Future progress in genetic improvement and the monitoring of genetic resources in beef cattle requires a detailed understanding of the population under selection. This study examines the gene flow in the UK beef population with an uncommon breeding structure involving interaction between the beef and dairy populations. British Cattle Movement Service records were used as the primary source of information, and these data were triangulated with UK government statistics, other industry information sources and existing literature to build up a profile of the UK beef industry. Estimates were made of the breed composition of suckler cows, breeding bulls and the prime slaughter population. Cross-bred animals made up 85% and 94%, respectively, of the commercial beef breeding cow and prime slaughter populations. Holstein/Friesian (through cross-breeding) made up the largest proportion of genes in both these populations with 33% and 28%, respectively. The next five most popular breeds were specialist beef breeds: Limousin (22% and 18%), Charolais (11% and 6%), Simmental (9% and 11%), Angus (7% and 8%) and Belgian Blue (6% and 6%). Combined, the top seven beef breeds accounted for 94% of beef genetics in the prime slaughter population, and 80% of this came from non-native breeds. The influence of dairy breeds in the commercial beef breeding population was highlighted by the fact that 44% of replacement commercial beef breeding females were sourced from beef-sired crosses in the dairy herd, and in total 74% of all maternal grand dams of prime slaughter animals were Holstein/Friesian. The use of selection index technology was also investigated by analysing breeding bull sale results, with the correlation between the terminal sire index and sale price of young breeding bulls being generally moderate but significant, ranging from 0.21 to 0.38 across the major beef breeds. The most influential source of genetics in the commercial suckler beef herd was natural service breeding bulls. These were mostly sourced from pedigree breeders, and accounted for 47.8% of the genetics in the prime beef population. Artificial insemination sires were responsible for 16.6% of prime beef genetics, with the remaining 35.6% coming from dairy breeds, 95% of which was Holstein/Friesian.

The outcome of 37 563 matings of pigs in the Padana Valley of Northern Italy over a 4-year period was studied. The results show a marked reduction in fertility in the hottest months when a fertility rate of less than 50% was found.

Separate studies of sows and gilts show a similar development in the dynamics of the phenomenon, with, however, a time change.

The effect of Oesophagostomum dentatum on the performance of growing pigs over the live-weight range 20 to 80 kg was investigated. Fourteen individually-penned pigs in Experiment 1 and 16 group-penned but individually fed pigs in Experiment 2 were orally dosed once with 80 000 or 20 000 larvae respectively at about 18 kg live weight. Worm-free but otherwise similar pigs served as controls. Three energy and nitrogen balance studies were undertaken in two open-circuit calorimeters on four infected gilts and their paired worm-free counterparts on two levels of feeding at 7, 21 and 49 days after infection. Worm burdens averaging 4 255 and 4 722 in Experiments 1 and 2 respectively were recorded post mortem but performance and carcass measurements were not affected, neither were there any clinical symptoms. No significant differences between infected and worm-free pigs were recorded for either apparent digestibility of nitrogen and gross energy or for nitrogen retention. Possible reasons for the lack of measurable effects on pig performance are discussed.

The present study investigated the presence of a single-nucleotide polymorphism (G > T) at base −8 upstream of ATG in 5′ untranslated region of cytochrome b5 (CYB5A) gene in Swedish pig populations and evaluated the significance of this polymorphism for androstenone and skatole levels, sexual development and performance parameters in pigs. Frequencies of the T allele were 6.7% for Swedish Yorkshire × Landrace crossbred pigs (n = 245), 6.5% for Swedish Yorkshire (n = 99) and 12.8% for Landrace breed (n = 74). No deviations from Hardy–Weinberg equilibrium were observed in the investigated populations. In Swedish Yorkshire × Landrace crossbred entire male pigs (n = 193), plasma samples were analysed for skatole, androstenone, testosterone and oestrone sulphate, and fat samples were analysed for androstenone, skatole and free oestrone. Additionally, testis weight and bulbourethral gland length for crossbred pigs were recorded. Plasma androstenone levels were significantly lower in the G/T genotype at 90 kg live weight compared with the wild G/G genotype at the same live weight (P = 0.006). In heavier pigs, plasma androstenone levels did not differ between genotypes (P = 0.382). Fat androstenone levels were not affected by CYB5A genotype (P = 0.252). Skatole levels in the G/T genotype at 115 kg live weight were lower compared with those in the G/G genotype in plasma (P = 0.048) and fat (P = 0.028), although no differences were observed in lighter pigs. Testis weight, bulbourethral gland length, testosterone and oestrone sulphate levels in plasma, and oestrone levels in fat were not affected by genotype. We concluded that the presence of the T allele in the CYB5A gene resulted in lower androstenone levels in plasma, and lower skatole levels in fat and plasma; this reduction, however, was dependent on the live weight of the animals. Reproductive hormones and growth rate did not differ between the pigs of different genotypes, whereas a higher lean meat content was found in the G/T genotype in comparison with the G/G genotype. The practical application of those results in Sweden is doubtful because of lack of the effect on androstenone in fat and the low frequency of the T allele in the studied Swedish pig populations.

Non-starch polysaccharides (NSP) present in wheat and barley can act as anti-nutrients leading to an increase in digesta viscosity and a reduction in nutrient digestibility. Xylanase, an NSP-degrading enzyme, has been shown to increase nutrient digestibility in pigs. The objectives of this study were: (1) to identify the optimum inclusion level of xylanase in grower pig diets by measuring the effect of increasing enzyme levels on growth performance, the concentration of volatile fatty acids (VFA) and peptide YY concentration in portal and peripheral blood of grower pigs and (2) to increase our understanding of the interrelationships between xylanase inclusion, VFA production and peptide YY secretion. A total of 512 grower pigs ((Large White×Landrace)×MAXGRO) were allocated to pens creating 32 replicates of four pigs per pen per treatment. Pigs were allocated to trial weighing 14.2±0.31 kg and remained on trial until ~41.5±3.31 kg. The experiment was a dose response design with four inclusion levels (0, 8000, 16 000 or 32 000 BXU/kg) of xylanase (Econase XT). Diets were cereal-based wheat, barley mix formulated to meet or exceed the nutrient requirements of grower pigs. Body weight and feed intake were recorded to calculate growth performance. Pen faecal samples were collected to estimate DM, organic matter (OM) and crude fibre (CF) apparent total-tract digestibility. At the end of the trial 16 pigs per treatment were euthanised by schedule 1 procedures. Peripheral and portal blood samples were collected for peptide YY and VFA analysis. The addition of xylanase to the diet had no effect on growth performance, DM, OM or CF total-tract digestibility; however, xylanase tended to have a quadratic effect on ileum pH with higher pH values recorded for pigs fed a diet supplemented with 8000 and 16 000 BXU/kg xylanase (P<0.1). Xylanase had no effect on peptide YY levels or VFA concentration. Total VFA concentration was higher in portal compared with peripheral blood (P<0.05). In conclusion, the addition of xylanase had no effect on grower pig performance, nutrient digestibility, VFA concentration or peptide YY concentration when fed up to 32 000 BXU/kg over a 35-day period. Pig performance was good for all treatments throughout the trial suggesting that diet quality was sufficient thus there were no beneficial effects of adding xylanase.

Recombinantly derived bovine somatotropin (bST) was administered to 25 Friesian cows by 2-weekly injections of a controlled release formulation at a dose rate equivalent to 25 mg/day. Treatment commenced 7 to 11 weeks after calving and continued for 26 weeks. A comparable group of 25 cows treated only with the slow release vehicle served as a control. During the treatment period, administration of bST increased yields of milk (controls 2358 v. bST 2598 (pooled s.e. = 39·8) kg; P < 0·01), fat (107·4 v. 119·3 (pooled s.e. = 1·9) kg; (P < 0·01) and protein (84·7 v. 93·7 (pooled s.e. = 1·2) kg; (P < 0·001). Magnitude of the treatment effect was strongly influenced by season, being greatest in spring/early summer (weeks 1 to 13 of treatment) and autumn (weeks 19 to 25) but not significant during the intervening summer dry period when herbage yield was low. Voluntary intakes, as measured by indigestible marker techniques at weeks 7 to 8 and 12 to 13 of treatment, were not influenced by bST administration. However, the net loss of body condition experienced by bST-treated cows (0·3 condition score units) was not sufficient to explain their responses in yield of milk and milk components, suggesting that some responses in voluntary intake had occurred. Administration of bST had little effect on milk composition, fatty acid composition of milk fat, live weight, reproductive performance or milk yield in the subsequent lactation.

Nitrous oxide (N2O) is a potent greenhouse gas and the dominant anthropogenic stratospheric ozone-depleting emission. The tropospheric concentration of N2O continues to increase, with animal production systems constituting the largest anthropogenic source. Stable isotopes of nitrogen (N) provide tools for constraining emission sources and, following the temporal dynamics of N2O, providing additional insight and unequivocal proof of N2O source, production pathways and consumption. The potential for using stable isotopes of N is underutilised. The intent of this article is to provide an overview of what these tools are and demonstrate where and how these tools could be applied to advance the mitigation of N2O emissions from animal production systems. Nitrogen inputs and outputs are dominated by fertiliser and excreta, respectively, both of which are substrates for N2O production. These substrates can be labelled with 15N to enable the substrate-N to be traced and linked to N2O emissions. Thus, the effects of changes to animal production systems to reduce feed-N wastage by animals and fertiliser wastage, aimed at N2O mitigation and/or improved animal or economic performance, can be traced. Further 15N-tracer studies are required to fully understand the dynamics and N2O fluxes associated with excreta, and the biological contribution to these fluxes. These data are also essential for the new generation of 15N models. Recent technique developments in isotopomer science along with stable isotope probing using multiple isotopes also offer exciting capability for addressing the N2O mitigation quest.

Six breeds differing widely in body size and milk yield were compared for growth and food intake between 24 and 120 weeks of age in a time-controlled feeding system based on Calan-Broadbent electronic feeding gates activated by time clocks to give six meals a day of length 4, 5 or 6 min. The breeds were South Devon, Charolais × British Friesian, British Friesian, Hereford, Aberdeen Angus and Jersey. Each breed was represented by 12 animals, with four allocated to each meal length.

At every age, voluntary food intake was strongly determined by meal length. For each meal length, and after adjustment for breed size, most breeds closely followed the same intake curve. Thus, when intake was restricted (either slightly or severely) by uniformly limiting the time available for eating, the reduced voluntary daily intake of a breed, like its ad libitum intake, was largely genetically determined by breed size. A time-controlled feeding system thus allowed acceptable breed comparisons under conditions of restricted nutrition.

The mean growth rates resulting from a wide variety of different time-controlled voluntary intakes were all adequately explained by a linear equation based on a constant maintenance efficiency and a partial efficiency of growth that declined linearly with degree of maturity in body weight.

Eating rate was surprisingly similar for the three different meal lengths. When averaged over breeds, it increased from 1 MJ metabolizable energy (ME) per min between 6 and 12 months of age up to about 2 MJ ME per min at 2 years of age. Over this range, eating rate could be expressed as an allometric function of degree of maturity in body weight. In consequence, time-controlled daily intakes could be predicted from eating rate within ad libitum limits, as could the total eating time needed to achieve a given growth rate.

The aim was to investigate if selection of a balanced diet by growing and finishing pigs from foods differing in protein content is modified by the intrinsic nutrient and chemical properties of the high protein food ingredient offered. The treatments were as follows: a free-choice was offered between milled barley and either soya-bean meal (SBM) or low-glucosinolate rapeseed meal (RSM) or an equal mixture of SBM and RSM (SBM+RSM). In two further treatments (SBM/RSM and RSM/SBM) the protein supplements were changed when pigs reached 50 kg. These were compared with a control diet (CONT) formulated to provide 13-0 MJ digestible energy (DE) and 10 g lysine per kg and containing barley (680 g/kg), SBM (150 g/kg) and RSM (150 g/kg). A total of 72 pigs weighing about 30 kg were randomly allocated to the treatments in groups of six (three boars and three gilts). Pigs were slaughtered at about 90 kg and the chilled carcasses were assessed by measuring subcutaneous fat depths and cross-sections of the eye-muscle at the last rib. Responses from 30 to 90 kg on treatments CONT, SBM, RSM and SBM+RSM were, for food intake 2·57, 2·37, 2·21 and 247 (s.e. 0·08) kg/day (P < 0·05), for growth rate 0·93, 0·87, 0·70 and 0·82 (s.e. 0·05) kg/day (P < 0·05) and for food conversion 2·77, 2·72, 3·17 and 3·01 (s.e. 0·181) kg food per kg growth (P > 0·05) respectively. The amount of protein supplement selected in the diet from 30 to 90 kg on treatments SBM, RSM and SBM+RSM averaged 524, 495 and 483 (s.e.d. 64·9) g/kg respectively. With SBM this proportion decreased with increasing body weight (P < 0·01; R2 = 0·58). Changing RSM to SBM at 50 kg increased preference for the protein supplement and intake of SBM averaged 983 g/kg from 50 to 90 kg. On the other hand, switching from SBM to RSM increased preference for barley and intake of RSM averaged 572 g/kg. There were no significant differences in carcass quality but treatments RSM and SBM/RSM tended to produce increased fat depths. In conclusion, the use of RSM did not give a satisfactory level of -performance under the restricted free-choice feeding environment of this study. Preference and nutrient intake were adversely modified by RSM possibly due to the undesirable effects of antinutritive factors.

Thirty-four pregnant Shorthorn cows were fed during the winter either grass silage from first crop material or rapeseed silage, both low in selenium content (less than 33 nanogram/g DM). Serum glutamic oxalacetic transaminase (SGOT) determinations were performed before and after the calves went to the pasture. There was no evidence either clinically, biochemically (SGOT) or at post-mortem examination, of any nutritional muscular dystrophy (NMD) disorder in the 34 calves, despite very low plasma selenium levels (4 to 5 ng/ml plasma).

An implantation technique using a slow-release selenium pellet also was evaluated as a means of controlling the disease. Fifteen calves from a total of 33 calves born to cows given a dystrophy-producing hay during the winter, were implanted a few days after birth with a pellet containing 15 mg of selenium. Four out of 18 calves in the control group showed clinical symptoms of NMD and two died with NMD lesions. SGOT levels in the implanted calves were normal during the experiment and none was affected by NMD. Plasma selenium levels in the implanted calves were significantly higher than in the deficient controls at each sampling period, but within normal ranges previously reported.

The aim of this experiment was to determine whether there is any physiological basis for concerns that selection for fleece mass may decrease fitness by increasing the partitioning of nutrients to wool at the expense of other body functions.

Forty-five Merino rams (24 months old) were given food at an ad libitum and a maintenance level of nutrition. Animals were grouped into high, average or low clean fleece growth-rate categories on the basis of measurements made during the ad libitum feeding period. During ad libitum feeding, high producers grew proportionately 0·42 more clean fleece, and deposited proportionately 0·36 more energy and 0·42 more nitrogen (N) as greasy fleece than average producers. This was achieved by partitioning a higher proportion of N consumed to wool (0·08 v. 0·06), and not by increased energy or N retention. High producers adapted to the maintenance diet by decreasing clean wool growth rate proportionately by 0·32. There were no differences between high and average wool producers in clean wool growth rate or the percentage of N or energy intake partitioned to wool at the maintenance level of feeding. Although there were no differences in initial live mass between groups, low producers gained proportionately 0·45 more live mass during the experiment than average producers.

It was concluded that Merino rams of high clean-wool production potential are not more efficient, but partition more of the available nutrients to wool production at the cost of body tissue deposition.

The objective was to assess the ability of the in situ mobile nylon bag method for predicting small intestinal and total tract starch digestibility. Starch disappearance was measured for 18 samples of different cereals and legumes subjected to different physical and chemical processing methods and compared with coherent in vivo digestibility. Starch disappearance was measured both with and without initial ruminal pre-incubation during 4 h. Bags were retrieved from either the ileal cannula or faeces. Two dry Danish Holstein cows fitted with rumen cannulas were used for rumen pre-incubations and two lactating Danish Holstein cows fitted with duodenal and ileal cannulas were used for intestinal incubations. Rumen pre-incubation had no significant effect on disappearance from bags recovered in faeces. The disappearance of legume starch was lower, both in the rumen and small intestine, compared with starch from barley, wheat, oats, ear maize and maize. Transit times of the mobile bags from duodenum to ileum were not significantly different between feeds. A weak positive correlation was found between in vivo small intestinal and total tract digestibility of starch and disappearance obtained using the mobile bag technique across a broad range of starch sources. Omitting two less conventional starch sources (NaOH wheat and xylose-treated barley) resulted in a high (0.87) correlation between total tract in vivo digestibility and mobile bag disappearance. The use of the mobile bag method for estimation of in vivo starch digestibility will therefore depend on the starch type.

Incubation with rumen liquor gave a lower rate of release of ammonia and a higher dehydrogenase activity with urea phosphate (UP) than with urea.

Four concentrate diets containing 13 % crude protein, 27% of which was supplied by urea or three different forms of UP, were each given to eight Awassi lambs. With twice-daily feeding (but not five-times daily feeding), a beneficial effect of UP over urea was observed, expressed in lower blood ammonia and urea levels. There was no effect on the pH of rumen liquor.

In a N-balance experiment with 24 lambs, four diets were examined: a basal diet containing 9·5% crude protein and three other diets in which the crude protein content was raised to 13% by addition of soya bean meal, urea or UP. The diets were given twice daily. Urea phosphate and the soya bean meal gave a significant increase in N retention whereas the urea treatment did not. However, the difference in N retention between the UP and urea treatments was not significant. Total volatile fatty acid concentrations in the rumen did not differ significantly between treatments but the ratio of acetic to propionic acids was significantly lower with the urea diet.

Two experiments were carried out to study the energy requirements of young fattening lambs for maintenance and production. Forty weaned lambs were used in each experiment, 20 being allocated to a high level of feeding (900 g air-dry feed per day) and 20 to a low level (540 g). The animals used in Experiment 1 were approximately 12 months of age and their mean live weight was 35·3±4·03 kg. Those in Experiment 2 were approximately seven months of age and their mean live weight was 36·7 ± 4·57 kg. Experiment 1 continued for 100 days and Experiment 2 for 47 days. Three digestibility trials, involving three animals from each feeding level, were carried out during the course of each experiment to obtain precise estimates of digestible organic matter intake (DOMI). The estimated mean DOMI required for maintenance for a 45-kg lamb was 400 g (0·88 lb) or 1500 kcal metabolizable energy per day. The estimated maintenance requirement was not affected by the age of the animal. The DOMI required for production ranged from 1·55 kg per kg live-weight gain for the younger animals to 1·71 kg for the older animals. Both these requirements were lower than those obtained by other workers and those suggested by the Agricultural Research Council (1965).

Most dairy cattle populations found in different countries around the world are small to medium sized and use many artificial insemination bulls imported from different foreign countries. The Walloon population in the southern part of Belgium is a good example for such a small-scale population. Wallonia has also a very active community of Holstein breeders requesting high level genetic evaluation services. Single-step Genomic BLUP (ssGBLUP) methods allow the simultaneous use of genomic, pedigree and phenotypic information and could reduce potential biases in the estimation of genomically enhanced breeding values (GEBV). Therefore, in the context of implementing a Walloon genomic evaluation system for Holsteins, it was considered as the best option. However, in contrast to multi-step genomic predictions, natively ssGBLUP will only use local phenotypic information and is unable to use directly important other sources of information coming from abroad, for example Multiple Across Country Evaluation (MACE) results as provided by the Interbull Center (Uppsala, Sweden). Therefore, we developed and implemented single-step Genomic Bayesian Prediction (ssGBayes), as an alternative method for the Walloon genomic evaluations. The ssGBayes method approximated the correct system of equations directly using estimated breeding values (EBV) and associated reliabilities (REL) without any explicit deregression step. In the Walloon genomic evaluation, local information refers to Walloon EBV and REL and foreign information refers to MACE EBV and associated REL. Combining simultaneously all available genotypes, pedigree, local and foreign information in an evaluation can be achieved but adding contributions to left-hand and right-hand sides subtracting double-counted contributions. Correct propagation of external information avoiding double counting of contributions due to relationships and due to records can be achieved. This ssGBayes method computed more accurate predictions for all types of animals. For example, for genotyped animals with low Walloon REL (<0.25) without MACE results but sired by genotyped bulls with MACE results, the average increase of REL for the studied traits was 0.38 points of which 0.08 points could be traced to the inclusion of MACE information. For other categories of genotyped animals, the contribution by MACE information was also high. The Walloon genomic evaluation system passed for the first time the Interbull GEBV tests for several traits in July 2013. Recent experiences reported here refer to its use in April 2016 for the routine genomic evaluations of milk production, udder health and type traits. Results showed that the proposed methodology should also be of interest for other, similar, populations.

In two experiments, the first with 96 pigs from 5 weeks of age and the second with 384 pigs from 3 weeks of age, high nutrient dense diets (HND) or conventional diets (CONV) were given with (50 g/kg diet) or without fish meal, up to slaughter at 90 kg live weight. Diets were unmedicated. In both experiments pigs were given food according to scales which equalized digestible energy intakes for the HND and the CONV diets. In experiment 1 pigs were individually fed; in experiment 2 group feeding was practised with pens of 16 pigs either floor or trough fed.

There was no mortality in experiment 1, but the mortality was high in experiment 2, particularly amongst those pigs receiving the CONV diet without fish meal. In experiment 1, in the first 56 days, inclusion of fish meal in the CONV and HND diets significantly improved growth rate but food conversion efficiency was significantly improved in the CONV diet only. Overall, up to slaughter, growth rate and food conversion efficiency were significantly poorer in pigs given the CONV diet without fish meal (cf. the three other diets) but the HND diets were significantly better than the CONV diet with fish meal. In experiment 2, overall there were no significant differences in performance between floor- and trough- feeding methods, CONV diets without fish meal gave significantly poorer growth rates in the first 56 days and overall than the other three diets, between which there were no significant differences. In both periods, for food conversion efficiency, fish meal inclusion was without significant effect in the HND diets but significantly improved the CONV diets, both of which were significantly inferior to the HND diets.

The low intake of medusahead grass (Taeniatherum caput-medusae ssp. asperum) by sheep is attributed to the high silica content of the plant and its negative impact on digestibility, making this weed a successful competitor in grazed plant communities. The goals of this study were to determine the influence of (1) plant maturity stage (from late vegetative stage to beginning of senescence and thatch), (2) particle size (1, 5, 10 and 20 mm), and (3) high-quality feeds (alfalfa hay and a high-energy concentrate) on fermentation kinetics and apparent digestibility of medusahead relative to palatable feeds (alfalfa and tall fescue hays, and high-energy concentrates). In vitro gas production was estimated and apparent digestible organic matter (DOM) of the substrates was assessed after incubation. Medusahead from late vegetative to senescence stage had greater DOM (65% to 71%; P<0.05) than alfalfa hay (53%), similar to tall fescue hay (67%; P>0.05), and lower than the high-energy concentrates assayed (77% to 79%; P<0.05). Fermentation kinetics showed slow fermentation rates for medusahead relative to alfalfa (P<0.05), and a decline in fermentation rates with plant maturity (P<0.05). Fermentation rates of the substrates were reduced with particle sizes ⩾5 mm (P<0.05), and apparent DOM for medusahead declined as particle size increased, a relationship not found for alfalfa or tall fescue hays (P<0.05). No effects (P>0.05) on digestibility parameters were observed by the addition of high-quality feeds to medusahead. Slow fermentation kinetics and a significant inhibitory effect of particle size on apparent digestibility of organic matter contribute to explain the low use of medusahead by sheep. Such inhibitory effect may also underlie the lack of positive associative effects observed during the study.

Bulls (½ Blonde d'Aquitaine ⅜ Charolais) were used in a 2 × 3 factorial design experiment with two planes of nutrition in the finishing period and three slaughter weights. High and low planes of nutrition were based on diets with similar forage to concentrate ratio (0·40 of dry matter (DM)) offered ad libitum or at 0·78 of ad libitum DM intake at equal live weight respectively. The target slaughter live weights were 550, 625 and 700 kg. Twelve bulls were taken to each slaughter point and an additional five animals were killed as a pre-experimental slaughter group. Mean initial live weight was 412 (s.e. 5·3) kg at a mean age of 342 (s.e. 2·5) days. No significant interactions were found between the main factors. For the high and low planes, live-weight and estimated carcass gains were 1251 and 989 (s.e. 47·7), and 816 and 668 (s.e. 35·3) g/day respectively, the reduction in gains being similar to the proportional degree of nutritional restriction. Plane of nutrition had no effect on live-weight or carcass gain per unit of energy intake. The low plane of nutrition produced significant decreases in body cavity fat depots, subcutaneous fat in the sample joint and increased the proportions of both saleable beef and high-priced joints in the carcass.

With increase in slaughter weight, energy intake per unit of live weight0·75 and rates of both live-weight and carcass gain tended to decline. The dressing proportions were 583,579 and 609 (s.e. 9·1) g/kg for the slaughter live weights of 550, 625 and 700 kg. Carcass conformation improved while fat depots in the body cavity and estimated concentration of separable fat in the carcass increased with increase in slaughter weight, and both estimated lean and bone concentrations decreased. Forequarter as a proportion of total side tended to increase with increase in slaughter weight. Slaughter weight had no effect on concentration of saleable meat or ultimate pH of carcass muscle. It is concluded that bulls of this genotype can be taken to high slaughter weights on diets having a relatively high proportion of forage as grass silage, with high rates of growth and acceptable carcass leanness.

The study describes the standardization of a suitable semen cryopreservation protocol for the first time in mithun (Bos frontalis) and birth of the first mithun calf through artificial insemination. The semen samples were collected from adult bulls through the rectal massage method and cryopreserved in liquid nitrogen using tris–egg yolk–glycerol diluent. The diluted semen samples were packaged in 0.50 ml straws and kept at 5°C for 4 h for equilibration. Following the equilibration, the straws were frozen into liquid nitrogen vapour for 10 min and then plunged into liquid nitrogen for storage. It was observed that the progressive motility (%) decreased significantly (P < 0.01) in cryopreserved semen (43.3 ± 4.1) compared with fresh samples (76.6 ± 3.3). The percentages of live spermatozoa (P < 0.01) and spermatozoa with intact acrosome (P < 0.05) also decreased significantly in cryopreserved semen (54.0 ± 3.3 and 64.6 ± 5.3) compared with fresh samples (79.3 ± 2.6 and 85.3 ± 1.8). Simultaneously, the total morphological abnormality (%) was found to be significantly (P < 0.01) higher in cryopreserved samples (15.46 ± 2.68) than in fresh semen (3.85 ± 0.63). A total of three mithun cows were inseminated using the cryopreserved semen. All the cows conceived following insemination and gave birth to healthy calves. The study revealed that mithun semen can be cryopreserved efficiently using tris–egg yolk–glycerol diluent, which can be further used for artificial insemination.

Four groups of 14 3-month-old Israeli Friesian male cattle were each given monensin supplement in their concentrates at the following rates: between 3 and 6 months of age, 0, 0, 25 and 35 p.p.m.; and between 6 months and slaughter, 0, 35, 35 and 35 p.p.m. They were offered hay at approximately 0·3 % of their live weight and concentrates ad libitum.

Daily gain between 3 and 6 months was 1·36, 1·40, 1·50 and 1·57 kg/day, respectively; between 6 months and slaughter it was 1·22, 1·32, 1·33 and 1·24 kg/day, respectively. Differences in intake of concentrates were small. There were no significant differences in slaughter data.

Daily carcass gain throughout the experiment was 0·71, 0·74, 0·77 and 0·76 kg/day, respectively.

Monensin-supplemented animals were approximately 9% more efficient in the conversion of metabolizable energy into live weight or carcass weight than the control animals.

Production of propionate in the rumen was significantly increased in response to monensin supplementation, and the acetate to propionate ratio was significantly reduced.