Two hundred and seventy-seven ewes were used in three experiments during late seasonal anoestrus to evaluate short-term progestogen primings for equine chorionic gonadotropin (eCG)-induced oestrus. In experiment 1, medroxy-progesterone acetate (MAP) sponges were inserted for 6, 9 or 13 days in nulliparous ewes. Percentage of ewes in oestrus (92.3, 85.7 and 96.4%, respectively) and conception rates (66.7, 75.0 and 63.0%, respectively) did not differ among groups (T > 0·05). In experiment 2, MAP sponges were inserted for 1, 2, 3, 6 or 12 days in multiparous ewes. Percentages of ewes in oestrus were higher with 3, 6 or 12 days than with 1 or 2 days of priming (72.2, 93.8 and 87.5% v. 25.0 and 33.3% respectively, P < 0.05) and maximum response was with 6-day priming. From both experiments we conclude that short-term progestogen (6 days) priming is as effective as long-term traditional primings for inducing oestrus. In experiment 3, level of progestogen priming was compared among treatments using a new progesterone releasing device (CIDR) for 6 days, a 6-day used CIDR for 6 days, or an 11-day used CIDR for 6 days. While percentages of oestrous response were similar among groups (95.9, 93.6 and 88.9%, respectively), pregnancy rates were higher with a new CIDR than with one that had been used for 11 days (57.1% v. 27.8%, P < 0.05), with the 6-day used CIDR being intermediate (51.1%). We conclude that a 6-day progestogen priming combined with eCG can be used successfully to induce fertile oestrus in seasonal anoestrous ewes if progestogen levels during priming are kept sufficiently high.

From 74 to 180 days of age, a complete diet was offered either ad libitum (AL) or at proportionately 0·8 of the observed consumption (R) to two groups of purebred Yorkshire gilts, comprising 128 and 127 animals, respectively. Half of the animals in each group was served at the first detected oestrus, and the other half at the third detected oestrus, according to a plan defined at the start of the experiment. Animals which failed to show oestrus before 240 days of age were culled.

At 100 kg live weight (LW), AL gilts were younger (-20 days) and had thicker backfat (+2.3 mm) than R gilts. At the first detected oestrus, AL females were also younger (198 v. 203 days), heavier (127 v. 117 kg LW) and fatter (17·8 v. 14·7 mm backfat thickness) than R gilts. No difference between feeding treatments during rearing was observed in the percentage of females detected on heat before day 240. Seventy-three animals were culled from the start of the experiment until service, half of them (54%) failing to show oestrus. At service, LW and backfat thickness in the four treatments ranged from 117 to 148 kg LW and 14·9 to 19·7 mm, respectively. The body fatness, estimated from the ratio of backfat to LW, was higher in AL than in R gilts (0·14 and 0·12 , respectively), whereas no difference was observed between E1 and E3 gilts (0·13 on average). After the first service 15% of the gilts came back into heat but the conception rate was not affected by feeding treatment during rearing.

A 2 x 2 factorial experiment was designed in order to study the effects of feeding level during rearing and of mating policy on the reproductive performance and food intake of first- and second-litter sows. Gilts were offered food during rearing either ad libitum (AL) or at 0·8 of the AL level (R) and served either at first (E1) or third (E3) detected oestrus. A total of 160 out of the 243 animals that started the experiment were culled by the end of the second lactation, with significantly more R than AL animals (71 and 60%, respectively). During the first pregnancy, the R sows gained more live weight (LW) and backfat thickness (BF) than their AL contemporaries (+5 kg and +1.2 mm, respectively) and lost less BF during the first lactation (1.2 mm less). At weaning, no difference remained in LW or BF between AL and R sows (174 kg LW on average). The E3 females gained less LW during both pregnancies compared with those on the E1 treatment, but they remained heavier until the second weaning (208 kg, on average). During the first lactation, R consumed more food during the weeks 2 and 3 (by 0·5 kg/day, on average) than those reared previously on the AL regime, and no difference was observed between E3 and E1 females. No difference in food consumption was noted during parity two. However, when measured over the first two parities, lean animals consumed more food than fat animals. The size and the weight of the litter at birth or at weaning were not influenced by the treatment prior to service. The weaning-to-oestrus interval was longer during parity one than during parity two (5·7 and 5·0 days, respectively; P < 0·01) but it was not affected by feeding or mating treatment.

Various dairy cattle production and health characteristics were studied with a view to identify easily available and measurable factors associated with the incidence of ketosis. The analyses were carried out using data from the Langhill Dairy Cattle Research Centre. Two approaches were used to assess the relative risk to cows of getting ketosis: one using information known at the beginning of lactation and one using information collected as the lactation progressed. In both approaches analyses were carried out using different amounts of the available information to simulate differences between recording systems. In the first approach the following were found to relate significantly to the level of recorded ketotic incidents: parity; ketosis in the previous lactation; calving condition score; 305-day milk yield in the previous lactation; and the average milk protein percentage in the previous lactation. The effects of these were quantified. In the second approach, where the change in ketosis incidence rate over the weeks of lactation was investigated, the average dry-matter intake in the previous week and changes in live weight and body condition score over the previous week were found to have a significant effect on the probability of getting ketosis in the coming week. The risk assessments varied depending on the information used and a flexible approach is recommended if potential risk factors are to be successfully incorporated into decision support systems.

The trade-off made by pigs between exposure to a concentration of ammonia gas recorded in commercial piggeries and thermal comfort was observed in two chronic choice tests. In the first experiment, eight pigs which were paired and eight pigs which were held as singles, were forced to choose between compartments of a preference chamber that were polluted with an ammonia gas concentration of 40 p.p.m. and heated with a 750 W radiant heater or compartments that were unpolluted and unheated, for 8 days. The location of the choice options was switched after 4 days to eliminate positional bias. Air temperature ranged from 0·5 °C to 15·0 °C. In the second experiment, eight pigs held as pairs, were free to choose between compartments that were polluted with an ammonia gas concentration of 40 p.p.m. and heated with a 750 W radiant heater, polluted and unheated, unpolluted and heated and unpolluted and unheated, for 14 days. The location of the choice options was switched after 7 days to eliminate positional bias. Air temperature ranged from 4·0 °C to 24·0 °C. All compartments contained food and water ad libitum; wood shavings were used as bedding material. In both experiments, the location of all pigs was scan sampled every 15 min and their behaviour at this time was recorded instantaneously. Location and behaviour were compared against air temperature. In the first, forced choice experiment, the pigs preferred the heated-polluted compartments when air temperature was less than the estimated lower critical temperature (LCT) (P < 0·001). As air temperature approached the estimated LCT, the pigs occupied the unheated-unpolluted compartments more often. Overall each visit made to the heated-polluted compartments lasted significantly longer at 265 min (paired), 208 min (single) than visits to the unheated-unpolluted compartments at 29 min (paired), 31 min (single) (P < 0·001). Although they could have huddled to conserve heat, the paired pigs spent less time, overall, in the unheated-unpolluted compartments (P < 0·001). When air temperatures were lower than the estimated LCT, the pigs huddled together but as air temperature increased, the pigs spent more time resting apart (P < 0·001) in the heated-polluted compartments. It is suggested that the paired pigs were motivated to remain in the heated-polluted compartments for companionship rather than thermal comfort. In the second, free choice experiment, the pigs preferred to remain in the unpolluted compartments, adjusting their occupancy of the heated and unheated compartments as ambient air temperature decreased or increased above the estimated LCT (P < 0·001). The pigs made fewer visits to the polluted compartments and each visit was shorter, at 44 min (P < 0·001). Visits to the unpolluted compartments lasted for 291 min. It is suggested that the delayed aversion shown to ammonia in both experiments was due to a progressive sense of malaise. However, both experiments indicated that this delayed ammonia aversion was weaker than preference for thermal comfort.

Seventy-two crossbred barrows (28.7 ± 0.3 kg live weight (LW)) were used to examine whether there is a relation between eating traits, and performance and carcass traits in ad libitum and restrictedly fed group-housed pigs. The experiment included two replicates, each consisting of 36 pigs. From day 1 to 42, all pigs were maintained with free access to a starter diet containing 12.7 MJ metabolizable energy (ME) and 8.2 g ileal apparent digestible lysine per kg. The experimental period was from day 42 (55.9 kg LW) to the end of the experiment (110.2 kg LW). The pigs in treatment 1 were maintained with free access to a high (H) energy diet (13.1 MJ ME and 7.1 g ileal apparent digestible lysine per kg). For pigs in treatments 2 and 3 the daily energy allowance per pig was restricted to 18 MJ ME above the daily energy requirement for maintenance using diet H, and a low (L) energy diet (12.5 MJ ME and 6.7 g ileal apparent digestible lysine per kg), respectively. The weekly measured LW was used to compute the energy requirements for maintenance (M = 0·719 MJ ME × LW (kg)0.63). Daily food intake and eating traits per pig were determined using transponders and an electronic feeding station equipped with an antenna.

Daily energy intake of the ad libitum and restrictedly fed pigs was correlated with growth and lean meat tissue content of the carcass. In the pigs given food ad libitum, daily energy intake was correlated with daily feeder visiting time, time per meal and food intake per meal, but not with number of meals per day and rate of food intake. In the restricted treatments, number of meals per day was correlated with energy intake, but not with lean tissue content of the carcass. In conclusion, number of meals per day explained part of the variation of lean tissue content of the carcass in ad libitum, but not in restrictedly fed group-housed pigs.

The main aims of this study were to predict the increase in the accuracy of selection and the response to selection achieved by including feeding pattern traits, such as number and size of meals, as selection criteria in indices to improve growth rate, lean content of the carcass and food conversion ratio. Genetic and phenotypic parameters obtained for pigs given food ad libitum using single space electronic feeders were used to construct the indices. The predicted genetic gain in the index increased for indices with more feeding pattern traits. The inclusion of part test records for feeding patterns resulted in similar predicted correlated responses and predicted accuracy of selection to those using whole test records of daily food intake. The inclusion of feeding patterns as selection criteria resulted in indices that were less robust to inaccurate parameter estimates. It was concluded that feeding pattern traits could be used to improve the predicted accuracy of selection for the efficiency of lean growth but the most effective and robust index would include only daily gain, backfat depth, daily food intake and mean number of visits to the feeders per day. These traits may also be useful in reducing the length of the test period necessary for accurate measures of food intake, so increasing the potential intensity of selection using a given number of feeders.

Records were analysed on more than 75 000 calvings by 685 Holstein-Friesian bulls tested in commercial dairy herds in England and Wales. The data were collected from 1988 to 1994. The traits analysed were the degree of difficulty at calving, assessed from no difficulty to serious difficulty, calf mortality to 48 h, gestation length and a subjective assessment of calf size. Information was available for the percentage Holstein genes in the sire, dam age (heifer or mature), sex of the calf and the year and month of the calving for all records, while lactation number of the dam and the regional location of the herd were also recorded in 1993 and 1994 (14988 records). Estimates of heritability and genetic and phenotypic correlations were obtained for all traits by restricted maximum likelihood (REML) procedures using a sire model, while also fitting the effects of dam age, calf sex, year and season of calving and significant interations.

Heifers had more difficult calvings, higher calf losses and shorter gestations than mature cows while seriously difficult calvings and mortality were higher for male calves (all P < 0·05). Summer months were associated with lower incidences of difficult calvings, lower mortality and shorter gestations. Heritability estimates were 0·05 (s.e. <0·01) for calving difficulty score, 0·45 (s.e. 0·02) for gestation length, 0·02 (s.e. <0·01) for mortality and 0·08 (s.e. <0·01) for calf size score. Heritability estimates for the scored categorical and binomial (mortality) traits were also obtained using threshold model analysis. As expected, these estimates were higher than the REML estimates; 0·12 (s.e. 0.01) for calving difficulty score, 0·08 (s.e. 0·01) for mortality and 0·14 (s.e. 0·01) for calf size score. Calving difficulty score was genetically correlated with calf size score (-0.81), mortality (0.40) and gestation length (0.34) and calf size score was moderately correlated with mortality (-0.40). In all cases, the genetic correlations were stronger than the corresponding phenotypic correlations.

Sire genetic merit was predicted for calving difficulty score and the distribution of these predictions is described. Sire predictions for calving difficulty score on the underlying scale were backtransformed to predict the expected incidence of serious difficulties in future calvings.

The Ministry of Agriculture, Fisheries and Food routinely publishes price information for 3-week-old beef + dairy calves sold at major livestock auction centres in England and Wales. For the period 1993/94 to 1996/97, there were average price premiums of £51 for male and £38 for female calves classed as ‘first quality’. We have shown previously that choosing an easy calving beef sire for use on dairy cows will generally lead to calves which are smaller in size and of poorer conformation. To enable dairy producers to maximize returns from calf sales, we propose that beef sires be evaluated for the predicted incidence of first quality’ calves, which can be derived from the sire’s evaluation for calf conformation and the breed incidence of first quality’ calves. Dairy farmers may then jointly consider a bull’s predicted merit for calving ease and calf quality when choosing a sire for use in their herd.

Weaning weight in a single flock of 600 ewes and 40 rams was simulated through 30 consecutive lambings. The objective was to compare the simple breeding value model with the maternal effects model for lamb evaluation under the Segureña selection scheme. Three selection strategies were tested: selection on breeding values estimated by a simple breeding value model that ignores maternal effects (method 1), selection on direct additive values only (method 2) or on the sum of direct and maternal additive values (method 3), both latter methods utilizing a maternal effects model. Average values obtained in the last lamb crop were about 18 kg for the phenotypic mean, about 5 kg for direct additive values and about -1 kg for maternal additive values, for all three methods. Average inbreeding coefficient of the last crop was more than 0·13 in method 1 but was less than 0·12 in the others. All differences were not statistically significant (P > 0·05). Consequently, the simple breeding value model can be used for the genetic evaluation of weaning weight of candidates for selection in the Segureña scheme. The effect of variation in the magnitude of parameters was evaluated through four sets of parameters. Results showed that with a higher additive maternal component, method (3) would become increasingly necessary. The need for method (3) is accentuated with more negative additive covariance between direct and maternal effects. Thus, for higher maternal effects or more negative additive correlation, the use of the complete model (with maternal effects) becomes unavoidable. Varying population size, however, affects only the inbreeding accumulated, as long as the same methods of selection are used.

Heritabilities, dominance variation and genetic correlations (rpc) among purebred and crossbred performance were estimated for egg production (number of eggs produced between 19 and 25, 26 and 38 and 26 and 54 weeks of age) and egg quality traits (average egg weight, shell strength) in four generations of two nucleus lines of egg-laying chickens and their cross, all reared in similar environments. The within-line genetic parameters were estimated using method R applied to an animal model (approach 1) and tilde-hat approximation to restricted maximum likelihood applied to a sire-dam model (approach 2). The genetic correlation between purebred and crossbred performance as well as the crossbred heritabilities were estimated based on a multivariate sire-dam model accounting for all relationships. For egg numbers and shell strength, the purebred heritabilities were low to moderate (0·12 to 0·42). They were higher when estimated under an additive model (0·25 to 0·51) but, in general, lower than the crossbred heritabilities. For egg weight, the heritabilities were always high (0·6 to 0·7). The ratio of dominance variance to total genetic variance varied between 11 and 36% with approach 1 and 5 and 56% with approach 2, indicating a large partial dominance for egg number traits and shell strength but also the difficulty of accurately estimating the dominance variance. For these traits, the estimates of the correlation between purebred and crossbred performance, rpc, were quite high (0·8 to 0·94) which contradicts the theory that traits with larger dominance and/or difference between purebred and crossbred heritabilities present lower rpc. These high rpc estimates, coupled with the absence of obvious heterosis, indicate little advantage to be gained from use of crossbred data in genetic improvement, where pure lines and crossbreds are reared in a similar non-stressful environment.

More accurate definition of Angora rabbit breeding objectives has been investigated by considering multiple expression of different traits. Data on 9672 fleece harvests produced by 1343 Angora does which had at least one wool harvest were analysed in order to study genetic variability according to age. The animals of the French breed were defleeced and weighed at 8 and 21 weeks of age for the first and second time respectively. Thereafter, does were defleeced every 14 weeks and weighed 9 weeks before defleecing. Total fleece weight and live body weight were recorded at each harvest.

Direct heritability estimates of total fleece weight were similar accross ages and ranged from 0·31 to 0·42 . A significant maternal heritability was also observed at all ages of harvest. Maternal genetic estimates decreased with age from 0·44 at the first harvest to 0·10 for an adult harvest. Except for 8 weeks of age, genetic correlations between total fleece weight and live weight were generally not significantly different from zero. Genetic correlations of total fleece weight between the first and subsequent harvests were low (from 0·22 to 0·39) but genetic correlation estimates between consecutive harvests after the first were high, and ranged from 0·68 to 0·89 . The results suggest that the second harvest would be the first good predictor of breeding value for total fleece weight in the adult Angora rabbit.

Field data of the Austrian Simmental population were analysed using restricted maximum likelihood (REML) with an animal model where additive direct, additive maternal and cytoplasmic effects were treated as random and the effect of the year of first calving as fixed. Traits analysed were milk yield, fat and protein content, persistency, days open and herd life. All dairy traits were pre-adjusted for best linear unbiased prediction (BLUP) herd-year effects, milk yield additionally for season, age at first calving and days open. After applying specific data restrictions, the number of records for the various traits ranged from 3360 to 51889. Identification of cow lineages was based on pedigree information from the official milk recording scheme, with a span of at least four and up to 16 generations. The number of lineages per trait varied and ranged from 484 to 3195, with an average size of 15 members (for herd life 7). Evaluations of the relevant variance components for the dairy and fitness-related traits investigated were separate for the first three lactations.

The estimated variance components for cytoplasmic effects were close to zero for all dairy traits with the exception of first lactation milk yield, where a significant value of 2.0% of the total phenotypic variance was found. Significant contributions of cytoplasmic lineages to total variance in all lactations, however, were estimated for persistency (2·6 to 3.8%), days open (1·8 to 2.9%) and for both true and functional herd life (4.6% each). The portions of additive maternal variance and covariance between additive direct and additive maternal effects on total variance were very close to zero for all traits investigated. The maximum differences between BLUP lineage effects were 373 kg for first lactation milk yield, 44 days for days open (first lactation), 1·6 and 2·8 years for true and functional herd life and, on average, 1·0 kg for standard deviation of test day milk yields (persistency) of the first three lactations.

Removing the cytoplasmic effect from the model led to increased estimates of the additive direct heritability. Further model aspects such as interaction between additive and cytoplasmic gene effects and possible confounding between cytoplasmic and herd effects are discussed.

In dairy cattle type classification schemes, heifers are condition scored (CS) only once during their first lactation. Although genetic analysis of condition-score changes is not possible using an animal model, the data can be analysed as repeated observations on the sire.

CS records for 100 078 Holstein Friesian heifers, the progeny of 797 sires, were available. Sires differed in the shape of the regression of mean daughter CS on stage of lactation at both the phenotypic and genetic level. Genetic analysis was carried out using a random regression model (RRM) which can account for differences between sires in the shape of the CS curves. CS curves for individual sires were modelled using a cubic polynomial.

Heritability estimates for CS at each stage of lactation generally increased through the lactation from 0·20 in stage 2 (days in milk 31 to 60) to 0·28 in later lactation stages. Genetic correlations between CS at different stages were generally high (0·80), with the exception of correlations with stage 1 (days in milk 1 to 30) which decreased to 0·63 with stages 6 and 7, suggesting that CS at stage 1 is under different biological control from CS at other stages of the lactation. Using RRM, sire estimated breeding values (EBVs) for CS at each stage of the lactation were estimated. Sire rankings on EBV at each stage were seen to change through early, mid and later lactation stages.

The influence of plane of nutrition and diet on the eating quality of fresh pork was investigated in a study involving 721 animals. Boars and gilts of three genotypes (0, 0·25 and 0·50 Duroc inclusion level) were reared from 30 to 90 kg on seven feeding regimens (combinations of diet formulation and feeding level) to achieve different rates of lean and fat tissue growth during two growth periods (30 to 60 or 75 kg; 60 or 75 kg to 90 kg), respectively. A diet of conventional energy and protein (CEP, 14·2 MJ/kg digestible energy, 205 g/kg crude protein, 10 g/kg lysine) was given using combinations of ad libitum and restricted feeding to produce six treatment groups with variation in lean and fat growth rates. An additional treatment group was given food ad libitum on a higher energy and lower protein diet (HELP, 14·7 MJ/kg digestible energy, 166 g/kg crude protein, 7·0 g/kg lysine) between 30 and 90 kg. Dissected carcass composition at 90 kg was predicted from equations based on P2 fat depth, which were developed from full-side and ham joint dissections on sub-samples of animals. Representative sub-samples of animals were dissected at start (30 kg) and at interim weights (60 or 75 kg) to allow lean and subcutaneous fat growth rates to be calculated for all or parts of the growth period. The feeding regimes produced substantial variation in live-weight gain (DLWG) (744 to 914 g/day) and lean tissue growth rate (LTGR 345 to 417 g/day) and subcutaneous fat growth rate (SFGR 81 to 97 g/day), between 30 and 90 kg, and in longissimus dorsi intramuscular fat content (10·37 to 23·87 g/kg). Pigs given the HELP diet had the highest intramuscular fat and the best eating quality. Pigs offered the CEP diet ad libitum throughout the growth period produced more tender but less juicy meat than those given food restrictedly (0·8 or 0·9 of ad libitum). The correlations between DLWG, LTGR and SFGR for the whole or parts of the growth period and sensory characteristics, although often positive, were generally low, suggesting weak relationships.

Boar and gilt pigs from three genotypes (with 0, 0·25 and 0·50 Duroc inclusion level) were reared from 30 to 90 kg live weight on seven feeding regimens which involved combinations of diet formulation and feeding level. A diet of conventional energy and protein level (CEP; 14·2 MJ/kg digestible energy, 205 g/kg crude protein, 10 g/kg lysine) and a diet of higher energy and lower protein (HELP; 14·7 M]/kg digestible energy, 166 g/kg crude protein, 7·0 g/kg lysine) were used. One treatment involved feeding the HELP diet ad libitum, with the other six treatments involving feeding the CEP diet ad libitum, restricted, or in combinations of ad libitum and restricted. A total of 721 animals comprising similar numbers of boars and gilts were used to estimate sex differences for growth performance, carcass and meat quality, and eating quality. Tissue growth rates were predicted from regression equations based on P2fat depths or ham-joint dissection, developed from subsamples of animals that were subjected to full-side dissection. Overall when compared with gilts, boars grew faster (838 v. 799 gtday, P < 0·001), had improved food conversion ratios (2·39 v.2-55, P < 0·001) but had similar daily food intakes and lean and subcutaneous fat growth rates. Lean tissue food conversions did not differ significantly between the sexes. Killing-out proportions were higher for gilts (0·766 v. 0·749 , P < 0·001), however P2 backfat thickness and lean proportions did not differ between the sexes. The firmness of the mid-back fat, assessed subjectively and using a penetrometer, was greater for gilts than for boars. The tenderness of pork loin chops, assessed by a trained sensory panel, was judged to be better for boars than for gilts but there was no sex difference in overall acceptability. The fat from boars had a higher level of abnormal odour and boar odour. There was a sex × dietary treatment interaction for boar odour with the HELP diet producing the highest levels and the biggest difference between the sexes for odour scores.

A study was carried out involving 721 pigs, comprising boars and gilts, with either 0, 0.25 , or 0.50 Duroc inclusion level, which were produced by mating Large White boars with Large White × British Landrace sows, Large White boars with Duroc × (Large White × British Landrace) sows, or Duroc boars with Large White × British Landrace sows, respectively. Animals were reared on one of seven different feeding regimens from 30 to 90 kg live weight. Tissue growth rates were determined using a triple sampling procedure based on a combination of full-side and ham joint dissection on subsamples of pigs (127 and 366 pigs, respectively) and P2 backfat thickness on the remainder. Initial body composition was determined at 30 kg on subsamples of the three genotypes. Daily food intakes increased with increasing Duroc inclusion but live-weight gains were similar for the three genotypes. Lean and fat growth rates and food conversion ratios were greatest for the 0·50 Duroc group, although the genotype differences were small. Killing-out proportions and P2 fat depths were higher for the 0.25 and 0·50 Duroc groups. The proportion of lean in the carcass was lower (P < 0·01) for 0·50 Duroc pigs. Japanese colour scores and EEL reflectance indicated that the longissimus muscle was darker for the 0·25 and 0·50 Duroc genotypes. Subcutaneous fat firmness scores and penetrometer readings taken in the mid back indicated softer fat for the 0 Duroc group. Intramuscular fat levels increased (P < 0·01) with increasing Duroc inclusion (10.4, 11.2, and 18·2 g/kg for the 0, 0.25, and 0.50 groups respectively). Cooked longissimus from pigs with 0·50 Duroc had a lower shear force and was judged to have a stronger pork odour and to be more tender and acceptable than that from the 0 Duroc group. The 0.25 Duroc group showed a small improvement in tenderness but a weaker pork odour and similar overall acceptability compared with the 0 Duroc group. This study suggests that the use of the Duroc in crossing systems in the United Kingdom will have limited impact on growth performance but that 0·50 Duroc inclusion will result in fatter carcasses, higher intramuscular fat levels and improved eating quality.

A genetic algorithm (GA) was used to find optimal male and female age distributions in a natural mating system that maximizes cumulative response to mass selection over a 20-year time horizon for the case where inbreeding affects reproduction at 0·0 (F-0) and 0·1 (F-10) per 0·1 inbreeding coefficient. Twenty breeding female population sizes were considered ranging from 25 to 500 breeding females distributed across five age groups. Loss of response due to inbreeding effects on reproduction ranged from 19.4% and 15.5% in small breeding female populations to 2.5% and 5.2% in large breeding female populations when number of males was fixed (FX) or optimized (OP), respectively. OP resulted in an increase in response over FX ranging from 0·0 % to 69.3% for F-0 and 0·0 % to 77.6% for F-10. The potential loss of genetic gain that resulted from ignoring the inbreeding effects upon reproduction when they really existed ranged from 0·1 % to 44.6%. The potential loss of genetic gain that resulted from including inbreeding effects upon reproduction when they did not exist ranged from 0·1% to 3.9%. Optimal male and female age structures depended upon breeding female population size, the number of breeding males and inbreeding effects. Ignoring inbreeding effects upon reproduction may result in over estimation of response to selection. Use of a GA allowed accounting for complex relationships in the optimization.

The colon of the simple-stomached animal comprises a gradually changing microbial environment, using the residues of digestion as substrates for fermentation. As carbohydrate sources decline along the length of the colon, the microflora degrade proteins to use as an energy supply, resulting in the formation of undesirable and potentially toxic metabolites. This study has examined the possibility of using dietary starches as a means of extending carbohydrate fermentation along the colon in order to reduce the effects of protein degradation, and the influence of these starches on the numbers of microbial groups within the total population. The study was carried out in weaned piglets, using native and retrograded forms of maize and waxy maize starches, containing proportionately about 0·25 and 0·01 amylose respectively. It was found that protein degradation in the mid and distal regions of the colon was best reduced by the inclusion of the retrograded form of waxy maize, although these data did not achieve significance. However, it was found that a reduced population of the protein-degrading Bacteroides spp. resulted from the inclusion of waxy maize rather than maize in the diets, (proximal colon P < 0·01 ; mid colon P < 0·001 , distal colon P < 0·05), while the retrograded waxy maize produced increased lactobacillixoliform ratios throughout the colon, which may result in an improved resistance to infection by intestinal pathogens. Retrogradation of these starches reduced the coliform populations throughout the colon, with significant (P < 0·05) effects observed in the proximal and distal regions. The data suggest that, of the starches tested, reduced protein-degrading activity and improved pathogen resistance may be achieved with retrograded waxy maize.

Endogenous ileal amino acid flows were determined in pigs fitted with simple T-cannulas using either the regression method (meat and bone meal (MBM) as the protein source at five levels of inclusion) or following protein-free alimentation. Amino acid flows were compared with those determined by feeding animals a diet the sole nitrogen source of which was enzyme-hydrolysed casein (EHC), followed by centrifugation and ultrafiltration of the ileal digesta. The EHC was a mixture of free amino acids and oligopeptides (molecular weight 5000 Da). For the EHC treatment, the ileal digesta precipitate plus retentate was used to determine the endogenous flows. The ultrafiltration step excludes unabsorbed dietary amino acids from the measure of endogenous loss. Chromium III oxide was the reference marker in all diets. Estimates of endogenous nitrogen and amino acid flows determined under protein-free alimentation and the comparable flows determined using the regression method were similar. However, endogenous flows of amino acids for the EHC-fed pigs were generally significantly higher (F < 0·01) than values found for pigs on the protein-free diet and were higher than values obtained after extrapolation for pigs given the MBM-based diets. Mean endogenous ileal nitrogen flow for the EHC-fed animals was 2526 (s.e. 33.9) compared with 1711 (s.e. 25.5) mg/kg dry-matter intake for pigs receiving the protein-free diet.