Growth characteristics of pigs predicted by means of asymmetric s-curve

The present study was performed on 24 pigs distributed over two MHS-genotypes (NN, Nn) and two feeding regimes (intensive, restrictive). These pigs were investigated as the last of four trials in the experiment carried out by Kušec et al. (2005). The data on muscle and fatty tissue volumes were obtained by means of Magnetic Resonance Imaging (MRI). For the growth depiction and for the predictions of live weight as well as of muscle and fat tissue, four models developed by Kušec et al. (2007) were used. These models were set up on the basis of the general form of asymmetric S-function. This function seemed to fit well to the data collected in the present study; but the inaccuracy of the models appeared to increase with age. At the age of 124 days, the estimated values of live weight, muscle and fat volumes were close to the actual values measured in the group of intensively fed pigs; in the group of restrictively fed pigs live weight and muscle volume were underestimated while the volume of fat was overestimated. At the time of the last MR imaging (154 days of age), live weight and muscle volume was to some extent overestimated in the pigs fed intensively and underestimated in those fed restrictively. The volume of fatty tissue was estimated with favourable accuracy in all investigated groups of pigs. For further predictions, two approaches were used. In the first approach to predict individual live weights, at the age of 124 days, the predictions were fairly accurate for most of the pigs, falling in the range within one week; 4 of them being estimated falsely by more than ±7 days. Generally, when expressed as absolute value, the average misestimate was ~4 days in all groups, except for the restrictively fed MHS-gene carrier pigs which were estimated with 6 days difference on the average. At the age of 154 days, the predictions were to some extent less accurate; 7 pigs (in total) were incorrectly predicted by more than a week. The prediction accuracy was lower in the intensively fed pigs, ~6 days on the average; in the restrictive group of pigs, misestimates of live weight predictions were on the average ~4 and ~5 days for NN and Nn genotypes, respectively. Finally, in the second approach, the time that particular group of pigs would need to achieve a predetermined live weight of 100 kg was calculated. The closest prediction was achieved in the group of intensively fed MHS-homozygous negative pigs (4 days) while other groups were estimated with 6 days divergence from the actual age at 100 kg live weight. It was concluded that the predictions made by means of asymmetric S-function were fair enough for a pig producer to make a fattening plan or some other important decisions, e.g. in selection on growth traits.