Top cows fail at low inputs
HIGH genetic index dairy cows fail to perform as well in low input systems as they do in high input, lower forage regimes.
Evidence comes from the latest report from the Scottish Agricultural Colleges Langhill Dairy Research Centre.
Ongoing research confirms that high merit animals out-perform their lower merit contemporaries on both high and low input systems. But it suggests that higher merit animals can eat more of a concentrate-based total mixed ration than a forage based TMR.
"High genetic index animals have difficulty eating more forage than lower merit cows," says Langhills Roel Veerkamp. These animals still gave more milk than the lower merit cows – but produced the extra milk from lost body tissue alone.
High merit cows on the high input system have the advantage of both higher intake and loss of body tissue during early lactation to put into milk production.
"This effect could be due to selection of animals under high input systems," says Mr Veerkamp. "Producers are still better off with high genetic merit animals but it could be that breeding strategies need to be fine-tuned to select for forage eating ability."
High genetic merit cows also suffer an energy gap in early lactation. This was expected to increase with genetic selection for yield which could have implications for health and fertility.