Dr. Kent Weigel
Associate Professor
Department of Dairy Science
University of Wisconsin – Madison
Dairy producers seeking to improve component percentages and milk quality through genetic selection can achieve these goals using within-breed selection or crossbreeding. Crossbreeding is widely accepted in plant breeding, as well as in other livestock species, such as beef, sheep, and swine. However, the historically strong role of breed associations, coupled with the presence of milk pricing systems that favored milk volume at the expense of component percentages, have limited the role of crossbreeding in dairy cattle. Within-breed selection can change milk quality and milk composition significantly, because substantial genetic variation exists for fat percentage, protein percentage, and somatic cell count. When mated to typical Holstein cows, the mean fat percentage of daughters of the best and worst Holstein artificial insemination (AI) sires ranges from 3.36% to 3.97%. The corresponding range among Jersey AI sires for fat percentage (when mated to typical Jersey cows) is from 4.23% to 5.09%. Likewise, mean protein percentage of daughters of the best and worst Holstein sires ranges from 2.81% to 3.18%, while the corresponding range for daughters of the best and worst Jersey sires is from 3.41% to 3.71%. Thus, it is clear that crossbreeding will provide more rapid genetic changes in milk composition than within-breed selection, as differences between breeds for these traits are much greater than differences within breeds. On the other hand, differences between breeds in somatic cell score (SCS) are much more modest. Daughters of the best and worst Holstein AI sires range from 2.45 to 3.50 for SCS, while the corresponding range for Jersey AI sires is from 2.66 to 3.22. This suggests that within-breed selection for improved milk quality will be as efficient as crossbreeding. Estimates of heterosis (hybrid vigor) for milk composition and milk quality in the scientific literature are relatively few, but it is reasonable to assume that an advantage of 5-10% (relative to the average of the parental breeds) can be achieved. Crossbreeding has received increasing attention among dairy producers in recent years, but it is interesting to note that the driving force behind this “crossbreeding movement” is a desire to improve health, fertility, and calving performance, rather than a desire to improve cheese yield. On large commercial dairies, volume premiums (or artificially low hauling charges) can negate the financial benefits a producer might otherwise achieve by improving milk composition through genetic selection or crossbreeding. Breeding programs are long-term ventures (10-15 year horizon), so it is critical for milk processors to create consistent, forward-looking incentives that will reward producers for shipping the type(s) of milk that lead to optimal processing efficiency.
