Using muscling selection line cows to inform maternal productivity modelling

Summary

This project studied the effect, in an Angus cow herd, of selection for divergent muscling on the maternal productivity of the cow herd under two levels of nutrition. The herd comprised a Low muscle line (D muscle score average); a High muscle line
(C muscle score average); and a HighHet line (B muscle score average) comprising
High muscled cows with one copy of the 821del11 mutation in the myostatin gene. The herd was managed on Low or Medium/High nutrition over three reproductive cycles, generating 750 joining records. High muscle cows had similar calving rates and maternal performance to Low muscle cows under nutritional challenge (average cow pre-join liveweight 498-508kg, rib fat 2.7-4.4mm), but the HighHet cows showed a slight reduction in calving rates. Low and High muscle cows weaned 191kg of calf/cow joined.year while HighHet cows weaned 165kg. This project also reports on the ability of 3D RGBD (Red, Green, Blue, + Depth) camera systems to estimate cow body condition, and on differences in plasma metabonomics with change in cow condition. Industry can be confident that moderate increases in muscling in cows will not affect maternal productivity, but using the myostatin gene to further increase muscling could result in reduced productivity under nutritional challenge.