Reproductive Performance and Wool Production Analysis of 1/4 Finn, 1/4 Dorset and 1/2 Targhee inter se mated Ewes Selected for Fall vs. Spring Lambing Seasons Under Range vs. Farm Flock Management Systems

Reproductive and wool measurements were taken for fall and spring lambing ¼ Finn, ¼ Dorset and½ Targhee ewes located at the Antelope Range Livestock Station near Buffalo, SD and the SDSU Sheep Teaching and Research Center at Brookings, SD. The first crossbred generation (G 1) consisted of 524 offspring from Finnsheep x Dorset rams mated to Targhee ewes (FDT) and 80 offspring from Hampshire rams mated to FDT ewes (HFDT). Ewes that lambed in the fall were assigned randomly to the fall range flock or fall farm flock. Ewes that were not pregnant were randomly assigned to the farm or range flocks for fall or spring lambing to equalize numbers and reach a goal of 150 ewes in each season and each location. Ewe and ram replacements were selected for early birth dates, multiple birth types, and reproductive soundness. Ewe traits measured included prebreeding weight, body condition score, fleece weight, number and weight of lambs born per ewe exposed and per ewe lambing, number and weight of lambs weaned per ewe exposed and per ewe lambing, ewe weight at time of lamb weaning, and litter weight born per ewe lambing. Lamb traits measured were birth weight, birth type, sex, rearing, weaning weight adjusted to 75 days, and lamb survival. Data from 893 ewes and 3012 lamb records for years 1994 to 1998 were collected. Traits were adjusted for ewe age and generation if the effect of these covariants were significant. Each individual animal received a generation level (G) using the formula [(Gsire + Gdarn)/2] + 1 = Gindividual. Spring flock ewes had lighter prebreeding weights and fleece weights than the fall flock ewes. Prebreeding weights were affected by lambing status, lambing ewes had heavier prebreeding weights (P\u3c.05). Fleece weights were not affected by lambing status. The heavier prebreeding and fleece weights in the fall flocks, especially the fall farm flock, may be attributed to the additional feed and minimal heat stress associated with the fall flock. The fall flocks had lower values for percent lambing, prolificacy, number of lambs weaned per ewe exposed and ewe lambing, and litter weight born (P\u3c .05). Ewe generation had little significance for all reproductive traits except ewe weight at lamb weaning, litter weight born per ewe lambing, and lamb weight weaned per ewe exposed. A decreasing trend was seen from generation one to generation three for litter weight born per ewe lambing for all seasons and locations. Spring born lambs had heavier birth and weaning weights (P\u3c .05). Lambs born in the farm system had heavier birth weights than those in the range system (P\u3c .05). Male and female single reared lambs had heavier weaning weights than lambs raised as twins. Improvement in fall flock reproductive traits was seen as years progressed, thus narrowing the gap between spring and fall lambing ewes. Additional years and generation levels maybe needed in order for the fall lambing flocks to be equal with the spring lambing flocks