Introduction of the poll gene can have serious consequences on fertility, carcase traits, and genetic diversity. In the Hereford and Brahman breeds there is a growing consensus that poll cattle have also lost their “survivability” traits.
1) Reduced Bull Fertility
Poll bulls have an increased incidence of dropped pizzles. Dropped pizzles are considered highly undesirable due to their increased susceptibility to trauma, infection and grass seed penetration. All of these conditions lead to infertility.
Spiral deviation of the penis is also a common cause of infertility in poll bulls. The condition is thought to be exacerbated in young bulls used too early. A bull with a spiral deviation is unable to “hit the target” which, if unnoticed, can lead to the financial loss of an entire breeding season.
Poll bull infertility is a very serious issue. There is currently a postdoctoral study examining the deleterious effects of the poll gene on bull fertility.
2) Loss of Carcase Traits
Fullblood European cattle are noted for their lean, heavily muscled carcase with full primal cuts. Poll European breeds often have a reduction in these carcase traits due to the influence of the base breed. A recent survey of poll Bazadais bull buyers revealed most poll bulls had failed to pass the unique Bazadais carcase traits onto their calves. The loss of important breed attributes when animals are selected for the presence of a single gene is well known and documented across many breeds. Therefore, the loss of carcase attributes is to be expected when purebred Bazadais are selected exclusively for the poll gene. As the poll gene is on the largest bovine chromosome, many other genes from the base breed are also introduced with the poll gene. It is highly probable these “unintended” introduced genes from the base breed influence carcase traits, explaining the loss of the unique carcase characteristics of Bazadais in poll bull progeny.
Inbreeding occurs when an animal’s genes are identical due to it having one or more common ancestors. It has a negative effect on fertility and growth rate and increases the chance of genetic diseases. Inbreeding is a very important issue in breeds which have a small gene pool, such as Bazadais. When poll lines are being developed, small numbers of poll animals are often used exclusively and repeatedly to distribute the poll gene across stud herds as quickly as possible. The gene pool is reduced and the likelihood of inbreeding rises rapidly in individual animals and in the breed as a whole (drift inbreeding). Inbreeding can be identified and averted if all animals in a Herd Book have DNA and parent verification. Unfortunately, many poll Bazadais cattle and their poll ancestors do not have DNA or parent verification.
4) Poll Herefords and Poll Brahmans - loss of “survivability” traits
There is a growing opinion that Poll Herefords have lost the “survivability” traits which placed the Hereford breed at the forefront of breed choice in the USA and Australia in the 1800 – 1900s. The breed was known to flourish in a wide range of climatic conditions and out-survive other breeds in times of extreme drought. It is thought that with the development of poll the highly desirable Hereford do-ability, fertility and maternal attributes were lost. In response, there is now a resurgence in Horned Herefords with a new breed society marketing their horned cattle “survivability” as a highly desirable quality.
The Brahman breed is renowned for its ability to thrive in harsh environments. However, some Western Queensland cattle producers are voicing concerns that poll Brahmans are now “too soft” to handle the difficult conditions. This loss of do-ability maybe similar to the poll Hereford experience.