131 CHARACTERISTICS OF PREGNANCIES AND OFFSPRING FOLLOWING TRANSFER OF BOVINE IN VIVO EMBRYOS ASSESSED BY NANORESPIROMETRY

Abstract

It has been speculated whether the metabolism of the pre-implantation embryo may be reflected on the pregnancy and characteristics of the newborn animal. The present study investigated whether respiration rates of individual embryos were correlated with gestation length, type of parturition, birth weight, sex, and viability of the offspring. In-vivo embryos (n = 47) were recovered on day 7 from 11 superovulated and inseminated Holstein-Friesian cows and embryonic respiration rates were measured individually by nanorespirometry. The embryos were classified according to morphological quality (I, II, III), stage of development, and diameter and were subsequently transferred individually (n = 43) to synchronized recipients. Gestation length of the recipients (n = 22) was calculated and the type of parturition (no assistance, light traction, heavy traction, or caesarean section) recorded. Sex, weight, and condition of the calves at birth (weak, normal, or very active) were also assessed. Results were evaluated by chi-square analysis and using a linear mixed model. The pregnancy rate was 60% (26/43), and the respiration rates of individual embryos influenced gestation length as well as the interaction of weight at birth and type of parturition (P < 0.05). Embryos with higher respiration rates tended to be associated with a slightly more difficult type of parturition, which was not affected by sex. When embryos were divided into two even-sized categories according to their respiration rates (high v. low), low embryonic respiration rates were associated with low birth weight in 73% of the newborn calves (Table 1). Neither sex nor condition of the calves was directly affected by the embryonic respiration rates. The diameter and morphology of the embryo affected birth weight (P < 0.05), with quality I embryos associated with heavier calves when compared to quality III embryos. Furthermore, light traction was more frequently used to retrieve heavier animals (P < 0.05), and male calves were 3.2 kg heavier than females (P < 0.05). These results suggest that the metabolism of the embryo might affect the weight of the newborn animal and consequently the type of parturition. However, birth weight is highly influenced by the recipients and season, and thus a more accurate correlation is likely to be established when the weight of the postpubertal offspring is considered.

Table 1. Birth weight of newborn calves according to respiratory category of bovine in-vivo embryos