Time trends of Gompertz growth parameters in ‘meat-type’ pigs

Abstract

Previously published data from serial slaughter trials on growing pigs of five genotypes were reanalysed. Gompertz curves were fitted to body protein and lipid mass in order to estimate mature protein and lipid mass (P∞,L∞) and the rate parameter (BGompJ that was presumed to be equal for the protein and lipid curves.L∞was expressed as its ratio toP∞, RL∞P∞. The maximum rate of protein deposition was derived as Pdep,max= P∞X BGomp/e. The analysed data encompass body weights of 10 to 133 kg, 13 to 217 kg, 18 to 106 kg, 20 to 110 kg and 11 to 145 kg. The Gompertz function fitted all data sets well, as judged by the standard deviations and distribution patterns of the residual terms. Autocorrelations among the residuals were non-significant.Averaged over sexes (females and entire and castrated males), the P estimates were all close to 31 kg; the RL∞/P∞estmates ranged from 1·4 to 4·7 kg/kg; the BGompestimates ranged from 0·009 to 0·017 kg/day per kg. The resulting Pdep,max estimates ranged from 110 to 193 g/day. The genotypes were placed in 1969, 1976, 1984, 1990 and 1993. Plotting the estimates against time (year) showed distinct time trends for all parameters except P∞. RL∞/P∞seems to gradually reach a plateau around unity, whereas BGompand Pdep/max increase linearly. These trends were confirmed by an analysis of body weight based on the same data plus data on three other genotypes that spanned the same time period. Analyses of the same protein and lipid data to fit a sigmoid growth function with a flexible point of inflexion did not change the apparently absent time trend of F. The estimates of the inflexion points of the fitted protein accretion curves, expressed as proportions ofF, were indistinguishable from the fixed 0·368 value of the Gompertz function for the earliest three genotypes and then showed a tendency to increase, up to 0·46 for the 1993 population. These time trends must be the consequence of a combination of changes in nutritional and other environmental factors and genetic changes. They cannot be the sole result of within-line selection for growth and body composition traits, since this should increase P∞. It seems as if pig breeders have repeatedly initiated their sire lines from genetic resources with small mature size, to subsequently increase this trait as an indirect result of within-line selection.

A family of protein growth curves with extension to other chemical body components together with application to animal nutrition and improvement

“…This is much lower than the values calculated for pigs by Knap (2000) from the Bridges equation. In contrast to equation (12), the growth data of Quiniou et al (1996;Table 5) indicate a point of inflection during their period 2, which cannot be reconciled with a value of P/a 5 0.161.…”

“…It therefore seems worthwhile to illustrate the fit of equation (7) on the data of Quiniou et al (1996) in Table 5. Roux (2005a) gives an example in which the fitting of power curves for the description of PB and PS gives estimates of limit or mature protein mass in agreement with the estimates from the fitting of Gompertz curves by Knap (2000). Knap's (2000) collation of data from the literature contains that of Tullis (1981) with some observations very near to maturity.…”

“…Roux (2005a) gives an example in which the fitting of power curves for the description of PB and PS gives estimates of limit or mature protein mass in agreement with the estimates from the fitting of Gompertz curves by Knap (2000). Knap's (2000) collation of data from the literature contains that of Tullis (1981) with some observations very near to maturity. The estimates obtained from Tullis (1981) are well contained within the confines of the total collection of estimates.…”

“…The estimates obtained from Tullis (1981) are well contained within the confines of the total collection of estimates. It seems, therefore, that the somewhat premature truncation of growth records in other cases did not cause any serious bias in Knap's (2000) estimates of protein limit mass. However, Knap's (2000) limit masses show clear sex differences with averages of a 5 26.4 for castrates, a 5 30.3 for females and a 5 32.9 for males, with n 5 3 for both males and castrates and n 5 4 for females, on discarding an outlying male estimate of a 5 38.5.…”

“…With X 1 Z 5 1, the maximum value of the point of inflection is the Gompertz value of P/a 5 0.368 with Y-0. However, fitting a Bridges curve with a flexible point of inflection, Knap (2000) obtained values for the inflection point on modern pig protein growth data, given in Table 4, with inflection points showing an increasing trend above the Gompertz value. On the assumption of Y 5 1/2, equivalent inflection points from equations (7) and (9) will require values of X 1 Z substantially above unity.…”