Mature weight and milk production of many commercial beef cows are both greater than they were 30 to 40 years ago. Many ranchers have not recently weighed the adult cows in their herd to know what average mature weight to expect. Therefore most commercial ranchers would underestimate the mature size of their cows. To expect large, heavy-milking cows to be in moderate body condition at calving and maintain condition through breeding, they must receive more feed than smaller lighter-milking cows.
The graph below uses the 1996 National Research Council’s guidelines to show the energy needs of two different body types and levels of milk production. These energy requirements would be representative for cows calving in February and March and weaned in October. The top line represents the energy needs of 1250 pound heavy-milking beef cows versus the lower line which represents the needs of 1100 pound moderate-milking beef cows. The values graphed are the megacalories per day required to maintain body weight throughout the year.
The larger heavier-milking cow requires about 34% more energy on the average for an entire year. Consequently, an operation that was carrying 100 of the smaller cows must carry only 66 of the larger cows in order to utilize the same quantity of forage from that farm or ranch. She also will need 34% more winter hay and supplement to maintain body condition. In some commercial herds, there are cows much larger than the 1250 pounders depicted in this graph.
As we take inventory at the end of 2016, this is a time to re-consider herd numbers and cow size to better fit the stocking rates required. Reduced stocking rates will be necessary if range and pasture condition has deteriorated in recent years. Diminished forage availability will lead to poorer cow body condition, more supplement and hay feeding or both. The start of a new year would be a good time to honestly review our cow herd weights and stocking rates The year 2017 would be an excellent time to better match the cows to the forage base at our ranch.