PSI-6 The Influence of a Single Administration of Prostaglandin on Estrus Synchronization in Range Sheep Production

Abstract

Abstract Administration of a single injection of prostaglandin after ram introduction has previously been reported as an effective method to synchronize estrus in ewes housed in a dry lot setting. The objective of this study was to investigate the effectiveness of a single injection of prostaglandin administered at the beginning of the breeding season after ram introduction, on estrus synchronization in range ewes. Western Whiteface cross ewes, of which thirty-six were ½ blood South African Meat Merino (SAMM) and seventeen ¼ blood SAMM (total n=53) were assigned to one of two treatments: control (CON; n=26) or one injection of prostaglandin (PG; n=27). Ewes were utilized in a complete randomized block design and were stratified by SAMM percentage, body condition score (BCS) and age. Ewes assigned to PG treatment were administered 3 mL of prostaglandin IM (Lutalyse, Zoetis Animal Health) approximately 60 h after rams were introduced with ewes. Rams (n=4) were applied with marking paint and placed with ewes on (d 0: December 21) and remained for the duration of the 56 d breeding season for natural service. Ewes were observed for estrus twice daily at 0730 h and 1700 h for d 0-10 and d 16-21 of the breeding season, by an experienced evaluator. At lambing, birth weight, sex, and type of birth was recorded. The MIXED and GLIMMIX procedures of SAS were used to analyze estrus response, ewes bred in the first 5 d of the breeding season, days to lambing, lambing date, number of lambs born, and lamb weight. South African Meat Merino percentage was included as an independent variable but was found to be nonsignificant and was removed from the statistical model. The proportion of ewes bred during the first 5 d of the breeding season was not different among the two treatments (P ≥ 0.60). There was no difference between the PG ewes and the CON ewes for the date of estrus (P ≥ 0.82). There was no difference between the PG ewes and the CON ewes for the lambing date (P = 0.60). Treatment did not influence days to lambing (P ≥ 0.25). The number of lambs born per ewe tended to be influenced by treatment (P < 0.08), with PG ewes tending to have more lambs than CON ewes. Lamb weights were not different among treatments (P ≥ 0.50). In conclusion, the administration of a single PG injection after ram exposure did not influence estrus expression, days to lambing, or lambing date, however, PG ewes did tend to have more lambs.