The digestive ability of growing pigs and large adult sows was compared in digestibility experiments with 26 foodstuffs and diets. In all cases, the sows showed superior digestibility of nutrients. On average, the sows digested 150 g more crude protein, 100 g more crude fat, 300 g more crude fibre per kg diet and proportionately 0·09 more gross energy than the young animals. The superior ability of the sows to digest gross energy was negatively correlated with the soluble carbohydrate and gross energy concentration of the food. A close linear relationship between digestibility in growing pigs and that in sows was found, making it possible to apply digestibility data for growing pigs in practical diet formulation for sows.

Growth rate and the concentrations of various biochemical constituents were measured in 2 years in lambs from two lines, selected on low (L) and high (H) copper (Cu) concentrations in plasma, and from two unselected pure breeds, Scottish Blackface (B) and Welsh Mountain (W). The lambs grazed improved hill pastures and half were given Cu supplements.

H lambs were always heavier and were fattened for slaughter earlier than were L lambs, differences that were not completely eliminated when supplementary Cu was given. In both years, the improvements in growth rate due to supplementary Cu varied with genetic type (average L 20·5 (s.e. 2·5); H 5·7 (s.e. 2·6); B 25·1 (s.e. 3·7); W 8·1 (s.e. 3·3) g/day). Growth rates of supplemented lambs were L 100 (s.e. 2), H 104 (s.e. 2), B 134 (s.e. 5), W 103 (s.e. 3) g/day.

At 6 weeks of age, unsupplemented lambs trom all genetic types were hypocupraemic and, at all ages, unsupplemented L and B lambs had lower concentrations of Cu in plasma and superoxide dismutase (SOD) activity than had unsupplemented H and W lambs. Supplemented lambs always had greater concentrations of Cu in plasma and SOD activities than had their unsupplemented counterparts. Supplementation increased the haemoglobin concentration for B (in year 2) and L lambs but not for H and W lambs. Cholesterol concentrations in plasma were unaffected by selection but were slightly higher in unsupplemented lambs. The concentration of total protein and the activity of aspartate transaminase were unaffected by genotype or Cu supplementation. In the liver of lambs at slaughter, the concentration of Cu was lower for unsupplemented lambs and inversely related to the concentration of iron.

It was concluded that (i) genotype was an important determinant of hypocuprosis; (ii) the degree of hypocuprosis could not be predicted from herbage analyses alone, but instead may be predicted from biochemical assessment of the lamb; and (iii) the dose of Cu supplement used was inadequate for L and B lambs and recommended levels could be increased, within limits, without risk of toxicity.

Circadian variation in the composition of digesta was examined in pigs fitted with replaceable T-cannulas in the proximal duodenum and terminal ileum. The pigs were fed twice daily with a cereal-based diet containing Cr2O3, as a marker. Digesta were collected hourly for 16 h following morning feeding (pig live weight (LW) 25 and 65 kg) or as a 12-h composite collection (pig LW 45 kg), and analysed for pH, dry matter (DM), ash, crude fat, crude protein, starch, neutral-detergent fibre (NDF) and Cr2O3,.

No statistically significant differences were found in the composition of digesta from pigs weighing 25 or 65 kg LW. Calculated relative to Cr2O3, recoveries in 12-h composite samples of duodenal and (ileal) digesta were 1·19 (0·34) for DM, 1·28 (0·31) for crude protein, 0·97 (0·05) for starch and 0·93 (0·79) for NDF. Composition of both duodenal and ileal digesta varied considerably during the sampling period and was particularly influenced by giving food. Between-hour coefficients of variation for the samples taken hourly were, in general, greater at the duodenum (mean 017) than at the ileum (mean 0·11), while mean within-hour (between pigs) coefficients of variation (0·19 and 0·18, respectively) were greater than those between hours. The Cr2O3 marker generally followed the flow of dietary matter through the gastrointestinal tract, although there was an indication of a partial separation of NDF from other dietary components in the stomach. Composition of the 12-h composite samples of digesta did not differ from that of the mean of the samples taken hourly for 16 h.

The effects of halothane phenotype on growth were estimated from generations 1 to 3 of British Landrace positive and negative selection lines. A total of 241 full-sib pairs (castrated male and gilt) from 133 second litters were performance tested from 25 to 85 kg live weight on either ad libitum or scale (0·69 g/g ad libitum daily food intake) feeding.

Compared with negative reactors over feeding regimes, positive pigs showed significant advantages in food conversion ratio (−0·07, s.e. 0·02), eye-muscle area (0·8, s.e. 0·3 cm2), proportion of lean in sample joints (16, s.e. 7 g/kg), and visual conformation scores, accompanied by disadvantages in meat colour (5·9, s.e. 2·1 EEL units), incidence of pale, soft, exudative (PSE) meat (0·36 v. 0·05, P < 0·001), post-weaning mortality (0·09 v. 0·01, P < 0·001) and ad libitum daily food consumption (−0·08, s.e. 0·02 kg). In addition, there were non-significant indications of an advantage in carcass lean proportion (11, s.e. 10 g/kg), with disadvantages in carcass length (−14, s.e. 7 mm) and proportion of lean in high-priced cuts (−6, s.e. 2 g/kg). Only daily food consumption showed significant selection line × feeding level interaction.

Averaged over feeding regimes, an estimated extra return of £1·70 (s.e. 0·50) from lean growth would be offset by increased PSE and mortality to give a net loss of roughly £3·90 (s.e. 1·00) per positive reactor. Taking these results as the minimum difference between homozygotes, and if the gene is additive for lean proportion but recessive for stress susceptibility, the heterozygote would have an advantage of £0·90 over the normal homozygote. The effects of the gene on growth and carcass traits in British Landrace appear similar to those reported in other breeds, although the advantage of positive reactors in lean proportion may be slightly smaller.

Eighty-eight first-litter sows were used in a factorial experiment to examine the effects of energy and protein intakes during lactation on subsequent performance. Some received either 45 MJ (E,) or 60 to 63 MJ (E2) digestible energy per day and either 508 to 511 (P,) or 703 to 815 (P2) g crude protein per day during a 28-day lactation.

Sows on the E2P2 treatment lost less body weight during lactation than sows on the other three treatments (P < 0·05). Average live-weight losses during lactation were 21·8, 20·8, 17·8 and 9·6 kg for the E1P1, E1P2, E2P1, and E2P2 sows, respectively. The corresponding reductions in backfat measurements during lactation were 5·5, 7·9, 3·2 and 4·0 mm. Backfat losses were greater for sows given either moderate energy intakes or high protein intakes (P < 0·01).

Neither protein intake nor energy intake during lactation affected subsequent ovulation rate, but piglets sucking sows given high protein intakes grew faster, particularly during the last week of lactation, than piglets sucking sows receiving low protein intakes (P < 0·05).

Within 8 days of weaning, more sows given high intakes of protein during lactation exhibited oestrus than did sows which received lower intakes of protein (27/44 v. 14/44, x2 = 7·7, P < 0·01). Protein intake during lactation affected the nitrogen balance of sows in a similar way. The nitrogen balances were estimated during the 3rd week of lactation, and for sows given rations E1P1, E1P2, E2P1, and E2P2were -20·2, -11·5, -17·5 and -7·2 g/day respectively.

Ninety entire male pigs were used in two experiments to investigate the effects of energy concentration on the performance of growing pigs given diets containing relatively high or low levels of fibre. A blended fat product was also compared with tallow as a source of dietary energy for pigs in the first experiment.

In experiment 1, 60 pigs growing between 20 and 45 kg live weight were given 10 diets containing approximately 120 g acid-detergent fibre per kg (80 g crude fibre per kg), and 10, 30, 50, 75 or 100 g/kg of either tallow or the blended fat product.

Although the source of fat had no significant effect on food intake or growth performance, voluntary energy intake and growth rate increased with increase in the level of fat added to the diet and with concomitant increase in dietary digestible energy (DE) concentration up to 50 g/kg and 13·2 MJ/kg respectively. Further increase in the level of fat added to the diet and in DE concentration resulted in a decline in voluntary food intake, whilst energy intake and growth rate remained relatively constant at 27 MJ/day and 720 g/day respectively.

In experiment 2, 30 pigs were used to investigate the animals' response to five levels of dietary DE concentration (11·8 to 15·1 MJ DE per kg) between 20 and 50 kg live weight. The highest level of acid-detergent fibre in the diets was 62 g/kg (50 g crude fibre per kg) and this declined with increase in energy concentration to 30 g/kg (25 g crude fibre per kg) in the diet of highest energy concentration.

Voluntary food intake was not significantly affected by dietary energy concentration, and voluntary energy intake and growth rate increased linearly with increase in dietary energy concentration up to 14·5 MJ DE per kg. Maximum energy intake (31 MJ DE per day) and growth rate (905 g/day) in experiment 2 was proportionately 0·15 and 0·26 higher than that achieved by pigs given the higher fibre diets in experiment 1.

The results for voluntary food intake and growth rate suggested that the pig's demand for energy and consequently its response to dietary energy concentration was affected by dietary fibre concentration.

The effects of an internal recirculating air filter on air hygiene and pig performance were studied using two groups each of 100 early-weaned pigs from a commercial herd. The two groups were housed in separate rooms under identical conditions except that one room contained a recirculating air filter. Five trials were carried out, but the same records were not kept in all trials. The air throughput of the filter was similar to the installed ventilation capacity (0·9 m3/s). The filter material nominally removed particles > 5 μm. Distribution ducts discharged the filtered air downwards over the pigs' lying area at a velocity of 0·3 m/s. At locations close to the pigs, the most representative proportional reductions of total particles, dust mass, and bacterial colony-forming particles were 0·58 (P < 0·01), 0·73 (P < 0·01), and 0·51 (P < 0·01), respectively. No differences in growth rate or health of pigs after 3 to 4 weeks were observed between the rooms but the pigs originating from the room containing the air filter reached a marketable state 6 to 8 days earlier than the control group pigs on the three occasions that this aspect was monitored (P < 0·0·01).

One hundred and twenty pigs were used in a 3 × 8 factorial design. The factors were sex, 40 trios of littermate boars, castrated males and gilts, and dietary lysine, eight concentrations from 7×5 to 14×5 g/kg diet with 1 g/kg diet intervals of lysine with corresponding crude protein (CP) concentrations from 114 to 226 g/kg diet. Increases in dietary lysine were associated with concomitant increases in the other essential amino acids so as to provide an ideal protein. All diets had similar digestible energy values (13·65 MJ/kg). Pigs were fed once daily on a restricted scale from 25 to 55 kg live weight. For growth and carcass characteristics there was a range of linear response followed by a plateau. The inflexion points of dietary lysine for growth characteristics were at 11·1, 10·2 and 10·9 g/kg diet (171, 157 and 168 g CP per kg diet) together with daily intakes of 18·0, 16·7 and 17·6 g (daily intake of 277, 257 and 271 g CP) for boars, castrated males and gilts respectively. The equivalent points for carcass characteristics were 10·4, 9·7 and 10·1 g/kg (160, 149 and 156 g CP per kg diet) with daily intakes of 16·9, 15·9 and 16·4 g lysine (daily intakes of 260, 245 and 252 g CP). Blood urea data gave good support for these observations.

The response to dietary lysine when provided as part of an ideal protein was examined in pigs over the range of live weight from 50 to 90 kg. Ninety-six pigs, 32 trios of littermate boars, castrated males and gilts were allocated to eight diets with lysine concentrations of 5·6, 6·2, 7·3, 8·3, 9·3, 10·3, 11·4 and 12·4 g/kg diet and corresponding concentrations of crude protein (CP) from 90 to 186 g/kg diet (all having a digestible energy of 13·38 MJ/kg). Pigs were given food on a restricted scale once daily. With increasing lysine concentration, there was a linear response (followed by a plateau) for growth and carcass characteristics up to dietary lysine concentrations of 91, 7·2 and 8·4 g/kg diet and CP concentrations of 142, 116 and 132 g/kg diet with daily lysine intakes of 22·9, 18·6 and 21·2 g and CP intakes of 357, 290 and 331 g for boars, castrated males and gilts respectively.

The number of beta-adrenergic receptors which influence the effectiveness of catecholamines was determined by 3H-dihydro-alprenolol in muscle, heart and fat tissue of stress-susceptible pigs (Pietrains) and non-susceptible pigs (Large Whites). In all investigated tissues proportionately 0·31 to 0·38 more receptors were found in the Pietrains than in the Large Whites, the differences being significant (P < 0·05). That the higher numbers of beta-adrenergic receptors in Pietrain pigs may be involved in accelerated muscle glycogenolysis (poor meat quality) and increased lipolysis (low carcass fat) in these animals and in other breds showing poor meat quality and low carcass fat is discussed.

A trial was carried out to examine some of the factors involved in the possible deterioration in pig meat quality associated with the trend towards leaner carcasses. Five batches of pigs, each one as far as possible from the same producer, were identified at each of 10 abattoirs. Three gilts and three entire males were selected from each batch to show a range of fatness. Overall mean fat thickness measurements over the m, longissimus at the last rib (P2, mm) for lean, average and fat carcasses were 8·8, 11·6, and 16·9 (gilts) and 8·4, 11·7 and 15·5 (entire males). The overall mean carcass weight was 58 kg. Loin and leg joints were assessed for cutting and presentational characteristics by a panel of 45 butchers. Loin chops and shoulder and leg joints were assessed for eating characteristics by consumer panels involving a total of 500 families. Butchers judged the fat of lean carcasses to be softer and the meat to be floppier and with more tissue separation. Entire males also had slight disadvantages in these respects. Consumers found the chops of lean carcasses to be less juicy on average (0·16 lean carcasses were judged to have dry chops compared with 0·09 for fat carcasses) with a tendency towards toughness and less flavour. There were no differences in overall acceptability. Meat from the two sexes did not differ in eating quality or overall acceptability to consumers. The butchers were more critical of overlean carcasses than were consumers. The trial indicates that the trend towards leaner carcasses is likely to create butchery problems but not consumer dissatisfaction.

Evaluations of meat quality were made of 300 carcasses, of average weight 58 kg, falling into three fatness groups, 8, 12 and 16 mm for P2 fat thickness. There were equal numbers of entire males and gilts. An increase in fat thickness was associated with an increase in the firmness of loin and shoulder backfat, a reduced incidence of fat separation and changes in the composition of both muscle and backfat: the concentration of lipid increased and that of water decreased, more markedly in backfat. In addition, the concentration of collagen in backfat decreased. The loin joint was visually most attractive when P2 was 11 mm, attractiveness decreasing below and particularly above this value. Eating quality of grilled chops was assessed in a representative subsample of 96 pigs falling into the 8-mm and 16-mm P2 categories. The only statistically significant difference observed between these extremes of fat thickness was in juiciness which was lower in the leaner pigs; the correlation between juiciness score and m. longissimus lipid concentration (‘marbling fat’) was 0·31. Juiciness did not influence the assessment of overall eating quality which showed no association with fatness. Entire males of similar backfat thickness to gilts (12 mm P2) had a higher concentration of water and lower concentration of lipid in backfat and slightly softer backfat. There were no differences in eating quality, or in the presence of abnormal odours or flavours, between entire males and gilts. These results confirm those obtained in butcher and consumer panel tests in the same carcasses.

Forty-eight Landrace × (Landrace × Large White) gilts were randomly allocated at 70 days of age to each of three rearing treatments: (1) fence-line contact with a mature boar, (2) olfactory/aural contact with a mature boar, (3) no boar contact. At 160 days of age, all gilts were relocated adjacent to a novel mature boar and exposed to full contact with a mature boar for 30 min each day. At the first, second and third oestrus, 16 gilts from each treatment group were mated twice and the reproductive tracts were examined at slaughter 21 days later, to determine ovulation rate and embryo survival. The rearing treatments had no significant effects on the attainment of puberty. Neither rearing treatment nor oestrus of mating had any significant effect on behaviour, sexual receptivity at first service, conception rate, ovulation rate, the number of embryos and embryo survival at 21 days of pregnancy.

Present day sows, particularly young sows, have smaller fat reserves than they did 10 to 20 years ago (Whittemore, Franklin and Pearce, 1980). Consequently, changes in the sows' body reserves during pregnancy and lactation have become much more critical in evaluating various nutritional strategies. The interpretation of many experiments designed ot investigate the effects of nutrition of the sow would be enhanced if changes in the body composition of the animal could be determined.

The two most widely adopted methods for measurement of milk production in sheep suckling lambs, the lamb-weight increment technique and milking-out following administration of oxytocin, give estimates which differ proportionately between 0·05 and 0·28 especially in early lactation (Doney, Peart, Smith and Louda, 1979). It is not easy to determine which method gives the most accurate estimate of milk production in suckling ewes. It is important, however, to understand the circumstances in which discrepancies between methods may occur and their magnitude. This note provides evidence that such discrepancies may vary with nutritional status of the ewe.

The use of profit equations for deriving economic weights (the value per unit improvement in a trait) in the genetic improvement of livestock has led to anomalies both in theory and in practice. These anomalies can be removed by imposing two conditions. One is that any extra profit from genetic change that can be matched by rescaling the size of the production enterprise should not be counted since it can be achieved without any genetic change. Only savings in cost per unit of product value should be included. The second condition is that changes that correct previous inefficiency in the production enterprise should not be counted. Thus, it is assumed that resources are efficiently used, and changes in output will require proportional changes in input. This means that fixed costs, like variable costs, should be expressed per unit of output, rather than as a fixed total enterprise cost. Improvement effort spent on traits that redress current inefficiencies in a production enterprise is of local and temporary value and is at the opportunity cost of improvement of other traits that save costs per unit of product value and are of permanent and general value. Application of these two conditions is shown to give economic weights that are identical on different bases; scaled output value, input or profit; fixed output value, input or profit; and zero profit. They were also equivalent to economic weights derived as the cost per unit product value from an economic efficiency index. The dilemma of different economic weights for different perspectives in production (unit of product, animal, producer, investor, and consumer) is also resolved.

Sugar-beet pulp as normally produced in Great Britain contains about 400 g molasses per kg dry matter (DM). It has been demonstrated that either a reduction in the amount or even the full removal of the molasses did not affect the yield or composition of the milk of cows (e.g. Ronning and Bath, 1962; Hemingway, Parkins and Fraser, 1986). The dried, shredded pulp without molasses was, however, generally less palatable.

Mid-Pregnancy nutrition has been shown to have both positive and negative effects on lamb birth weight in primiparous Scottish Blackface ewes. The direction of the effect depends on the level of body condition at mating, being negative in ewes in high body condition (Russel, Foot, White and Davies, 1981). In the same study, it was argued that the effect in younger ewes could be due to their greater sensitivity to both under- and over-nutrition during the earlier to mid stages of their first pregnancy than is evident in older ewes. Russel et al. (1981) also suggested that the level of mid-pregnancy nutrition is likely to have effects on other aspects of production such as embryonic loss, foetal mortality and even ewe mortality.

One of the major limitations to the widespread use of artificial insemination (AI) in the United Kingdom (UK) sheep industry is that with frozen-thawed semen current insemination techniques result in lowered fertility. Consequently, only fresh or liquid-chilled ram semen can be used if commercially acceptable conception rates are to be achieved.