How Cow Weight and Milk Output Effect Revenue

October 2010

Depending on the operation, feed costs are usually between 40% to 60% of annual cow costs. From a cost standpoint, continual focus on feed cost results in the greatest opportunity to increase profit potential of the cow/calf enterprise. Breed sire summaries indicate that the genetic trends for growth traits, carcass weight, and milk production have increased over the years. It is hard to see how milk production and mature weight of commercial cow herds has not continue increased over time. In addition, it hard to see how nutrient needs of the commercial cow herd haven't increased over time as well. McMurray (Feedstuffs article, 2008) suggested that average cow weight had increased 322 pounds between 1975 and 2005. McMurray indicates that average cow weight (weight for cows at body condition score 5) in 2005 was 1,369 pounds compared to 1,047 pounds in 1975.

As a refresher, maintenance feed is proportional to the animal's metabolic body weight. Metabolic body weight is defined as body weight to the 3/4 power (body weight3/4) which also describes the surface area and is representative of the active tissue mass or metabolic mass of an animal. So as cow weight increases, maintenance feed increases because metabolic body weight increases. In addition, as daily milk output increase, so does nutrient needs. In regard to milk production, not only are nutrient needs increased during the time of lactation, but the nutrient needs are also increased during the dry period because high milk potential females have a greater visceral organ weight compared to cows that have lower milk potential.

If milk output per day is fixed at 20 pounds per day and cow mature weight changes from 1,000 to 1,200 pounds or 1,400 pounds and cows are managed on a fixed resource base, with some assumptions, gross sale dollars can be determined. If par is a set of cows with a mature weight of 1,200 pounds and daily milk production is 20 pounds, using annual maintenance energy needs, 100 head of 1,200 pound cows producing 20 pounds of milk daily could be managed on a fixed resource base, using similar calculations, about 90 head of 1,400 pounds cows producing 20 pounds of milk daily or about 112 head of 1,000 pound cows could be managed on the same fixed resource base.

Again, if cows in each weight group had a weaning rate of 85%, 85 calves, 77 calves, and 95 calves would be weaned from cows that weighed 1,200, 1,400, and 1,000 pounds respectively. It is a little more difficult to determine weaning weight of the calves as a percent of cow weight for cows of similar daily milk production. On a limited resource base, larger cows have potential to wean off heavy calves, but because of the limited resources, that genetic potential is not met. Bigger calves have greater nutrient needs. Just the opposite would be expected for calves from light mature weight dams. If the group of 1,200 pound cows wean 47% of their mature weight, 1,400 pound cows will wean about 44% of their mature weight. In comparisons, the 1,000 pound cow of similar milk production would wean of about 49% of their mature weight.

Remember, these calculations are based on cows being managed on the same resource base in the same environment. Using the percentages above, it calculates that 1,400 pound cows wean about 616 pound calves, 1,200 cows wean 564 pound calves and 1,000 lb cows wean 490 pound calves. All groups of cows on the same fixed resource base, 85% of the cows that are exposed to a bull during the breeding season wean a calf. Gross pay weigh at weaning for each of the groups would calculate to 47,432 pounds, 47,940 pounds, and 46,550 pounds for the group of 1,400 pound, 1,200 pound, and 1,000 pound mature weight cows.

If 500 pound calves sell for $100/cwt and there is a $5/cwt price slide, 616 pound calves sell for $94.20/cwt, 564 pound calves sell for $96.80 and of course, 490 pound calves sell for $100.50/cwt. There likely needs to be a discount for frame. Too much frame or not enough. The calves from large mature weight female will be discounted another $0.50 and calves from the small mature weight females will be discounted another $1.50/cwt. This discount seems to make sense as frame impacts carcass weight at which they will grade USDA Choice. The question might be should both large and frame size be discounted equally. Gross sale dollars generated from the sale of calves from 1,400 pound cows would be $44,444, calves from 1,200 pound cows would generate $46,406 , and calves from 1,000 pound cows would generate $46,085.

The above calculations do illustrate the importance of weaning weight and reproductive rate. Can a producer continue to drive weaning weight up at the expense of weaning rate.

An extra calf to sell appears more important than extra weaning weight per calf. If the genetic trends continue in the direction they have been, how does a producer maintain the genetic package that they have worked so hard to fit their resources and environment? The idea is to help you keep your eye on the target of what genetics package fits your environment and to make an attempt to relate the amount of revenue generate in a cow herds that differ in mature size managed in the same environment and resources.

Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska–Lincoln, Lincoln, NE