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 below.
Factors Influencing Bull to Female Ratio:
Distribution of the
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 bulls.
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.