However, if you are fortunate to have enough heifers to choose from, what criteria do you use? Weight? Height? Bull genetics?
What about pelvic size? There is a correlation between the area of the pelvic opening in a heifer and how easy it will be for her to calve without assistance. By measuring the pelvic area and comparing one heifer’s pelvic size to other animals in a group, an indication of which animals may calve easier can be made.
It may also highlight animals with particularly small pelvises, which you may choose not to retain for breeding. Interestingly, we have found that just because a heifer is well grown and tall/ heavy enough to serve doesn’t necessarily mean that she has a large pelvic opening!
Pelvic Measurement Service
We are now able to offer a pelvic measurement service. The procedure is carried out in a standing animal and involves using a special set of callipers that are inserted rectally allowing two measurements to be taken (vertical pelvic height and horizontal pelvic width), from which we can calculate the pelvic area.
The procedure is well tolerated and can be done at the same time as a reproductive tract examination (where we can examine the reproductive tract to ensure that the heifer is cycling and that there is no evidence of free-martinism or other reproductive tract abnormalities). The pelvic area is then correlated against the animal’s age to categorise the pelvis size as small (red), adequate (amber) or large (green).
Factors Affecting Assisted Calvings
The procedure is not a guarantee of assistance-free calvings, however if we can choose not to breed from animals with particularly small pelvises then this should likely reduce the interventions needed at calving.
It is worth remembering that pelvic size is only one factor affecting the likelihood of assisted calvings. Sire selection is also very important and looking into the EBVs (estimated breeding values) of the intended sire to check calving ease (and calving ease of his daughters to ensure less problems in future generations) is important too! Ensuring that heifers don’t get too fat is also a way of reducing the likelihood of calving problems.