Abstract
Twin sheep fetuses have reduced skeletal muscle weight near birth relative to singles as a result of restricted muscle hypertrophy. Intracellular free amino acids (FAA) are reported to regulate metabolic pathways which control muscle protein accretion, whereby reduced intracellular content of specific FAA may reduce their activation and therefore, muscle hypertrophy. The aim of this study was to determine whether differences in muscle weight between singleton and twin fetuses, under different maternal conditions is associated with reduced concentration of specific FAA. The FAA content in the semitendinosus muscle (ST) in singleton and twin fetuses (rank) at 140 days of gestation from heavy (H) or light (L) ewes fed ad libitum (A) or maintenance (M) level of nutrition was measured. Muscle weight was reduced in twin fetuses compared to singletons in all groups. Reduced concentrations of leucine, threonine and valine, but higher concentrations of methionine, ornithine, lysine and serine were found in twin fetuses compared to singletons. Maternal size and nutrition interaction with rank resulted in reduced glutamine in twins from HM-ewes (H-ewes under M nutrition) compared to their singleton counterparts. Maternal weight interaction with pregnancy rank reduced the concentration of arginine in twins, with a larger effect on H-ewes compared with L-ewes. Maternal size interaction with pregnancy rank resulted in twins from M-ewes to have lower alanine, while twins from A-ewes had lower aspartic acid concentration compared to singletons. The ST muscle weight was positively correlated only with arginine concentration after taking into account rank, size and nutrition. The present results indicate that reduced concentrations of specific intracellular FAA, such as arginine, leucine, valine, glutamine, which are known to play a role in muscle growth, could be acting as limiting factors for muscle hypertrophy in twin fetuses during late gestation. Ewe size and nutrition can influence the concentration of specific FAA in muscle and should be considered in any intervention plan to improve twin fetal muscle growth.
Highlights
Increasing prolificacy is an effective way to improve profitability in sheep production systems (Gootwine et al 2001)
The present results indicate that reduced concentrations of specific intracellular free amino acids (FAA), such as arginine, leucine, valine, glutamine, which are known to play a role in muscle growth, could be acting as limiting factors for muscle hypertrophy in twin fetuses during late gestation
A three-way interaction between pregnancy rank, maternal size and plane of nutrition was observed for semitendinosus muscle (ST) intracellular concentrations of free glutamine and tyrosine (Table 1)
Summary
Increasing prolificacy is an effective way to improve profitability in sheep production systems (Gootwine et al 2001). Birth weight, postnatal survival, growth, body composition and lifetime production performance may be reduced as litter size increases (Barker 1998; Greenwood et al 1998; Morel et al 2009). Reduced fetal weight near term in twins compared to singletons is associated with decreased skeletal muscle. Animal Nutrition Team, Animal Nutrition and Health Group, AgResearch, Grasslands Research Centre, Palmerston North, New Zealand. Gravida: National Research Centre for Growth and Development, Auckland, New Zealand. Maternal undernutrition has a direct effect on fetal and skeletal muscle growth during gestation (Fahey et al 2005), reduced fetal weight and muscle weight in twins compared to singles is observed even in well-nourished ewes This suggests maternal nutrition is not the only factor to impact fetal and muscle growth as litter size increases.
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