Bypass Fat in Ewes with Different Thickness of Dorsal Fat, Hormonal Response and Main Reproductive Variables

The objective of this study was to evaluate the effect of bypass fat in ewes with low (1-2 mm) and high (3-4 mm) dorsal fat thickness and estrous synchronization on estrous presentation (beginning and duration) and seric levels of luteinizing hormone (LH), estradiol (E-2), progesterone (P-4) and insulin (INS), gestation rate and prolificity. Fifty nine ewes with two levels of dorsal fat thickness determined by ultrasonography, low and high (DFI, DFh), without and with addition of 150 g of bypass fat (0 and 150 g), respectively, were assigned to the following treatments: DFI +0 g (n=16), DFI +150 g (n=14), DFh+0g (n=14) and DFh+150 g (n=15). All ewes were synchronized with fluorogesterone acetate impregnated sponges (FGA, 20 mg) for 12 d and two days before sponge removal received 15 mg of PGF(2 alpha). Experimental design was a 2X2 factorial arrangement and results were analyzed by SAS. There were no differences (P>0.05) for beginning and duration of estrous, begin-fling and duration of preovulatory LH surge and prolificity due to the addition of bypass fat, however, LH amplitude and gestation rate were different between treatments (P<0.05). P-4 seric concentrations were greater (P<0.05) on ewes without addition of bypass fat (Og). E-2 and INS concentration were increased (P<0.05) on DFh ewes. It is concluded that addition of bypass fat does not modify reproductive variables response, but decreased P-4 concentration. On the other hand, E-2 and INS concentration were increased in ewes with high dorsal fat (DFh), which is attributed to a better metabolic, nutritional and corporal of the animal.