The half carcasses of 39 pre- and postnatal Romney sheep were dissected into anatomical units of bone and, where possible, into 32 muscle units which comprised nine functional groups. The growth of wet weight of the total bone and of the muscle groups (and their chemical components, which included deoxyribonucleic acid, protein, and total lipid) was compared with the growth of the carcass using allometric analysis.

Although bone grew faster prenatally than postnatally relative to carcass weight, the growth of total muscle and of all the muscle groups and their chemical components occurred at a constant, linear rate throughout the growth period studied.

The muscle: bone ratio decreased during prenatal growth, reached a minimum at around parturition and then increased postnatally.

The abdominal, m. longissimus and thigh muscle groups grew faster than total side muscle, relative to carcass weight.

Protein, and especially triglyceride, grew at relative rates which exceeded that of muscle wet weight.

The amount and proportion of intramuscular triglyceride, and the weights of the muscle groups in sheep at three different stages of growth, were predicted from allometric equations. The content of triglyceride was greatest in the cutaneous and neck muscle groups. As a proportion of total muscle, the thigh, m. longissimus and abdominal groups increased as carcass weight increased from 1 kg to 15 kg.

Five ewes, with a wool depth of approximately 5 mm, were placed in a neutral (20 + 2°C) environmental temperature on day 139 of pregnancy, and five similar ewes were placed in a cold (0±2°C) temperature. They remained in these environments until their lambs were 8 days old. Samples of udder secretions, when present, and right-atrial blood were taken from the ewes at 12-h intervals.

Milk from ewes in the neutral environment had a high fat concentration for a brief period after parturition, before the full development of lactose secretion occurred.

In ewes exposed to the cold environment, plasma cortisol concentration was increased during the 2 days before parturition. Cold exposure had no effect on the onset of milk lactose secretion but increased the concentration of fatty acids in milk during the period −0·5 to +4·5 days relative to parturition.

Total follicle density, primary follicle density, secondary follicle density, secondary/primary ratio and incidence of medullated fibres were studied in skin specimens from 78 2-year-old Merilin rams representing nine parent studs in Uruguay. The limited data available suggest that the studs sampled may fall into various groups, although separation into distinct groups is not equally well defined for all variables measured. Consequently, a firm conclusion about the Merilin awaits further information on fleece weight, staple length and body weight.

Two groups of ewes in good body condition at the start of the breeding season were given either sufficient feed to maintain their body weight or 500 g/kg of a maintenance ration such that they showed a continuous fall in body weight. On three separate occasions after introducing the nutritional regimens, all ewes were challenged on day 12 of the oestrous cycle with 150 μg luteinizing hormone-releasing hormone. Prolonged chronic undernutrition resulted in a significant increase in luteinizing hormone release in response to luteinizing hormone-releasing hormone injection (P < 0·05), whereas the mean pre-injection luteinizing hormone concentrations were significantly reduced by undernutrition (P < 0·01).

Nine Cheviot × Shetland castrated male lambs from a group of 24 of 28 kg initial live weight, were subcutaneously implanted with a combination of 60 mg trenbolone acetate and 12 mg oestradiol-17β at 105 days and again at 45 days before slaughter. Of the remaining lambs, nine were untreated and six were slaughtered at the start of the experiment as part of a comparative slaughter procedure. The lambs treated with the anabolic preparation grew significantly faster (P < 0·05), converted food to live weight and estimated carcass gain more efficiently, had heavier carcasses which were larger, and had greater estimated gains for protein, moisture and ash. Implanted animals also tended to have a smaller deposition of carcass and kidney fat, but significantly heavier kidneys and less wool when the latter three weights were related to empty body weight. The mean values for plasma urea and serum total protein as indicators of protein metabolism were significantly decreased and increased respectively in treated lambs, but no other significant differences in blood metabolites and hormones were recorded. A significant increase in teat length of implanted lambs indicated the oestrogenic nature of the anabolic preparation.

The effect of barley level and monensin on feedlot performance by lambs and steers was investigated in two experiments. Monensin was given at 0 and 33mg/kg of food in lamb and steer diets, which contained bailey at levels from 300 to 900g/kg. Food consumption by lambs was not affected by monensin but intakes decreased with increasing levels of barley (P < 0·05). Food intake by steers decreased in a linear manner with increasing levels of barley (P < 0·01) and averaged 80g/kg lower when monensin was fed (P < 0·05). Monensin improved lamb gains by 350g/kg (P < 0·001), but had no effect on steer performance. Feeding monensin improved average food efficiency in lambs and steers by 27 and 4%, respectively. Carcass characteristics were not influenced by monensin, but heavier carcasses (P < 0·01) in steers given the high barley rations were also fatter (P < 0·001).

An analysis of published data on the effects of feeding frequency on cattle gave the following results. On average, increasing feeding frequency increased average daily gain by 16·2±4·8%. The efficiency of growth was increased by 18·7±60·%, indicating that improvements in average daily gain were due largely to improvements in efficiency of food utilization. Much of the improvement in average daily gain and efficiency of food utilization was attributable to increasing feeding frequency from one or two meals per day to four, but there was some evidence of further improvement at higher feeding frequencies.

In terms of experimentation it was concluded that, in general, nutritional or genetic comparisons of growth and efficiency should be carried out with a strict control of feeding frequency. In terms of animal production it was concluded that cattle should be fed at least four times daily to ensure maximum food efficiency for growth.

The magnitude of the response of average daily gain to feeding frequency was dependent on several experimental variables. In particular, the response appeared to be greater when the level of average daily gain was low and when the level of concentrates was high. The variables examined seemed unable to account wholly for the differences in response found in different experiments. Predicting the magnitude of the response under defined experimental conditions therefore remains extremely difficult.

Although rather more limited, results with sheep supported the conclusions drawn from the results with cattle.

1. The primary growth and first regrowth of perennial ryegrass were preserved either without additive (NA), or with a mixture consisting of equal volumes of formic acid and formalin at 10·0 and 13·01/t fresh crop for primary growth and regrowth herbage respectively (35 g formaldehyde per kg crude protein) (FF). The silages were given ad libitum to 40 lactating British Friesian heifers and cows, with a supplement of either pelleted ground maize (104 g crude protein per kg dry matter) (LP) or pelleted ground maize and soya bean meal (254 g crude protein per kg dry matter) (HP), at 6·1 and 7·1 kg per head per day for heifers and cows respectively. The primary growth silage was given from weeks 4 to 14 and the regrowth from weeks 15 to 22 of lactation. The silages were supplemented with urea so that the dietary supply of rumen degradable protein exceeded 7·8g/MJ metabolizable energy.

2. Silage FF had lower concentrations of both fermentation acids and ammonia-nitrogen than silage NA. The digestibility of the dry matter, energy and crude protein of the diet containing silage FF was significantly less than that of diets containing silage NA when cows were given primary growth material (P < 0·001). But silage treatment had no significant effect on the digestibility of cellulose. When cows were given regrowth silage, silage treatment had no significant effect on the digestibility of dry matter, energy and cellulose, but formic acid/formaldehyde reduced the digestibility of crude protein (P < 0·01). The inclusion of soya bean meal in the supplement significantly increased the digestibility of crude protein, dry matter and energy, but when cows were given the primary growth silage the effect on the digestibility of dry matter and energy was only apparent with silage NA.

3. Cows and heifers given silage FF from primary growth consumed 160g/kg more dry matter than those given silage NA (P < 0·01). This effect was not apparent when the animals were given regrowth silage. The effect of formic acid/formaldehyde on the intake of digestible energy was not significant in either period on the trial, but the inclusion of soya bean meal in the pellet significantly increased the intake of digestible energy (P < 0·01).

4. Cows and heifers given silage FF from primary growth produced 90g/kg more milk and 50g/kg more solids-corrected milk than those given silage NA, but the differences were not significant and these trends were not apparent when regrowth silage was given. An increase in the crude protein content of supplement increased the milk (P < 0·01) and protein yield (P < 0·05) of cows, but not heifers, when they were given primary growth silage. The effect was less when milk output was expressed in terms of solids-corrected milk since milk fat content tended to fall when cows were given the HP supplement. Treatments had no significant effect on live-weight change.

5. It is suggested that the increases in milk output were mediated via changes in the supply of energy rather than of protein.

Results are reported from four trials in which neonatal calves were given either whole milk or milk substitute containing the lactoperoxidase system.

Trial 1 was a pilot trial conducted in Sweden in which calves given whole milk with the lactoperoxidase system gained significantly more weight than controls (P < 0·05). Trials 2, 3 and 4 were carried out in successive years at the National Institute for Research in Dairying, using large numbers of newborn, female Friesian calves. In trial 2 a significant positive effect of the lactoperoxidase system with whole milk on live-weight gain was established by 3 weeks of age (P < 0·05) and sustained until weaning at 5 weeks. There was no significant effect of the lactoperoxidase system for the milk substitute treatment. In trial 3 the whole milk comparison from trial 2 was repeated. There was a significant positive effect of the lactoperoxidase system on the live-weight change after 2 weeks of age only (P < 0·05). In trial 4 two different methods of activating the lactoperoxidase system were compared for calves given whole milk. There was no effect of either method on the live-weight gain of the calves. However, as the levels of scouring were extremely low for all calves, a comparison of the two methods of activating the lactoperoxidase system was not justified. The combined results from trials 2, 3 and 4 confirmed that the lactoperoxidase system significantly increased the live-weight gain of calves given whole milk, despite the fact that the overall level of mortality and incidence of scouring was low in these trials.

Three experiments were carried out to investigate the effect of different forage types on the performance of male British Friesian calves up to 6 months of age. Unwilted and wilted silages were compared in all experiments, and in experiment 1 hay was also compared with the two silages. All the forages were compared at different levels of concentrate supplementation ranging, in different experiments, from none to ad libitum.

Calves fed wilted silage consumed 490, 90 and 200g/kg more forage dry matter respectively than those fed unwilted silage in the three experiments but this extra intake was generally not reflected in an increased rate of gain. Hay which was of lower digestibility than silage gave significantly lower live-weight gain. Quantities of silage consumed at an early age were small, with a mean daily intake over the first five weeks of 0·13 kg dry matter. Concentrate reduced silage dry-matter intake by 0·49 kg/kg concentrate dry matter consumed. Estimated mean concentrate intake required to achieve a daily gain of 0·75 kg in 1- to 6-month-old calves with silage offered ad libitum was 0·83 kg dry matter.

In an experiment on the occurrence of lactational oestrus, 92 multiparous Camborough sows and their litters were grouped in multi-accommodation pens at either 10, 15, 20 or 25 days post partum. The sows were fed ad libitum on a proprietary diet containing 160g crude protein per kg. A boar was introduced to the group the day following grouping. Weaning took place at 42 days post partum.

All sows except one showed oestrus in the period from grouping to weaning. Lactational oestrus occurred on average 10·9, 9·2, 12·2 and 7·3 (s.e. of difference 1·3) days after grouping (P < 0·05), and 21·0, 24·6, 32·2 and 32·8 (s.e. of difference 1·4) days following farrowing (P < 0·001) for the grouping treatments at 10, 15, 20 and 25 days. Subsequent farrowing rates were 48, 61, 78 and 45% and the number of pigs born 9·2, 9·5, 12·2 and 10·6 (s.e. of difference 1·3), respectively.

Piglet mortality in the suckling litters was higher on the day 10 treatment than either the day 20 or day 25 treatment. This led to a significantly lower litter weight for the day 10 treatment compared with any of the other treatments.

The reproductive performance of does of New Zealand White (N) and Californian (C) strains of rabbit was compared with that of the two reciprocal crosses, C × N and N × C (sire × dam). Both types of crossbred doe showed a reproductive performance superior to the purebred strains, having both a higher conception rate and mean litter size at birth. C × N, N × C, N and C does reared on average 6·6, 7·4, 5·0 and 4·9 pups to weaning age respectively. Expressed in terms of an estimated annual production of weanlings the N × C does produced nearly twice as many progeny to 4 weeks of age as the purebreds N and C (37 pups cf. 21 and 19 pups respectively). Total losses prior to weaning were approximately 25% in all breeds, largely from stillbirths, and subsequent chilling and/or starvation in the nest (36% and 38% of diagnosed deaths respectively). Other contributory factors are discussed.

A simple and general procedure for calculating the equilibrium improvement lag in a livestock dissemination system is presented. The lag is conveniently measured in terms of the number of years of genetic change that it represents, and depends on the age and on the genetic superiority of the parents used in each step of the dissemination system. The total lag is the sum of the lags in all steps, weighting each step by the proportion of genes going through it.

Twenty-five Greyface wether lambs were allocated at approximately 40 kg live weight to be slaughtered, to be untreated controls, or to be implanted with 57·5 mg trenbolone acetate plus 8·1 mg oestradiol-17β (treatment To8), 60mg trenbolone acetate plus lOmg oestradiol-17β (treatment To10) or 70mg trenbolone acetate plus 12 mg zeranol (treatment TZ). The control and treated lambs were slaughtered after 63 days. Effects on live-weight gain were small and not significant. On average, hormonal treatments resulted in: (a) significant increases in dressing percentage, gain in carcass weight and carcass protein, kidney weight (g/kg live weight), depth of thorax and in the activity of liver tyrosine amino transferase; and (b) variable reductions in hind leg length, concentration of plasma urea and (g/kg live weight) kidney fat, mesenteric fat and fleece. Significant differences recorded between treatments included the conversion of food into carcass protein (treatments To8 and TO10 v. TZ) and mesenteric fat (g/kg live weight) and fat cover at the 12th rib (treatment To8v To10).

A single intra-muscular injection of either 6mg or 12 mg Dexamethasone on day 142 of gestation resulted in a high degree of synchrony in the time of lambing compared with untreated controls, with no increase in lambing difficulty or perinatal mortality. Birth weight and growth rate of lambs born to treated ewes were not significantly different from those of untreated control ewes.

A single intra-muscular injection of 12 mg Dexamethasone on day 125 of gestation resulted in abortion in nearly half of the ewes, and their lambs were either stillborn or died soon after birth.

These data demonstrate the need to know precise mating dates if parturition is to be induced in this way.

Forty-five crossbred cattle were scanned by ultrasonics at three sites on the body and were ‘condition scored’ before slaughter and subsequent dissection of a sample rib joint.

Ultrasonic measurements gave a better indicator of fat content than did ‘condition score’. The third lumbar vertebra site on the body gave a better prediction of sample joint composition than did the 10th or 13th rib.

The mean ultrasonic measurement of fat depth at the three sites did not improve the prediction of composition as compared with the value obtained at the third lumbar vertebra. The overall standard deviation for total fat concentration was 42·1 g/kg and for lean concentration was 35·4 g/kg. Area of fat at the third lumbar vertebra was the best single indicator of fat concentration and lean concentration in the sample joint, with residual standard deviations of 25·1 and 23·1 g/kg respectively. A combination of fat measurements at the 3rd lumbar position was the best overall predictor (residual standard deviation: 23·8g fat and 23·0g lean per kg).

An alternative form, y = Anmce−cn, of the lactation model of Wood, y = Anbe−cn, is suggested. The new parameter, m, is the time required to achieve maximum milk yield. The correlations between non-linear parameters are reduced.