93 POSTCRYOPRESERVATION VIABILITY OF EMBRYOS FROM NELLORE HEIFERS SUPPLEMENTED WITH RUMEN-PROTECTED FAT.

Polyunsaturated fatty acids seem to exert an extra-caloric positive effect on ruminant reproduction, although the reasons for that are still unclear. Although some studies have detected a positive effect of feeding unsaturated fatty acids on embryo development of superovulated Bos tauruscattle (Thangavelu et al.2007 Theriogenology 68, 949-957), others have not (Petit et al.2008 J. Dairy Sci. 91, 1786-1790). Our hypothesis was that, although number and quality of embryos from superovulated heifers would not be affected by diet, supplemental fat would improve embryo cryotolerance. Therefore, this study evaluated superovulatory response and embryo production, as well as cryotolerance of embryos cryopreserved through freezing or vitrification in Nellore heifers supplemented with rumen-protected fat. Forty heifers (24 to 36 mo old) were kept in pasture and randomly divided into 2 experimental groups according to supplemental source [F = concentrate with rumen-protected fat (100 g/d of Megalac-E®) and C = control, without fat supplementation]. Supplements were formulated to be isocaloric and isoproteic. Each female underwent both treatments in a cross-over design with approximately 68 d between replicates. After 50 d of feeding, emergence of the wave was synchronized with the aid of hormones to initiate the superovulation protocol. Recovered embryos were frozen or vitrified, and subsequently in vitroembryo development evaluation was accomplished. Data were analyzed using generalized linear models. There was no difference between F and C groups (P> 0.10) regarding superstimulatory response, number of total embryos/ova, viable embryos, degenerate embryos, or unfertilized oocytes recovered. However, group C had a greater superovulatory response than F (18.0 ± 1.3 v.15.7 ± 1.2 CL; P= 0.06). Group C embryos presented greater hatching rate, independently of the cryopreservation method, at 48 h (33.1 ± 4.0%; n= 148 v.17.3 ± 3.3%; n= 137; P= 0.009) and at 72 h (44.3 ± 4.2%; n= 148 v.30.9 ± 4.0%; n= 137; P= 0.04) of in vitroculture. Under the conditions of the present study, supplementation with protected fat did not affect superstimulatory response and quantity or quality of embryos. However embryos from the F group were less tolerant to cryopreservation. Financial support from FAPESP, EMBRAPA, Arm & Hammer, Integral Produbon, and Pfizer of Brazil. [ABSTRACT FROM AUTHOR]