About nine months ago, British pork producers began to see a steady surge of sow infertility problems. A new “infertility syndrome” was suspected.

The possibility is being investigated on a national scale, but it is too early to speculate on several complicated possible causes.

Although we have been warned not to jump to conclusions, some of the individual and combined causes being suggested include:

  • Fish meal, which was rarely added to diets, now used due to concerns over post-BSE “animal” protein;

  • More gilts being home-bred after foot-and-mouth disease movement restrictions;

  • Over-familiarity and carelessness with artificial insemination, erratic semen deliveries and semen handling and storage problems; and

  • Some easing up on parvovirus vaccinations due to low profits.

I have noticed, among other problems, far more cases of weak heats over this past year. Whether this is part of our overall fertility fall-away, no one here knows. But, for those American producers whose herds suffer from this annoying disorder, I'll offer my thoughts.

I define “weak heat” as a sow's partial reluctance to stand for a boar. This reluctance is not as prevalent in gilts.

These sows and gilts display normal signs of estrus but then are reluctant to accept service. The stockperson withdraws the boar, assuming she is not fully ready, and unfortunately misses the service window.

Weak Heat Causes in Gilts

  1. Hot weather/overcrowding, bullying and anxiety.

  2. If all the gilts show weak heats, check their condition, especially if they:

  • Are too fat for their age;

  • Show low-level signs of illness (veterinarian check);

  • Need adjustments to acclimatization program (veterinarian check);

  • Are being flushed according to latest techniques.

  • The latest ideas on stimulating a firm, demonstrable heat in lean, fast-growing gilts moved to the breeding pool weighing under 210 lb. include:

  • Feed well on a good grower diet for the first 12 days after arrival (covers first heat);

  • From 13 days until 4½ weeks after arrival, lower the plane of nutrition to slow them down — unless the gilts are cold or overcrowded (covers the second “true” heat);

  • From then until about six weeks after arrival, feed generously (covers the third-service heat).

Tips for Gilts

  1. Don't raise gilt replacements close to boars; use a 6-8 gilt pool (10-12 maximum) with ample get-away space.

  2. Excitement and competition stimulate estrus. Stress hinders it.

  3. Put a smelly, friendly boar in with a group of “weak heaters” with ample space and supervise at all times.

  4. Move weak-heaters to a previously occupied boar pen.

  5. Check lighting. Use 300 lux for 16-18 hours and 25 lux for 6-8 hours; light should shine directly into eyes, not from above or behind. Some say this is not proven, but my experience suggests it works.

Weak Heat Causes in Sows

  1. The “nose-dive” in lactation is a common cause. See “anti-nose-dive” checklist in my new textbook: “Pig Production Problems” available from Iowa State University Press at 800-862-6657 or visit: www.iowastatepress.com. Cost: $109.99 +$6 shipping/handling, plus applicable sales tax.

  2. Uterine infection after farrowing (veterinarian check).

  3. Hot conditions in farrowing house.

  4. Cold or harsh conditions in breeding barn.

  5. Molds (mycotoxins); over-red, swollen vulvas but a poor heat.

  6. Check lighting (see “Tips for Gilts” above).

  7. A submissive sow forced next to a “bully” sow.

  8. Boar preference: the sow may show weak heats next to a boar she doesn't fancy.

  9. Lameness, hurt back, sunburn, scratches or sores.

  10. Nutrition is rarely involved these days, except when flushing. Diets should be adequately supplemented with vitamin E (organic at 0.3 ppm), fats, choline, biotin and riboflavin.

Tips for Sows

  1. Weak-heaters with a history should be moved past a boar every day after weaning. Identify and record.

  2. First-litter weak-heaters can be housed together in a surplus boar pen of the breeding barn.

  3. Very early weaned sows (10-14 days) often lead to later heats (1-2 days); and weaker heats that are 12-18 hours shorter. I would never wean less than 17 days and prefer 28-30 days.

  4. Provide a succession of visible, smelly boars — a 36-in. space excites more than touching.

  5. In all-vegetable protein diets, try 250 g. of the best white fish meal and 50 g. of dried skim milk powder, once a day for 2-3 days. If it works, draw your nutritionist's attention to it.