 and 18. In the GO group, the CL diameter decreased between days 10 and 15 and most of the cows (9/12; 75%) were in estrus before day 18. The CL volume was significantly higher (p < 0.05) in the GC group, during all instances, than that in the GO group on day 15. The GC group had a higher pregnancy rate (41.7%) in comparison with the GO group (25%). The conception and maintenance of pregnancy rates indicate a low reproductive efficiency in the GO group (p = 0.0022). With successive inseminations, at 90 days, one and seven cows were not pregnant in the GC (8.33%) and GO groups (58.3%), respectively. The development pattern and CL regression confirm the involvement of OT in the reproductive activity of dairy cows, thus confirming the hypothesis that exogenous OT can negatively affect the reproduction of crossbred cows.