Wean to service intervals can average between four and six days, farrowing rates can rotate around 90% and total born per litter in the United States can range between 15 and 16. While those impressive sow records give the industry something to shoot for, Robert Knox says a critical driver for all figures is follicular development.

“Follicular development is actually one of the most important aspects for driving reproductive fertility … most of the follicular development from weaned sows, or even from replacement gilts for puberty, all of this really occurs over a short period of time, in four to six days,” Knox says. “So, these follicles actually move from smaller or medium sized to large and ovulatory size in a really quick period, and the follicles themselves are secreting estrogen into circulation. When all of that occurs properly, we can wind up with a strong estrus expression in these females.”

During the recent Iowa Pork Industry Center Sow Summit, the professor and Extension specialist in swine reproduction with the University of Illinois Urbana-Champaign also pointed out the number of follicles, that are developing to ovulate in this four-to-six-day period, also sets the upper limit for litter size. But farms can't easily determine follicle size, so estrus is the best indicator of what's going on, and that can be impacted by boar exposure and wean to service interval.

“The majority of your sows are very likely expressing estrus on days four or five,” Knox says. “The animals that come back on day three, however, are more likely to be the ones that are receiving three services. They have a longer estrus, and those animals that are returning on day six are the ones that are more likely to receive just a single service because they have shorter estrus.”

Sows showing estrus on days one and two after weaning is what concerns Knox, since follicle development takes about four to five days.

“Something's going wrong there, and it's important to find out what is going on, because their fertility is probably not very good,” Knox says.

For weaned sows there could be an issue in lactation. Data has shown two consecutive days off feed or even reduced feed is problematic. Interrupted nursing, if the litter is ill, or if the sow is ill, that can stop nursing, and as soon as the nursing stimulus stops, follicle development can start.

“Problems can start somewhere after day 10 of lactation,” Knox says. “So, you can wind up having follicles start to grow and then if they start nursing again, then you get a suppression. And this causes some oddities, like cystic ovaries, and ovulation while the sow is still in the crate.”

The other thing to consider is since all the sows are not farrowing on the same day, anytime these rooms are weaned, there can be variation in lactation length.

Estrus detection relies on two behaviors: proceptive behavior, where the sow actually seeks out the boar, and receptive behavior, with boar exposure and back pressure tests. Knox sees robotics and artificial boar stimuli being part of the process in the near future. In addition to robotics assisting labor with moving and controlling boars, enhanced stimuli could be useful as all boars are not the same, and all females in a row don’t receive the same stimuli. This could also be an opportunity to include pheromones and boar audio.

Knox questions if induced ovulation and single AI will ever be practical? His answer, maybe, if a diagnostic tool can tell producers who not to induce and breed.

“Females that do not develop follicles will not ovulate and are not fertile,” Knox says. “But without any way to tell that, these systems require everybody to be fertile, so diagnostics could be a game changer in this as well.”

The key will be how these treatments and procedures are administered on commercial farms, he says.

He also questions if frozen sperm will ever be practical? While the concept has been around for decades, its use remains limited. However, Knox argues that it is probably more important than ever, with emerging global diseases. But it does have its limitations, such as damaged sperm in the cryo-preservation process, increased costs to produce, and no practical system for using it on farm.

“One of the things that will be hard to overcome is the total born,” Knox says. “When you have lower numbers  of fertile sperm, you're more likely to get smaller litter size, even if you get your AI timing correct.”

Fertility diagnostics is an area Knox also sees needing improvement. The ultrasound has had great success in diagnosing pregnancy, but the industry could use other tools such as vaginal conductivity or pH sensors, behavior monitoring cameras and technology to measure vulva color and temperature.

Many stressors can impact ovulation rate, estrus expression,  embryo development, pregnancy establishment and even fetal development. Knox points to one stressor in particular—whether grouping all the pregnant sows in one day has an impact on fertility?

“Even with seasonal fertility, there is a subpopulation of females that are sensitive to heat stress and to grouping stress. It's not all of them. Another opportunity I think is to find that subpopulation, rather than saying the whole group is sensitive,” Knox says. “But in that subpopulation, at least from a grouping standpoint, I believe the problem stems from  fear, fighting, injury, and limits to rest.”

Hyper-prolific sows, where their born alive exceeds their number of functional teats, also have to be managed differently. In Europe, they've now coined the term “super-prolific sows,” with as many as 18 to 20 born alive, far exceeding the number of functional teats. Both hyper-prolific sows and super-prolific sows have longer durations of farrowing.

“As litter size increases, farrowing duration continues to increase, with a really high correlation rate here,” Knox says. “The longer duration of farrowing is associated with more stillborns, and weaker pigs at birth. The sow gets fatigued. The uterus gets fatigued. It's a tough process.”

Most of those stillborns occur in the last third of the litter, which result from  hypoxia and those that survive may be weak pigs at birth. Ninety-three percent of all stillborns are due to premature umbilical rupture, and the failure of the sow to be able to push that piglet out through the birth canal.

Knox notes there is some data that shows increasing the frequency of feeding relevant to farrowing can increase glucose levels in that sow, potentially offering more energy for that sow, to avoid farrowing fatigue, especially with long farrowings.

With the hyper-prolific sow and increased litter size, colostrum production has not kept pace and piglet intake has declined. Immune components peak six hours after the first pig, and are nearly at baseline by 24 hours, which means the last pigs born in the litter are at a disadvantage to not only find an available teat, but to get the required amount of colostrum, Knox says.

Knox prefers the two-sow system, putting extra newborn pigs on a day seven sow, whose milk is better suited in volume and content for a  newborn pig.

“One of the things that we've found, in parity one sows nursing a large litter, with matched functional teats is that the  sows nursing 15 to 16 pigs weaned more pigs, but they also lost more pigs, early on to crushing, and fallback,” Knox says. “So, I think this is an opportunity, at least for management, if you have these large litters that are nursing, if you're watching them, you can actually help them very early on and pull them out if they're at risk.”

Finally, Knox points out that environmental conditions, such as barn lighting, cold weather drafts and cold stress, can impact fertility.

“These animals that are chilled, they limit floor contact, and  they stand more. They do not want to be on the cold concrete. If they could, they would try to contact, lay on another animal, but in stalls, that's really limited,” Knox says.

“They're using their feed resources, not for production and not for replacing weight. Those parity ones or parity twos, or any sows that lost weight during lactation, they're using that feed to thermoregulate, and they are stressed and their cortisol level is higher as well.”