Genetic Selection Rules Haven’t Changed

Select for component pounds, not percent. ( Maureen Hanson )

Restraints on milk production and the possibility of dairy processors imposing quotas on the volume of milk shipped might lead some dairy farmers to change genetic selection criteria.

In fact, some AI bull studs are already promoting the idea of selecting on component percent rather than pounds, particularly if their sire lineups offer bulls that are high in fat percent.

The problem is farmers are still being paid for pounds of milk, fat and protein they ship each day—not on a percentage of the fat and protein in the milk. So the genetic selection rules haven’t changed, says Kent Weigel, a dairy geneticist with the University of Wisconsin. “We still recommend pounds of fat and pounds of protein,” he says.

Chad Dechow, a dairy geneticist with Pennsylvania State University, agrees. “The reality is that you are not selecting for just percent,” he says. Decades ago, selecting on percent fat would mean a loss of fat pounds because percent and volume were negatively correlated. Today, the genetic correlations between milk yield and fat and protein percentages are slightly negative—0.3% to 0.4%.

AI firms have done a good job of weeding out bulls low in fat pounds. “We are already starting out with a good population of bulls that are high in pounds of fat,” Dechow says. “Fat percent and fat pounds are positively correlated within a bull population, which has already been selected for fat pounds. Having said that, I do think that you would have made more progress for pounds if you select for pounds,” he says. Complicating the picture is milk processors typically pay for total solids. And the picture is less clear with protein. “Protein is correlated with pounds protein, and total solids would grow more with selecting for pounds protein,” he adds. 

Quotas Could Change Picture

Recommendations could change if quotas are enforced. “A quota on milk volume would change the equation, but I don’t think that’s an issue now,” Weigel says.

“By putting a negative weight on milk volume (or a positive weight on fat percent and protein percent) in the index, I can now give extra benefit or preference to those bulls whose daughters can produce +150 combined fat plus protein (CFP) from more concentrated milk rather than just more milk volume,” Weigel says.

“That’s reasonable to consider if all the milk is going for cheese and we want to account for hauling costs, though I don’t think it would make a huge difference.”

That’s essentially what you are doing by using Cheese Merit $ (CM$) instead of Net Merit $ (NM$), the geneticists say. NM$ puts a 1% negative weight on milk volume whereas CM$ has a negative 8% weight on milk volume.

There’s another management strategy beyond genetics if quotas were imposed. That would be to continue to breed for volume, but reduce overstocking rates in facilities. That likely would result in better cow health and longevity.

Lenders might initially frown on this approach because it would reduce farm equity by reducing cow numbers, Dechow says. Long term, however, overall profitability could improve with less stress and lower culling rates.


Note: This story appears in the February 2018 magazine issue of Dairy Herd Management.