Genetic and non-genetic effects on plasma LH concentrations in lambs at 4 and 8 weeks of age

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Abstract
Plasma LH [luteinizing hormone] was measured at 4 and 8 wk of age in purebred lambs born to Finnish Landrace, Galway, Fingalway and High Fertility ewes. The average litter sizes for these breeds vary from 1.4 to 2.5. Lambs born after the transfer of fertilized eggs (all Fingalway) to Finnish Landrace, Galway and Fingalway ewes were also studied. There was evidence for a significant positive effect of selection for litter size within the Galway breed on plasma LH at 8 wk of age. Finnish Landrace lambs had significantly higher levels of plasma LH at 8 wk of age than did Galway Control lambs. These 2 groups did not differ with respect to plasma LH at 4 wk of age. Non-additive genetic effects were significant at 4 wk of age. The ranking of genetic groups on plasma LH was not consistent with their ranking for litter size. There was no evidence for a maternal effect associated with breed of dam on plasma LH and the effects of litter size were generally insignificant. Female lambs had significantly higher levels of LH at 4 wk of age but there was no sex difference at 8 wk because LH levels in males had increased. The correlation between the level of plasma LH at 4 and 8 wk of age was -0.04. Plasma LH is unlikely to prove a practical aid to selection for increased fecundity in sheep.

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