Relationships between hemoglobin type and reproduction, lamb, wool and milk production and health-related traits in crossbred ewes.

Relationships among hemoglobin (Hb) types and production traits were examined in 294 crossbred ewes from North Country Cheviot, Dorset, Finnsheep and Romney rams, and Suffolk and Columbia-type ewes. Hb BB ewe lambs were youngest at first estrus, while Hb AA ewe lambs were oldest. Ewe lamb fertility was similar for Hb AB and Hb BB ewes, and both were superior to Hb AA ewes. When Finnsheep crossbreds were excluded, from which Hb BB was absent, Hb BB ewes had higher ewe lamb fertility than did Hb AB ewes. There was a minor advantage of the A over the B allele in ewe lamb prolificacy. Hb BB ewes were highest, Hb AB ewes were intermediate and Hb AA ewes were lowest for average fertility, prolificacy per ewe lambing, lambs born per ewe exposed to mating, total number of lambs weaned and total kilograms of lamb weaned. Grease wool production, staple length, fiber diameter grade, incidence of medullated fibers and incidence of cotted fleeces all were similar across Hb types. Likewise, Hb type did not affect milk production or composition. Ewes with Hb AB had the lowest incidence of footrot; Hb AA and Hb BB ewes were similar. Ewes with Hb AA had the lowest fecal parasite egg counts, while ewes with Hb AB or Hb BB were similar. Ewes with Hb AA also had the lowest incidence of mastitis, Hb BB ewes were intermediate and Hb AB ewes were highest. The combination of overdominance (as for footrot resistance), beneficial effects of the A allele on health-related traits (as for mastitis and parasite resistance) and the beneficial effect of the B allele on reproductive traits, if real, could partly explain the genetic polymorphism commonly reported at the Hb locus in sheep.