Estrus synchronization in beef heifers with progestin-based protocols. I. Differences in response based on pubertal status at the initiation of treatment.

摘要: Abstract Two progestin-based protocols for estrus synchronization in replacement beef heifers were compared on the basis of estrous response, interval to and synchrony estrus, pregnancy rate. The objective was determine, whether addition GnRH a melengestrol acetate (MGA)-prostaglandin F 2α (PGF ) protocol would improve without compromising fertility yearling heifers. Heifers at two locations (Location 1, n = 60 Location 2, 64) assigned randomly one treatments by breed pubertal status. defined as, when concentrations progesterone serum elevated (≥1ng/mL) either samples obtained 10 1 day prior treatment initiation. Prior MGA administration, 18/60 (30%) 36/64 (56%) Locations respectively, pubertal. both fed (0.5mg/head/day 1.8kg/head/day supplement) 14 days followed 25mg PGF i.m. (MGA-PGF 19 after withdrawal (Day 33 treatment). One-half each location received 100μg 12days 26 treatment; ® Select). control group only MGA-PGF . observed signs behavioral continuously during daylight hours 7 beginning administered. inseminated 12h estrus. There status interaction ( P Select had longer intervals whereas prepubertal higher number 2 associated with reduced variance among treated Total response synchronized conception rates similar between locations. These data suggest that may however, degree be influenced time are imposed. Further studies needed define production systems which is warranted use