| Abstrakt: |
A flock of 288 Rambouillet, Suffolk, Columbia, Finn × Rambouillet, Finn × Suffolk and Finn × Columbia ewes was split into three groups. Control ewes were bred once per year (October). The other two groups were intensively managed to lamb every 8 mo, but 4 mo out of phase with each other. Estrus was synchronized in intensively managed ewes using intravaginal sponges impregnated with medroxyprogesterone acetate. Breedings occurred in January, May and September. Estrus was induced by photoperiod manipulation for out-of-season breeding. The percentage of ewes lambing of those put to the ram was not affected by breed, but was affected by season of breeding. Results were similar for January (93 ± 1%) and October breedings (control, 90 ± 3%; P>.1), lower for September (81 ± 3%; P<.05), and lowest for May (64 ± 5%; P<.05). The number of lambs per 100 ewes lambing was higher for crossbred (216 ± 10%) than purebred ewes (165 ± 8%), but was lower following May breedings (172 ± 6%) compared with January breedings (207 ± 11%). September and October breedings did not differ (180 ± 7%, 190 ± 10%; P>.05). Intensive management increased annual lamb production by 37%. Crossbred and purebred ewes produced 254 ± 16 and 198 ± 14 (P<.05) lambs per 100 ewes, respectively, under intensive management with a high of 283 ± 26 for Finn × Columbia ewes. Lamb weaning weights were not significantly affected by season, but were lower under intensive management (16.7 ± .1 kg, intensive; 17.7 ± .4 kg, controls; P<.05). Lamb losses from birth to weaning were not affected by breed, management regimen or season (P>.1). However, losses of lambs from purebred ewes were 11 ± 4% and from crossbred ewes 15 ± 4% (P<1) |
