Technical information - Reproduction

Fertility Have you done the calculations?


BRAHMAN NEWS MARCH 2008 Issue #158

Most cattle breeders would agree that fertility is an extremely important trait due to its huge economic impact on an enterprise.

That is in commercial terms the higher the percentage of calves born each year the more available for sale. Maximising fertility thus makes a lot of sense but it is often something that can be hard to identify, unless we actually do the calculations.

Figures 1 & 2 show the distribution of female’s age at first calf and also the distribution of females calving interval for a herd based in southern QLD that I recently analysed. The interesting point is the amount of variation within this herd for the two key fertility indicators.



Calving interval is simply the average number of days between calves for a particular female. We would all like to think that our females have a calf every 360 days, but this is not always the case especially in more harsh environments. In regards to improving fertility it is not about achieving a particular interval but more about identifying animals that perform better then the rest no matter the environment.

Age at first calf as a fertility indicator raises a few interesting questions in regards to first calving at two or three years of age. If you are selling bulls at two years of age and are expecting them to be ready to work then you should also expect the same of your females. This means providing the opportunity for them to go in calf prior to two years of age. Regardless of your preferred heifer age of calving, you can still use age at first calf as a measurement to identify more fertile animals.

When I asked the owner of the herd described in figures 1 and 2 to estimate their average age at first calf and calving interval the reply was “the heifers calve at 24 months and all females calve once a year”. When we actually did the calculations the average age at first calf was in fact 27.6 months and the average calving interval was 567 days.

What the calculations told us was that there was significant room for improvement in order to achieve the breeder’s objectives. The calculations also clearly identified those animals that were performing well below expectations. In this example if we culled the females with an age at first calf above 30 months then the herd average becomes 24.4 months. Similarly if we culled the females with a calving interval above 500 days then the herd average becomes 363 days.

The important point is that, if we have the objective measurements we can manage the herd more precisely. People may say that simply culling dry cows once a year would remove the extremely long calving interval females in this example, but what about the females in the in the 400 – 500 days range? Also how do we identify those animals that are genetically superior for these traits so that we can focus our selection on them thus to maxmise improvement?

Every population or herd will display a distribution for any particular trait. The majority of animals will be close to the average but it is the identification of those animals at the high and low end that enable us to improve the herd average and thus the herds’ profitability. In order to most effectively make improvement we need to use accurate objective measurements and not estimations.

Calving interval and age at first calf can easily be calculated from your pedigree recording with the Australian Brahman Breeders Association and are both readily available to BREEDPLAN members as part of their annual GROUP report.

For more information please contact TBTS on 07 4927 6066 or

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