Impact of Cow Size on Nutrient Needs
By Dr. Rick Rasby, Professor of Animal Science, Animal Science, University of Nebraska - Lincoln, Lincoln, NE.
15 November 2006
1 minute read
Nutrient needs for cows of different body weights are not the same. Cows that weigh 1,300 pounds have a greater nutrient (pounds of protein, pounds of energy (TDN), ounces of mineral, etc) requirement compared to cows that weigh 1,000 pounds. If a 1,000 pound cow and a 1,300 pound cow are grazing the same forage resource, the 1,300 pound cow will need to consume more of that forage to meet her requirements.
Maintenance feed intake is proportional to metabolic body weight which is described as body weight to the 3/4 power (body wt.3/4). Metabolic body weight isn't just weight of the animal but also describes the surface area of the animal. Heavier cows eat more feed to meet their requirements.
The question is: how much more do heavier cows eat?? Data suggests that for each 10% increase in body weight, there is not a 10% increase in maintenance feed intake. The data suggests about a 7% increase in feed intake for each 10% increase in live weight. A 1,300 pound cow is will consume 22% more feed than the 1,000 pound female although there is a 30% difference in body weight.
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