Angus Australia


Collecting Gestation Length


Gestation length information is used to calculate Gestation Length EBVs within Angus BREEDPLAN.

Angus BREEDPLAN will calculate Gestation Length EBVs based on the joining and birth records for calves conceived by either artificial insemination (AI) or hand mating.





  • Gestation length information should only be submitted for calves conceived by either AI or hand mating. Hand mating refers to situations where the female is given limited exposure to a bull (e.g. in a yard), mating occurs, and then the bull is removed.
  • No information from natural paddock matings is used in the calculation of Gestation Length EBVs. Although some natural matings may be observed, they are not currently used in the calculation of gestation length as there is no guarantee that the observed mating is the one that successfully results in the conception of the calf.
  • Gestation length information should be recorded for all calves conceived via AI or hand mating in a calf drop. Only submitting gestation length information for a subset of calves is of no value and may result in biased Gestation Length EBVs.
  • A birth management group should be recorded if there are different treatments of the females prior to calving that may affect gestation length. For example, where one group of cows have had different feed availability. Likewise, a separate birth management group should be assigned for any premature calves, or calves whose gestation length has been affected by special circumstances. (e.g. the dam was sick).
  • Gestation length information is currently excluded from the BREEDPLAN analysis if (a) the calf is an embryo transfer calf, (b) the calf is a twin, (c) only one animal is represented in a contemporary group, or (d) more than 2/3 of animals in a contemporary group have the same gestation length.

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