We read R. Tom Bass’ article “100-pound herds: What are the secrets to their success?” with great interest – and fully support six of his seven observations.

However, in secret No. 7, Dr. Bass states, “Large bodies, the large rumens that come with them and the proportionately lower maintenance costs of bigger cows offer several undeniable advantages when elite production is the goal.” This statement raised our concern for several reasons.

Comprehensive data compiled by the USDA-ARS Animal Improvement Program, Animal Genomics and Improvement Laboratory for Holstein cattle show a genetic correlation between milk yield and body size of -0.1. Fat and protein are also negatively correlated with body size.

These data are virtually identical across dairy breeds and are also essentially unchanged over several decades of industry data evaluation, indicating that increasing body size in Holsteins is not necessary to increase genetic milk yield.

Further data from 5,700 Holstein cows in the USDA-AFRI National Institute of Food and Agriculture project 2011-68004-30340, which is led by Dr. Mike VandeHaar at Michigan State University, also do not support No. 7 in his article.

In this analysis, the estimated genetic correlation between metabolic bodyweight and milk yield is 0.06, with a standard error of plus or minus 0.06, which indicates that it is not significantly different from zero.

This means selection for larger body size is not necessary to genetically improve high milk production, though we would also contend that net profit is a more suitable goal than high milk production.

More importantly, the genetic correlation between metabolic bodyweight and gross efficiency (defined as the proportion of total energy intake that is devoted to production of milk and formation of body tissue) is -0.28, indicating that cows with a genetic predisposition for larger body size are less efficient in terms of feed utilization.

In contrast, the genetic correlation between energy-corrected milk yield and gross efficiency is 0.66, indicating that selection for higher milk yield will increase the gross efficiency of feed utilization.

By comparing the magnitude of these correlations, we can see that selection for higher milk yield should be the primary goal. Selection for larger body size, though commonly practiced by pedigree breeders and A.I. industry sire analysts, is not supported by this research.

Consequently, ending the trend toward selection for larger body size should be a priority in the short term, and if and when we achieve this objective, our selection programs should continue to focus on higher milk yield and improved production efficiencies as primary goals, with smaller body size as a secondary goal.

New tools are emerging that will allow direct selection for increased feed efficiency, most likely in the form of genomic predicted transmitting abilities for residual feed intake.

Finally, larger and larger cows are exacerbating challenges with practical dairying in many important areas: reduced reproductive fitness, increased injury and lameness, wear and tear on facilities and housing, and increased safety issues for cows and human handlers; all of which combine, making the selection for ever-larger cows clearly an unsustainable practice, particularly for the Holstein breed.

Focus must be reapplied to improving the net profit of the dairy industry through simultaneous improvements in production capacity, production efficiencies and reduced environmental impacts.  PD

Mark Boggess
Director, USDA-ARS
U.S. Dairy Forage Research Center

Kent Weigel
Chair, Department of Dairy Science
University of Wisconsin

Mike VandeHaar
Professor, Dairy Nutrition and Metabolism
Michigan State University