David Lalman, Amanda Holder, and Mark Z. Johnson, Oklahoma State University Department of Animal and Food Sciences Extension
This week we continue with a multi-part series on what information collected on cows at weaning can indicate with regard to making informed management decisions on our cowherd. As we continue to see high temperatures and little rain across Oklahoma, forage budgeting and planning for supplementation needs are critical. Both are impacted by cow weights and body condition scores.
In an ongoing research project at OSU, 42 registered Angus cows are being used to investigate the influence of cow size, body condition and diet quality on feed or forage intake. These cows were purposefully sourced to create a wide range in mature weight, feed intake and growth potential. In fact, cow weight ranged from 1,130 to 2,006 pounds during this experiment. The cows were split into two roughly equal groups and individual feed intake was measured for 45 days after a 14-day adaptation period. After the first period, each group’s diet was switched and after another 14-day adaptation period, feed intake was measured for an additional 45 days. We found that each 100 pounds of additional cow weight was associated with 1.4 pounds of additional daily hay intake. On the other hand, with a high-quality mixed diet, each 100 pounds of additional cow weight was associated with 1.9 pounds per day more feed consumption. In other words, if the average of these two diets represents average annual forage quality on a ranch, a 1,400 pound cow would need about 1,861 pounds more forage dry matter each year compared to an 1,100 pound cow. This is equivalent to an additional 1.8 grazing acres per cow annually on land producing 3,500 pounds of forage and 30% harvest efficiency. If large round bales are fed to make up the difference, an additional 1.7 bales are required for the larger cows assuming 1,300 pound bales and 15% hay waste during storage and feeding.
Animal scientists have suggested for many years that fatter cows eat less feed per unit of body weight, although there is little data available to quantify this influence. Sure enough, in this study, there was a strong negative relationship between body condition score and feed intake. Interestingly, daily feed intake was reduced by 4 pounds per unit of body condition score when fed the high-quality diet and by only 1.6 pounds per unit of body condition score when fed the grass hay diet. These results simply point out that cows in thin condition can only do so much to make up for thin body condition when forage quality is low. When diet quality is high (more similar to early growing season), thin cows will be able to catch up at a much faster pace. Mother nature rides the brakes just a little when cows are fat and diet quality is low. But when diet quality is high and cows are already in good condition, she a puts a lot more pressure on those brakes.
Bottomline, knowing cows weights and body condition scores at this time of year is beneficial in cost effectively planning a our nutritional program so that cows are in optimum body condition at the beginning of calving season a few months down the road.