Thirteen pairs of Suffolk rams were selected on high and low 18-month adjusted live weight from six farms over 2 years, to establish the relationship between 18-month weight and early lamb growth. Progeny were first produced in recorded crossbred flocks (618 lambs) and then in an experimental flock of crossbred ewes (1083 lambs). Different results were obtained from the recorded and experimental flocks. The regressions of lamb 12- to 13-week weight on ram 18-month weight (within farm deviation) were 0·053 ± 0·022 kg and –0·004 ± 0·020 kg, respectively. These regressions for indirect selection correspond to ‘effective’ heritabilities for direct selection for lamb growth of 0·18 ± 0·07 and 0·02 ± 0·06 respectively. Improvement of early Iamb growth is discussed and it is concluded that selection for 18-month weight is unlikely to be a useful method.

Understanding the relationships between food intake, milk output and body condition in high-yielding dairy cows is crucial in determining suitable management strategies. During two winter feeding periods 38 and 37 cows were individually fed, to appetite, complete diets which on average contained 11·7 MJ metabolizable energy per kg dry matter and comprised grass silage, concentrate meal and brewers' grains (draff). The groups' mean 305-day yield was 7 240 kg (s.d. 1 281) with 42 g (s.d. 4·3) fat per kg. Regression analysis was carried out to describe dry-matter intake both for 26 weeks post calving and for four successive 6-week periods from calving. The final equations, which had a residual s.d. of 0·07 to 0·10 of the observed intake, included milk yield, cow size and a measure of body-condition change. The cows were divided into three groups (high, medium and low) on two criteria: (1) mean milk yield (MJ/day) during the first 26 weeks of lactation and (2) post-calving backfat index determined ultrasonically. Differences were found between milk-yield groups from gross efficiency (milk yield (MJ)/energy intake (MJ metabolizable energy)) (P < 0·001), mean metabolizable energy intake (MJ/day) (P < 0·01), dry-matter intake as a proportion of live weight (P < 0·05), and post calving live weight (kg) (P < 0·05). Differences were found between backfat-index groups for maximum backfat loss and loss to day 42 (P < 0·001); also for mean live weight during the 26 weeks and post calving live weight (P < 0·001), dry-matter intake as a proportion of live weight (P < 0·05) and lactation number (P < 0·05). Interactions were found between the milk yield groups and backfat groups for milk yield (P < 0·01) and gross efficiency (P < 0·05) with the fattest group containing the highest and lowest yields and efficiencies.

In 40 ewes exposed to thermoneutral or cold environments during the last 5 to 6 weeks of pregnancy (experiment 1), and in 10 ewes treated in the same way during the last 3 to 9 days of pregnancy (experiment 2), cold exposure lengthened mean gestation times by 1·7 and 2 days respectively. This effect was statistically significant only in experiment 1. Blood samples were taken from the right atrium of ewes in experiment 2 and the concentrations of some hormones in the plasma were measured. Cortisol concentrations were higher in plasma from cold-exposed ewes than control ewes. Plasma progesterone concentrations were lower in cold-exposed ewes than control ewes during a period from 36 h before parturition to 36 h after parturition, but the changes in plasma total unconjugated oestrogens, 17a, 20o-dihydroxypregn-4-en-3-one and oestrogen sulphates were associated with parturition in the normal way.

The mechanism underlying the prolongation of gestation during cold exposure requires further investigation; events that precede the change of steroid production by the placenta at parturition are most likely to be involved.

Maturing patterns are established for 93 individual muscles, and nine anatomical groups of muscles, using half carcass dissection data from 39 rams of two strains of Merinos of different mature size (91 and 116 kg). The maturity coefficients of the individual muscles and muscle groups are tabulated. Seventy-eight of the 93 muscles, and eight of the nine anatomical muscle groups, had maturing patterns which were not significantly different for the strains of sheep. In general, the muscles of the limbs and muscles surrounding the spinal column were earlier-maturing than total muscle and the muscles in the cranial end of the trunk were late maturing. The muscles of the abdominal wall matured at the same rate as total muscle.

Differences in the distribution of muscle weight of the two strains of rams, when compared at the same total muscle weight, were reduced when compared at the same proportion' of mature total muscle weight. It was concluded, therefore, that apparent differences in the distribution of muscle weights, when breeds are compared at the same total muscle weight, may be due largely to differences in mature size.

A survey was carried out of 1 640 British Friesian heifers calving predominantly in the autumn of 1979. The monthly samples of 1 055 animals showing no reported evidence of udder infection were used to evaluate the parameters of a lactation curve in milk cell count. The model was

C = 190 n−0.4880exp(0·178n)

where C is the monthly cell count in millions per 1 during the nth month of lactation. The cell count varied from 230 × 106 in week 1 and 190 × 106 in week 11 to 400 × 106 in week 44 of lactation.

On applying the model to the whole sample, milk sampled within a month before or after antibiotic treatment for clinical mastitis contained more than 200 × 106 cells per 1 above the level suggested by the lactation curve. Lactation mean cell counts of treated cows were 400 × 106 cells per 1 higher than those of untreated cows. It was not possible to identify periods in which cows required treatment, or those with high cell counts, by reference to the lactose concentration in the milk samples. Among the untreated cows, the cell count at the third monthly test-day was lower than at any other time, and was more highly correlated with the lactation mean cell count.

Individual dry matter intakes were measured using four groups of 16 ewes, indoors or at sparse winter grazing. In periods of varying duration (14 to 35 days) the ewe groups received 14 feedblock supplements competitively, eight trough supplements competitively or two feedblock supplements individually. In each period hay was available ad libitum. All supplements contained chromic oxide and individual supplement intakes were estimated by total faecal collection. Individual hay and total dry-matter intakes were estimated by faecal apportionment according to indigestibility of dietary components.

Metabolizable energy content (0·81 × digestible energy) of the feedblocks ranged from 7·9 to 9·2 MJ/kg dry matter compared with a value of 13·0 MJ metabolizable energy/kg dry matter for concentrates. The variation in individual supplement intake was large, irrespective of type of supplement. However the mean coefficient of intake variation for 14 feedblock supplements (0·56) significantly (P < 0·05) exceeded that (0·39) for eight trough supplements at equivalent mean dry-matter intakes.

Thus, ‘free-access’ feedblocks did not allow a more uniform supplementation than trough supplements. Supplement intake variation was higher outdoors and increased as total feedblock intake reduced.

The variation in individual hay and total dry-matter intake was lower, and generally independent of that for the supplements. Mean coefficient of variation of 0·24 and 0·22 were obtained for hay and total dry matter, respectively, based on 22 collections with competitively fed sheep.

Total daily metabolizable energy intakes of individual ewes outdoors ranged from 5 to 22 MJ per collection.

Groups of Merino lambs were exposed to wheat at different ages, for different durations, and with or without their mothers, in two experiments. Acceptance of wheat was tested during the week following weaning.

In experiment 1 the mothers had never eaten wheat; all but one group were exposed without their mothers. Lambs showed more interest in wheat at 1 to 2 weeks of age than at any other age. The only group in which there was good acceptance of wheat during testing was the group which was exposed with their mothers. The latter had been given wheat for the first time in the week prior to the lamb's exposure. The average intake of this group in 2.5 h of testing (0.5 h per day for 5 days) was 290 g per head.

In experiment 2, groups of lambs, together with their mothers who were experienced in eating wheat, had uncontrolled access to wheat trailed on the ground for different periods within the first 4 weeks after birth. Lambs in one group had access to wheat for 1 to 5 days following birth.

All lambs in experiment 2 ate wheat during testing and there were no differences in either intake or feeding times between groups. Mean intake of all groups during the 5 day test period was 810 g per head.

The results demonstrate the importance of early experience and in particular maternal influences in determining the subsequent acceptance of a wheat supplement by lambs. The results also raise questions concerning not only the nature, but also the extent of maternal influences on dietary selection.

Possibilities for increased rates of genetic change in dairy cattle through embryo transfer and embryo splitting are examined, using the multiple ovulation and embryo transfer systems previously proposed. These involve embryo transfer from 1-year-old females (juvenile scheme, generation interval 1·8 years) and from females after 1 lactation (adult scheme, generation interval 3·7 years), with use of males at similar ages. Though selection is less accurate than in conventional progeny testing, the annual rate of genetic improvement can be increased, and even doubled. If the number of transfers is restricted andm the inbreeding rate is limiting, the adult scheme for both sexes is preferred. A scheme with 1 024 transfers per year and 512 females milk-recorded per year will sustain a rate of genetic improvement some 30% above that possible by a conventional national progeny-testing programme. Because of the relatively small number of animals involved, it is argued that greater control over recording, breeding and selection should be possible, leading to a larger proportion of the possible genetic gains being realized in practice. Other advantages, and disadvantages of these systems, and their integration in dairy cattle improvement are discussed.

Masham ewes carrying single, twin or triplet foetuses were offered a ration of concentrates which increased from 200 to 650 g per ewe per day over the last 7 weeks of pregnancy in 2 years. Silage was offered ad libitum and the voluntary intake of each ewe was measured. In the first year, 30 ewes were offered a poorly-preserved, wet silage (A) which had a low digestibility, followed by a better-preserved silage (B) which had a higher digestibility and dry-matter concentration. There was an increase in silage intake when the change was made from A to B. In the following year, 32 ewes were offered silage (C) which was well preserved, similar in digestibility to B but with a lower dry-matter concentration. The ewes ate more silage organic matter (g/kg live weight) with C than A (12·77 v. 9·34) in weeks 15 to 17 of pregnancy but more of B than C (13·76 v. 10·38) in weeks 19 to 20. Ewes carrying single lambs ate more silage and had a slower rate of decrease in silage intake when the concentrate ration was increased as pregnancy progressed. As litter size increased there-was either greater loss or smaller gain in body condition score.

Thirty-six entire male pigs were used to investigate the effects of two levels of dietary crude protein (150 and 220 g/kg) each in combination with four levels of feeding (1·0, 1·32, 1·64 MJ digestible energy/kg M0·73 per day and ad libitum) on growth, body composition and energy utilization over the live-weight range 7 to 19 kg.

Growth rate responded linearly (P < 0·001) to increasing energy intake but was depressed (P < 0·05) when dietary crude protein was reduced from 220 to 150 g/kg.

Raising digestible energy intake increased and decreased respectively the proportions of fat and protein in the empty body at 19 kg live weight. However, the magnitude of the response of both components to change in digestible energy intake was reduced in the case of pigs fed the lower protein diet.

Total energy retained and that retained as fat and as protein responded linearly (P < 0·001) to change in digestible energy intake of either diet. Extrapolation of the regression of total energy retained on digestible energy intake yielded a digestible energy requirement for maintenance of 510 kJ/kg M0·75 per day, which was unaffected by level of dietary protein.

The partial efficiencies of protein utilization, estimated from the regressions of protein deposition (g/day) on protein intake (g/day), were 0·616 and 0·411 for pigs given the diets containing 150 and 220 g crude protein per kg respectively.

Correlation between circulating thyroid hormones and live-weight gain during the first year of life were observed in four trials on cattle of the two main Belgian breeds: Belgian Blue and Friesian. Thyroid hormones assayed and considered as potential predictors of growth rate were: thyroxine (T4), triiodothyronine (T3) and free thyroxine (FT4). Triiodothyronine uptake (T,U), thyroid stimulating hormone (TSH) and free thyroxine index (FTI) were also estimated.

No significant correlation was found between live-weight gain and T4 or T3 in 13 Belgian Blue heifers (trial 1). In 49 bulls submitted to a performance test, T4 and FTI increased from 3 to 12 months whilst T3U decreased (trial 2). Significant correlations between live-weight gain and T4 and between live-weight gain and FTI were obtained from samples taken between 66 and 95 days. Live-weight gain was correlated with T3U when animals were between 96 and 125 days, and 126 to 155 days of age. It is possible that the interaction between total T4 and T3U is important in controlling growth. In 13 young calves, beef merit, expressed as live-weight gain in 1 year, was highly correlated with T4 concentration at 8 to 10 days of age (trial 3). T3 and FT4 did not seem to be directly associated with the growth processes. In trial 4, live-weight gains of 42 young animals housed on a commercial farm were negatively correlated with T4 and with FTI. The conflicting results encountered may perhaps be explained by the lack of information on the use of anabolic preparations in field conditions. T4 concentration and FTI may be considered as potential parameters for the estimation of beef merit but the results are insufficient to draw definite conclusions.

Maturing patterns of carcass muscle, bone and fat were established using dissection data from 20 large mature size strain and 19 small mature size strain Merino rams. The rams were fed a pelleted ration soon after weaning and individual rams from both strains slaughtered at 6 kg increments in live weight from 18 kg to maturity at 116 and 91 kg for the large and small strains respectively.

Composition of mature rams of both strains was similar for the proportion of muscle and bone but there was a slightly greater proportion of fat in the larger strain.

The progress of each carcass tissue to maturity was assessed relative to progress of shorn full live weight to maturity. Maturing patterns of the three carcass tissues were not significantly different in the two strains. Muscle and bone were early maturing relative to live weight and fat late maturing.

The composition of the large and small mature size strains at the same live weight and at the same proportion of maturity was predicted from the maturity patterns of the carcass tissues and the composition of the mature rams. At the same live weight the large mature size strain had a greater proportion of bone and a smaller proportion of fat than the small mature size strain. At the same proportion of mature live weight, differences between the strains in proportional composition were reduced, and the large mature size strain had slightly more fat.

Some guidelines for comparison of strains of animals of different mature size are developed.

One hundred and fourteen castrated male cattle of various breeds were measured ultrasonically immediately prior to slaughter and the data were examined for correlations with the proportion of adipose tissue in the carcasses. Two flaw detectors and a simple scanner, the Scanogram, were used to make ultrasonic pulse-echo measurements of tissue thicknesses and areas. These were used to compute volumes of adipose tissue and muscle in a region of the back of each animal and the ratio of the volumes of the two tissues was examined for correlation with carcass fatness. Three individuals interpreted the Scanogram photographs and two made measurements using flaw detectors.

In general, pulse-echo measurements made by different individuals differed in magnitude and predictive value, even when identical scans were measured. Equally there were substantial differences between measurements when the same animals were measured by the same individual using different ultrasonic instruments.

In a parallel experiment, the speed of ultrasound transmission was measured at various locations on the living animal and the data were examined for correlations with carcass fatness. Unlike the pulse-echo technique, the transmission method was not prone to errors of subjective interpretation and did not require skill to interpret. Predictions based on speed measurements at two sites in the hind limb were as well related to carcass fatness as were those made on the basis of the best estimate of tissue volumes in the back. The use of two speed measurements in a multiple regression with the best Scanogram data significantly improved the accuracy of predictions of side fatness made on the basis of speed or pulseecho measurements alone.

Two types of analysis were used to examine the effectiveness of Ultrasonic selection of lean animals from a group of 50 Hereford castrated males of similar age and weight.

Forty-two pigs representing equal numbers of entire males and females were used to study the effects on the performance and body composition of four restricted levels of feeding (14·5, 20·3, 24·9 and 29·4 MJ digestible energy per day), and of offering the same diet (14·5 MJ digestible energy per kg and 210 g crude protein per kg) ad libitum between 20 and 45 kg live weight.

Over the four restricted feeding treatments there were no significant differences between the sexes for the performance and body composition of four restricted levels of feeding (14·5, 20·3, 24·9 and 29·4 MJ digestible energy per day), and of offering the same diet (14·5 MJ digestible energy per kg and 210 g crude protein per kg) ad libitum between 20 and 45 kg live weight.

Although ad libitum energy intake was the same for both sexes (34·2 MJ digestible energy per day), raising digestible energy intake from that provided by the highest restricted feeding treatment (29·4 MJ/day) to ad libitum resulted in marked differences between the sexes for performance and body composition.

For males, raising digestible energy intake from 29·3 to 34·2 MJ/day improved the rate of live-weight gain and protein deposition by 0·15 and 0·10 respectively but had no further effect on food conversion ratio or body fat. The same increase in digestible energy intake for females improved growth rate by only 0·065, had no further effect on the rate of protein deposition but increased markedly food conversion ratio and body fat.

Whole-crop barley (cv. Midas) was harvested when the grain dry matter (DM) reached 640 g/kg and was treated with either anhydrous ammonia at 40 g/kg DM or propionic acid (30 g/kg DM) and stored in polythene-lined tower silos. Anhydrous ammonia and propionic acid preserved the early harvested barley whole crop but distribution of ammonia through the silos was not uniform. Coefficients of DM and starch losses from whole grains separated from the ammonia- or propionic acid-treated whole crops or from rolled barley grains and suspended in the rumen of steers in nylon bags weqe, after 42 h incubation 0.73,0.85,0.26,0.21 and 0.78,0.96 respectively. Coefficients of digestibility of the ammonia-treated (AWC), of the propionic acid-treated (PWC) whole crops and of a diet of rolled barley and ammonia-treated straw (RB) with the same grain to straw DM proportion as that in the whole crops were 0·62 (AWC), 0·55 (PWC) and 0K57 (RB). Daily live-weight gains (kg/day) of 350 kg Hereford × Friesian steers offered the diets for up to 100 days were 0·33 (AWC), ·0·61 (PWC) and 0·74 (RB) and DM feed intakes (kg/day) were 4·7,3·4 and 7·6 respectively.

Using a model to simulate food intake and the partition of food between milk production and live-weight gain, an attempt has been made to explore the financial implications of different levels and patterns of concentrate feeding, where silage is fed ad libitum. In the case of high-yielding cows it appeared that, although feeding more concentrates increased overall lactation yield, profits per cow and per hectare declined with increasing concentrate usage. This raises doubts concerning the traditional view that higher profits result from increasing yields per cow. Comparing different patterns of feeding it also appeared that there was no significant economic loss from flat-rate compared to stepped feeding of concentrates, where cows had ad libitum access to silage.

Metabolism trials were conducted with entire male pigs (average initial weight 44·4 ± 0·2 kg) to determine the apparent digestibility of the major chemical components of diets containing 0·05, 0·10, 0·15 and 0·20 cell-wall material (determined as neutral detergent fibre) from lucerne leaf meal, when added to a constant daily allowance of a semi-synthetic basal diet. Concurrent rate of passage studies were also carried out.

Increasing the proportion of cell-wall material in the diet resulted in a linear decrease in the apparent digestibility of dry matter, crude protein and ether extract and the apparent digestibility and metabolizability of gross energy. Daily nitrogen retention (g) increased linearly with an increasing proportion of cell-wall material in the diet. Coefficients of apparent digestibility and cell-wall material fractions did not differ significantly with changes in the dietary proportions.

Although the rate of passage of digesta was slower (F < 0·001) in animals fed the diets containing 0·05 and 0·10 cell-wall material than in those fed the two diets with higher proportions, it did not appear to be a major factor contributing to the observed decline in the apparent digestibility of dietary chemical components as the proportion was raised.

Increase in dietary proportion of cell wall material was associated with marked linear increase in weight and/or length of various segments of the gastro-intestinal tract.

Primary growths of perennial ryegrass and red clover were ensiled with formic acid (2 1/t fresh crop), o an equal quantity of formic acid together with formaldehyde (46 or 49 g/kg crude protein in the ryegrass or red clover respectively). The four silages were offered ad libitum to 12 groups, each of five British Friesian steer calves, either alone or with urea or maize starch supplements at 18·4 or 185·2 g/kg total dry-matter intake respectively.

Digestible organic matter and digestible energy intake, live-weight gain, carcass weight, nitrogen retention and all digestibility measurements were higher on the ryegrass silages than on the red clover silages. However, dry-matter intake was higher on the red clover silages.

Formaldehyde treatment reduced lactic and total acid content, and protein degradation in the silages. It also increased intake, live-weight gain and nitrogen retention on ryegrass but not on red clover, the effect being greater when the urea supplement was given. Digestibility measurements were depressed by formaldehyde treatment, although cellulose digestibility was only depressed in the ryegrass silage.

Supplementation with starch depressed silage intake and nitrogen and cellulose digestibility, but increased dry matter, organic matter and energy digestibilities, digestible organic matter and digestible energy intakes, live-weight gain and carcass weight. The positive intake, live-weight gain and carcass weight responses were greater on the silages treated with formic acid, while the digestibility and the live-weight gain responses were greater on the red clover silages. Starch supplementation did not improve nitrogen retention.

The different animal production responses to formaldehyde treatment on the ryegrass and red clover silages are discussed.

Analyses of variance were conducted on first lactation milk, fat and protein production records in England and Wales of daughters of British Friesian sires. Herds were split on milk yield into high and low levels of mean production and, in subsequent analyses, into high and low levels of within herd variance and coefficient of variation using all first lactation records. Data were then extracted on daughters of 798 young sires undergoing progeny test and on 118 widely used proven sires to generate connections. Least squares analyses were conducted within levels and genetic correlations estimated from the covariance of sire effects. W ith data split on mean yield, the heritability of milk yield was 0·24 at the low level and 0·30 at the high level, that of log transformed yield being 0·25 and 0·35 respectively.

With data split on variance the corresponding figures were 0·24, 0·30, 0·27 and 0·36 respectively, and when split on coefficient of variation, 0·22,0·26,0·26 and 0·32. There were similar increases for fat and protein yield, proportionately smaller increases for fat and protein content.

Genetic correlations were close to 1·0 between high and low levels for all traits on all criteria of data splitting. As a consequence progeny testing of bulls is rather more accurate at high mean or variance of production levels and data can be combined optimally without scaling. Cows of the highest predicted value using an index will be found in high variance herds.

Sixty Landrace × Large White gilts were allocated at random to one of three treatments. Treatment A gilts were fed 16 mg allyl-trenbolone once a day for 18 days. Treatment B gilts were fed 20 mg allyl-trenbolone per day for 18 days. Treatment C gilts were controls. The gilts were allocated to treatment at 111·3 ± 1·91 kg live weight, moved to a pen with individual feeders and put into groups of four gilts to a pen with a sexually mature boar in the adjacent pen. Treatment A and B gilts were tested for heat with a boar for 20 min each day beginning on the day after the last allyl-trenbolone feed. Treatment C gilts were tested with a boar in the same way after allocation. The time from the last allyl-trenbolone feed to oestrus for treatments A and B was 7·05 ± 0·44 and 8·4 ± 0·49 days. The time from the beginning of heat detection to oestrus for group C gilts was 22·4 ± 4·5 days. At oestrus, all gilts were mated twice on successive days with a fertile boar. The mean litter size at farrowing for treatment A was 9·1 ± 0·62; B, 11·2 ± 0·75 and C, 9·3 ± 0·65 piglets born alive (P < 0·05). It is concluded that giving 20 mg of allyl-trenbolone for 18 days to groups of peripubertal gilts is a very effective means of controlling oestrus and ovulation.