Because feed costs are between 40% to 60% of annual cow costs, what are the forage feed costs differences between herds that have cows different mature weights but the same milk output? To set the parameters, all groups of cows are managed on a fixed resource base. On the same fixed resource base, if there are 100 head of 1,200 pound cows, there are 90 head of 1,400 pound cows, and 112 head of 1,000 pound mature weigh cows. 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 needs also increases because metabolic body weight increases. Annual maintenance energy is needs for a 1,400 pound cow with 20 pounds per day milk out-put is 9,249 mcal/year, for the 1,200 pound cow with the same milk out-put maintenance is 8,339 mcal/year, and for the 1,000 pound 7,415 mcal/year. Maintenance energy needs seem to make sense, as cow weight increases, so do maintenance energy needs because as body mass increases there is more surface area and therefore increased nutrient needs. The maintenance energy need reported here take into account the fact that cows will have lower needs when they are not lactating and that the cow’s nutrient needs increase as they progress from early gestation to late gestation and will be greatest during lactation.

Annual maintenance energy needs for the cow in Mcals units may be a little difficult to understand because producers are not familiar with this way to express energy. If you were to divide annual maintenance needs by 365 days you arrive at the average daily Mcals need. As an example, for the 1,200 pound cow producing 20 pounds pf milk daily, average daily maintenance energy would calculate to 22.8 Mcal per day. If the cows were eating a grass hay that was 9% crude protein, 57 percent TDN and 0.95 Mcals per pound of hay, this females would need to consume about 24 pounds of this hay daily on a dry matter basis (22.8 Mcal / 0.95 mcal per pound). If the hay were 85% dry matter, she would eat 28 pounds daily on an “as-fed” basis. Similar calculation indicate that the 1,400 pound mature weight cow would need on the average 25.3 Mcal per day and the 1,000 pound mature weight female would consume, on the average, 20.3 Mcal per day.

It is difficult to determine an annual forage feed costs, but if the calculations are calculated the same for each group of cows that differ only in mature cow weight, the groups could be ranked in terms of forage feed costs. If we assume that the average quality of the forage consumed annually is the same as that described above, and a price for the forage is the same for all weight groups, then a forage feed cost can be calculated. If the forage has about 0.95 Mcals per pound and it costs on average \$70 per ton of forage dry matter then the calculations can be made. The group of 1,200 pound mature weight cows will consume 24 pounds of dry matter per day; therefore; 4.4 tons of dry matter annually. That calculates to a cost of \$308 dollars per cow annually for forage costs. In contrast, a herd of cows with a 1,400 pound mature weight would eat 26.7 pounds of dry matter daily or would eat 4.9 tons annually and the forage costs calculates to \$343 annually. Using the same process, the herd of 1,000 pound mature weight cow would eat 3.9 tons annually and forage costs would be \$273 annually.

This isn’t rocket science math that the calculations on a per cow basis for forage costs are greater for the herd of 1,400 pound mature weight cows compared to the herd of 1,000 pound cows and the herd of 1,200 pound cows are intermediate. The cows are being managed on a fixed set of resources and there are more females in the herd when they weigh 1,000 pound as compared to when they weigh 1,400 pounds. In the first article, it was determined if there were enough feed resources to have 100, 1,200 pound females, that there would be 90, 1,400 pound females and 112, 1,000 pound females. Forage feed costs for the 1,400 pound cow herd is \$30,870, for the 1,200 pound cow herd is \$30,800, and for the 1,000 pound cow herd is \$30,576. Not much difference in forage costs for the three different groups of cows. From the previous article, the group of 1,200 pound cows generated more dollars from the calf crop, followed by the herd of 1,000 pound mature weight cows, followed by the 1,400 pound group of cows. There are fewer dollars left to pay for the other costs in the 1,400 pound cows herd compared to the other two groups. When comparing the 1,200 pound and 1,000 pound groups it is about a wash with regard to the dollars left after forage feed costs to pay for all other cows cost, with a narrow edge favoring the herd of 1,200 pound cows.

Mature cow size and milk output impact nutrient needs, dollars generated, and input costs, especially feed costs. What can a cow/calf producer do from a selection standpoint, to keep costs, especially feed costs manageable; 1. avoid extremes in cow size (mature weight) and milk output. This will result in less growth and carcass weight, but appears to be the most cost effective; 2. cull non-pregnant cows as they may be telling you that they don’t fit your resources or management style; 3. adjust calving and/or weaning to manage body condition and to reduce feed costs; 4. stayability in a commercial cow/calf operation is related to profit potential. Use cow maintenance EPDs as part of the bull selection criteria when possible; 5. as we continue to get a better understanding of residue feed intake and its relationship with cows that are foraging range/pasture, source seedstock producers that include RFI in a selection index. Still the challenge remains, as genetic trends for many of the important traits continues to increase, producers may find it harder and harder to maintain the genetic package that fit their resources and environment even when avoiding selecting the extremes. This has the potential to impact feed costs and profitability of the cow/calf enterprise.

Source: Dr. Rick Rasby, Professor of Animal Science, University of Nebraska - Lincoln