Here we are at the start of warmer, brighter late spring/early summer days, writes John Gadd. It’s such a relief to walk outdoor farms (I live in a predominantly outdoor-sow area) after those drab and cold winter call-out hikes round the arks.
But, these outdoor breeders seem to get as much seasonal infertility (see table 1) as the rest of us, and an accumulation of experience leads me to suspect that bright sunshine after the shorter winter days could possibly be implicated.
My suspicion that very bright light, with its high UV content affecting the pineal gland, might be one of the factors involved in seasonal infertility first started from advisory tours in New Zealand. Driving from farm to farm with my rolled-up arm sleeve resting on the open car door caused sunburn in only a few minutes.
Spring sunshine in that part of the world, so close to clear mountain air, was noticeably fearsome, and even the locals remarked on it. I soon covered up my driving arm!
I always carry a photographer’s light meter as part of my “diagnostic kit” and readings of 500 lux were common in New Zealand in full sunlight. In Europe, we’re more used to 350-400.
Quite a few New Zealand breeders were careful to provide a degree of shade protection in sow yards or outdoors at this early time of the year. In so doing they seemed not to be unduly worried about seasonal infertility compared to us in Europe, where it continues to be a nuisance – even if there are precautionary measures we can take to anticipate it and so reduce incidence.
Erecting some form of shade as soon as winter is over (Galebreaker hung between four poles is simple and inexpensive) could well help with seasonal infertility later on.
A touch of bedding next to a wind shield to provide a shaded lying area out of the usually cold springtime winds, especially up on our UK downland, with sparse distribution of sow nuts to search-for, encourages them to rest out of the bright sun.
Yes, of course, a wallow helps, but the “suncream” thus provided is unlikely to cover the back of the head covering the pineal gland.
Anyway, it’s reception through the retina of the eye which over-stimulates it and disrupts the breeding cycle. And sunglasses for sows have yet to be invented!
|Table 1: Some signs of seasonal infertility.|
|Abortions||1 in 100 served females||13 or more for short periods|
|Stillbirths.||3% true stillbirths (bucket tested)||8% or more|
|Mummies||Small 0.5% / Large 1.0%||Small 1.5-2.0% / Large 3%|
|Returns||Less than 10%||Rising towards 20% (particularly in gilts)|
|Weaning to conception interval||Less than 6-8 days||10-12 days|
|Also, watch for reduced farrowing rate below 85% (over 100 samples) from gilts and first-litter sows that are poor in cycling, and delayed puberty in gilts.|
> John Gadd, who is celebrating 60 years’ involvement in pig production this year, has had more than 2,800 articles about pigs published and has written three best-selling pig textbooks. With hands-on experience that includes managing a grow-out herd at 1,800 ft in Banffshire, Scotland, and 20 years in the allied industries with Boots’ Farm Department, RHM Agriculture and Taymix, he set up his own international pig management consultantcy in the mid 1980s and has now visited more than 3,000 pig units in 33 countries as a pig management adviser. (Photo courtesy Bournemouth Daily Echo)