Mice were selected for high and low growth (i.e. weight gain from 3 to 6 weeks of age), within litters for thirteen generations. This was carried out on a full and on a diluted diet which provided a good and a poor plane of nutrition. A randomly bred control line was maintained on each diet. Responses to selection were obtained in both directions and on both diets, although the diluted diet was subject to an unexplained deterioration. The indirect responses on either plane of nutrition were equal to the direct responses on the same plane. Hence selection for growth could be as well carried out in the environment in which the animal was to perform, as in any other environment. These results were discussed in relation to similar studies and to their practical implications.

Continuous measurements of heat loss throughout the 24 hours have been made on groups of pigs living in a large direct calorimeter equipped as a pig pen. Five experiments, each lasting 24 days, were carried out on groups of six pigs each weighing about 20 kg, and these were repeated when body weight was 60 kg on groups of three pigs, chosen from the original six in each case. Each group was exposed initially to an environmental temperature of 20°C for 10 days, followed by either 9°C (two groups at each weight), 30°C (two groups at each weight), or a continuation of 20°C (one group at each weight). In another experiment lasting 66 days a group of four pigs was exposed to 12 and 20°C at two levels of air movement.

Heat loss from the groups showed a marked 24-hr cycle, with a maximum n i the afternoon and a minimum in the early morning. The mean amplitude of the cycle at 20°C was 20% of the mean value; this proportion increased at 9 and 12°C.

Heat loss was approximately proportional to (body weight)1·0 over the weight range 17·34 kg, and to (body weight)0·8 over the weight range 35·54 kg, when food intake increased in proportion to (body weight)1·0. Over the weight range 55·67 kg, when food intake was constant at 1·83 kg/day per pig, heat loss was proportional to (body weight)0·4. In both 20 and 60-kg pigs, heat losses showed little difference between 20 and 30°C, but were increased at 9°C.

Evaporative loss from the pen, as a proportion of total heat loss, was approximately 21% at 9°C, 29% at 20°C, and 61% at 30°C. Voluntary water intake exhibited a marked 24-hr cycle similar in timing to the heat loss cycle.

There was no lasting effect on heat loss associated with raising the mean air movement rate in the pen from 10 to 26 cm/sec.

Rectal and surface temperatures, and respiration and pulse rates, were obtained for groups of Duroc pigs that were exposed to air temperatures that varied sinusoidally over a 24-hour period. Two groups averaging 37 and 108 kg were exposed to a constant temperature of 21·1°C and then to temperatures that cycled about a mean of 21·1°C (15·6–26·7°C, 10·0–32·2°C, and 4·4–37·8°C). For a third group averaging 53 kg, the minimum was always near 21·1°C, and the maximum air temperature of the cycle was 33·2, 42·5 or 48·8°C.

The response of rectal and surface temperatures, and pulse and respiration rates, to the various 24-hour cycling air temperatures are discussed and com-pared with inherent daily fluctuations in these responses that are present even when there is no variation in air temperature.

Three sheep with permanent fistulas of the rumen were each given dried grass and two hays, each in three different amounts, and the apparent digesti-bility of the roughages in the rumen and distal to the rumen was determined. A lignin ratio method was used to measure digestibility.

With increase in the amount of the poorest hay given, the proportion digested in the rumen fell and that distal to the rumen increased. With the second hay this effect was also noted but was not statistically significant. The voluntary intakes ofdry matter varied from 1·94 kg/day for the dried grass to 1·28 for the poorest hay. The volumes of distribution of polyethylene glycol in the rumen when feed was offered ad libitum, however, were the same, irrespective of the type of feed, at between 14·1 and 15·2 litres. These observations were confirmed at slaughter. The results support the hypothesis that sheep voluntarily consume roughages of different qualities to achieve constant fill of their rumens, and that little regulation of voluntary intake can be attributed to distension of the hind gut.

A group often female and five male Finnish Landrace sheep were taken to Scotland in 1962. In subsequent purebreeding for four years they and their offspring have shown average litter sizes (at birth) of 2·0, 3·0 and 3·4 for ewes aged one, two and three or more years respectively.

Body weights of breeding ewes prior to mating were on average 72, 106 and 128 lb for ewes of the three age groups.

Mean ewe fleece weights were 4·5 lb with the wide range of 1·7 to 7·1 lb due in part to some shedding of fleece wool in spring. The quality of the true wool in the undercoat was estimated at 54–56's.

1. Two experiments are described in which the effects of ammonium acetate on the yield and composition of the milk from heifers given (1) a fat-depressing diet consisting mainly of cereals or (2) a normal diet of silage and sugar beet pulp for maintenance and rationed concentrates according to yield.

2. In the first experiment acetate increased the content of butterfat in the milk from 2·76 to 3·12. This difference was almost significant (P < 0·1). There was no significant effect of acetate on the total solids content of the milk.

3. In the second experiment acetate very slightly depressed the total solids and the butterfat content of the milk.

4. In Experiment 1 there was no significant difference between treatments i n the pH of rumen liquor, or in its concentration of total steam volatile fatty acids, but the proportions of acetic and isobutyric acids were higher on the acetate treatment.

5. In Experiment 2 there were no differences in the relative proportions of the fatty acids although the total steam volatile fatty acid concentration was higher on the acetate treatment.

Experiments were carried out to measure the effects of wearing jute coats on the heat production and external insulation of Blackface and Cheviot sheep during exposure to different types of cold environment. The results showed that wearing coats did not appreciably increase external insulation in cold conditions at wind speeds up to 10 mph when the fleece was dry. In cold, wet and windy conditions, wearing coats prevented moisture from penetrating the fleece of the sheep so that external insulation was 25–27 units when the sheep were wearing coats, but only 15–18 units when they were not.

It has been shown that few environments likely to occur in Britain constitute a cold stress for grazing sheep if their external insulation is above 25 units. Wind and rain reduced the external insulation of sheep with full winter fleeces below this value only when they were not wearing coats. It is concluded, therefore, that jute coats have a considerable value in ameliorating the effects of cold stresses of the type likely to be encountered by hill sheep wintered out of doors in the British Isles.

1. An analysis has been made of the association between transferrin genotype and progeny test for both milk yield and fat content in a sample of 879 bulls of five dairy cattle breeds, the majority used in artificial insemination in Great Britain. Although significant effects were found in only one of the ten analyses when the breeds were considered separately, a significant effect on milk yield was found when the results from all breeds were combined. A significant effect was not found for fat content, although the effects of the allele substitutions were in the opposite direction to that on milk yield in five cases out of six.

2. Although our results were in the same direction as those of Ashton, the effects were smaller. It was estimated that the locus accounted for 1·1% of the genetic variation in yield and 0·4% of the genetic variation in fat content.

3. Some information based on the production records of 178 experimental cows with known genotypes was also analysed. For milk yield, the pattern of effects was similar to that in the sire data though the differences were much larger. The variance removed by fitting constants was not statistically significant for milk yield or fat content. It was estimated that the sire data contained some fifty times as much information as did the cow data.

1. Investigations into possible ways of rearing artificially the lambs surplus to the ewe's capacity are described and the results discussed.

2. A ewe-milk replacer with a high fat content was used from 2 days of age until weaning at 11.4 kg live weight. Two levels of milk feeding, restricted and ad libitum, were given in the second year. Significant differences were observed in live weight gain per day, milk consumption per kg live weight gain and solid food intake prior to weaning. Live weight gain and solid food intake in the period immediately after weaning also differed markedly. Sex and birth weight had little effect on performance.

3. Food costs were lower on the restricted level of milk feeding than on the ad libitum level.

1. Two experiments concerned with the voluntary intake of food by artificially reared lambs are described and the results discussed.

2. When the diets were pelleted the addition of finely ground oat husks to form as much as 40% of the diet had practically no effect on live weight gain since the lambs controlled their consumption to achieve the same energy intake on the various diets. When the diets were given as a meal, the addition of 20% oat husks caused food intake to increase, digestible dry-matter intake to remain the same and growth rate to be somewhat poorer; but the addition of 40% oat husks caused no further increase in intake so that digestible drymatter intake fell markedly and growth rate was much reduced. It is argued that the relationship between food intake and digestibility is dependent on the physical form of the diet.

3. Addition of beef tallow to the meal diets had very little effect on the lambs' performance.

4. Lambs which had received a restricted quantity of milk replacer from birth to 11·4 kg live weight had a slower growth rate and poorer food conversion efficiency during the subsequent feeding period (13·6–34·1 kg) than lambs which had received milk ad libitum. This effect was greater with meal diets containing 40% oat husks than with more concentrated diets.

5. On a pelleted diet containing 85% barley a conversion ratio of 3·21 was achieved over the whole fattening period, indicating the commercial feasibility of intensive lamb production on cereal diets.

The aim of the investigation was to evaluate the specific effect, if any, of grass protein on the birth weight of lambs born to ewes wintered indoors. Grass meal was used as a substitute for fresh grass, and soya bean meal—representing a more conventional source of protein for winter diets—was compared with it. Both sources of protein were included at two levels, providing a high (90 g or 0·2 lb/day) and a low (45 g or 0·1 lb/day) intake of digestible crude protein.

The digestibility of dry matter was significantly higher for the diets containing soya bean meal (67·7%) than for those containing grass meal (58·2%). Dry-matter digestibility was not affected by level of protein intake. The digestibility of crude protein was significantly affected by protein source and level of intake.

Lamb birth weights were not significantly affected by source or level of dietary protein. There was a tendency for birth weights to be higher on the diet containing grass meal at low protein intakes. Ewe weight gains during the last eight weeks of gestation were significantly affected by level of dietary protein, and net body weight change was significantly affected by both source and level of protein. Gestation treatments had no effect on the performance of ewes or lambs during the first three weeks of lactation.

The retention of nitrogen during the 18th–20th weeks of gestation was affected by both source and level of dietary protein. Mean nitrogen retention was higher with diets containing soya bean meal (5·8 g per day) than with diets containing grass meal (3·6 g per day). There was no correlation between nitrogen retention and lamb birth weight.

Thirty-seven Blackface wether sheep, ranging from birth to eighteen months of age, were used to derive the allometric relationship between carcass muscle and carcass bone.

The equation

log10 muscle (g) = 1·36 log10 bone (g)—0·804

fitted the data well. (r = 0·995, b = 1·36±0·05, Sy.x = 0·0595.)

The deviations from this equation had a coefficient of variation of 14% indicating that other factors may influence the relationship of muscle to bone.

It is suggested that the variable

log10M—1·36 log10 5 + 0·804

is independent of differences due to different stages of natural development and can be used to examine the effects of different treatments on the muscle: bone ratio. The constant applies to sheep only.

1. A factorial split-plot experiment was conducted to investigate the growth of entire and castrate male pigs on conventional diets and diets containing higher levels of protein. Thirty-two Large White pigs were fed ad libitum from 50 lb to slaughter at 260 lb live weight. The carcasses were dissected.

2. The live-weight gain of entire males was the same as that of castrates on the conventional diet, but they grew non-significantly faster than castrates on the higher protein diet.

3. The entire males had a lower dressing percentage and less fat in the carcass than the castrates, but more lean, bone and rind, and a similar lean: bone ratio. The leanness of the entire males was increased on the higher level of dietary protein whereas the leanness of the castrates was unaffected except in the leg. The interactions were not significant.

4. The carcasses of the entire males were proportionately heavier in the head and shoulders and lighter in the middle than those of the castrates.

5. The majority of the entire males had flesh with a slightly tainted flavour.

Three trials with pregnant sows tied in stalls have been conducted to measure the effects on ration digestibility: (a) of a pelleted compound given once or twice per day, (b) of half the daily ration fed as barley at a separate time from the pelleted concentrate and (c) when the order during the day in which the barley and concentrate were fed was reversed.

Giving pelleted complete rations twice as opposed to once per day led to slight improvements in the apparent digestibility of dietary dry matter, grpss energy, crude fibre and phosphorus. When half the daily ration was given as crushed barley in the morning the apparent digestibility of phosphorus was slightly higher than it was when barley was given in the afternoon. Nevertheless the apparent digestibility of dry matter and crude protein was greater for the complete mixture given twice per day. All these effects were statistically significant.

In experiments involving measurements on beef carcasses, the animals can be slaughtered at a given degree of fatness, at a prescribed live weight or at a prescribed age. The ultimate choice depends upon the purpose of the experiment but where comparisons are being made between different breeds receiving the same diet it is usual to slaughter animals at the same degree of fatness. This subjective assessment of the time at which the animals are to be slaughtered results in widely different slaughter weights and ages. In order to aid the interpretation of results, Pomeroy (1965) suggested that animals should be killed at at least three different live weights so that an estimate of the rate of change of various parameters can be derived.

Perry (1964) has shown that piglets failed to absorb homologous Brucella abortus antibodies, whereas they absorbed homologous Salmonella pullorum antibodies much more readily. When S. pullorum antibody was used, piglets showed marked differences in their efficiency of absorption. These differences existed whether the antibodies were administered in serum or in colostrum (Perry and Watson, 1967a, b). Moreover, they could not be entirely accounted for by variation in concentration of antibody in the dose, age at dosage, genetical effects or maternal effects (Perry and Watson, 1967a).

Chromic oxide (Cr2O3) has been used for some time as an inert marker to estimate the faecal output of livestock. Although several methods of administration have been reported (Grassland Research Institute, 1961) the more widely used form would appear to be that of purchased gelatin capsules containing a suspension of Cr2O3 in maize oil. An alternative is to include the Cr2O3 in a concentrated feeding stuff. This method was widely used by early workers (e.g. Edin, Kihlén and Nordfeldt, 1944).

Diethylstilbestrol (DES) implants have consistently increased the weight gains and feed efficiency of 5 to 7 month old fattening lambs. The effects of DES on young sucking lambs is less well delineated. Twelve mg DES implants used by Perry, Andrews and Beeson (1951) and Clegg, Albaugh, Lucas and Weir (1955) and 3 mg DES implants used by Lewis, Hines and Mansfield (1966) resulted in significant increases in weight gains of 6-to 14-week-old lambs. Conversely Jordan and Dinusson (1950), Jordan (1953) and England (1959) using 3 mg implants reported no significant increase in weight gains of 2- to 4-month-old grazing sucking Iambs. Wilkinson, Carter and Copenhaver (1955) implanted 6 to 8 week old grazing, sucking lambs with 10 mg of oestradiol and 250 mg progesterone. No increase in weight gains resulted and 5 of 28 lambs treated were lost from prolapse of the rectum.