Comparison of Reproductive Performance and Wool Production of Crossbred Ewes Maintained as a Fall or Spring Lambing Flock at Two Different Locations

Reproductive performance and wool production of 524 1/4-Finn 1/4-Dorset 1/2-Targhee (FDT) and 80 Hampshire x FDT ewes managed as a fall or spring lambing flock either on the range or farm flock systems were evaluated for ewe fertiliy, percent of ewes exposed that weaned a lamb, prolificacy, lambs weaned per ewe lambing, lambs born and weaned per ewe exposed, litter weight born per ewe lambing, litter weight weaned per ewe lambing and exposed adjusted to 75 days of age, ewe body characteristics (prebreeding weight and condition score, weight at weaning, and weight change) and fleece weight. Data included 1781 ewe exposures resulting in 2180 lambs born. Original ewes were born in April, 1992-1994 at the Antelope Range Livestock Station and transported to Brookings where they were all exposed for fall lambing. Those ewes that lambed in the fall were divided between the range and farm system. Open ewes were randomly allocated between the fall and spring flocks at both range and farm systems so that each group had approximately 50 ewes entering. Replacement ewes were selected from early lambing ewes and from multiple births (when available) within each flock group. The basic model included location, season, ewe age and all interactions. Only the least square means and standard errors for the location*season*ewe age interaction were reported, regardless of significance level, due to empty cells and therefore the inability to calculate some main effect least square means. Improvement was found for all traits as ewe age increased within the location*season groups. For most traits, ewes of the same age at the same location lambing in the spring performed better than those in the fall. Also, farm flock ewes tended to perform better than range flock ewes of the same age lambing in the same season. In the farm flock system, as ewe age increased the difference between ewes lambing in the fall and those lambing in the spring decreased, indicating that progress can be made to improve the reproductive performance of the fall lambing ewes. Individual lamb birth and weaning data were also analyzed including birth type, rearing and sex to the basic model. Lambs born in the farm spring group were heavier at birth than farm fall, range spring and range fall (4.80 ± .038, 4.13 ± .044, 4.12 ± .042 and 3.93 ± .070 kg, p\u3c.05, respectively). Farm fall and range spring lambs had similar birth weights (p\u3e.05). The same pattern was observed at weaning except none of the location *season groups were similar (FS=27.2 ± .251, FF=25.9 ± .285, RS=23.8 ± .278, and RF=l9.6 ± .442 kg). Lamb survival was greater in the fall than the spring when bum lambs were not included (86.9 ± 1.59 vs. 81.4 ± .999, p=.003) but was not different when bum lambs were considered saved (87.9 ± 1.42 vs. 86.4 ± .889, p=.371). This indicates that more lambs are raised by their dams in the fall than in the spring. The current study demonstrated that with time, maintaining a separate ewe flock lambing in the fall can be a viable alternative to traditional spring-only lambing and to shortened interval lambing. Results indicate that the fall lambing system is better suited to the farm flock management system