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.

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.

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.

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.

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.

In the winter feeding phase of a lifetime study of spring-born cattle managed in a 20-month beef system, a total of four feeding treatments were imposed by increasing the level of concentrate supplement offered with ad libitum grass silage. The objective was to achieve a difference in live weight at the end of the winter of about 25 kg between food treatments. 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).

There were no significant differences between breeds but highly significant (P < 0·001) differences for method of rearing and sex. As a consequence live-weight differences at the end of the winter between breed types (18 kg) were less than the difference between the sexes (23 kg) and for method of rearing (25 kg) although all were highly significant. Although suckled animals had significantly lower growth rates they were still significantly fatter at the end of the winter as were heifers and Hereford crosses. Differences in dry-matter intake were reflected in growth rate.

Plane of winter nutrition had a highly significant effect (P < 0·001) on live weight and condition score at the end of the winter resulting in increments of about 23 kg and 0·12 units of condition for each level of feeding.

Interactions between the main production variables were not significant with the exception of feeding level and method of rearing. Suckled animals showed a significant (Y < 0·001) reduction in winter gain (proportionately 0·85 for that of bucket-reared animals) when offered the same diet. This reduction ranged proportionately between 0·25 and 0·08 for the lowest and highest daily levels of concentrate supplementation respectively. An extra 1 kg concentrates per day was required for suckled animals to achieve similar live-weight gains to bucket-reared animals.

Twenty-five Border Leicester ♂ × Blackface ♀ wether lambs aged about 4 months and weighing on average 28·5 kg were allocated to be treated with the naturally occurring steroid testosterone or trenbolone acetate or nandrolone phenylpropionate which are steroids synthetically produced. Treatment groups were as follows: untreated controls (C); 50 mg testosterone (T); 50 mg trenbolone acetate (TA); 50 mg testosterone + 50 mg trenbolone acetate (TTA) or 50 mg nandrolone phenylpropionate (N). Implants were given at 100 and again at 63 days before slaughter. The lambs were offered to appetite a good quality diet containing, per kg dry matter, an estimated 11·0 MJ metabolizable energy and 185 g crude protein. Comparisons were made for the main effects of T and TA and also interactions between T and TA. Effects due to N were assessed statistically against untreated controls. Treatment with T, on average, increased live-weight gain (LWG), empty body weight (EBW) and reduced backfat thickness and the weight (g/kg EBW) of perirenal and retroperitoneal fat. Main effects due to TA were increases in killing-out ratio and depth of the gigot joint and reductions in backfat thickness. Treatment with N increased the empty body weight and (g/kg) carcass ash. Non-significant (P > 0·05) trends were suggested for increases in carcass crude protein due to T and TA treatments. T and TA but not N treatments exhibited marked androgenic activity in increasing the weight (mg/kg EBW) of the accessary vesicular gland. TA and N, but not T, reduced the weight (g/kg EBW) of the thymus gland.

The maximum binding capacity of post-morte m skeletal muscle (m. gluteus) for (3H)-dexamethasone was reduced by TA but increased by T and N. These results suggest differences in the binding capacity of corticosteroid receptors which may be related to differences in the effects of T and TA on protein metabolism in skeletal muscle.

Forty-five local Omani ram, wether and ewe lambs were reared from birth until slaughter at 18, 28 or 38 kg live weight (five of each ‘sex’ at each weight group) on an ad libitum concentrate diet and Rhodesgrass hay.

Ram lambs grew faster from birth and reached predetermined slaughter weights earlier than wether and ewe lambs. At 28 kg live weight, ram lambs had: heavier heads, feet, reticulo-rumens and livers; higher muscle and bone and lower fat proportions in the carcass; lower muscle: bone and higher muscle: fat ratios; higher proportions of carcass but lower non-carcass fat than had wether and ewe lambs. The head, feet, alimentary tract, liver and heart of Omani sheep grew at a lower rate; the skin grew at a similar rate and the carcass grew at a rate faster than empty body weight (EBW). Relative to EBW, muscle grew at a similar rate, fat faster and bone slower. Both carcass and non-carcass fats grew at a rate higher than that of the growth of EBW, with non-carcass fat growing at a higher rate than that of carcass fat. The growth rate of omental fat was the fastest followed by kidney, mesenteric, subcutaneous, tail, scrotal, intermuscular and pelvic fats respectively.

This study demonstrated that Omani sheep have good potential for growth if they are managed and fed satisfactorily. Omani sheep are early maturing for which reason it is recommended that they be slaughtered at lighter weights to avoid higher fat content in the carcass. Castration in Omani sheep is not recommended for production of meat lambs under intensive systems as it resulted in reduced growth rates and deposition of excess fat at lower slaughter weights.

Distribution of tissue weight in the musculature and skeleton was studied in ram, wether and ewe Omani sheep raised under an intensive management system and slaughtered over the range 18 to 38 kg live weight. Ram lambs had higher muscle weight in the forequarters than wether and ewe lambs whereas the latter ‘sexes’ had heavier hindquarters and slightly more muscle in the muscle groups of proximal hind- and forelimbs and those surrounding the spinal column. Some of the neck region muscles, e.g. m. splenius and m. longissimus capitis et atlantis, were more developed in ram than in wether and ewe lambs. The proportions in the side muscle weight of some muscles (mainly in the hindquarter) decreased with increased slaughter weight whereas others (mainly in forequarter) increased, with the majority of the muscles showing no significant slaughter weight effects. The magnitude of change in proportions of individual muscles with increased slaughter weight was small and unlikely to have a commercial impact on meat production from Omani sheep.

As a proportion of total carcass bone, the axial skeleton and the hindlimb decreased with increased slaughter weight whereas the forelimb did not show a significant change. Ram lambs had heavier individual bones than wether and ewe lambs and higher proportions of the axial skeleton and lower proportions of the hindlimb than wethers at 28 kg live weight. There were few differences between the various ‘sexes’ in length, width or circumference of bones. Except for the 12th rib, individual bones, in all sexes, grew at a rate lower than empty body weight.

It is suggested that future improvement of Omani sheep should take into consideration the high proportion of bone in the carcass of these animals as well as the relatively higher proportion of bone in the limbs than in the axial skeleton.

Voluntary food intake (VFI) of chopped timothy hay and metabolic rate were each measured in each month of the year in six non-breeding ewes of each of three breeds. Metabolic rate was measured using indirect calorimetry over a range of food intakes and adjusted for intake to an estimated maintenance metabolic rate (MMR). The breeds compared were the Dorset Horn (DT), Scottish Blackface (BF) and Shetland (SH), the first being less seasonal in reproductive and other characteristics than the other two which are hill or northern latitude breeds. There was significant overall variation between months in VFI which was higher in the summer (July to September) than in the winter (December to February) months (P < 0·001). There was a significant breed × month interaction (P < 0·01), the seasonal effect being most strongly observed in the BF and SH ewes, whose VFI in summer was proportionately 0-1 greater than the year-round mean but was 0-1 lower in the winter. The DT ewes showed much less seasonal variation in VFI. There was no overall difference in VFI between breeeds (DT: 43-7; BF: 49-5; SH: 48-1 g dry matter per M075 live weight per day, P > 0·1). Although MMR varied significantly between months (P < 0·001), there was no systematic variation between summer and winter. There was no significant breed × month interaction, but the MMR differed significantly (P < 0·001) between breeds giving a high overall MMR in BF (DT: 322-7; BF: 356-6; SH: 324-5 kf/kg M0·75 per day). No significant correlation existed (P > 0·05) between the monthly mean MMR and VFI in any of the breeds. The causal relationship between seasonal cycles of basal metabolic rate and VFI is questioned.

Two groups of five sheep (7 months of age) were moved and isolated in pens which did not allow visual and tactile contact with other sheep for 24 h. They were then moved back to their original pens where visual and tactile contact was possible. After 24 h the procedure was repeated seven times for one group (group 8-1) and thirteen times for the other group (group 14-1). One group (control) of five sheep remained in pens where visual and tactile contact was possible. When isolated the lambs spent more time standing still in an alert posture, less time eating and resting, and vocalized more than control lambs. The heart rate of the lambs increased when they were moved between pens and during isolation. The plasma concentration of cortisol was significantly increased after 1·5 h and 3 h of isolation. The plasma concentration of prolactin was increased after 1·5 h of isolation. After 3 h of isolation the number of neutrophils in the blood was increased and the numbers of T-lymphocytes (CD2), T-helper-lymphocytes (CD4) and yd-lymphocytes (T19) were decreased. After 24 h of isolation the lymphocyte blastogenic response to Con A was lower and the numbers of T-lymphocytes and T-helper-lymphocytes were still less than those in control lambs. Although there were still behavioural changes when the lambs were isolated for the seventh time, no cortisol, prolactin and leucocyte changes were found. These results suggest that stressors similar to isolation, which can occur during normal management practice, may elicit short-term leucocyte changes in lambs.

In four experiments, 189 gilts either received PMSG antiserum around the time of a PMSG- (experiments 1, 2 and 3) or PMSG/hCG-induced (experiment 4) oestrus or served as controls. Ovulation rates were not affected by treatment. There was no treatment effect on pregnancy rate (experiments 2, 3 and 4). In experiment 2, numbers of embryos in PMSG-treated control gilts were quite low and were higher (P < 0·05) in those gilts subsequently receiving anti-PMSG treatment. In experiment 3, the mean number of embryos in control gilts were higher than in experiment 2 and there was no effect of immunoneutralization of PMSG. No treatment effect was evident in PMSG/hCG treated gilts (experiment 4). These data indicate that the immunoneutralization of PMSG is unlikely to improve the reproductive performance of gilts following a gonadotropin-induced oestrus except in gilts that otherwise would have poor performance.

Twelve Large White × Landrace boars, initial mean live weight (kg) 5·51 (s.e. 0·8) were offered cereal-based diets containing 0 (diet C) or 150 g sugar-beet pulp per kg (containing no molasses or other additive) (diet 15SB) and the indigestible marker titanium dioxide from 21 to 57 days of age. The daily intakes, live-weight gains and food conversion ratios of the piglets were monitored from day 28. The apparent digestibilities of nitrogen (N), gross energy (GE) and non-starch polysaccharides (NSP) were measured on days 32 and 56. There were no significant differences either in voluntary intakes, or in the daily live-weight gains and food conversion ratios between the two diets. Likewise, there were no significant differences in the apparent digestibility of N and GE of the two diets. However, the capacity at 56 days of age to digest N from diet 15SB was greater than at 32 days of age. The apparent digestibility of total NSP at both 32 and 56 days of age was significantly greater for diet 15SB (averaging 0·75) than for diet C (averaging 0·54) (P < 0·001). The major NSP components of diet 15SB were arabinose, glucose and uronic acids, but the predominant NSP constituents of diet C were arabinose, xylose and glucose. The apparent digestibilities of arabinose (P < 0·05), mannose (P < 0·05), glucose (P < 0·05) and uronic acids (P < 0·001) were significantly greater from diet 15SB than from diet C. The apparent digestibility of NSP components from both diets tended to increase with age of piglet. These results are discussed in relation to the early establishment of an efficient gut microflora and indicate that the fermentative capacity of very young pigs may be higher than previously thought.

The effect of degree of saturation (ratio of unsaturated to saturated fatty acids, U/S) and free fatty acid (FFA) content of fats upon their digestible energy (DE) values was investigated in post-weaning pigs. The two fats evaluated were soya-bean oil (SO) and tallow (T) (representing extremes of saturation) together with their acid oils (SAO and TAO respectively) providing high FFA levels). Blends of the four fats provided treatments with varying FFA content and U/S ratios. The experimental fats were evaluated by substitution, at 40, 80 and 120 g/kg into a basal diet, in a randomized-block design, with 98 gilts and 98 boars of approximately 12 kg live weight. Pigs had been weaned at 28 days of age and experimental diets were given 7 days after weaning. When pigs obtained a weight of 10 kg the inert marker titanium dioxide was added to the diets as a reference substance. A 5-day adjustment period was allowed followed by a 5-day collection period of faeces by grab sampling. Fat content of food and faeces, with methodology based on acid hydrolysis, allowed calculation of apparent digestible fat (AFD) of experimental diets. Analysis of variance demonstrated effects of fats, rates of inclusion, and fats × rates (P < 0·001 in all cases). There was no effect of sex. Extrapolation of the function obtained by regressing AFD of diets (y) on rate of inclusion of fat (x) to × = 1000 generated values for the fats. The product of the coefficient of fat apparent digestibility of fats and their respective gross energies gave DE values for fats which were: SO = 37·2 MJ/kg, SAO = 35·0 MJ/kg, T = 34·3 MJ/kg and TAO = 27·4 MJ/kg. Data for fat blends intermediary between these fats showed that DE improved as a function of U/S and that DE declined linearly with increasing FFA content.

Two experiments were performed to evaluate the influence of relaxin on the fertility of gilts inseminated with aged boar semen. For experiment 1, oestrus was induced in 43 Yorkshire × Landrace gilts by injection of 400 i.u. PMSG plus 200 i.u. hCG. At 24 h after oestrus detection, gilts were inseminated with fresh semen (1 to 2 day old; no. = 15), aged semen (5 to 6 days old; no. = 15) or aged semen containing 400 fig/l of relaxin added at the time of semen extension (no. = 13). Pregnancy rates 24 days after insemination were lower in gilts receiving aged semen (P < 0·05), an effect not prevented by added relaxin. There was no effect of either semen age or relaxin on numbers of embryos. In experiment 2, the ejaculates of eight boars were extended with or without the addition of 400 fig/I relaxin and motility monitored for 7 days. Fresh sperm motility decreased from 87-5 (s.e. 2·5)% at collection to 71-2 (s.e. 3·3)% after 7 days. The attenuation of sperm motility was not affected by relaxin.

Four groups of 10 indigenous goats, suckling indigenous or crossbred, single or twin kids, were used to study the effect of sucking stimulus on milk yield and composition during a 12-week suckling period and over the first 20 weeks of the subsequent milking period. During the suckling period, goats with twins produced more milk (F < 0·001) than those with singles. There was no effect of kid genotype in goats rearing twins but single crossbreds took 1·11 times more milk than indigenous. Goats with single kids had higher concentrations of fat (F < 0·001), protein (F < 0·05) and lactose (F < 0·05) in milk than did those with twins. Growth rate of kids was related to differences in milk intake, with singles higher than twins (F < 0·001) and crossbred singles higher than indigenous singles (F < 0·05). It is concluded that the indigenous breed can respond to the increased sucking demand of twins but not sufficiently to meet their needs. During the milking period the mean yield was reduced to about one-third and was not dependent on the corresponding yield in the suckling period. There were minor differences of milk composition associated with number or genotype of kids suckled.