Data for individually recorded silage dry-matter intake (SDMI), concentrate dry-matter intake (CDMI), live weight, milk yield and milk composition of lactating dairy cows offered silage ad libitum and concentrates on a flat-rate basis, together with data for silage composition from experiments conducted at four sites, were used to obtain simple and multiple regressions of SDMI on other variables.

Simple regressions showed that the most important variables affecting SDMI were, in order of importance: silage ammonia nitrogen, fat yield, CDMI, silage digestible organic matter concentration (DOMD) and live weight. The best multiple regression for the mean SDMI over weeks 4 to 13 of lactation accounted for proportionately 0·649 of the variation. Examination of week by week data for weeks 3 to 20 of lactation showed that two models for early and mid lactation were required to give a reasonable pattern of residual variances. These models accounted for 0·627 and 0·581 of the variation respectively. It was necessary to fit time effects explicitly in early lactation. Live weight was best represented by fitting post-calving live weight and deviations from post-calving live weight separately. A number of models requiring fewer input variables were also obtained to allow for use in situations where the full range of measurements is not made.

The new models were tested using independent data from three sites. They performed better than a number of previously published models but the best model still gave a prediction error of proportionately 0·17 about the mean actual silage intake in early lactation and 015 in late lactation.

The results suggest that there is little to be gained from further refinement of the functional form of the models and that the construction of a number of models for specific food and management situations is preferable to the use of global models.

A protocol of infrequent, but strategically timed milk-sampling was established for predicting the time of ovulation, and thus the optimum time for insemination, in lactating dairy cows. In the experimental group (no. = 49), the time of ovulation was predicted on the basis of a fall in milk progesterone concentrations, which was identified by the use of ‘on-farm’ progesterone assay kits. Reproductive performance in these animals was compared with that in control cows (no. = 45) that were inseminated solely on the basis of oestrous detection by stockmen. The accuracy of ovulation prediction, and of oestrous detection, was assessed from progesterone profiles based on milk samples collected three times weekly from all 94 cows. These milk samples were analysed by laboratory enzyme-immunoassay after the end of the trial.

Over the period during which milk samples were monitored with ‘on-farm’ progesterone kits, a total of 88 ovulations occurred in the experimental group. The progesterone-testing protocol accurately predicted 87 (99%) of these. Over the same period, there was a total of 81 ovulations in the control group and 63 (78%) of these were associated with correct oestrous detection. Conception rates to correctly timed insemination did not differ significantly between groups, but by the end of the three-cycle experimental period, significantly more of the cows in the experimental group (21·8%) than in the control group (4·8%; P < 0·05). In contrast, the use of ‘on-farm’ progesterone results to confirm oestrus avoided any mistimed inseminations (13% of inseminations in the control group). By using the milk-sampling and ‘on-farm’ progesterone-testing protocol, only 1% of ovulations were not accompanied by a correctly timed insemination. This compared with 22% of ovulations in the control group not associated with an insemination because oestrus was not detected. By ensuring that all ovulations are associated with a correctly timed insemination, herd reproductive performance can be significantly improved.

The effects of fish meal and monensin supplementation of silage on the growth and composition Friesian steers was examined in winter and subsequently during grazing. Four-month-old steers were given grass silage ad libitum, alone (U) or mixed with fish meal and monensin at 100 and 0·005 g/ dry matter (DM) of silage (S) for 17 weeks. Empty body weight (EBW) and carcass weight (CW) gains were significantly increased by supplementation (810 v. 495, and 553 v. 332 g/day, respectively). Although treatment S steers were heavier, their composition at turn-out was similar to that of the treatment U animals: mean fat, crude protein (CP), water, ash and energy contents were 121, 187, 640, 51 g/kg and 9·10MJ/kg EBW, respectively. During the following 20 weeks, six animals from each treatment grazed a perennial ryegrass/white clover sward unsupplemented (UU and SU), supplemented with a fish meal/maize/molassine meal (50:35: 15) pelleted diet and monensin at 4 g/kg live weight (LW) per day and 0·1 mg/kg LW per day, respectively, (UMF and SMF). A further group of six steers from treatment S received the pelleted diet without monensin during grazing (SF). Steers from treatment U showed significant compensation in EBW and in carcass growth at pasture, irrespective of whether they received a supplement, which led to a marked reduction of the differences in EBW and CW by final slaughter. Composition at final slaughter showed no significant effect winter nutrition, with the exception of fat content (g/kg EBW), which was significantly lower animals from treatment SU. Steers from treatments UMF and SMF had slightly higher rates of fat, CP, water and energy deposition, which resulted in higher fat and lower water contents (g/kg EBW) than those from treatments UU and SU, although these differences were not significant. Steers on treatment SF had gains and final compositions intermediate between those on treatments SU and SMF. Supplementation was cost effective in winter, but marginal in summer.

Twenty-four Hereford ♂ × Friesian ♀ heifers were divided into four equal treatment groups and given subcutaneous ear implants as appropriate 14 days after prostaglandin treatment for the induction of synchronized cycles. Subsequently, they were observed for 75 days. One group was an untreated control, one was given 300 mg trenbolone acetate, one 36 mg zeranol and one 45 mg oestradiol-176. Growth and ovarian cyclicity, assessed by periodic progesterone measurement, were monitored. Trenbolone acetate-treated heifers grew faster (P < 0·05) than other groups which did not differ significantly. Trenbolone acetate shortened the oestrous cycle in which treatment was started in two of five heifers and lengthened it in two others. Subsequent cycles were either suppressed or of short duration. Zeranol and oestradiol-176 treatment had little effect on ovarian cyclicity apart from a small increase in the number of short cycles. It is concluded that, at the doses used, trenbolone acetate suppresses mechanisms leading to ovulation or pre-ovulatory follicular development.

An experiment was carried out to investigate the effects of compound composition and silage characteristics on silage intake, feeding behaviour and productive performance of dairy cows during the first 25 weeks of lactation. Over a period of 3 years, 36 lactating British Friesian cows (12 per year), in their third or later lactations, were divided into two groups. The cows in each group received either compound S, in which the principal energy source was cereal starch, or compound F containing a mixture of high quality digestible fibre. Cows given compound F ate 2·2 kg more silage dry matter per day (P < 0·05). The type of compound had no effect on the frequency of silage feeding and the time spent eating was significantly different only over weeks 10 to 25 of lactation (P < 0·05), with cows on compound F spending on average 20 min longer feeding per day. Cows on compound F produced 1·7 kg more milk per day than cows on compound S. Although there were no significant differences in the concentration of milk constituents, compound F was associated with higher yields of milk constituents. Significant differences were found between the years of experiment in the frequency of feeding (P < 0·05) and also in the concentration of milk protein and milk fat. There were no significant differences in the magnitude of live-weight change between treatments or year of experiment.

Nucleus breeding schemes for dairy cattle give opportunities for selection on characteristics other than milk production, such as food intake or efficiency, and for the application of reproductive technologies such as embryo transfer. The emphasis in such schemes involving embryo transfer will be on early lactation measurements of production and food intake, to minimize generation intervals. The aim of this study was to examine the value of early lactation measurements of food intake and other characteristics in predicting longer-term food intake. Intakes of a complete diet, offered ad libitum, were available for 101 heifers up to week 38 of lactation, from the Edinburgh School of Agriculture's Langhill herd. Partial correlations between weekly dry-matter (DM) or metabolizable energy (ME) intakes in early lactation and cumulated intakes to week 38 of lactation, after fitting year and month of calving as fixed effects, and proportion of Holstein blood as a covariate, ranged from 0·27 for week 1, to 0·70 for week 12. Cumulated ME intakes, up to week 38, were regressed on shorter measures of ME intake, together with fat plus protein yield in weeks 1 to 10 of lactation. Other independent variables, such as point estimates of, or changes in, live weight, condition score and backfat depth did not further increase the precision of prediction. The means and standard deviations for milk yield, DM intake and ME intake up to week 38 of lactation were 5877 (s.d. 1087) kg, 4070 (s.d. 400) kg and 51579 (s.d. 4614) MJ respectively. For a fixed duration of intake recording, measurements taken later in lactation gave the most precise prediction of 38-week ME intake (e.g. residual s.d.s from models including 4-week cumulated ME intakes in weeks 1 to 4, 3 to 6 and 5 to 8 of lactation were 2865, 2636 and 2501 MJ respectively, with R2 values of 0·62, 0·67 and 0·71). Shorter periods of intake recording started in week 5 of lactation gave slightly more precise prediction than longer periods of recording started in weeks 1 to 4 (e.g. residual s.d.s from models including cumulative ME intakes in weeks 1 to 10, 3 to 10 and 5 to 10 were 2391, 2298 and 2277 respectively, with R2 values of 0·69, 0·75 and 0·76). These results have implications for the cost: benefit of food intake recording in breeding schemes.

Records on milk yield, fat plus protein yield, food intake, food efficiency, calving live weight and mean live weight, up to 26 and 38 weeks of lactation, were obtained from dairy cows, fed ad libitum, in the Edinburgh School of Agriculture's Langhill herd. The data were divided into first and later lactations and restricted maximum likelihood analyses carried out on heifer, cow and pooled data, fitting an animal model, with repeat lactations as an additional random effect. Univariate analyses were done after canonical transformation of heifer data and approximate canonical transformation of cow and pooled data. Heritability estimates for food efficiency and food intake, from pooled data, were 0·13 (s.e. 0·09) and 0·37 (s.e. 0·11) for 26-week and 0·13 (s.e. 0·12) and 0·52 (s.e. 0·14) for 38-week lactation periods, respectively. Over the same periods, estimates for milk yield were 0·20 (s.e. 0·08) and 0·20 (s.e. 0·11), respectively. Estimates from the analyses of cow and heifer data separately were higher, as were their standard errors. Genetic correlations between milk production traits and efficiency, from the pooled data analysis, ranged from 0·44 to 0·61 and those between milk production traits and food intake from 0·32 to 0·74. Genetic correlations between live-weight traits and efficiency ranged from −0·81 to −;0·99, and those between food intake and live-weight traits from 0·28 to 0·46. The results indicate that when selection is on yield, the correlated responses in efficiency may be smaller under ad libitum feeding, compared with published values where cows were given food according to yield. Including live weight in the selection criterion may give higher responses in efficiency compared with selection on yield alone. In MOET nucleus schemes it may be worthwhile to include food intake or efficiency directly in the selection criteria.

The effect of increased female reproductive rates on selection response, on efficiency of progeny testing and on the openness of the nucleus was investigated in open nucleus breeding plans. Conventional progeny testing plans and closed nucleus plans are special classes of open nucleus plans. In the open nucleus plans, generation intervals and selection across tiers were optimized. The number of offspring per elite dam was varied from 1 to 41, progeny testing of young bulls in the female base population was varied from 0 to 100 test records and the size of the nucleus was varied from 250 to 2000 young bulls born per year. Also efficiency of selection was varied: efficient selection in T(heoretical)-schemes and less efficient selection in P(ractical)-schemes. Especially, selection of base parents was less efficient i n P-schemes.

The deterministic prediction model took account of variance reduction due to selection and reduction of selection differentials due to correlations between estimated breeding values of relatives (order statistics). For closed nucleus plans, the results of the model were verified with Monte Carlo simulation results.

By increasing female reproductive rates, genetic gain increased by a factor 0·08 and 0·16 for the T- and P-schemes respectively. The nuclei in P-schemes were less open, due to the less efficient selection in the female base population. Schemes that were less open benefited more from increased female reproductive rates because selection differentials in small nuclei increased more than those in large base populations. The optimal open nucleus plan became less open with increasing female reproduction. Generally, progeny testing of bulls reduced genetic gain (by up to a factor 0·1) but it also reduced inbreeding rates. Progeny testing was more efficient in schemes that were less open: in P-schemes with 41 offspring per dam, progeny testing increased genetic gain. With many offspring per dam there were fewer full-sib families, causing lower selection differentials due to order statistics effects. This effect could be prevented by increasing the size of the nucleus.

A method for the iterative set-up of optimum designs for crossbreeding experiments was used to study the robustness of designs to differences in the biological interpretation of two-locus epistatic interaction. Designs could be found which are efficient for the estimation of genetic models including, alternatively, seven different types of epistatic effects. Also, the design efficiency of a large-scale beef cattle crossbreeding experiment between Angus and Hereford cattle conducted at the Clay Center, Nebraska, and reported by Koch, Dickerson, Cundiff and Gregory (1985) was investigated and found to be high (proportionately 0·88 of the optimum). It was concluded that choice of the right genetic groups (i.e. types of crossbreds) seems to be more important for a good design than the exact number of observations allocated to each group.

Measurements were made of the speed of ultrasound transmission through sites in the hind limbs of 125 pedigree Hereford bulls. Twenty-five of these were measured twice at weekly intervals on three occasions prior to slaughter to assess the short-term repeatability of the measurement and the magnitude of long-term changes. Analyses of variance of the means of the measurements at two sites showed that the residual standard deviation (within animal and occasion), was 0·01 (μs/cm. There was a decrease of 0·01 (μs/cm in the group mean over the 2-week period and a significant time × animal interaction. This showed that lipid concentration at the measurement sites decreased as the bulls adjusted to their new surroundings following delivery to the Institute's farm. When a separate group of 64 bulls was measured at the farm at which they were being reared an increase in the group mean of 0·006 iμs/cm was recorded over a 30·day period, indicating an increase in lipid concentration. The residual standard deviation for that group was 0·007 μs/cm, similar to that recorded above.

The mean of the reciprocal speeds at the two sites, when used in a multiple regression with live mass, yielded a residual standard deviation in predicted proportion of lean in the side of 20·0 g/kg and in total fat proportion of 22·1 g/kg. These corresponded to population standard deviations, adjusted for live mass, of 29·7 and 34·1 g/kg respectively. It was concluded that the measurement of ultrasound speed in the hind limbs of Hereford bulls could be used to predict lean proportion in the carcass. The method does not require subjective interpretation and responds equally to subcutaneous and interand intra-muscular fat.

The importance of family sizes in adult multiple ovulation and embryo transfer (MOET) nucleus schemes with discrete generations of single trait selection was examined using Monte Carlo simulation. Two areas were investigated. Firstly, the number of sons and daughters per dam was varied in schemes using hierarchical mating designs. With four or eight sires and 32 dams selected, increasing the number of sons per dam from one up to four achieved 1 to 8% higher rates of response but at the expense of increased variation in response and 10 to 56% higher rates of inbreeding. With four or eight sires and 16, 32 or 64 dams selected, the number of daughters was set to two, four or eight (with one son per dam in each case). For schemes transferring equal numbers of embryos, responses were lower with two daughters per dam but were fairly similar with four or eight daughters per dam while inbreeding rates increased as fewer sires and dams were selected. Secondly, the effects of variation in family sizes due to biological factors and chance were investigated with eight sires and 32 dams selected and with hierarchical or factorial (two or four sires per dam) mating designs. When all selected cows yielded embryos, changes in family sizes due to differences in sex ratios, in survival rates of embryos to selection and to variation in the number of embryos per donor reduced response by 1 to 4%. However, when 20% or 33% of the superovulated females yielded no embryos, thus requiring the use of genetically inferior replacements, response was reduced by a further 9 to 13%

Records on fat plus protein yield, food intake and food efficiency up to 26 and 38 weeks of lactation, were obtained from dairy cows fed ad libitum in the Edinburgh School of Agriculture's Langhill herd. After discarding the first 2 weeks data, the records were divided into successive 6-week periods. Restricted maximum likelihood analyses were carried out on each period for each trait, fitting an animal model, with repeat lactations as an additional random effect. Univariate analyses were done after approximate canonical transformation of the data. Heritability estimates for 6-week fat plus protein yield, food intake and efficiency, from the 38-week lactation data, ranged from 0·08 (s.e. 0·10) to 0·17 (s.e. 0·12), 0·15 (s.e. 0·09) to 0·49 (s.e. 0·15) and 0·08 (s.e. 0·14) to 0·25 (s.e. 0·11), respectively. Generally, lower heritabilities were obtained for earlier part measures of fat plus protein yield and efficiency and for later part measures of food intake. Genetic correlations between part measures and ‘total’ lactation fat plus protein yield, food intake, and efficiency ranged from 0·82 to 100, 0·85 to 0·98, and 0·60 to 1·00, respectively. Corresponding phenotypic correlations ranged from 0·76 to 0·94, 0·68 to 0·87, and 0·73 to 0·89, respectively. The correlations were lowest for the first 6-week period then gradually increased up to a maximum in the third or fourth periods and declined thereafter. The results indicate that selection on a part measure of food intake or efficiency, taken between 15 to 20 weeks of lactation, will be equally effective in improving intake and efficiency compared with selection on total lactation measures. Other 6-week measures taken between weeks 9 to 14 and 21 to 26 will also give good prediction of total lactation intake and efficiency.

The mineral balance of male calves given neutralized (with HC1) and unneutralized 35 g NaOH per kg treated wheat straw (WS), was determined in a digestibility trial in which WS was offered at inclusion levels of 300, 500 and 700 g/kg diet. The ratio of apparently retained sodium (Na) and potassium (K) increased with increasing proportion of straw in the diet and was lower on neutralized straw diets.

The effect of supplementation with 3 and 6 g K per kg diet dry matter in a diet comprising approximately 500 g/kg of 35 g NaOH per kg treated WS, on performance, mineral status and acidbase balance was examined in a growth trial with 56 Israeli-Friesian male calves. The animals on the untreated WS diet had significantly (P < 0·05) less fat in the large depots and lower fat trim of carcass than did animals on the treated WS diets. No other differences in performance were significant. Ammonia concentration in rumen liquor and urea in blood were lower in the animals given alkali-treated WS. The concentrations of Na, K and chlorine in blood serum of the experimental animals were not affected by the treatment. The data on Na, K and magnesium (Mg) in muscle show depletion of Na and K and a trend towards a decrease in Mg concentration. K supplementation reduced the extent of depletion of Na and K. In bone, only Na was affected by the feeding of alkali-treated WS, the pattern being the same as in the muscle. The blood acid-base balance of the experimental animals was not significantly affected by treatments. The values of pH, actual bicarbonate and pCO2 of the animals given 35 g/kg alkali-treated WS indicate mild alkalosis in those animals. This alkalotic state did not affect performance. It appears that there is no Na loading problem which might interfere with growth.

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

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

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

Dairy cattle were injected at intervals of 4 weeks with recombinantly derived bovine somatotropin (bST) i n a slow-release form (somidobove, Lilly Research Centre Ltd, Windlesham, Surrey), to examine the effect on milk production. In the first experiment with 38 autumn-calving animals in a randomized-block design, treatment lasted for 28 weeks and a control and three doses of bST: 320 (low), 640 (medium) and 960 (high) mg were compared. Over the 28 weeks the mean daily milk yields were: control 23·4, low 23·4, medium 25·4 and high 25·4 (s.e.d. 1·17) kg. Milk composition was not affected by bST. In experiment 2 with 40 autumn-calving animals, the medium dose of bST was used for 24 weeks in animals given two levels of concentrate in a factorial design. On average there was a non-significant increase in daily milk yield of 1·3 kg in the bST-treated cattle; there was no interaction between bST and level of concentrate. There were no effects of bST on milk composition. Changes in live weight and body condition of the cattle and their food intake were measured. It was concluded that the trends toward higher milk yields were supported initially at the expense of live weignt and possibly later by increased food intake. In a third experiment 10 grazing cows were given three consecutive doses of 640 mg bST and 10 similar cows acted as controls. There were no significant effects of bST on milk production and food intake. Reasons for the low responses in milk production compared with several recent American and European experiments may possibly be the pattern of use of the slow-release form of bST and the low content of dry matter in the maize silages which restricted forage intake and response in milk production.

Three types of straw were used, a spring barley (variety Corgi) untreated (UC), ammonia-treated Corgi (AC) and an ammonia-treated winter wheat (variety Longbow) (AW). Each straw was included in a complete diet containing either 350 (L), 450 (M) or 550 (H) g/kg straw. The other principal ingredients were rolled barley, molassed sugar-beet pulp and fish meal. Hereford cross steers approximately 16 months old and weighing 350 kg live weight were given the diets ad libitum in both a main trial lasting 80 days, to assess intakes, live-weight gains and food efficiency, and in a subsidiary trial to measure in vivo apparent digestibility.

The live-weight gains during 80 days for steers given the UC diet at L, M and H inclusion were 117, 102 and 0·70 kg/day respectively. The respective live-weight gains for AC were 1·32, 1·27 and 1 02 kg/day and for AW 1 ·26, 1 ·20 and 0·95 kg/day.

While experimental comparisons were terminated at 80 days when the first steers were slaughtered, all except five with the lowest growth rate reached the target fat class for slaughter before 6 months on the diets. While differences in intake and performance between steers given the straws closely reflected differences in degradation characteristics determined by in sacco measurements, the increase in in vivo apparent digestibility between untreated (0·510) and treated (0·545) was small. It is concluded that a large proportion of high quality or treated straw can be incorporated and utilized in diets for finishing cattle.

Resting heat production (H), respiratory rate (RR) and rectal temperature (Tr) were measured at different controlled temperatures (Tt) in Hariana (Bos indicus) and its F, crosses with Jersey (JH), Brown Swiss (BH) and Holstein Friesian (FH) (Bos taurus) breeds and the values obtained were used to assess their relative thermosensitivity.

The lowest Tt at which H significantly decreased from that at 17°c was 32°c for Hariana, JH and BH and 27°c for FH after exposure for 8 days. The corresponding values after exposure for 18 days were 37°c for Hariana and 32°c for all the three crossbred groups. Differences between the genetic groups were also significant. The lowest Tt at which metabolizable energy (ME) decreased significantly in comparison with those at 17CC was 32°c in all the genetic groups. The differences in ME intake between genetic groups were significant only at 32°c Tt. The lowest Tt at which RR significantly increased from those at 17°c were 32°c in Hariana, 27°c in JH, BH and FH for both 5 to 7 and 15 to 17 days of exposure. The corresponding Tt for increase in Tr was 37°c in Hariana, 32°c in JH and 27°c in BH and FH at both 5 to 7 and 15 to 17 days of exposure.

The ambient temperature at which H would have significantly decreased and RR and Tr increased from the respective values at 17CC Tt were calculated curvilinearly for different genetic groups. There were differences in these values of calculated ambient temperatures between genetic groups and between exposure durations in respect of H, RR, and Tr, indicating differences in thermosensitivity.

Voluntary food intake (VFI) was measured daily and live weight (LW) was measured weekly in a total of 39 growing lambs of six genotypes given a similar complete chopped-straw based diet in experiments in 1983, 1985, 1987 and 1988. The six genotypes and the years of study were: Scottish Blackface (BF), 1983 and 1988; Suffolk × (Border Leicester × BF) (BL × BF), Suffolk × (East Friesland × Cheviot) (EF × NCC), Suffolk × (East Friesland × BF) (EF × BF), 1985; Welsh mountain (WM) and Beulah (BH), 1985. Measurements were made on lambs penned individually within 6 weeks of weaning at 5 to 6 months of age through to slaughter in the following spring. During this period there was an increase in LW and VFI associated with growth. Regression lines were fitted to LW and weekly means of daily VFI against week for each individual. Analysis of deviations about these lines showed a decline in VFI in BF lambs around December and to a lesser e×tent in BL × BF from December to January. The decline in VFI in BF was observed in two different years. A negative deviation from the normal rate of increase in LW was also apparent although it was much less marked and present in EF × NCC lambs as well as BF and BF × NCC. Any such variability of seasonal cycles between genotypes of growing lamb would influence the e×tent to which nutrition and growth may be manipulated. This should be considered when choosing a feeding or growth regime for a particular genotype, or vice versa.

Changes in plasma cortisol and B-endorphin concentrations and behaviour in sheep subjected to a change in environment have been studied. Three male and three female sheep were transferred from pasture to indoor crates for a 9-week period. Behaviour was observed by scan sampling for 1-h periods morning and afternoon 5 days/week. Blood samples were taken hourly for 24-h periods on days 1, 5, 30 and 60, and assayed for β-endorphin and cortisol.

Plasma cortisol concentration decreased significantly between days 30 and 60 (P < 0·001) but there was no significant change in plasma B-endorphin concentration over the experimental period. After an initial period of ‘withdrawal’ in weeks 2 and 3, when the amount of time spent resting increased, the occurrence of active behaviours increased with length of confinement. The results suggest that animals had not fully acclimatized to the new surroundings within the 9-week period. This raises important welfare issues concerning experimental animals.

Two experiments have been carried out to examine the effects of the level of protein supplementation given with grass silage-based diets on the performance and carcass composition of bulls, and to compare diets based on silage and dried forage. The five treatments used consisted of grass silage offered ad libitum and supplemented with 2·5 kg dry matter (DM) of barley-based concentrates containing (1) zero (2) 200 (3) 400 and (4) 600 g soya-bean meal per kg and (5) artificially dried grass and hay supplemented with 3·2 kg concentrate DM. The silages used in both experiments were well preserved, containing on average 200 g DM per kg; 140 g crude protein (CP) per kg DM; 63 g ammonia-nitrogen per kg total N and 731 g digestible organic matter per kg DM. The bulls were of late-maturing breed type and were initially 12 months old and 412 and 405 kg live weight in experiments 1 and 2 respectively. For treatments 1, 2, 4 and 5 in experiment 1 respectively (treatment 3 was not used) total DM intakes were 8·3, 8·3, 81 and 110 (s.e. 0·21) kg/day; CP intakes 1063, 1271, 1664 and 1539g/day; metabolizable energy intakes (MEI) 98, 99, 96 and 87 MJ/day; carcass weights 317, 316, 317 and 316 (s.e. 3·2) kg; carcass saleable meat concentrations 714, 712, 718 and 716 (s.e. 5·8) g/kg and carcass fat trims 73, 81, 73 and 68 (s.e. 3·9) g/kg. In experiment 2 for treatments 1 to 5 respectively total DM intakes were 8·3, 8·5, 8·3, 8·4 and 11·2 (s.e. 0·26) kg/day; CP intakes were 1090, 1329, 1504, 1720 and 1561 g/day; MEI 102, 106, 103, 103 and 94 MJ/day; carcass weights 318, 331, 330, 327 and 321 (s.e. 3·3) kg; carcass saleable meat concentrations 726, 721, 725, 721 and 732 (s.e. 60) g/kg and fat trims 71, 77, 78, 80 and 64 (s.e. 4·5) g/kg. It is concluded that protein supplementation of a silage-based diet did not affect performance or carcass fatness in experiment 1 or carcass fatness in experiment 2, but including 200 or 400 g soya-bean meal per kg concentrate increased performance in experiment 2. Animals given silage produced fatter carcasses than those given dried forage in experiment 2 but not in experiment 1.