Summer Infertility in Free Range Pastured Pigs
By Lee McCosker
Historically, the sow only produced one litter per year in spring as many livestock species do. Spring usually offers the best conditions for young animals by providing a more pleasant climate and good feed availability and all contribute to the survival of these offspring. Selective breeding and controlled climatic conditions inside commercial pig sheds has meant that the pig is now expected to have at least two litters per year. Nature often intervenes however and even under commercial conditions summer infertility can wreak havoc on the number of sows that fall pregnant and the number of litters born. Heritage breed pigs such as the English Large Black or Wessex Saddleback are more prone to mimicking their ancestors and often only produce one litter in a year under sub optimal conditions.
Day length and sows returning to heat
Summer, or seasonal, infertility is a natural reaction to day length and exposure to intense ultra violet light. High temperatures also have an effect and combined with long hours of daylight may cause the sow to abort a pregnancy very early, or temporarily halt the heat or oestrous cycle. When abortion occurs, it is often so early that the sow simply appears to have returned to heat, sometimes a bit later than expected, or seems to have missed a cycle. The heat cycle of a sow is approximately 21 days. So, long hot summers will have an impact on the number of sows that farrow in the following months and can mean that there will not be as many pigs available for sale as anticipated. Some years are worse than others especially if there has been an extended number of continuous hot days.
Its not just the temperature affecting sow productivity
It is important to know that it is not just high temperatures that cause summer infertility. The length of day is always going to trigger this very natural occurrence in some sows. Hormonal changes maintain a pregnancy and progesterone is produced by the corpus luteum (located in the ovary) and without it the pregnancy will fail. When days are long and ultra violet light exposure is high, the corpus luteum may respond by disappearing which will result in the termination of the pregnancy. Summer infertility is said to effect white breeds more than coloured pigs so maintaining a cross breeding program infused with a coloured breed may be of benefit.
There are many things you can do to lessen the effect of summer infertility but you will most likely experience it with some sows each year and you need to manage for that so the interruptions to the breeding program are minimal and you are not left with a hole in your production and unable to supply standing orders or have the pork available that you had anticipated. The type of grazing available to sows can have on impact the amount of heat generated in the sows body and therefore her overall temperature. If the sow has access to long, dry and fibrous pasture she will attempt to ferment a lot of it in the hind gut (caecum, colon) and this process produces a lot of heat. During summer give your sows access to green and more digestible pastures or if this is not possible, keep dry pastures slashed or mown so that over consumption of these dry older grasses cannot occur. When pigs are hot they tend to eat a lot less so provide a highly nutritious and easily digestible feed to encourage the sow to eat and maintain her condition during the three weeks after mating.
Tips to minimize the effects of summer infertility
Following are steps you can take to minimize the effects of summer infertility:
This article is an exert from Pigs, Pasture and Profit by Lee McCosker and will be available from the PROOF website