title: Breed and sire effects on crossbred lamb production from Panama ewes and on spermatozoan midpiece length.
abstract: Three-hundred mature Panama-type range ewes were mated to Clun Forest, Dorset, Border Leicester, Polypay and Suffolk rams during the 1979 and 1980 breeding seasons. Sire breed and ram within breed effects on lamb growth, ewe reproduction, spermatozoan midpiece length (MPL) and midpiece length coefficient of variation (MPLCV) were examined. Associations among MPL and MPLCV and economically important traits also were assessed. Suffolk-sired lambs weighted .18, 2.0 and 1.5 kg more, at birth, weaning and post-weaning, respectively, than the average of all groups. Dorset-sired lambs had the lightest postweaning weight. Variation was greatest among Suffolk rams for average weaning and postweaning weights of their progeny. The Border Leicester breed had the least among ram variation for progeny weaning weight; while variation among Dorset rams was least for progeny postweaning weight. Fertility (ewes lambing/ewe exposed) and prolificacy (lambs born/ewe lambing) of the rams' mates were not influenced significantly by sire breed. Lamb mortality also was not influenced by breed of sire nor by rams within a breed. For variation in MPL, 26.4% was due to the breed effect (P less than or equal to .01) and 21.6% was attributable to ram variation within a breed (P less than or equal to .01). Clun Forest rams had the longest average MPL and greatest MPLCV, while Dorsets had the shortest MPL and smallest MPLCV. There were no important associations between either MPL or MPLCV and any of the economic traits.
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D001835:Body Weight; D003433:Crosses, Genetic; D005260:Female; D008297:Male; D008957:Models, Genetic; D009026:Mortality; D012098:Reproduction; D012756:Sheep / Q000235:genetics* / Q000502:physiology; D013094:Spermatozoa / Q000166:cytology*; D014886:Weaning