THE EFFECT OF PONDERAL INDEX ON PLASMA CONCENTRATION OF INSULIN- LIKE GROWTH FACTOR-1 (IGF-1) IN NEONATAL PIGS.

THE EFFECT OF PONDERAL INDEX ON PLASMA CONCENTRATION OF INSULIN- LIKE GROWTH FACTOR-1 (IGF-1) IN NEONATAL PIGS.

J. C. Litten, K. S. Perkins, J. Laws, A. M.Corson and L. Clarke.

Department of Agricultural Sciences, Imperial College London (Wye Campus), Wye, Ashford, Kent, TN25 5AH, UK.

Introduction. Recent evidence has suggested that body shape, rather than birth weight alone, may be a more important diagnostic indicator of future growth and development

. It is well documented that IGF-1 plays an important role in the regulation of growth and energy metabolism. This study examined whether plasma concentrations of IGF-1 were influenced by body shape in neonatal pigs.

Methods. 171 newborn piglets were entered into the study and reared by their mother. Piglets were weaned at 28 days of age and were fed t ad libitum (Growlean OP meal, 14 MJ kg-1, BOCM, UK). Individual body-weight and crown-to-rump length were measured on day 3 of life to enable Ponderal Index (PI: kg/m3) to be calculated. Fat-free mass (FFM) was estimated on day 3 of life via a TOBEC (Total Electrical Body Conductivity) analysing system using the following equation: √(TOBEC reading *CRL). A blood sample was taken from each pig on day 3 and 24 hours prior to slaughter (5-6 months) for subsequent determination of plasma IGF-1 concentration (ELISA kit: DSL-10- 5600). A normal probability test was performed on the PI data to describe the distribution of the pigs (LOW, <10th, n=12: NORMAL, 11-89th, n=128: HIGH,

>90th, n=31). Differences in plasma IGF-1 concentration were assessed using General Linear Model ANOVA with body weight as a covariate; values are presented as mean ±SEM and similar superscripts denote significant differences (a P<0.001; b P<0.001; c, d or e P<0.05). PI (P<0.001) and fat-free mass (P<0.001) were different between all sub-populations (Table 1).

Results. Plasma IGF-1 was elevated in the HIGH group (P<0.01) on day 3 of life but had returned to normal values by 6 m of age. In contrast, IGF-1 approximately doubled (P<0.05) over the first 6 months of life in the LOW group.

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LOW (<10

)

(n=5)

NORMAL (11-89

) (n=96)

HIGH (>90

) (n=15)

PI (kg/m

) 11.5±0.5

15.4±0.1

21.8±0.3

FFM: day 3 (arb units) 333±11

247±3

176±3

IGF-1: day 3 (µg/ml) 66±35

81±8

166±25

IGF-1:5-6 months

(µg/ml)

124±19

93±4 97±13

Conclusions. Body shape at birth has a pronounced influence on the changes in plasma IGF-1 from day 3 to 5-6 months of age. Piglets that are short-for weight (i.e. HIGH PI) in early life have elevated concentrations of IGF-1, which may in part be due to their greater body fat mass. The increasing plasma IGF-1 in LOW PI piglets may be related to catch up growth and enhanced promotion of fat deposition, similar to that seen in human babies that are long and thin at birth.

Keywords. Pigs; shape, growth, IGF1 Funded by DEFRA.

1

Litten J.C. et al. 2002. Early Hum Dev. 66:1, 57-58.

Table 1: PI, FFM and plasma IGF-1 concentration in the different sub-

populations