The effect of litter size relative to functional teat count on lactating sow and litter performance.

Researchers: Abigail Jenkins, Sierra Collier, Joel DeRouchey, Mike Tokach, Jason Woodworth, Katelyn Gaffield, Jordan Gebhardt, and Robert Goodband, all of Kansas State University

Today’s modern hyper-prolific sow will often give birth to more piglets than the number of functional teats she possesses.

For the farm business, it means that the producers are faced with the decision of having to either allow the sow to try and nurse the additional piglets above functional teat count or create more nurse sows.

Nurse sows are females who have just weaned a litter of their own and are then moved into a new room to support the additional pigs born above the teat count.

The potential drawbacks of having high nurse sow usage include:

• No additional colostrum intake for pigs crossfostered onto her;
• Increased risk of disease transmission when moving sows between farrowing rooms, and;
• Decreased breeding targets as empty crates are needed to make room for nurse sows.

If we have a hyperprolific female but want to limit nurse sow usage, we must first consider the impact of having more pigs than functional teats. How will it impact pre-weaning mortality, fall-behind pigs, piglet growth, sow body condition, or any subsequent reproduction efforts?

Photo Credit: Kansas State University

In an effort to answer these questions, a recent study was conducted at a commercial sow farm in northwest Texas.

A total of 1,005 sows (average parity 3.5, PIC Line 1050) and their litters (15,278 piglets) were utilized to determine the impact of litter size relative to teat count on sow lactation measurements, litter performance, and subsequent reproductive performance under commercial conditions.

Sows were allocated piglets according to four treatments with:

1. One fewer pig than functional teats (-1);
2. The same number of pigs as functional teats (0);
3. One more pig than functional teats (+1);
4. Two more pigs than functional teats (+2).

In the context of this study, a functional teat is any teat that produces enough milk to sustain the life of a piglet. Therefore, any blunt teats, blind teats, and teats connected to mammary glands with severe edema were considered non-functional. The average functional teat count in this study was 14.7 teats.

Measurements of sow body condition (body weight, backfat depth, and caliper score) were collected at the time of loading into the farrowing house (day 112 of gestation) and at weaning.

After each sow was done farrowing, she was randomly assigned to a treatment such that functional teat count, parity, and sow body condition were equalized across all treatments.

Any pigs born weighing less than two lbs. were not included in this study, as they were cross-fostered into litters receiving specialized care as per the normal standard operating procedure of this farm.

To attain the correct number of pigs relative to functional teat count, average birth weight pigs were cross-fostered to maintain the normal body weight variation within the litter and to keep the average piglet starting weight across all four treatments the same (3.4 lbs.). Pigs were individually weighed after cross-fostering was complete for that litter and on the day before weaning.

The average weaning age of this trial was 22 days. No supplemental nutrition (creep or milk) was provided to any of the litters in this study. Starting at day 3 of lactation, fall-behind pigs were identified and removed from the farrowing crate. Fall-behind pigs were any pigs identified as being gaunt in appearance with evidence of ribs and backbone becoming visible and empty bellies. Removals and mortalities were not replaced in the litter.

The results showed that the percentage of removals and mortality increased as litter size relative to functional teat count increased. However, it did so at a diminishing rate, which means that the increase in removals and mortality when moving from 0 to +1 sows was smaller than the increase when moving from -1 to 0 sows.

Also, the increase in removals and mortality did not happen at the same rate as the starting litter size increased. This means that even though there was an increase in removals and mortality, there was still an increase in litter size at weaning as litter size relative to functional teat count increased, with litter size at weaning increasing from 12 pigs in -1 sows to 13.5 pigs in +2 sows.

As expected, piglet average daily gain decreased as litter size relative to functional teat count increased, which translated to a reduction in average piglet weaning weight. Average weaning weight decreased from 14.4 lbs. in -1 sows to 13.6 lbs. in +2 sows. However, it should be emphasized that all four treatments still weaned pigs that were heavier than 13.5 lbs. on average.

Even though -1 sows weaned a heavier pig, the difference in weaning weight was not enough to make up for differences in litter size at weaning. Thus, litter weaning weight increased as litter size relative to teat count increased, with +2 sows weaning litters that were 11.5 lbs. heavier on average than litters weaned by -1 sows.

We discussed litter size relative to teat count at the beginning of the trial, but how many pigs did sows wean relative to teat count?

Figure 1. Effect of pigs placed relative to teat count on the proportion of litters weaned relative to teat count (Jenkins et al. 2025).

Figure 1 shows the proportion of the litters in each treatment that weaned at different pig counts relative to teat count.

The green bars are those sows that weaned above the teat count, the yellow bars are sows that weaned at the teat count, and the orange and red bars are sows that weaned below the teat count.

In total, 47% of the -1 sows weaned at three or more pigs below the teat count. The percentage of sows that weaned at three pigs below teat count or worse decreases as you increase the starting litter size relative to teat count, with only 15% of +2 sows weaning three or more pigs below teat count.

Conversely, 48% of the +2 sows weaned at a teat count or above. That means that almost half the +2 sows were utilizing all functional teats throughout the entire lactation period. The percentage of sows that weaned at teat count or above decreases as you decrease starting litter size relative to functional teat count, with none of the -1 sows weaning at teat count or above because none of the sows in this treatment even started at teat count.

As you would expect, sow body weight loss increased as the number of pigs nursing relative to functional teat count increased. However, the difference in sow body weight loss between the -1 and +2 treatments was only eight lbs. We saw a similar trend in sow caliper score and backfat depth change over lactation, where there was an increase in sow body condition loss over lactation with more pigs nursing relative to functional teat count, but the differences between the treatments were relatively small.

If the sow lost more body condition during lactation, then you would expect her subsequent reproduction to be impacted, right?

Throughout this trial, we were reminded that today’s modern sow is resilient.

Yes, sows lost more body condition during lactation when the number of pigs relative to functional teats was increased, but there were no differences in the percentage of sows bred by day 7 post-weaning, the percentage of sows culled, or subsequent farrowing rate. In fact, +2 sows had a shorter wean-to-estrus interval than 0 sows (5.0 and 5.6 days, respectively).

Figure 2. Effect of pigs placed relative to teat count on pigs weaned/sow/year (PSY) assuming a litters/sow/year of 2.43. (Jenkins et al., 2025).

We also found that sows tended to have increased total born and higher liveborn in the subsequent litter as litter size relative to functional teat count increased. In the subsequent litter, +2 sows had 1.2 more liveborn pigs on average than -1 sows (15.4 and 14.2 liveborn pigs, respectively). Lastly, pigs weaned/sow/year increased as litter size relative to functional teat count increased (Figure 2).

Bottom line: The optimal strategy is ultimately dependent on your primary criteria of interest.

If you want to optimize individual performance and have the lowest pre-weaning mortality, lowest sow body condition loss, and highest piglet weaning weight, then utilizing the -1 loading strategy was the best option.

However, if you want to maximize farm throughput for the highest pigs weaned/litter, highest litter weaning weight, and highest pigs weaned/sow/year, then the +2 strategy was the best option.

Keys to Success With More Pigs Than Teats:

1. Good entry sow body condition: The farm in which this study was conducted averaged 15 mm of backfat, and and had fewer than 10% of its sows classified as skinny when utilizing the PIC caliper at entry into the farrowing house. The sows that enter lactation in better condition are more resilient, and we believe this makes them better equipped to nurse more pigs than functional teats.
2. Teamwork: Implementation will require everyone in the farrowing room to be clear on the new standard operating procedure and why these changes are important.
3. Proactiveness: Loading more pigs than available teats requires that the farrowing team must remain cognizant of a sow's limitations—that not every sow is a +2 sow. As well, any fall-behind pigs need to be removed early. This will help maximize their chance of survival and weaning to provide full value. This is why nurse sows are still required. It's just that fewer nurse sows are required than when loading sows with fewer pigs.

The full research report will be available at the 2025 K-State Swine Day on November 20, 2025, in Manhattan, Kansas. This project was supported by the National Pork Board (PR-005981) and the Foundation for Food and Agriculture Research.

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Abigail Jenkins
Abigail Jenkins is a Ph.D. candidate with the Applied Swine Nutrition team at Kansas State University and is expected to complete her Ph.D. in June. In 2022, she obtained her Master’s degree in Swine Reproductive Physiology from North Carolina State University under the direction of Dr. William Flowers.

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