As we continue to see high temperatures and little rain across the Great Plains states, 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 Oklahoma State University (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.
Researchers found that each 100 lbs. of additional cow weight was associated with 1.4 lbs. of additional daily hay intake. On the other hand, with a high quality mixed diet, each 100 lbs. of additional cow weight was associated with 1.9 lbs. 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-lb. cow would need about 1,861 lbs. more forage dry matter each year compared to a 1,100-lb. cow. This is equivalent to an additional 1.8 grazing acres per cow annually on land producing 3,500 lbs. of forage and 30 percent 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 lb. bales and 15 percent 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 lbs. per unit of body condition score when fed the high quality diet and by only 1.6 lbs. 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 puts a lot more pressure on those brakes.
Bottom line, knowing cows’ weights and body condition scores at this time of year is beneficial in cost effectively planning a nutritional program so that cows are in optimum body condition at the beginning of calving season a few months down the road. — David Lalman, Amanda Holder and Mark Z. Johnson, OSU Department of Animal and Food Sciences Extension
