West Central Iowa | mlfarm - 1/22/2017 10:02
Here is my question...with cow efficiency and size. Everyone says you can run 100, 1200 pound cows or roughly 89, 1350 pound cows on the same amount of grass because the total pounds equal 120,000 total weight. Doesn't it take more grass just to sustain life for the 1200 cows. Like how much energy is required just to keep the heart beating and blood flowing. Or weather extremes such as blizzards and extreme heat. I would think 100 vs. 89 would take way more energy just to maintain. I'm not doubting that you can't run more 1200 vs 1350 but is it exactly pound for pound. Hope I am getting my point so that you can understand. Granted there are a lot of more factors that play into this but is there any actual data that can support what I am trying to say.
You are correct, the formula for estimating net energy maintenance (NEm) is NEm=0.077BW^0.75 where BW is body weight. So lets plug in a 1200lb beef cow 0.077(1200^0.75)=15.70 Mcal/day. Now lets assume you have a 1600lb cow in the same condition (there is a condition adjustment for this formula also), so 0.077(1600^0.75)=19.48 Mcal/day. To show this is not linear you can; 19.48 Mcal/1600lbs=0.01217 Mcal/lb of cow/day and 15.70 Mcal/1200lbs=0.01308 Mcal/lb of cow/day. There are also breed adjustments for maintenance energy for instance Simmentals and most the dairy breeds (except jerseys) use a formula more like 0.080BW^0.75. Both these formulas are just for dry cows. So a 1520lb simmental takes close to the same energy as a 1600lb angus. However I would say there's a lot of within breed variation as well. As to the original question I would say feed the cows like you want to feed them and the ones that don't breed back, cull. Calves aren't sold by the lb they're sold by the head, you would never buy one 1200lb animal for the price of three 400lb calves. The cow efficiency studies I have seen indicate that you cannot visually judge efficient cattle. |
Cow Efficiency
