PRODUCTIVITY OF PELIBUEY AND BLACKBELLY EWES MATED AT YEARLY AND 8-MONTHLY INTERVALS OVER 6 YEARS

The productivity of two hair breeds (Pelibuey and Blackbelly), raised in the tropics, was studied under two breeding programs over a period of six years: annual and accelerated lambing. Breeding seasons for ann ual lambing were from December 5 to January 10, and every eight months for the intensive program (December 5 to January 10; August 5 to Sept ember 10 and April 5 to May 10). Other than breeding seasons, all othe r management practices were the same for both programs. Information on a total of six and nine mating-lambing seasons for annual and acceler ated programs, respectively, were analyzed by the least-square method with models of fixed effects. Fertility, prolificacy, and weaning rate were all different among breeding systems (P<0.01). More ewes were de tected in estrus and lambed in the annual system (98.4 and 82.1%, resp ectively) than in the accelerated system (88.2 and 79.4%, respectively ). Litter size was also greater for the annual program (1.50 vs. 1.42) . Total weaned lamb weight per ewe lambing and per ewe exposed were si milar (P>0.05) among flocks (13.3+/-0.25 and 7.5+/-0.28 kg with the fr equent lambing program; and 13.4+/-0.3 and 8.1+/-0.3 kg in the flock u nder annual program). Lambing rate was greater for Pelibuey ewes but l itter size and adjusted lamb weaning weight were greater for Blackbell y ewes. Although the productive traits were better under yearly lambin g, results from the present study favor the accelerated system and enh ance productivity over the years. However, it is necessary to consider increases in feeding and labor costs implicated in the latter system. (C) 1998 Elsevier Science B.V. All rights reserved.