Gains in sow productivity are one of the most impressive areas in pork production. Currently, some units are exceeding 30 pigs weaned/sow/year (p/s/y); 28 or 29 p/s/y are no longer considered unusual.

However, with this improvement come concerns about “unintended consequences” of larger litter size, such as increased level of management to maintain pre-weaning mortality at acceptable levels, reduced performance in grow-finish, greater variability of growth, and impaired pork quality. Pork quality concerns surfaced when research showed low birth weight piglets have fewer primary muscle fibers at birth than normal birth weight piglets.

A study was undertaken at a 600-sow commercial research facility at which 98 litters were fully attended at birth to allow accurate recording of birth weight and birth order. Piglets weighing less than 1.7 lb. at birth were excluded from the study, as they were considered non-viable piglets. Standard operating procedures were followed.

In the first analysis of the data, litters were divided into three categories based on number born alive: less than 10, 10 to 13 and more than 13, resulting in mean litter sizes of 9.3, 12.9 and 15.0 (Table 1).

Table 1 shows the performance of pigs from the three litter size categories. Birth weight declined as litter size increased; however, of particular interest is the fact that the variation in birth weights (standard deviation) was similar across litter size groups. In other words, as litter size increased, birth weight declined but the variation in birth weight was unaffected. Indeed, throughout the growout period, there was no increase in body weight variation due to litter size. And, by the end of the nursery phase, there was no difference in body weight due to litter weight either.

Although the data are not shown, there was no difference in any carcass parameters, such as dressing percentage, backfat thickness, loin thickness or estimated lean yield.

A subset of 24 litters was selected for detailed carcass and pork quality analysis. Within each of the 24 litters, piglets were chosen in each of four birth weight quartiles: 1.65 to 2.64 lb., 2.75 to 3.20 lb., 3.31 to 3.75 lb., and 3.85 to 5.50 lb.

When the data were divided according to birth weight, there were differences in weights at all ages, culminating in average days to market of 159, 155, 152 and 150 days for the four increasing birth weight categories, respectively. However, there were no differences in dressing percentage, loin thickness, backfat thickness and estimated lean yield.

Similarly, there were no differences in more detailed carcass quality measurements, such as color, pH, cooler losses, fat firmness, total lean, total bone or total fat. Taste panel evaluation also found no difference in such parameters as tenderness, palatability and juiciness. There was a tendency for lower flavor desirability scores in the intermediate birth weight piglets.

Overall, these data suggest that concerns regarding increasing sow productivity leading to greater variation in growth rates or inferior eating quality of pork are unfounded.

Also of interest, we observed different results if the performance data were summarized according to litter size or by birth weight. Differences observed as a result of lower birth weight was not seen when litter size was considered.

While there is obviously a biological limit to the productive capability of the sow, current levels of performance indicate that such a limit has not yet been reached, at least in terms of animal growth performance, carcass composition or pork eating quality.

Researchers: John Patience, Denise Beaulieu, Prairie Swine Centre; Jennifer Aalhaus, Lacombe Research Centre. Contact Patience by phone (306) 667-7442 or e-mail john.patience@usask.ca.