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Dairy Pipeline: March 2005
Bennet Cassell
Extension Dairy Scientist
Genetics and Management
(540) 231-4762
email: bcassell@vt.edu
The trait called "dairy character" or "dairy form" is losing its luster in genetic selection indexes. Research has shown that cows that lose a lot of weight after calving to support high milk production tend to have greater health and fertility problems. Such cows cannot meet their energy requirements from the feed they eat, and they mobilize stored body energy, fat mostly, to meet the deficit. For many years, one of the "holy grails" of dairy cattle breeding was the high producing, very clean, non-fleshy dairy cow. Looking back on that era, I recall the doubt that many (me included) had in high milk records on cows with substantial amounts of body tissue -muscle and fat reserves - across the withers, down the topline, and in the seat of the pants. "Fat" cows got that way because they used feed for body fat instead of milk. Certainly, there were cows like that in the dairy population 30 and 40 years ago, but it's a different story today. The genes for production are in our dairy cows, but we haven't tried to control whether the energy to make that milk came from feed consumed or body fat. Recent changes to the TPI formula put negative weight on dairy form, favoring a slightly less "dairy" cow. Really good work has been done in Scotland in recent years on energy balance in selection (for fat plus protein) and control line Holsteins on high and low concentrate diets. That project had several objectives, but the conclusions of a recent paper (J. Dairy Sci 87:4318) included this statement: "Selection primarily for yield perhaps exacerbated by additional selection for angularity (or dairy form) has led to cows that mobilize more of their body energy in early lactation and do not replenish all lost body lipid later in their productive life." Some measure of changes in body energy during peak production periods could well be part of future selection indexes. The search for the cow with the ability to maintain body condition under the energy demands of high production through feed consumed will be a tough nut to crack. We will not likely have feed intakes and changes in body weights on large numbers of daughters in progeny test programs. Indicator traits will be necessary. Dairy form is one such trait. The negative weight it receives in the new TPI reflects the findings of the Scottish study.