Three experiments were conducted in the early grazing seasons of 1982–84 inclusive. Autumn-calved lactating British Friesian cows grazed a perennial ryegrass pasture either by strip grazing to leave 80 mm residual herbage (SG) or by rotationally grazing six paddocks on a fixed pre-determined cycle (PG). They were offered grazing only or grazing and average quality grass silage (S) or a 1: 1 mix of silage and ensiled brewers' grains (SB) given individually overnight in a cubicle house.

In experiment 1, cows received treatments SG or SGS. The intake of silage dry matter (DM) was 4·3 kg/day and the estimated intakes of herbage DM from measured animal performance were 15·2 and 8·9 kg/day respectively. Milk yields were 18·4 and 15·3 kg/day, the concentrations of fat and protein in the milk were 38·0, 41·8 and 33·3, 30·8 g/kg and live-weight change was +679 and +348 g/day for treatments SG and SGS respectively.

For experiment 2, cows received treatments SG, PG or PGS and grazing stocking rates were 5·2, 5·5 and 11·0 cows per ha respectively. Silage intake was 6·1 kg/day DM and the estimated intakes of herbage DM were 14·2, 15·3 and 7·7 kg/day respectively. Milk yields were 18·2, 18·2 and 16·1 kg/day, the concentrations of fat and protein were 41·6, 39·8, 42·3 and 33·3, 33·0, 30·4 g/kg and live-weight change was +325, +540 and +161 g/day for treatments SG, PG and PGS respectively.

For experiment 3, cows received treatments PG, PGS or PGSB and grazing stocking rates were 5·8, 11·6 and 11·6 cows per ha respectively. The intakes of silage and silage plus brewers' grains DM were 6·5 and 8·5 kg/day. The estimated intakes of herbage DM were 14·2, 7·2 and 7·3 kg/day, milk yields were 18·7, 14·6 and 18·9 kg/day, the concentration of fat and protein in the milk were 37·3, 42·1, 40·3 and 33·4, 32·6, 32·9 g/kg and live-weight change was +425, +415 and +441 g/day for treatments PG, PGS and PGSB respectively.

The results show that offering silage overnight allowed grazing stocking rates to be doubled, raised the concentration of fat in the milk and depressed the yields of milk and protein. When brewers' grains were given with the silage, yields of milk fat and protein were greater compared with when silage was offered alone and the yield of fat was greater than for herbage alone.

Differences between Friesians and Jerseys and between progeny of high and low contemporary comparison (CC) sires were sought by examining nine blood constituent concentrations around first and second calvings and during lactation. A total of 1359 samples from animals at first lactation and 1148 samples at second lactation were collected. All animals were individually fed a complete pelleted diet ad libitum. Blood constituents analysed were free fatty acids (FFA), ketones, glucose, calcium, magnesium, copper, phosphorus, albumin and globulin. All nine constituents showed marked changes around parturition and early lactation and several constituents showed changes with age. Jerseys had higher average copper and albumin levels and lower globulin levels than Friesians at both lactations and higher FFA concentrations at second lactation. Changes in plasma concentrations of FFA, ketones and glucose around calving were consistent in suggesting that Jerseys and progeny of high CC sires had a substantially greater energy deficit in early lactation than Friesians and progeny of low CC sires at the first but not the second lactation. Predicted requirements v. recorded intakes suggested that the Jerseys and high CC progeny had the greater energy deficit at both lactations. Although the incidence of hypocalcaemia was nearly zero, changes of calcium and magnesium concentrations were consistent with reports of Jerseys being more susceptible to hypocalcaemia in later life.

Despite large differences in milk yield, differences in plasma concentrations between animals classified as either high or low achieved yielders within their genetic class were generally smaller than differences between progeny of high and low CC sires.

Records on birth weight and pre-weaning growth of 3959 Boran calves, which were progeny of 51 sires and 979 dams, were analysed by least-squares analysis of variance. The variance components for sires, dams and maternal grandsires were estimated from the data. On the basis of assumed genetic correlations −0·44 and −0·55 between direct and maternal effects on birth weight and weaning weight, respectively, the maternal genetic component and the genetic covariance between direct and maternal effects were estimated. The heritabilities for direct effects on birth weight and weaning weight were 0·11 and 0·22, respectively, while the heritabilities of maternal effects were estimated as 0·02 and 0·11, respectively for the same traits. Selection indices for direct and maternal genetic components of weaning weight were constructed for practical use. These selection indices combined information on the individual, the parents and sibs.

Four groups of calves (10 bulls, 10 steers, 10 heifers and 10 ovariectomized heifers) of Simmental- Hereford breeding were individually given a high-energy diet from 10 to 16 months of age. At the end of the experiment, the 9-10-11th rib section was dissected into fat, lean and bone and chemical analysis was performed on the dissected soft tissue. For each group, the relationship between food intake and change in body weight was examined by a method designed to separate intake into its simultaneous maintenance and gain components: least-squares estimates for the maintenance coefficient (βm, kg/day per kg body weight) and the gain coefficient (βg, kg food per kg gain) were obtained for each animal. Conventional measures of food conversion ratio (kg food per kg gain) were examined on both common age and common weight-gain bases. Bulls, followed by steers, accumulated the most lean and least fat while heifers and ovariectomized heifers accumulated the least lean and most fat. Maintenance coefficients (βm) were lower in males than in females but did not differ within gender. Gain coefficients (βg) did not differ among the groups, although the coefficients appeared to be similar within gender. Food conversion ratio computed over a common age interval did not differ among groups. Food conversion ratio computed over common weight intervals was lowest in bulls followed in increasing order by steers then the two female groups. It is concluded that males grow more efficiently than females while accumulating more lean and less adipose tisue and that this greater efficiency is achieved by consuming less food per unit of body weight for maintenance, leaving proportionately more of the total intake available for gain.

Eighteen bulls each of double-muscled (DM), Beef Synthetic (SY) and Hereford (HE) breed types, serially slaughtered from about 250 to 800 kg live weight, were used to examine muscle-bone relationships in double-muscled and normal cattle.

Relative to total side bone, DM animals differed significantly from the other breed types in relative growth rate of muscles in all regions which exhibited gross muscular hypertrophy. They showed generalized and regionally differentiated muscular hypertrophy. At equal bone weight in the given anatomical region, DM/HE and DM/SY muscle:bone ratios were respectively: proximal hindlimb 1·35 and 1·24; proximal forelimb 1·25 and 117; back and loin 1·20 and 1·10; and the expensive regions 1·30 and 1·20. In the limbs of DM animals, muscular hypertrophy in the proximal region was associated with bone hypotrophy while minimal muscular hypertrophy in the distal parts was associated with relatively heavier bones. Consequently, increased muscle:bone ratios were most pronounced in the proximal region, which suggests that muscles in these animals had increased in weight without proportionate increase of bones, i.e. muscle and bone growth were to some extent independent. Bone response in the distal limbs may have been influenced by a relative increase in weight support function.

Four diets containing either 0 or 50 g fat per kg were prepared from a basal mix of barley, sugar-beet pulp, soya-bean meal and molasses. The fats used were tallow (saturated), soya-acid oil (unsaturated), or a 45:5 mixture of both fats. The diets were given with chopped dried grass to adult wether sheep in the ratio 4:1 of diet to dried grass. Measurements of heat production of the sheep were made in closed-circuit respiration chambers and from the data the efficiencies of utilization of energy for maintenance (km) and production (kf) were calculated for each diet, together with the metabolizable energy (ME) values for the fats.

Values for both km and kf were not significantly different between diets, the means were 0·81 and 0·61 respectively. The ME values (MJ/kg DM) of the fats were for tallow 36·2, for soya-acid oil 36·6 and for the tallow/soya mixture 31·6; these values were not significantly different.

No evidence of any synergistic effect caused by the addition of an unsaturated fat to a saturated fat was seen in this experiment.

The effects of strain, season, type of birth, age and body weight at breeding on fertility and fecundity of ewe lambs raised in a controlled environment were evaluated. Data were derived from 2776 ewe lambs of a synthetic sire strain, two synthetic dam strains and two control strains (Suffolk and Finnish Landrace breeds) mated to 719 rams over 15 breeding periods during January, May or September over 9 years. The ewe lambs were exposed to rams at a synchronized and follow-up oestrus at 6·5 to 7·5 months of age. There were significant differences among strains. Fertility and fecundity were highest for lambs of the Finnish Landrace breed, intermediate for the two synthetic dam strains and lowest for the synthetic sire strain and the Suffolk breed. Although period of breeding and season had an effect on reproductive traits, the strain differences were not consistent. Type of birth did not affect performance of lambs at the synchronized oestrus. However, overall fertility and fecundity increased progressively as the type of birth of the lambs increased from singles to triplets and greater. Increased age and body weight at the synchronized oestrus had a significant and positive effect on fertility and fecundity.

Three experiments were carried out in which plasma cortisol concentrations were measured hourly in lambs treated with various anabolic steroids. In the first experiment, female lambs were implanted with trenbolone acetate (TBA) and plasma cortisol was measured for 24-h periods 4 weeks after implantation and 1 week after reimplantation. Plasma cortisol levels were unaltered 4 weeks after treatment, but were found to be significantly lower 1 week after retreatment. On this occasion, peak concentrations of cortisol after ACTH challenge were also reduced by TBA. In the second experiment, female lambs were implanted with a mixture of TBA and oestradiol and plasma cortisol measured 1 and 4 weeks later. Results were similar to the first experiment although the reduction in plasma cortisol was less. In the third experiment, castrated male lambs were implanted with either TBA, TBA plus oestradiol or a long-acting oestradiol implant. In this experiment, only oestradiol affected plasma cortisol levels, causing a large elevation. All three treatments stimulated growth. Measurement of bound and free cortisol concentration in the third experiment indicated that oestradiol treatment tended to increase the proportion of cortisol present in the free form.

These results suggest that an inhibition of cortisol secretion may be important in the anabolic response of female sheep to TBA. In the male, however, cortisol concentrations are naturally lower and are not further reduced by TBA treatment.

Plasma insulin concentrations were also measured in the castrated males. Neither TBA nor the combined implant altered insulin levels, but oestrogen treatment resulted in a small increase in insulin. The diurnal pattern of plasma insulin closely paralleled that of cortisol.

Two experiments were designed to test the efficacy of two different methods of administering prostglandin F2α-tham salt for oestrous synchronization in mature cyclic ewes maintained under normal husbandry conditions. The effect of these agents on ewe fertility and lambing performance was also assessed.

A total of 180 Clun Forest ewes were used in this investigation conducted during the 1983 and 1984 breeding seasons. In the 1983 breeding season, 80% of ewes treated with a single injection of 20 mg prostaglandin F2α-tham salt were mated by fertile rams within a 3-day period, compared with 100% of ewes treated with progestagen pessaries or 23% of ewes treated with saline. Returns to service for the three groups were 23%, 3% and 16%, respectively. In 1984, a single injection of 20 mg prostaglandin F2α-tham salt resulted in oestrus synchronization in 73% of treated ewes, compared with 27% of saline-treated controls and 97% of ewes given two injections of prostaglandin F2α-tham salt, 11 days apart. Returns to service following these treatments were 36%, 6% and 20%, respectively. There was no difference between treatments in lambing performance.

The results indicate that acceptable levels of oestrus synchronization and fertility can be obtained with a single injection of 20 mg prostaglandin F2α. Furthermore, two injections of 20 mg prostaglandin F2α given 11 days apart produce levels of synchronization of oestrus comparable to those previously obtained with commercially available progestagen pessaries.

Lambs were allocated to three treatments: control (C), monensin (M) and lasalocid sodium (L) in a concentrate diet containing 36 mg copper per kg food. After 2 months deaths from copper toxicity occurred and the trial was terminated. All lambs were slaughtered. The mean liver copper concentration (mg/kg dry matter) of 1907 in the M treatment was higher than the mean concentrations of 1342 and 1229 in the C and L groups respectively (P < 0·01). Total liver copper was 234, 260 and 230 mg and the retention of dietary copper in the liver was 93·5, 108·5 and 93·3 g/kg for the C, M and L treatments respectively. These differences were not significant. From reduced liver size (as a proportion of body weight) and high copper levels in the kidneys, it was concluded that the group given monensin had accumulated copper to a level closer to the toxicity threshold than the other two groups.

Log-linear relationships between various measurements of the chemical and physical body composition of the pig were obtained in four datasets representing a range of sexes, genotypes and feeding treatments. One of these datasets (dataset 1) comprised genetic control and selection line Large White pigs. There were significant differences between datasets for most of the relationships investigated. The causes of the differences cannot be determined. Within datasets, relationships between various body components and the weight of crude protein in the whole body were unaffected by genotype or sex. The relationships of both intermuscular fat and trimmed carcass lipid with whole body lipid differed significantly between the control and selection lines in dataset 1. Fat thickness measurements taken over the m. longissimus at the last rib were less at the same body lipid in the selection line than the control line suggesting a redistribution of fat away from this area as a result of selection. Relationships between viscera, lungs and empty body weight were significantly affected by line while those between trimmed carcass, liver, kidneys and empty body weight were significantly affected by sex. Selection line pigs had less perinephric and retroperitoneal fat than controls at the same whole body fat weight and less subcutaneous fat at the same cold carcass weight. There were no significant line effects on lean or bone weight distribution. Selection line pigs had significantly less subcutaneous fat in the collar joint and more intermuscular fat in the ham. There were few significant sex effects on tissue weight distribution.

Two experiments were performed to study the effect of ambient temperature and feeding level on energy and protein metabolism of individually housed pregnant sows. In experiment 1, 12 pregnant animals were used. The stage of pregnancy at the start of the experiment ranged from 34 to 41 days. In experiment 2, 10 pregnant animals were used. The stage of pregnancy at the start of the experiment ranged from 38 to 47 days. In each experiment two groups of animals were used. Each group of five or six animals was individually tethered in one of two identical calorimeters and given one of two feeding levels. At the high feeding level the animals received about 1·35 × maintenance. At the low feeding level the animals received about 1·1 × maintenance. The temperature in experiment 1 changed stepwise in both calorimeters by 3°C every 5 to 7 days from 21 to 12°C and then in reverse order. Temperature in experiment 2 changed stepwise in both calorimeters by 2°C every 3·5 days from 25°C to 11°C and then in reverse order.

Energy gain was negative in animals at the low feeding level at the temperatures below 15 to 18°C. At the high feeding level sows lost energy at 12°C or lower in experiment 2. Protein gain was depressed by both low feeding level and low temperatures. Energy balance was depressed by about 90 kJ/kg M0·75 per day at the lower feeding level and by 19 kJ/kg M0·75 per day per °C below thermoneutrality. Protein gain was depressed by about 26 g/day at the low feeding level and by about 6 g/day per °C below thermoneutrality. Fat gain at low feeding level was depressed by about 92 g/day and by about 154 g/day at the lowest temperature. At low feeding level below the critical temperature, gain of fat was negative. Feeding levels used in these experiments did not supply sufficient energy for energy equilibrium or fat gain for the pregnant sow kept for longer periods below the thermoneutral zone.

Forty Large White ♂ × (Large White (f × Landrace ♀) pre-pubertal gilts were used to study the influence of five different doses of parenteral oestradiol benzoate (OB) on the attainment of puberty. Five gilts from eight litters were treated at 140 days of age with either 5, 10, 15, 20 or 25 μg OB per kg body weight (BW). The doses were split equally into three bolus injections given on consecutive days. Daily boar contact commenced on the day that the first oestrogen injection was given and continued until the gilts were mated. All gilts were slaughtered at either 20 days post coitum or at 235 days of age for those gilts not exhibiting a second oestrus.

The numbers of gilts which ovulated within 10 days after OB injection were: 5/8, 7/8, 8/8, 6/8 and 5/8 for treatments 5 ng/kg BW through to 25 fig/kg BW, respectively. These differences were not significant (P > 0·05). The duration of behavioural oestrus after OB injection was positively correlated to the dose of oestrogen administered (r = 0·98, P < 0·01). There were no significant differences in age at puberty between treatments, and no significant differences were found in the subsequent reproductive performance.

Two experiments employing 72 and 48 pre-pubertal Large White ♂ × (Large White ♂ × Landrace ♀) gilts respectively were carried out to investigate the involvement of various boar stimuli in the induction of precocious puberty in the gilt. Experiment 1 consisted of the following treatments commencing at 165 days of age: (1) contact with an androgenized, castrated male; (2) contact with an androgenized castrated male plus a recording of boar chants; (3) as treatment (2) plus exposure to a solution of 16-androstene steroids, 3α-androstenol (5α-androst-16-en-3α-ol) and 5α-androstenone (5α-androst-16-en-3-one); and (4) contact with an entire boar. In experiment 2, additional exposure to boar urine occurred in treatments (2) and (3).

Exposure of gilts to tactile, visual and auditory cues from the boar had little effect on puberty attainment. The additional exposure to 16-androstene steroids did stimulate puberty but was not as efficacious as boar exposure. Additional exposure to boar urine improved the puberty-stimulating effect of the castrated males, and further additional exposure to 16-androstenes produced a response approaching that obtained by boar exposure.

These results confirm the involvement of olfactory cues from the boar in stimulating puberty in the gilt. The olfactory cues appear to be 16-androstene steroids present in boar saliva and some undefined compound(s) present in boar urine. These experiments suggest that olfactory stimuli from the boar require the simultaneous exposure to tactile and possibly also visual and auditory cues from the boar in order to stimulate the onset of puberty in the gilt.

cues from the mature boar are also involved in mediating the stimulation of puberty. Exposure of gilts to isolated sources of androstene pheromones was ineffective in stimulating puberty (Kirkwood et al., 1983), whereas exposure to contact with a sialectomized boar order to stimulate the onset of puberty in the gilt.

A performance test of pigs was conducted according to an adapted version of the ‘Kielanowski system’ in which the feeding level and the termination point of the test period were changed. A total of 119 pigs of six genotypes (participants in the Commercial Pig Evaluation in The Netherlands, 1981) averaging 22 kg weight, were fed for 17 weeks on a scheme according to days on test. The regime was such that not all the pigs could consume their total allocation of food. The fast-growing pigs were expected to be more efficient and therefore the leanest.

Forty-eight pigs consumed their total food allocation, whereas the remainder left an average of 5·89 kg food. Pigs that consumed their total allocation of food had a significantly better food conversion ratio (0·07 kg/kg; P < 0·01) and a higher daily gain (33 g/day), but they had significantly less lean (10 g/kg; P < 0·05) in their carcasses than pigs that could not consume their whole allocation. The ranking of genotypes for average daily food intake closely agreed (rs = 0·94) with the ranking in another trial with ad libitum feeding, which points to the possibility for selection on food intake capacity in the proposed system. For the other variates, the ranking correlations were moderate.

Among the pigs that consumed the total amount of food offered, a moderately strong relation (r = 0·70) was found between daily gain and lean tissue growth rate. With the system tested, it was not possible to determine leanness simply by weighing the pigs afterwards. Nevertheless, the results of the modified Kielanowski system show some interesting aspects which contribute to the design of a test system for a genetically unbiased comparison among pigs.

A study of the effects of low birth weight on muscle cellularity was performed on 48 pedigree Large White pigs selected, from a total of 17 litters, on the basis of their weight at birth. Where possible, the largest male (mean birth weight of 1544 g), smallest male (1135 g), and runt (776 g) littermates were chosen. Fresh frozen, whole mid belly, sections of m. semitendinosus and samples of m. trapezius from each animal were stained for the demonstration of acid pre-incubated myosin adenosine triphosphatase. The use of this stain demonstrated groups of positively stained, slow-contracting, myofibres which were each surrounded by a compliment of negatively stained, fast-contracting, fibres which together constituted ‘metabolic bundles’. The positions of metabolic bundles are indicative of the presence of single primary myofibres in the foetal muscle, all the other myofibres in the metabolic bundles being derived from subsequently formed secondary fibres. Determination of total myofibre number and primary fibre number were made for m. semitendinosus together with an estimation of the secondary to primary fibre-number ratios for both this muscle and for m. trapezius. Low birth weight was associated with a permanently reduced total muscle fibre number, proportionately in the order of 0·19 (P < 0·001) between large and runt littermates. A reduced muscle fibre number was not always associated with low birth weight, but when this was the case it was generated through a reduced secondary to primary fibre-number ratio (P < 0·01). Primary fibre number was not significantly affected in low birth-weight pigs except in extreme cases of runting.

Ileal digesta are often sampled from the pig through either re-entrant or simple T-piece cannulas. There is conflicting evidence, however, concerning the effects of cannulation on nutrient digestion and absorption. In several studies with the pig, cannulation has not influenced overall protein digestibility (Furuya, Takahashi and Omori, 1974; Sauer, Stothers and Parker, 1977; Taverner, 1979; Huisman, Weerden, Leeuwen, Hof and Sauer, 1984) or energy metabolism (Close, Heavens, Stephens and Sambrook, 1984) while in other studies (Laplace and Borgida, 1976; Sauer, Aherne and Thacker, 1979) there have been indications of adverse effects of cannulation on nutrient digestibility. Livingstone and McWilliam (1985) showed an effect of simple ileal cannulation on pig growth which may have been due to decreased nutrient digestibility or utilization.

In formulating a genetic index for use in cow and sire evaluation, there is a need to account for all environmental factors which influence an animal's yield. To this end, milk production records are currently adjusted for, amongst other things, age at calving and month of calving. In Norway, Sweden and West Germany, records are corrected for calving interval, i.e. the number of days between subsequent calvings (Philipsson, Dommerholt, Fimland, Gaillard, Gjøl-Christensen, Lederer, McClintock and Mocquot, 1978), but in Britain no account is taken of calving interval or days dry. Analysis has shown (McClintock, 1982) that both these factors have a significant effect on yield, and hence further investigation into the value and methods of adjusting for these factors was required.

It has been demonstrated with Australian breeds and conditions that active immunization of ewes against androstenedione can induce increases in lambing rate of 20 or more lambs per 100 ewes mated (Cox, Wilson, Scaramuzzi, Hoskinson, George and Bindon, 1982; Geldard and Scaramuzzi, 1983). More recent work (Geldard, 1985) involving active immunization against androstenedione (Fecundin®, Coopers Animal Health, UK) has shown that similar results can also be achieved with some United Kingdom breeds. However, the successful application of this product in practice requires a knowledge of the patterns of reproductive response that can be obtained with a much wider range of genotypes and production systems.