In a lifetime study of spring-born cattle in a 20-month beef system the effects of production factors on carcass characteristics were examined using 302 serially slaughtered animals born in three consecutive years. A multifactorial design was used with three animal factors — maturity (early maturing Hereford crosses v. late maturing Charolais crosses), sex (heifer v. steer) and method of rearing (suckled calves v. bucket-reared calves). After an initial rearing period, feeding treatments were imposed during the subsequent winter period, followed by the imposition of two sward heights (low 6 to 8 cm and high 8 to 10 cm) during the subsequent grazing season. An initial representative group of 16 cattle was slaughtered at the start of the grazing season and most of the remaining cattle were subsequently slaughtered off grass at three randomly allocated slaughter times, on average 67, 110 and 154 days post turn-out. Interactions between the main production factors were not significant with the exception of slaughter date with winter feeding levels for fat in rib joint and weight of saleable meat, and slaughter date and sex for live weight, carcass weight and weight of saleable meat. Breed type, sex and method of rearing affected the weight of saleable meat off grass by 14·7, 14·8 and 5·6 kg respectively. The influence of the winter feeding treatments on the weight of saleable meat was small by the time the final group were slaughtered. Sward height had a transient effect on weight, condition and carcass composition, the effects becoming less evident as the grazing season progressed. The effect of delaying slaughter had the largest and most significant influence on carcass composition of all the production factors studied, although changes in body composition between slaughter dates were relatively slow.

This study examined whether work applied at different stages of lactation had any effect on reproduction of cows under two feeding regimes. Twenty-four F1 crossbred dairy cows (12 Friesian × Boran and 12 Simmental × Boran) were allocated one of two diets (H + 3: natural pasture hay + 3 kg concentrate per day; and H + 5: natural pasture hay + 5 kg concentrate per day) and one of three work treatments — starting 45 days (D45), 90 days (D90) and 135 days (D135) post partum — using a principal component analysis score based on milk yield, live weight, calving interval and parity. Cows pulled sledges for 50 days (pull = 108 N per 100 kg live weight). Over the experimental period of 315 days, cows on diet H + 5 travelled a similar distance and produced amounts of fat-corrected milk (FCM) similar to those of cows on diet H + 3. Total intake of dry matter per kg live weight 0·75 was higher for cows on diet H + 5 than for cows on diet H + 3 and was similar across work times. Hay dry-matter intake was greater for the H + 3 group than for the H + 5 group at 180 days post partum and thereafter. Cows on diet H + 5 lost less weight in early lactation and gained more in mid and late lactation than cows on diet H + 3. During the work period, live-weight change was similar across diets but it was different between work treatments D45 and D135. The interval from calving to conception decreased by 63 and 101 days when start of work was delayed from D45 to D90 and from D45 to D 135, respectively. Output/input ratios of metabolizable energy equivalents were 0·35 for H + 3 and 0·37 for H + 5 diet, and 0·34, 0·37 and 0·40 for work times D45, D90 and D135, respectively. These results indicate that work started in early lactation significantly increased days to conception and decreased overall productivity of lactating working cows. Farmers must weigh the relative importance and cost of delayed ploughing against those of delayed oestrus or against the cost of borrowing draught power.

Compared with small groups, housing in large groups offers the pig more total available space, resulting potentially in an increased degree of control over its (micro) environment. For the producer, large groups require fewer pen divisions and offer more possibilities for the sharing of resources such as feeders and drinkers. However, whilst large groups may offer benefits to higher ranking animals in the group, there may be serious disadvantages for those further down the social hierarchy, who also need to compete for access to resources. This study investigated the interactive effects on welfare of food availability (one single space hopper per 20 or per 10 pigs) and group size (20, 40 or 80 pigs per pen), at constant stocking density (0·55 m2 per pig) in part-slatted pens. Groups provided with two feeding spaces per 20 pigs were less active than groups with one feeding space per 20 pigs. The number of aggressive interactions per pig at the food trough was not affected by group size but decreased with number of feeder spaces per 20 pigs. The number of skin lesions increased with group size. Average daily gain in the first half of the finishing period was negatively influenced by group size and positively by number of feeding spaces. No effect on weight gain was found subsequently. Within-group variation in growth was not affected by group size or number of feeder spaces. No differences between treatments were found in the number of pigs removed for health reasons. Interactive effects of the two treatments were found on some behaviours but not on any of the performance variables measured. It is concluded that, from a welfare point of view, the number of pigs per feeder space should be lower than 20, although performance levels appear acceptable at 20 pigs per feeder. Further research will have to identify whether the effects of group size on general aggression is common to all finishing pig systems, or whether the presence of straw can serve as a mitigating factor.

Performance, water intake and feeding behaviour of two groups of 30 (trial 1), 40 (trial 2) or 50 (trial 3) weaned pigs offered either pellets or meal of the same formulation were compared.

Average daily weight gains (ADG) were higher for pigs given pellets rather than meal in trials 2 (413 v. 363 g/day,

P < 0·001) and 3 (356 v. 324 g/day, P < 0·05). Mean daily water intake (DWI) was higher with meal than with pellets but only during trial 1 (2·31 v. 1·65 I/day, P < 0·01).

The occupation time (ОT) and the number of animals using the feeder simultaneously (N) were higher when pigs were given meal rather than pellets, whatever the animal density: trial 1: 82·6 v. 69·9% (P = 0·05) and 3·8 v. 2·3 (P < 0·01); trial 2: 90·9 v. 77·9% (P > 0·05) and 5·2 v. 3·1 (P < 0·01); trial 3: 96·2 v. 83·6% (P < 0·05) and 5·9 v. 3·8 (P < 0Ό1). When using pellets, ОT and N were always significantly lower during the night than during the day but when using meal in groups of 40 and 50, ОT during the night was almost as high as during the day.

The greater the group size, the lower were ADG (both diets) and DWI (only with meal) and the higher were ОT and N (both diets). Furthermore, significant linear and curvilinear regressions of DWI, ОT and N according to time were calculated.

In conclusion, pigs need more time to eat meal than to eat pellets. Thus the number of pigs per feeder has to be adapted to the food presentation. Too high a number of pigs per feeder impairs feeding behaviour and eventually welfare, by preventing preferential diurnal feeding activity and this may affect productivity.

In data collected for feeding behaviour analysis, feeding events are generally separated by many very short to very long intervals during which no feeding occurs. When feeding is clustered in bouts, a meal criterion (that is the longest non-feeding interval accepted as part of a meal) must be estimated before events can be grouped into meals. Until recently, three methods that estimate quantitative meal criteria were available. These methods consist of fitting a ‘broken-stick’ (two straight intersecting lines, both with a negative slope) to the frequency distribution (method 1), the loge-transformed cumulative frequency distribution (the log-survivorship curve; method 2) or the loge-transformed frequency distribution (method 3) of intervals between events. Recently, new methods have been proposed that fit either two (method 4) or three (method 5) Gaussians to the frequency distribution of loge-transformed interval length (log-normal models). We compare the estimates obtained with these five methods when applied to a data set of 79575 intervals between visits to food dispensers. These were recorded with 16 lactating cows during an average period of 156·6 (s.d. 51·5) days per cow. Meal criteria were estimated as 1·9, 6·0, 7·5, 32·4 and 49·1 min by methods 1 to 5, respectively. Estimated daily number of meals ranged from 5·7 to 12·1 per cow and estimated average meal size from 4·0 to 8·4 kg. The observed probabilities of cows initiating feeding in relation to time since feeding last showed best agreement with the predictions of the log-normal models. We conclude that the first three methods do not, while log-normal models do, have an adequate biological basis for a clear interpretation of the estimated meal criteria. Log-normal models are, therefore, the most promising for estimating meal criteria in cattle and probably in other species as well.

This paper demonstrates how interactions between host genotype for resistance to an infectious disease and the epidemiology of that disease can have large influences on animal productivity and hence on breeding goals for domestic livestock. This is illustrated for the case of gastro-intestinal parasitism in lambs. A model of the parasite infection was developed to include between-animal variation (genetic, permanent and temporary environmental) for live-weight gain, food intake, larval establishment rate in the host, worm fecundity and worm mortality rate. Achieved live-weight gain was defined as the sum of potential live-weight gain under conditions of no parasite infection, a trait correlated with food intake and growth-rate reduction due to the infection. The reduction in growth-rate was calculated from cumulative larval challenge and cumulative worm mass in the lamb. Genetic parameters were then estimated for the output traits of observed live weight at 6 months of age, growth rate reduction and faecal egg count. Model parameters were chosen so that the output means and heritabilities for faecal egg count and live-weight gain mimicked field data for Scottish Blackface lambs and growth-rate reductions were proportionately 0·25 , on average. The model predicted a weak phenotypic correlation (mean = -0·10) between observed live weight and faecal egg count, the indicator of resistance but a stronger favourable (negative) genetic correlation between these traits (mean = -0·27). The severity, or epidemiology, of the disease greatly influenced the results - the genetic correlation between observed live weight and faecal egg count strengthened from -0·02 to -0·46 as the disease severity changed from mild to severe. Selection for reduced faecal egg count resulted in large correlated increases in live-weight gain, more than twice that predicted by quantitative genetic theory, due to the reductions in growth rate losses as the disease challenge to the animals decreased. Conversely, selection for increased live-weight gain resulted in reductions in faecal egg count close to expectations. This asymmetry of selection response emphasizes the epidemiological benefits obtainable from selection for resistance to infectious chronic diseases - such selection will result in improvements in both animal health and productivity not seen when selection is for improved productivity, alone. Breeding goals should be designed to take account of such effects.

Carcass quality was evaluated in 35 male and 41 female lambs, 38 expressing the callipyge phenotype (Cg) and 38 controls expressing the normal phenotype (N). Lambs were from Romanov and Suffolk × Romanov ewes mated to two rams heterozygous for the callipyge locus and slaughtered at approximately 44 kg live weight. The Cg lambs reached slaughter weight at 163 days of age, 13 days younger, and had a dressing proportion 0·524 , 0·029 points higher. Also they had more leg (341 v. 308 g/kg), less loin (315 v. 328 g/kg) and less shoulder (340 v. 360 g/kg) than the N lambs. The leg, loin and shoulder wholesale cuts and half the carcass of Cg lambs had 81, 113, 77, and 92 g/kg more lean and 52, 98, 59, and 72 g/kg less fat than N lambs, respectively. The Cg lambs also had larger loin-eye area (18·5 v.13·1 cm2), less backfat at the C (4·1 v. 6·1 mm) and at the GR locations (11·0 v. 15·2 mm) and less internal fat (202 v. 339 g) than the N lambs. Dissection of the 12th rib indicated that Cg lambs had more muscle (574 v. 462 g/kg), less fat (276 v. 358 g/kg) (both P < 0·001) and similar (V > 0·05) bone (155 v. 265 g/kg) to N lambs. Colour of the longissimus muscle was significantly paler in Cg lambs. Intramuscular fat and dry matter of longissimus muscle were significantly lower (49 v. 120 and 247 v. 253 g/kg) in Cg than in N lambs. Cg lambs were significantly different (P < 0·05) from N lambs for all traits studied except age at slaughter, tissues at the GR location, proportion of bone in the 12th rib and the L* colour of the longissimus muscle. Breed type effect was significant only for age at slaughter, whereas the effect of sex was significant for all traits except for proportion of lean in the leg, b* colour and intramuscular fat content of the longissimus muscle. No interactions were significant except phenotype × breed type on fat thickness over the longissimus muscle. Post-mortem ageing of the longissimus muscle for 9 or 15 days caused a significant reduction in muscle toughness in Cg lambs compared with those aged for 3 days (113 v. 98 Newtons) but the muscle was still tougher than that from N lambs (with a shear force of 64 and 51 Newtons at 3 and 9 or 15 days post mortem). The principle component analysis including carcass conformation and composition traits as well as meat quality traits was indicative of a distinctly different carcass ofCg compared with N lambs. The first two principal components explained 0·70 of the total variation.

The effects on genetic and economic responses of adding faecal egg count (FEC) in the aggregate genotype of dairy sheep in Greece were investigated. The extra responses obtained in the full aggregate genotype were expressed as a percentage change of the responses in terms of genetic gain, profit and selection response of single traits before adding the trait. The initial aggregate genotype included the traits milk fat yield (FY) and number of lambs weaned per ewe per year (NLW). Inclusion of FEC in the aggregate genotype resulted always in increased genetic gain and profit. The extra responses from adding the FEC in the index selection were variable and often very large, depending on the parameters varied i.e. the economic weight of FEC and the genetic correlation of FEC with the other production traits. For a wide range in the size of the genetic correlations between FEC and other traits, gains of FEC and no appreciable losses of responses for FY and NLW were predicted when FEC accounted proportionately for 0·10 to 0·20 of the total monetary genetic deviation. While FEC showed a wide range of change, selection responses of FY and NLW remained remarkably insensitive under various weightings of FEC and different genetic correlations of FEC with the production traits. The genetic and economic efficiency of alternative selection schemes were also evaluated. A two-stage selection procedure involving preliminary selection of rams on dam’s FEC, FY, NLW and on their own FEC and final culling on progeny’s FEC, FY and NLW was predicted to be the most efficient in both genetic and economic terms. Female replacements should be selected on dam’s FEC, FY and NLW (first stage) and their own FEC, FY and NLW (second stage). When repeated measurements of FEC are taken, the recommended number of FEC measurements was found to be 4.

A genetic epidemiological model (GEM) for investigating the effect of selection for disease resistance on the epidemiology of infectious diseases is presented and applied to a pig breeding scenario. Fundamental to the model is R0, the basic reproductive ratio. R0 is the expected number of secondary infections caused by a single infection. If R0 is greater than 1, there will be an epidemic. The aim of the model is to quantify the effect of selection on R0 and the consequences this has on disease epidemiology. Two implementations are presented: selection for reduced susceptibility/infectivity to a disease and introgression of a major resistance gene. The results suggest that the effects of selection for reduced susceptibility I infectivity are critically dependent on the infectiousness of the disease. Under the assumptions made in the model, for a disease with a low infection level, it takes approximately 15 years of selection until R0 is less than 1 and the population is safe from epidemics should the infectious agent be present. For a highly infectious disease, this time may be as long as 100 years. For gene introgression, the population is expected to be free from epidemics within 5 years and the time to reduce R0 to less than 1 is largely independent of the disease being considered. With gene introgression, the proportion of the population which needs to be resistant to ensure that R0 is less than one is shown to be a function of the initial R0 for the disease. Although selection, as modelled, results in a linear decline in R0, the reduction in the proportion of animals infected during an epidemic is non-linear. The selection process reduces the amount of infectious material that is in the environment when an infection occurs and this decreases the force of infection on unselected animals. This phenomenon results in a marked interaction between host genotype and disease epidemiology. Thus, the results of the model show that altering the genetics of individual animals affects the epidemiology of the disease at the population level. The model can be applied to any farm structure and any microparasitic infectious disease.

The aim of this study was to estimate genetic and phenotypic (co)variances between objective measures and carcass visual scores, as a test of the potential value of visual scores in selection programmes to improve carcass composition in crossbred lambs. In each of 1986, 1987 and 1988, 22 Suffolk rams were chosen with either high or low scores on an index designed to increase lean growth rate. These rams were joined with 18 to 20 crossbred ewes each and their lambs were grown on grass to one of three target live weights (35·5, 41·5 and 47·0 kg) for slaughter. The carcasses of 1881 lambs were visually scored for overall conformation and fatness using the standard Meat and Livestock Commission methods. Additionally, a more detailed 15-point scale assessment of conformation and a direct visual score of subcutaneous fat on the carcass were taken on 1252 lambs during the latter 2 years of the study. Carcass composition was estimated by dissection of a shoulder joint into lean, fat and bone. The possibility of combining data collected on lambs slaughtered at each of the three target live weights, for the estimation of genetic parameters was investigated. Results indicated that heritability estimates for a trait using data collected within each of the slaughter groups were homogeneous. Genetic correlations between records collected for a trait within each of the slaughter groups were not significantly different from one. These results indicated that data collected at each of the target slaughter weights could justifiably be combined. Heritability estimates were generally higher for shoulder tissue proportions (0·3) than for visual scores (0-2). Genetic correlations between all conformation scores and tissue proportions were not significantly different from 0 and therefore of little or no value in predicting carcass composition. Genetic correlations between visual scores of fat and both tissue proportions and ratios were generally high (around 0·65). These results suggest that fat scores collected on crossbred animals could be valuable in purebred selection programmes where improving carcass composition of the crossbred generation is the underlying objective.

Fifty double-muscled Belgian Blue bulls were divided into five groups. The first group (control, CG) was given, on an ad libitum basis, a fattening diet based on sugar-beet pulp. In G2 and G3, fattening was interrupted 103 and 187 days, respectively after the beginning of the experiment, by approximately a 2-month period of food restriction during which the animals received a maintenance ration. The last two groups, namely G4 and G5, received for about 4 months a limited amount of the restriction diet to support growth of 0·5 and 0 kg/day, respectively, before being fattened as CG. The average daily gain was 1·48 kg/day in CG v. 1·33, 1·30, 1·43 and 1·61 kg/day during the period of ad libitum feeding in G2, G3, G4 and G5. Higher nitrogen (N) balance during compensatory growth in G2, G4 and G5 (78·8, 81·0 and 74·6 v. 53·3 g N per day in CG, P < 0·001) resulted mainly from a higher efficiency of N retention. In G3, however, compensatory growth was characterized by lower N digestibility and efficiency of N retention. Muscle proportion in the carcass was higher in G3 while fat plus connective tissue proportion was lower (P < 0·05). Muscle pH values in CG were lower than in the other groups (P < 0·01) but ether extract values were higher. The intramuscular fat of G2 and G3 was characterized by higher proportions of polyunsaturated fatty acids.

A time series model was used to describe the daily milk yield of healthy cows in the first 48 days of lactation. A moving average (MA) model of order 1 on the first-order differences of the data was selected — the same chosen in a previous study by Deluyker et al. (1990). When the model was used to generate predicted daily yields in a second data set, for cows in which clinical ketosis had been diagnosed, it was found that significant deviations of actual yield below the daily forecast occurred from 3 days before the day of diagnosis. The model appeared to be transportable to healthy cows from another herd. Threshold values were defined to identify ailing animals by their deviation from predicted yield. However, the thresholds were not very sensitive, and required that a fairly high level of false positives be accepted (25% of a healthy herd over a 5-day period).

This experiment measured the consequences of manipulating body fat reserves at farrowing by nutritional means in three sow breed types. A 3 ×2× 2 factorial experiment involving 83 second parity sows (previously given food to achieve a standard backfat measurement of 25 mm at first farrowing) was used to investigate the influence of breed type (Meishan synthetic 50% (M) or purebred European Landrace (LR) and Large White (LW) on response to isoenergetic diets of differing protein levels (180 g crude protein (CP) per kg, 9 g lysine per kg; or 240 g CP per kg, 12 g lysine per kg) offered to appetite over a 28-day lactation. Body fat reserves were adjusted during the preceding pregnancy by supplementing a set quantity of basal diet (131 g CP per kg, 12·7 MJ digestible energy per kg) with an energy source (maize starch + soya oil), to attain a backfat at P2 of either 23 mm (T) or 28 mm (F) at farrowing. No lactation diet effects on performance were observed. There were no significant breed or diet differences in backfat at farrowing. M sows were lighter at farrowing than LW and LR (M = 19·4, LW = 22·3, LR = 21·4 kg, P < 0·001). M consumed more food throughout lactation than LR and LW (M = 7·02, LW = 5·02, LR = 5·86 kg/day, P < 0·01) but weight loss was higher for M than for LW and LR sows (M = 11·7, LW = 5·4, LR = 6·1 kg, P < 0·05). Fat loss also showed a breed effect (M = 3·6, LW = 2·1, LR = 2·7 mm P2, P < 0·05), as did litter growth rates (M = 2·33, LW = 1·74, LR = 2·07 kg/day, P < 0·01). However, the breed effect disappeared when litter size was added as a covariate. The proportion of sows that was served within 5 days of weaning was higher for M than for the White breed types (W) (M = 0·74 , W = 0·51 , P < 0·05). The Meishan synthetics still mobilized more body tissue and produced greater milk yields than the W sows when backfat levels were standardized between breeds. The use of a very high protein food did not offer any advantage for the sow in terms of milk production or conservation of maternal body reserves.

The nutritional value of different categories of peas was measured in mash or pelleted diets using adult cockerels. Twenty-five round and white-flowered peas (feed peas), 12 round and coloured-flowered peas and five wrinkled and white-flowered peas were used in mash diets. From the same batches, 11 feed peas, five coloured peas and four wrinkled peas were tested in pelleted diets.

Mean apparent metabolizable energy (AME) values were 12·02, 11·35 and 10·50 MJ/kg dry matter (DM) for feed peas, coloured peas and wrinkled peas respectively in mash diets and 13·18, 12·72 and 11·63 MJ/kg DM for the same categories in pelleted diets.

Mean starch digestibility was 0·905, 0·887 and 0·802 for feed peas, coloured peas and wrinkled peas respectively in mash diets and 0·985, 0·984 and 0·840 for these categories in pelleted diets.

Mean protein digestibility was 0·788, 0·643 and 0·798 for feed peas, coloured peas and wrinkled peas respectively in mash diets and corresponding values for peas in pelleted diets were 0·855, 0·743 and 0·853.

Pelleting thus had a positive effect on the nutritional value of peas and this improvement was all the more important because the AME and protein digestibility of the pea in mash diets was low.

The nutritional value of feed peas for cockerels was not strongly correlated with chemical composition or to digestibility data obtained in the pig.

The purpose of this experiment was to determine whether body temperature is a sensitive parameter to measure long-term effects of stress in pigs. Mixing of unacquainted pigs is a severe stressor that has detrimental effects on health, production and welfare. We measured deep body temperature after mixing growing pigs. Five pigs of 15 weeks of age, each individually housed with a companion pig, were mixed with two unacquainted congeners. Deep body temperature, heart rate and activity were recorded by radiotelemetry 9 days prior to until 8 days after mixing. These parameters were also recorded in five control pigs (individually housed with a companion pig) during the same time span. Behaviour during the light period was recorded on videotape on the day of mixing and on three subsequent days. Mixing induced a significant rise in body temperature that lasted for 8 h after mixing. Although heart rate and general activity level did not significantly differ between mixed and control pigs, mixing significantly increased the frequency of fighting and reduced the frequency of eating. In conclusion, the present experiment shows that mixing induces a long-lasting hyperthermia in pigs. Thus, deep body temperature may be used as a sensitive parameter to measure long-term effects of stress in pigs.

Two experiments determined the effects of daily oral supplements of vitamin A (retinol) and injected preparations of vitamin A on liver vitamin A concentration and plasma carotenoid (PC) concentration. Vetade is an oily injectable vitamin A preparation, while Nov-a-Vit is an aqueous injectable vitamin A preparation. Angus crossbred heifers were used in experiment 1 and Angus and Simmental crossbred steers were used in experiment 2. All cattle grazed pasture but were given also 1 kg per head of pellets daily and vitamin A supplements were included in the pellets when required. In experiment 1, one group of heifers was given 1 × 106 i.u. vitamin A per head daily for 31 days, while a second group in another part of the paddock was not supplemented with vitamin A. A third group of heifers grazed with this latter group and was injected with 2·5 × 106 i.u. vitamin A (Vetade) three times weekly. The oral vitamin A supplement proportionately reduced plasma and liver carotenoid concentrations by 0·49 and 0·41 respectively, while increasing liver vitamin A concentration three-fold. By contrast, the Vetade failed to increase liver vitamin A concentration or to reduce liver and plasma carotenoid concentrations. In experiment 2, two groups of steers were injected twice weekly for 7 weeks with 2 × 106 i.u. vitamin A as Nov-A-Vit or as Vetade. A third treatment group, grazing with these steers, received no vitamin A injection, while a fourth group grazing in a separate area of the paddock was supplemented daily with 1 × 106 i.u. vitamin A per head in their diet. The injection of Nov-A-Vit and the oral vitamin A supplement decreased PC concentration by a similar amount but the increase in liver vitamin A concentration was larger for steers injected with Nov-A-Vit. Vetade injections failed to increase liver vitamin A concentration and there was no decrease in PC concentration. The plasma cholesterol concentration for the treatment groups varied over the duration of the experiment but could not be related to the vitamin A treatment or to the changes in PC concentration. These results indicate that vitamin A injections can be used to reduce PC concentration provided they increase liver vitamin A concentration.

The effects of three fat supplements on milk yield and composition were measured using 12 mid-lactation in-calf Hoistein-Friesian cows in a balanced incomplete change-over design over three periods each of 3 weeks. All cows received a basal diet consisting of 36 kg/day grass silage (dry matter (DM) 270 g/kg, metabolizable energy (ME) 11·6 MJ/kg DM) and 7 kg/day o f a concentrate mixture containing (g/kg) rolled barley (501), molassed sugar-beet pulp shreds (277), soya-bean meal (208) and a standard cow mineral supplement (14). Treatments were CON (control-no supplement); LIN and FISH (250 gl day of either linseed oil or marine oil, providing approximately 0·046 of ME intake) or TOA (95 glday of tuna orbital oil, providing 0·018 of total ME intake).

There were no significant effects on silage DM intake or milk yield (means 9·25 and 17·2 kg/day respectively). The FISH and TOA treatments depressed (F < 0·05) milk fat concentration (45·4, 44·6, 34·5 and 41·6 (s.e.d. 1·08) g/kg for CON, LIN, FISH and TOA respectively; note — the same treatment order is used for all results quoted). Compared with values for CON, yield of f at (glday) was significantly (F < 0·05) greater for LIN and significantly lower for FISH (739, 808, 572 and 732, s.e.d. 28·7). All three oil supplements reduced (F < 0·05) milk protein content (33·6, 32·5, 30·6 and 32·4 (s.e.d. 0·43) g/kg) but, apart from a small increase for LIN, protein yield (glday) was unaffected (545, 586, 510 and 574, s.e.d. 20·2).

The concentrations (g/100 g) of short-chain fatty acids (< C14) and C16 : 0 in milk f at were lower (F < 0·05) for LIN than for the other treatments. All supplements increased the concentrations ofC18:1 (F < 0·05), the value for LIN being greater (F < 0·05) than for the other treatments (21·0, 27·2, 25·3 and 23·7, s.e.d. 0·74). The FISH and TOA treatments increased (F < 0·05) the concentrations of long chain (< C2O) (n-3) poly-unsaturated fatty acids (PUFA), (0·19, 0·17, 0·49 and 0·27, s.e.d. 0·026) but less than proportionately 0·03 of dietary intake of these acids was transferred to milk, probably because they were found to be mostly in the phospholipid and cholesterol ester fractions of plasma. The FISH and TOA treatments increased (F < 0·05) the percentages of total trans fatty acids in milk fat (1·13, 2·19, 10·26 and 3·62, s.e.d. 0·728) whilst a significant (F < 0·05) increase in conjugated linoleic acid (CLA) was observed only for FISH (0·16, 0·28, 1·55, and 0·52, s.e.d. 0·154). Concentrations of CLA and total trans acids in milk were highly correlated (r = 0·91, no. =36, F < 0·001) whilst trans acids in milk were inversely correlated with milk fat content (r = -0·63, no. = 36, F < 0·001) supporting the theory that milk fat depression may be caused by increased supply of trans fatty acids to the mammary gland. The health implications of these changes in milk fat composition are discussed.

The effects of diets formulated to have two rates of organic matter (OM) release and to be either synchronous or asynchronous with respect to their hourly release of OM and nitrogen (N) in the rumen on N retention, microbial N production, growth and metabolism of ram lambs offered food at a restricted level was studied in two experiments. Four diets were formulated to differ in their rate and extent of OM and N release in the rumen based on the sum of in situ degradability data of the ingredients. All diets were formulated to have a similar metabolizable energy (10·4 MJ/kg dry matter (DM)), crude protein (140 g/kg DM) and daily ratio of N : OM released (34 g N per kg OM) and were either synchronous or asynchronous with respect to their hourly N : OM release. The four diets were slow energy, synchronous (SS), slow energy asynchronous (SA), fast energy, synchronous (FS) and fast energy asynchronous (FA). In both experiments the diets were offered at a rate of 1·75 maintenance energy requirements as two equal meals at 09:00 and 17:00 h. In experiment 1 there was no significant effect of diet on OM apparent digestibility or N retention. Lambs given diet FS had the highest daily production of allantoin (7·82 mmol per day; P < 0·05) and microbial N (7·80 g/day; P < 0Ό5). Hourly plasma urea and ß-hydroxy butyrate (3-OHB) concentrations exhibited a cyclical trend between meals with maximum concentrations occurring within 3 h of feeding and were higher in lambs given diet FA.

In experiment 2 the four diets were offered to 32 growing ram lambs. Animals given synchronous diets (SS and FS) had a significantly higher live-weight gain than those given asynchronous diets (SA and FA; (132 g/day v. 107 g/day respectively; P < 0·001). Food conversion efficiency (FCE; kg gain per kg DM intake) was improved proportionately by 0·23 in animals offered synchronous diets compared with asynchronous diets (P < 0·001). There was little effect of diet on carcass composition except kidney fat, which was greater in lambs offered the synchronous diets (P < 0·01). Plasma 3-OHB concentrations were higher throughout the growth period in lambs given diet FA whilst plasma urea concentrations were greater in lambs given the diet SS. In conclusion, greater attention to the formulation of diets to be synchronous for their hourly release of N : OM in the rumen can improve the growth rate and FCE of lambs. This effect may be due to an improvement in energy rather than N metabolism.

In order to examine the effects of diets, with two hay to concentrate ratios and two forms of concentrates on the rumen fermentation of dry sheep and milk production of lactating ewes, three trials were conducted.

In the first trial, four wether sheep, each fitted with a rumen cannula, were used in a 4 × 4 Latin-square design, by allocating them to one of four diets with different hay to concentrate ratio and concentrate type. The diets consisted of 0·5 kg hay and 0·75 kg either starchy (HRSC) or fibrous (HRFC) concentrates, or 0·25 kg hay and 1·0 kg either starchy (LRSC) or fibrous (LRFC) concentrates. The diets were designed to provide similar intakes of energy and crude protein. Volatile fatty acids (VFA) and ammonia concentrations, pH values and number of protozoa were determined in wether rumen fluid.

Total VFA concentration was not significantly affected by diet but acetate and n-butyrate proportions were higher (P < 0·002) on the higher forage diets and propionate higher (P < 0·002) on the lower forage diets. pH values and number of protozoa in sheep rumen fluid were unaffected by treatment, while ammonia concentration was lower (P < 0·05) on the HRFC diet.

In the second trial, 60 lactating dairy ewes were allocated to one of four diets for weeks 11 to 15 of lactation (period 1). Ewes were given food daily: 0·87 kg hay and 1·3 kg either HRFC or HRSC concentrates, or 0·4 kg hay and 1·6 kg either LRFC or LRSC concentrates. During weeks 16 to 20 of lactation (period 2), the ewes were given the same amount and type of concentrates but hay was supplied ad libitum and this period formed the third trial.

Milk yield and milk composition were affected significantly by hay to concentrate ratio with the lower hay to concentrate ratio resulting in a significant increase in milk yield, milk protein efficiency, protein content and protein and lactose yields. Milk fat content and yield were reduced. Hay intake was proportionately greater (P < 0·002) by 0·15 to 0·20 with starchy than with fibrous concentrate diets in period 2. Problems such as acidosis or ‘off-food’ periods in ewes given the low hay to concentrate ratio diets were not observed, irrespective of concentrate type.

The effect of the duration of grazing (experiment 1) and starvation time and placement in the rumen of inert bulk material before grazing (experiment 2), on the rumen content ferment ability, was investigated by means of measuring cumulative gas production. In experiment 1, a comparison was made of four durations of grazing (1, 1·75, 2·50 and 3·25 h) after overnight starvation. Rumen samples taken from the cows after 1 h of grazing had higher values of total accumulated gas with less (P < 0·05) time required to reach the maximum fermentation rate than cows grazed for 3·25 h. Following grazing, a 7·75·h starvation period was imposed on the four treatments. The extent of fermentation was significantly lower (P < 0·01) after starvation than immediately after grazing (49·7 v. 60·8% of incubated dry matter (DM), respectively). Experiment 2 consisted of a factorial combination of two durations of starvation before grazing (16·5 (LS) and 2·5 (SS) h) with the presence or absence in the rumen of 12·5 kg of a synthetic indigestible material. Before grazing the total accumulated gas production was less (P < 0·05) for the LS than for the SS cows. After the grazing session, the total gas of rumen samples from the LS cows was significantly higher (P < 0·05) than for the SS cows.

This was in agreement with the observed higher DM intake during grazing and DM rumen pools after grazing in LS cows. For both starvation periods, the presence of inert rumen bulk led to a higher total gas, a shorter half-time and less DM left unfermented. The measurement of fermentation kinetics by cumulative gas production was suitable to detect changes in rumen content fermentation patterns due to the clearance of material from the rumen (effect of starvation) or DM intake during the grazing sessions.