Breed differences in response of wool growth to annual nutritional and climatic cycles

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Abstract
Nine Cheviot and nine ¾ Merino, ¼ Cheviot sheep were fed at similar annual maintenance levels. The annual ration was provided in three ways–in simulation of the ‘natural’ intake cycle, the reversed intake cycle or as a constant daily ration. Liveweight curves for both breeds corresponded fairly closely with the feed intake curves but considerable genotype/environment interaction was found in the response of unscoured wool growth to variation in feed intake.After an extended period of adjustment, the between sheep variation in intake, in the Merino group, was reflected in variation in wool-growth rate at all times. In the Cheviot group, intake and wool growth were related in summer but not in winter. It is suggested that not only is the efficiency of wool growth subject to genetic control but that the modification of efficiency in response to variation in environmentally controlled metabolic processes is also a function of the genetic background.