Strategies for managing seasonal infertility in pigs

Estimated reading time: 7 minutes

  • The phenomenon of seasonal infertility among pigs is real, says Dr Pieter Grimbeek. However, it can be mitigated and even avoided.
  • Seasonal infertility is nothing new and is more prominent in wild boars in the northern hemisphere – these animals do not breed after September and hence no winter litters are delivered.
  • Seasonal infertility is a multifactorial syndrome with several elements that can be the cause – this includes temperature, photoperiod (day length), nutrition and genetics.
  • Changes in day length serve as the most reliable indicator of seasons. Most animal species use this environmental indicator to predict what conditions will look like in the coming season and which period will be most favourable for the survival of their offspring.

Slaughter pig shortages are a regular occurrence at certain times of the year. These periods are marked by high prices and often leave producers wondering why they did not have twice as many slaughter-ready animals to satisfy market demand. What are producers to do in this case and can seasonal infertility be avoided in the process?

The phenomenon of seasonal infertility is real, says Dr Pieter Grimbeek, a swine industry consultant and chief veterinarian at Agri FARMACY SA. However, it is an issue that can be mitigated and even avoided by working smarter and implementing certain strategies.

Reasons for seasonal infertility

In an article on best practices for managing seasonal infertility in pigs by Perle Boyer and Glen Almond (nationalhogfarmer.com, 11 July 2017), the authors state that one should first gain an understanding of the underlying causes and mechanisms responsible for the clinical consequences of seasonal infertility. Reduced reproductive parameters in pigs, which are usually noticeable during late summer and/or early autumn, are characteristic of this phenomenon.

Seasonal infertility is nothing new and is more prominent in wild boars in the northern hemisphere – these animals do not breed after September and hence no winter litters are delivered. Of course the reverse applies to the southern hemisphere, says Dr Grimbeek.

According to the article, seasonal infertility is a multifactorial syndrome with several elements that can be the cause – this includes temperature, photoperiod (day length), nutrition and genetics. Most of these parameters are influenced by the time of year, which is why the concept of ‘summer infertility’ was first linked to this syndrome, followed by ‘seasonal infertility’.

Seasonal infertility has a major impact on some local production units, explains Dr Grimbeek. The modern pig, Sus scrofa domesticus, is descended from the European wild boar and is a seasonal animal.

In most cases in the wild, bears only become an intimate part of the herd once the breeding season commences. A bear will mate with a maximum of four to five sows, with each producing a litter per year, normally in spring. Lactation lengths range from 12 to 13 weeks. Lactation suppresses oestrus activity.

The availability of feed also influences the initiation of the cycle. Breeding is extended when plenty of feed is available, and delayed when there is a shortage. As a result, breeding commences in late autumn and, along with the arrival of lower temperatures, bears also experience a surge in testosterone and a greater sex drive. Young sows are then often out of phase with the natural cycle, and sows that have lost their litters often produce a second litter which is also out of phase with the rest of the herd.

Read more about the dietary requirements of pigs.

Role of climate variables

Production is influenced by the seasons, says Dr Grimbeek, and therefore temperature and day length play a key role. Changes in day length serve as the most reliable indicator of seasons. Most animal species use this environmental indicator to predict what conditions will look like in the coming season and which period will be most favourable for the survival of their offspring. Temperatures vary and are therefore a less useful predictor, he says; however, it still has a more immediate and direct effect on production.

The supply of feed is another variable that influences reproduction. “Most commercial swine units make use of ad lib feeding, and restrictions only apply to the sow diet. Therefore, feed intake and body condition are very important variables.”

Endocrinology of seasonality

Much like sheep, he explains, a pig is considered a short-day breeder (photoperiod sensitive). Despite much confusion regarding the importance of melatonin, it is now accepted that plasma melatonin increases during the dark hours. Light suppresses the synthesis and release of melatonin from the pineal gland, whereas darkness stimulates it.

“We are not certain what level of light intensity is required to suppress melatonin secretion in a sow, but numerous studies on humans have shown linear responses to different light intensities, and this is most likely also the case with a sow.”

He says this explains why the seasons have such an adverse effect on sows that are kept outside, as opposed to sows housed indoors where light filtration and diffusion take place. However, this theory pertaining to threshold-bound duration versus the period-bound ‘per chance theory’ is still being widely debated. It is common for long periods of six to eight weeks to pass before any clinical signs appear.

More reproductive variation

In wild pigs, seasonal variation has an influence on feed supply, says Dr Grimbeek. Ideally, the pig accumulates body reserves when feed is plentiful; these reserves are utilised when feed is scarce. Subcutaneous body reserves assist with thermal conductivity, and reproductive hormones are fat soluble.

Given that the more modern genotype is bred to be leaner, it is logical for reproductive variation to increase, he says. Gonadotropin release and especially somatotropin (pST) secretion, as well as the effects it has on both appetite and voluntary feed intake, are well documented as is the influence of temperature, photoperiod and feed intake on short- and long-term metabolic profiles.

Dr Grimbeek says bears usually mature earlier when the days are short, such as in winter. Consequently, so-called boar taint is more prominent in the winter period. Seasonality therefore affects puberty, weaning-to-oestrus intervals, as well as the farrowing rate of sows, while affecting bears’ fertility.

Strategies to implement

There are numerous new strategies that can mitigate the effects of seasonality on productivity. However, many of these, which he personally tested over the years, often yield variable and poor results. He advises producers to maintain between 60 to 40 light-dark periods during gestation and lactation.

For example, exposure intervals of 14 hours of light and ten hours of darkness can be maintained – producers must also strive for consistency in this regard. The intensity of the light must be between 250 and 300 lux units (light intensity is measured in lux). “On the farm, inside a building, a person must be able to read a newspaper with ease.”

Pay attention to nutrition

It is very difficult, and of course uneconomical, to feed modern genotypes up to the point of obesity. Dr Grimbeek says producers who are least affected by seasonal infertility in their herds are those with sows that show the least fluctuation in condition – these sows are also placed in individual pens after mating.

These days there is a big move towards group housing for sows, which requires more management inputs. These producers also practice the following steps:

  • They group animals according to similar parity and size.
  • They do not move groups or mix or regroup animals.
  • They feed good quality, balanced and palatable fresh feed.
  • They make sure that sows, after they are mated, have access to enough feed so as to avoid any stress.
  • They select and manage young sows well.
  • They manage feed consumption well. An intake target of around 1 200kg/sow/year is recommended. This includes rations for dry as well as lactating sows.
  • Cases of bears suffering from the effects of summer infertility have decreased over the years, as most progressive producers practice 100% artificial insemination in their herds.
  • Bears are housed in environmentally controlled buildings and all aspects of production and reproduction are addressed.

Consistent ambient temperatures

Because pigs are being bred to be leaner, voluntary feed intake tends to lag. Producers who are able to keep ambient temperatures constant, or at least avoid or reduce normal daily variation, he concludes, tend to achieve better outcomes than those who don’t.

For more information, contact Dr Pieter Grimbeek on 018 297 8155 or pigvet@agrifarmacysa.co.za.

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