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 decreas e in muscle fiber number, and a reduction in postnatal growth rate. Th e effect on fiber number is mediated via a reduced secondary fiber pop ulation. Within a litter of pigs, lighter-weight pigs have probably su ffered some deficit in muscle fiber number. In an attempt to improve t he number of fibers in the lighter-weight pig fetuses, four maternal f eeding regimens were used, one serving as the control. Maternal feed i ntake 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 develo pmental events. Controls were fed at levels routinely used for pregnan t 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 sign ificantly 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 sug gest that the mean number of secondary fibers formed in a litter of pi gs can be improved by increasing maternal feed intake during d 25 to 5 0 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.