As weaning age has shrunk, pork producers have focused on improved housing, diets and management of those early weaned pigs.
Now producers must turn their attention to getting sows' reproductive systems functioning so they can be successfully rebred as soon as possible.
"We have to cope with the biology of the early weaned sow in order to manage early weaning," observes Jack Britt, associate dean of research programs at the College of Veterinary Medicine, North Carolina State University.
When To Wean If you are weaning at 14 days of age or older, generally you will be okay when it comes time to rebreed the sows, says Britt. Weaning at day 10-14 will create marginal problems, erratic estrus and anestrus because the system that causes the sow to ovulate is still refractory from the previous pregnancy.
"These sows either come into heat, don't ovulate, show irregular heat patterns and anestrus, or they may show constant periods of estrus. Sows are highly unpredictable when weaning at this age in terms of reproductive performance," he explains.
Very Early Weaning If you must wean within the first few days after farrowing, and you plan to rebreed the sow, allow the litter to nurse at least the first 24-48 hours. This will help suppress secretion of the gonadotropin hormone responsible for follicle growth. This will help prevent development of cystic follicles and improve the chances of the sow showing estrus during the second week after farrowing. Fertility will still be low, however, if the sow is bred during the first 2 weeks after farrowing.
"Many sows weaned during the first two days after farrowing will not breed back normally until five to eight weeks postpartum," says Britt.
And, the reproductive physiologist urges, pay close attention to feed intake in those very early weaned sows. "We typically ignore feed intake in this sow. Just because we have weaned her in the first two days doesn't mean she is going to have adequate feed intake. Actually, the sow is going to have a suppressed appetite because of farrowing. She will go into a negative energy balance because she is making milk and we want to restore that," he notes. The goal should be to avoid weight loss until they are rebred.
For sows weaned after day 2, return to estrus should occur in 6 to 10 days. Split weaning of the litter may promote earlier breeding in early weaned sows, says Britt, particularly during summer, when postweaning anestrus delays breeding.
Split Weaning Tips For split weaning, leave an interval of two days between weaning the heaviest half of the litter and weaning the balance of the litter. During this interval, the sow will produce hormones associated with reduced suckling intensity. But Britt says if the lightest pigs are allowed to nurse beyond two days, they will begin to suckle both the occupied teats and those vacated by their heavier littermates. A compensatory increase in suckling intensity will suppress hormones in the sow linked to weaning.
Three- To 14-Day Weaning For sows weaned from day 3 to day 14 after farrowing, Britt suggests treatment with an estrus control product (P.G. 600 from Intervet) at weaning to stimulate a prompt return to estrus.
In one study, involving 25 sows weaned between days 5 and 11 postpartum, more sows treated with an estrus control product (75"percent" vs. 21"percent" in untreated sows) came into heat within 10 days of weaning and the interval to heat was shorter (4.1 vs. 5.9 days). Treated sows also had a higher ovulation rate and more viable embryos 11.5 days after breeding (16.4 vs. 10.9 in untreated sows).
"Another strategy is to use an estrus control product only in sows that have not returned to estrus by seven days after weaning," comments Britt. "This strategy permits sows that would return to heat spontaneously to do so without treatment, but it permits active stimulation of potentially anestrous sows in time to get them bred back with minimal delay."
For breeding early weaned sows on the first heat after weaning, embryo survival is enhanced by treatment with 1 million IU (international units) of vitamin A at weaning, says Britt. In one study, embryo survival 11.5 days after breeding was 78"percent" in the vitamin-treated group, 66"percent" in the control group.
Sow Feeding Tips Feed management is also very critical in sows weaned 3-14 days after farrowing, stresses Britt. Controlling feed intake in the first week after farrowing is the most important thing a producer can do to influence hormonal development and affect how quickly those sows will come back into heat after weaning.
Make sure to feed sows all they will eat from weaning to estrus to promote the most follicle growth (responsible for secretion of estrogen leading to the onset of estrus).
Post-farrowing feed intake is also greatly affected by how much sows consume during gestation. In a study done at the University of Nebraska, a control group of sows was fed 4 lb. a day throughout gestation. A second group was also restricted to 4 lb./day until the last six weeks before farrowing when they were allowed to eat all they wanted. Those sows increased their consumption to about 9-10 lb./day, then began to decline about 10 days before farrowing, dropping to nearly zero by the day of farrowing, says Britt.
"What this really says is sows that get fat in late gestation have a reduced appetite," he adds. "We may want to feed these sows at higher levels for the last 10 days because we've really got increased growth of pigs there," he says. Ad libitum feeding during late gestation has an adverse effect on feed intake during lactation, he points out.
Remember, just as with regular weaning programs, there are also seasonal and parity differences when it comes to feeding early weaned sows. Summer diets should contain more lysine because lysine will be rate-limiting if sows are fed normal diets but their feed intake is voluntarily lower