Seasonal infertility is one of the most common challenges faced by pig producers during the summer and autumn period. It’s a natural phenomenon that remains common within today’s modern farming systems in general and outdoor units in particular
The issue of seasonal infertility was inherited from the wild pig, which was naturally a short-day seasonal breeder that evolved to be less fertile after the summer solstice to avoid farrowing during winter. It still occurs in modern genotypes, albeit at varying levels, and is a phenomenon that has management implications.
Triggered by two seasonal changes, temperature and day length, the typical effects include delayed puberty in gilts, reduced farrowing rate, lower litter size, a longer interval from weaning to oestrus and reduced fertility in boars. But it can also impact on the feeding regime, according to ABN’s pig nutritionist Steve Jagger.
“Today it’s the reduced farrowing rate (figure 1) that’s been found to have the greatest financial significance, with the potential to continue for 16 weeks after the longest day,” he says, noting that, while not all producers experience the problem, it’s most prevalent in pigs that are reared outside as, in these situations, it’s more difficult to control the causes.
“Low farrowing rates lead to peaks and troughs in productivity, so clearly increasing the number of sows served four months in advance of the trough in productivity is a key means of maintaining production levels, but feed intake also plays a key role,” Steve adds.
Temperature
Addressing the issue of rising temperatures and its role in stimulating seasonal infertility, Steve warns that feed intake can play an important part. Temperatures above 22C will significantly depress feed intake and increase the amount of body weight lost by sows throughout lactation. Excessive weight loss has been shown to lead to an increased rebreeding interval and a reduction in the number of piglets born in the next litter.
So, while he advocates attention to sow condition throughout the year, he says it’s especially important during lactation and gestation in the summer when sows become more sensitive to the environmental fertility triggers.
“Feeding high-density diets in lactation, feeding more frequently during the cooler parts of the day and ensuring an adequate supply of cool water are useful counter measures,” he says. “This can help lessen the time between weaning to oestrus and increase the size of subsequent litters.”
In case where weight loss during lactation adds to the potential issue, and where weight must be regained during early pregnancy, Steve advises increasing feeding levels by 0.5kg/day until the desired condition has been achieved.
A further factor of high temperatures is the potential for heat stress to affect boars. Following exposure to heat stress for a period of 3-7 days, reduced fertility can continue for up to six weeks. It affects the boar’s sperm quantity and mobility, and is most easily addressed through the provision of shade and wallows.
Day length
It’s been demonstrated that the duration of daylight can induce changes in hormone levels in both sows and boars – and again has feed implications.
“Longer daylight hours reduce the release of the hormone melatonin, which in turn decreases the effect or release of several of the reproductive hormones,” says Steve. “This reduces uterine secretions required to maintain embryo development after day 12 of conception.”
He recommends rethinking the sow’s feeding regime during the first 2-4 weeks of pregnancy, advising that increasing feeding levels in summer during early pregnancy can help reduce embryo loss, and guard against the negative impacts of seasonal infertility.
Longer days have also been associated with delayed puberty in gilts. In an Australian study, during longer days, only 13% of the gilts achieved puberty by 225 days of age, yet 53% of gilts reached puberty under a short-day regime when separated from the boar.
Steve also highlights research into seasonal infertility that suggests an integrated approach will deliver best overall results to managing the effects of seasonal infertility. This includes ensuring daily physical boar contact to stimulate oestrus; providing wallows outdoors; not mixing young sows in early pregnancy with older pregnant animals to avoid a negative pheromone impact; and housing gilts in spacious conditions separate to the older sows.
Finally, he points out that applying a short-day lighting regime may help reduce the impact of seasonal infertility. However, he advises that more information is required in this area and additional research would be beneficial to determine the most suitable regime.