1. An experiment is described in which the individual feed intakes of 16 cows under winter housing conditions in yards, during the transition to spring grazing and on. summer grazing, were determined by faecal indexdigestibility methods. The influence of quality of feed before calving on intake and subsequent performance and the influence of pasture quality and availability on feed intake were included in the study.

2. The provision of a diet of 67% organic matter digestibility, either as high quality hay or as low quality hay with concentrates, increased feed intake before calving when compared with a diet of low quality hay (digestibility 62%) alone. Compared with previous lactation yields the better diets were associated with the maintenance of milk yield, while the low quality hay diet before calving was associated with a 10%, but non-significant, reduction in milk yield.

3. There was a marked rise in faecal output and digestible organic matter (DOM) intake after calving. During lactation, and especially on pasture, faecal output and DOM intake were both correlated with milk yield and metabolic live-weight. Total DOM intake was lower when the availability of feed was restricted and increased when feed was readily available; this increase was associated with a high maintenance requirement.

4. When herbage with OM digestibility of 74–82% was consumed, faecal output rose with decreasing digestibility, but DOM intakes were relatively constant. Provided that efficient utilisation can be achieved, total utilisation per acre might be increased if herbage were grazed at the lower end of this range of digestibility.

Four litters each containing six female pigs were used to compare the influence of the level of feeding of suckled pigs on subsequent weight gain and efficiency of feed conversion, and on carcass quality and ham composition.

The high level pigs always remained on their dam until weaning at 56 days of age and had free access to a starter ration from the beginning of the 4th week of age. From 7 days of age until weaning the low plane pigs were removed from their dam for 12 hours per day and had no access to starter ration during this time. After weaning the pigs were fed ad libitum on dry feed.

It was found that live-weight gain and feed conversion efficiency during fattening were increased by lowering the feed intake of pigs in the first weeks of life. There were no statistically significant differences between the different butcher's joints of the two groups. Although the differences were statistically non-significant, the ham of the low level pigs had a higher protein content (P = 0·06), a higher water content (P = 0·10), a lower fat content (P = 0·07) and a lower energy content (P = 0·12).

Regression analyses were made of the inter-relations among weights at day-old, 3 and 8 weeks, teat order, social order and litter size in 41 litters of young pigs.

Birth weight and teat order accounted for 40 % of the variation of 3-week weight within litters. Social rank was strongly influenced by 3-week weight, but not by birth weight or teat order except through their effects on 3-week weight. About 70% of the within-litter variation in 8-week weight was attributable to 3-week weight and social rank. Of the total variation in 8-week weight about 55 % could be explained in terms of the other variables. The effect of litter size on 8-week weight appeared to differ considerably in the Berkshire and Large White pigs used in this study.

On the assumption of a causal sequence in time, the within-litter variation in 8-week weight was partitioned into fractions of 19% due to birth weight, 5 % due to teat order, 29 % due to 3-week weight and 17 % due to social rank.

This experiment was designed to compare the average performance of Charollais-Hereford and Hereford-Charbray calves with the average performance of purebred Hereford and Charbray calves as a measure of hybrid vigour in various traits of economic importance.

The ratio of lumbar length to carcass length was larger in the crossbreds. With this exception there was no significant difference between purebreds and crossbreds in any of the measurements that characterise performance of the live animal or the carcass. However, the trend of the carcass measurements possibly indicated that the purebreds were fatter and higher in carcass grade than the crossbreds.

Studies on three cuts of meat from each carcass indicated larger cooking losses (percentage drip loss) in steaks from purebreds and larger ‘shear’ values for steaks from crossbreds. The panel of judges found no significant differences in tenderness, flavour or juiciness. There were no significant differences in colour of lean meat from crossbred and purebred animals.

Meat from the purebred Herefords appeared fatter and more tender than that from the Charbray cattle, but this comparison may be biased due to sire differences.

Groups of Friesian bull calves were reared on a high intake of milk substitute for either 21 or 28 days, and were then weaned over 7 or 14 days. Dried grass cubes were offered, as the only source of solid food, for 6 weeks from the start of weaning.

The rate of increase of solid food intake of calves weaned from 28 days was considerably greater than that of calves weaned from 21 days, and the later weaned groups were less severely affected by weaning. There was little difference in either the development of solid food intake, or in the severity of the weaning check, between groups weaned at different rates, though the slower rate of weaning tended to delay the intake of solid food temporarily.

The severity of the post-weaning check was inversely related to age at weaning, but was not affected by weaning weight. Growth after weaning was not related to either weight or age at weaning.

There were significant correlations between weight or age at weaning and solid food intake 5 weeks later, and a close correlation between the level of liquid intake established before weaning, and subsequent solid food intake. It was not possible to evaluate the effect of each of these variables, in isolation, on food intake after weaning.

All possible inter-age genetic correlations were calculated for each of twelve linear body measurements taken at 3-monthly intervals up to 2 years of age on 120 pairs of uniformly reared, liberally fed one-egg and two-egg twin dairy heifers. Genetic correlations between first and second-year mean size are also given. The influences of age, age interval, degree of maturity and body part on genetic correlation are examined.

Genetic correlation was in general very high. No significant difference was found between body parts in mean genetic correlation over the period studied. For a fixed age interval, genetic correlation increased with age; from a fixed age, it decreased with lengthening age-interval.

The main systematic trends found in the data were accounted for in terms of the amount of development taking place. Genetic correlation appeared to decrease exponentially with difference in degree of maturity, and a formula is given for calculating an approximate value for the expected genetic correlation between size at any two ages. Its range of applicability and its place in a general study of the genetic properties of a population of growth curves are discussed.

Pellets of chromic oxide (Cr2O3) and dental plaster for administration of Cr2O3 to ruminants were developed by Pigden and Brisson (1957). When Cr2O3 was administered to sheep in this manner, Troelsen (1961) observed that digestibility coefficients determined by the Cr2O3-ratio method were very variable, and deviated from those obtained by total collection of faeces. It was also observed that the rate at which the pellets disappeared from the rumen or reticulum was correlated with the percentage of alfalfa hay (r = 0 83) and oat grain (r = –0 80) in the diet and that the abomasal ingesta contained pellets or pieces of same in the process of disintegration.

Three methods were used to make differential counts of living and dead bull spermatozoa in samples of frozen semen in an egg-yolk citrate medium containing glycerol.

With two methods (‘phase’ and ‘nigrosin’ methods) dead spermatozoa were identified by their altered structure. With a third method (nigrosineosin) dead spermatozoa were identified by their staining affinity. With the phase method spermatozoa were immobilised by treatment with approximately M/40 sodium fluoride and were examined by phase-contrast microscopy in unfixed wet preparations. With the other two methods the spermatozoa were examined in smears stained either with nigrosin alone (nigrosin method) or with nigrosin and eosin (nigrosin-eosin method).

Analysis of variance of the results of a factorial experiment involving fluoride-treated and untreated samples from 6 bulls with the three methods showed that differences between semen samples contributed 66% of the variation. A defect of the phase method was that the variance between counts was greater than the theoretically expected value.

All spermatozoa in nigrosin-eosin stained preparations were stained with eosin within a few days of the smears being made, so that living and dead spermatozoa could not be distinguished by their differing affinities for eosin. Repeat counts on nigrosin-stained preparations did not differ significantly from counts made several days previously. Sodium fluoride in the concentration used here (M/40) tended to reduce the percentage of dead spermatozoa.

1. An experiment is described in which 194 pairs of piglets on 10 commercial farms were reared out of doors with access to soil, either on free range or in field pens. One piglet from each pair received 200 mg. of iron as a parenterally administered iron dextrin complex. The soil type and the iron content of the soil were determined on each farm.

2. During the first 8 weeks of life, the treated piglets showed a small but significant positive growth response of 1–2 lb. (3·0%). The response was greater (2·1 lb.) in piglets reared in field pens, but was non-significant in those reared on free range.

3. Differences in blood haemoglobin levels, mortality and the incidence of runt piglets were not significant.

4. Total body iron increased during the first 3 weeks of life by a mean of 339 mg., of which approximately 295 mg. appeared to be derived from the soil.

1. All-concentrate diets given ad libitum and containing different levels of fish meal, and varying in crude protein content from 16 to 22% in dry matter were given to eight Friesian steers at 150 kg. and at 240 kg. live-weight.

2. At a mean live-weight of 150 kg., the retention of nitrogen increased significantly to a maximum of 41.5 g. per day on the diet having 22% crude protein in dry matter. At 240 kg. live-weight, the maximum retention of 37 g. per day was achieved at 20% crude protein in dry matter.

3. Faecal nitrogen excretion per unit of metabolic body weight was approximately constant at all protein levels and at both live-weights.

4. Urinary nitrogen excretion per unit of metabolic body weight increased with increasing crude protein level in the diet and for any crude protein level was higher at 240 kg. than at 150 kg. live-weight.

In 1956 the authors showed that formalin could be satisfactorily used for the preservation of skim milk subsequently given to growing pigs from weaning to slaughter (Barber, Braude and Mitchell, 1956). Since then a large proportion of the skim milk used by pig producers in this country has had formalin added to it. No evidence from controlled experiments was hitherto available concerning the value of formalin-treated skim milk for the sucking pig, and it was for this purpose that the experiment reported was carried out.

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.

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.

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.

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.

Progress by selecting in a single line for overall merit is compared with the progress by selecting and crossing specialised sire and dam lines. The sire line is selected for growth and carcass traits, the dam line for number of offspring produced. The rate of improvement through specialised lines is never less than that in a single line and can be considerably greater but only i f there is an unfavourable genetic correlation between progeny number and performance and if there is a certain balance between the heritabilities and economic weights of the two sets of traits. In a sire line the selection may ignore progeny number without loss in efficiency but in a dam line progeny growth and carcass performance must be considered in addition to the number of offspring or else substantial losses in the efficiency of improvement may be suffered.

From estimates of the relative economic weights and relative heritabilities of number of progeny produced and the efficiency of feed conversion in several meat species it was concluded that selecting in specialised lines will have little advantage over selecting for overall performance in a single line.