Growth rates and chemical compositions were measured with ram lambs grazing pure stands of perennial ryegrass, timothy, cocksfoot and tall fescue. A group of lambs slaughtered at the start of the trial enabled estimates to be made of the live-weight gains over the summer and the composition of these gains. The composition of the grass was also measured in samples taken at weekly intervals and estimates were made of the nutrients consumed from the different grass plots.

The quantities of ash, Ca, P and Mg in the empty bodies of the lambs were within the range of published values from similar studies. They support the contention that grass-fed lambs tend to have larger contents of ash, Ca and P in their empty bodies than concentrate-fed lambs of similar weight. Perennial ryegrass provided a superior diet in that lambs eating this grass grew more quickly, with leaner tissues and higher levels of ash, Ca and P in their empty-body gains. Lambs consuming tall fescue grew most slowly but their mineral contents were as large as the ryegrass-fed lambs when data were adjusted for differences in empty-body weight. Lambs fed on timothy or cocksfoot were the most poorly mineralized in spite of consuming considerably more Ca, P and Mg than the lambs on ryegrass. The data suggest that the efficiencies of absorption of Ca and P in ryegrass may be high, at about 0·64 for Ca and 0·71 for P.

The cellular characteristics of dissected carcass (subcutaneous and intermuscular fat) and non-carcass (kidney fat, omental and mesenteric fat) fat partitions were examined at maturity in a total of 34 rams and ewes from flocks of Peppin Merino sheep selected for high (weight-plus) or low (weight-minus) weaning weight and from a randomly bred control flock. Strain and sex effects on the rate of change in adipocyte volume in each fat partition relative to the change in chemical-fat weight in that partition, were examined in 60 immature animals.

Selection for high or low weaning weight had no effect on adipocyte volume in the mature animals, with the increased weight of fat in the weight-plus animals due to an increased number of adipocytes in the dissected fat partitions. Consequently, hyperplasia had a greater contribution to increases in chemical-fat weight in the weight-plus, compared with the weight-minus animals.

Mature ewes had larger and fewer adipocytes in the subcutaneous and intermuscular partitions than the mature rams, whereas there was no difference between the sexes in adipocyte volume in the kidney, omental and mesenteric fat partitions. Mature ewes had fewer adipocytes than the mature rams in the subcutaneous, intermuscular, omental and mesenteric fat partitions. With the exception of the kidney fat partition, there was no sex effect on the relative contribution of hypertrophy to increases in chemical-fat weight of the dissected carcass and non-carcass fat partitions.

Four groups each of 14 sheep aged 11 to 13 months comprising outbred (O) and inbred (I, inbreeding coefficient 0·37 or 0·5) sheep reared on either a low plane (L, maintenance) or on a high plane (H, ad libitum) of nutrition from the age of 6 months were exposed first to acute cold and 1 week later to heat. Exposures in climate chambers ended for each sheep when rectal temperature decreased to 36°C (in the cold) or increased to 42·5°C (in the heat) subject to a limit of 8 h. Throughout the experiment, sheep were kept in matched quartets comprising one sheep of each type.

The average cold resistance times (min) were 161, 267, 348 and 381 for the LI, LO, HI and HO groups respectively, showing a significant effect of both inbreeding and plane of nutrition (P < 0·01). Five sheep in the HO group lasted the full 8 h in the cold chamber with little or no reduction in rectal temperature. Skin temperature at the mid side was significantly higher in L than in H sheep throughout cold exposure, but there was no effect of inbreeding.

Respiration rates were much higher before and during cold exposure in the H sheep, but there was no effect of inbreeding.

The residual correlation of cold resistance with live weight was 0·58, but differences in live weight do not explain all the differences in cold resistance and particularly do not explain the rapid decrease in rectal temperature of the LI sheep. It was concluded that under cold exposure a high level of nutrition was able to compensate partly for the disadvantages of inbreeding, and that outbreeding was able to compensate partly for the adverse effects of poor nutrition.

With heat exposure, there were no significant differences among the four groups in heat tolerance time, but within the 1st h, H sheep had slightly higher rectal temperatures and much higher respiration rates than L sheep. Inbreeding affected only the time taken to reach a respiration rate > 200 per min, which was longer in I (131 min) than in O sheep (113 min) and longer in L (149 min) than in H animals (96 min).

In three separate experiments a total of 144 Greyface ewes was offered direct-cut or wilted silage from week 4 to 5 of pregnancy until lambing with varying levels of concentrate during the last 6 weeks of pregnancy. Wilting resulted in a proportional increase in the intake of silage dry matter of 0·08 on average but, because digestibility of the wilted silages was lower, digestible energy intake of both silages was similar. Average change in ewe live weight from housing until after lambing was not affected by silage type and there was a small, non-significant increase in lamb birth weight on direct-cut silage. There was no evidence of any reduction in silage intake as total concentrate intake over the last 6 weeks of pregnancy increased to about 18 kg, and limited evidence of a reduction at higher levels with some indication of a greater reduction on direct-cut than on wilted silage. Compared with no-concentrate feeding the highest level increased ewe live weight by 252 g/kg concentrate and there was a non-significant effect on lamb birth weight of 13 g/kg concentrate.

The responses to supplements differing in protein concentration and degradability were measured in lactating ewes and their twin lambs when offered fresh ryegrass either cut or grazed. Housed Scottish Halfbred ewes, offered fresh-cut grass ad libitum received no supplement (N) or supplements with barley and maize starch (B); barley and soya-bean meal (S); barley, soya-bean meal and fish meal (SF) or barley and fish meal (F) in weeks 2 to 7 of lactation. By feeding supplements, herbage organic-matter (OM) intake was depressed (2·00 v. 1·74 kg/day). Mean daily milk yield was increased when protein supplements were given and, because milk protein concentration was higher for supplement F and similar for all other diets, mean daily milk protein output increased with increasing fish meal in the diet. Milk yields were N 2·55, B 2·59, S 3·17, SF 3·15 and F 3·17 kg/day. Total milk solids and fat concentrations were also higher for S, SF and F than N or B. Lambs from ewes supplemented with protein grew faster and the ewes generally lost less weight and body condition compared with unsupplemented ewes.

At pasture, Masham ewes grazed at herbage allowances of either 4 (L) or 10 (H) kg OM per day and received no supplement (N) or supplements B or F, for the first 6 weeks of lactation and then, in weeks 7 to 12, grazed without supplements. For NL, BL, FL, NH, BH and FH respectively lamb growth rates from birth to 6 weeks were 235, 242, 274, 267, 286 and 302 g/day; from birth to 12 weeks were 210, 209, 249, 255, 275 and 287 g/day and losses in ewe body-condition score from birth to 12 weeks were 1·28, 1·22, 1·06, 0·97, 0·62 and 0·76.

It is concluded that protein supplements increased milk yield and lamb growth rates and that the response tended to be greater with fish meal.

Eighty crossbred sows, following a standard feeding regime in pregnancy, received daily either 2·0, 3·5. 5·0 or 6·5 kg diet containing 130 g digestible crude protein, 8·0 g lysine and 13·1 MJ digestible energy per kg over a 28-day lactation to produce variation in body fatness and live weight. Sows on the highest level of feeding gained 13 kg and lost some 3 mm backfat between farrowing and weaning; corresponding changes on the lowest level of feeding were –31 kg and –9 mm backfat. Live weight of the litter at weaning was positively related to sow daily food allowance in lactation, but the major benefit of increasing lactation food allowance was in reducing the rate of maternal body weight and fatty tissue loss. These effects were described by the regression equations: maternal live-weight change in lactation (kg/day) = —1·7+0·34 lactation food intake (kg/day); maternal backfat change in lactation (mm LJSP2) = —0·40+0·05 lactation food intake fkg/day). Sows ingesting less food in lactation catabolized proportionately more body tissue to maintain milk yield and piglet growth, although they achieved this imperfectly, having lighter litters at weaning. Calculation of an overall net balance, taking into account the need subsequently to replenish tissues catabolized in lactation and ensuring efficient rebreeding of the sow, favoured a lactation feeding strategy towards ad libitum.

Crossbreeding of desert goat does with the temperate Saanen x Toggenburg buck was found to result in a significant increase in the daily live-weight gain and the empty body weight of their progeny slaughtered at about 30 kg live weight when compared with purebred desert goat kids (P < 0·001). Food intake did not differ between the two types of kids, but live-weight food conversion efficiency was significantly superior in crossbred kids (P < 0·05).

Carcass weight and killing-out proportion tended to be greater in the crossbred kids reflecting lower weights of head, skin, internal organs and gut fill. Breed types did not differ in the weights of individual wholesale cuts. Carcass dissection revealed significantly higher muscle proportion (P < 0·05), significantly lower fat proportion (P < 0·01) and higher muscle: bone ratio in the crossbred kids.

The use of family selection indices has been proposed as a promising selection method for increasing prolificacy in pigs. Responses of up to 0-50 pigs per litter per generation are predicted from selection programmes using information from the dam and from relatives (full and half-sibs) of the dam and sire. In order to test this method in populations of finite size, the rates of selection response and the accumulation of inbreeding have been studied by simulation along 10 generations in a selected herd of 10 sires and 100 dams using five different family selection indices (Id, Ifd, Ihd, Ifs, Ihs). Two undesirable features were evident: (a) the standard deviations of indices were lower than those expected; and (b) the increase of inbreeding was up to three times that expected without selection. Both effects increased with the complexity of the family index reducing the rates of selection responses per generation, when a genetic model with dominance was assumed, to values close to 0·20 piglets, similar to those obtained with the basic index (Id). Some results of inbreeding effects on reproductive traits in three strains of an old closed herd of Iberian pigs are also presented. Multiple regression analysis of data from 4657 litters indicated a decrease in the number of live born ranging from 0·14 to 0·35 piglets per 10% increase in dam or litter inbreeding coefficient.

In a 2 × 2 × 2 × 2 factorial experiment, the effects on reproductive performance of active immunization against androstenedione and of two sward heights in two periods, August to October (period 1) and October to November (period 2), were investigated in 144 Beulah Speckled-face and 146 Brecknock Cheviot ewes. Sward heights of either 5 to 6 cm (2200 kg dry matter (DM) per ha) (high) or 2 to 3 cm (650 kg DM per ha) (low) were achieved by adjustment of stocking rate during period 1. Two groups of ewes were balanced for body condition score across breed and sward height and the ewes of one group were actively immunized against androstenedione by injection with Fecundin® at 8 and 5 weeks before mating at the second synchronized oestrus after progestagen pessary withdrawal. Ewes were reallocated to the high (at 15 ewes per ha) and low (at 20 ewes per ha) swards at the start of period 2 by breed and immunization treatment, balanced for live weight, body condition score and sward height in period 1. After mating in mid November, all ewes were run at 19 ewes per ha on the residual pasture of the high sward until slaughtered either at return to service or at 4 weeks after first mating when corpora lutea and embryos were counted.

There were no effects or interactions due to sward height in period 1 on the reproductive responses to sward height in period 2. Ovulation and potential lambing rates were greater in the Beulah breed than in the Cheviot, and on the high sward than on the low in period 2. Ovulation rates were higher in immunized ewes than in control ewes but the effects of immunization and sward height on potential lambing rate were not independent. Potential lambing rates were higher in immunized ewes than in control ewes at the low sward height but not at the high sward height.

Adjustment of stocking rate during period 1 served to increase the range in ewe body condition at the start of period 2 in mid October. Reproductive response to body condition at this time differed between the breeds, the relationship being strongly positive in the more prolific Beulah control ewes but less so in the less prolific Cheviot control ewes. The response to immunization in both breeds was relatively greater at lower levels of body condition, thereby reducing the effect of body condition in immunized ewes.

The use of Fecundin® is therefore unlikely to produce much advantage when pre-mating nutrition or body condition are high but there may be some advantage in using it when nutritional resources are limited in the autumn, particularly in ewes in poorer body condition.

Two experiments were conducted to test different milking procedures for dual-purpose goats that would be suitable for smallholder farmers. In experiment 1, 105 East African and Galla does that kidded to singles were randomly assigned to three treatments: (a) milking in absence of kid and kid sucking residual; (b) milking in presence of kid and kid sucking residual; and (c) milking once a week and kid sucking all milk 6 days of the week. In experiment 2, 45 Galla does that kidded to singles were randomly assigned to three treatments: (a) weigh-suckle-weigh; (b) milking half udder while kid sucking other half and (c) kid sucking all milk in the evening and milking mornings. Measurements of milk yield, milk sucked and weights of kids were taken for 12 weeks of lactation.

Results were analysed using least-squares techniques for unequal subclass numbers. Milking in the presence of kids increased does' milk yield. This increase was attributed to the stimulation of milk let-down by the presence of kids. Although this method potentially provided most milk for dairy use, less residual milk was left to sustain growth of kids. Estimates of total milk yield by milking once a week underestimated milk yield potential of the East African and Galla breeds. Results indicated an appropriate method for estimating milk potential should combine both milked and sucked milk measurements. Restricting milk available to the kids reduced their growth rates and thus indirectly affected their maturing rates. No milking procedure proved to be superior all-around for the smallholder for milking goats. To resolve this dilemma, use of an optimizing technique including socio-economic weighting of milk for family use relative to milk for kids was proposed.

The interaction of sire with feeding regime (ad libitum and restricted) was assessed in the first stage of a selection experiment. There were 79 sires (59 Large White (Edinburgh) and 20 British Landrace (Wye)) with 1549 progeny (745 at Edinburgh and 804 at Wye) in the study. Progeny within each litter were allocated at random to each feeding regime. Pigs started test at 30 (± 3) kg and finished test at 85 (± 5) kg for ad libitum fed pigs or after 84 days on test for restricted fed pigs. All pigs were individually penned. At the end of test, food intake, weight off test and ultrasonic backfat depths were recorded. Variance components were estimated using restricted maximum likelihood and a weighted analysis took account of the different residual variances between feeding regimes, within each breed.

There were differences in some genetic parameters due to feeding regime within breeds. No evidence of a sire with feeding regime interaction for average daily gain or food conversion ratio was detected in Large White pigs (genetic correlations between ad libitum and restricted feeding were 1·21 (s.e. 0·17) and 0·89 (s.e. 0·19) respectively). Similar conclusions could not be made for the sample of British Landrace pigs due to the large standard errors of the genetic correlation estimates. For ultrasonic backfat depths, the negative estimates of sire variances under restricted feeding prevent calculation of the genetic correlations and conclusions to be made about the sire with feeding regime interaction.

An experiment involving 320 gilts was conducted to investigate the effects of age and growth traits on puberty attainment and reproductive performance in gilts given boar stimulation with or without exogenous gonadotropins. Following ad libitum feeding during rearing, groups of gilts were stimulated for puberty at one of four ages, namely 130, 150, 170 or 190 days. Within each age group, gilts were selected to maximize the variation in live weight, relocated, mixed and allocated to two treatments in a randomized-block design: (a) mature boar contact (boars only) and (b) boar contact plus an intramuscular injection of 400 i.u. pregnant mare's serum gonadotropin + 200 i.u. human chorionic gonadotropin (boars + PG600). Gilts were mated at puberty and slaughtered at 35 days post coitum.

For the gilts on the boars-only treatment, the interval from stimulation to puberty decreased significantly (P < 0·05) and became less variable with ascending age at stimulation. Increasing live weight at a given age also reduced the interval from stimulation to puberty. Multiple regression equations involving age, live weight and backfat thickness at stimulation and growth rate from birth to stimulation were calculated to obtain a prediction equation for the interval from stimulation to puberty. The effects of age and live weight at mating on ovulation rate, embryo survival and number of live embryos 35 days post coitum were not significant.

For the gilts on the boars + PG600 treatment, 92% attained puberty within 6 days of treatment, with a non-significant trend to improve with increasing age. Mating rates were similar to those on the boars-only treatment (90%). Ovulation rates were higher (P < 0·001) but embryo survival rates were lower (P < 0·001) in the boars + PG600 group, resulting in similar litter size at 35 days post coitum in the boars-only and boars + PG600 treatments. There was a non-significant trend for litter size to increase with age in the boars + PG600 treatment. Thirty-eight of the gilts treated with hormones failed to conceive and 53% were found by ovarian morphology at slaughter to be cycling normally with a tendency for this proportion to increase with age.

Outflow rate of small particles from the rumen of dry and lactating Chios ewes and Damascus goats were measured in two separate trials using Cr-treated soya-bean meal (SBM). In another trial, the in situ degradation of fish meal (FM) and SBM in the rumen of Chios ewes and Damascus goats were measured. Outflow rate (per h) of small particles from the rumen of the two species was similar but higher outflow rates were observed in lactating than in dry animals (dry ewes 0·054, lactating ewes 0·086, dry goats 0·057, lactating goats 0·081). With the exception of dry-matter degradability of SBM at 6-h incubation periods there were no significant differences between ewes and goats in crude protein or dry-matter degradability of both supplements at all incubation intervals. Degradation measurements at various incubation periods and effective degradation values were different between supplements.

Estimates were made of total body protein in 45 unimproved crossbred pigs slaughtered serially between 20 and 200 kg live weight. Allometric functions were used to estimate protein weight at any given body weight and the Gompertz function was used to express live-weight changes in relation to time and to predict weight at maturity. Predicted values for daily protein retention increased rapidly from 20 kg to attain, at around 75 kg live weight, maxima of 130 g for entire males, 120 g for females and 105 g for castrated males. Between 45 and 110 kg live weight rates of protein retention were maintained within 10 g of the maximum rate. Mature live weights were estimated to be 240, 215 and 225 kg for entire males, females and castrated males. The allometric exponents for whole body protein as a function of body weight were 0·963 (s.e. 0·025), 0·927 (s.e. 0·021) and 0·850 (s.e. 0·049) for entire males, females and castrated males respectively.

The gene frequency of the halothane gene was estimated in nine British Landrace and Large White nucleus herds. Two hundred and sixty British Landrace and 186 Large White pigs purchased from these herd, to be used as foundation stock for a joint experiment on lean growth at the Physiology and Genetics Research Station, Edinburgh at Wye College, were test mated to homozygous halothane reactors (nn). One thousand six hundred and forty-six British Landrace and 1764 Large White offspring were given a 4-min halothane test at average ages of 76 and 50 days respectively. Maximum-likelihood estimates of the halothane gene frequency were 0·33 (s.e. 0·03) in British Landrace and 0·11 (s.e. 0·02) in Large White. Estimated proportions of reactors amongst heterozygotes (Nn) and halothane homozygotes (nn) were 0·00 and 0·70 in Large White, and 0·02 and 0·85 in British Landrace. There was significant heterogeneity between the herds for both breeds (P < 0·05). The proportion of halothane reactors in British Landrace herds has increased significantly (P < 0·05) from 0·13 in 1979 to 0·18 in 1982, and the proportion of Large White reactors has increased from zero to 0·01 in the same time period.

Two trials, one with 36 twin-suckling Chios ewes and the other with 32 twin-suckling Damascus goats, were conducted to study the effect of protein source (fish meal v. soya-bean meal) on the pre-weaning milk yield of the dams, and the growth performance of their offspring. The control (C) concentrate mixture was similar in both trials, using soya-bean meal (SBM) (195 kg/t) as a source of supplemental protein. In the experimental diet (FME) of the ewe trial, SBM was replaced completely by fish meal (FM) whereas in the goat trial (FMG) 83 kg of SBM were replaced by 50 kg FM. Dry matter (DM) and crude protein (CP) degradation of the three isonitrogenous mixtures were measured using nylon bags incubated in the rumens (2, 6, 16, 24 and 32 h) of three Damascus goats. There were no significant differences between mixtures for DM and CP effective degradability at 005 per h outflow rate. At 0·08 per h outflow rate however, lower degradability values were obtained with the FME than with the C diet. There were differences in the effective CP degradability of SBM and FM used in the ewe trial, but the FM used in the goat trial was of higher CP degradability and similar to that of SBM. Ewes on FM produced more milk than those on the control diet (C 3·44 v. FME 3·84 kg/day), whereas milk yield of goats was similar in the two treatments (C 3·87 v. FMG 3·82 kg/day). There were no differences between treatments for ewe milk fat (C 44 v. FME 43 g/kg) or protein concentration (C 54 v. FME 53 g/kg). Goats on fish meal (FMG) produced milk of higher protein (C 37 v. FMG 40 g/kg), but of similar fat (C 42 v. FMG 43 g/kg) concentration to those on the SBM (C) diet. With the exception of the better conversion (milk: gain ratio) efficiency (C 5·17 v. FME 4·44) of male lambs sucking ewes on the FM diet, no other differences were observed in the performance of lambs or kids. Lambs consumed less milk than kids (lambs: males 4·69, females 5·13; kids: males 6·63, females 6·98) per unit of weight gain.

A study was made of the behavioural development of domestic piglets living in a spacious, ecologically and socially diverse environment. The effects of age and sex of piglet on the frequencies of 30 behaviour patterns over the period from birth to 14 weeks of age were examined through focal animal sampling of 35 piglets from six litters. It was found that the frequencies of lying and standing in contact with other pigs declined significantly with age while walking, wagging the tail, sniffing the ground and the biting of objects increased with age (P < 0·05). Trotting, scampering and circling with other piglets were most frequent between 2 and 6 weeks of age. The frequencies of shaking the head, ‘quacking’, rooting, shovelling, and chewing at, and shoving, other pigs also varied significantly with age. Females wagged their tails more frequently than males whereas males circled, shoved and mounted more frequently than females (P < 0·05). Results are discussed with reference to the behaviour of young pigs kept under intensive housing conditions.

During the transportation of pigs over a long distance, the environment in individual compartments may be related to the climate outside the trailer and may affect the animals. During three international and six experimental transport trials over long distances the relationships between outside and inside temperature and humidity were determined. During the experimental journey pig behaviour was studied and the effect of the environment on meat quality was also measured subsequently.

During the three international journeys the correlation coefficients between the outside and inside temperatures of the trailer were 0·88, 0·81 and 0·54, respectively, whereas there were low positive or negative correlations for relative humidity. The live-weight losses were 60, 80 and 60 g/kg, respectively, and the mortality averaged 0·3%.

The live-weight loss averaged 40 (s.d. 6) g/kg during each 25-h experimental journey, while the mortality was 1·4%. During the course of the journey, a majority of pigs was sitting or lying. During the night and at stops in transit most pigs were lying down.

The correlation coefficients between the outside and inside temperature averaged 0·94 in the artificially, and 0·95 in the naturally, ventilated compartments, while the coefficients for the humidity were 0·66 and 0·77, respectively. Pigs ventilated artificially showed a lower rigor mortis and lower temperatures of the m. longissimus dorsi (LD) and m. semimembranosus (SM) muscles post mortem compared with those ventilated naturally.

A higher temperature in the compartment was related to a lower temperature in the LD and SM muscles at 24 h (P ≤ 0·05) and a higher pH of the SM muscle in the carcass (P ≤ 0·05). However this was also affected by the location of the compartment on the vehicle. A major temperature fluctuation was related to a lower rigor value (P ≤ 0·05).

I t may be concluded from these experiments that the environmental conditions during transport over a long distance may change markedly. High temperatures in the compartment may increase stress, while correct artificial ventilation may decrease stress.

Two trials involving young pigs (total numbers 288 and 400, respectively) were performed to compare the biological activity of Dl- and L-tryptophan under restricted (trial 1) and ad libitum (trial 2) feeding conditions. In trial 1, three additions of Dl-tryptophan (0·3, 0·6 and 0·9 g/kg) and two additions of L-tryptophan (0·3 and 0·6 g/kg) to a basal diet containing 0·9 g natural tryptophan per kg were tested. In trial 2, the treatments were additions of 0·4, 0·8 and 1·2 g Dl- or L-tryptophan per kg to a basal diet having 1·3 g natural tryptophan per kg. Both trials were of 6 weeks duration. In trial 1, almost equal performance was achieved with both tryptophan sources at a dietary level of 0·3 g/kg, whereas at a level of 0·6 g/kg, Dl-tryptophan produced slightly better performance in weight gain, food intake and food conversion efficiency than did L-tryptophan. In trial 2, the supplemental level of 0·4 g L-tryptophan per kg produced weight gain and food intake results which were significantly superior to those of Dl-tryptophan. However, at supplemental levels of 0·8 and 1·2 g/kg, diets with Dl-tryptophan produced somewhat better performance than did L-tryptophan. Based on the results of trial 2, it was estimated that the pig's need for total tryptophan over the weight range of 10 to 35 kg is at least 2·3 g/kg in a diet having 10·3 MJ net energy per kg.

An experiment was carried out over 11 years to investigate selection for economy of production and carcass lean content under ad libitum feeding in Large White pigs. Two lines, a selection (S) and a control (C) line, were involved in the study. The S line comprised 80 females and 10 males and was based at two centres. Boars were performance tested centrally at one of the centres and gilts were on-farm tested. Testing was carried out in groups of two or three full-sibs over the live-weight range 27 o t 87 kg. Selection was based on an index (I) incorporating individual daily live-weight gain (DLWG) and ultrasonically measured backfat thickness (USBF) and a group food conversion ratio (FCR) and generations were overlapping. The C line (32 females and 16 males) was maintained at one centre and males were performance tested alongside S boars to monitor genetic progress. Cumulative realized selection differentials over years 1 to 10 were equivalent to 5·5, 51, 7·0 and 9·4 phenotypic standard deviations for DLWG, USBF, FCR and I respectively and generation intervals averaged 17·0 months. There was little genetic change in DLWG, however, USBF, FCR and I showed substantial improvements with cumulative responses in year 11 of —12·3 mm, —0·22 kg/kg and +45·2 points respectively. The reduction in USBF occurred in the first half of the study with no further improvements being achieved after year 6. This study illustrates the effectiveness of index selection for a limited number of economically important traits but highlights limitations to this approach.