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.

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.

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.

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.

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.

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. 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.

Animal Production, Volume 6, Part 1, p. 53

In Table 5, the identification numbers of twin pairs should read 3, 4, 1, 2 (and not 1, 2, 3, 4)

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.

The teat preference system of sucking behaviour in young pigs has been described by Donald (1937), Braude (1948) and McBride (1963). Briefly, the piglets develop a preference for particular teats during the first few hours of life. Though they may change their teat, particularly during the first two days, they then drink from the same teat or teats until weaning. It is the aim of this note to record some information on this teat preference system collected on litters farrowed at the Queensland Agricultural College at Gatton.

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.

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.

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.

1. Three group feeding trials and two individual feeding experiments, involving a total of 202 pigs from 8 to 10 weeks of age to bacon weight, were conducted to determine the effect of processing (steaming, followed by rolling and grinding) of maize and barley on pig performance. The effect of supplementation of raw and processed cereal diets with two crude enzyme preparations was also studied.

2. Processing of maize or barley had no significant effects on rate of growth or efficiency of food utilisation in pigs fed on diets containing a proportion of bran and pollard, or of pigs fed on diets in which maize or barley constituted the entire cereal portion.

3. Neither enzyme preparation affected pig performance.

4. The growth rate and efficiency of food utilisation of pigs given diets high in maize were significantly better than for those given diets high in barley.