The influence of maternal nutrition on muscle fiber number development in the porcine fetus and on subsequent postnatal growth

In the pig, undernutrition in utero causes low birth weight, a decrease in muscle fiber number, and a reduction in postnatal growth rate. The effect on fiber number is mediated via a reduced secondary fiber population. Within a litter of pigs, lighter-weight pigs have probably suffered some deficit in muscle fiber number. In an attempt to improve the number of fibers in the lighter-weight pig fetuses, four maternal feeding regimens were used, one serving as the control. Maternal feed intake was doubled for one of three time periods during pregnancy: 1) d 25 to 50 (HE) immediately before fiber hyperplasia; 2) d 50 to 80 (HL) during fiber hyperplasia; or 3) d 25 to 80 (HT) covering both developmental events. Controls were fed at levels routinely used for pregnant sows on the farm. Sows farrowed normally and pig birth weights were recorded. Estimates were made of total myofiber number, total primary fiber number, and mean secondary:primary fiber number ratio (S:P) for the semitendinosus of each pig at 5 wk postnatal or 80 kg (HT and two control litters only). The progeny of all supplemented sows had a significantly greater mean S:P ratio (P < .05), and the HE pigs tended to have a greater number of muscle fibers than control pigs (403,840 +/- 8,197 vs 370,970 +/- 12,720). Postnatal growth rate to 80 kg was also investigated for the HT group of pigs. The HT pigs had a faster growth rate from d 70 to slaughter at 80 kg (924.4 +/- 18.75 g/d vs 840.1 +/- 17.48 g/d, P = .017) and an increased gain:feed ratio (.433 +/- .011 vs .401 +/- .007, P = .025) compared with controls. These results suggest that the mean number of secondary fibers formed in a litter of pigs can be improved by increasing maternal feed intake during d 25 to 50 of gestation. This may have additional benefits in terms of improved growth rate and growth efficiency in the latter stages of pig growth to 80 kg.