In deterministic comparisons of breeding schemes it is necessary to take account of variance reduction due to selection. This can take place as multi-stage selection within generations and it takes place across generations when offspring of selected parents are selected. A standard way to deal with this is to set up selection index equations where the parameters are altered as a consequence of selection. It is shown that if the breeding schemes use a univariate or multivariate best linear unbiased prediction (BLUP) animal model for prediction of breeding values this procedure can be simplified. This is done by modelling the distribution of estimated breeding value (EBV) utilizing that changes in EBV of an individual are independent of selection. In the univariate case the variance reduction and the resulting genetic gain can be calculated from the selection intensities and the accuracies in the unselected population. An expression is given for the response in each generation when selection is started in a base population with complete pedigree. This shows that a limiting value is obtained within three to four generations. The asymptotic response for several traits is described in the case where selection is on multitrait BLUP.

Records on total of 1746 calvings of principally Milking Criollos and their crosses were collected between 1972 and 1990 at the experiment station of the Mexican Association of Animal Production on the Gulf Coast of Mexico. Traits of interest were 305-day milk yield, days in lactation, number of services per lactation (raised to power 1/2), age at first calving and lifetime milk yield. Data were analysed by restricted maximum likelihood (REML) under an individual animal model based on 584 animals of which 146 were female ancestors and 35 were male ancestors. Heritabilities of 305-day milk and age at first calving were 0·17 and 0·07, respectively, but heritabilities of other traits were close to zero. Genetic trend in the Milking Criollos for 305-day milk was small and not significant (0·76 (s.e. 2·38) kg/year). Of crosses with Criollo sires, those involving Holstein and Canadienne breeding had highest 305-day and lifetime milk yields and those involving Brown Swiss and native Mexican (mostly Oaxaca) had lowest yields. Jersey crosses were intermediate for 305-day yield. The F1 Criollo × Jersey cross had highest lifetime yield, but backcrosses involving Jersey breeding were poor for lifetime milk. Additive breed effects for Jersey and Canadienne, relative to Milking Criollo, were 88 (s.e. 91) and 227 (s.e. 74) kg 305-day milk, respectively. Heterosis was 144 (s.e. 55) kg (11·6%) for 305-day milk, 16–4 (s.e. 9·6) (5·0%) for days in milk, −0·107 (s.e. 0–042) (7·7%) for number of services per lactation raised to power 1/2, −25·6 (s.e. 41·4) days (2•3%) for age at first calving and 1789 (s.e. 664) kg (60·0%) for lifetime milk. A plan was designed to develop a nucleus breeding scheme utilizing multiple ovulation and embryo transfer technology (MOET) for the genetic improvement of the Milking Criollo breed in Mexico.

Hormonal growth promoters (growth hormone (GH), β-adrenergic agonists, steroids) which improve growth rate and/or lean: fat ratios in the carcass have received considerable adverse publicity and are either banned or have no licence for their use in countries of the European Community. This has led to the development of a number of techniques, involving the use of antibodies, aimed at regulating metabolic processes involved in determining growth and body composition.

A number of these approaches have focused upon the GH axis, for example immunoneutralization of somatostatin (which normally inhibits GH secretion) to improve growth, the use of antibodies to GH which can enhance its effects in vivo and the development of antibodies which mimic the actions of GH. Although immunization against somatostatin has led to increased growth rates in a number of studies other studies have failed to demonstrate such an effect. A precise understanding of the mechanism of action of this approach is required before we can begin to understand why success is not assured. Antibodies which enhance GH action clearly do work reproducibly but the major problem in developing this approach is to produce an inexpensive peptide immunogen (its sequence derived from GH) which can be used to actively immunize animals so that their own antibodies enhance endogenous GH activity. Anti-idiotypic mimics of GH have also been produced which have GH actions in vivo but again this approach is of limited value until appropriate vaccines can be developed.

A different approach to the problem of excess fat deposition involves the use of antibodies directed against the plasma membranes of adipocytes in order to elicit their destruction and thereby limit the storage capacity for fat. This technique has been demonstrated in rats, sheep and pigs in both passive and active immunization techniques. Once again, however, this promising approach is limited by the lack of a commercially suitable vaccine. The identification of individual membrane proteins which are antigenic has been achieved and this provides the prospect of producing recombinant DNA-derived vaccines.

Whether these new approaches will be perceived as acceptable to the general public remains a serious concern and a potential limitation to their development as many would-be sponsors cut back their support for research in these areas.

The aim of this study was to examine the relationship between pedigree index for kg fat plus protein and the financial margins between milk returns and food, health and reproduction costs in individual lactations. Records of milk and milk component production, food intake, health and reproduction were obtained for individual Holstein-Friesian cows over 38 weeks of lactation over a 7-year period, at the University of Edinburgh/Scottish Agricultural College Langhill dairy cattle research centre. Records for a total of 302 lactations were collected. Milk prices, input costs and margins were calculated for individual animals, using 1989/90 values. Regressions of margin over food costs (MF) and margin over food, health and reproduction costs (MFHR) on pedigree index (PI) for kg fat plus protein were all positive and ranged from £2·50± 3·00 per kg PI for MFHR for heifers, to £6·50 ± 2·10 per kg PI for MFHR for all animals. The lower regression for heifers was attributed to higher reproduction costs in animals of higher genetic merit, though the standard error for the regression estimated in this smaller data set was high. Sensitivity analyses showed that the regression coefficients remained very similar, even with ±50% changes in food, health or reproduction costs. It was concluded that selection on PI for kg fat plus protein is likely to lead to increased margin over food, health and reproduction costs.

Methods which estimate the effects on farm profit of a change in a genetic trait (economic weight) are compared. A neoclassical economic model based on a Cobb Douglas type production function, is extended to the long run and compared with a conventional profit equation for two types of trait changes. With this model, an optimal production plan can be derived for the farm which depends on input prices and the production function parameters. In the calculation of economic weights by animal breeders, costs are usually linear with respect to farm output, and so input levels and output are determined arbitrarily. Differences between methods for the estimation of both absolute and relative economic weights are shown to be small for proportional trait changes of 0·01 to 0·05. However, for proportional trait changes of 0·3, proportional differences were from 0·01 to 0·75 and from 0 to 0·6 for absolute and relative economic weights respectively, depending on the production function parameters. This dependence on the size of the trait change is attributed to the non-linearity of the production function. The effects of ‘rescaling’, which implicitly discounts economic weights for output increasing traits, are also evaluated. Absolute and relative ‘rescaled’ economic weights for 0·01 proportional trait changes are shown to differ proportionally from those estimated by the neoclassical economic model by from 0·14 and 0·12 to 0·50 respectively. For 0·3 trait changes, proportional differences were from 0·16 to 0·79 and from 0·8 to 0·43 for absolute and relative trait changes respectively. The results have important implications for conventional breeding programmes, and the economic evaluation of breeds and major genes.

Forty-eight spring-calving, Holstein-Friesian cows were continuously stocked on perennial ryegrass-white clover swards maintained at compressed sward heights of 4, 6 or 8 cm and offered 0 (U) or 4 (S) kg concentrates. Milk yields and composition, live weights and intakes (estimated by the n-alkane technique) were recorded for periods 24 May to 27 June (P1) and 28 June to 8 August 1992 (P2) with 4 cm swards not used in P2. Milk and component yields were significantly lower at 4 cm than at 6 or 8 cm in P1 and significantly higher when supplements were offered in both periods with no significant interaction. Herbage intakes were reduced more by supplementation at lower sward heights. Live weight was significantly lower on the 4 cm sward. Fat concentrations were unaffected by height and supplementation in P1 but significantly increased by supplementation in P2. These results suggest that maintaining a sward height of 6 cm offers advantages in terms of individual animal output and output per ha compared with grazing at greater or lower sward heights.

An experiment was carried out to evaluate the effects of forage type and level of concentrate supplementation on forage intake, diet apparent digestibility, purine excretion and milk production. Twelve crossbred cows (Bos taurus × Bos indicus), in early lactation, were allocated to the following six dietary treatments: maize-lablab forage (ML) or oat-vetch forage (OV), offered ad libitum, and supplemented with either 0, 2·5 or 5·0 kg per cow per day of a supplement (wheat middlings). A four-period, partially balanced, change-over design was used and the treatments were arranged as 2 × 3 factorial.

Mean organic matter (OM) intake was 670 g higher with cows on ML-based diets compared with those on OV-based diets (P <0·02). The apparent digestibilities of crude protein (CP) and neutral detergent fibre (NDF) were similar for cows given ML- or OV-based diets but the apparent digestibility of OM was higher for ML diets (P <0·05). Values of the degradation parameters (a, b and c) of DM and NDF were greater for ML forage than for the OV forage. Forage type did not affect daily milk yield nor excretion of purine derivatives in urine used to estimate microbial-nitrogen supply (P >0·05). The concentration of milk fat and total solids in the milk were similar for the two forage types offered but the concentration of milk protein was slightly higher for the cows given ML-based diets (P <0·05).

Daily OM intake increased by 3·75 and 2·70 kg per cow per day (P <0·001) respectively, when the amount of concentrate increased from 0 to 5·0 kg per cow per day for the ML- and OV-based diets. The CP apparent digestibilities of the diets were higher when the diets were supplemented with concentrates but there was no effect of supplementation on the apparent digestibilities of OM and NDF. The supply of microbial-nitrogen increased linearly with increasing level of concentrate supplementation (P <0·05). Milk yield increased linearly when the level of concentrate supplement increased from 0 to 5 kg (P <0·001), resulting in 0·39 and 0·29 kg more milk per day per kg additional concentrate given in cows on ML and OV, respectively. There was also a tendency for a quadratic effect (P <0·12), especially with ML diets, showing that when the level of concentrate increased from 0 to 2·5 or from 2·5 to 5·0 kg/day, the milk yield increased respectively by 0·62 and 0·15 kg/day per kg additional concentrate given.

Forty-four Borana × Friesian F1 crossbred calves born to Borana (Bos indicus) cows were randomly assigned to either suck their dams hvice daily or bucket-feeding with 1341 milk over a 57-day pre-weaning period. Their dams were also allocated either to a supplement group with grass hayad libitumand 5 kg per head per day of a concentrate ration or to an unsupplemented group withad libitumgrass hay only. Calves were fed in individual boxes in a calf house. The mean birth weight of calves was 24·8 (s.e. 1·8) kg. Suckled calves were heavier (P < 0·01) at weaning (47·7 (s.e. 1·9) v.37·1 (s.e. 1·8) kg) and had faster pre-weaning growth rate (411 (s.e. 30)v.215 (s.e. 29) g/day) than bucket-fed calves. Calves which sucked supplemented cows were heavier (P < 0·001) at weaning (51·2 (s.e. 2·6)v. 44·2 (s.e. 2·6) kg), had faster (P < 0·01) pre-weaning growth rate (477 (s.e. 41)v.346 (s.e. 41) glday) and higher (P<0·01) daily milk intake (2·6 (s.e. 0·2)v.1·6 (s.e. 0·2) I/day) than those which sucked unsupplemented cows. Mean concentrate intake was 302 (s.e. 30) g/day for bucket-fed calves and 341 (s.e. 33) and 408 (s.e. 33) g/day for calves which sucked supplemented and unsupplemented cows. Cow milk production was higher (P < 0·01) in suckled than in milked cows (3·3 (s.e. 0·2)v.1·0 (s.e. 0·2) I/day) and in supplemented than unsupplemented cows (3·9 (s.e. 0·2)v.2·7 (s.e. 0·2) I/day). Concentrations of milk protein, fat and total solids averaged 39 (s.e. 15), 49 (s.e. 16) and 143 (s.e. 21) g/kg, respectively and were not significantly influenced by either concentrate supplementation or suckling. Restricted suckling and early weaning coupled with appropriate calf and cow feeding regimes could be one of the alternatives for calf rearing under smallholder and small scale peri-urban dairy production systems. However, further studies are warranted to evaluate the effects of such a strategy on both calf and cow performances under these production systems.

Inbreeding leads to reduction of the additive variance, whereas inbreeding depression reduces the performance of milk producing cows in both the nucleus and the commercial population. In this study, the cumulative additive response to 30 years of selection corrected for variance reduction due to inbreeding and inbreeding depression in the commercial cow population (denoted as expected phenotypic level or P) was evaluated in a closed (1024 cows tested per year) dairy cattle nucleus scheme, assuming a large number of gametes available per female. No dominance effects were simulated nor estimated in the nucleus. Various hierarchical and factorial designs with fewer sires than dams, an equal number of sires and dams, or even a larger number of sires than dams were compared for P. The trait considered was overall economic merit for milk production with a heritability of the unselected base population of 0·30. Sires and dams were selected on their animal model estimated additive effect for the trait considered at either 15 or 27 months of age. All full-sibs were available for selection. In the absence of inbreeding depression, a complete factorial scheme with more sires than dams resulted in the highest P. With increasing inbreeding depression, the optimal number of sires increased relatively more than the optimal number of dams. Increasing the number of sires decreased inbreeding relatively more than increasing the number of dams, and resulted in a relatively higher P. This is due to the fact that correlations between estimated additive effects of male selection candidates are higher than between those of female selection candidates.

Breeding programmes for Wakwa and Ngaundere Gudali cattle breeds were initiated in Wakwa (Cameroon) in 1952 and 1965, respectively, to improve growth performance of the indigenous breeds. Animals were selected on 240-day weaning weight (WWT). Data analysed covered the period 1971 through 1985 and consisted of 2211 calf birth weight (BWT) and 1409 WWT records on Gudali and 1196 BWT and 763 WWT records on Wakwa. Selection responses in BWT and WWT were estimated as regressions of average sire estimated transmitting abilities (ETAs) and average dam estimated breeding values (EBVs) on year of calving. ETAs and EBVs were predicted using best linear unbiased prediction procedures. Estimated annual changes in sire ETAs for WWT were 0·67 (s.e. 0·17) and 1·69 (s.e. 1·13) kg/year for Gudali and Wakwa, respectively. Corresponding trends in dam EBVs were –0·03 (s.e. 0·03) and –0·24 (s.e. 0·19) kg/year. Estimated correlated trends in BWT among Gudali and Wakwa sires were 0·09 (s.e. 0·05) and –0·14 (s.e. 0·04) kg/year, respectively. Corresponding correlated trends in BWT associated with dam selection were essentially zero, being –0·001 (s.e. 0·001) and –0·01 (s.e. 0·01) kg/year. Environmental trends were negative for all traits except Gudali WWT. Phenotypic trends were all positive, except that of Wakwa BWT. Overall, selection on WWT yielded moderate selection reponse despite substantial infrastructural constraints in the breeding programme. Trends in sire ETAs and dam EBVs for WWT jointly accounted for estimated genetic gains of 8·60 kg in Gudali and 20·4 kg in Wakwa over the study period. Overall correlated response in BWT during the study period was significant (P < 0·001) and negative for Wakwa. It was positive but not significant for Gudali.

Twenty-four years of data from a Boran cattle breeding and improvement ranch in the Rift Valley of Ethiopia were used to study the influence of genetic and environmental factors on age at first calving (AFC) and calving interval (CD using an individual animal model.

The mean AFC and Cl were 41-8 months and 442 days, respectively. The h2 values for AFC were 0·062 and 0·075 when estimated on the original and selected data, from which cows that did not calve after 5 years of age were deleted, respectively. The h2 values for CI were 0·037 and 0·043 when estimated on the original and selected data, from which cows with AFC higher than 5 years and CI longer than 2 years were deleted, respectively. The corresponding c2 values (ratio of permanent environmental variance to total) were 0·031 and 0·028 for the respective data sets. Parameter estimates of the original data from bivariate analysis were 0·012 (h2), 0·065 (h2), -0·054 and -0·176 for first CI, AFC, their genetic and environmental correlation, respectively. The h2 values estimated in a bivariate analysis of the first three CIs varied between 0·002 and 0·093. Year and season had significant effects on both traits. The annual genetic change for both traits was not significant while the solutions for year effects were highly variable. The regression of the solutions of year effects for AFC on year showed that it increased by about 10 days while the variation in CI was due to random year to year fluctuation.

Twenty lactating dairy cows were used to investigate the relationship between the site of milk storage in the udder and the short-term response to thrice-daily milking. Cisternal and alveolar milk volumes were measured 8 h after an ordinary morning milking by catheter drainage and machine milking with oxytocin respectively. The response to thrice-daily milking was assessed using a half-udder technique and the relative milk yields quotient (RMYQ). Over the first 7 days, both halves were milked twice daily (8/16 h intervals) and milk yields over the final 4 days of this period were higher for left fore/right hind (LF/RH) (12·4 (s.e. 0·85) kg/day) than for RF/LH (10·5 (s.e. 0·63) kg/day) which was milked after LF/RH throughout the experiment. Over the following week, LF/RH quarters were milked an additional time (8/8/8 h intervals) and yields over the final 4 days were increased (15•7 (s.e. 0·95) kg/day) compared with control quarters (9·8 (s.e. 0·73) kg/day). In a final 4-day period, animals were milked twice daily and half udder yields were 13·1 (s.e. 0·89) kg/day and 10•6 (s.e. 0·77) kg/day respectively. Differences between yields from the two halves of the udders were highly significant in all 3 weeks of the experiment (P < 0·001). Cistern milk yield as a proportion of total milk yield at 8 h (cistern proportion) averaged 0·170 (s.e. = 0·0275; range 0·020 to 0·334) and tended to be greater for multiparous (0·215, s.e. 0·0279) than for primiparous animals (0·118, s.e. 0·0437; P = 0·076). During the periods of twice-daily milking, the proportion of milk yielded from LF/RH quarters was not significantly related to cistern proportion (P = 0·70 and 0·43 for weeks 1 and 3 respectively). However the response to thrice-daily milking, assessed as RMYQ, was significantly related to cistern proportion both when changing up to, and down from, thrice-daily milking (P < 0·01). Animals with low cistern proportions showed larger responses to thrice-daily milking. There was a significant relationship (P < 0·05) between the responses on changing up to, and down from, thrice-daily milking. Primiparous animals tended to exhibit smaller declines on returning to twice-daily milking than multiparous animals with equivalent responses to thrice-daily milking.

Forty Charolais and 40 Limousin × Holstein Friesian bulls, 8 months old and weighing 315 kg live weight at the start of the experiment, were given grass silage to appetite throughout.

From 315 to 425 kg live weight they received: no supplement (S0), 1 kg (S1), 2 kg (S2) or 4 kg (S4) of a rolled barley supplement per head per day. After a mean treatment live weight of 425 kg had been achieved for each breed, the daily supplement of all treatments was changed to 3 kg of rolled barley per head per day until individual animals were adjudged to have attained a European Community (EC) external fatness score of 3 to 4L, at which point they were slaughtered.

Daily growth rates from 315 to 425 kg live weight were 0·67, 0·82, 0·94 and 1·25 (s.e.d. 0·042) kg for treatments S0, S1, S2 and S4 respectively. Following the change of supplement rate at 425 kg live weight, daily gains were 1·46, 1·36, 1·27 and 1·16 (s.e.d. 0·051) kg/day, giving overall gains of 0·99, 1·05, 1·08 and 1·19 (s.e.d. 0·033) kg/day respectively. The numbers of days taken to achieve slaughter condition from the start of the trial at 315 kg were 277, 251, 243 and 207 (s.e.d. 5·3) days respectively. Bulls were slaughtered at 17·0, 16·2, 15·9 and 14·7 months of age and produced carcass weights of 330, 324, 322 and 305 (s.e.d. 6·5) kg respectively.

Silage dry-matter intakes were 5·9, 5·1, 4·8 and 4·2 kg/day during the initial phase when differential supplement levels were being given and 7·0, 6·8, 6·2 and 5·8 respectively during the finishing period when all groups were being given 3 kg barley supplement daily. Food conversion ratios (kg dry matter intake per kg gain) were 9·1, 7·3, 6·9 and 5·8 during the initial phase and 6·4, 6·9, 6·9 and 7·2 respectively after 425 kg live weight.

It is concluded that barley supplements of 0 to 2 kg/day offered with high-quality grass silage during the growing stage (8 to 12 months of age), followed by at least 3 kg/day will produce finished bulls at an average of 325 kg carcass weight at 16 to 17 months of age. A higher level of 4 kg barley during the growing stage will reduce the slaughter period to approximately 15 months of age but carcass weight will also be reduced. Further studies are required to define the precise level of barley supplement during this earlier period.

First lactation records for production traits (milk, fat and protein yields) and 17 linear type traits for 7169 Ayrshire heifers were analysed to estimate genetic parameters for type traits and to examine the relationship between type and production traits. A multivariate restricted maximum likelihood procedure fitting a sire model with sire relationships included was used for all analyses.

Heritabilities for production traits were approximately 0·3 and genetic correlations among them were high (>0·84). The estimates of heritabilities for type traits were mainly low to moderate ranging from 0·04 to 0·42. Angularity (0·80), beef shape (0·49), foot angle (0·53) and stature (0·46) had higher heritabilities. Generally phenotypic correlations among type traits were lower than the genetic correlations. The highest negative genetic correlation was between rear legs side and rear legs rear (-0·95) and the highest positive correlation between chest width and beef shape (0·93).

Genetic correlations between type and production were low to moderate and were similar for milk, fat and protein yields. The genetic correlations between the production traits and chest width, udder depth and beef shape were negative but were positive between production and angularity, rear udder width and teat placement side.

The accuracy of progeny testing for a continuous trait when the auxiliary information was based on ‘all-or-none’ type of traits with a multi-factorial threshold model was examined. The accuracy of the progeny test was found always to increase with the inclusion of the auxiliary trait. It followed the same pattern as in the case of continuous auxiliary trait. However, there was an additional feature in that the accuracy was also dependent on the probability of incidence of the discrete trait unless either the progeny group size was very large, and/or there was no genetic correlation or else the probability of incidence was itself extremely low. Compared with the case when the auxiliary trait was continuous, there was a loss in accuracy which can be looked upon in two ways. First, the continuous auxiliary trait is itself made ‘all-or-none’ type by a threshold and the accuracies compared in the two cases. The loss increases symmetrically in either direction with increase in positive or negative directions of the difference in genotypic and phenotypic correlations. Secondly, a comparison can be made of the accuracy when the auxiliary trait is normally distributed with that when it is binomially distributed but with the same amount of genetic information on the observed scale as given by the heritabilities and genetic correlations. No loss now occurs if the two classes of the binomial trait are equally likely and the loss in accuracy increases with the decrease in the standard deviation of the binomial distribution for given values of other parameters. It was found also that the use of binomial auxiliary trait reduced the number of progeny required to attain a pre-assigned level of accuracy, resulting in a decreased cost of the programme compared with that when no binomial auxiliary trait was used.

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.

In the first experiment the animals were worked for 5h/day and/or given 17 h access to food. In the second experiment they were worked for 4 h/day and/or given 20 h access to food. When animals were prevented from feeding on barley straw for 7 h/day their dry-matter intake (DMI) was significantly less than when they were given 24 h access to food. When feeding was prevented for only 4 h/day food intake was not significantly different from that with 24-h access.

A study of feeding behaviour (experiment 2) suggested that when most animals were deprived of food for 4 h they maintained similar intakes to those on ad libitum feeding by increasing their rate of eating, rather than by increasing the time they spent eating. Preventing food intake for 4 h/day was associated with little change in time spent ruminating during the day. On all treatments, the buffalo spent significantly less time eating and more time ruminating than the cattle.

Work, during the periods when food was withheld, had little effect on the DMI of either the buffalo or cattle compared with restricted feeding. No rumination occurred during the time that the animals were at work. However on working days, time spent ruminating was similar to that seen on restricted feeding days, but the animals spent more time ruminating later in the day than when they were able to ruminate during the middle of the day.

An experiment was conducted to examine the response of three genotypes of beef cows to contrasting levels of nutrition supplied from grazed pasture. Twenty-two Hereford × Friesian (HF), 20 Aberdeen Angus × Friesian (AF) and 24 Welsh Black (WB) spring-calving beef cows with their Charolais-cross calves were used in 4 years consecutively. During the summer grazing period they grazed permanent pasture maintained at either 4 to 5 cm (short) or 7 to 8 cm (tall) sward surface height. Sward height treatment significantly (P < 0·001) affected cow and calf live-weight gain (0·498 v. 0·041 (s.e.d. 0·0405) kg/day and 1·12 v. 0·90 (s.e.d. 0·021) kg/day for cow and calf live-weight gain on the tall and short swards respectively). The live-weight gains of the HF and WB cows were similar, but the AF cows gained less weight on the tall sward and lost weight on the short sward. Calf live-weight gain reflected cow milk yield, with the calves from HF and AF cows having similar live weight gains (1·06 and 1·02 kg/day respectively) and those from WB cows having lower gains (0·95 kg/day; P < 0·001). The effect of sward height on calf live-weight gain was greatest in the WB-born calves because of the lower milk yield from WB cows. Body chemical composition changes of cows were predicted from live weight and body condition score, using prediction equations derived from separate groups of cows which were slaughtered at a range of body compositions for determination of chemical composition. Energy balances, calculated from changes in chemical composition, showed the AF cows to have the lowest energy balances with the WB cows the highest. Calculation of energetic efficiency and land use efficiency of weaned calf production taking account of annual food requirements indicated that the HF cows were most efficient, and the WB cows least efficient. The effect of increasing nutritional environment (as represented by sward height treatment) was such as to increase energetic efficiency for all genotypes, but land use efficiency was increased for HF and AF cows, and decreased for WB cows. These results indicate the factors such as size of cows, milk yield potential and pattern of nutrient partitioning can influence energetic land use efficiency of weaned calf production, and that important interactions between genotype and nutritional environment can occur in different measures of efficiency.

Thirty-six individually penned lambs (mean live weight 32·4 (s.d. 2·27) kg) were offered maize silagead libitumand one of three concentrate mixes, two of which contained extracted rapeseed meal (control and HR) and the other fish meal (FM). The concentrates were given according to live weight and in sufficient quantities to provide proportionately about 0·4 of the dry matter (DM) intake of the lambs. The dietary concentrations of nitrogen (N) g/kg DM were 22·4, 27·4 and 27·5 and of rumen undegradable N 6·6, 7·3 and 11·6 for the control, HR and FM diets respectively.

Both the HR and FM diets depressed maize silage intakes compared with the control during the first 21 days (P < 0·05) and lambs given the FM diet continued to have lower intakes than control lambs (P < 0·05) throughout the experiment. The live-weight gain of HR lambs was considerably depressed in comparison with the control and FM lambs during the first 21 days of the experiment (P < 0·05). Overall HR lambs gained weight more slowly than control and FM lambs up to 45 kg live weight but the difference was not statistically significant. Food conversion ratio was better for FM than HR (P < 0·01). There were no treatment differences in wool growth.

The results obtained provide little evidence that fish meal had any beneficial effects upon lamb growth compared with the control diet except a possible increase in the efficiency of metabolizable energy utilization.

A 3-year experiment was carried out to compare systems of bull beef production involving continuous housing or pasture grazing from 5 to 10 months of age and to examine the effects of herbage allowance and concentrate supplementation on lifetime performance and carcass quality. Animals were either set-stocked at pasture to maintain nominal sward heights of 7, 9 and 11 cm or were offered grass silage (700 g digestible organic matter per kg dry matter (DM)) supplemented with 1·5 and 3·0 kg barley-based concentrates (183 g crude protein per kg DM) per head daily. Half of the animals grazed at each sward height were given 1·5 kg concentrates per head daily while the remainder received no supplement. A total of 160 continental X Friesian and 48 Friesian calves which were initially 197 kg live weight were used. From 10 months of age until slaughter at about 17 months all animals were given grass silage ad libitum and supplemented with 3·0 (year 1) or 3·75 (years 2 and 3) kg cereal-based concentrates per head daily.

Animals which grazed the 9- and 11-cm swards produced carcasses of similar weight to those given silage and 3·0 kg concentrates per day, while those grazing the 6·7-cm swards produced carcasses of similar weight to those given silage supplemented with 1·5 kg concentrates. Reducing sward surface height from 11·0 to 9·3 cm did not affect performance but further reductions to 7·9 (year 1) and 6·7 (years 2 and 3) cm reduced live-weight gain by 0·13 and 0·32 kg/day respectively. Concentrate supplementation did not affect the performance of animals grazing swards which were 7·9 cm or taller but increased live-weight gain by 93 and 193 g/kg concentrates for those grazing the 6·7 cm swards and those receiving silage respectively. Differences in live weight at 10 months of age due to the feeding treatments imposed from 5 to 10 months of age were largely retained until slaughter at 17 months as there was little compensatory growth during the residual period. The treatments did not affect carcass composition when the data were adjusted to a constant carcass weight, or meat quality which was satisfactory for all treatments.