‘The Mammary Gland Is an Amazing Biological Factory’
Feb 27, 2012
The productive efficiency of the modern dairy cow is four times greater than it was in 1944. It’s one of the many reasons why dairy products will continue to have a major place in human diets.
The title is a quote from Dr. Dale Bauman of Cornell University. I spent last weekend with Dr. Bauman in a small group discussion of topics ranging from gene regulation of milk fat synthesis to sustainability and dairy production. Dr. Bauman is just as comfortable studying the cow from a microscopic view as he is standing back and looking at the big picture.
Not only is the mammary gland an efficient biological factory, but the productive efficiency of the modern dairy cow is four times greater than it was in 1944. This productive efficiency is one of the many reasons why dairy products will continue to have a major place in human diets. Two-thirds of these gains are estimated to be from genetics and one-third from nutrition and management.
What’s the genetic basis for this improvement in productive efficiency? Interestingly, we have not been able to improve upon the efficiency of milk synthesis in the mammary gland. Animals differ very little in the efficiency of nutrient use for milk synthesis, and Dr. Bauman states that there is no relationship between genetic merit and partial efficiency of nutrient usage for milk synthesis. Neither has genetic selection for milk yield altered the efficiency of digestion and nutrient absorption. The efficiency of nutrient use for maintenance is also similar for all mammals on a metabolic body weight basis and has not been affected by genetic selection.
So, then what does account for the huge improvements in productive efficiency? The main source of genetic gain is through nutrient partitioning; in other words, where the available nutrients are used. In the modern dairy cow, the body coordinates many tissues and body processes to direct and support the demand for nutrients by the mammary gland. This, in turn dilutes the mandatory nutrients for maintenance, making the cow more efficient.
Our improvements in nutrition, management and cow comfort support these genetic gains in nutrient partitioning. Heat stress, for example, not only reduces feed intake but also redirects the nutrients available for milk production. The result is that milk yield decreases more than what can be explained by the reduction in dry matter intake.
Dr. Bauman pointed out two other interesting concepts that need to be considered when discussing the efficiency of modern dairy production and its impact on the environment:
1. The environmental impact of producing food should be measured by the nutrient contribution of that food, not just on the basis of weight or calories. On the basis of nutrient density per unit of green house gas emission, milk really shines.
2. The dairy industry should get carbon credits for using byproducts that would otherwise have very little value. The majority of the nutrients used to produce milk are not from human usable sources. Milk production is even more efficient when you consider this.
Dr. Bauman’s scientific approach to sustainability in dairy production and his understanding of the regulation of nutrient use in the cow is an asset to the dairy industry. His website is http://www.ansci.cornell.edu/bauman/
Contact Lundquist at SiestaDog@aol.com.