Effects of progesterone pretreatment and duration of ram exposure on synchronization of estrus, conception and pregnancy by prostaglandin during seasonal anestrus

Four experiments were conducted to compare effectiveness of three intervals from introduction of rams to synchronization of estrus and the effect of treatment with progesterone at ram introduction on the optimum interval in Rasa Aragonesa ewes. In Experiment 1, data from 292 ewes revealed that treatment with prostaglandin at 12, 14 or 16 days after ram introduction improved pregnancy rate after two service periods compared to introduction of rams alone (64 vs. 45%; P <0.05). Occurrence of estrus was highest after prostaglandin on Day 12 (86%) but conception rate to first service was highest after prostaglandin on Day 16 (80%). In Experiment 2, with 250 ewes, occurrence of estrus and pregnancy rate to first service were higher (P < 0.05) when prostaglandin was given on Day 14 (77 and 53%, respectively) after introduction of rams, compared with Day 12 (58 and 40%). In Experiment 3, with 503 ewes, Day 14 and 16 were compared as intervals from ram introduction to cloprostenol. Occurrence of estrus, conception rate to first service and pregnancy rates to first and second services did not differ. Experiment 4, conducted with 626 ewes, examined effects of injection of 25 mg progesterone i.m. at ram introduction on responses to prostaglandin on Day 14 or 16. Occurrence of estrus was 9 percentage points higher with treatment on Day 16 (P < 0.05) and 8 percentage points higher in ewes pretreated with progesterone (P < 0.05). Pregnancy rates to first service (71%) and after two services (75%) were highest in progesterone-pretreated ewes receiving prostaglandin 16 days after ram introduction (day × treatment, P < 0.05). Pregnancy rate to first service was 49 to 53% in the other three groups. It is concluded that 14 or 16 days is a satisfactory interval from ram introduction to prostaglandin treatment, but that numbers of ewes lambing to first service can be maximized if progesterone pretreatment and the 16 day interval are combined. © 1988.

Bibliographic Details

Main Authors:	López Sebastián, Antonio, Inskeep, E. K.
Format:	journal article biblioteca
Language:	English
Published:	Elsevier 1988
Online Access:	http://hdl.handle.net/20.500.12792/2438 http://hdl.handle.net/10261/293268
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