Lifetime traits comparison between annual and accelerated lambing systems for dairy ewes

Two sets of data with a sum of 6318 lactations for 1391 Spanish Churra ewes, belonging to 10 flocks were used to study phenotypic, genetic and system efficiency parameters of lifetime traits in annual and accelerated lambing systems. The study included four life span traits, three productive traits and two reproductive traits. Trait averages for both milk yield and revenues from sold milk and weaned lambs were calculated per-day of lifetime, productive life and useful life. The animal model included flock and ewe birth year as fixed effects. Both effects contributed significantly to variation in most traits in the annual system while birth year was non-significant for most variables of the accelerated system. Milk production level was included in the model to analyze life span traits. It contributed significantly to variation in all life span traits in both systems. Means for productive and life span traits were significantly higher in the accelerated system compared with the annual system. The average interval between successive lambings was significantly shorter in the accelerated system, while age at first lambing was significantly lower in the annual system. Except for age at first lambing, heritability estimates were clearly lower in the case of the accelerated system (0.02 to 0.20) than in the annual system (0.08 to 0.45). Genetic correlations among traits were also lower in the case of the accelerated system. Failure to lamb three times in two consecutive years and the varying reproductive management among flocks in the accelerated system may be responsible for the differences in genetic results between the two systems. Improving reproductive performance is necessary, especially for the young high yielding ewes in the accelerated system. Management to ensure high fertility, especially among young ewes, would be of more importance than removing non-lambing ewes.