What Causes the Negative Genetic Correlation between Maternal and Direct Effects for Lamb Birth Weight?

An antagonistic genetic relationship between direct and maternal effects for birth weight (and weaning weight) makes the concurrent genetic improvement of the two traits more challenging than if the correlation was zero or favourable. The direction and magnitude of the genetic correlation between maternal and direct effects for lamb birth weight are equivocal with several moderate negative and several near zero estimates being reported. A number of experiments over the last decade undertaken at Massey University in the pursuit of developmental programming effects in sheep, have provided serendipitous results that suggest a negative phenotypic correlation between dam and offspring birth weight can be induced by some environmental stressors during pregnancy. These correlations could be interpreted as having an underlying genetic effect, since the relationship is generated without any experimental manipulation of second generation lambs. It is proposed that mining existing datasets might be a fertile ground to conduct research for further exploration of this possible explanation of the negative genetic correlation between direct – maternal effects for birth weight.