Phenotypic study on total and partial lifetime traits for dairy ewes.

A data file on 36,396 lactations was used to determine the strength of the phenotypic relationship between productive, reproductive and lifespan traits for 7935 Spanish Churra ewes. These ewes first lambed between 1989 and 1997 and belonged to 23 flocks. The study took into account four lifespan traits (lifetime, productive life, useful life and lifetime score), three productive traits (total milk yield produced during lifetime, lambs weaned during ewe lifetime and total revenues from sold milk and weaned lambs during lifetime) and two reproductive traits (age at first lambing and mean interval between successive lambings). Moreover, milk yield and revenues from sold milk and weaned lambs were calculated per day of lifetime, productive life and useful life. Partial lifespan traits were considered for the first three parities. The model included flock, birth year within flock and season of birth of the ewe as fixed effects. The first two effects contributed significantly to variation in all traits, while season significantly affected lifespan traits, productive traits and age at first lambing. Milk production level was added to the model for lifespan traits only. It significantly contributed to explaining the variation in all lifespan traits with high percentage of variance explained averaging 14.91%. Lifetime averaged 2324 d. Productive life accounted for 57% of lifetime while useful life represented 50% of productive life. Age at first lambing averaged 622 d and average days dry during lifetime was 560. During lifetime, ewes gave an average of 4.6 parities, 6.5 weaned lambs and 636 l of milk. Average revenue from milk and lambs during lifetime was 673 euros. Milk/day of lifetime, productive life and useful life averaged 0.26, 0.51 and 0.93 l, respectively. The corresponding per-day revenues from sold milk and weaned lambs were, 0.27 euros, 0.55 euros and 1.01 euros, respectively. Lifespan and productive traits had strong relationships (rp among these traits ranged between 0.75 and 0.95). Two-parity and three-parity per-day milk yield had moderately high correlation (0.70-0.83) with total lifetime per-day milk yield traits. Therefore, good use of these traits would be helpful in determining best individuals early in life.