This week, we take a look at an example of what happens to expected herd performance in the next generation based on the bull we use.
First, last fall at weaning, the following measures of herd performance were taken:
• 1,400 pound average mature cow size (4-7-year-old cows).
• 85 percent pregnancy rate.
• 82 percent calf crop weaned.
• Average weaning weight: 500 lbs.
• Pounds of calf weaned per exposed female: 410 lbs.
This data indicates that we need to improve the pounds of calf weaned per exposed female on a whole-herd basis to improve the profit potential of this operation. Traits of economic significance to improve this number are weaning weight (WW), cow herd fertility (heifer pregnancy, HP), cow milk level and mature weight (MW) of cows. An EPD exists for each and can be used as a basis of selection to improve the 410 lb. value.
In this example, we use herd bulls as rotational sires, selecting the best 20 percent of heifers to develop as replacements and selling all other calves at weaning.
Since genetic values are comparable across time and geography, we can use the registration numbers of the five bulls used over the past decade that sired our existing cow herd and find the following EPDs specific to our selection goal (Table 1).
Table 1.
Tattoo WW HP Milk MW
3348 85 10 27 104
5405 75 8 15 101
0A36 81 13 25 111
7008 63 9 25 63
5133 50 6 17 63
Average: 71 9 20 88
Now we consider the genetic values of two new potential herd bulls:
• New herd bull No. 1: 71 WW, 15 HP, 20 Milk and 68 MW.
• New herd bull No. 2: 101 WW, 9 HP, 20 Milk and 122 MW.
By comparing the EPDs of the new bulls we are considering to the five bulls that sired our existing cow herd, we can predict the genetic change expected in the next generation of cows in our operation.
For example: Bull No. 2 should raise weaning weights by 30 lbs. and mature weights by 34 lbs. Bull No. 1 should sire daughters 6 percent more likely to get pregnant and raise a calf to weaning while lowering the mature weight of cows by 20 lbs. Neither bull is expected to change the milk level of the cow herd.
The question is, which bull transmits more profit potential to this operation? Take some time to consider the question. — Mark Z. Johnson, Oklahoma State University Extension beef cattle breeding specialist
