Previous studies have demonstrated that sperm head morphometry can be used as a potential diagnostic tool for detecting biophysical changes associated with sperm viability in bovine spermatozoa. In this study, sperm head morphometry was used to investigate its value as a biophysical marker for detecting volumetric changes in bovine spermatozoa under in vitro capacitating and non-capacitating incubation conditions. To further test this hypotesis, aliquots of pooled, washed bovine sperm were incubated in either Tyrode’s complete medium with heparin (TCMH; a capacitating medium containing Ca2+, NaHCO3 and heparin), Tyrode’s complete medium heparin-free (TCM; a medium containing just Ca2+ and NaHCO3) or Tyrode’s basal medium (TBM; a non-capacitating medium free of Ca2+, NaHCO3 and heparin, used as control). Aliquots of sperm were processed for morphometric analysis at different incubation-time intervals (0, 3 and 6 h at 38°C), and the chlortetracycline assay was used simultaneously to confirm the ability of the sperm to undergo capacitation (B pattern) and the acrosome reaction (AR pattern) status in each medium. After 3 h of incubation under TCMH conditions, a significant increase was observed in the percentage of B and AR patterns and a significant decrease was found in all sperm morphometric parameters (P<0.01). Interestingly, after 6 h of incubation in TCMH, the percentage of B and AR patterns increased drastically over time and marked differences were found in the dimensional and shape parameters, which were significantly smaller compared with TBM or TCM media (P<0.001). Significant correlations were observed between sperm size and AR pattern (r=−0.875, P<0.01). In conclusion, sperm head morphometry can be used as a potential biophysical marker for detecting volumetric changes during capacitation process in bovine spermatozoa.

Androstenone production increases during pubertal development and plays a major role in boar taint. The objective of the present study was to evaluate the effect of a subclinical inflammation on the pubertal development of boars and hence on fat androstenone. Contrasted hygiene conditions were applied during rearing to increase the variability of the inflammatory status. Boars from a commercial cross line were allocated at 139±0.9 days of age (Day 0) and 81.3±5.9 kg of live weight either to Good (n=61) or Poor (n=54) hygiene conditions until slaughter at 172.9±4.8 days of age and 116.7±4.5 kg live weight. Inflammatory status, growth and pubertal development were evaluated on Day 0, Day 27 and at slaughter by analysing the blood formula, plasma inflammatory proteins; testosterone and oestradiol, salivary cortisol, rectal temperature, live weight, back fat thickness, weight of reproductive organs and clinical scores of organs (lungs, stomach, snout). Fat was collected on Day 27 by biopsy and at slaughter to measure androstenone concentration. A principal component analysis including inflammatory indicators followed by a clustering procedure was performed to identify pigs with a high (Infl+, n=50) or a low (Infl−, n=65) inflammatory status. Infl+ pigs had more granulocytes/ml, higher concentrations of haptoglobin, C-reative protein and cortisol (P<0.05), lower growth rate and higher lung pneumonia score. However, regardless of stage, the inflammatory status had no significant effect on plasma testosterone or oestradiol, fat androstenone or sexual organ development. Present data suggest that a mild inflammatory status has no influence on pubertal development or fat concentration of androstenone in boars.

Accounting for environmental heteroscedasticity and genetics by environment interaction (G×E) in genetic evaluation is important because animals may not perform predictably across environments. The objectives of this study were to evaluate the presence and consequences of heteroscedasticity and G×E on genetic evaluation. The population considered was crossbred lambs sired by terminal sires and reared under commercial conditions in the UK. Data on 6325 lambs sired by Charollais, Suffolk and Texel rams were obtained. The experiment was conducted between 1999 and 2002 on three farms located in England, Scotland and Wales. There were 2322, 2137 and 1866 lambs in England, Scotland and Wales, respectively. A total of 89 sires were mated to 1984 ewes of two types (Welsh and Scottish Mules). Most rams were used for two breeding seasons with some rotated among farms to create genetic links. Lambs were reared on pasture and had their parentage, birth, 5 week, 10 week, and slaughter weights recorded. Lambs were slaughtered at a constant fatness, at which they were ultrasonically scanned for fat and muscle depth. Heteroscedasticity was evaluated in two ways. First, data were separated into three subsets by farm. Within-farm variance component estimates were then compared with those derived from the complete data (Model 1). Second, the combined data were fitted, but with a heterogeneous (by farm) environmental variance structure (Model 2). To investigate G×E, a model with a random farm by sire (F×S) interaction was used (Model 3). The ratio of the F×S variance to total variance was a measure of the level of G×E in the population. Heterogeneity in environmental variability across farm was identified for all traits (P<0.01). Rank correlations of sire estimated breeding value between farms differed for Model 1 for all traits. However, sires ranked similarly (rank correlation of 0.99) for weight traits with Model 2, but less so for ultrasonic measures. Including the F×S interaction (Model 3) improved model fit for all traits. However, the F×S term explained a small proportion of variation in weights (<2%) although more in ultrasonic traits (at least 10%). In conclusion, heteroscedasticity and G×E were not large for these data, and can be ignored in genetic evaluation of weight but, perhaps, not ultrasonic traits. Still, before incorporating heteroscedasticity and G×E into routine evaluations of even ultrasonic traits, their consequences on selection response in the breeding goal should be evaluated.

Each individual in the population has a distinct maximum growth potential, and the growth curve may vary depending on the response to nutrient intake, growth phase and variability among animals. The present study aimed to (1) model weight gain (WG) response to methionine+cystine (Met+Cys) supply using different mathematical functions, (2) identify functions that better fit the growth responses of pullets, (3) determine the Met+Cys requirements that maximize WG based on breeding standards and (4) partition the Met+Cys requirements for WG and maintenance. Three trials were performed using 1448 laying-type pullets. We adopted a completely randomized design with eight treatments and six replicates. The first trial (2 to 6 weeks, P1) used 15 pullets per experimental unit. The second and third trials (8 to 12 weeks, P2; 14 to 18 weeks, P3) were used eight pullets per replicate. The Met+Cys levels were obtained using a dilution technique. The mathematical functions used to describe WG responses to Met+Cys intake were broken line, broken line with curvilinear ascendancy, Michaelis–Menten, saturation kinetics and three logistic and three exponential models. Models were selected using the Bayesian information criterion and evaluated by residual analysis. It was possible to model the responses using the studied functions. The best functions were obtained by logistic and sigmoidal models in P1 and P2, and with the broken line by the curvilinear ascendancy model in P3. The Met+Cys intake that determined the maximum potential for WG (WGmax) in P1, P2 and P3 were 313, 381 and 318 mg/day, respectively. The Met+Cys requirements for WG were 20, 22 and 27 mg/g, and for maintenance were 214, 53 and 30 mg/kgBW0.75 for P1, P2 and P3, respectively.

Ractopamine hydrochloride (RH) alters protein metabolism and improves growth performance in Bos taurus cattle with high carcass fat. Our objective was to evaluate the effects of RH, dietary CP and RH×CP interaction on performance, blood metabolites, carcass characteristics and meat quality of young Nellore bulls. A total of 48 bulls were randomly assigned to four treatments in a 2×2 factorial arrangement. The factors were two levels of dietary CP (100% and 120% of metabolizable protein requirement, defined as CP100 and CP120, respectively), and two levels of RH (0 and 300 mg/animal·per day). Treated animal received RH for the final 35 days before slaughter. Animals were weighed at the beginning of the feedlot period (day 63), at the beginning of ractopamine supplementation (day 0), after 18 days of supplementation (day 18) and before slaughter (day 34). Animals were slaughtered and hot carcass weights recorded. After chilling, carcass data was collected and longissimus samples were obtained for determination of meat quality. The 9–11th rib section was removed for carcass composition analysis. Supplementation with RH increased ADG independently of dietary CP. There was a RH×CP interaction on dry matter intake (DMI), where RH reduced DMI at CP120, with no effect at CP100. Ractopamine improved feed efficiency, without RH×CP interaction. Ractopamine had no effect on plasma creatinine and urea concentration. Greater dietary CP tended to increase blood urea, and there was a RH×CP interaction for plasma total protein. Ractopamine supplementation increased plasma total protein at CP120, and had no effect at CP100. Ractopamine also decreased plasma glucose concentration at CP100, but had no effect at CP120. Ractopamine increased alkaline phosphatase activity at CP120 and had no effect at CP100. There was a tendency for RH to increase longissimus muscle area, independently of dietary CP. Ractopamine did not alter fat thickness; however, fat thickness was reduced by greater CP in the diet. Supplementation with RH decreased meat shear force, but only at day 0 of aging, having no effect after 7, 14 or 21 days. Greater dietary protein increased meat shear force after 0 and 7 days of aging, with no effect after 14 or 21 days. These results demonstrate for the first time the efficacy of ractopamine supplementation to improve gain and feed efficiency of intact Bos indicus males, with relatively low carcass fat content. Ractopamine effects were not further improved by increasing dietary protein content above requirements.

The BW has been largely used as a selection criterion in genetic selection programmes; however, increases in BW can affect animal metabolism and metabolites. The knowledge of how genetic potential for growth affects the metabolites can give a footprint of growth metabolism. This research aimed to evaluate the effect of genetic potential for post-weaning growth (GG) on performance, carcass traits and serum metabolome of non-castrated Nellore males during the finishing phase. Forty-eight Nellore non-castrated males, with divergent potential for post-weaning growth, were selected and divided into two groups: high potential for post-weaning growth (HG; n = 24) and low potential for post-weaning growth (LG; n = 24). Animals were kept and fed for 90 days where performance and ultrasound carcass traits were evaluated. Blood samples were collected at the beginning and end of feeding period to analyse serum metabolites concentration. The hot carcass weight and dressing percentage were recorded at slaughter. The feedlot performance and carcass traits were not affected by genetic potential. The HG animals had a lower glucose (P = 0.039), glutamate (P = 0.038), glutamine (P = 0.004), greater betaine (P = 0.039) and pyruvate (P = 0.039) compared to the LG group at the beginning of feedlot. In addition, higher creatine phosphate concentrations were observed at the beginning of feeding period, compared to final, for both groups (P = 0.039). In conclusion, the genetic potential for post-weaning growth does not affect performance and carcass traits during the finishing period. Differences in metabolite concentrations can be better found at the beginning of feedlot, providing a footprint of growth metabolism, but similar metabolite concentration at the end of finishing period.

Grazing animals cause major alterations to vegetation structure and botanical composition through their selective grazing, trampling and excretal deposition (Hester et al., 2005). Through these effects they modify habitats and thus the populations of invertebrates and other organisms at higher trophic levels. Herbivores are thus key drivers of ecosystem function and nutrient dynamics within grazed plant communities. Changes in grazing intensity and the species mix of grazing livestock can therefore have important implications for resulting biodiversity. Ongoing reform of the European Union Common Agricultural Policy (CAP) will lead to a shift in the way financial support for livestock is distributed and hence to changes in grazing management practices. Farmers will increasingly receive financial support subject to cross-compliance with various environmental conditions and for delivery of specific environmental and social objectives. In some areas, livestock are likely to be increasingly viewed as tools for habitat management rather than solely as producers of food and other commodities.

Against this backdrop of policy change the British Society of Animal Science and the British Ecological Society organized a joint symposium at the BSAS Annual Meeting in April 2005 on the links between farm animals and biodiversity. Four papers from this symposium are presented as mini-reviews in the current issue of Animal Science.

David Oglethorpe set the policy context in his review of the environmental implications of CAP reform (Oglethorpe, 2005). His paper highlighted the likely changes in the livestock sector that will ensue including a polarization of agriculture into intensive producers versus environmental managers, increasing extensification in the uplands and some substitution of beef with sheep. Jerry Tallowin then presented a review of the impact of grazing management on grassland biodiversity (Tallowin et al., 2005). His paper showed that lenient grazing pressure by cattle in species-rich grassland was sufficient to maintain botanical diversity but did not enhance it over a 5-year period. For species-poor grassland, grazing management could alter sward structure but, in the absence of seed sources, botanical diversity was resistant to change. There is obviously much research still be done in this area to support the development of suitable agri-environment measures under Pillar 2 support mechanisms. David Buckingham went on to consider the extent to which grassland management might influence habitat quality for farmland birds (Buckingham and Peach, 2005). His paper showed that the exacting requirements of declining granivorous birds pose the greatest challenges while the needs of soil invertebrate feeding species are more easily met under agri-environmental schemes. In the final paper by Bruno Martin, the influence of pasture diversity on cheese quality was the theme (Martin et al., 2005). This paper reviewed recent work, primarily from France, which has examined the links between the diet of grazing animals and the sensory characteristics of various Protected Designation of Origin cheeses. The review highlighted the sometimes subtle, but none the less important influence of the grazing environment on food quality.

The purpose of the symposium was to draw together animal scientists, conservation biologists, ecologists and socio-economists to consider the changing rôle of farm livestock within the new ‘decoupled’ economic environment. Judging by the popularity of the symposium and the vibrant nature of the discussion that followed each paper, there are plenty of issues still to consider and the hope is that some of the contacts made at the meeting will yield fruitful collaborations in the future.

We examined short- and long-term effects of high milking frequency (HMF) for the first 21 days of lactation. The study included 122 Israeli Holstein cows – 32 pregnant heifers, 40 cows in second lactation and 50 cows in >second lactation. Heifers were paired according to predicted transmitting ability and cows according to energy-corrected milk (ECM) production, age, days in milk and expected calving date. Thin cows (body condition score <2.75) were not included. One cow from each pair was arbitrarily allocated to a control group milked three times daily (3× milking cows) and the counterpart to an experimental group milked six times daily for the first 21 days of lactation and then three times daily for the rest of the lactation (6× milking cows). During the first 21 days of lactation, 6× milking cows produced 9.3 kg more milk (26.5%) and 7.16 kg more ECM (19%) than the 3× milking cows. The higher milk production persisted throughout the entire lactation (305 days), as reflected by treatment×age interaction showing higher milk production for the first and second (7%) but not >second lactation cows relative to their control counterparts (−0.37%); ECM production was also higher in 6× milking first and second lactation (7.6% and 5%, respectively) but not for >second lactation cows. Furthermore, HMF had long-lasting effects, expressed as significantly higher milk production through the succeeding lactation in the previous first lactation cows (10%); a tendency toward significance in the second lactation cows relative to the controls (4.7%), but a deleterious effect on the >second lactation cows, reflected by lower milk production (−5.25%) than in controls; similar patterns were found for the ECM. For the entire 305 days of lactation, fat and protein yields were higher for first and second lactation cows, whereas protein yield for >second lactation cows was lower in the 6× milking v. control group. Given that HMF during the first 21 days of first or second lactation increases milk and ECM yields throughout the concurrent and successive lactation with no adverse effect on energy balance, mastitis, metabolic diseases or reproduction, it seems to be economically beneficial. However, caution should be paid for >second lactation cows due to absence of significant effect in the entire of the first HMF applied lactation and the deleterious effect in the succeeding lactation.

A study was made of the levels of oestrous activity of two indigenous breeds of sheep (Somali and Nandi) and three exotic breeds of sheep (Merino, Karakul and New Zealand Romney Marsh) over a period of 3 years, in an equatorial environment. Breed was the only significant source of variation for the length of the oestrous cycle (P < 0·01). The mean lengths of the oestrous cycle were 17·2 (s.d. 3·21), 17·5 (s.d. 2·24), 17·9 (s.d. 2·99), 17·5 (s.d. 2·57) and 16·5 (s.d. 3·41) days for the Somali, Nandi, Merino, Karakul and Romney Marsh breeds, respectively.

The mean percentage of ewes of the different breeds showing oestrus in 20-day periods were 69·8 (s.d. 22·57), 49·9 (s.d. 18·67), 63·4 (s.d. 25·70), 79·2 (s.d. 20·30) and 33·2 (s.d. 23·50) % for the Somali, Nandi, Merino, Karakul and Romney Marsh breeds, respectively. Time-series analysis did not detect any evidence of seasonal variation in oestrous activity, although there was an indication that the Merino and Romney Marsh breeds showed a marked increase in oestrous activity following, the introduction of rams. It was concluded that the variation in level of oestrous activity was short term and random.

Eighty calves of both sexes, 4 months of age, of two lines, differing in genetic merit for fat plus protein production by 70 kg per 305-day lactation, were given one of four diets differing in protein content to give an estimated range of protein intakes from 299 to 530 g/day. After 21 days the calves were fasted for 72 h. Samples of blood were taken before and after feeding in the morning and afternoon prior to fasting, seven further samples were taken throughout the fast and five samples were taken ranging from 0·5 to 7·5 h after food was re-introduced. The samples were analysed for concentrations of urea, free fatty acids (FFA), glucose, triglyceride and f5-hydroxybutyrate.

No association between metabolite concentrations and predicted breeding value (PBV) were found at any stage of the trial except for the effect of feeding on FFA concentration, the rate of increase of FFA during the fast and its ultimate concentration. These associations with FFA depended on the sex of the calf and were either absent or less marked in males. The results strengthen the possibility that FFA concentrations during fasting are related to PBV in females, and that sexual dimorphism may explain differing conclusions amongst previous trials.

The magnitude of the estimate of coheritability of urea concentration during fasting with PBV, pooled across experiments, is reduced from -0·193 to -0·066 (s.e. 0·037) by inclusion of these results. However, heterogeneity between experiments is evident and remains to be explained. This suggests that urea concentrations are not consistent predictors of genetic merit and cannot be considered to be reliable for use in practice.

Ruminal ammonia and blood urea levels were compared in fistulated steers eating paddy straw to appetite and given urea alone, urea plus oxalate, and complexes of urea with either formaldehyde (UFC) or oxalate (UOC), introduced into the rumen in a single daily dose. The solubilities of UFC and UOC in rumen liquor were 23·7 and 4·6% respectively of that of urea. Higher levels of ruminal ammonia and blood urea were recorded on urea than on other supplements.

Fattening performance and carcass characteristics were evaluated in 202 lambs sired by D’man (D), Timahdite (T) and terminal sires of the Ile-de-France (IF), Lacaune (L), and Mérinos Précoce (MP) breeds. Previous results had suggested that the three latter improved breeds had relatively similar growth and carcass performance in crossbreeding. They were, therefore, pooled in this study into one meat group breed (M) to facilitate comparisons between the five genotypes of interest: two purebreds (T, D), two single crosses (D ✕ T (DT), M ✕ T), and one three-breed cross (M ✕ DT). Results showed important improvements of performance in crossbred lambs especially those sired by meat breed rams. M ✕ T and M ✕ DT lambs grew fastest (238 and 256 g/day, respectively) and showed the best food conversion ratio. D purebred lambs realized the lowest fattening gains (196 g/day) while, T and D ✕ T lambs were intermediate (209 and 218 g/day, respectively). The D lambs deposited relatively more internal fat and relatively less subcutaneous backfat, and their carcasses had the lowest conformation score and smallest longissimus muscle area (11·23 cm2). The carcasses of M ✕ T and M ✕ DT crossbred lambs had larger longissimus muscle areas 13·97 and 13·88 cm2, respectively, thicker subcutaneous fat cover and better conformation scores than other genotypes. The effects of M as a terminal sire breed were favourable for the majority of fattening and carcass characteristics. The absence of differences between M ✕ T and M ✕ DT genotypes on post-weaning growth, food conversion ratio and on objective and subjective measurements of carcass conformation indicated that the infusion of 25% of D genes in M ✕ DT lambs did not affect post-weaning growth and carcass traits. The results on the use of M sires and DT dams, which have above average reproductive rates, in M ✕ DT crossbreeding indicate that a two-stage crossbreeding system could enhance the quantity and the quality of meat sheep production in Morocco.

This study aimed to investigate the pattern of nitrogen (N) metabolites flux across the portal-drained viscera (PDV) of mature sheep over a wide range of forage intake, and to determine the effect of dry matter intake (DMI) on the PDV recovery of an abomasally infused amino acids (AA) mixture. Four Suffolk mature sheep (61.4 ± 3.6 kg BW) surgically fitted with abomasal cannulae and multi-catheters were fed four levels of DMI of lucerne hay cubes ranging from 0.4 to 1.6 fold the metabolizable energy requirements for maintenance. Each period lasted for 17 days: 7 days for diet adaptation, 5 days for measurement of N balance and N metabolites flux under basal pre-infusion conditions (basal phase) and 5 days for determining the recovery of the infused AA (584 mmol/day) across the PDV (infusion phase). Six sets of blood samples were collected on the last day of both basal and infusion phases. Increasing DMI increased portal release of AA and enhanced N retention. At 0.4 M and as a proportion of digested N, there was a marked drop in total AA-N release accompanied by greater ammonia-N release and urea-N uptake across the PDV. The incremental recovery ratio of infused AA across the PDV was altered with increasing DMI accounting for 0.88, 1.12, 1.23 and 1.31 at 0.4, 0.8, 1.2 and 1.6 M, respectively. In addition, across the individual AA, the net portal recovery ratio of infused methionine and valine increased linearly (P < 0.05) while that of phenylalanine, branched-chain AA and total essential AA tended to increase linearly (P < 0.10) with increasing DMI. These results indicated that DMI affects the net portal recovery of AA available in the small intestine of mature sheep.

On the basis of experimental results, Forbes, Rees and Boas (1967) recommended that silage for pregnant ewes should have a DM content of at least 200 g/kg. Higher silage intakes and improved animal performance may be achieved by feeding silage of DM content in excess of this level.

Increases in lamb birth weight have been achieved with additional protein supplementation to ewes on hay based rations in late pregnancy (Clark and Speedy, 1981). The response to protein supplementation on silage based diets is less well documented.

In a 3 x 2 factorial experiment, 23A Border Leicester x Welsh Mountain in-lamb ewes, penned in groups of 18 or 21,were offered either an unwilted silage 199 g DM/kg) made with a formalin/formic acid additive (UA); a wilted, silage (287 g DM/kg) made with additive (WA) or a wilted silage (272 g DM/kg) made without additive (WO). The silages were offered ad-libitum from housing in January until lambing in mid-March.

1. The model of the energy system of lactating, and pregnant, cows proposed by Bruce, Broadbent and Topps (1984) has been evaluated using data relating to 166 lactations for dairy cows and 48 lactations for beef cows. The cows in both sets of data were subjected to various nutritional and managerial regimes.

2. The discrepancies between observed and predicted values of milk (energy) and live weight were small, both as a proportion of the measured values and total energy intake. For Danish Black and White dairy cows the discrepancies for milk were virtually zero on both bases; those for live weight represented 0·020 of the total energy intake, or an over-prediction by 0·054 in late lactation. For Hereford × British Friesian beef cows, suckled by one or two calves, the discrepancies as a proportion of the total energy intake ranged from 0·005 to 0·051 for milk and 0·001 to 0·063 for live-weight change across the nutritional and managerial regimes.

3. It was concluded that the model of Bruce et al. (1984), which considers genetic potential for milk production and growth, nutritional (energy), reproductive and environmental status, may be used to predict milk yield and live-weight change simultaneously from food (energy) input.

Abstract The study evaluates the effects of two dietary Ca: P ratios (1·5: 1 v. 2·5: 1) and metabolizable energy (ME) contents (17·3 MJ/kg dry matter (DM) v. 19·2 MJ/kg DM) on the development of osteochondrosis, foot bending and performance in juvenile male blue foxes (Alopex lagopus). Four experimental groups (no. = 10 per group) were formed : (1) low energy, lagopus). low Ca: P (LELC); (2) normal energy, low Ca: P (NELC); (3) low energy, normal Ca: P (LENC); and (4) normal energy, normal Ca: P (NENC). The experiment started at weaning in mid July and finished in early October. From mid August onwards, animals on the normal energy diets (NELC, NENC) grew significantly faster (P < 0·001) than animals on the low energy diets (LELC, LENC). The final body weights of the normal energy groups were 1·5 kg higher than those of the low energy groups (P < 0·001). The dietary Ca: P ratio did not affect live-weight gain. Foot bending increased significantly from summer to autumn (P < 0·001). Changes in foot bending between initial and final evaluations showed that bending was significantly greater (P < 0·05) in animals on normal energy (NELC, NENC) than on low energy diets (LELC, LENC). Significant differences were not found in the mean degree of damage in foot and cartilage between the groups. Ulna breaking strength was significantly higher (P < 0·05) in normal energy (NELC, NENC) than in low energy (LELC, LENC) animals. Ulna calcium and phosphorus concentrations of the normal Ca: P (LENC, NENC) groups were significantly higher (P < 0·001, P < 0·05) than those of the lower Ca: P (LELC, NELC) groups. The bone (ulna) calcium and phosphorus concentrations tended to be higher in the normal energy (NELC, NENC) than in the low energy (LELC, LENC) groups (calcium P = 0·07; phosphorus P = 0·06). The bone Ca: P ratio was higher (P < 0·001) in the normal (LENC, NENC) than in the low Ca: P diet (LELC, NELC) animals. The carcass weights of normal energy animals (NELC, NENC) were significantly higher (P < 0·001) than those of low energy (LELC, LENC) animals. The fat : dry matter ratio was higher (P < 0·05) in normal (NELC, NENC) than in low energy (LELC, LENC) carcasses. We conclude that the Ca: P ratio of the diet has no effect on the development of osteochondrosis or bending of the foot. The higher body weight caused by normal as opposed to low metabolizable energy content seems, however, to increase the incidence of foot bending.

1. Twenty newborn Ayrshire male calves were used in a comparison of milk substitute diets containing two different margarine fats. The liquid diets were offered in two feeds daily ad libitum and the calves were slaughtered at 118 kg live weight.

2. The two diets consisted of reconstituted spray-dried skim milk powder containing 200 g margarine fat/kg. One fat contained coconut and palm oils (CP) and the other coconut, palm and groundnut oils (CPG). The essential fatty acid content of margarine CP was less than half that of margarine CPG.

3. The incidence of diarrhoea and of a high rectal temperature, and the severity of lung lesions tended to be higher, the incidence of nasal discharge was higher and daily dry-matter intake and liveweight gain were lower for calves given margarine CPG.

4. Digestibility and balance trials were made at 1, 4 and 10 weeks of age. Nitrogen balance and apparent digestibility of the fat and other nutrients were not affected by the source of margarine, but the digestibility of dry matter and of fat was highest at 4 weeks of age, and of protein was lowest at 1 week of age. Apparent absorption of ash and calcium declined with age and absolute calcium retention was highest at 4 weeks. Total plasma lipids at 13 weeks of age did not differ between treatments.

5. Age at slaughter was greater for calves given margarine CPG but dressed-carcass weight, killing-out percentage, perirenal fat deposition and kidney weight did not differ between treatments. Skin weight tended to be lower for the calves given margarine CPG. 6. It is suggested that the apparent increased susceptibility to infection of calves given margarine CPG was associated with its higher unsaturated fatty acid content.

A synthetic sire line has been developed over 11 generations by a process of selection accompanied by immigration. In each generation prospective immigrants of any breed were mated to native pigs already i n the Sire Line, and, ignoring breed, their progeny were given the same opportunity of being selected as the progeny from matings involving natives alone. This method of immigration is shown to be biased as a result of (a) heterosis in crosses of immigrants with natives, and (b) treating natives and immigrants as if they were members of the same population. When affected by both sources of bias, the breeding values of inferior immigrant progeny may be seriously overestimated with the result that inferior genes may enter the native population and hold back genetic progress. Methods of removing the bias and alternative systems of immigration are discussed.

Ninety-nine indigenous Greek goats (Capra prisca) on natural pasture were used to study reproductive performance as affected by method of breeding. At the beginning of the breeding season oestrus was induced with 45 mg fluorogestone acetate-impregnated vaginal sponges and 300 to 500 i.u. PMSG, given on day 15. The animals were separated into groups of 33 for mating: (i) by natural service (natural mating); (2) by artificial insemination with fresh semen (AI fresh); and (3) by insemination with frozen semen (AI frozen). Alpine bucks and Alpine semen were used for natural mating and AI of does.

No effect of method of breeding was found on gestation length and sex ratio. Reproductive performance was significantly affected by method of breeding; at 21 days after insemination, fertility of does bred with fresh semen (69·7%) was comparable with that obtained with natural mating (72·7%) but the fertility of does bred with frozen semen (48·5%) was much lower. This difference was statistically significant at kidding (P < 0·05). Litter size was 2·14 and 1·86 (P < 0·05) for the AI fresh and AI frozen groups, respectively, and was 1·96 for the natural mating group. More multiple litters were obtained with the AI fresh group (P < 0·05). It is concluded that, induction and synchronization of oestrus and ovulation at the beginning of the breeding season gave reproductive performance with fresh semen comparable to that obtained with natural service, but use of frozen semen gave unsatisfactory results.