Evaluation of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds of sheep: I. Effects of ram breed on productivity of ewes of two crossbred populations

Effects of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds for perf ormance as sires were estimated in the initial phase of a comprehensive eva luation of these breeds as contributors to sheep crossbreeding systems. Obj ectives were to evaluate the effects of ram breed, ewe breed, season of mat ing, and two-way interactions. Rams from the five breeds were single-sire-m ated with ewes from two breed types to produce lambs over a 3-yr period. Ew es were assigned to one of three distinct 35-d mating seasons initiated eac h year in August, October, and December. A different sample of six rams per breed was used each year across all three seasons, and each ram was penned with ewes of both breeds. Traits evaluated and number of ewe records were conception rate and litter weaning weight per ewe exposed (n = 3,261) and n umber born, litter birth weight, average birth weight, number weaned, and l itter weaning weight per ewe lambing (n = 2,751). Ram breed and ewe breed i nteracted (P < .01) for conception rate and litter weaning weight per ewe e xposed, implicating mating preferences, particularly of Romanov rams. In mi xed groups of ewes exposed to Romanov rams, conception rate was 12.7% lower and litter weight weaned was 8.4 kg lower in the ewe breed presumably less preferred far mating by the rams. On a per ewe exposed basis, Romanov-sire d litters produced either the largest or the smallest values for litter wea ning weight, depending on the breed of ewe. Effects of ram breed on number born and litter birth weight interacted (P < .05) with season of mating. Th e largest litters within each ram breed were associated with the October ma ting season. Montadale and Romanov rams sired larger and heavier litters fr om August matings than from December matings, whereas the opposite was true for Dorset-sired litters. Texel- and Finnsheep-sired litters were similar in size and weight from August and December matings. Breed of ram differenc es affected per ewe lambing productivity measurements (P < .01). Difference s between ram breeds for ewe productivity were noted, with increased number born and improved survival of crossbred progeny to weaning for Romanov-sir ed litters. These results may have implications for using these ram breeds as sires in different crossbreeding systems. Structured mating systems or t he creation of new composite populations involving these breeds could be us ed to match the resources, environment, and market of specific production s ituations.