Selecting the most appropriate bulls for an operation is critical. Selections should be based on price, the potential to make meaningful genetic impact and other factors important to the operation. One factor that may not get as much attention is determining how many bulls are truly needed based on desired bull-to-cow ratios.
Desired ratios will vary depending on geographic location, single- or multiple-sire breeding groups, purchase price, bull age and other factors. There is not a correct bull-to-cow ratio, and opinions vary on the most appropriate ratios.
In low-rainfall areas with extremely large pastures, it would be reasonable to have a lower bull-to-cow ratio. This increases the chance of having a bull with each group of cows if the cows spread out over long distances. However, in areas with more rainfall and smaller pastures, increasing the bull-to-cow ratio can be economically advantageous and may also reduce bull fighting and injury.
In multiple-sire breeding groups, there can be significant differences in the number of calves sired by each bull. Research from Dr. Alison Van Eenannaam and her colleagues illustrates this. The average bull-to-cow ratio from 15 calf crops evaluated averaged 1 to 25. The maximum number of calves sired by a single bull in each group ranged from 30 to 64. In 11 of the 15 calf crops, one bull sired at least 45 calves. Additionally, in several cases a bull only sired one calf or none at all.
Dominance, libido and fertility are all potential reasons for differences in the number of calves sired by a bull in a multiple-sire breeding group. Bulls will establish a hierarchy with the dominant bull breeding the largest number of cows – and in some cases, most of the cows. Additionally, some bulls just don’t have as much libido as others. Fertility differences due to semen quality and other factors will also affect how many calves a bull might sire.
Below are some guidelines assuming the bulls are fertile, structurally sound and in good health.
- 12- to 18-month-old bulls: One bull to 15 to 20 cows
- 2-year-old bulls: One bull to 20 to 30 cows
- 3- to 7-year-old bulls: One bull to 30 to 50 cows
Increasing the bull-to-cow ratio would reduce the number of bulls needed, allow for more cows to be bred to the top bulls in an operation and reduce breeding cost per cow.
