Temporal growth and development of body tissues of pigs as assessed by X-ray computed tomography

Abstract

Data from 54 hybrid (mainly Large White × Landrace) pigs, comprising 18 male, 18 female and 18 castrated pigs, were used to quantify and mathematically describe the temporal growth and development of body tissues of live pigs. The pigs were 31.1 ± 3.6 kg liveweight (LW) and 70 ± 1 day of age (mean ± s.d.) at the start of the study, were individually penned, fed ad libitum and were weighed weekly. Computed tomography (CT) imaging was used to determine the weights of lean, fat and bone tissues of each pig at five different times during the study, which corresponded to ~30, 60, 90, 120 and 150 kg LW. The highest age and LW achieved by a pig were 31.4 weeks and 166.6 kg, respectively. A nonlinear mixed effects model of Gompertz function with sigmoidal behaviour was fitted to the data for each of the three sexes (male, female and castrate) to study the temporal growth and development of CT LW and the body tissues (lean, fat and bone). The estimate for CT LW at maturity was 237.5, 198.6 and 210.1 kg for males, females and castrates, respectively, and the corresponding prediction for the point of inflection (maximum growth rate) was 87.4, 73.1 and 77.3 kg. The predicted point of inflection for lean tissue was 47.0, 37.5 and 34.3 kg for males, females and castrates, respectively. In general, male pigs were the leanest, and castrates were the fattest, with females in between. Within sex, the ages at the point of inflection for lean tissue and bone tissue were lower than those for CT LW, whereas those for fat tissue were higher than those for CT LW. The percentage of bone tissue in the body generally remained stable with age (e.g. castrates had 9.2 and 9.0% at 14 and 26 weeks of age, respectively), whereas the percentage of lean tissue decreased with age (e.g. castrates had 61.3 and 50.4% at 14 and 26 weeks of age, respectively), and that of fat tissue increased with age (e.g. castrates had 16.8 and 25.8% at 14 and 26 weeks of age, respectively). Accurate mathematical models are required to develop management strategies to optimise pig production. The results of this study indicate that serial data on live pigs generated by CT imaging technology can be used to describe temporal growth and development of LW and body tissues of pigs using sigmoidal growth functions.