Impact of dietary L-arginine supply during early gestation on myofiber development in newborn pigs exposed to intra-uterine crowding

Background: Intra-uterine crowding (IUC) observed in hyperprolific sows impairs myofiber hyperplasia and overall fetal growth. Arginine supplementation (ARG) in gestation diets has been shown to positively affect litter and muscle development. The study objective was to assess whether the effect of ARG on offspring characteristics, with special emphasis on myofiber hyperplasia, differs under IUC conditions from these responses, because in that situation growth retardation is particularly prevalent due to reduced fetal nutrient supply. Unilateral oviduct ligation (OL) was used as a model for an uncrowded and hyperprolificacy (IN) as a model for a crowded intra-uterine environment. Methods: Five OL and five IN sows were fed a diet supplemented daily with either 43 g l-alanine (Ctrl) or 25 g l-arginine from d 14 to 28 of gestation in a cross-over design (two periods: 5^th and 6^th parity). At farrowing, two male and two female offspring, respectively, with a low and intermediate birth weight (BtW) were selected. After euthanization, the Semitendinosus muscle (STM) was removed and weighed, and the light and dark portions (STM_d and STM_l) were prepared for myofiber histochemistry using ATPase staining and the entire STM for gene expression analysis of myogenesis-related genes using RT-qPCR. In addition, various organs were removed and weighed. Data were analyzed using the MIXED model in SYSTAT. Results: No effect of either IUC or dietary treatment was found in litter characteristics. Offspring of ARG sows displayed a greater muscle area in STM (P < 0.01) as a result of the greater myofiber hyperplasia (P < 0.01). The increase was more distinct in the STM_l (P < 0.05) than in the STM_d (P = 0.131). Offspring of OL sows were heavier at birth (P < 0.01), had a heavier STM (P < 0.05), liver (P < 0.01) and kidney (P < 0.05), but when expressed relative to birth weight, these differences were absent. In addition, IUC had an effect (P < 0.05) on the expression of one of the myogenesis-related genes investigated. Conclusions: Independent from the extent of IUC, ARG improved BtW, muscle and organ weights and myofiber hyperplasia in offspring.