Project aims to reduce cost of low boar fertility
By Emma Penny
UK PIG breeders could be losing up to £14.2m a year due to poor boar fertility, but a new project at Brunel and Cambridge Universities could help redress that loss.
Researchers have received a total of £140,000 from the Biotechnology and Biological Sciences Research Council to help develop a better fertility test for boars, says Brunel University lecturer Darren Griffin.
"Todays boars are bred for genetic merit – for instance, low backfat – and often little consideration is given to their fertility."
The effects of poor fertility are likely to be magnified as artificial insemination becomes more popular and the sow-to-boar ratio rises from 18:1 to 40:1, says Dr Griffin. Pig semen is inspected at AI centres for sperm concentration, structure and motility. But these tests are not strongly correlated with how prolific a boar will be, he adds.
"There is no current test with good correlation to fertility, but high non-return rates have a serious effect on cost, time and environmental concerns."
Dr Griffin estimates that for every 5% drop in sow productivity due to infertile boars a producer will lose about £20 a sow a year. Multiply this by the 710,000 sows within the UK and poor fertility can be estimated to cost £14.2m a year.
"It takes several months to collate fertility data, by which time boars are reaching the end of their reproductive life, and may have already passed on any fertility defect to their male offspring, perpetuating the problem. In many cases, sperm quality might be fine, and it might fertilise the egg, but the embryo might not develop beyond the early stages."
This suggests that genetic factors are involved, and Dr Griffin says the most recent evidence suggests that chromosome abnormalities are the most common cause of infertility. "Recent studies suggested that about 10% of boars are infertile, and about half of those boars carry a visible chromosome abnormality.
"Bearing in mind the financial problems facing the pig industry, it is essential that all boars are screened for chromosome abnormalities before sperm collection, and that a high quality AI boar is free from them."
The abnormalities come to the forefront when chromosomes line up in identical pairs at cell division. Where there is an abnormality, bits from one chromosome might join the end of another, making it impossible for chromosomes to line up as identical pairs.
"This means that the chromosomes cant line up in the normal way, and you may end up with extra bits of DNA. There may be problems achieving fertilisation, or embryos might not develop beyond the early stages."
Chromosomes can be assessed by eye under a high powered microscope, but it is a specialised task, requiring about three years training, says Dr Griffin. "Often, by the time staff are trained, they move on. Realistically, it would have to be done by a centralised lab, but costs would need to come down too."
The alternative Dr Griffin is researching involves using a fluorescent dye – known as a probe -to label either end of individual chromosome pairs. Each pair would have a specific probe, so pairs of identical chromosomes – without any additional pieces or bits missing – will show up easily under a microscope, as will damaged chromosomes.
This is likely to be easier and more cost effective than traditional chromosome screening, he says. It will allow boars likely to carry a genetic fertility defect to be identified before they depress sow fertility within herds.
The same technique is likely to be applied by scientists at Cambridge University who are aiming to find out whether the male, or Y chromosome, has an effect on fertility, says Dr Griffin.
Researchers are planning to unravel the DNA within the boars Y chromosome, break it into segments and add the fluorescent marker dye. Because DNA is the only molecule where like attracts like, areas with an exact match will light up or fluoresce; this wont happen where DNA is missing.
"This technique should allow us to test whether Y chromosome deletions are another cause of infertility in pigs. If it is, and we find a common deleted region in pigs, we could add it to the first test, and use both together to produce a probe for boar fertility."
This probe could be produced as a screening kit, and should cost about £20, he says. "It would still need some lab expertise, and is most likely to be used by breeding companies, but it could be offered as a service to producers wishing to use home-bred boars."
One key advantage is that testing can be carried out as soon a blood sample can be taken from an animal. This means suitable boars with high levels of fertility could be identified at an early age – as piglets – as could those with poor fertility which should be finished rather than used for breeding. *
• Genetic fertility concerns.
• Research to develop tests.
• Results early in boars life.