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.

Spreadsheet models were constructed to assess the economic impact of some 30 non-notifiable diseases of farm animals in Great Britain. A standardized methodology and common valuation base were used to derive estimates of the direct costs to livestock production of each disease, separately identifying the costs associated with disease output losses and those relating to disease treatment and prevention. Disease data limitations and uncertainties are incorporated into the estimation procedure. The spreadsheet models are highly transparent with calculations and the origin of parameter values clearly documented. The assessments of six bovine diseases, are presented: BVD, fasciolosis, lameness, leptospirosis, mastitis, and summer mastitis, and full details of the analyses of all the diseases can he accessed on the internet. The models do not consider the wider economic impacts of disease, such as effects on markets, human health and animal welfare. However, the approach is a simple and transparent one which enables exploration of the direct costs associated with a range of livestock diseases and which is easily communicated to policy makers and others.

This study quantified individual phenotypic variation in live weight and live-weight changes during the first three lactations and estimated the effects of age, lactation week and pregnancy on live weight. Data comprised weekly averaged live weight (calculated from daily observations) during 452 lactations of 239 Holstein-Friesian cows. Unadjusted mean live weights were 553 (s.d. 50), 611 (s.d. 55) and 654 (s.d. 57) kg during first, second and third parity, respectively. Estimated effect of growth during parity was 46, 52 and 23 kg for the first three parities. Mean maximum weight loss was 26, 22 and 22 kg for first, second and third parity and variation was large among individuals. Week of lactation when cows had their maximum weight loss ranged from 7 weeks in first lactation to 13 weeks in third lactation. Estimated maximum effect of pregnancy on live weight during the lactation varied from 27 to 59 kg. Phenotypic variance in live weight increased with parity. Repeatabilities of live-weight observations within parity were 0.85 . Across parities, high repeatabilities were found for calving weight and mean live weight but not for parameters associated with maximum weight loss. Correlations between weekly means and mean live weight during the whole of lactation were high. It was concluded that single live-weight observations of heifers are a good measurement of mean live weight during the first three panties.

Two experiments were conducted to corroborate or refute the theory that animals will choose a food that will allow them to use it with maximum efficiency. Pigs have been shown to utilize foods of high nutrient density more efficiently than those of low density, so the choices made by pigs when offered such foods could be used to test the above optimization theory. In experiment 1, 48 Large White × Landrace gilts were used, for an 8-week period starting at 22 kg live weight, while in experiment 2, 48 boars of the same cross but of a genetically improved strain were used from 24 to 60 kg live weight. In both experiments use was made of high nutrient density summit foods which were used alone, or diluted in the ratio 80 summit: 20 milled sunflower husk to provide the low density foods. In experiment 1, the high density diet (HI) contained 7·5 g lysine per kg and 13·20 MJ digestible energy (DE) per kg, whereas in experiment 2 two summit foods were formulated, the first diet (H2) was offered for 3 weeks from 24 kg live weight and the second (H3) followed until 60 kg live weight. Foods H2 and H3 contained 11·0 and 8·40 g lysine per kg respectively and 15·0 and 14·0 MJ DE per kg, respectively. Both experiments made use of a high (H1 and H2, respectively) and a low nutrient density (L1 and L2, respectively) control treatment in which pigs were given ad libitum access to H1 and H2/H3, and L1 and L2/L3 in experiments 1 and 2 respectively (no. =4). In addition, a medium density treatment (Ml) consisting of a 50: 50 mixture of H1 and L1 (no. = 4) was given in experiment 1. Two choice-feeding treatments where used in both experiments, the first in which H1 and H2IH3 were placed in the left bin (CL1 (no. =18) and CL2 (no. = 20), respectively) and the appropriate dilution diet in the right bin, and the second in which H1 and H2/H3 were placed in the right bin (CR1 (no. = 18) and CR2 (no = 20)). There were no differences in average daily growth rates between treatments within experiments but there were significant differences (P < 0·05) in food intakes and efficiency of food utilization (FCE) between treatments. The highest intakes and lowest FCE were obtained on the L1 and L2 treatments while the lowest intakes were recorded on the choice-feeding treatments. There were no significant differences in FCE neither between H1, CL1 and CR1 nor between H2, CL2 and CR2. Only in experiment 1 were there significant differences (P < 0·05) between choice-feeding treatments on the basis of the position of the food bin but there was no preference for a particular position. The results indicated that pigs were able to differentiate successfully between two foods on the basis of their nutrient density, that bin position was not used as a cue in the choice made, that a small amount of the ‘unwanted’ food was consumed throughout the experiment and that the diet selected maximized FCE.

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.

Current feeding recommendations for lactating sows may be inappropriate for modern genotypes with high milk production. The introduction of the prolific but obese Meishan breed into sow lines also necessitates a review of nutrient requirements. A 2 × 2 factorial experiment was used to investigate the influence of breed type (Meishan synthetic 50% (M) and purebred European White (W) on response to dietary protein level (L = 140 g crude protein (CP) per kg, 6 g lysine per kg; H = 181 g CP per kg, 9 g lysine per kg) over a 5-week lactation. Milk yield (days 5, 9, 13,17, 21 and 28), milk composition and piglet growth and body composition were measured to quantify aspects of lactational performance. M had higher litter sizes throughout lactation (P < 0·001) and produced more milk than W(M = 10·04 W = 7·85 (s.e.d. 0·521) kg/day, P < 0·001) and milk of a higher fat content (M = 79·6 W = 75·0 (s.e.d. 5·71 g/kg, P < 0·05). Total solids were not significantly different between treatments. H produced higher milk protein content than L (L = 43·0 H = 55·7 (s.e.d. 3.01) g/kg, P = 0·05). Litter growth rates showed a breed effect (P < 0·001), diet effect (P < 0·001) and a breed × diet interaction (ML = 2·41 MH = 3·21 WL = 2·07 WH = 2·07 (s.e.d. 0·658) kg/day, P < 0·001). M piglets had higher fat deposition rates (M = 37 W = 24 (s.e.d. 4.5) g/day, P < 0·05). L piglets had a lower protein (P < 0·05) and fat (P < 0·05) deposition rate compared with H piglets. Higher litter growth rates of M sows resulted from a combination of increased milk yield and f at content and this was further enhanced by additional dietary protein. W sows showed no milk yield response to dietary protein but reduced maternal tissue catabolism.

Responses in carcass composition and meat quality after seven generations of selection for components of lean growth rate were examined in a population of Large White pigs. There were four selection groups in the study, with divergent selection for lean growth rate on ad libitum (LGA) or restricted (LGS) feeding regimes, lean food conversion ratio (LFC) and daily food intake (DFI). In generations six and seven, two offspring from each of 10 sires, within each selection line, were to be allocated for half-carcass dissection and measurement of meat quality. There were 320 animals in the study, with 40 animals from each of the high and low selection lines and, within each selection line, two offspring per sire.

Responses in carcass composition were similar in the three selection groups given food ad libitum, but rates of lean and fat growth rate differed between selection lines. Intramuscular fat content was reduced with selection for high LGA and high LFC but was increased with selection for low DFI (-1·7 and -3·2 v. 2·7 (s.e.d. 0·7) mg/g), which was unexpected given the higher carcass fat content of the low DFI line, relative to the high line (249 v. 190 (s.e.d. 7) g/kg). Muscle colour was darker, as measured by trained sensory panel assessment, in selection lines which reduced the rate of fat deposition to achieve a leaner carcass (high LFC and low DFI) but there was no response in muscle colour with selection for LGA (0·4 and 0·3 v. 0·0 (s.e.d. 0·1)). Responses in muscle shear force (5·3 v. 4·4 (s.e.d. 0·4) kg) and flavour liking (4·0 v. 4·3 (s.e.d. 0·12)) were limited to the LGA and LFC selection groups, respectively. There were no significant responses in muscle moisture content, muscle pH or myofibrillar fragmentation index, nor were there any responses in meat quality with selection on LGS. Therefore, decreasing the rate of fat deposition was associated with darker meat and increasing the rate of lean growth was associated with higher shear force. There were selection strategy specific responses in the fatty acid composition of intramuscular fat, which may have contributed to the responses in eating quality.

In general, responses in meat quality were small, such that incorporation of meat quality traits in selection objectives, which are primarily focused on increasing the efficiency of lean meat production, may not be necessary. However, it would be pertinent to evaluate periodically genotypes of breeding companies for muscle quality traits.

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.

Our laboratory recently reported that the ratio of a piglet’s weight to that of its placenta (RATIO) varies approximately three-fold within a litter, due predominantly to variation in placental size which is known to be a limiting factor in litter size. It was further determined that selection of boars and gilts with a higher than average RATIO for breeding resulted in an increased litter size and reduced placental weights. The objective of this experiment was to examine the effects of RATIO on economically important production traits (piglet survival to weaning, 21-day weights, days to 105 kg, backfat depth and loin muscle area at 105 kg) in a purebred breeding stock herd of Finnish Yorkshire and Landrace pigs. Sows were monitored throughout farrowing and each piglet was matched to its placenta. Each piglet and its placenta were individually weighed and a RATIO determined. Placental weight but not piglet birth weight exhibited a strong (P < 0·001) negative correlation with RATIO (r = -073). Up to three-fold differences in RATIO were observed within a single litter. These differences were much greater than the variation noted between litters and litter mean RATIO was not significantly associated with litter size. The distribution of individual piglet RATIOS across the entire group of pigs ranged from 2·8 to 11·4 suggesting a marked difference in placental efficiencies. No significant association was seen between RATIO and 21-day weight, days to 105 kg, backfat depth or loin muscle area. Thus, an above average ratio of a piglet’s weight to that of its placenta is indicative of a smaller more efficient placenta and appears to have no subsequent detrimental effects on growth efficiency.

For purely hypertrophic muscle it is postulated that the growth rate in number of nuclei is proportional to the cytoplasmic mass per nucleus multiplied by a growth constraining supplementary function. Growth constraint depends on the distance from any one of the limit number of nuclei, the limit muscle mass or the limit cytoplasmic mass per nucleus. Furthermore, theory and evidence are presented for a power (allometric) relationship between total number of nuclei (n) and muscle mass (m) given by the equation n = gmh. Evidence points to two clusters of values for h, one in the vicinity of h = 2/3 and the other h = 1/2. Both may depend on a linear relationship between number of nuclei inside muscle fibre and fibre cross-sectional area. The difference between the two situations can be derived from basic assumptions on either local or systemic diffusion mediated control of the number or division of satellite cell nuclei, leading directly to values of h either equal to 2/3 or V2. For likely values of h and suitable choices of growth constraints, almost all well known growth functions in the literature are derived as potentially applicable to total number of nuclei, or muscle mass or their ratio. Muscle mass growth will show a sigmoidal form for h = 1. This explains sigmoidal growth in body mass as it is mostly dominated by muscle mass. A possible linear growth phase before maturity is explicable from the cessation of either length (h = 1) or nuclear (h = 0) growth in muscle fibres, while cytoplasmic growth continues to maturity. Furthermore, two rat examples indicate that whole body protein growth can be described by the equations derived for muscle mass growth.

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.

Machine vision can be used to collect images of pigs and analyse them to identify and measure specific areas and dimensions related to their growth, shape and hence conformation. This information could improve the stockman’s ability to maximize production efficiency and also to monitor health by detecting abnormalities in growth rates. This work introduces fully automated algorithms which find the plan view outline of animals in a normal housing situation, divide the outline into major body components and measure specified dimensions and areas. Special attention is paid to determining whether the results are sufficiently repeatable to be useful in estimating these parameters. Problems in compensating for changes in the optical geometry are outlined and methods proposed to deal with them. The repeatability of the image analysis process coupled with the subsequent signal processing for outlier rejection gives s.e. values on areas of < 0·005 and on linear dimensions of < 0·0025. For example, the plan view area less head and neck (A4) can be used to predict the weight of the group of pigs at 34 kg, 66 kg and 98 kg with standard errors of 0·25 kg, 0·17 kg and 0·39 kg respectively when using manual weighing results to calibrate the system. If an individual pig is weighed once at 75 days (e.g. 34 kg) to calibrate the A4-to-weight relationship, subsequent A4 measurements can be used to predict its weight when 125 days old (approx. 80 kg) to within 1 kg. This matches the accuracy of the manual weighing system used in the trials. The effect of pig gender on the area to weight relationships is not significant (P = 0·074), but there is a small yet significant gender effect with the linear dimensions.

Responses to intravenous glucose challenge (no. = 26) and basal metabolite and hormone concentrations (no. = 68) were determined in dairy cows selected for high (HFI) or low (LFI) milk-fat concentration but with similar 40 g/kg fat-corrected milk (FCM) yields. All cows were given a mixed diet ad libitum. Following a glucose challenge the insulin release was higher (P < 0·05) and the glucose clearance rate faster (P < 0·05) in the HFI cows compared with the LFI cows. Basal plasma concentrations of the metabolites alanine, β -hydroxybutyrate, glucose, non-esterified fatty acids and urea and the hormones insulin-like growth factor-1 (IGF-1), insulin and leptin were not influenced by selection line.

The silver fox is an extreme seasonal breeder with one reproductive season during the year. Males are sexually mature at the age of 9 to 10 months. In the present study reproductive function in yearling and adult silver fox males before and during the reproductive period was examined. The aim was to determine the age-dependent features of their reproductive system. It was found that yearling males mate with a smaller number of females and that their first mating period is shorter compared with adult foxes. A high proportion of yearling males did not mate at all (27%) or their sexual activity was reduced (26%), although the number of pups horn from mating males was normal. During the peak of male sexual activity, the number of spermatozoa in the ejaculate was lower in yearling compared with adult males. However, there was no difference in the number of abnormal forms of spermatozoa between the two groups. There was no significant difference in sperm numbers between sexually active and inactive yearlings. Before the reproductive season, yearling males did not differ from adults in plasma concentration of testosterone, while body and testes weights and level of oestradiol were lower. At the end of the breeding season, yearlings did not differ from adults in any trait. It is concluded that the reproductive capacity of yearling male foxes might he immature before the first breeding seasons but that this immaturity did not decrease their reproductive success.

Experiment I. One hundred and twenty-five lactations from 88 New Zealand × Californian does were used to study the influence of high fat diets on the performance and milk yield of multiparous rabbit does in two high productivity situations: housed in hot conditions (minimum temperature above 24°C) with eight pups (group H8), or housed in warm conditions (minimum temperature under 21 °C) with 11 pups (group W11). Starting from a control diet (diet C) with 26 g ether extract (ЕЕ) per kg dry matter (DM), two isoenergetic diets were formulated adding fat from vegetable sources up to 99 g ЕЕ per kg DM (diet V) or animal sources up to 117 g ЕЕ per kg DM (diet A). The lactating does showed similar food daily intakes (⋍105 g DM per kg), therefore digestible energy intake of does on high fat diets was significantly higher (P < 0·001). The addition of f at to the diets increased (P < 0·001) milk yield of does (+21 and 24 g/day for diets V and A, respectively) and litter weight at weaning (P < 0·05), and decreased the number of pups replaced (P < 0·01) during lactation. Group H8 does had significantly lower DM intakes, litter growth rates and milk production levels than group Wll does (P < 0·001).

Experiment 2. The effect of these diets on milk composition was determined in 62 lactations from 28 multiparous rabbit does, in which litter size was maintained at eight pups. Milk samples were collected manually on the 7th, 21st and 28th days of lactation. Milk of does given high fat diets, especially diet A, had higher fat and energy contents (P < 0·001) and a lower protein content (P < 0·001) than those given diet C. Milk of does given diet A had a greater DM content than those given the diets С or V (P < 0·001). There was a correlation between the fatty acid composition of milk and dietary fat. The proportion of odd chain fatty acids in the milk fat was lower for does given diet V (P < 0·05) than those given diet A. In conclusion, high fat diets were related to a higher milk yield and energy content of milk, allowing a higher litter weight gain and a lower mortality of sucking pups.

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.

Active immunization against gonadotropin-releasing hormone (GnRH), commonly known as immunocastration, has been proposed as an alternative to traditional methods of castrating bulls. This study evaluated the effects of immunocastration on growth, behaviour and meat quality of post-pubertal bulls. Bulls were either vaccinated against GnRH (no. = 30, I) or left intact (no. = 30, B). A third treatment consisted of steers (no. = 20, S) that had been castrated pre-pubertally. The animals were run in eight single treatment groups (no. = 10 per group), three of each of В and I and two groups of S. Anti-GnRH antibodies developed and plasma testosterone concentrations declined in I following immunization. Aggressive behaviour of I declined to be lower (P < 0·5) than B and no different from S, 5 weeks after primary immunization. Seven weeks after immunocastration all animals were slaughtered. The hot carcass weight of I was between that of B and S but not significantly different from either. There were no effects of treatment on pHu or meat colour measurements. Taste panel assessment rated I higher than B, but lower than S for tenderness, juiciness and overall palatability. These results demonstrate that immunocastration of post-pubertal bulls 7 weeks before slaughter is a potential means of reducing problematic bull behaviour and improving meat quality although this is likely to be at the cost of reduced weight gain.

Changes in the formulation and flavour of concentrate foods may temporarily reduce their acceptability to cattle, leading to reduced intake when they are offered for a limited time during milking. The rate of intake of 12 dairy cows offered 1 kg of salty or bitter concentrates was compared with a sweet concentrate, with or without an artificial sweetener to mask adverse flavours. The cows were offered the test concentrates twice a day in a Latin-square design with seven feeding occasions per period and the apparent and actual (excluding non-feeding time) food intake rates were recorded for all seven feeding occasions. Both apparent and actual intake rates were slower for the bitter compared with the salty and sweet flavoured concentrate.

For the first two feeding occasions the intake rate was recorded separately for the 1st min and the subsequent period until the end of feeding. The intake rate was faster in the 1st min because of more rapid prehension of the food and fewer interruptions to the feeding process. Where no mask was included there was no effect of flavour on the apparent intake rate in the 1st min of the first feeding occasion but in the 1st min of the second feeding occasion the apparent intake rate of the salty concentrate was less than that for the sweet or bitter concentrates. The actual intake rates of the bitter and salty concentrates were less than for the sweet concentrate. The mask increased the apparent intake rate of the bitter and sweet concentrates in the 1st min of both the first and second feeding occasions, by reducing the non-feeding time and it also increased the actual intake rate of salty concentrates.

After the 1st min the apparent intake rate of the salty concentrate was faster than that of the bitter and sweet concentrates, where no mask was included. The mask increased the apparent intake rate of the sweet concentrates at this time but reduced it for salty and bitter concentrates. It therefore reduced the acclimatization to the salty and bitter concentrates and enhanced the attractiveness of the sweet concentrates.

There was a residual effect from the previous period of concentrates which were eaten slowly i.e. salty concentrates, which reduced the 1st min intake of foods that were eaten rapidly, i.e. sweet concentrates, in the subsequent period. This was largely due to increases in the time spent pausing between bouts of food ingestion. After the 1st min the apparent intake rate of cows receiving salty concentrate for a second consecutive period was increased, suggesting acclimatization. The opposite effect was observed for the sweet concentrate, probably because the novelty of the sweetness had diminished, making it relatively less attractive to the cow. This experiment therefore provides evidence that bitter and to some extent salty concentrates are consumed at a slower rate than sweet concentrates, except for the 1st min in which they are offered to cattle and that a reduced concentrate intake rate may persist after the flavour is removed from the food. Cattle did, however, demonstrate an ability to acclimatize to salty concentrate over time.

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.