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How to maximise spring sales

By Dr Tom Spencer
There are numerous factors playing a role in the phenomenon known as Summer Infertility that affects the reproductive performance of many sows on farms in autumn each year. It is not restricted to South Africa or only the Southern hemisphere.The impact

  • Reduced farrowing rates in sows mated in summer — autumn. The sows  mated in the immediate post Christmas period have a reduced chance of farrowing. This may be because of the boar being less fertile, poorer conception or she loses the pregnancy later.
  • Delayed oestrus especially gilts brought in to fill the gaps. The sows come into oestrus slower after weaning during this time and the frustrating part is that the gilts brought-in to minimise the effect are also slow to show oestrus. The hot weather will reduce the appetite of the pigs so there will be less energy consumed to allow the sow to get to optimal body condition quickly after weaning.
  • All or none law with respect to litter size. There is confusing findings on farms but generally there is a reduced litter size born to aggrevate the situation. Initial literature indicated that if a sow was pregnant the litter size was unaffected. The current feeling is that there are many factors playing a role and litter size born is reduced.
  • Too few pigs to market when market seeks pigs. This is the harsh reality as sows not conceiving to January to March matings are those that should be producing the piglets to go to market in the pre-Christmas demand. This is also when prices for pigs increases and many farmers are greatful for the increased income per pig sold.
  • Cashflow and “lost” profits at year end. The reduced number of weaners and grower pigs to feed in May to January is a short-term pleasure. One reasonable sized unit calculated the “lost income” and immediately decided to institute remedial action to not suffer the loss again.


  • Varying reasons. There have been many studies on this phenomenon but what is interesting is that on most farms the problem is a hardy annual. Some aspects may be changed in management, nutrition, housing and even genetics but the incidence of reduced farrowing rates in the key period may be better or poorer than previous years. No simple overall advice to farmers can remove the problem.
  • Stress. Stress is a useful generic term for an advisor. This stress may come in many forms: physical- sows being uncomfortable, often due to high environmental temperatures.
  • emotional — grouped dry sows will have to contend with their pen or camp mates
  • nutritional — sows and boars are fed incorrect rations or rations that contain toxins
  • hormonal — most stressors and infections induce the body to liberate cortisone and PGf2a. As well as mycotoxins mimicking oestrogen and suppressing the hormone of pregnancy — progesterone.

Stress will cause a sow to produce more cortisol a normal hormone produced in times of anxiety. This cortisol, deleteriously affects the delicate hormone levels in the sow and she will not conceive or resorb or abort depending on the phase of pregnancy.

  • Temperature — sow — boar. Temperature has been blamed as a major cause of reduced fertility in both sexes. The adult pig enjoys a temperature around 20ºC. Many sows are exposed to diurnal temperature fluctuations of 20ºC in a day, let alone a constant 20ºC. Why are there reduced farrowing rates in environmentally controlled buildings, worldwide? This question is still vexing the mind of many farmers who have spent large sums of capital “improving” the environment of the sow.
  • Photoperiod. The wild pig has evolved to farrow in spring when food for her and the litter will be plentiful. Many researchers have tried many ways to offer extended “daylight” time to the sow as the days get shorter in autumn. This problem is also observed close to the Equator where daylight lengths are very constant.
  • Moulds. The waste products of mould growth on feed are powerful toxins that mimick hormones or affect body organ functions detrimentally. Very small quantities are required to precipitate disastrious effects.
  • Sow condition and feed levels. Table 1 indicates how feed levels and the consequent sow condition affect farrowing rates. The table also confirms that group housed sows perform poorly. With welfare requirements necessitating sows to be kept in open housing for half of pregnancy, this is a management challenge at farm level.
  • Too low LH. Low levels of Lutenising Hormone, for various reasons, reduce the oestrus shown by the sow and the number of ova released from the ovary during oestrus. The main reason being too little feed and poor body condition just prior to oestrus.
  • Progesterone and secondary oestrogen too low in uterus for attachment. Again hormone levels are important during the days after mating. The fertilised embryos float in the uterus till about day 15 post- mating and if the hormone environment is not adequate then attachment does not occur, thereby reducing conception.
  • Groups VS individual. Table 1 confirms this finding. The sows are under stress in groups unless extremely well cared for.
  • Solutions
  • Good condition at weaning. Feed the sow large quantities of a good quality diet during lactation. A good sow will lose condition during lactation if she is to produce a large and heavy litter but aim to wean her in condition score three? (on score of one to five (being a fat sow)). It is not easy if she has a large litter and environmental temperatures reduce her appetite. Cooling the sow, wet feeding, feeding in the evening when day temperatures are decreasing, high density rations are aspects to be implemented.
  • Flush feeding. In the hopefully short period from weaning to oestrus feed the sow ad lib. She must be encouraged to take in as much feed as possible to have the energy that is needed to get 30 ova ready to be ovulated. The more energy she takes in the more energy there is to improve her condition and have the energy circulating in her bloodstream to ripen the ova and prepare the uterus for the imminent arrival of ova and semen to make embryos.
  • Mycotoxin binders. The mycotoxins in the feed, especially the maize or energy part, can be minimised by adding binders to the feed. It is almost universal now that there are one or two mycotoxin binders in the dry sow feed to absorb the toxins and make them inactive to the sow. There are about 600 mycotoxins known but probably only six that affect pigs badly. These binders do allow the sow to maintain her pregnancy as well as eat more during lactation.
  • Good eros area. Good bio-stimulation is important for the sow. Sows weaned without the presence of a boar ovulate low numbers of ova. The sow should be able to see, hear, touch and smell the boar. A quiet, comfortable area where the boar and sow can enjoy foreplay is ideal.
  • Mild stress — ride, group, hormones. MILD STRESS is the operative term. Some farmers “stress” the sows on the day of weaning with a 20 minute ride on a bakkie or truck. Think of gilts that are delivered to the farm, they ovulate three to five days after arrival. Housing the weaned sows in groups with a self-feeder to optimise feed intake. Hormone injections are available but in my opinion should be reserved for sows weaned after their first litter and very thin sows.
  • AI. By employing AI the risk factors on the boar are largely eliminated.  The boar also suffers temperature dysfunction, being a reluctant worker and if the testes have been exposed to high temperatures then the quality of sperm produced is poor. AI likewise reduces the risk of the boar being a mechanical infector of the uterus during mating.
  • Pooled semen. It has been observed that when semen from different boars is mixed or different boars are used on the sow during the same oestrus that litter size improves. This is an easy assistance because if there are more embryos implanted even if some are lost during pregnancy then there will be a larger, or even a, litter born.
  • AI plus boar. This is similar to pooled semen with an added benefit. If the boar is used to identify the sow in oestrus and mates her 12 hours later the ejaculate contains hormones that are useful to trigger the sow to ovulate. This is mainly the prostaglandins that aid hormonal level and enhance the ova popping out of the little bags they are housed in on the ovary.
  • Restrict movement and mixing. Human interference with mated sows, other than feeding, is perceived by them to be a stress. Keep sows in the group they were mated in or placed in a dry sow crate within two days of mating so she can settle before the critical period of implantation.
  • Cool environment. Sows and boars prefer a constant 20ºC. If the respiration rate increases to 40/min from the normal of 15 – 25/min = HEAT. The easiest way a pig has to cool itself is to pant. So monitor the breathing.

There is no simple rule that will ensure all piggeries will maintain a constant farrowing rate throughout the year. Some piggeries are lucky in that the effects of “Summer Infertility” are seen as a minor blip on the farrowing rate while other farms can drop their farrowing rate by 20 to 30%.
On a 200 sow unit aiming at eight farrowing per week, it can mean only six farrow. The two sows short per week is equivalent to 20 pigs per week, four to six months later that are not there to go to market. Over a couple of weeks the numbers mount up and the potential profit decreases rapidly. Remember the sow’s costs must now be covered by fewer pigs sent to market.
The easiest way round the problem is to accept there will be a decrease in farrowing rates for sows mated in autumn and budget 30% more sows and gilts to be mated.
The irony is that the gilts to be selected are those that were probably sent to market to take advantage of the higher market prices prior to Christmas. Each farm is unique so work on all the aspects high-lighted above.

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