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.

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.

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.

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.

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.

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.

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.

Three trials were conducted on commercial premises using sows naturally infested with gastro-intestinal nematodes, primarily Oesophagostomum spp. In two trials the farrowing performance of sows treated approximately 7 days before farrowing with thiophanate (‘Nemafax’) in-feed at a median dosage of 62·5 mg/kg was compared with that of untreated controls. In the third trial a similar comparison was made between sows treated approximately 7 days before expected service and untreated controls. In all cases faecal egg counts indicated thiophanate was highly effective against the nematode burdens present. Administered pre-farrowing, thiophanate resulted in better pre-weaning weight gains and relatively lower creep feed consumptions of the piglets. This effect was most marked in the trial with a higher level of Oesophagostomum spp. infestation in the sows. Under similar circumstances, pre-service medication produced a response in terms of live piglets born and those surviving to weaning.

Ultrastructural parameters of muscle growth were measured in lines of mice which had undergone 15 generations of selection for high and low body weight. Previous light microscopic studies of these lines had shown that selection for altered body weight evokes correlated responses in the weight of skeletal muscles as a result of changes in both the number and the longitudinal and transverse dimensions of the fibres.

The length of the myosin filaments and of the actin filaments (including the Z disc) did not differ significantly from the controls in the mm. sternomastoideus, biceps brachii and tibialis anterior of mature male mice from the two selection lines. The mean cross-sectional area of the myofibrils of the mm. sternomastoideus and biceps brachii were also unaltered by selection for high and low body weight. Changes in the area of the fibres were brought about by increases and decreases in the number of their constituent myofibrils and corresponding changes in the non-contractile elements.

Selection for high and low body weight did not affect the dimensions of the contractile elements of the muscle fibres. The genetically determined alterations in the length and cross-sectional area of the fibres were due to changes in the number of their constituent sarcomeres and myofibrils. These changes are similar to those which occur during growth.

Twenty-five Californian does were mated and given pelleted diets of either 8(LE) or 10(HE) MJ/kg dry matter (ruminant metabolizable energy values) throughout gestation and lactation. Litter sizes were adjusted to six offspring per doe. Milk yield was estimated from the weight differences of the litters before and after suckling, when the opportunity for nursing was confined to once daily. The young rabbits were allowed access to either the LE or HE diets from 18 days of age. Weaning took place at 32 days of age when four rabbits from each doe grouP × pre-weaning diet were slaughtered. Diet had no effect on litter size or birth weight, but does on the LE diet had lower live weights post partum (P < 0·05). Dry-matter consumption by the does on the LE diet was greater than for the HE diet (P < 0·05) both during gestation and lactation, but calculated metabolizable energy intakes were lower during lactation. There were no statistically significant differences between treatments for milk yield or live-weight gain to weaning and dry-matter intakes of the young at weaning, but daily live-weight gain from fostering to 18 days of age was greater for litters of does fed the HE rather than the LE diet (P < 0·05). There were no statistically significant differences between diets for carcass traits at weaning.

After weaning, 32 rabbits were given either the LE or HE diet until 2 kg live weight when they were slaughtered. A post-weaning × pre-weaning diet interaction (P < 0·05) occurred for live weights of the rabbits at the start of the post-weaning trial (i.e. after a 10-day adaptation period) with LE: LE rabbits being lighter than other rabbits as a results of poor live-weight gains during the adaptation period. Live-weight gains to slaughter were greater for the pre-weaning LE diet (P < 0·05) and the post-weaning HE diet (P < 0·01), although dry-matter intakes of the HE diet were less (P < 0·05). Rabbits on the LE diet had greater empty gut weights (P < 0·05) and lighter livers (P < 0·05) at slaughter.

Twenty-four bull calves, eight Hereford × Friesian, eight Aberdeen Angus × Friesian and eight Friesian, were reared from birth to slaughter at 13 weeks of age solely on a milk substitute diet given ad libitum.

Samples of jugular blood were taken at weekly intervals from 5 days to 89 days of age for determination of concentrations of prolactin, growth hormone (GH), insulin and total thyroxine (T4) in plasma, tri-iodothyronine (T3) uptake, and thus free T4 index (FTI).

The Friesian calves had a higher mean body temperature and lower mean T3 uptake than did either of the beef crosses.

The Aberdeen Angus cross had a higher mean dry-matter intake per unit of metabolic body size (DMI/W0·73), heart rate and plasma insulin concentration than did the Hereford cross, and a higher insulin concentration but not a higher heart rate than did the Friesian. Live-weight gain and DMI/W0·73 for the Friesian was intermediate between that of the Aberdeen Augus cross and the Hereford cross.

DMI/W0·73 was positively correlated with insulin: GH ratio, prolactin: GH ratio and T4: GH ratio.

The increase in heart rate per unit DMI/W073, a measure of the heat increment of feeding, was negatively correlated with the plasma insulin concentration, insulin: T4 and insulin: GH ratios.

Prolactin concentration, GH concentration and T3 uptake declined with age, whereas insulin concentration, T4 concentration and FTI increased with age. The relationship was linear for prolactin and insulin concentrations, but curvilinear for the other variables. The Friesian breed had a higher GH concentration than did the beef crosses during the first 12 days of life. The large increase in insulin concentration for the Aberdeen Angus × Friesian occurred from about 47 days of age. The peak T4 concentration and the lowest T3 uptake of the breeds occurred between 33 and 42 days of age.

Possible mechanisms for the control of dry-matter intake by preruminant calves and the difficulties associated with prediction of performance from plasma metabolic hormone concentrations obtained at a young age are discussed.

Twenty-two pairs of female Friesian twin calvxs, fed a standard pelleted diet with an ME value of 9·3 MJ 'kg, were split between the following nutritional treatments: (a)ad libitum (b) a weekly amount equal to 24% of body weight or (c) equal to 20% of body weight. Each proportionally-fed animal eventually reached a break-point when the amount of food it was offered exceeded its intake capacity.

For the ‘24%’ and ‘20%’ regimes respectively, break-points occurred at a mean age of 40 and 48 weeks and at a mean body weight of 222 and 258 kg. Surprisingly, the mean body weights at these ages on the ad libitum regime were virtually the same (223 and 265 kg). Thus growth up to break-point was, on average, just as fast for proportional feeding as for ad libitum.

In general, growth up to break-point was significantly slower than the exponential rate expected from a simple linear model. Nevertheless, animals fed at the 20% level grew almost exponentially beyond 6 months of age, and the normally expected decline in the food efficiency ratio was delayed.

The hypothesis being tested was that a proportional feeding system, while in operation, would ensure highly efficient growth and that the break-point could be used as a self-determined optimal slaughter point for each individual. On the evidence obtained, further investigation would be worthwhile, especially at proportional feeding levels giving break-points beyond 1 year of age.

In experiment 1, nine Hereford × Friesian steers weighing 325 kg were used in a changeover design and offered long barley straw that had been treated with 30 g anhydrous ammonia per kg for 8 weeks, a solution providing 25 g urea per kg straw dry matter or a solution providing 23 g urea and 3 g ammonium sulphate per kg straw dry matter. In addition they were offered 3 kg/day of mineralized rolled barley. In experiment 2, 30 Hereford × Friesian steers weighing 380 kg were used in a continuous growth trial of 10 weeks duration. They were allocated to one of the following barley straw treatments, straw that had been exposed to 30 g anhydrous ammonia per kg for 4 weeks, untreated straw with a urea supplement in the barley or untreated straw. The straw was fed ad libitum with either 2·8 or 4·4 kg rolled barley daily.

The barley straw contained 43 and 27 g crude protein per kg dry matter in experiment 1 and 2 respectively. In both experiments, ammonia treatment increased the crude protein content of the straw and resulted in improved straw intakes and higher live-weight gains. The results of experiment 2 cast doubt on the practice of providing supplementary nitrogen with food based on long barley straw and barley when steers weighing about 400 kg are used.

The study was based on 1156 lactation records of 545 Murrah buffaloes. Initial milk yield, peak yield, ascending phase milk yield and days to attain peak daily production, the means of which were 26·7 kg, 10·3 kg, 407 kg and 58·9 days respectively, were all affected by period, season and parity of calving. Heifers recorded the least initial milk yield and peak yield and took the longest time to reach peak production. Peak yield was the most important single factor (R2 = 0·41) in causing variation in 43-week milk yield. The heritability estimates for initial, peak and ascending phase milk yields and days to attain peak yield were 0·35, 0·51, 0·27 and 0·13 respectively, whilst that for 43-week milk yield was 0·18. Peak yield had the highest phenotypic (rP = 0·64) and genetic correlations (ra = 0·68 ± 0·19) with the 43-week milk yield. Other genetic correlations with the 43-week milk yield were low and non-significant. The results indicated that indirect selection for peak yield would be more effective than direct selection for improving the 43-week milk yield in buffaloes.

Dairy Shorthorn (DS), Red Friesian (RF), Red Holstein (RH), Danish Red (DR), Meuse-Rhine-Yssel (MR), Simmental (SM), British beef breeds (BB) and hybrid (HY, RF♂ × DS9 and RH♀ × DS?) bulls were progeny tested on DS, RF and HY cows as part of a breed improvement project. Live-weight records for 4 450 animals in 17 herds by 350 sires were used to calculate adjusted hundred-day weights from 100 to 700 days of age. Genotype × environment interactions were significant (P < 0·001) and data for two production systems (cereals and grass) were analysed separately. RF, RH, DR and MR progeny were, proportionally, 0·10 to 012 heavier than DS (P < 0·001). On cereals the SM were significantly heavier than these crosses (0·095, P < 0·001 at 400 days) but not on grass. BB and HY were generally not significantly different from DS. Only DS dams were represented on cereal systems. On grass, breed differences were similar for different dam breeds but estimates of hybrid vigour averaged 0·051 in RF♂ × DS♀, 0·061 in RF♂ × (RF♂ × DS♀)♀ and were not significantly different from zero in DS♂ × (RF♂ × DS♀)♀. Apparent heritability averaged 0·50 ± 0·12 but was lower during a period of feed restriction. The within-breed genetic correlation for live weight on the two systems of production was unity.

Carcass characteristics of 246 bulls and steers by Dairy Shorthorn (DS), Red Friesian (RF), Red Holstein (RH), Danish Red (DR), Meuse-Rhine-Yssel (MR), Simmental (SM) and North Devon (BB) bulls were recorded as part of a breed improvement programme. Carcasses of animals on grass-feeding systems were older, had lower fat and conformation scores and higher estimated lean yield than on intensive cereal systems, BB were fatter, and MR and SM leaner, than the remaining breed groups which were similar to DS and SM progeny had high conformation scores. Estimated lean in the live weight (g/kg) relative to DS was RF +5, RH −3, DR +5, MR +16, SM +16 and BB +6 with an average standard error of 3.

Forty purchased male Hereford ♂ × Friesian ♀ calves (about 14 days old) were offered concentrate diets containing 0, 170, 230 or 320 g chopped (20 mm) straw per kg. Food intake and live-weight gains of calves were increased by the inclusion of straw, but the 320 g straw treatment tended to depress intake and gain. The optimum concentration of fibre for maximizing live-weight gains was 150 g trichloracetic acid fibre per kg of diet (220 g chopped straw per kg).

The influence of the level of dry-matter intake and the dry-matter concentration in the diet on the water consumption of dairy cows in early lactation was investigated for a 2-month period from early August to early October. The importance of the various components of weather on voluntary water intake was also examined. The cows used in the experiment either grazed pasture alone, or were offered pasture and pasture hay supplements. Mean voluntary water intake increased by 2·30 kg per cow per day for every additional kg dry matter consumed and also increased by 0·053 kg per cow per day for each g/kg increase in dry matter concentration. Of the climatic factors, rainfall had the greatest single influence on the daily fluctuations in voluntary water intake and this was negative. Intake was also negatively related to minimum temperature, relative humidity and wind, and positively related to sunshine and evaporation. Although maximum temperature per se had no apparent influence on intake, it showed a positive relationship after the removal of the effects of rainfall. A model for the prediction of total water consumption is:

Total water consumption (kg per cow per day) = 11·34 + 4·63 dry-matter intake (kg per cow per day) –0·036 dry-matter concentration (g/kg) + 0·84 mean temperature (°C).

This can only be used to predict the water requirements of lactating dairy cows in different environments.

The relations between the gross energy concentration of milk and its concentration of fat and protein were calculated for samples of Jersey and Friesian milk. Stage of lactation and level of feeding had no consistent effects on the relations.

The calculated equations can be used to predict the energy concentrations of milk from Jersey or Friesian cows fed on pasture, from the concentrations of fat alone or from the concentrations of fat and protein. The predicted values agree with those predicted by earlier published equations.

A urfia-formaldehyde-molasses complex appeared to be a promising slow ammonia-releasing urea derivative in in vitro studies. It was compared with urea-molasses mixtures as a non-protein nitrogen supplement to an ad libitum wheat chaff ration for steers. The significantly lower (P < 0·01) crude protein digestibility and intake of digestible crude protein, and the non-significantly lower nitrogen retention on the urea-formaldehyde-molasses complex ration revealed the superiority of simple urea-molasses mixtures as a non-protein nitrogen supplement.