Bull Fertility Update

Genomic technologies are expected to contribute the most for traits that are expensive to measure, e.g cattle fertility, feed efficiency, and those related to the immune response. Given that in Australia most of the cattle are bull-mated, the relevance of the male fertility indicators becomes unquestionable.

This project aims at furthering our understanding of bull fertility, bringing together old and new datasets to link biological knowledge with genomics to identify causative mutations leading to better estimates of breeding values.

We are working with legacy data of the Beef CRC projects that include 2500+ bulls with fertility data and DNA profiles (SNP genotypes). To complement this resource, we are collecting data on additional 5,000+ bulls of four different breeds. The fertility indicators are those observed during the Bull Breeding Soundness Evaluation (BBSE), from the animal conformation to the full semen evaluation, which is known to be associated with the bull’s calf-ability.

A key objective of this project is the identification of genetic variants affecting bull fertility. For that, we will impute SNP genotypes up to the whole-genome sequence using the latest reference genome. Then, candidate causative mutations responsible for at least 50% of the genetic variance for many phenotypes of economic importance will be identified, including bull pathologies and semen quality among others. The current literature supports the concept that the use of genome sequence analyses is the most effective way to detect mutations directly affecting production traits, and with the use of such mutations, most of the genetic variance can be captured.

The use of only causative mutations for each observed trait allows accurate animal selection and consequently speeds genetic progress. Once the causative mutations for each trait are identified, this information can be passed on for the estimation of breeding values. Therefore, the project will inform which markers should be included in the prediction of genomic breeding values on a trait-by-trait basis. Furthermore, some bull pathologies (i.e. spiral penile deviation) might be caused by one or a few major genes and if this is confirmed, DNA diagnostic tests that are stand-alone can be proposed and implemented (similar pathway to commercialization as occurred to the poll gene test).

Work is ongoing. We have brought the Beef CRC II and III datasets up to date on the current genomic technology. The dataset includes Brahman (n=1,116) and Tropical Composite (n=1,453) bulls, with 38 observed traits, including several related to bull fertility (e.g. semen quality). Additionally, we enrolled four tropical bull breeders that are contributing bull breeding soundness evaluation (BBSE) records and DNA samples to the project. There are almost 6,000 BBSE results that are linked within-herd by full pedigree and can be linked across herds using the SNP data collected during this project and by the breeders themselves. Finally, we are also collating samples with specific conditions (e.g. penile spiral deviation) to be genotyped and included in case/control studies to locate candidate causative mutations.

CSIRO Livestock contact

Laercio Porto-Neto