Sperm from male pigs bred with more well-being gives rise to piglets with less fear and anxiety

Without having had any contact with their parents, piglets fathered by boars housed in cramped conditions for four weeks exhibited elevated levels of cortisol, among other indicators of stress. Offspring of pigs housed in roomier pens and given showers and tactile stimuli coped better with stressful situations.

By André Julião  |  Agência FAPESP – An article reporting a study of commercial pig farming conditions published in the journal Frontiers in Animal Science shows that the environment in which not just sows but also breeding boars (male pigs) are housed profoundly affects how their offspring deal with stress and hence influences piglet welfare. The study was supported by FAPESP.

A series of experiments conducted at the University of São Paulo’s School of Veterinary Medicine and Animal Science (FMVZ-USP) in Pirassununga (Brazil) showed that a period of four weeks living in cramped conditions was sufficient for boars to have offspring with emotional alterations associated with fear and anxiety, as well as elevated levels of cortisol in their saliva when exposed to challenges.

“In females, eggs are formed while they’re still in the womb, whereas in males, sperm production occurs continuously after puberty. Males can therefore serve as sentinels of what’s happening, so that it’s possible to intervene to improve piglet welfare,” said Adroaldo José Zanella, a professor at FMVZ-USP and principal investigator (PI) for the study.

The study was part of the project “The male contribution to the development of robust phenotypes and the mitigating role of sow welfare”, also supported by FAPESP with Zanella as PI.

In the experiment, 138 25-day-old piglets were submitted to behavioral tests to assess emotionality. In addition, their saliva was analyzed to measure levels of cortisol, a stress indicator.

Hair samples were collected for DNA paternity tests to determine which treatment was administered to the father of each piglet. This was done at the end of the experiment because semen from boars housed under contrasting conditions was mixed before insemination of the gilts (breeding females), so that each gilt bore piglets from several fathers.

Semen was obtained from 18 12-month-old boars, which were housed for four weeks in one of three treatment systems: crates (metal cages used in commercial breeding), with room only for them to stand, sit and lie down; individual pens with more room; and environmentally enriched individual pens, where they were brushed, showered, and provided with hay as rooting material for the pen floor. Diet and ad libitum water supply were the same in all treatments.

The researchers demonstrated that the fathers’ housing conditions influenced the behavior of their offspring. In all behavioral tests, piglets fathered by boars housed in crates displayed alterations in their emotional states indicative of anxiety and fear.

After the behavioral tests, saliva cortisol levels were found to have risen in piglets fathered by boars kept in crates and small pens. In piglets fathered by boars housed in enriched pens, cortisol levels were the same before and after the tests.

The results were consistent with the findings of a previous study, published by the group in April 2023 using the same animals and treatments, and showing that boars housed in enriched pens fathered more live-born piglets and piglets that survived until they were weaned (at 29 days of age).

Moreover, piglets fathered by boars housed in crates had a lower pain perception threshold, showing that the environment in which the fathers were housed altered their offsprings’ nociception and potentially influenced their well-being.

Next steps

“We’re conducting other studies to show that the type of treatment to which boars are submitted may cause epigenetic changes [to the genome], which could possibly be transmitted to their offspring,” said Leandro Sabei, first author of the article. The study was conducted during his PhD research at FMVZ-USP.

In a still earlier study, published in May 2022, the researchers demonstrated that the type of confinement influenced the physiology of the adult animals’ testicles. 

“In the animals housed in crates, testicular degeneration began, with semen becoming more agglutinated and testicle temperature higher, potentially impairing fertility,” said Thiago Bernardino de Almeida, first author of the May 2022 article and a co-author of the July 2023 article. Both of these studies were conducted during his PhD research with a scholarship from FAPESP. 

In another study linked to the same project, the group showed that the environment in which pregnant sows were housed affected the development of their offsprings’ brains.

Another publication by the same researchers showed how five days in crates during estrus caused stress in gilts and adversely altered their vaginal microbiota, affecting absorption of nutrients and impairing protection of offspring from disease.

“Our research findings are influencing the decisions of pig farmers, who can see that enhancing well-being boosts productivity and profit,” Zanella said. “Our goal now is to conduct even more robust studies on all stages of the animal’s life cycle, and to offer the swine model for relevant studies of humans.”

More details of the latest study can be found in the full version of the article “Inheriting the sins of their fathers: boar life experiences can shape the emotional responses of their offspring”, available in open access at: www.frontiersin.org/articles/10.3389/fanim.2023.1208768/.