Thirty-two N'Dama bulls aged 3 to 4 years were used to study the interactions between work, trypanosomosis and nutrition. The bulls were randomly allocated to two treatments, working (W) and non-working (N). Half in each treatment were placed on an andropogon hay basal diet (B), the other half on a better quality groundnut hay diet (H). Five days a week, four pairs of animals in the BW group and and four pairs in the HW group pulled weighted sledges four times around a 2056-m track. Loads were set to ensure energy expenditure was equivalent to 1·4 times maintenance. After 4 weeks all 32 bulls were injected intradermally with 104 Trypanosoma congolense organisms. The trial continued for a further 8 weeks.

Trypanosome infection caused a significant (P < 0·001) decline in packed cell volume (PCV), and the anaemia was more severe (P < 0·05) in working animals; three pairs in the HW group and two pairs in the BW group were withdrawn because PCV fell below 17%. Diet had no effect on PCV or parasitaemia. Infection caused a decline in food intake (P < 0·001) but with significant interactions between diet and work. Intake patterns were similar in the BN and BW groups whilst the HW animals consumed significantly more groundnut hay compared with the HN group (P < 0·01). However, nutrition had no significant effect on lap times or the team's ability to work under trypanosomosis challenge. Post-infection, diet was the dominant factor determining weight change, HN and HW animals weighed significantly more than BN and BW animals (P < 0·01) and the interaction between period, diet and work demonstrated that BWhad the lowest weights in the latter stages of the trial (P < 0·05).

The results suggest that supplementation with better quality forages confers no benefit to an animal infected with trypanosomes. Nor can trypanotolerant cattle sustain long periods of work if subiected to a primary challenge of trypanosomes.

A deterministic simulation model was constructed to develop breeding objectives and estimate biological and economic values. The model simulates life-cycle production of a breeding cow and growth performance of her offspring. Input variables are divided into four categories: animal traits, nutritional variables, management variables and economic variables. The economic variables assume typical beef cattle production in Japan. The outputs from the model include cow-calf performance, feedlot performance and biological and economic efficiency. The model's ability to simulate herd composition, food intake of cow and calves, cow body-weight changes, empty body and carcass composition of feedlot animals and production efficiencies is illustrated.

Sixty-five primiparous cows were used in two experiments to study the effects of feeding high or low levels of concentrate during the last 2 to 3 weeks before calving on performance in early lactation. During early lactation (until 12 or 16 weeks after calving) all the 23 cows in experiment 1 were given the same diet. In experiment 2, the 42 cows were given diets with a ratio of concentrate/forage of either 60:40 or 40: 60, each providing the same energy level.

The food intake of almost all the cows decreased in the few days before calving but the decrease was less pronounced among those on the low concentrate level before calving. The average daily food intake during the calving week gave a metabolizable energy intake about 30 MJ higher on the high compared with the low feeding level. The level of feeding before calving had no effect on the cows' food intake after calving, or on their milk yield, health and fertility, or on scores for udder oedema and sole haemorrhages. The high level offeeding before calving was associated with significantly higher concentrations of insulin and lower concentrations of free fatty acids in the calving week of lactation but the level offeeding either before or after calving had no effect on these concentrations in the 8th week of lactation. The feeding of a high ratio of concentrate/forage after calving was associated with a significantly lower milk fat content. It can be concluded that the concentrate/forage ratio at calving does not seem to have any significance for the performance after calving.

Ninety-four silages were made over 5 years from predominantly perennial ryegrass swards using a range of cutting dates (19 May to 18 September), wilting periods (0 to 48 h) and additives (none, acids, inoculants, sugar, sugar + acids, sugar + inoculants). A wide range of silage composition was achieved (CV for dry matter (DM), crude protein (CP), digestible organic matter (DOMD), lactic acid, total volatile fatty acids (VFA) and sugar were 0–2. Silage dry-matter intake (SDMI) was measured for 88 silages using lambs (mean live weight (M) 28 kg) given silage as their sole diet in four incomplete block design experiments using four lambs per silage and a standard hay given every third period for covariance correction. Thirty-four of the silages were also evaluated using early lactation cows (M, 561 kg and milk yield 27 kg/day) with 7 kg/day of concentrate in eight incomplete block change-over experiments each using 12 cows.

Intakes (SDMI mean, range, s.d. glkg M075) were 56, 25 to 84, 13·7 for lambs and 90, 64 to 119, 13·4 for cows. Scaling lamb SDMI by M1'47 accounted best for the effect of lamb weight on intake (mean, range 5·07, 2·43 to 7·68). Silage predictors were grouped as follows: traditional values (BASAL) - DM, CP, organic matter (OM), DOMD,

neutral-detergent fibre (NDF), acid-detergent fibre (ADF), ammonia nitrogen (NH3N), pH, acid hydrolysed ether extract (AHEE); silage fermentation values obtained by high-performance liquid chromatography (HPLC); or by electrometric titration (ET); and near infra-red reflectance spectra (NIRS) obtained on either 100°C dried (NIRSdry) orfreshsamples (NIRSwetl using a vertical transport mechanism and NIRSwet2 using a rotating cup). The most useful predictors within each group were firstly identified by step-wise multiple linear regression and models were then derived by partial least squares.

Standard errors of cross validation (SECV) obtained by the ‘leave one out’ method were for lamb SDMI (g/M1·47) 0·81, 0·81, 0·75, 0·52, 0·82 and 0·56 for BASAL, BASAL + HPLC, BASAL + ET, NIRSdry, NIRSwetl and NIRSwet2 respectively. Corresponding values for cows (g/M0·75) were 7·3, 7·3, 5·9, 5·1, 6·2, and 2·5. Inclusion of fermentation measurements made by ET, but not by HPLC, improved SDMI prediction over that obtainedfromthe BASAL set. However, NIRSdry and NIRSwet2 were the most accurate methods giving values for s.d. (reference population)ISECV of 2·27 and 2·13 for lambs and 2·65 and 5·28 for dairy cows. Use of these methods in advisory silage evaluation should substantially reduce the errors of predicting the intake potential ofgrass silages.

A deterministic bio-economic model simulating beef production during the life cycle of a cow and her offspring was used to estimate biological and economic values of daily gain, marbling score, birth weight, weaning weight and mature weight for three production systems (cow-calf, feedlot and integrated) and alternative production circumstances in Japan. Biological efficiency (live-weight basis and lean-weight basis) and economic efficiency (returns over costs) were regarded as breeding objectives. Alternatives included reducing the maximum number of reproductive cycles, marketing by constant slaughter weight (BASE), constant age or constant carcass fat content, lighter slaughter weight and doubling food prices. Biological efficiency on a live-weight basis for the cow-calf system was most influenced by increasing weaning weight; for the feedlot and integrated system, increasing daily gain had the largest influence. For biological efficiency of lean production, increasing daily gain and mature weight had the largest influence in the feedlot and integrated systems, respectively. For economic efficiency, increasing weaning weight was most beneficial in the cow-calf system and increasing marbling score was most beneficial in the feedlot and integrated systems. Economic values of daily gain and weaning weight decreased markedly with increasing genetic levels of these traits. Marketing by age decreased the biological values of daily gain but increased the economic value of daily gain. Marketing at a constant carcass fat content decreased biological values of mature weight but increased the economic value of mature weight. Decreasing slaughter weight provided negative economic values of daily gain and weaning weight. Economic values were reduced when food prices were doubled.

Laparoscopic insemination with frozen-thawed semen is currently used for planned matings in the Sarda breeding programme. In order to find a fast and less intrusive artificial insemination (AI) method that could replace laparoscopic insemination, a field comparison of laparoscopic and transcervical techniques was carried out on 200 mature Sarda ewes. After AI, ewes were assigned to teaser and fertile rams for 2 months. Return rates and cumulative (AI + natural mating) lambing rates were recorded over three subsequent 23-day periods. Lambing rates to AI were significantly different (P < 0·01), and were 62% and 7% respectively for laparoscopic and transcervical AI. Cumulative lambing rates after two further 23-day periods of natural mating were no longer significantly different (P > 0·05) and reached 82% and 74% respectively. Ewes with body condition scores at AI higher than 2·75 showed better overall reproductive performance, but not higher pregnancy rate to AI. Plasma cortisol concentrations, sampled twice, before and after AI, were higher (P < 0·01) in the last sample, suggesting a stress response to insemination. Cortisol levels after AI were lower (P < 0·01) for ewes submitted to transcervical rather than laparoscopic insemination (P < 0·01). However, cortisol levels after AI were no greater than those recorded when ewes were restrained in a milking yoke different from that usually employed. Laparoscopic AI was confirmed as the most suitable technique for insemination offrozen semen in the Sarda breeding scheme.

Thirty-two post-partum Mediterranean river buffalo cows were continuously observed for signs of oestrus from September to December with the aid of two vasectomized bulls. Symptoms of oestrus among female Mediterranean buffaloes are weak, therefore oestrus was assessed based on bull behaviour (following and licking a cow and trying to mount her). Oestrus was divided into three phases based on the bull behaviour assessment. Status of the uterus and ovarian follicles were checked rectally every day for each cow which was detected by a teaser bull to be in oestrus. All cows in oestrus were bred twice by artificial insemination (AI), the first at ovulation and the second (using a different bull) 22 h later.

The average duration of interest shown by the bull towards a cow (from the very first to the last sign of interest) was 68 h and the average length of the three phases was: phase 1 = 21 (s.d. 29) h, phase II = 32 (s.d. 24) h and phase III = 15 (s.d. 15) h. Fifteen buffaloes were bled during oestrus, and LH profiles were determined. No differences were evident among oestruses followed by pregnancy (no. = 18) and the others (no. = 26) for the variables describing behavioural events. Neither intensity of the bull courtship, presence or clarity of mucous discharge, or housing system affected the success of AI. The only differences between pregnant and non-pregnant cows were in the timing between the LH peak and the end of phase II (2·4 v. 14·7 h, P < 0·001), end of phase III (22 v. 40 h, P > 0·05) and ovulation (25 v. 46 h, P < 0·05). Successful pregnancies occurred 34 (s.d. 14) h after the end of phase II. The endocrinology and behavioural patterns of buffalo reproduction need further research to clarify the reasons for non-optimal pregnancy rates after AI.

Thirty crossbreed steer calves were randomly assigned to one of three feedlot treatment groups to evaluate the effectiveness of diatomaceous earth (DE) as an anthelmintic treatment and its effect on subsequent growth performance. Steers were adapted to a cereal-based diet for 15 days on the farm of origin and given an additional 21 days to adjust to the feedlot diet. Calves had not been dewormed prior to starting the study. On day 0 (2 January 1996) the positive control group of steers (CONV; no. = 11) was given 10 mg/kg of albendazole, a second group began receiving (on day 2) 0·3 kg of diatomaceous earth (DE; no. = 9) mixed daily with their food for 46 days and the negative control group (CTRL, no. = 9) received no anthelmintic treatment. Rectal faecal samples were collected upon arrival at the feedlot and the resulting egg counts showed that all steers were positive for nematodes and coccidia. Faecal samples were collected on days 0, 15, 28 and every 28 days thereafter to determine faecal egg counts. The last sample was taken on the day of slaughter. On day 0, the average count for all calves was over 70 eggs per g faeces (epg) for trichostrongyle type eggs; counts for Nematodirus sp., Strongyloides sp., Trichuris sp. and Capillaria sp. were negligible. CTRL and DE steers had higher parasite levels than CONV steers during the 1st (P < 0·01) and 2nd months (P < 0·05) after treatment. Egg counts for CTRL and DE groups decreased in March and none of the groups differed (P > 0·05) significantly for the remainder of the study. Coccidia levels decreased over time similarly for all groups. Offering 20 g DE per kg food intake for 46 days to beef steers on a high cereal -based diet had no effect (P > 0·05) on body weight, average daily gain, dry-matter intake, food conversion or days on food compared with the untreated control steers. Cumulative food conversion during the first 2 months was better for CONV than for DE and CTRL steers (P < 0·01) but did not differ between the latter two groups (P > 0·05). Cumulative food conversion for the rest of the study remained the same for all groups (P > 0·05). CONV calves required fewer days on food than DE calves (P < 0·05) but about the same number as CTRL calves (P > 0·10). Steers in the DE group required a similar number of days on food (230·22 ± 7·86 days) to reach target end points as CTRL steers (218·75 ± 8·34 days; P > 0·05) but more days than CONV calves (201·64 ± 7·11 days; P > 0·05).

The preweaning growth and carcass characteristics offour lamb genotypes were analysed for variation attributable to the intrauterine cohabitant (IUC) phenomenon, where within-sex variation is attributed to the sex of a twin's womb-mate. The four genotypes resulted from the following matings: Poll Dorset rams × Merino ewes, Poll Dorset rams × (Border Leicester × Merino) ewes, Texel rams × Merino ewes and Texel rams × (Border Leicester × Merino) ewes. Four hundred and twenty twin lambs participated in the preweaning study and of these, 209 were slaughtered to generate carcass data. Some of these genotypes displayed within-sex variation in weaning weight and fat score, preweaning average daily gain, skin-fold thickness, carcass fatness and eye muscle dimensions attributable to the IUC phenomenon. Genotypic differences in the responses of lambs to the IUC phenomenon were also observed. The IUC phenomenon appears to involve prenatal programming, an hypothesis that attributes postnatal characteristics to events during differentiation. The IUC phenomenon is analogous to the intrauterine position phenomenon in fecund mammals, where variations in prenatal steroid concentrations programme for permanent alterations in postnatal reproductive characteristics. The growth responses reported in this paper provide evidence of variation due to prenatal programming. While the magnitude of the responses to the IUC phenomenon were not large, the data presented indicate that under field conditions, the magnitude of growth responses to the IUC phenomenon may be as great as those observed between breeds. If so, further examination of the role that an animal's IUC may have on its subsequent performance could aid the development of more sensitive indices for breed evaluation and progeny selection.

Subtropical grasslands are low in organic matter digestibility (OMD) (0·60) and nitrogen (N) (15 g/kg) for much of the year and this limits cattle production which is characterized by low calving rates and low weaning weights. Production has been based on Bos taurus British breeds of cattle but this is changing and now many breeding herds comprise B. indicus cows and their crosses. This change has increased some aspects of production, but low calving rates persist.

A 4-year study was undertaken with a view to improve calving rates and weaner output by supplementing cows grazing either native or improved pastures with a high protein oilseed meal (cottonseed meal; CSM) on four sites. These sites were subdivided into a total of 36 paddocks to allow for two replications in a 3 breeds × 3 supplementation rates × 2 pastures factorial design. Selected cows (no. = 216) from Hereford (H), Brahman (B) and Brahman × Hereford (BH) breed types were set to graze either native pastures (0·45 to 0·62 OMD, 8 to 15 gN per kg; low quality) or improved pastures (0·47 to 0·67 OMD, 10 to 22 g N per kg; medium quality). Cows were given either 0, 750 or 1500 glday of CSM for 130 days from calving until 4 weeks into a 12- to 13-week mating period. The CSM was given as two meals per week.

Live weight at mating of cows on the low quality pasture was increased (P < 0·01) over those not supplemented by feeding either 750 g CSM per day (H and B cows) or 1500 g CSM per day (all cows). There was no significant effect of supplementation on the mating weights ofB cows grazing the medium quality sites. Calving rate ofB cows was not increased by their supplementation on either low (4-year mean 58·3 %) or medium quality pastures (66·8%) but did tend to be higher in H cows when supplemented at 1500 g CSM per day on the low (66·7 v. 78·0 (s.e. 6·09) %; P < 0·1) and medium quality pastures (70·5 v. 93·5 (s.e. 4·72) %). An increased calving rate (65·8 (s.e. 6·6) % to 83·2 (s.e. 5·82) % in supplemented BH cows grazing low quality pastures approached significance (P < 0·1) when given CSM at 1500 glday but there was no increased trend in calving rate when this breed type was supplemented on medium quality pastures.

Weaning weights of calves from and B and BH cows were increased (P < 0·05) by supplementation of their dams at 750 glday and for calves weaned from H cows supplemented at 1500 glday of CSM. Supplementation at 1500 glday on low quality pastures increased weaner output per cow mated by 120% for H, by 65% for BH cows and by 50% for B cows. Weaner output was increased by 34 and 40%, respectively, for B and H cows when supplemented at 750 glday and grazing medium quality pastures but there was no significant effect of supplementation on output from BH cows. Responses in many parameters differed between years. These results were interpreted as a response to the protein in the oilseed meal supplement by B. taurus and B. taurus × B. indicus cross cows grazing on the subtropical pastures. The study also highlighted that responses to the meal differed between breed types, between the quality of the grazed pasture and between the years of supplementation.

The accumulative effects of different levels of annual energy intake over the first two parities on four breeds of beef cow (small size and low milk potential, Aberdeen Angus; small size and high milk potential, Welsh Black; large size and low milk potential, Charolais; and large size and high milk potential, Simmental) were assessed for various production traits and calf performance. Heifers were allocated to each of two levels of annual energy intake relative to metabolic body weight (M0·75) (mean daily intakes equivalent to 705 and 820 kj M0·75) and for the next 2 years these animals (10 per breed) were continuously housed and given diets designed to represent energy intakes while grazing during the summer and conserved forage feeding during the winter. Changes in live weight and body composition were measured throughout both years and milk yield, milk composition and calf performance during both lactations.

Animals from each of the four breeds gained weight but lost body condition during their first two parities in a manner that was dependent on their annual level of dietary energy intake. Welsh Black cows grew more than Aberdeen Angus cows and Charolais cows more than Simmental cows so that, by weaning during the second parity, the rank order of live weights between breeds was Charolais > Simmental > Welsh Black > Aberdeen Angus. Welsh Black and Simmental cows produced higher yields of milk (7·9 and 8·7 kg respectively) than Aberdeen Angus and Charolais cows (6·5 and 5·7 kg respectively; P < 0·001). Calves from the two large breeds grew more quickly than those from the two small breeds (1·13 v. 0·99 kg/day; P < 0·01) and calf performance was influenced by milk consumption. Biological efficiency, defined as weight of calf at weaning per GJ metabolizable energy (ME) on an annual basis, increased as annual energy intake decreased and tended to be higher for large breeds on 33 GJ ME per year than for small breeds on the same level of annual energy intake (7·19 v. 6·75). The complex means by which the different breed types interacted with their nutritional environment is discussed.

Juke was expressed from two silages of contrasting fermentation type with either high (H) or low (L) levels of lactic acid and reconstituted either with the silage from which it had been expressed or the other silage. This procedure produced four dietary treatments (HH, HL, LL, LH) each differing in fermentation characteristics. The dietary treatments HH, HL, LL, and LH contained 81, 71, 59, and 49 g lactic acid per kg dry matter (DM) and 101, 133, 193 and 159 g ammonia-N per kg total nitrogen (TN) respectively. The four diets were offered to four steers (mean live weight 679 (s.e. 49) kg) in a four-period change-over design experiment. Each period was of 17 days duration. DM intakes were recorded daily, with intakes on days 8 to 17 used in the statistical analysis of data. On day 12 of each experimental period, rumen fluid samples were taken throughout a 24-h period. The rates of disappearance of DM, nitrogen (N), modified acid-detergent fibre (MADF) and neutral-detergent fibre (NDF) in the rumen were determined on days 14 to 17 using the polyester bag technique. DM intakes were 7·2, 6·9, 6·0 and 6·0 (s.e. 0·50) kg/day (P = 0·08) for HH, HL, LL and LH dietary treatments respectively. Diet had no significant effect on eating behaviour, rumen fermentation parameters or degradability of DM, N, MADF and NDF fractions (P > 0·05). Silage L increased rumen fluid pH (P < 0·05), reduced buffering capacity (P < 0·05) and increased the molar proportion of propionic acid and n-butyric acid (P < 0·05 and P < 0·01) compared with silage H. Silage L also had a lower DM apparent digestibility, D-value and DM, (P < 0·001), N and MADF (P < 0·05) degradabilities than silage H. The higher DM intake of dietary treatment HH compared with dietary treatments LL and LH could not be explained by any single constituent of the silages although it was apparent that physical characteristics of the silage were more important in determining intake than the chemical characteristics.

This study consisted of two experiments. In experiment 1, stress responses of sheep which were restrained either in a laparoscopy cradle or a roll-over cradle were compared. The results of this experiment indicated that restraint in roll-over cradle is less (P < 0·05) stressful than that in a laparoscopy cradle when assessed in terms of the elevation and duration of both the mean heart rate and plasma cortisol responses. Experiment 2 compared the stress responses of sheep subjected to restraint in a laparoscopy cradle, restraint in a laparoscopy cradle with intrauterine artificial insemination (AI) by laparoscopy, minimal restraint with cervical AI or restraint in a roll-over cradle plus foot-trimming. All treatments resulted in significant elevations in both heart rate and plasma cortisol concentrations (F < 0·001). The peak heart rate was significantly (P < 0·05) higher in ewes subjected to cervical AI than in those subjected to intrauterine insemination, with other treatments intermediate. The peak cortisol response did not differ among different treatments. The duration over which both the mean heart rate and -plasma cortisol concentrations remained significantly elevated above pre-treatment concentrations did not differ among treatment groups. The results of this study suggest that while restraint using a laparoscopy cradle is more stressful than that using a rollover cradle, the stress inflicted by intrauterine insemination by laparoscopy itself is no greater than that due to restraint using the laparoscopy cradle alone, cervical AI or the management practice offoot-trimming using a rollover cradle.

A study was conducted to compare apparent digestibility and digesta flow kinetics in the whole digestive tract in two breeds of sheep (Churra and Merino) offered alfalfa hay at about maintenance. Ten mature sheep (five Churra and five Merino) each fitted with a rumen cannula were used in the study. Apparent digestibility was determined by total faecal collection. Liquid (Co-EDTA) and solid (Cr-mordanted fibre) markers were used to estimate rumen volumes and digesta flows. There were no significant differences between Churra and Merino sheep either in dry-matter or fibre apparent digestibility (P > 0·05). Liquid and solid passage rates did not differ between breeds and the estimated total mean retention times were similar for both genotypes. The volume of liquid in the rumen was proportionately 0·14 greater in Churra than in Merino sheep, although the difference was not significant. Estimated saliva secretion was greater in Churra (11·6 (s.e. 0·77) I/day) than in Merino sheep (10·5 (s.e. 0·72) I/day) but the difference did not reach statistical significance. Solid contents of the rumen did not differ between breeds. Rumen particle density was lowest at 2 h after feeding and remained stable at other sampling times, with no significant differences between breeds. There were no significant differences between breeds in the urinary excretion of total purine derivatives but urinary excretion of allantoin and microbial nitrogen supply tended to be higher in Merino than in Churra sheep (P < 0·20). This was attributed to the smaller rumen pool size of Merino (8·0 (s.e. 0·62) kg) compared with Churra sheep (9·2 (s.e. 0·63) kg). The study indicated that there were no apparent breed differences between Churra and Merino sheep in digestibility and digesta passage when they were given a good-quality forage at a low level of intake.

The metabolic status and reproductive performance of four pure breeds of beef cow (small size and low milk potential, Aberdeen Angus; small size and high milk potential, Welsh Black; large size and low milk potential, Charolais; and large size and high milk potential, Simmental) were monitored during their first two parities. Heifers from each breed were allocated to one of two levels of annual energy intake relative to metabolic body weight (M075) (mean daily intakes equivalent to 705 and 820 kj/kg M0·75) in a factorial design. In the 1st year 64 heifers (eight per treatment) which had calved as a consequence of first or second service were selected for the experiment. In the 2nd year 40 of these animals (five per treatment) which held to first or second service remained on experiment. Animals were housed all year round and given diets designed to represent energy intakes while grazing during the summer and conserved feeding during the winter. Pregnancy was established in late July of each year using a combination of oestrous synchronization and artificial insemination. Blood samples were collected at monthly intervals from weaning in November until calving in May; three times weekly from calving until oestrous synchronization (11 weeks later); and fortnightly thereafter until weaning.

For the annual levels of dietary energy intake offered, two breeds (Welsh Black and Charolais) exhibited relatively high growth rates and had the longest post-partum anovulatory periods; and Charolais cows also had the poorest conception rates of all breeds. Relatively lean cows at calving (body condition score < 2·5 units) were sensitive, in terms of the duration of the anovulatory period, to live-weight loss during the early post-partum period, particularly when blood glucose levels were low, whereas relatively fat cows at calving (body condition score > 2·5 units) were not. The data suggest: (i) that mechanisms controlling the anabolic processes governing maternal growth are antagonistic towards those that control reproduction; and (ii) the catabolism of lean tissue rather than fat tissue during the early post-partum period is also antagonistic towards the mechanisms that govern reproductive function in cows.

A partially balanced change-over design experiment involving 192 beef steers, which were initially 14 months old and 415 kg live weight, was carried out to determine the intakes of 136 silages from commercial farms in Northern Ireland. Each silage was offered ad libitum as the sole food to 10 animals, with eight silages offered in each of 17 periods over 2 years. A standard grass hay was offered to 16 animals in each period to enable period effects on intake to be removed. Detailed chemical and biological compositions of the silages were also determined. The ranges for pH and dry matter (DM), crude protein, ammonia-nitrogen and apparent digestible organic matter (in vivo) concentrations in the silages and silage dry DM intakes were 3·50 to 5·49 (s.d. 0·396); 155 to 413 (s.d. 43·1) g/kg; 79 to 212 (s.d. 24·4) g/kg DM; 45 to 384 (s.d. 63·2) g/kg total nitrogen; 528 to 769 (s.d. 58) g/kg DM and 4·3 to 10·9 (s.d. 1·13) kg/day respectively. Relationships between intake and individual parameters or groups of parameters have been developed using simple and multiple linear regression analysis and partial least-squares analyses. Silage intake was closely related to factors which influence the extent of digestion and rate of passage of the material through the animal, as indicated by the strong relationships (R2 of regressions = 0·28 to 0·50) with in vivo apparent digestibility and rumen degradability and the concentrations of the fibre and nitrogen factors. Intake was poorly correlated with factors such as pH, total acidity, buffering capacity and the concentrations of lactic, acetic and butyric acids (R2 of regressions = zero to 0·11). Near infrared reflectance spectrometry (NIRS) provided the best fit relationship with intake (R2 of relationship = 0·90). The results also indicate that the intake potential of silages can be directly predicted with a high degree of accuracy from the NIRS of both dried and undried samples of silage, provided the appropriate sample preparation and scanning methods are used.

A 3-year experiment has been carried out to compare systems of bull beef production involving pasture grazing and continuous storage feeding and to examine the effects of sward surface height and concentrate input from 5·5 to 11 months of age on grazing behaviour, growth rate and body composition at the end of the treatment period and on subsequent growth rate and carcass composition at commercial slaughter weight. Animals were either set-stocked at pasture to maintain sward surface heights of 6·5 and 10·0 cm or were given grass silage (725 g digestible organic matter per kg dry matter (DM)) supplemented with 0·8, 1·6, 2·4, 3·2 and 4·0 kg cereal-based concentrates (188 g crude protein per kg DM) per head daily. Half of the animals grazed at each sward height were given 1 -6 kg concentrates per head daily while the remainder received no supplement. A total of 255 continental beef breed × Friesian calves which were initially 198 kg live weight were used. From 11 months of age until slaughter at a mean live weight of 620 kg all animals were given grass silage supplemented with 3 kg cereal-based concentrate DM per head daily.

Reducing sward surface height from 10·0 to 6·5 cm increased the proportion of time spent grazing (P < 0·001), reduced the proportion of time involved in other activities and reduced live-weight gain (P < 0·001) from 1·21 to 0·84 kg/day. Offering concentrates at pasture reduced (P < 0·001) the proportion of time spent grazing (the effect being greater with the animals grazing the shorter swards) but did not affect the performance of the animals grazing the taller swards and produced only a modest increase in the live-weight gain (70 g/kg concentrates) of those grazing the shorter swards. At the end of the treatment period, the carcasses of the animals which had been given silage contained proportionally 0·39 more lipid than those of animals which had been at pasture and had the same growth rate. Differences in live weight at 11 months of age due to differences in feeding from 5·5 to 11 months were largely retained until the end of a 7-month period of realimentation while differences in carcass composition at II months were eliminated by slaughter at a constant live weight of 622 kg.

The relationship between weaning stress-induced changes in stress hormone profiles and immune function was investigated in groups of 10 lambs immunized against adrenocorticotrophic hormone (ACTH; treatment A) or fi-endorphin (treatment B) to reduce the circulating concentrations of cortisol and fi-endorphin respectively. Control animals (treatment C) were immunized against a porcine thyroglobulin carrier protein. Application of weaning stress was associated with significantly elevated plasma cortisol concentrations but no significant increase in fi-endorphin concentrations in C lambs. Immunization against ACTH suppressed the post-weaning increase in cortisol concentration. This was associated with a transient reduction in the lymphocyte stimulation response to keyhole limpet haemocyanin (KLH) antigen in the A animals but there was no effect on the antibody response or interferon-y production by antigen stimulated lymphocytes. There were no significant effects of immunization against fi-endorphin on the capacity to mount antibody or cell-mediated immune responses. It is concluded that weaning stress-induced increases in cortisol did not inhibit the immune response. Since cortisol concentrations and the cell mediated immune response at 8 days after immunization were positively associated it is concluded that these indices are not independent measures of stress.

Thirty single-bearing Merino ewes were used to examine the effect of feeding supplement, from 91 to 140 days of gestation, on changes in chemical composition of the ewes, on the relationships with live weight and body condition score and on the foetus. Ewes grazed a perennial ryegrass pasture and were offered either no supplement or 500 g per head per day of a concentrate supplement from days 30 to 90 and (or) from days 91 to 140 of pregnancy. Maternal carcass and non-carcass components, uterine wall, foetus and placenta plus cotyledons were chemically analysed. Live weight (LW) and body condition score (BCS) on day 140 were both affected by supplementation during late pregnancy, mobilization of protein and fat being lower in animals receiving supplement. BCS accounted for more variation than LW in the carcass fat depot. Because this depot was the most important source of energy from days 91 to 140 of gestation, this suggests that BCS is a useful estimator of mobilization of maternal fat reserves during this stage of pregnancy. The ability to mobilize reserves and protect foetal growth by Merino ewes in southern Europe, where large fluctuations in grass growth rate exposes them to considerable undernutrition as pregnancy proceeds, was confirmed in this experiment. However, when the nutritional regime is extreme, supplementary feeding to the ewes is recommended, in order to make the whole system economically profitable.

The objective of this study was to determine any differences in the competitive ability of rams differing in levels of sexual performance. Twenty sexually experienced Targhee-type rams were preselected from a population of 95 males for exhibiting relatively high and low ejaculation rates when individually exposed to oestrous ewes for 30 min. Each of 10 high performers (HP) were paired with each of 10 low performers (LP) on three occasions when competing for food (after food deprivation) and twice when competing for an oestrous female. Tests were 5 min in duration. Food-deprived HP and LP rams were equally aggressive when competing for a source offood that could only be accessed by one ram at a time. Time offeeding by HP and LP rams did not differ. HP rams spent more time with the oestrous ewe and attained more mounts in a greater number of pairings than LP rams even though HP and LP rams did not differ in number of successful agonistic interactions (active displacements and successful defences) when competing for the ewe. It was concluded that HP and LP rams, taken as groups, do not differ in their basic competitive ability and that the greater mating success of HP rams can be explained by their higher levels of libido.