Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, C24
Prenatal vs. postnatal influences on fat and lean mass in sheep
R. Coleman1, D. Gardner1
1. School of Veterinary Medicine and Science, University of Nottingham, Nottingham, United Kingdom.
It has been suggested that poor prenatal growth may predispose to increased adiposity later in life. In this retrospective analysis, a large cohort of sheep was utilised to interrogate the a priori hypothesis that intrauterine growth restriction leads to fatter adolescent offspring and this effect is modified by their subsequent postnatal growth rate. Data for five flocks of pedigree Suffolk sheep (n=13,630) were available in which multiple variables were recorded as standard (for inclusion in the Signet pedigree database, MLC) including birth weight, weaning weight at 8 weeks of age and weight and body composition at 20 weeks of age. Body composition was assessed in two ways; 1) by ultrasound at the 11th rib by a skilled operator (n=7,671) and 2) by computed tomography (CT, n=220). Postnatal growth was assessed in absolute (g.day-1) or relative (g.day-1.kg-1 birth weight) terms. Data are presented as estimated marginal means ± S.E.M. and were analysed by General Linear Mixed Models using Genstat v11. P<0.05 was accepted as indicating a statistically significant effect. Birth weight or postnatal growth were modelled as continuous or categorical variables; categories conforming to 1kg increments in birth weight from <3kg to >8kg. In this cohort of sheep there was a 5-fold natural variation in birth weight (Mean 5.13, range 2-10). Lambs born relatively small (IUGR, -2S.D. or <3kgs) tended to exhibit postnatal growth acceleration during the first 8 weeks of life only. Ultrasound determined fat mass correlated well with CT determined fat mass (r=0.72, P<0.0001). There was a strong positive relationship between birth weight and/or relative postnatal growth and fat mass at 20 weeks of age (Figure 1). This effect was apparent and similar in both sexes. Adjustment for random effects in the model such as flock and shared genes from either parent (ewe and ram) did not materially affect the conclusions. In a large cohort of sheep, natural variations in birth weight as a result of unknown environmental aetiologies had a pronounced effect on body composition in the young, adolescent offspring. Being born of relatively high birth weight is strongly linked to increased fat mass later in life. Similarly, a tendency to exhibit relative postnatal growth acceleration during early life is also, independently, associated with increased fat mass later in life. The data recapitulate observations in human epidemiological studies suggesting that the early developmental environment is key to determining later body composition; observing similar effects in species with widely different metabolic function and life history gives biological plausibility to programming of later body composition by early environment.
Where applicable, experiments conform with Society ethical requirements