240 GESTATION LENGTH AND BIRTH WEIGHT OF IN VITRO PRODUCED EMBRYOS FROM ZEBU DAIRY CATTLE

Abstract

Gir cattle are a popular zebu dairy breed in tropical and subtropical regions because of their tolerance of heat stress and resistance to tick-borne disease. The use of in vitro embryo production (IVP) technology may help accelerate genetic improvement of this breed. However, in general, IVP systems have been implicated in the production of large offspring and a greater proportion of male calves. Natural breeding results in newborn Gir calves weighing around 25 kg despite the fact that dams may weigh over 500 kg. It is unknown whether in vitro-produced Gir embryos also result in large offspring. The aim of this work was to evaluate the effect of in vitro embryo production on gestation length, birth weight, and sex ratio in Gir cattle. COCs were harvested by oocyte pickup from mature non-lactating Gir cows and in vitro-matured in TCM 199 medium (Gibco, Sao Paulo, Brazil) with 10% inactivated estrous cow serum for 24 h under 5% CO₂ at 38.5°C in air. Gir spermatozoa were obtained through the swim-up method and co-incubated with oocytes in Fert-TALP media (Parrish JJ et al. 1988 Biol. Reprod. 38, 1171–1180) with 10 μg/mL heparin (Sigma, Sao Paulo, Brazil) and 6 mg/mL fatty acid-free bovine albumin (Sigma) for 18 h in 5% CO₂ at 38.5°C in air. Presumptive zygotes were co-cultured with their own cumulus cells in CR2aa medium (Wilkinson RF et al. 1996 Theriogenology 45, 41–49) with 10% fetal calf serum in humid atmosphere of 5% CO₂ at 38.5°C in air. Fresh Day 7 blastocysts were transferred to synchronized B. indicus × B. taurus crossbred recipients. Data of gestation length, birth weight, and gender ratio from 26 IVP calves (IVP group) were recorded and compared to data obtained from Gir calves produced by artificial insemination or natural mating (n = 24; control group) using ANOVA or chi-square analysis. There was no difference (P > 0.05) in gestation length between pregnancies of the IVP and control groups (mean ± SEM, 285.4 ± 1.5 vs. 284.4 ± 1.1 days, respectively). IVP and control calves showed similar (P > 0.05) weight at calving (29.6 ± 0.9 vs. 26.9 ± 1.2 kg for IVP and control male calves, and 27.0 ± 2.5 vs. 25.2 ± 0.5 kg for IVP and control female calves, respectively). The percentage of male calves was greater (P < 0.05) in the IVP group than in the control group (76.9% vs. 43.4%, respectively). IVP calves did not show abnormalities associated with Large Offspring Syndrome, such as breathing difficulty and perinatal death. These data suggest that in vitro production may affect the development of Gir embryos, biasing the sex ratio in a manner similar to previously reported for in vitro-produced embryos from Bos taurus breeds.

This work was supported by FAPEMIG and CNPq.