Twenty-six pregnant Holstein-Friesian × zebu heifers, arranged in pairs according to age, body weight, expected calving date and amount of zebu breeding, were allocated at random to two nutritional regimens during the last 12 weeks before calving. If was planned that the animals in treatment A should calve at a pre-calving live weight of 480 kg and those in treatment B should calve at 380 kg. The diet consisted of maize silage or elephant grass silage, soya-bean meal and minerals. During the first 21 days of the post-partum period both groups were given 6 kg concentrate per head daily. After this period, the feeding level was adjusted every 14 days according to the current milk yield. The mean total milk yields were 2132 kg and 1283 kg (P < 0·05) and the lengths of lactation were 239 days and 156 days (P < 0·01) for cows in treatments A and B, respectively. There was no statistically significant difference between treatments in the intervals from calving to first heat or calving to conception.

A system of feeding concentrates at a flat rate was compared with a step system in which the rate was reduced every 6 weeks. Each system was evaluated at either medium or high level concentrates. There were two trials involving 40 British Friesian cows for weeks 3 to 20 of lactation. The flat rate treatments were 71 (medium) and 9·3 kg dry matter (DM) per day (high) and corresponding step allocations were 8·8, 7·1 and 5·4 kg DM per day or 11·7, 9·3 and 7·0 kg DM per day. Silage was given to appetite. In trial 1 this was lucerne silage of moderate quality (metabolizable energy (ME) = 8·9 MJ/kg DM) and in trial 2 high quality grass silage (ME = 11·1 MJ/kg DM) was used.

In the comparison between systems of concentrate allocation, food intakes, milk production and live-weight change were similar in each trial. In the comparison between medium or high levels of concentrates, silage DM intakes were similar in trial 1 (7·1 v. 7·0 kg/day) but not in trial 2 (9·8 v. 8·7 kg·day, P < 0·05), and milk yields were lower in trial 1 (19·0 v. 21·4 kg/day, P < 0·001) but not in trial 2 (24·1 v. 25·2 kg/day). Milk composition was similar for medium and high concentrate intakes in both trials. Cows given the medium level of concentrates had higher live-weight losses than those given the high level in trial 1 (–58 v. –24 kg, P < 0·01) and trial 2 (–22 v. –kg). When concentrates were given at the medium level with moderate quality silage several cows had acetonaemia. Also, this feeding combination, especially when concentrates were given at a flat rate, reduced the proportion of cows which conceived within a limited breeding period.

Thirty-two Friesian cows in early lactation were divided into four treatment groups to receive ad libitum a mixed diet consisting of silage (0·70) and grain-based concentrate (0·30). Fish meal was subsequently mixed into the diet at levels of 0, 40, 80 and 120 g/kg to provide crude protein concentration (g/kg dry matter) in the complete diets of 156, 181, 200 and 212 respectively. In the 2nd week after calving the yields of fat-corrected milk (FCM) were 28·5, 29·2, 32·0 and 34·9 kg/day for the four levels respectively; at this time, food intake was sufficient only to meet the calculated energy requirement for 15 kg FCM per day. Due to recurring problems with ketosis on the diet containing 120 g fish meal per kg, this treatment was terminated and the experiment continued for 15 weeks with the groups receiving 0, 40 and 80 g/kg fish meal supplements. During this time average yields of FCM were 23·5, 25·6 and 28-0 kg FCM per day respectively and energy intakes were calculated to be sufficient to meet the requirement for 18 kg FCM per day.

It appeared possible to increase milk yield by stimulating fat mobilization through giving undegraded protein supplements to underfed cows in early lactation. However, when an excessive mobilization occurred with a high supplement, and when the animals were yielding 15 to 20 kg FCM more than their metabolizable energy intake was calculated to sustain, some cows became ketotic.

The effects of long-term administration of bovine growth hormone (GH) on pre-pubertal mammogenesis and subsequent milk production were examined in pasture-fed dairy heifers. Purified bovine GH (specific activity 0·78 i.u. per mg) was administered daily for 21 weeks (0·6 mg GH per kg M 0·75) to one member of each of 12 sets of twins from 3·5 (range 2·5 to 4-5) months of age. GH administration resulted in a significantly smaller mammary gland compared with control heifers at slaughter at the end of treatment (717 v. 839 g; P < 005 (no. = 4)) and increased the proportion of mammary fat pad containing parenchyma (461 v. 383 g/kg; P < 0·01). Mammary parenchymal dry, fat-free tissue was increased in the GH-treated group (25·8 v. 22·5 g; P < 0·05), and fat-pad adipose tissue was reduced (323 v. 435 g; P < 005), compared with the control group. Morphometric analysis of the mammary gland revealed an increase in the volume fraction of connective tissue (P < 0·1) and a tendency toward less fat in GH-treated heifers compared with control heifers. Estimates of the composition of the whole gland confirmed that GH treatment reduced total mammary fat (372 v. 496 g; P < 0·05). At calving, udder volume was greater in the heifers treated with GH compared with the untreated group (14·8 v. 11·2 1; P < 0·05 (no. = 4)). However, there were no differences in the mean daily yields of milk or milk components between groups.

Sixty-four (48 female and 16 male) spring-born Hereford × Friesian calves were used to examine the effects of sex type, heifer slaughter age and implantation with anabolic agents on growth and carcass composition. Non-implanted and implanted heifers were slaughtered after 491, 612 and 731 days and non-implanted and implanted steers (castrated on day 81) were slaughtered after 731 days. Implantation was with 36 mg resorcylic acid lactone (RAL) on days 81 and 171 and RAL plus 300 mg trenbolone acetate on days 395, 491, 583 and 658.

Carcass weights of non-implanted and implanted heifers slaughtered at 491, 612 and 731 days were 189 and 206, 218 and 235 and 290 and 326 (s.e.d. 10·1) kg respectively. Carcass lean, bone and fat weights and fat proportion increased with increasing slaughter age but proportions of lean and bone decreased.

There was no difference between heifers and steers in growth rate to 395 days but from 395 to 731 days the steers grew faster than the heifers. Non-implanted and implanted steer carcass weights at 731 days were 297 and 355 (s.e.d. 9·5) kg respectively. Steer carcasses had higher lean and bone proportions and a lower fat proportion than heifer carcasses. Implanted animals had heavier carcasses than non-implanted animals and all of the extra carcass weight consisted of lean and bone. The results indicate that non-implanted and implanted heifers and steers had similar lean proportions when the heifers were 31 and 70 kg carcass weight respectively lighter than the steers.

An experiment was carried out to examine the performance of young steers given basal diets of either silage or ammoniated hay ad libitum, with or without a daily supplement of fish meal, equivalent to 0·75 g/kg live weight, over 16 weeks. Serial slaughter of animals was carried out to examine changes in body composition during the winter feeding period and the subsequent grazing season.

There was no difference in the intakes of hay and silage organic matter over the 16 weeks of treatment. Despite the increased intake of nitrogen on the ammoniated-hay diet there was no increase in the rate of protein gain. By turn-out the steers given silage had higher empty body and carcass weights, and greater contents of fat and energy. The increased rates of empty body-weight, carcass, protein, water and energy gains achieved when the supplement was given were similar for both basal diets. There was no effect of winter feeding treatment on changes in body composition during the grazing period, so that at the end of the summer period the silage-fed animals still had heavier empty body and carcass weights. Attention is also drawn to the possible dangers of feeding hay treated with anhydrous ammonia at high temperatures to such cattle.

Groups of eight Friesian steers were given one of eight diets from 114 to 300 kg live weight. The iso-energetic diets were formulated to supply four levels of protein degradability within two concentrations of crude protein (CP), giving a range of rumen-degradable protein (RDP) and undegradable dietary protein (UDP) concentrations both above and below Agricultural Research Council (1980) recommendations. There were significant (P < 0·05), positive, linear responses of mean daily dry-matter (DM) intake (DMI) (g/kg M°75) to RDP concentration (g/kg DM) for both the low CP diets (DMI = -98·0 + 1·76 (RDP); P = 0·013) and the high CP diets (DMI = -157·5 + 218 (RDP; P = 0017). For the high CP diets, there was a significant (P = 0·045) positive, linear response of live-weight gain (LWG) (kg/day) to UDP concentration (LWG = 0·47 + 0·017 (UDP); P = 0·045). No such response was observed for the low CP diets, where the range of UDP concentrations supplied was smaller than expected. For both the low and high CP diets, LWG decreased as metabolizable energy, UDP and RDP intake increased. These negative responses to nutrient intake were reflected in a wide discrepancy between observed rates of gain and those predicted by current energy and protein nutrition systems. Interactions between food intake and digestive processes, which obstruct effective interpretation of these results, should form an explicit part of any revised protein nutrition scheme.

An experiment was conducted to examine factors affecting the length of the post-partum anoestrous period and associated effects on LH, FSH and prolactin. Forty-six cows (24 Hereford × Friesian and 22 Blue-Grey) ranging in body condition score at calving from 1·50 to 2·75 were used. They were individually fed chopped barley straw and concentrate at either 50 (low) or 91 (high) MJ metabolizable energy per day from calving. At 34 days post partum half the cows were separated from their calves for 48 h. The duration of the post-partum anoestrous period was estimated from progesterone concentrations in thrice weekly blood samples. Blood samples were collected every 20 min for 10 h periods immediately prior to calf separation, during the last 10 h of calf separation and 1 week later. All samples were analysed for LH, and every third sample was analysed for FSH and prolactin.

There were no significant effects of genotype, feeding level or calf separation on the length of the post-partum anoestrous period. There was a negative association between body condition score at calving and the length of the anoestrous period, with each unit increase in body condition score reducing the anoestrous period by 43 (s.e. 20) days. There was some evidence that feeding level affected the number of thin cows (body condition score ≤2·25 at calving) which were still acyclic at the end of the experiment, but not the number of fat cows (body condition score ≥2·5 at calving).

FSH levels were not affected by any of the factors examined. Prolactin concentrations were higher in fatter cows, in cows on the higher level of feeding and in Blue-Grey cows. Prolactin concentrations decreased during the period of calf separation. Genotype and feeding level had no effect on LH concentration or LH pulse frequency. LH pulse frequency was increased (P < 0·05) during the period of calf separation, but there was no effect 1 week later. There was a significant positive relationship between LH puise frequency and body condition score at calving in two of the three sampling periods.

It is suggested that the effect of body condition on the duration of the post-partum anoestrous period i s mediated through effects on LH pulse frequency.

The effects of dietary supplements of iron, molybdenum and sulphur on copper metabolism in calves were examined. In one experiment, 27 castrated male pre-ruminant Friesian calves were given a milk-substitute ration containing 0·9, 4·5 or 9 mmol iron per kg dry matter for 8 weeks. The iron supplements had no effect on liver copper retention. When 24 of these calves were then given a diet based on barley grains and barley straw containing 0, 4·5, 9 or 13·5 mmols iron per kg for up to 24 weeks, liver and plasma copper concentrations were greatly reduced in all iron-supplemented animals but no clinical signs of copper deficiency developed. Reduction in the dietary sulphur concentration from 88 o t 47 mmol/kg after 12 weeks did not prevent the iron-induced reduction in liver copper concentrations n i animals given 9 or 13·5 mmol iron per kg. Plasma copper concentrations increased in all iron-treated calves given the low-sulphur diets, except in animals given 13·5 mmol iron per kg. The results indicate that iron is a potent antagonist of copper metabolism in weaned calves and that its effects are probably independent of dietary sulphur supply.

In a second experiment 20 Hereford × Friesian female calves were given diets with supplements of 2·7 mmol iron and 20 μmol molybdenum per kg, separately and together, for 41 weeks. Both supplements reduced liver and plasma copper concentrations but only in the molybdenum-treated animals were live-weight gains reduced. The rate of decline in liver and plasma copper concentrations tended to be greatest in animals given both supplements, indicating that additive action of these antagonists is possible.

Dutch Friesian purebred and Holstein Friesian-Dutch Friesian crossbred veal calves were used to study effects of genotype and feeding level on carcass composition. Carcass analyses were carried out on a total of 56 calves of two genotypes. Calves were reared for 22 weeks and given food dependent on age. From 1 to 16 weeks calves were given the same amount of milk replacer. At week 16, calves were assigned to either a high or low feeding level. Total energy intakes for the two groups were 5062 MJ metabolizable energy (ME) and 5408 MJ ME, respectively. Carcass weight and carcass composition traits showed no significant interaction between genotype and feeding level. Dutch Friesians had higher lean: bone ratios than Holstein Friesian crossbreds (3·85 v. 3·67). Differences between the two genotypes for fat and lean proportions in the carcass were not significant. Average proportions for lean and fat were 653 and 134 g/kg.

Differences between the two feeding levels for carcass composition were significant. Calves on the low feeding level had 655 g lean and 131 g fat per kg, while calves on the high level had 645 g lean and 143 g fat per kg.

The influence of the dissection technique on the differences in lean and muscle proportion between groups was studied on 18 carcasses using a standardized butcher's method (the Institute of Animal Husbandry (IVO) standard method) and the European Economic Community (EEC) reference method for beef. Average proportion of lean was 640 g/kg by the IVO method and of muscle was 557 g/kg by the EEC method. The difference between the two genotypes for lean proportion was smaller by the' EEC method due to the more complete separation between muscle and fatty tissue. Dutch Friesians had more intermuscular fat than Holstein Friesian crossbreds. Results of the EEC reference method indicate differences between the two feeding levels for fat as well as for protein deposition.

Thirty-five Charolais × Blue-Grey and Charolais × (Hereford × Friesian) weaned suckled calves which had been reared as either singles or twins and 19 single-reared Luing and Charolais × Luing weaned suckled calves were given silage ad libitum supplemented with either 0·75 or 2·5 kg rolled barley per day during the post-weaning winter. During summer the cattle continuously grazed perennial ryegrass swards. The high level of barley supplementation increased winter live-weight gain by 0·25 kg/day (P < 0·001). During summer the cattle from the low level of feeding gained weight at 0·09 kg/day (P < 0·05) faster than those from the high level of feeding. However, by the end of the summer grazing period the cattle on the low level of feeding were proportionately only 0·97 the weight of the animals on the high level of feeding.

During winter the performance of all genotypes was similar, but at pasture the Luing cattle gained less weight (P < 0·01) than the single-reared Charolais-cross genotypes.

Twin-reared cattle took 55 days longer to reach slaughter condition, but produced carcasses of equal weight and fatness to those from single-reared cattle.

The twin-reared cattle on the high level of feeding and the single-reared cattle on the low level of feeding attained a similar weight, body condition and ultrasonic backfat at turn-out. Thereafter, their herbage intakes and live-weight gains were identical suggesting that previous level of feeding per se is unimportant in determining an animal's subsequent intake and performance. Rather it is the body composition at a given age, irrespective of the pathway followed to attain that composition, that determines performance thereafter. It is also suggested that the inability of cattle to compensate for a reduction in level of nutrition during the first 3 to 4 months of life is due to the lack of potential for fat deposition, and there is thus limited opportunity for nutritional manipulation of body composition at that age.

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

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

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

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

Maximum eating rate, rmax in kj metabolizable energy per min, at a given body weight W kg, can be predicted in normally growing cattle when adult body weight, A kg, is known, by the formula of Taylor and Murray (1987) as rmax = 31μ0·86 A0·73 where u = W/A is degree of maturity in body weight. When the pattern of normal growth is disturbed by fluctuating levels of food intake, a better prediction can be obtained in terms of incisor arcade breadth. This paper gives the allometric relationship between degree of maturity in body weight, u, and degree of maturity in incisor arcade breadth uD, fo r both cattle and sheep, as uD = u0·29.

Combining this allometric relationship with that of Illius and Gordon (1987) gives the following formula for incisor arcade breadth, Du(mm), in the rth species at age, t, in relation to degree of maturity in body weight, uit, and adult body weight, Aikg): Dit = 7·8 uit0·29Ai0·36. Substituting uD and adult arcade breadth, Dadult, for u and A in the formula of Taylor and Murray (1987) gives the following more robust formula for predicting maximum eating rate, namely, rmax = 0·53 u3DD2adut.

An experiment was carried out at Bahia Blanca (38°44' S, 62°10' W) to estimate the seasonal variation in ovulation rate and its components shown by Lincoln ewes of constant live weight.

Twenty-three 5-year-old ewes were subjected to nine 17-day observation periods which were evenly spaced within 405 days.

Percentage of ewes showing oestrus and ovulation, incidence of multiple ovulations and ovulation rate were estimated for each period by using vasectomized rams and performing iaparoscopies.

Traits showed a similar seasonality which was presumably induced by the natural light regime to which the ewes became exposed before and during each observation period.

A significant and periodic relationship was found between each trait and the number of days elapsed from the longest day.

The predicted maximum values for each parameter were reached about 40 days before the shortest day. Prior to and after this date both the percentage of ewes showing oestrus and ovulation and the incidence of multiple ovulations declined so that the expected ovulation rate values became zero for a period of about 3 months before the longest day.

An economic selection index was derived for terminal sire sheep breeds or strains, using physical and financial results from New Zealand export lamb-producing flocks. The aggregate breeding value of the index comprised carcass lean weight and carcass total fat weight. Index measurements were live weight, ultrasonic fat depth and ultrasonic muscle depth. Economic values used for lean and fat weights (NZ$5·65 and NZ$–1·2 per kg, respectively) were the change in profit per kg increase in lean or fat weight from that in the average carcass of lambs slaughtered in 1984/85. The s.d. of the aggregate breeding value was NZS3·20, and the correlation between the full index and the aggregate breeding value was 0·23. This correlation fell to 0·18, 0·15 and 0·07, respectively, when muscle depth or fat depth or muscle and fat depths were omitted from the index. Selection on the full index, or on the index omitting muscle depth was expected to lead to an increase in carcass lean weight and a slight decrease in carcass fat weight. Selection on the index omitting fat depth, or selection on live weight alone, was expected to lead to an increase in both fat and lean weights.

The resistance to body cooling of 594 newborn Scottish Blackface lambs was measured in a water bath during a programme of upwards and downwards genetic selection. Cold resistance was defined as the time taken for rectal temperature to fall to 35°C in the water bath.

Upwards selection produced increased cold resistance which was genetically associated with increased skin thickness, increased total body insulation and greater persistence of high metabolic rate during cold exposure. The first two correlated responses to selection were more pronounced in twins than in singles.

High cold resistance was phenotypically, but not genetically, associated with greater body weight, increased coat depth and higher levels of cold-induced metabolic rate (heat production). Single lambs showed higher weight-adjusted metabolic rates and higher cold resistance than twins. Singles recovered from hypothermia faster than twins in the low selection line only.

Female lambs showed higher metabolic rate (whether weight-adjusted or not) and greater total body insulation than males. Their greater cold resistance was not quite significant. Increasing age (range 0·3 to 36 h) was associated with a small but significant decline in cold resistance.

Thermoneutral metabolic rate was proportional to body surface area, whereas peak metabolic rate was proportional to body weight such that peak metabolic rate per unit body weight was independent of changes in body weight. These findings are discussed in relation to lamb survival.

The responses of growing pigs to dietary lysine as influenced by sex (male and female) and cereal (barley and wheat) were investigated in an 8 × 2 × 2 factorial experiment involving 128 pigs. The basal barley-soya bean (13·4 MJ digestible energy (DE) per kg) and wheat-soya bean (14·1 MJ DE per kg) diets were offered ad libitum from 20 to 50 kg live weight. The eight dietary lysine concentrations were 70 to 140 g/kg in increments of 1·0 g/kg. The experiment was repeated with pigs given food according to a restricted scale. Performance in both experiments was assessed by multiple regression analysis based on data from successive 10-kg live-weight intervals. Analysis of variance was used to assess chemical carcass composition and retention of protein and fat after slaughter at 50 kg live weight.

Average daily DE intake (MJ) of pigs fed ad libitum was not significantly different for barley-based (27·4) and wheat-based diets (29·1). For pigs fed on a restricted scale, average daily DE intake was 18 MJ for barley-based and 17·5 MJ for wheat-based diets. The daily energy retained in the empty carcass, expressed as a proportion of daily DE intake, was proportionately 0·08 less for barley-based than for wheat-based diets irrespective of whether food was offered ad libitum (0·347 v. 0·379) or restricted (0·311 v. 0·337).

The average daily gain of females fed ad libitum was not affected by dietary lysine concentration. With males, the response of daily gain to lysine concentration was curvilinear, increasing to a maximum of 120 g dietary lysine per kg up to 40·3 kg and 7·0 g/kg at greater weights for both cereals. For pigs fed on a restricted scale the daily gain on barley diets increased linearly up to the maximum dietary lysine concentration (14 g/kg), while for those on wheat-based diets maximum daily gain occurred with a lysine concentration of 11·2 g/kg for males and 131 g/kg for females. Carcass P2 backfat (mean = 15·4 mm), carcass fat proportion (mean = 242 g/kg) and carcass protein retention (mean = 89 g/day) were not significantly affected by dietary lysine concentration from 7 to 14 g/kg when pigs were fed ad libitum. However, when pigs were fed at a restricted level carcass fatness decreased to a minimum at 12 g lysine per kg.

Sixty Large White d♂ × (Large White ♂ × Landrace ♀) pre-pubertal gilts were allocated at random to one of five treatments. Treatment consisted of a combination of three factors to induce puberty and maintain cyclicity: the administration of exogenous oestradiol benzoate (OB), the application of an orally active synthetic progestagen, allyl-trenbolone (AT), and exposure to mature boars. Treatment A gilts were given OB at 160 days of age (15 μg/kg body weight). This was followed by the administration of 20 mg/day of AT from 166 days of age for 18 days. These gilts were also allowed exposure to a mature boar for 30 min/day from 160 days of age until they were mated. Treatment B gilts were given OB at 160 days of age and were allowed boar exposure from 160 days of age but were not given AT. Treatment C gilts were given OB and AT but were not allowed exposure to a mature boar. Treatment D gilts were not given OB at the beginning of the experiment but were given AT for 18 days from 166 days of age and were allowed boar exposure. Treatment E gilts were not given any exogenous hormones but were allowed boar exposure from 160 days of age. The dose of OB was split equally into three bolus injections given on consecutive days beginning at 160 days of age. All gilts were mated twice during the first 2 days of their second oestrous period, and were slaughtered at either 25 days post coitum or at 220 days for anoestrous gilts.

The percentages of OB-treated gilts with normal oestrous cycles (oestrous cycles of between 15 and 30 days from one oestrus to the next) were: 91·7%(11/12), 45·5%(5/ll) and 58·3%(7·12) for gilts in treatments A, B and C respectively (P < 0·05). The OB-treated gilts (treatments A, B and C) attained puberty at a significantly younger age than did the control gilts in treatment E (F < 0·05). No significant differences were found in ovulation rate and the percentage embryo survival between treatments.

The results demonstrate that the combination of AT and boar exposure was an effective means of maintaining oestrous cycles in OB-treated gilts.

The effects of date of weaning, weaning live weight, autumn grazing management and level and pattern of winter nutrition in relation to summer grazing on the live-weight gain of farmed red deer calves to 16 months of age were tested in three experiments.

In experiment 1, the effect of two weaning live weights (37 and 46 kg) in September and two levels of autumn and winter nutrition were examined with 48 calves. In October, live-weight gains were positively related to sward height and herbage mass. The calves lost live weight in November. Compensatory live-weight gains of 28 g/day occurred at summer pasture after the low level of winter nutrition. Weaning live weight had a major influence on live weight at 16 months of age.

In experiment 2, the effects of maintenance, ad libitum and intermediate treatments were compared using 50 calves given a complete diet in winter. The intermediate treatment consisted of a maintenance followed by an ad libitum level of feeding. Compensatory live-weight gains of 49 g/day occurred at pasture with the intermediate treatment achieving complete live-weight compensation at 16 months of age.

In experiment 3, the effect of two weaning dates (19 September and 14 November) on live-weight gain of calves and on the date of subsequent calving of hinds were compared with 34 lactating hinds. There was no difference in live-weight gain of calves between weaning dates but the subsequent calving date was delayed by 8 days from those hinds weaning in November.

A management system is advocated with weaning in September, housing in November after grazing sown swards greater than 6 cm, a pattern of a low followed by a high level of nutrition in winter and the summer grazing of sown swards maintained at 4 to 6 cm.

As a result of more intensive rearing and specialization in modern production, pigs are often moved to a new location. In addition, mixing of previously unacquainted pigs usually occurs following transportation to new facilities. Mixing of pigs results in agonistic behaviour (Ewbank, 1976) eliciting social stress (Arnone and Dantzer, 1980) that may produce gastro-intestinal disturbances which adversely affect pig performance.