Graduate Thesis Or Dissertation
 

Genetic and environmental differences in age at first estrus and in wool and lamb production of crossbred ewe lambs

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  • Genetic and environmental factors affecting age of first estrus, wool production, reproduction and lamb production were examined in eight groups of crossbred ewe lambs from two birth years. The 399 ewe lambs whose first year production was analyzed were from eight crossbred groups resulting from mating North Country Cheviot, Dorset, Finnsheep and Romney rams to Suffolk or whiteface Columbia-type range ewes. The ewe lambs were born January through March of both 1973 and 1974, and were raised to weaning on western Oregon hill pastures. They were summered and maintained through the breeding season on irrigated pastures. At the end of the breeding season each year, ewes within each of the eight groups were randomly divided between hill pasture and irrigated valley pasture management systems. After lambing in common facilities, they were returned to the appropriate management environment where they remained throughout lactation. Average age at first estrus for the 90 percent of ewes which did cycle their first fall was 205 days. Age at estrus between years differed by 18 days (P<.01). Sire breed and the sire x dam breed interaction were not significant effects, but ewes with Suffolk dams cycled ten days earlier than ewes with Columbia dams (P<.01). Also a greater proportion of ewes with Columbia dams failed to cycle their first fall (18 percent versus 2 percent for ewes with Suffolk dams). None of the birth year interactions was significant. The regression of age at estrus on birth date of ewe was -.85 days per day (P<.01). The regression of age at estrus on ewe weight at first estrus (estimated by interpolation between bracketing weights) was 0.39 days per pound (P<.01). The unexpected signs of the two regression coefficients probably resulted from shortened day length in the fall triggering estrus at a fairly constant calendar time but at varying ages and weights, depending upon when the lamb was born the previous spring lambing season. Breed of the ewe's dam significantly affected wool grade with Columbia crosses having finer wool. Staple length was longest and about equal for Finn and Romney sired ewes; Dorset crosses produced the shortest wool. Columbia cross wool was longer than Suffolk cross wool only in Finn and Dorset cross ewes. Grease fleece weight of Columbia crosses was consistently heavier than that of Suffolk crosses. Romney sired ewes had the heaviest fleeces followed by Cheviot, Dorset and Finn sired ewes. Observable medullation was most severe in the two Cheviot crossbred groups, with a tendency for slightly greater medullation in Suffolk than in Columbia crosses. Romney x Columbia ewes generated the most wool income, due to heavy fleece weight and high value per pound of clean wool. Ewes with Columbia dams generated higher wool income than did those with Suffolk dams. The reproductive performance of ewes with Finn sires was superior to that of ewes with Dorset, Cheviot or Romney sires, while ewes with Suffolk dams were superior to ewes with Columbia dams. Finn crossbreds had the greater percentage of ewes lambing per ewe bred (72 percent), while Romney x Columbia ewes were lowest (18 percent). Finn sired crossbred ewes averaged 1.62 lambs born per ewe lambing compared to 1.18 for the average of the other crosses. Finn cross ewes excelled for total weight of lamb weaned, followed by Dorset, Cheviot and Romney sired ewes. The greater lamb production of the Suffolk cross ewes more than compensated for their lower wool production. They generated $6.00 more total gross income than did Columbia crosses. Also for gross income, ewes with Finn sires were highest followed by Dorset, Cheviot and Romney sired ewes.
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