Inbreeding advice revised for dairy cattle
The target for dairy producers to maintain inbreeding at less than 6.25% has been called into question following the extensive analysis of data both internationally and in the UK.
The target was set many decades ago in order to limit the undesirable effects of inbreeding depression, which sees an animal’s performance decline as inbreeding increases, particularly in traits such as health and fertility, and inevitably in milk yield too.
However, in today’s dairy population, attempts to limit a herd’s inbreeding coefficient to 6.25% have become unrealistic if dairy producers wish to make genetic progress.
Speaking at this week’s British Cattle Breeders Conference, Marco Winters, head of animal genetics for AHDB said the industry has been alert to this dilemma for many years and keeps a constant watch on the levels and effects of inbreeding across the national herd.
He says there is a fine line to tread between making genetic gain and avoiding excessive inbreeding, but that the historically important figure of 6.25% has little relevance today.
“Producers should keep an eye on inbreeding within their herds but if they strive to maintain their average at 6.25% or below, they could seriously compromise their genetic gain and therefore their future herd efficiency,” he says.
A study by AHDB has demonstrated this clearly, revealing that if the 6.25% inbreeding threshold were enforced, in most cases – even using the best matings – the Profitable Lifetime Index (£PLI) of the offspring would be lower than that of the dam. In other words, genetic improvement would go backwards.
Only matings of the very lowest £PLI dams – these generally being in herds which have not engaged with genetic improvement – could result in genetic gains in the next generation while keeping within the threshold.
“In reality, keeping within the 6.25% threshold would mean many producers could not breed from their best genetics,” he says.
However, in spite of this, the performance of dairy cows today is far better than in the past across a wide range of traits, including those for health and welfare. Much of this is attributed to genetic improvement brought about by farmers’ use of genetic tools and their proven ability to make desirable genetic selections.
He says: “In the commercial dairy population, where farmers are selecting for improvements in traits such as fertility, lameness and cell counts, they are actively countering the effects of inbreeding depression.”
On average, UK producers have driven an increase in PLI of £52 per head per year, which far outweighs the accompanying inbreeding losses in terms of performance and profitability.
Historic v recent inbreeding
Furthermore, he says there’s another syndrome at play which results from historic inbreeding as opposed to that which has happened in more recent years.
“Studies from around the world, including by AHDB, have demonstrated that historic inbreeding could be conferring benefits as repeated positive selection over many generations has helped purge undesirable traits,” he says.
However, despite the positive outcomes from historic inbreeding, he warns against allowing it to run away, as inbreeding depression will always exist.
“Inbreeding should definitely be a consideration by today’s breeders whose particular focus should be on reducing its rate of increase in their own herds.
“This means using your team of bulls to give the lowest inbreeding outcomes, avoiding matings between close family members and using breeding programmes and the AHDB Inbreeding Checker to flag the best and worst matings,” he says.
Genetic diversity
The loss of genetic diversity through inbreeding is also a potential concern but is said to be less so than many propose.
“Genetic variance is important as without it, we can’t make genetic improvement,” he says. “Equally, there is a concern that a narrowing gene pool may raise the susceptibility of a population exposed to an unforeseen challenge.
“However, our evidence indicates that the gene pool is just as diverse as it was 30 years ago and there is no sign of genetic improvement reaching a plateau.”
Equally, the uptake of genomic testing provides more accurate and biologically meaningful inbreeding coefficients than in the past, while also identifying animals carrying undesirable recessive genes, which can be readily excluded from breeding programmes.
He acknowledges there may be a place for gene banks to preserve diversity but says this is more of an insurance for an unforeseen future than something to tap into today.
“Just because something might happen at some point in the future does not mean we should allow fears about inbreeding to compromise genetic improvement,” he says. “The farmer runs a business, not a zoo. We need to make sure it is sustainable.
“This means making sure the next generation is better than the last. It may or it may not be able to withstand some unforeseen risk at some point in the future, but a business which stands still – genetically or otherwise – will not be in business to find out.”
AHDB Inbreeding Checker
Producers who would like to check the inbreeding level of any proposed mating can do so by using the AHDB Inbreeding Checker. First, they need to register for the Herd Genetic Report and then follow the link ahdb.org.uk/inbreeding-checker
