Milk: Pounds of What?

By Lindsay Upperman, Ph.D.

Names or labels can sometimes be misleading. As producers in the beef industry, many of us have noticed labels on food products that don’t always represent the largest portion of the nutritional components for a given item. Yet, for someone wanting more protein in their diet, they may be more likely to grab a bag of chips that has 5 grams of protein, although we all know there is usually 2-3 times more carbohydrates in a single serving than protein. The milk EPD is one of those things that can sometimes be confusing, which is why it is important when looking at EPDs to remember the units that the EPDs are reported in.

EPDs Bull A Bull B

Milk 22 5

Weaning Weight (WW) 50 50

Total Maternal (TM) 47 30

Milk is not a measure of pounds of milk, but rather it reflects the maternal ability of an animal’s daughters and is expressed as additional pounds of calf weaned due to maternal effects. In the table above, Bull A’s daughters should produce calves that are 17 pounds heavier at weaning due to milk production. This is the result of differences in the daughters’ milk production and mothering ability. Unlike milk, weaning weight is the pounds due to growth. In this case, both bulls chosen had the same weaning weight EPDs, so neither bull has the advantage here. A combination of these two traits provides the total maternal EPD. The calculation for total maternal is given below: Total Maternal EPD for Bull A = Milk EPD + ½ Weaning Weight EPD =22 + ½(50) = 22 + 25 = 47

Thus, daughters from Bull A will produce calves that are 17 pounds heavier at weaning due to their combined genetics for growth and milk. In this scenario, with weaning weight being the same for both bulls, the difference in total maternal is due to the milk EPD alone. The following graph depicts the comparison of the same two bulls in the table above for milk, weaning weight, and total maternal EPDs. About 47% of total maternal for Bull A is coming from his milk EPD value of 22. However, for Bull B, the opposite is true, in that 83% of his total maternal EPD is coming from the weaning weight EPD.

One of the challenges for selection based on the milk EPD is finding the optimum level of milk production for the herd. Yet, in this situation, optimum does not necessarily mean maximum. The optimum level of milk production within a herd should fit the feed and forage resources available. Thus, ensuring that the nutrient requirements of the lactating females are met, and rebreeding is not delayed by inadequate nutrition. The genetic potential for milk production varies widely among cattle. A moderate level of milk production is generally most appropriate; however, various levels can be applicable depending on the production and marketing conditions.

Furthermore, there are other factors, such as nutritional and environmental, that will affect the how the genetic potential for milk production is expressed. So even though a female may have a given level of genetic potential for milk production, the level of milk production may never be achieved.

For instance, as milk production increases, a lactating female will pass more energy and nutrients to her suckling calf through the milk. This will certainly be advantageous to the calf, but it also increases the dam’s nutrient requirements. If no additional nutrients are provided, then the lactating females will lose body condition, which may be detrimental to reproductive rates if body condition score drops below a moderate level. Additionally, a higher milking cow, not only requires higher quantities of nutrients, but also higher quality nutrients. A low-quality forage will not be the best nutrient source for a higher milking female, as these females often cannot consume enough of it to meet their nutritional demands. Although, a proper feeding program can certainly meet the nutrient requirements of a high milk production female, this would then lead to increased expenditures for the extra feed inputs. Ultimately, there is a balancing act when optimizing milk production levels with associated nutrition costs.

As with all traits, selection for various milk production levels should be assessed, including evaluating the allotted resources and marketing goals for a given operation. There is no single right answer that will fit each and every operation. Selection decisions should focus on finding a balance between milk production and other economically important traits within the beef production system. The opportunities for improving production efficiency are possible through informed cattle selection and culling decisions within your herd. FF