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Swine productivity has been improved dramatically due to development in genetics, nutrition and disease control. In some herds, sow productivity has been increased up to 15 total born piglets per litter, with genetic improvement of three piglets per year.
In contrast to the improvement, pre-weaning mortality of piglets remains a problem. As litter size increases, piglet mortality increases as well because of lighter birth weights and greater within-litter variance. Meanwhile, number of stillborn is positively correlated with litter size, so the improved genetic merit in litter size has been offset by piglet mortality.
In farrowing crates, pre-weaning mortality of piglets is about 10 to 15 percent of born-alive piglets. In farrowing pens piglet mortality ranges from 20 to 30 percent of live born piglets. Most of the piglet death occurs during the first three days after birth.
Starving, crushing and hypothermia are the major causes of piglet deaths in farrowing crates. In loose farrowing systems, piglet crushing (being laid on by the sow) is the predominant cause, accounting for 75 percent of the total deaths.
Our research group at the University of Minnesota West Central Research and Outreach Center in Morris studied causes of piglet death in farrowing pens before weaning. Pre-weaning mortality of piglets varies with litter size and sow parity. The influences of litter size and sow parity are hard to separate because mature sows usually have larger litter sizes compared with younger sows.
In confinement farrowing crates, when litter size is standardized, sows of parity 3 to 5 wean larger litters with lower piglet mortality compared with either younger or older sows. However, the optimal sow parity for low pre-weaning mortality and larger litter size at weaning in loose farrowing systems is not clear because sows perform and behave differently than sows in farrowing crates.
To investigate the effect of sow parity on piglet pre-weaning mortality in farrowing pens, we equalized litter size to 11 to 13 piglets per litter after farrowing by cross-fostering.
The results indicated that after litter size was equalized, parity 1 sows weaned more piglets (10.8 vs. 9.5 piglets per litter) and had lower piglet mortality (11 vs. 22 percent) compared with mature sows (parity 3 and older). However, parity 1 sows farrowed and weaned lighter piglets compared with mature sows. On average, piglets gained about 0.5 pound of weight daily, and the effect of sow parity on daily gain of piglets was negligible.
These results indicate that although parity 1 sows had lighter piglets at birth, they weaned larger litters compared to mature sows in farrowing pens. In contrast to parity 1 sows, mature sows lost more piglets before weaning even though their piglets were heavier at birth. One of the reasons for the high piglet mortality in older sows could be their body size and weight.
Most incidents of piglet crushing occur when sows are making posture changes in farrowing pens. Old sows are usually bigger and heavier than younger sows, so it is more difficult for old sows to control the descent of their body when lying down from standing.
Rails and slop walls can help old sows lying down slowly and consequently, can reduce piglet death in farrowing pens.
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"The Pork Professor" is a monthly column created by members of the University of Minnesota Swine Extension team. This column was written by Yuzhi Li, assistant professor at the West Central Research and Outreach Center in Morris.
