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.

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.

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.

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.

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 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.

A study has been made of the performance of crosses and backcrosses of Bos taurus and Bos indicus cattle using records covering a period of 15 years from the Experimental Station, Tanga. The gene combinations found in ½-bred animals were the most productive in this environment, and ¼-bred Bos taurus animals gave higher average daily yields of milk between calvings than those with ¾ taurus blood.

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.

1. Four groups of diets made up with differing proportions of roughage and concentrates were each given ad lib. to 4 Blackhead Persian wether sheep. The four diets in each group contained approximately 4, 6, 8 and 10% crude protein. The distribution of nitrogen in the rumen at various times after feeding and the nitrogen balance of the sheep were measured.

2. Total N and ammoniacal N content of the rumen liquor were both closely related to the N content of the diet. Diurnal changes in the concentrations of these components were most marked with the diets which had the highest concentration of protein, and consisted of rapid increases after feeding followed by declines later in the day. Each group of diets produced characteristic patterns of change and these changes appeared to be related to the proportion of concentrates in the diet.

3. With sheep given poorly digested veldt grass, very low in protein, levels of ammonia in the rumen were unusually high. This effect was thought t o be due to the recycling of urea and its conversion to ammonia in the rumen.

4. The amounts of digestible N required by the sheep for N equilibrium differed between groups of diets. High apparent requirements of digestible N were associated with relatively high ruminal ammonia levels, but the latter were not considered to be the cause of high requirements.

5. On all groups of diets, sheep were in N equilibrium only when their intakes of total digestible nutrients (TDN) were adequate for maintenance. This indicates that the protein requirement for maintenance was a function of protein content and TDN content of the diet and the effect of these factors on voluntary intake of TDN.

Six comparable groups, each of 4 castrate pigs, were used to compare the feed value of maize and sorghum as estimated by live-weight gain, food conversion efficiency, slaughter quality and ham composition.

The maize ration contained 40% yellow maize and the sorghum ration 40% Sorghum vulgare subglabrescens, all other ingredients being the same for both diets.

No statistically significant differences were found between the maize and sorghum pigs with regard to the criteria mentioned.

It is concluded that no difference exists between the feed value of the maize and the sorghum used. This result is in better agreement with the net energy values of maize and sorghum as calculated by the formula of Hoff-mann and digestion coefficients for pigs, than with “classical” starch equivalents.

1. Normal rations containing oleandomycin (2·5 g./ton), oxytetracycline (10 g./ton) and oleandomycin (2·5 g./ton)plus oxytetracycline (10 g./ton) were given to females and castrates which had previously received creep feed with or without oxytetracycline.

2. Forty-eight pigs were individually fed on the rations from 50 to 200 lb. live-weight, a restricted scale of intake based on live-weight being adopted.

3. Pigs receiving the mixed supplement and those given oxytetracycline alone grew significantly faster and utilised their feed more efficiently than those given oleandomycin alone. Differences between the mixed supplement group and those receiving oxytetracycline were not significant.

4. Treatment with antibiotic, either in the creep feed or after weaning, had no effect on carcass measurements. Females had less depth of fat at the shoulder, mid-back and loin compared with castrates and the carcasses were significantly longer.

5. Visceral weights were not influenced by antibiotic treatment but pigs supplemented with oleandomycin had a shorter gut than those receiving a combination of antibiotics. There was a significant reduction in gut weight n i pigs which had received unsupplemented creep feed but no consistent effect on the thickness of the intestine wall or gut diameter. Females had significantly heavier kidneys and spleens than castrates.

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.

Foote, Tyler and Casida (1959) found that the birth weight of Holstein calves from the right horn was significantly heavier than that of calves from the left horn but found no significant effect of side on gestation length. In a further study Foote, Hauser and Casida (1960) found no effect of side of pregnancy on either birth weight or gestation length in an analysis of 128 gestations among Angus and Shorthorn cows. They did find, however, a significant interaction of breed and side of pregnancy on gestation length.

Natural scrapie can develop in sheep at any age later than about 18 months old. In order to formulate a realistic policy for experimental investigation of the disease as it occurs naturally, it is necessary to understand what factors might affect the incidence in sheep of different ages. Any attempt to use data from commercial sheep flocks to draw conclusions about the age distribution of scrapie cases must make allowance for the fact that the population at risk is being culled on commercial criteria and incurs losses by death from various causes.