Nutritionally induced adipose hypertrophy in young pigs is transient and independent of changes in the expression of the obese and peroxisome proliferator activated receptor genes

Previous studies have shown that piglets weaned to a liquid milk replacer (MR), rather than a typical dry diet (DD) regimen, have improved growth rates and deposit more energy as body fat. In the present study, we used this model to determine whether changes in the expression of genes linked to the regulation of adiposity were related to the accelerated fat accretion. We also determined whether the increase in body fat was sustained throughout a substantial proportion of the growth curve. At weaning (19 ± 2 days of age), 96 piglets were placed in 12 replicate pens per diet (4 pigs per pen, 2 barrows and 2 gilts), and fed a liquid MR or conventional DD regimen for 5 weeks. Thereafter, 6 barrows and 6 gilts pigs from each diet were killed for determination of whole body chemical composition (less gastrointestinal contents). The remaining pigs were assigned randomly to weight target groups (60, 85, and 110 kg), placed in individual pens, and fed a conventional dietary regimen until killed at their respective weight targets for tissue sampling and determination of whole body chemical composition. Over the 5-week period in which the MR was fed, the growth rate of the pigs consuming the MR exceeded that of the pigs fed the DD by 36% (P < .05). Fat gain in these pigs was increased to 1.8 times that of the pigs fed the DD, and percentage body fat was 45% greater (P < .05). Acetyl Co-A carboxylase (ACC) activity (per mg of adipose extract protein) was not different between the two diet groups at the conclusion of the 5-week period, or at 110 kg body weight. During the MR period, actual protein gain was increased (P < .05) 22% in the pigs fed the MR as well. By 110 kg of body weight, body fat was reduced (P < .05) by 7.7% (total fat mass) and 8.3% (percentage of body weight basis) in the pigs fed MR vs. the DD group. The expression of the peroxisome proliferator activated receptors (PPAR) α and γ was not influenced by diet or by body weight. Expression of the obese gene was independent of diet, but was greater (P < .09) in pigs at 110 kg body weight than at 60 kg. These data provide additional evidence that piglets weaned to liquid diets have greater rates of growth and deposit more body fat, but that this difference subsides quickly when a typical dry dietary regimen is imposed. Furthermore, the biochemical changes responsible for the increased adiposity are independent of changes in the expression of the obese or PPAR genes, at least at the mRNA level.