Genetic and phenotypic parameters and correlated responses in performance test traits were estimated for populations of Large White (LW) and British Landrace (LR) pigs tested in Edinburgh andWye respectively, to four generations of divergent selection for lean growth rate (LGA), lean food conversion (LFC) and daily food intake (DFI) with ad-libitum feeding. There were differences between the two populations in genetic parameters, as LW heritabilities for growth rate, daily food intake and backfat depths were higher and the correlation between growth rate and backfat was positive for LW, but negative for LR. However, heritabilities, genetic and phenotypic correlations were generally comparable between selection groups, within each population. Genetic and phenotypic correlations indicated that animals with high daily food intakes were faster growing, had positive residual food intakes (RFI), were fatter with higher food conversion ratios. RFI was highly correlated with daily food intake and food conversion ratio, but phenotypically independent of growth rate and backfat, as expected. Selection for LGA, in LW and LR populations, increased growth rate (54 and 101 g/day), but reduced backfat (-3-9 and -2-0 mm), food conversion ratio (-0-23 and -0-25) and total food intake (-11-8 and -12-6 kg). There was no change in daily food intake in LW pigs (-19 g/day), but daily food intake increased in the LR pigs (69 g/day). With selection for LFC in LW and LR populations, there was no response in groivth rate (9 and 9 g/day), but backfat (-4-1 and -2-1 mm), total (-6-6 and -11-8 kg) and daily food intake (-90 and -172 g) were reduced, as animals had lower food conversion ratios (-0-13 and -0-22). LW and LR pigs selected for DFI ate more food in total (6-8 and 5-9 kg) and on a daily basis (314 and 230 g), grew faster (94 and 51 g/day) and had higher food conversion ratios (0-12 and 0-13). Backfat was increased in LW pigs (3-7 mm), but not in the LR population. In general, efficiency of lean growth was improved by increasing groivth rate, with little change in daily food intake from selection for LGA, but was primarily due to reduced daily food intake with selection on LFC.

Increasing amounts of sewage sludge will be applied to agricultural land over the next 10 years as a result of the prohibition of its disposal to the sea. The addition of potentially toxic elements (PTEs) to the soil via sewage sludge is controlled by European legislation designed to limit the accumulation of PTEs in soil which could give rise to toxicity to plants or livestock. However the possibility exists that direct ingestion of sewage sludge and soil together with grazed herbage may result in accumulation of PTEs in body tissues. To assess the extent of accumulation of PTEs by direct ingestion of soil and sewage sludge 12 groups of housed weaned lambs were given diets ad libitum comprising dried grass (900 g/kg total diet dry matter (DM)) and three different soils (100 glkg total diet DM). Soil was replaced by dried digested sewage sludge at levels ofO (level 0), 75 (level 1), 150 (level 2) and 300 g/kg soil DM (level 3). Voluntary intake of DM was markedly depressed by the inclusion of sewage sludge in the diet (on average by 24 g DM per g sewage sludge DM addition). There was no effect of sewage sludge on diet apparent digestibility. Live-weight gain was depressed (P < 0·001) by the addition of sewage sludge to the diet from 236 glday (level 0) to 141 glday (level 3). Liver and kidney weights were also reduced (P < 0·01). The apparent availability coefficients for Cd, Pb and Cu increased with increasing level of sewage sludge in the diet fP < 0·05), as did their concentrations in the liver and kidney (P < 0·01). Concentrations of Cd and Pb in liver increased from <0·07 mg/kg DM and <0·40 mg/kg DM (level 0) respectively to 0·61 mg/kg DM and 4·60 mg/kg DM (level 3) respectively at the end of the trial. Similarly the concentrations of Cd and Pb in kidneys increased from 0·19 mg/kg DM and <0·56 mg/kg DM (level 0) respectively to 0·80 mg/kg DM and 7·10 mg/kg DM (level 3) respectively by the end of the trial. No increases were observed in concentrations of Cd or Pb in muscle tissue. The main effect of type of soil on concentrations of PTEs in body tissues was not significant The daily rate of accumulation ofPb in kidney ranged from 1·1 to 51·5 uglg daily tissue DM growth during the first 57 days of the experiment and from 0·33 to 6·78 /xg/g daily tissue DM growth between day 57 and day 112. A decrease in the second period was also observed for Cd, with accumulation in kidney ranging from 0·31 to 4·44 fig/g daily tissue DM growth during the first 57 days and from 0·21 to 1·44 /jg/g daily tissue DM growth between day 57 and 112. Concentrations of Pb in liver of lambs given the highest level of sludge approached the statutory limit set for human food. The results indicate that in relation to accumulation of PTEs in liver and kidney there would appear to be little margin of safety with respect to the current United Kingdom statutory limits for the concentrations of Cd and Pb in sludge-amended soils. Confirmation of these results is required in the grazing situation.

Responses to four generations of divergent selection in pigs for lean growth rate (LGS) with restricted feeding were studied. The selection criterion was designed to obtain equal correlated responses in growth rate and carcass lean content, measured in phenotypic s.d. Animals were to be performance tested in individual pens with a mean starting weight of 30 kg for a period of 84 days. Daily food intake was equal to 0-75 gig of the daily food intake for pigs offered food ad-libitum. In the high, low and control lines, there ivere 1250 Large White-Edinburgh (LW) pigs and 875 British Landrace-Wye (LR) pigs. Each selection line consisted of 10 sires and 20 dams, with a generation interval ofl year. After four generations of selection, cumulative selection differentials were 5-9 and 4-8 phenotypic s.d. for LW and LR populations, with similar responses, 1-8 (s.e. 0-17) phenotypic s.d. Mean weight at the end of test, growth rate and backfat depths at the shoulder, mid back and loin were 89 kg, 712 g/day, 26,13 and 13 mm for LW and for LR pigs were 87 kg, 683 g/day, 28,10 and 10 mm. High line pigs were heavier at the end of test (4-3 (s.e.d. 1-4) kg and 4-0 (s.e.d. 1-6) kg) for LW and LR populations, with corresponding responses in growth rate (54 (s.e.d. 16) g/day and 47 (s.e.d. 18) g/day). Responses in the three backfat depths were -4-1 (s.e.d. 1-2) mm, -2-6 (s.e.d. 0-7) mm and -2-9 (s.e.d. 0-7) mm for LW and -2-2 (s.e.d. 0-05) mm, -2-2 (s.e.d. 0-4) mm and -2-4 (s.e.d. 0-5) mm for LR populations. Responses in weight off test and backfat depths were symmetric about the control lines. Heritabilities for LGS were 0-34 and 0-28 (s.e.d. 0-5) for the LW and LR populations, when estimated by residual maximum likelihood. Common environmental effects for LGS were 0-11 (s.e. 0-03) for LW and 0-17 (s.e. 0-04) for LR. Heritabilities for growth rate and average backfat depth were similar for , as were common environmental effects (0-10 s.e. 0-04). Average phenotypic and genetic correlations between growth rate and backfat, for LW and LR populations, and -0-06 (s.e. 0-16), respectively).Responses to selection and genetic parameter estimates demonstrate that there is substantial genetic variation in growth and fat deposition when pigs are performance tested on restricted feeding.

Carcass composition was measured after six generations of divergent selection for lean growth rate on ad-libitum and restricted feeding, lean food conversion and daily food intake in populations of Large White (LW) and Landrace (LR) pigs. There were 161 half-carcass dissections in LW pigs and for LR pigs, a double sampling procedure combined information from 53 half-carcass and 53 hand joint dissections. The performance test started at 30 kg and finished at 85 kg with ad-libitum feeding and after 84 days with restricted feeding, and pigs were slaughtered at the end of the test.In the LR population, selection for lean growth on restricted feeding increased carcass lean content (605 v. 557 (s.e.d. 19) g/kg), but there were no significant responses in carcass lean content with the selection strategies on adlibitum feeding. Selection for lean food conversion and high lean growth on restricted feeding reduced carcass fat content (201 v. 241 (s.e.d. 14) and 150 v. 218 (s.e.d. 18) g/kg), but selection for high lean growth rate with adlibitum increased carcass fat content (212 v. 185 (s.e.d. 11) g/kg). Responses in carcass composition were not significant with selection on daily food intake.In the LW population, selection for high lean food conversion or low daily food intake increased carcass lean content (539 v. 494 and 543 v. 477 (s.e.d. 11) g/kg) to a greater extent than selection on lean growth rate (509 v. 475 g/kg). Responses in carcass fat content were equal and opposite to those in carcass lean content. Selection on lean growth rate with ad-libitum feeding increased lean tissue growth rate (LTGR) (491 v. 422 (s.e.d. 23) g/day), but there was no change in fat tissue growth rate (FTGR) (206 v. 217 (s.e.d. 15) g/day). In contrast, FTGR was reduced with selection on lean food conversion (169 v. 225 g/day), but LTGR was not significantly increased (520 v. 482 g/day). Selection for lean growth rate with restricted feeding combined the desirable strategies of lean growth rate on adlibitum feeding and lean food conversion, as LTGR was increased (416 v. 359 (s.e.d. 12) g/day) and FTGR decreased (126 v. 156 (s.e.d. 7) g/day). The preferred selection strategy may be lean growth rate on restricted feeding, which simultaneously emphasizes rate and efficiency of lean growth.For ad-libitum fed LW pigs, coheritabilities for growth rate, daily food intake and backfat depth with carcass lean content were negative (-0·12, -0·22 and -0·50 (s.e. 0·05), but positive with carcass subcutaneous fat content (0·22, 0·24 and 0·50), when estimated from six generations of performance test data and carcass dissection data in generations 2, 4 and 6.