1. Peck order position was assessed by aggressiveness scores for birds housed intensively on deep litter on the floor and in cages.

2. Relationships were shown between scores and egg weight, egg number and egg mass for the birds on the floor but not for the caged birds. The nature of the relationships found was discussed.

3. The correlation between egg weight and egg number was higher in the flock on the floor than in the caged flock. This appeared to be due to a significant positive correlation among the lowest scoring birds on the floor.

The litter production of various purebred and crossbred groups of pigs were studied in data collected from 1959 to 1961 on some 34,800 litters recorded on over 800 farms in Britain. A least squares analysis was performed to obtain within-farm estimates of performance for five litter traits in sixteen specified breeding groups and to analyse the total variation in litter performance.

The ranking of the purebreds and crossbreds is presented. In general there was a lower mortality in crossbred litters which had 2 % more pigs at birth and 5 % more pigs at weaning than purebred litters. The total litter weight at weaning was 10% greater in crossbred litters. Crossbred sows showed more heterosis with 5 % more pigs at birth, 8 % more pigs at weaning and an advantage of 11 % in total litter weight at weaning.

Farm differences accounted for a major portion of the total variation n i litter production, 8–9% for litter numbers and 15–25% for litter weights. On the other hand the interactions of farms and breeding groups, though highly significant, contributed only 1–2% of the total variation in litter production.

1. The normal pattern of social behaviour in growing Large White and Berkshire pigs is described. The pigs were observed from 8 to 16 weeks of age in pens of 6 to 10 pigs. Large Whites were more aggressive than Berkshires.

2. Social rank was found to be positively correlated with initial weight.

3. Initial weight and social rank both influenced growth; the relative effect of rank compared with that of initial weight was greater in the second month than in the first.

4. The contribution of social rank to the total variance in growth over the 2-month period was estimated at about 13%.

5. It is suggested that the use of individual housing in pig progeny test schemes may not be desirable because of the absence of social environmental effects.

1. From a review of the literature it has been shown that there are two opposing views regarding the best method of interpreting growth data, which arise from conflicting opinions as to the role of fat deposition in the growth of the animal.

2. Data of McMeekan and Palsson and Verges have been re-analysed and their own results are compared with results obtained when the effects of variation in fat content are eliminated.

3. No evidence has been found of any effect of plane of nutrition on the total weights of bone and muscle relative to the weight of bone plus muscle together.

4. The weight of bone plus muscle in the head and neck was increased relative to the total weight of bone plus muscle during periods of restricted nutrition. Apart from this there was no clear evidence of a relationship between the order of maturity of the joints and their relative retardation of development.

5. Huxley's allometry equation was found appropriate for standardising the measurements, and the exponent was taken as a numerical expression of the relative maturity of each tissue or part.

Data on 1,795 Scottish Blackface sheep were examined to see what effect treatment during the animal's first winter had on subsequent performance. Two treatments were used, wintering on the hill with the breeding ewe flock, or wintering away on low-ground farms. Away-wintered sheep gained on average about 16 lb. more than hill-wintered sheep between 6 and 12 months of age. These live-weight differences declined with age to about ⅔lb. at 5–6 years of age. Away-wintered sheep also had heavier first fleeces by about fIb. on average and had a lower mortality rate. However, differences in subsequent fleece weights and lamb production were small and not sufficient to cover the cost of away wintering.

Behaviour observations and measurements were carried out on three classes of beef steers kept in yards under drought feeding conditions. The classes were (i) 2-year-old Brahman × Hereford crossbreds, (ii) 2-year-old Herefords and (iii) 3-year-old Herefords.

Animals of each class were placed in two groups and fed on low quality bush hay, one group ad lib. and the other on a restricted basis. An intermingled group comprised two animals from each class and was fed ad lib.

Fairly stable linear social orders were observed in each yard, social success depending mainly upon height. In the intermingled group, the crossbreds dominated the 3-year-old Herefords, which in turn dominated the 2-year-old Herefords.

Crossbreds bunted more actively and were more often disturbed at feeding during the day. They consequently consumed proportionately more feed at night than the Herefords.

Although high social ranking animals had priority at the feed trough there was no relationship between social rank and growth.

The orders in which the 2-year-old Herefords and crossbreds entered a crush were non-random. These orders appeared not to be related to social rank.

1. Wool production and fleece structure were studied by fibre analysis in six groups of lambs subjected to different pre- and post-natal levels of nutrition. Samples were taken at 6, 12, 28 and 48 weeks of age.

2. Pre-natal limitation (twin pregnancy) reduced the number of secondary fibres present at birth but, providing post-natal nutrition was adequate, this difference had disappeared by 6 weeks. There were no permanent effects on fibre number, wool production or fleece structure.

3. Severe post-natal restriction of feed intake during the first few weeks of life had a marked effect on the development of the secondary fibre population, on wool production and on the birthcoat shedding cycle. The effects persisted beyond the period of nutritional limitation but had disappeared by 12 months of age.

4. The results are discussed in relation to the normal development of the adult Blackface fleece.

Milk production records from 5740 first lactation Holstein-Friesian daughter-dam pairs were studied to determine if heritability was related to herd production level. Heritability from daughter-dam regression was essentially constant at 10 environmental levels based on either the dam's or daughter's herdmate deviation from season average yield. The heritability estimate over all levels of yield was 0·43 (with standard error 0·03) which is higher than most estimates. Estimates of heritability from paternal half-sib correlations for four environmental levels and based on data from 2568 daughters of A.I. sires generally increased as the herd production level increased. The highest half-sib estimate was 0·42 and the lowest 0·17. Daughter-dam estimates from the same data were essentially constant over the four herd levels.

Total variation increased as herd level increased, in agreement with previous reports.

Heritability was found not to differ between seasons of calving.

1. Nitrogen balance studies have been conducted on eight early-weaned calves receiving four diets containing, respectively, groundnut meal, groundnut+lysine, groundnut+lysine+methionine and white-fish meal as the major protein source.

2. There were no significant differences between groundnut meal diets i n any of the measurements examined. On the fish meal diet all measures of nitrogen retention tended to be higher than the corresponding values for groundnut meals.

3. Daily live-weight gains were significantly higher on the fish meal diet than on any of the groundnut diets (P<0·05).

4. It is suggested that the supplementary amino acids, being highly soluble, were rapidly deaminated by rumen micro-organisms.

While it is generally agreed that fish meal protein is of high biological value for non-ruminants, variations in quality are known to occur as a result of differences in the nature of the parent material (Duckworth, Woodham and McDonald, 1961) or in the method of processing (Grau et al., 1959; Ousterhout and Snyder, 1961). Duckworth, Woodham and McDonald (1961) have shown that the Gross Protein Value offish meals can range from 92 to 119; within this range white-fish meals had a mean value of 102 while the mean value for herring meals was 113. Differences of a similar order have been reported by other workers (Record and Bethke, 1933; Heiman, Carver and Cook, 1939; Robertson, Carver and Cook, 1940; March, Stupich and Biely, 1949; Carpenter, 1954; Carpenter, Ellinger and Shrimpton, 1954; Duckworth, 1955).

1. Thirty Suffolk × Half bred lambs were slaughtered at the following ages: two twin lambs at birth and two singles and two twins at 1, 2, 3, 4, 6, 8 and 16 weeks of age.

2. The following weights were recorded: live-weight immediately before slaughter; and carcass, head, skin, feet, alimentary tract, heart, liver, kidneys, lungs and trachea, and blood immediately afterwards.

3. The alimentary tract was emptied and weighed in four separate parts; reticulo-rumen, omasum-abomasum, small intestine, large intestine.

4. The volumes of the reticulo-rumen and the omasum-abomasum were measured by immersing in water and filling the organs with water to 2 cm. pressure.

5. The in vitro digestive efficiency of rumen liquor from lambs of 1, 2, 3 and 4 weeks of age was assessed.

6. Empty body weight was considered to be valuable in comparing animals of different ages or from different feeding regimes or at different times of the year because variations in gut ‘fill’ were eliminated.

7. There were no differences between singles and twins in the relationship of the fresh weights of the parts of the body to empty body weight, except that development of the liver and the blood was rather slower for singles.

8. Little evidence was found of a difference in rate of development of the alimentary tract between singles an d twins, although the log an d square root transformation suggested a possible difference in reticulo-rumen size in favour of twins, significant at the 5% level.

Effects of castration on growth, wool production, carcass characteristics, and meat quality in sheep were investigated.

The experiment included two flocks (similar in their effect on pre-weaning performance, but representing high and low planes of nutrition after weaning), two years, and two slaughter ages. Rams weighed approximately 5 % more thanwethers at weaning, and 15 % and 23 % more as yearlings on the low- and high planes of nutrition respectively. Differences in favour of rams in terms of skeletal and muscle size and wool production were also greater on the higher plane of nutrition. Carcass weight was approximately 4%, 8% and 19% higher for rams among lambs, low plane and high plane yearlings, respectively. Proportion of carcass weight in the forequarters was 0·5 %, 1·1 % and 2·3 % higher for rams in these three groups. Rams had less kidney fat and the same percentage of the carcass weight in loin and trimmed leg as wethers in all groups.

Carcass grade and eating quality as evaluated by a taste panel did not differ between ram and wether lambs. Among the lighter yearling group, meat from the loin of ram carcasses was less tender. Quality was appreciably lower for rams in the heavier yearling group. Meat from ram carcasses had 1 to 2% higher cooking loss than that from wethers.

Sixteen blocks of eight littermate pigs were weaned at 3 weeks of age and each divided into four groups. Various levels of nutrition were applied to the pigs so that the four groups reached 20 kg. at 59, 68, 80 and 91 days of age, respectively.

Only small differences were observed between groups in feed conversion ratio to 20 kg.; however, Group 4 required more feed per kg. gain than the three other groups.

During the second period (20–90 kg.) the pigs in each group were divided into two sub-groups, which were on a high and a low plane of nutrition respectively. In both sub-groups the type of feeding before 20 kg. influenced the average daily gain and feed conversion ratio. The older the pigs were at 20 kg. the higher the daily gain and the lower the feed conversion ratio in the following period. There was an increase in daily feed intake with increased age at 20 kg. for pigs fed ad lib. during the second period.

An increase in age at 20 kg. caused a significant decrease in thickness of backfat, a greater area of eye muscle and a smaller area of fat overlying muscle. For pigs fed ad lib. the area of eye muscle was significantly increased by a higher age at 20 kg. live-weight.

Results have been presented from a small scale investigation into operational and theoretical aspects of progeny testing Down rams as sires of crossbred fat lambs. Twenty-six Suffolk rams were evaluated from the growth records of 922 lambs out of Border Leicester × Cheviot ewes. In addition measurements were recorded on 260 carcasses. Significant differences were found between corrected progeny means, which were equivalent t o heritabilities of between 0·03 and 0·13 for live-weights up to 15 weeks, and o t higher values for skeletal measurements.

A scheme for the selection of Down rams was considered which involved measuring the individual performance of all ram lambs and then progeny testing the best of these by measuring a fixed total number of crossbred lambs. It was concluded that the proportion to be progeny tested could be varied within quite wide limits without seriously changing the genetic merit of the selected group.

It has been estimated (Mason, 1963) that about 70% of beef stores bred in Britain are out of dairy cows. Some 30–40% of them are by beef bulls, so that about 40–50% of animals slaughtered for beef are of pure dairy breeding.

The possibility of using hormones to increase the productivity of meat animals has been considered for a number of years (Hammond, 1957 and Scarisbrick, 1960). Lamming (1957) has pointed out that most of the work with hormones and beef cattle has been done in the U.S.A. under feedlot conditions. In this country Aitken and Crichton (1956), Dodsworth (1957) and Lamming (1957 and 1958) all obtained increases in rates of gain with implantation. Lamming found that responses in steers varied from 0 to 15% increase in gain per day in spring, about 20% in summer, 40% in autumn, i n each case on pasture and up to 60% under winter feeding conditions. He also used several levels of implantation, from which it appeared that the optimum level was about 45 mg. hexoestrol. Smith (1958) described trials conducted at eight farms in the North of Scotland in which 189 steers fattened solely on grass were implanted with hexoestrol. Implantation resulted in an extra daily live-weight gain of about 0·5 lb. Increases in dose levels above 60 mg. produced no significant response in terms of live-weight gain. Eighteen experiments at Experimental Husbandry Farms and the Norfolk Agricultural Station, described by Jones (1961), also showed that live-weight gain was increased by implanting; that the correct dose to give maximum response appeared to be 45 to 60 mg. hexoestrol; and that the implant should be made from 100 to 130 days before slaughter. Second implantations were made in several of these experiments and it appeared doubtful if this practice was desirable. In New Zealand, Lucas (1958) and Everitt (1959) also found that hexoestrol implantation increased weight gains of grazing steers.

1. Body shape and carcass composition have been measured in a dated series of Romney-Southdown cross and Australian Merino sheep foetuses.

2. Large differences in shape exist between the two breed groups and these result from growth rate differences in certain components of the bone and muscle tissue.

3. Carcass composition at any particular foetal weight, however, is more uniform. In relation to body weight, the Merino has a higher proportion of bone in the body but the proportion of muscle is the same in both breed groups. Nevertheless, the distribution of muscle tissue is changed as there s i a higher proportion of muscle in the hind limb of the Romney-Southdown cross.

1. The effects of gonadotrophins administered during the follicular phase of the oestrous cycle were studied in forty gilts; these were purebred Large White or Large White crosses weighing from 200-275 lb.

2. Superovulation was induced by a subcutaneous injection of PMS; half of the animals received in addition an intramuscular injection of LH.

3. All animals which received gonadotrophins exhibited normal oestrous behaviour and only four of the gilts failed to come into oestrus by Day 21 of the cycle.

4. A relationship has been established between the PMS dose and the mean ovarian response.

5. An injection of LH was not essential for ovulation after treatment with PMS. Similarly, it had no significant effect on ovarian response.

6. Egg recovery was 75% in the group of animals that exhibited fertility. Of these eggs, 93% were fertilised and undergoing cleavage.

1. The data relating to 16 multi-location trials involving several varieties of egg-laying chickens per trial have been analysed to obtain estimates of variety × location (genotype-environment) interactions for rearing and laying mortality, hen-month and hen-housed egg production and 32-week egg weight. Significant interactions were found in about a third of the trials for all five traits though in only two cases did the interaction variance account for more than 20% of the total variance.

2. Genetic correlations for varieties between locations have been calculated as 0·49 for rearing mortality, 0·50 for laying mortality, 0·72 for hen-month production, 0·76 for hen-housed production and 0·91 for egg weight. These are in close agreement with previous published estimates.

3. The between-and within-variety components of variance have been calculated for each trait on each location separately. The regressions within trials and pooled values of the components on the mean level of all varieties on the location have been calculated. For hen-month production the pooled regres-son of the within-variety component on mean was negative, whilst for all other traits the pooled regressions were positive. The pooled regressions of the between-variety components on mean were all positive. It is suggested that this information indicates that comparison of varieties for single traits should be carried out on locations favourable for maximum expression of the trait. The difficulties which variety comparisons, for several traits having different optimum management regimes, would cause and the need for a more intensive investigation of the conditions conducive to genotype-environment interactions are stressed.

The effects of maternal age and birth weight on survival of twin lambs has been studied in a Blackface and a Welsh Mountain flock. The time of death was also investigated for both singles and twins.

Twin mortality was higher than mortality of singles, mainly due to the lower average birth weight of twins. Twin mortality declined with increasing birth weight although it showed a tendency to increase at the top of the scale. Weight for weight, mortality was similar for singles and twins. Twin mortality declined with increasing age of ewe in a very similar pattern to single mortality.

Lamb mortality was heavy at birth and during the first 14 days of life with only 30% of the mortality occurring after this age. Approximately 12% of the dead lambs were stillborn. Among singles a similar proportion died as a result of difficult births, but this cause of mortality was rare in twins.

Stillbirth mortality rates were very high for very small birth weights and declined with increasing weight of lamb. Difficult births, on the other hand, increased with increasing birth weight. The association of birth weight with mortality was particularly important in the first 14 days of life but thereafter its significance was less.

Although mortality in lambs of younger ewes was heavier than that of older ewes, similar causes of death operated. Younger ewes, however, having lower birth weights tended to have more stillbirths but few losses due to difficult lambings.