An ‘indicator muscle’ (m. flexor digiti V brevis) was removed in its entirety from several Large White and Landrace pigs of varying fat depth (measured over the eye-muscle area). The total muscle fibre number was measured in transverse sections for each muscle. Significant inverse relationships were found between this fibre number and fat depth measurements. These and other results suggest that fibre number is related to lean meat content. Fibre number was also shown to be highly correlated with fibre density and as thinner fibres (i.e. higher fibre density) are associated with more tender meat, fibre number may be associated with quality as well as quantity of meat.

Previous reports have indicated that a proportion of pigs, homozygous normal for the skeletal muscle ryanodine receptor gene (RYR1), was halothane sensitive, and this was associated with poor meat quality when pigs were handled aggressively. This study was conducted to evaluate halothane sensitivity in RYR1-normal pigs, managed under simulated commercial conditions, to ascertain the association of halothane sensitivity with growth rate and meat quality. A total of 363 pigs across four farrowing groups, from seven Landrace sires and 38 Yorkshire–Landrace F1 dams, were tested at 8 weeks of age for halothane sensitivity using a closed system that delivered 5% halothane at 2 l/min for 3 (group 1) or 2 (groups 2 to 4) min. After 1 min, limb rigidity, limb tremors and abdominal discoloration were evaluated on a binomial scale with 0 indicating no reaction and 1 indicating reaction. Testing was repeated 2 days later. At 10 weeks of age, pigs were moved to finishing pens and not moved again until marketing. Within farrowing group, pigs were harvested in one of two groups, and at marketing were moved a distance of 91 m, weighed, tattooed, loaded and transported a distance of 550 km to a commercial harvest plant. After overnight rest, pigs were harvested and the pH of the loin muscle was measured at 45 min (pH45) after stunning. After an 18-h chill, loin muscle pH (pHu), International Commission on Illumination (CIE) L*, a*, b*, color (1 to 6) and marbling (1 to 10) scores and fluid loss percent were collected. Generalized linear mixed models were used to estimate repeatabilities for response to halothane challenge. Repeatabilities for limb rigidity for the front right and left legs were 0.24 and 0.31, respectively, whereas rear right and left leg repeatabilities were 0.19 and 0.17, respectively. Repeatabilities for front right and left leg tremors were 0.16 and 0.20, respectively. Growth rate was not influenced by any measure of halothane sensitivity. Carcasses from pigs exhibiting limb rigidity tended to have lower pH45 (5.88 v. 5.97; P = 0.06), similar pHu (5.47 v. 5.49; P = 0.32), less pH decline from 45 min to 18 h (−0.40 v. −0.50; P = 0.04) and a tendency for greater fluid loss percent (5.01 v. 4.55; P = 0.08) than carcasses from pigs that did not exhibit limb rigidity during halothane challenge. A proportion of pigs normal for RYR1 did exhibit limb rigidity during halothane gas challenge, and subsequently tended to have lower 45 min pH and greater longissimus muscle fluid loss post harvest.

The occurrence of Hb N in sheep has been investigated by means of starch gel electrophoresis.

In lambs, Hb N occurred in higher relative amounts than in adults, but not until 9 days of age. One-month-old lambs often showed an Hb N content as high as 10–30%.

Haemoglobin N was observed most in sheep of phenotype AA, less in those of type AB and was found to be absent in BB animals. It was also provoked experimentally by bleedings in sheep of types AA and AB but not in those of type BB.

Comparisons between breeds showed differences in the expression of Hb N. It occurred most regularly in Old Norwegian sheep (Spæl), but usually in concentrations of less than 1%. Hb N was, however, also found in other Norwegian breeds, in Cheviots and in Spanish sheep but not in sheep of the Oxford Down breed.

In two flocks of Spæl and Dala sheep where frequent bleedings were made, Hb N was observed at all times of the year.

In three trials involving 288 hoggets the influence on growth rate of implanting 15 mg. hexoestrol or 12 mg. stilboestrol was compared. In one trial the influence of adding excipient to either stilboestrol or hexoestrol to increase the surface area of the implant was also assessed. Live-weight gain was calculated for each time interval after implantation and it was concluded that after approximately 140 days the influence of implantation had largely disappeared. For optimum benefit to live-weight gain implantations should be made approximately 100 days prior to slaughter.

In all trials, implantation with synthetic oestrogens resulted in extra daily live-weight gain, the increase for all animals amounting to 31% extra daily gain for hexoestrol and 26% for stilboestrol. The addition of excipient to the implant diminished the initial growth response and reduced the extra gain achieved.

Implantation with the synthetic oestrogens significantly increased the final live-weight on the farm, live-weight before slaughter and carcass weights when groups of animals from each treatment were slaughtered together.

Stilboestrol and hexoestrol implantation resulted in an extra 4·7 and 6·1 lb. full live-weight; 3·7 and 5·3 lb. empty live-weight and 1·3 and 2·8 lb. extra carcass weight respectively, compared to controls killed at the same time.

Where hoggets had received a high-plane diet, treatment did not affect killing-out percentage, but where the level of nutrition was lower a decrease of up to 1% was observed. In all trials treatment with the synthetic oestrogens resulted in an increase in pelt weight and in one trial this increase was up to 2 lb.

Implantation with hexoestrol and stilboestrol increased the size of the gut full and empty in two of the trials. The differences were reduced when the gut weights were corrected to 100 lb. empty live-weight. The weight of the thyroid gland or the total weight of the trachea, heart and lungs were not affected by treatment.

The approximate rate of uptake of hormone from a 12 mg. implant of stilboestrol was assessed by the decrease in the weight of dried tablet removed at slaughter from 30 to 200 days after implantation. The linear regression y (uptake in mg.)=3·029+0·039x (days from implantation) fitted the data best, giving an approximate average uptake over this period of 39 micrograms of stilboestrol per day.

Relationships between specific gravity and carcass tissue were studied in 83 purebred Clun Forest lambs slaughtered at approximately 80 lb. liveweight and ranging in carcass weight from 29 to 42 lb. Carcass specific gravity accounted for 86·1% and 78·1% of the respective variances in carcass fat percentage and muscle percentage. Specific gravity determinations on a single joint were also highly correlated with the carcass tissues. Correlation coefficients between loin specific gravity and carcass fat and muscle were −0·89 and 0·82 respectively; corresponding figures for best-neck specific gravity were −0·86 with carcass fat percentage, and 0·76 with carcass muscle percentage. In partial correlation analyses, muscle/bone ratio failed to have a significant effect on these relationships. The usefulness of estimates of carcass composition based on specific gravity determinations is discussed in relation to the maximum probable errors associated with predicted values and with reference to the accuracy of these estimates under different experimental conditions. The magnitude of the confidence limits (P = 0·05) on individual predictions varied from ±2·98% to ±3·48% for fat and muscle respectively and for group (n = 12) predictions, from ±0·88% to ±1·01% respectively. This suggests that little confidence can be placed in specific gravity determinations as a reflection of real individual differences or small treatment differences.

Sows which had lactated for 2 days were allocated either to a control group or to a group in which oestrus was delayed by the administration of 75 mg methallibure per day for 12 consecutive days, followed by an intramuscular injection of 1000 IU pregnant mare serum gonadotrophin. All sows were mated whenever they were receptive to a boar. The mean time to first mating for the control group of 12 sows was 7·3 days but the mean time to conception was 22·3 days. The corresponding figures for the 9 treated sows were 17·0 and 22·2 days. The treated sows had significantly (P < 0·025) larger litters than the control sows (11·7 v. 8·5). For those sows which conceived at the first post-weaning service, the delayed oestrus treatment increased litter size on average by more than four pigs per litter.

Two hundred and forty Suffolk × (Cadzow Improver × Scottish Blackface) female sheep were housed at 4 months of age and average live weight (± s.d.) of 30·6 ± 501 kg, and divided into four equal treatment groups: HH, HL, LH and LL. They were group-fed such that HH and HL sheep were 39·7 ± 5·27 kg, and LH and LL were 35·6 ± 4·64 kg, at puberty, which was recorded in all sheep. There were no differences in average date at puberty.

After puberty the sheep were gradually transferred to different levels of feeding by the time of mating with fertile rams at the second oestrus such that HH and LH were group-fed 1·50, and HL and LL 0·75 of maintenance requirement. The sheep were slaughtered at return or 25 ± 3 days after mating.

The proportion of sheep with live embryos was 0·48,0·40,0·50 and 0·41 for HH, HL, LH and LL groups respectively (NS). Ova wastage was 0·59, 0·68, 0·51 and 0·59 for the treatments, with statistically significant differences in losses between treatments in sheep with two corpora lutea (P<0·05). Ovulation rate also differed between treatments (HH > HL, P < 0·01; HH > LH and LL, P < 0·05). Differences occurred between treatments in the proportion of multiple cycles between first and second oestrus (P<0·05), and HL sheep had a greater proportion of sheep failing to return to service but without embryos (HH>HL, P<0·05). The pooled results showed that pregnant sheep were heavier at 4 months of age (P < 0·05), but not at mating, than non-pregnant sheep. Sheep with two corpora lutea were more likely to be pregnant than sheep with one corpus luteum (P < 0·05).

Recent reports on livestock environmental impact based on life cycle assessment (LCA) did not fully consider the case of the dairy goat. Assignment of an environmental impact (e.g. global warming potential) to a specific product needs to be related to the appropriate ‘unitary amount’ or functional unit (FU). For milk, the energy content may provide a common basis for a definition of the FU. To date, no ad hoc formulations for the FU of goat milk have been proposed. For these reasons, this study aimed to develop and test one or more predictive models (DPMs) for the gross energy (GE) content of goat milk, based on published compositional data, such as fat (F), protein, total solids (TS), solid non-fat matter (SNF), lactose (Lac) and ash. The DPMs were developed, selected and tested using a linear regression approach, as a meta-analysis (i.e. meta-regression) was not applicable. However, in the final stage, a control procedure for spurious findings was carried out using a Monte Carlo permutation test. Because several published predictive models (PPMs) for GE in cow milk and goat milk were found in the literature, they were tested on the same data set with which the DPMs were developed. The best-performing DPMs and PPMs were compared directly with a subset of the individual data retrieved from the literature. Overall, the paucity of direct measurements of the GE in goat milk was a limiting factor in collecting data from the literature; thus, only a small data set (n=26) was established, even though it was considered sufficiently representative of milks from different goat breeds. The three best PPMs based on F alone gave more biased estimates of the GE content of the goat milk than the three new DPMs based on F, F and SNF and F and TS, respectively. Accordingly, three different formulations of FU are proposed, depending on the availability of data including both F and TS (or F and SNF) or F alone. Even though several metrics can be used in defining the FU for milk to be used in LCAs of goat farming systems, the proposed FU formulations should be adopted in place of the similar energy-based ones developed for other dairy species.

One hundred and twenty-seven groups of cattle were studied in a slaughterhouse lairage to determine the factors affecting their ability to rest. The cattle were studied by direct observation over one 30-min period during their first 3·5 h in the lairage. An ethogram/time budget analysis of one focal Hereford × Friesian steer or heifer per group was undertaken and the lying behaviour of the whole group was recorded. Linear regression analysis was used to examine the effect of length of time in the lairage on behaviour. The effects of source, sex, group size, space allowance and bedding were examined by a comparison of regression lines. In cattle from markets, standing and moving behaviour, and the number of aggressive interactions decreased and lying behaviour increased with time in the lairage. This was not the case in cattle coming direct from farms. In cattle from markets, steers settled down at a faster rate than heifers, and cattle kept in group sizes >5 settled down at a faster rate than those kept in group sizes ≤5. The presence of straw bedding was associated with greater lying behaviour in market heifers and in market cattle kept in group sizes ≤5 than in similar cattle without straw bedding. Cattle from markets but not those from farms started to settle down within 3·5 h of arrival in the lairage and their behaviour was affected by the social and physical environment.

There is a commitment by the European pig sector to ban surgical castration of male piglets in the European Union in 2018. One alternative to castration is to raise entire male pigs, with an increased risk of boar taint. A field study was performed to: (1) evaluate inter- and intra-farm variation in boar taint prevalence, (2) investigate factors measured at slaughter influencing boar taint and (3) evaluate the relationship between sensorial scoring by a trained panel and the concentration of boar taint components. From 34 farms, neck fat samples were collected from all entire male pigs in at least two slaughter batches per farm (78 batches; 9167 animals). In addition to olfactory boar taint analysis, data were also collected on fresh skin lesions (score 0 to 3) at the slaughter line, slaughter weight, lean meat percentage, duration of transport, time spent in lairage, total delivery duration, day length, shortening of days and outdoor mean temperature. Using the hot iron method, neck fat samples were scored (eight-point scale) for boar taint. Average boar taint prevalence (score ≥3) was 5.6±2.5% and the mean difference between the maximum and minimum prevalence per farm was 4.3±3.2%. Androstenone (AND), skatole (SKA) and indole concentrations were measured for a subset (n=254) of the samples. According to binomial univariate mixed models, entire male pigs with a higher skin lesion score had higher odds of having boar taint (P=0.031), as did fatter entire male pigs (P<0.001). In the binomial multivariate mixed model lean meat percentage (P<0.001) and outdoor mean temperature (P=0.005) remained as only significant factors. Based on our results, we can conclude that these statistically significant at least partially influence the prevalence of boar taint. According to the binomial univariate mixed models SKA concentration in liquid fat seems a better predictor for boar taint than AND. There were no significant synergetic effects between boar taint compounds.

Thirty-six male and thirty-six female lambs (mean live weight 31·6 kg) were used to investigate the effect of fish-meal supplementation upon voluntary intake of NaOH-treated straw in a 3 × 3 factorial experiment with three levels of fish meal (0, 45 and 90 g/day) and three allowances of concentrate (57, 10·0 and 14·3 g/kg live weight) (experiment 1). The fish meal × concentrate allowance interaction was significant (P < 0·05) for straw dry matter (DM), total DM and metabolizable energy (ME) intake. Thus, as concentrate allowance increased, straw DM intake remained largely unchanged when fish meal was included in the diet whereas concentrate progressively substituted for straw DM intake when fish meal was not included in the diet. Increasing concentrate levels increased total DM intake linearly for all levels of fish meal but the rate of increase was positively associated with level of fish meal.

In experiment 2, 24 castrated male lambs (mean live weight 40·7 kg) were used to measure apparent digestibilities and nitrogen (N) balance on four of the diets used in experiment 1. The overall effects of concentrate and fish-meal levels upon voluntary intake were similar to those found in experiment 1 but the interaction term was not significant either for intake or for the digestibility coefficients. Increasing fish-meal level increased apparent digestibility of DM, organic matter (OM) and aciddetergent fibre (ADF) (P < 0·01) while increasing concentrate allowance increased apparent digestibility of DM (P < 0·001) and OM (P < 0·01) but decreased that of ADF (F < 0·01). Nitrogen (N) retention was improved by the inclusion of fish meal in the diet (P < 0·001) and by high allowance of concentrate (P < 0·001).

The voluntary intake response observed in experiment 1 could not be explained by the digestibility and N balance results obtained in experiment 2.

Foetal life malnutrition has been studied intensively in a number of animal models. Results show that especially foetal life protein malnutrition can lead to metabolic changes later in life. This might be of particular importance for strict carnivores, for example, cat and mink (Neovison vison) because of their higher protein requirement than in other domestic mammals. This study aimed to investigate the effects of low protein provision during foetal life to male mink kits on their protein metabolism during the early post-weaning period of rapid growth and to investigate whether foetal life protein deficiency affects the response to adequate or deficient protein provision post weaning. Further, we intended to study whether the changes in the gene expression of key enzymes in foetal hepatic tissue caused by maternal protein deficiency were manifested post-weaning. A total of 32 male mink kits born to mothers fed either a low-protein diet (LP), that is, 14% of metabolizable energy (ME) from protein (foetal low – FL), n = 16, or an adequate-protein (AP) diet, that is, 29% of ME from protein (foetal adequate – FA), n = 16) in the last 16.3 ± 1.8 days of pregnancy were used. The FL offspring had lower birth weight and lower relative abundance of fructose-1,6-bisphosphatase (Fru-1,6-P2ase) and pyruvate kinase mRNA in foetal hepatic tissue than FA kits. The mothers were fed a diet containing adequate protein until weaning. At weaning (7 weeks of age), half of the kits from each foetal treatment group were fed an AP diet (32% of ME from protein; n = 8 FA and 8 FL) and the other half were fed a LP diet (18% of ME from protein; n = 8 FA and 8 FL) until 9.5 weeks of age, yielding four treatment groups (i.e. FA-AP, FA-LP, FL-AP and FL-LP). Low protein provision in foetal life lowered the protein oxidation post-weaning compared with the controls (P = 0.006), indicating metabolic flexibility and a better ability to conserve protein. This could not, however, be supported by changes in liver mass because of foetal life experience. A lower relative abundance of Fru-1,6-P2ase mRNA was observed (P < 0.05), being lower in 9.5-week-old FL than in FA kits. It can be concluded that foetal life protein restriction leads to changes in post-weaning protein metabolism through lower protein oxidation of male mink kits.

The coefficients of inbreeding and the degree of relationship for British Friesian bulls used for artificial insemination by the Milk Marketing Board in sample years between 1955 and 1972 and for random samples of registered females from the same years have been calculated. The average coefficient of inbreeding was lower in bulls (0·5%) than in registered females (2·7%). The average degree of relationship was 0·7% for bulls and 2·6% for heifers.

Feed efficiency traits (FETs) are important economic indicators in poultry production. Because feed intake (FI) is a time-dependent variable, longitudinal models can provide insights into the genetic basis of FET variation over time. It is expected that the application of longitudinal models as part of genome-wide association (GWA) and genomic selection (i.e. genome-wide selection (GS)) studies will lead to an increase in accuracy of selection. Thus, the objectives of this study were to evaluate the accuracy of estimated breeding values (EBVs) based on pedigree as well as high-density single nucleotide polymorphism (SNP) genotypes, and to conduct a GWA study on longitudinal FI and residual feed intake (RFI) in a total of 312 chickens with phenotype and genotype in the F2 population. The GWA and GS studies reported in this paper were conducted using β-spline random regression models for FI and RFI traits in a chicken F2 population, with FI and BW recorded for each bird weekly between 2 and 10 weeks of age. A single SNP regression approach was used on spline coefficients for weekly FI and RFI traits, with results showing that two significant SNPs for FI occur in the synuclein (SNCAIP) gene. Results also show that these regions are significantly associated with the spline coefficients (q2) for 5- and 6-week-old birds, while GWA study results showed no SNP association with RFI in F2 chickens. Estimated breeding value predictions obtained using a pedigree-based best linear unbiased prediction (ABLUP) model were then compared with predictions based on genomic best linear unbiased prediction (GBLUP). The accuracy was measured as correlation between genomic EBV and EBV with the phenotypic value corrected for fixed effects divided by the square root of heritability. The regression of observed on predicted values was used to estimate bias of methods. Results show that prediction accuracies using GBLUP and ABLUP for the FI measured from 2nd to 10th week were between 0.06 and 0.46 and 0.03 and 0.37, respectively. These results demonstrate that genomic methods are able to increase the accuracy of predicted breeding values at later ages on the basis of both traits, and indicate that use of a longitudinal model can improve selection accuracy for the trajectory of traits in F2 chickens when compared with conventional methods.

Four silages were prepared from perennial ryegrass. Half the crop was picked up soon after mowing and the remainder left to wilt for 24 h. Half the unwilted and half the wilted grass was chopped by a forage harvester with its normal complement of knives; the remainder was chopped by a forage harvester with all but two of its knives removed. The ensiled material was offered ad libitum for 80 days as the sole food to 32 British Friesian male castrates initially 14 weeks of age and 111 kg live weight.

Wilting raised silage dry-matter content by 31 g/kg fresh weight and gave lower concentrations of acetic acid whilst short chopping gave lower butyric acid. Concentrations of acetic acid, butyric acid and ammonia nitrogen were high on all treatments. Organic matter digestibility was significantly increased by wilting (P < 0·001) and significantly depressed by chopping (P < 0·001). There was no response in dry-matter intake to short chopping, but wilting raised daily intake from 18·4 to 19·9 g silage dry matter per kg live weight (P < 0·001). Live-weight gain was increased from 0·42 to 0·46 kg/day by short chopping (P < 0·05) and from 0·40 to 0·48 kg/day by wilting (P < 0·01)

Priming with a progestagen-impregnated vaginal pessary followed by an injection of 750 i.u. pregnant mare serum gonadotropin at pessary withdrawal was used to induce oestrus and ovulation during anoestrus (13 June, latitude 57°N) in 58 Border Leicester × Scottish Blackface ewes that had lambed previously in late March/early April. At 54 to 58 h after pessary withdrawal the uterus of each ewe was viewed by laparoscopy and 50 × 106 viable sperm deposited into each uterine horn. Mean ovulation rate was 2·9 (s.d. 0·12; range 1 to 5). Plasma progesterone concentrations remained >1·5 μg/l in 54 (93%) of the ewes until at least day 21 after insemination implying a high fertilization rate. After allowing for three ewes that were observed to abort between 39 and 55 days after insemination and another three, carrying nine normally developed lambs, that died between 102 and 136 days of gestation, 40 of the remaining 48 ewes (i.e. 69% of the original 58) produced 76 viable lambs in early November. These conception and lambing rates obtained following the intrauterine insemination of 100× 106 viable sperm per ewe are more than double those obtained following natural mating or conventional cervical insemination with four times the number of viable sperm and imply that intrauterine insemination may enhance lamb production from ewes induced to breed during seasonal anoestrus.

A single intra-muscular injection of either 6mg or 12 mg Dexamethasone on day 142 of gestation resulted in a high degree of synchrony in the time of lambing compared with untreated controls, with no increase in lambing difficulty or perinatal mortality. Birth weight and growth rate of lambs born to treated ewes were not significantly different from those of untreated control ewes.

A single intra-muscular injection of 12 mg Dexamethasone on day 125 of gestation resulted in abortion in nearly half of the ewes, and their lambs were either stillborn or died soon after birth.

These data demonstrate the need to know precise mating dates if parturition is to be induced in this way.

The current study compared beef production, quality and fatty acid (FA) profiles of yearling steers fed a control diet containing 70 : 30 red clover silage (RCS) : barley-based concentrate, a diet containing 11% sunflower seed (SS) substituted for barley, and diets containing SS with15% or 30% wheat dried distillers’ grain with solubles (DDGS). Additions of DDGS were balanced by reductions in RCS and SS to maintain crude fat levels in diets. A total of two pens of eight animals were fed per diet for an average period of 208 days. Relative to the control diet, feeding the SS diet increased (P<0.05) average daily gain, final live weight and proportions of total n-6 FA, non-conjugated 18:2 biohydrogenation products (i.e. atypical dienes) with the first double bond at carbon 8 or 9 from the carboxyl end, conjugated linoleic acid isomers with the first double bond from carbon 7 to 10 from the carboxyl end, t-18:1 isomers, and reduced (P<0.05) the proportions of total n-3 FA, conjugated linolenic acids, branched-chain FA, odd-chain FA and 16:0. Feeding DDGS-15 and DDGS-30 diets v. the SS diet further increased (P<0.05) average daily gains, final live weight, carcass weight, hot dressing percentage, fat thickness, rib-eye muscle area, and improved instrumental and sensory panel meat tenderness. However, in general feeding DGGS-15 or DDGS-30 diets did not change FA proportions relative to feeding the SS diet. Overall, adding SS to a RCS-based diet enhanced muscle proportions of 18:2n-6 biohydrogenation products, and further substitutions of DDGS in the diet improved beef production, and quality while maintaining proportions of potentially functional bioactive FA including vaccenic and rumenic acids.

The additive genetic response per generation and the genetic superiority of female genotype(s) selected for commercial cloning (clonal response) were maximized for a closed adult nucleus scheme, with 256 or 1024 test places, by varying the mating design (number of clones, full-sibs and half-sibs). Responses were corrected for effects of finite sample size and correlated index values on the selection intensity, and variance reduction due to selection. Additive genetic responses, which varied from 0·153 to 0·514 phenotypic standard deviations per generation, were 0·68 to 0·89 of corresponding uncorrected predictions. Reductions were largest when the intensity and accuracy of male selection were high. Clonal responses varied from 0·460 to 2·506 phenotypic standard deviations, increasing with the intra-clone correlation, the intensity of clonal selection and the test capacity. Reductions in clonal responses, which varied from proportionally 0·04 to 0·27, were smallest when dominance variance was high. Increasing the test capacity resulted in a proportionally 0·21 to 1·55 increase in genetic responses, while proportional increases in clonal responses varied from 0·09 to 0·36. With selection of only one male per full-sib family, designs which maximized genetic and clonal responses were different in all cases. Differences were largest when the heritability and the intra-clone correlation were low and the intensity of clonal selection was high. Without the restriction on male selection, optimal mating designs were different, unless dominance variance and intensity of clonal selection were both low.

The intention of the current study was to gain more insight into the endocrine and molecular control mechanisms of growth in the pig. For this purpose various growth related parameters were determined in 4-month-old barrows of two extreme pig genotyes, the small, obese Göttingen Miniature (GM) and the large and lean German Landrace (DL). Mean growth hormone (GH) concentration, GH pulse frequency and GH pulse amplitude did not differ between breeds. Likewise, plasma IGF-1, thyroxine, tri-iodothyronine (T3) concentrations were similar in both breeds. However the plasma GH response (maximum level and area under curve) to a single i.v. injection of GHRH in DL was higher than in GM (P < 0·05). Furthermore, basal plasma insulin and in particular plasma cortisol concentrations were higher in GM compared with DL pigs (P 0·05 and 0·01 respectively). Analysis of cortisol during 4-h frequent blood sampling indicated higher cortisol amplitudes in GM compared with DL (P ≤ 0·01). Specific bGH-binding to hepatic membrane preparations was not different between breeds and IGF-1 m RNA concentrations determined by reverse transcription-polymerase chain reaction in liver, m. semimenbranosus and m. longissimus dorsi were similar in both breeds. I.m. treatment with recombinant porcine somatotropin (rpST; 70 µg/kg live weight) over an 8-day period in contemporary barrows increased without any breed difference, plasma IGF-1, T3 and insulin concentrations and hepatic specific bGH-binding, but did not affect thyroxine or cortisol concentrations in plasma. IGF-1 gene expression was also elevated in liver and muscle tissues in rpST-treated animals without obvious breed effects. The observations underline the complexity of the hormonal and molecular control of growth and support the notion that differences in growth potential are the consequence of differences at various levels of the somatotropic axis and apparently relate to differences in other control systems of energy metabolism such as the pituitary adrenal axis or the endocrine pancreas as well.