Mention the “Fantastic Four” to most people and they’ll think about a team of comic-strip superheroes. As a reproductive physiologist working in the pork industry, however, I tend to make a different association. 

My idea of the fantastic four is when a sow has her fourth litter.  Economic studies based on net present value show that it takes at least three successful parities for a replacement gilt to pay for itself. At that point, you’ve covered all or most of your fixed costs for bringing that gilt into the herd.

While cost/benefit analyses show that a goal for gilt introductions should be around 35 percent to optimize a herd’s parity distribution and returns, current replacement rates are approximately 50 percent to 65 percent per year. That means producers are leaving lots of money on the table. Higher replacement rates also have a ripple effect on the health and long-term profitability of an operation.

Get off the merry-go-round

Pork producers stuck in the greater-than-50-percent replacement scenario are often caught in a self-perpetuating cycle. Poor gilt-development practices result in more females being culled as gilts and first-parity sows due to failures in breeding and/or lameness issues. This in turn forces less-qualified (younger) gilts to be bred as replacements. If those gilts then fail to meet breeding targets, the producer has no choice but to retain older, less-productive females in the sow herd.

Today, with more than 50 percent of the sow herd being culled and replaced annually, sows are weaning only 30 to 40 pigs per lifetime. Additionally, nearly 20 percent of premature culling occurs at parity 0. That’s simply not acceptable. A comprehensive, well-implemented gilt-development program with production benchmarks is needed to change these numbers.

Treat her right

Focusing on gilt development beginning at 40 pounds (18 kg) bodyweight and making it a herd priority is the first step toward achieving the fantastic four. Herd records show 8 percent to 15 percent of gilts are culled due to lameness issues prior to making it into the herd for the first parity, while 10 percent to 20 percent are culled for reproductive issues.

Providing a larger pen space per pig, better flooring and feeding a balanced diet that includes complexed trace minerals (amino acid complexes) can help improve gilt-retention rates within the sow herd by up to 50 percent. Here are some other points:

  • A common denominator found in high-performing gilts — before and after entering the herd — is rearing them in small groups. Once heat detection commences, grouping six to 12 gilts per pen with 10 to 14 square feet (0.9 to 1.3 square meters) per gilt means less fighting and competition within the group.
  • Improving footing by utilizing 5-inch (12.7-cm) slats and decreasing slat spacing to a 1-inch opening results in less foot stress and injuries to developing gilts.
  • Research shows that feeding gilts a balanced diet containing complexed trace minerals (zinc, manganese and copper) decreases claw lesions and associated lameness.

While the obvious effects of lameness account for up to 15 percent of total culls through parity 1, lameness and the stress it produces for the sow also influences reproductive capacity through a longer wean-to-estrus interval, more non-productive sow days, smaller litter size and fewer pigs weaned.

Maximizing reproduction potential

Since 70 percent of the gilt-development cost from the grow/finish unit can be found in the feed bill, pork producers who wait to develop gilts in the finisher are leaving profits at the door.

One option is to consider the gilt’s nutrient needs, slightly slowing growth and feeding correct levels of essential nutrients (including complexed trace minerals) to help it reach physiological maturity at 230 days and 300 pounds (135 kg) bodyweight with an improved skeletal-structure-to-weight balance.

Why? Research shows that breeding on the basis of age and backfat indices has little relationship to a successful first parity. Cost/benefit analysis shows that gilts should be bred at 300 to 330 pounds (135 to 150 kg) bodyweight on second or third estrus. Gilts need this weight and maturity to continue to grow, gestate and lactate for a litter of pigs and then rebreed. Studies show gilts bred at less than 300 pounds (135 kg) bodyweight had fewer total pigs born over three parities.

Another big challenge in the pork industry today is getting enough calories into a lactating gilt to support a large litter while sustaining her growth and body condition. Reported herd data show that sows failing to reach 400 pounds (180 kg) bodyweight at the end of the first parity, while losing lean tissue, are more likely to be culled for reproductive issues. To meet this goal, sows need a ration that’s not only nutrient-dense but also palatable, because you need to keep them eating. A 2.2-pound (1-kg) increase in daily feed intake cuts a sow’s chance of being culled by 30 percent.

Also, while poor fertility is the common denominator for sows exiting the herd early, lameness causes many intermediate factors that lead to poor fertility. Foot lesions are commonly found on 15 percent to 40 percent of developing gilts. Inflammatory lesions cause pain and stress, directly impacting reproductive performance.

In 2011, records from five farms in Spain showed that adding complexed trace minerals (zinc, manganese and copper) to sow diets dramatically reduced the cull rate of young females due to lameness. At the outset, 42 percent of bred gilts were not reaching third parity. Within two years that number had dropped to 23 percent — a nearly 20 percent improvement in young sow retention.

Being able to cull for age or poor milking performance, the pork producers saw a boost in reproductive performance through increases in the number of pigs born alive and weaned, with dramatically improved profits.

A strong benchmark, and the ability to pursue your own fantastic four, can be concluded like this: A production standard that includes 86 percent of breeding gilts reaching the first parity with no more than 10 percent fallout over the next three parities will enable a herd to reach the goal of at least four productive parities per sow.