Pork from sexually mature, uncastrated male pigs can have a distinctive, pungent odour known as boar taint – which puts off consumers.

“The challenge lies in selectively breeding pigs with minimal taint, without sacrificing fertility,” explains Researcher Eli Grindflek of Norsvin, the Norwegian pig producers’ cooperative. Together with her colleagues at Norsvin, the Norwegian University of Life Sciences (UMB) and the Centre for Integrative Genetics (CIGENE), Dr Grindflek is searching for gene variants in order to breed for pork without the smell.

For meat production, uncastrated male pigs are preferable; their slaughter quality is superior and they utilise feed more efficiently compared to castrated pigs. (Photo: Shutterstock)

Castration dilemma

Castration of boars is highly controversial due to animal welfare considerations. Furthermore, uncastrated boars are of higher slaughter quality and utilise feed more efficiently compared to their castrated pen mates. The disadvantage of raising uncastrated boars is that their meat often has that unappetising smell and taste.

With funding from three sources – the Research Council, the Agricultural Agreement Research Fund, and the Foundation for Research Levy on Agricultural Products – Norwegian researchers are searching for sound alternatives to castration for eliminating the less-than-agreeable scent. Genetic studies are a promising path to follow.

The culprits: androstenone and skatole

“What triggers the boar taint is high levels of the substances androstenone and skatole,” says Dr Grindflek.

Androstenone is a pheromone synthesised in the testicles and secreted via the salivary gland in male pigs. The pheromone cause oestrous sows to take up the mating stance. Skatole is the product of the bacterial breakdown of tryptophan, the amino acid absorbed from the large intestine and stored in fatty tissue.

“The objective is to selectively breed male pigs with low levels of these substances,” summarises Dr Grindflek.

Advantages and drawbacks

Researcher Eli Grindflek of Norsvin has identified genes to counteract boar taint. (Photo: Ingunn Haraldsen) The genetic makeup of pigs is complex. The research group has thoroughly investigated specific genes or DNA segments that influence tainted odour and taste. Samples from the blood, liver, testicles and fat of over 3 000 boars have been collected and analysed.

Both skatole and androstenone levels happen to be highly hereditary in pigs. Unfortunately, the answer is not as straightforward as simply selecting gene variants for low levels of these substances and breeding from there. As is often the case, such a choice yields advantages – but some disadvantages as well.

“Fertility can be negatively affected by reducing the androstenone level, because androstenone is synthesised through approximately the same process as the other sex hormones. The researchers have discovered very high genetic correlations between androstenone and these other hormones.”

Closing in on a solution

“By studying genetic variations in the genome,” says Dr Grindflek, “we have for the first time found individual genes that actually reduce the amount of androstenone in male pigs without affecting their other sex hormones. And when it comes to skatole, we find several gene variants that influence this one trait specifically. These are findings that will be valuable to the industry.”

Extensive international cooperation

The boar taint research being carried out at Norsvin and UMB is an important component of efforts to raise food quality and improve the health of production animals. This work has also proved to be the Norsvin and UMB researchers’ admission ticket to several international collaborative projects, since castration of male pigs is hotly debated internationally, including in the EU countries.

“We participate in SABRE (the EU programme “Cutting Edge Genomics for Sustainable Animal Breeding”) in which many countries are cooperating on mapping genes for boar taint across different pig breeds. In addition, we are underway with a new research project to confirm and fine map the detected gene variants, and we need more knowledge on the effects of lower androstenone levels. And after that,” concludes Dr Grindflek, “begins the exciting work of selecting individuals free of boar taint.”