AVERAGE MILK YIELDS AND ENVIRONMENTAL-EFFECTS ON LATXA SHEEP

Average quantitative milk yield and environmental effects have been estimated in 214 flocks of the Latxa breed of sheep under milk recording during 1988, 1989, and 1990. For this study, 57,725 lactations of the Black-Faced Latxa strain and 9564 of the Blond-Faced Latxa strain were used. Average yield per lactation (from d 31 after lambing to the end of lactation) was 93.9 L for Black-Faced Latxa and 93.2 L for Blond-Faced Latxa with lactation lengths of 114.3 and 126.7 d, respectively. Yields by age of ewes at lambing follows a quadratic curve; minimum yields occur at 1 yr of age, and maximum yields occur between 4 and 7 yr of age. Persistency between the first 2 test days decreases with age in Black-Faced Latxa. Within age at lambing, increase in the total number of lambings by ewes affects yield favorably. Lactations after early lambing (November and December) yield most. Yield estimated per lactation, as well as milk yielded at the first 2 test days, increases as the number of live lambs at lambing increases. The more relevant correlations between yield variables are those between the milk yield on a specific test day and the persistency between that test day and next. These correlations are always negative (between -.31 and -.37).