Abstract:
Data from 53 hybrid (mainly Large White x Landrace) pigs, comprising 18 males, 18 females and 17 castrates, were used to examine the relationships among growth and feed efficiency traits measured in the growing animal, and their relationships with body composition and carcass traits at two target liveweight (90 and 120 kg) endpoints. The data were from individually penned pigs involved in a longitudinal experiment that started when the pigs were 32.4 ± 3.2 kg liveweight and 70 ± 1 days of age (mean ± s.d.). Weekly feed intake and liveweight, and body components data measured at 60, 90 and 120 kg by computed tomography scanning were used. Growth traits studied were: start of test liveweight, average daily gain (ADG), Kleiber ratio and relative growth rate. The feed efficiency traits were daily feed intake (DFI), feed conversion ratio (FCR) and residual feed intake. Body components and carcass traits were the weight of the body components (lean, fat, bone and skin tissues) and their percentages relative to liveweight. Three models were used for residual feed intake. The standard model (RFIstd) had metabolic weight and ADG as explanatory variables for feed intake, RFIadg had only ADG as explanatory variable, and the other (RFIfat) had percentage fat at 60 kg target liveweight included in the standard model. The RFIadg model resulted in R2 values of 36.9, 72.1 and 19.1% for males, females and castrates, respectively. The corresponding R2 values for the RFIstd model were 63.7, 72.1 and 37.1%, and those for the RFIfat model were 86.1, 80.0 and 71.9%. These results indicate that RFIfat may be a better trait to use for efficiency of feed utilisation, especially in castrates. There were significant interrelationships among growth traits (r = –0.46 to 0.98), and also among feed efficiency traits (r = 0.44 to 0.76). Of the feed efficiency traits studied, only FCR was significantly correlated with all the growth traits (r = 0.33 to –0.61), and DFI was correlated with start liveweight (r = 0.43) and ADG (r = 0.57). Growth traits per se were not correlated with body composition and carcass traits at each of the weight-constant target endpoints; however, feed intake was. High DFI was associated with high percentage fat (r = 0.39 to 0.49) and low percentage lean (r = –0.40 to –0.52) at both 90 and 120 kg target liveweights. As with DFI, high FCR, RFIadg and RFIstd were associated with high percentage fat and low percentage lean at both 90 and 120 kg target liveweights. There were no significant correlations between RFIfat and the body components and carcass traits. These results will enable the development of programs aimed at reducing feed costs and improving the economic value of the pig carcass.