Ask the experts: Do not use your bull on his daughters

1 February 2024

Question: I have a small cattle farm with about 20 heifers. I started two years ago and bought a Hereford bull from another farmer. At the time, I had 10 heifers. The calves I got from the bull were 70% heifers and are now ready for slaughter. I want to find out if I can use the bull to cover his own calves for the first season, or should I buy a new bull to cover the calves? I heard from my neighbours that you can do it. I just want to seek expert advice.

Answer: Using a bull on his own daughters is not a good idea and should be avoided as much as possible. Basically, there are two significant dangers:

1. Scientific studies show that animals with high levels of inbreeding (that is, offspring from parents that are closely related) are severely affected for so-called fitness traits. These traits are related to survival, namely reproduction (fertility) and the ability to survive, especially until puberty (the age at which the animal can be bred). Each calf born receives half of its genetic composition from each of the parents. A heifer calf is thus at least 50% related to her father (more, if they are also more closely related in the rest of the pedigree). The offspring from such mating is therefore a minimum of 25% inbred. The recommended maximum level of inbreeding is only 6,5%.
2. The second significant danger is that if the bull is a carrier of an undesirable and even lethal (fatal) gene, there is a chance that he will transmit it to his daughters, who will not show its effects because they are also carriers. The mating of two carriers results in as much as 25% of the calves resulting from such mating being affected by the undesirable genes. Examples of this are various genes that lead to early death of embryos (and resorption), double muscling and a host of other abnormalities. This risk is small if the bull is not a carrier of one of the genes responsible for the conditions, but without genomic testing it is unknown.

My recommendation is, therefore, to avoid sire-to-daughter crosses. The same applies to the mating of all closely related family members, even half-siblings (half-brothers and sisters, son-mother, etc.).

• Answered by Dr Japie van der Westhuizen, Studbook’s CEO.
African Farming and the expert accept no responsibility or liability for any damage or personal disadvantage you may suffer by using this content.