Date of this Version
Presented at Range Beef Cow Symposium XXII, November 29, 30, and December 1, 2011, Mitchell, Nebraska. Sponsored by Cooperative Extension Services and the Animal Science Departments of the University of Wyoming, Colorado State University, South Dakota State University, and the University of Nebraska–Lincoln.
Do relationships exist between cow size, nutrient requirements, and production capability? We can assume that a bigger cow will require more nutrients. What are the characteristics of that relationship? Is it a direct response wherein a cow that is 10% bigger than another will require 10% more nutrients, or is there economy of scale, so to speak? Can we assume that a bigger cow will be more productive? Is it automatic that bigger size means faster growth so we can expect the calves of bigger cows to grow faster? We will explore these relationships.
It is commonly understood that cows are getting bigger. When one considers that the cow population in the US has shrunk since 1974 (as depicted in the cow inventory figure below) while total pounds of beef produced annually has been maintained at nearly 50 billion lb over the same time period (as depicted by the line depicting lb of cattle produced in the various meat sources figure), it is obvious that cattle have had to steadily increase growth potential and size.
Perhaps the more important question is how big is the modern cow? More particularly, each of you might wonder how big your cows are. If everyone had a scale on the ranch, this would be known. Perhaps the best alternative on a ranch-specific basis is to look at sale weights of cull cows and then try to adjust for any differences between the culls and the cows that remain in the herd.
In place of thinking specifically of each ranch, let’s look at indicators of cow size in general. One indicator is the shift in EPD genetic trends for cattle weights. As depicted in the following figure, the genetic trend through time for the Angus breed has displayed a steady increase in weaning, yearling, and mature cow weight. In particular, yearling weight, which is considered a reliable indicator of mature weight, has increased by 96 lb over the span represented in this graph. We can expect that an increasing trend has occurred in other breeds as well.