Relationships between hemoglobin genotype and production in cross-bred ewes. I. Reproduction and lamb production : II. Wool and milk production and health related traits Public Deposited

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  • I. REPRODUCTION AND LAMB PRODUCTION Relationships among hemoglobin (Hb) genotypes and reproduction and production traits were examined in 294 four- and five-year-old North Country Cheviot, Dorset, Finnsheep or Romney x Suffolk or Columbia-type crossbred ewes. Hb BB ewe lambs were youngest at first estrus and Hb AA ewe lambs were oldest. The differences were small but consistent across crossbred groups. Ewe lamb fertility was similar for Hb AB and Hb BB ewes, and both were superior to Hb AA ewes. The difference among Hb genotypes in ewe lamb fertility, when the two Finnsheep groups (in which the Hb BB genotype was absent) were excluded, favored ewes with Hb BB over ewes with Hb AB. Results suggested heterozygote advantage in prolificacy of ewe lambs with a minor advantage of the A over the B allele. Hb BB ewes were highest, Hb AB ewes were intermediate and Hb AA ewes were lowest for average fertility over all production years. For prolificacy per ewe lambing and prolificacy per ewe exposed to mating, Hb BB ewes were superior to Hb AB and Hb AA ewes. Hb BB ewes were also superior, Hb AB ewes were intermediate and Hb AA ewes were lowest for total number and total kg. of lambs weaned. Results suggested that-the B allele enhances most traits associated with reproductive fitness. There was little suggestion of heterozygote advantage for those same characteristics. II. WOOL AND MILK PRODUCTION AND HEALTH RELATED TRAITS Relationships among hemoglobin (Hb) genotypes (Hb AA, Hb AB or Hb BB) and wool production, milk production and health related traits were examined in 294 North Country Cheviot, Dorset, Finnsheep or Romney, Suffolk or Columbia-type crossbred ewes. Grease wool production, staple length and side and britch fiber grades were very similar across Hb genotypes. Incidence of medullated fibers also did not differ significantly among ewes of varying Hb type. Within crossbred groups found to have some cotted fleeces, no significant difference in cotting incidence existed among Hb genotypes. Milk production, percentage milk fat and percentage milk protein also did not differ significantly among Hb genotypes. Ewes with Hb AB averaged the lowest incidence of footrot with Hb AA and Hb BB having similar scores. Ewes with Hb AA had the lowest fecal parasite egg counts while ewes with Hb AB or Hb BB were quite similar. These differences were not significant but they were reasonably consistent across crossbred groups. Ewes with Hb AA also had the lowest incidence of positive mastitis test scores with Hb BB ewes intermediate and Hb AB ewes having the highest incidence. Overdominance (as for footrot resistance) and the moderate beneficial effect of the A allele on health related traits (as for mastitis and parasite resistance) that are suggested by our findings, if real, could contribute to variation in longevity which in turn could partly explain the genetic polymorphism commonly encountered at the Hb locus in sheep.
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