Submitted to: Archives of Animal Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 16, 2012
Publication Date: March 20, 2012
Citation: Mitchell, A.D., Ramsay, T.G., Caperna, T.J., Scholz, A.M. 2012. Body composition of piglets exhibiting different growth rates. Archives of Animal Breeding. 55(4):356-363. Interpretive Summary: The neonatal growth period of the pig, from birth to weaning, is a critical phase in pork production. Genetic selection for larger litter size has also resulted in a reduction in mean piglet birth weight, increased within-litter variation in birth weight, and a rise in the proportion of low birth weight piglets within these large litters. In addition to the low birth weight pigs, frequently within a litter there are other pigs that grow at a rate well below the average during the period between birth and weaning. The purpose of the present study was to examine differences in body composition of faster and slower growing pigs, in particular, contrasting the largest and smallest pigs of the litter at weaning and also pigs of the same birth weight but exhibiting differences in growth rate. Results of this study revealed that, at weaning, the fastest and slowest growing pigs had similar proportions of fat, lean, and bone mineral and, consistent with previous results, the rates of both fat and lean deposition were highly correlated (P<0.001) with total body growth rate.Thus, during the period between birth and weaning slower growing pigs, regardless of birth weight, deposited proportionally less fat and more lean when compared to their faster growing littermates.
Technical Abstract: The growth and composition of the neonatal pig is of interest because of potential impact on subsequent growth and finally, composition at market weight. The purpose of this study was to compare at weaning the growth and body composition of the largest and smallest pigs (excluding runts) from each of 38 litters. The pigs used in this study were of a Large White X Poland China X Landrace cross. At weaning (27±1.7d) the entire litter was weighed and the largest and smallest pig was selected for body composition measurement. Body composition was measured by dual X-ray absorptiometry (DXA) scanning which measures total body fat, lean and bone mineral content (BMC) plus bone mineral density (BMD). At birth the pigs that were largest at weaning weighed 21% more than did the pigs that were smallest at weaning (1.64±0.27 vs. 1.30±0.29, P=0.003), however at weaning there was a 33% difference in body weight (BW). At weaning the largest pigs weighed 9.3±1.1 kg compared to 6.2±1.5 kg for the smallest pigs (P<0.001). Also at weaning the body composition of the largest pigs consisted of 0.44±0.28 kg (38%) more fat, 2.55±0.77 kg (32%) more lean, and 57±16 g (29%) more BMC (P<0.001). The largest pigs also had higher BMD (P=0.002). However, when expressed as a percentage of BW, there was no difference in the fat, lean or BMC content of the two groups of pigs (P>0.05). A second study consisted of 12 pairs of pigs from 8 litters. These pigs were selected on the basis of having the same birth weight, but one pig out gaining the other by at least 50 g/day, thus being substantially (>10%) larger than the other at 21 days of age. At 21 days of age the selected pigs were scanned by DXA. For both groups combined, the correlation (r) between BW and lean mass was 0.99, between BW and fat mass it was 0.87, and between BW at birth and BW at weaning it was 0.56. In conclusion, results of this study revealed that, at weaning, the fastest and slowest growing pigs had similar proportions of fat, lean, and bone mineral and, consistent with previous results, the rates of both fat and lean deposition were highly correlated (P<0.001) with total body growth rate.