USE OF THE OVSYNCH PROTOCOL IN DAIRY HEIFERS WITH OR WITHOUT A FUNCTIONAL CORPUS LUTEUM AT THE INITIATION OF TREATMENT.
Abstract
With the objective of compare ovarian response and pregnancy rates in dairy heifers that received two presynchronisation treatments with prostaglandines to induce presence (CLF+) or absence (CLF-) of a functional corpus luteum at the initiation of the Ovsynch protocol, 22 Holando Argentino heifers were assigned randomly to receive two injection of 750 ug of tiaprost, at days -22 and -11 (CLF+ group, n=11) or at days -14 and -3 (CLF- group, n=11). Presence or absence of a functional corpus luteum was confirmed by ultrasonography and measurement of plasma progesterone concentrations, therefore two CLF+ and one CLF-heifers were dropped from the experiment. At day 0 both groups received 8 mg of buserelin; at day 7, 750 mg of tiaprost and at day 9,8 mg of buserelin. Heifers were bred by fixed-time artificial insemination 15 hours after treatment. Percentage of animals with a ≥8 mm follicle at day 0 and its diameter were similar between gropus (P>0.05). Following first buserelin injection ovulation occurred in 94.1% and luteinization in 5.9% of these follicles (P>0.05). Percentages of animals with a functional corpus luteum at day 7 were similar between groups (100% and 90%, for CLF+ and CLF-, respectively; P>0.05) while its progesterone concentrations were greater in CLF+ (3.5 +-0.7 vs 2.2 +- 1.2 ng/ml; P<0.01). Percentages of luteolysis were 100% (P>0.05). Dominant follicle diameter was greater in CLF- so much at day 7 (P=0.05) as at day 9 (P<0.01); its percentage of ovulation after second buserelin injection was not different among groups (88.9% and 100%; P>0.05). Pregnancy rates were similar between groups (66.7% and 70%; P>0.05). In conclusion, used of two presynchronisation treatments with prostaglandines to induce presence (11 days post-second PGF2a) or absence (3 days post-second PGF2a) of a functional corpus luteum at the initiation of the Ovsynch protocol produces similar ovarian response (ovulation, luteal phase synchronisation and luteolysis), what would explain similarity between pregnancy rates obtained in both groups.Downloads
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