1.Nitrogen balance (NB) was determined in entire male pigs weighing 75.6 (SE 0.56) kg and given 1.43 MJ metabolizable energy (ME)/kg live weight (LW)n'75 per d of semi-synthetic liquid diets which vaned in crude protein (N x 6.38):ME from 2.5 to 14.5 g/MJ. Maximum NB of 20.8 g/d was reached with diets containing at least 6.2 g protein/MJ ME.2. The relation between energy intake and NB was then examined in pigs of comparable live weight (mean 73.8 (SE 0.39) kg) and receiving a liquid diet not limiting in protein. The diet, containing 10.0 g protein/MJ ME, was given at eight rates from 0.24 MJ ME/kg LW0'5 per d to ad lib. by approximately equal increments. Two animals were allocated to each level and two animals were fasted during the balance period. Nitrogen utilization in animals can be studied using either short-term experiments measuring N intake (NI) and N losses (balance studies) or experiments involving the slaughter of animals at the beginning and at the end of longer-term treatment periods. The former provides an estimate of N balance (NB) at a specific live weight (LW) whereas the latter provides an estimate of N retention (NR) which is the mean value for a considerable weight range. In the present paper, the terms NB and NR are used to distinguish between results derived from balance and slaughter experiments respectively.The relation between energy intake and N utilization in the growing pig and the extent to which it is modified by stage of growth, sex and strain of pig is unclear. On the basis of limited information involving results from balance and slaughter experiments, the Agricultural Research Council (1 98 1) concluded that the relation between energy intake and NR was probably linear. However, it was pointed out that most information was derived from young animals, that few experiments of appropriate design had been reported, and that the relation may be affected by the variables mentioned previously. While subsequent evidence supports the view that, in pigs weighing less than 20 kg, N R responds linearly to energy up to high intakes (Campbell & Dunkin 1983a,b), the relation in heavier pigs remains unclear.The experiments reported involved pigs of approximately 75 kg LW. Dietary protein : energy necessary for maximum NB in pigs receiving a high-energy intake was first established. The response to increasing intakes of metabolizable energy (ME) was then determined using a diet that was not limiting in protein. M E T H O D S A N D M A T E R I A L SIn two experiments, NB was determined in Large White, entire male pigs given semi-synthetic liquid diets and held in metabolism crates. Room temperature was maintained close to 22 O.

Data from 54 hybrid (mainly Large White x Landrace) pigs (18 boars, 18 gilts, and 18 barrows) were used to quantify and mathematically describe the differential growth and development of body components of live pigs. The pigs were 32.4 +/- 3.2 kg of BW and 70 +/- 1 d of age (mean +/- SD) at the beginning of the study, were individually penned and fed ad libitum, and were weighed weekly. Computed tomography (CT) imaging was used to determine the weights of lean, fat, bone, and skin tissue in the live pig at 30, 60, 90, 120, and 150 kg of BW. For each target BW, the sum of all the weights of the body components, as assessed by CT, was referred to as CT BW. Linear and nonlinear models were developed to evaluate the patterns of growth and development of each body component relative to CT BW. The correlation between the actual BW and CT BW was close to unity (r = 0.99), indicating that CT scanning could accurately predict the BW of pigs. Across sex and castrate status, percentage of fat (fat weight/CT BW) in the pig was least (11.2%) at the 30-kg target BW and continued to increase to 22.6% by the 150-kg target BW. Percentage of lean, however, was greatest (67.2%) at the 30-kg target BW and continued to decrease to 53.4% by the 150-kg target BW. The sex or castrate status x target BW interaction was significant (P < 0.05) for all the body components, indicating that the developmental patterns were different among sex or castrate status. Barrows were fatter relative to gilts, which in turn were fatter than boars. For lean, the observed pattern for sex or castrate status differences was opposite that for fat. To predict responses to management strategies on growth and development in pigs, accurate mathematical models are required, and the results of this study indicate that the nonlinear (e.g., augmented allometric and generalized nonlinear) functions provided better descriptions of the growth and development of most body components of the live pig than did the simpler (e.g., linear and allometric) models.

Data from 53 hybrid (mainly Large White × 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.

A system for rapid freezing and containment of pasture and forage samples in the field is described. Core temperatures of pasture samples of 2–5 kg mass can be reduced to below 0°C in a few minutes using liquified carbon dioxide in the ratio of 1 to 2 kg carbon dioxide to 1 kg of green plant material. Changes in the pH of the plant extract were very small (ca. 0 1 pH unit). The system is especially suitable for use in areas remote from normal laboratory facilities, where rapid freezing of herbage samples is essential.