Thirty female Large White £ Landrace pigs (average weight 57·2 (SD 1·9) kg) were allocated to one of six dietary treatments containing 0, 1·25, 2·5, 5·0, 7·5 or 10·0 g 55 % conjugated linoleic acids (CLA) isomers (CLA-55)/kg diet and fed for 8 weeks. Each pig was scanned at 0, 28 and 56 d and again at post slaughter using dual-energy X-ray absorptiometry (DXA) to determine the temporal pattern of body composition responses. Values determined by DXA were adjusted using regression equations generated from validation experiments between chemically and DXA-predicted values. Overall, there was a significant linear reduction in fat content with the increasing levels of CLA in the diet (P¼0·007, P¼0·011, P¼ 0·008 at week 4, week 8 and for the carcass, respectively). The greatest improvement was recorded at the early stages of CLA supplementation and for the highest dose of CLA (week 4, 219·2 % compared with week 8, 2 13·7 %). In the first 4 weeks of feeding CLA, pigs receiving 10 g CLA-55/kg diet deposited 93 g less fat/d than pigs fed basal diets (P¼0·002) compared with only 6 g less fat than control animals in the final 4 weeks. Lean content and lean deposition rate were maximised at 5 and 2·5 g CLA-55/kg diet for the first 4 weeks (P¼ 0·016) and the final 4 weeks of treatment ðP ¼ 0·17Þ; respectively. DXA estimates of bone mineral content and bone mineral density were not affected by CLA supplementation throughout the experiment. These data demonstrate that dietary CLA decreases body fat in a dose-dependent manner and that the response is greatest over the initial 4 weeks of treatment.Conjugated linoleic acid: Dual-energy X-ray absorptiometry: Body composition: Pig Conjugated linoleic acid (CLA) represents a mixture of positional and geometric isomers (18 : 2n-6) of linoleic acid with conjugated double bonds located at positions 7,9-, 8,10-, 9,11-, 10,12-or 11,13-on the C chain. CLA exerts many positive health effects in experimental models including anticarcinogenic and anti-tumorogenic as well as anti-atherogenic and antidiabetogenic properties (for reviews, see Whigham et al. 2000;Pariza et al. 2001). Another biological effect of CLA relates to fat accretion and nutrient partitioning. Dietary CLA supplementation reduces body fat mass in rodents (Chin et al. 1994;Park et al. 1995;DeLany et al. 1999) and pigs (Ostrowska et al. 1999). These findings were based on experiments involving slaughter and subsequent chemical analysis in which the ultimate rates of change in body composition were determined at the conclusion of CLA supplementation. However, little is known about the longitudinal effects of CLA supplementation on body composition and generation of such data requires killing large numbers of animals at various stages of development. Alternatively, body composition can be measured in live animals and carcasses using dual-energy X-ray absorptiometry (DXA) (Mitchell et al. 1998;Lukaski et al. 1999;Suster et al. 2000), which is non-invasive and allows longitudinal studies in the same animal. The DXA apparatus can...

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Two hundred and twenty-four pigs (112 boars, 112 gilts) housed in pens of seven pigs per pen were used in a 2 x 2 x 2 factorial design, with the factors of vaccination with a gonadotropin-releasing factor (GnRF) vaccine (Improvac; 0 or 2 mL at 13 and 17 wk of age), porcine somatotropin (pST; 0 or 5 mg/d from 17 wk of age), and gender. Pigs were weighed and feed intake was measured from 17 wk of age until slaughter at 21 wk of age. Body composition was estimated by dual-energy X-ray absorptiometry in two focus pigs per pen at 17 and 21 wk of age. Testes and ovary weights at slaughter were decreased by Improvac treatment (P < 0.001), but were not altered by pST treatment (P > 0.44). Daily gain was lower for gilts than boars (1,128 vs. 1,299 g/d, P < 0.001) and was increased by pST (1,172 vs. 1,255 g/d, P = 0.003) and Improvac (1,150 vs. 1,276 g/d, P < 0.001) treatments. Feed intake (as-fed basis) was lower in gilts than in boars (2,774 vs. 3,033 g/d, P = 0.002), was decreased by pST (3,037 vs. 2,770 g/ d, P = 0.002), and was increased by Improvac treatment (2,702 vs. 3,105 g/d, P < 0.001). As a result of the differences in feed intake and daily gain, feed conversion efficiency (gain:feed) was lower for gilts than for boars (0.403 vs. 0.427 P = 0.025), was improved by pST (0.385 vs. 0.452, P < 0.001), but was unchanged by Improvac treatment (0.423 vs. 0.410, P = 0.22). Carcass weight was lower in gilts than in boars (75.3 vs. 77.0 kg, P = 0.012), was unchanged by pST treatment (75.9 vs. 76.4 kg, P = 0.40), and was increased by Improvac treatment (75.1 vs. 77.2 kg, P = 0.003). Lean tissue deposition rate was lower in gilts than in boars (579 vs. 725 g/d, P < 0.001), was increased by pST (609 vs. 696 g/d, P < 0.001) and by Improvac treatment (623 vs. 682 g/d, P = 0.014). Fat deposition rate tended to be lower in gilts than in boars (214 vs. 247 g/d, P = 0.063), decreased by pST treatment (263 vs. 198 g/d, P < 0.001), and increased by Improvac treatment (197 vs. 264 g/d, P < 0.001). For pigs treated with both pST and Improvac, daily gain and lean tissue deposition rate was greater than for pigs that received either treatment alone, whereas fat deposition rate and feed intake did not differ from untreated control pigs. In conclusion, Improvac increased growth rate through increased lean and fat deposition, but concomitant use of Improvac and pST increased lean gain above either alone, while negating the increase in fat deposition in pigs treated with Improvac.

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Fifty-six individually penned boars (initial weight 64 kg) were used to investigate the interactions between dietary betaine, dietary energy, and porcine somatotropin (pST) treatment. The study was a 2 × 2 × 2 factorial experiment with the respective factors being dietary betaine (0 or 1.5 g/kg) and energy level (80% or 100% ad libitum) and treatment with pST (0 or 5 mg/day). A Hologic QDR4500A Dual Energy X-ray Absorptiometer (DXA) was used to determine body composition of pigs at the beginning and end of the study at Day 35. After slaughter, the composition of the whole half-carcass as well as the shoulder, ham, belly, and loin primal cuts was determined with DXA and verified with manual dissection. The main effects of dietary betaine were most pronounced when dietary energy was restricted. Under these conditions, daily gain was increased by dietary betaine (1188 v. 1271 g/day, P = 0.049) and pST (1115 v. 1344 g/day, P < 0.001). When dietary energy was restricted, lean tissue deposition was increased by dietary betaine (830 v. 908 g/day, P = 0.032) and pST (764 v. 974 g/day, P < 0.001), and these effects were additive. As a result, the lean meat yield in the half-carcass was increased by both dietary betaine (23.9 v. 25.1 kg, P = 0.043) and pST (23.3 v. 25.7 kg, P < 0.001). Lean tissue responses in primal cuts were more variable but followed a similar pattern. There was little effect of either dietary betaine or pST on fat deposition. These data demonstrate that when energy intake is limiting the potential for growth (as is normally the case for the improved boar), then both dietary betaine and pST treatment, either alone or in combination, can increase lean tissue deposition without increasing fat deposition.