Bull To Cow Ratio
Number of cows to expect a bull to cover in one breeding
The three major goals of any breeding season should be
to: get the cows settled as early in the breeding season as possible; get them bred to the bulls with the
highest possible genetic worth; and achieve both as economically as possible, by getting the cows bred with the
fewest possible bulls. Defining the optimum bull to female ratio is important to a successful breeding
season. However, no one ratio is optimal for all ranches or small herd operations. The number of
bulls required to adequately cover the breeding females is related to many factors, some of which are listed
Factors Influencing Bull to Female Ratio:
Distribution of the breeding females
Carrying capacity--feed intensity
Bull variation is caused by:
Management decisions include:
Length of breeding season
Amount of observation
Most of these factors must be considered to define the optimum
bull to cow ratio in a beef cattle operation. The following graph illustrates how difficult it is for
producers to know what the optimum cow to bull ratio should be. This study, conducted in Colorado, shows
the percentage of synchronized cows that bulls impregnated when given the opportunity to breed 3 to 51
synchronized females. Notice that some bulls had a poor percentage pregnant even when exposed to small
numbers of beef cows and some bulls had a high percentage pregnant even though they were running with 30 or
more synchronized beef cows. The vertical axis depicts the percentage pregnant after one opportunity to
mate with the group of synchronized females.
Figure 1. Effect of number of females exhibiting estrus on the percentage pregnant by each bull in
single-sire mating of estrus synchronized females. (Pexton, et al. 1990)
Proper management during the breeding season should result
in each cow being bred by a single fertile bull each time she is in estrus. Bull overlap (more than one
bull breeding a cow in heat) is not desirable, primarily because it does not enhance pregnancy rates.
Disadvantages of bull overlap are increased risk of bull injury (through competition for estrous females),
additional pressure from social dominance and the extra costs incurred by purchasing and maintaining more
Recent research at an Eastern Colorado research station, where the
average carrying capacity is 25 acres per-animal-unit-year, showed similar conception rates for bull to cow
ratios of 1:25 and 1:50. This research was conducted with multi-sire breeding pastures. All of the
bulls were experienced bulls that had previously passed a breeding soundness examination.
Bull overlap can be decreased by eliminating bull
congregation within breeding pastures. This can be achieved by dividing the breeding herd into
separate pastures or by using pastures that have natural barriers that reduce mixing of breeding groups.
In addition, riders can be used to keep bulls well distributed among breeding groups.
These large cow to bull ratios can reduce bull costs on very
large ranches with minimal risk. On a small 50 to 100 cow operation, using just one bull that happens to
undergo an injury or disease could spell disaster for an entire calf crop.
Recommendations for smaller herds that will utilize only one
bull per pasture may need to be more conservative.
A time honored rule-of-thumb is to place about the same
number of cows or heifers with a young bull as his age is in months.
For instance a bull that is 14 months old going into his
first breeding season should be expected to breed 14 or 15 cows; whereas as a two-year old bull may be placed
with 20 - 25 cows. Mature bulls that have been examined by a veterinarian and have passed a breeding
soundness exam can be placed with 25 - 35 cows and normally give good results.