260 The induction and synchronization of estrus in sheep during the fall and late spring (season and out of season) using controlled internal drug release (CIDR) devices on Delmarva

Abstract

Changing U.S. demographics have increased lamb demand, which usually follows holidays, changing from year-to-year coinciding with traditions/festivals. In 2013, >80,000 t (metric tons) of lamb were imported to USA. A chief constraint to continuous year-round lamb supply is the influence of season on sheep reproduction. The purpose of this project was not to determine FDA approved CIDRs' (2009) efficacy in sheep but to resolve applicability and practicality of CIDR use in commercial flocks to condense lambing periods and target peak lamb demands. From 2012 to 2015, purebred and crossbred Katahdin ewes (n = 201) were separated into two groups, synchronized (CIDR) or not (CONTROL), for breeding in late Spring (anestrus-season) or Fall (natural-breeding-season). At each breeding event, CIDRs were inserted for 12 to 18 d, and at the time of CIDR removal, ewes were grouped for mating in single sire groups of no more than 6 ewes/group. The FDA approved protocol (12 to 18 d) was followed because pre-trials at this station gave inconsistent results following the label's CIDR insertion and removal time (5 d). At birth, lambs were tagged, weighed, and sexed, and litter size was recorded (LSZ) (lambs/ewe exposed). Data were analyzed using Chi-square and analysis of variance (SAS software package) for effect of synchronization and season on pregnancy rates (PR) (pregnant ewes/exposed ewes) and LSZ at birth. Overall PR did not differ from one year to the other in CIDR or CONTROL ewes. PR was higher (P < 0.0001) in CIDR ewes (63.4%) than in CONTROL ewes (34.3%) but was similar between breeding seasons (62.4% and 37.6% for CIDR and 52.8% and 47.2% for CONTROL in Fall and Spring, respectively). During Spring, PRs were higher (P < 0.0001) in CIDR ewes (71.4%) than in CONTROL ewes (17.6%). During Fall, PRs were similar (58.5% and 49.1% for CIDR and CONTROL, respectively). Overall, ewe LSZ was influenced by season bred and use of CIDRs, with CONTROL Spring-bred ewes having a lower (P < 0.0001) litter size (0.3 ± 0.1) compared to CONTROL-Fall, CIDR-Fall, and CIDR-Spring bred ewes (1.0 ± 0.1, 1.2 ± 0.1, and 1.3 ± 0.1, respectively). The results encourage using CIDRs in commercial sheep flocks to increase pregnancy rate and litter size. Additionally, CIDR synchronization in our station reduced a 60 to 90 d lambing period to 10 d, allowing operators to arrange facilities, labor, and supplies accordingly, enhancing lamb survival and ewe welfare. Project funded by Evans-Allen grant USDA/NIFA MDX-AS1012001.