1. The effect of A.I. on the structure of the pedigree British Friesian breed has been assessed from analyses of pedigrees of systematic samples of 221 registered females and 200 registered males born in 1960. Samples of 200 registered females and 200 registered males born in alternate years from 1946 to 1958 inclusive were used to estimate the trend in the proportion sired by A.I. bulls.

2. By 1960, A.I. had not affected the hierarchical structure of the breed and had not, therefore, narrowed its base. Current inbreeding was lower in artificially than in naturally sired stock but there was little difference between the two groups in the level of non-current inbreeding.

3. Over 50% of artificially sired stock were sired by bulls likely to have progeny test information. Of the naturally sired stock, only 17% of females and 29% of males were sired by such bulls.

4. 12·2% of genes of registered females born in 1960 derived from the 1950 importation from the Netherlands. At comparable points in time the contributions of earlier importations from the Netherlands were: 1914–39·9%; 1936–24·3%. The increased size of the pedigree breed and the development of progeny testing methods giving an earlier and more accurate assessment of the breeding worth of individual sires, probably contributed to the relatively small influence of the 1950 importation.

(1) Observations were made on a group of dairy bulls at pasture during the summer of 1964. The grazing behaviour of the bulls was similar to that of cows except that they were more sensitive to disturbance and the herd instinct as seen in cows was absent.

(2) Dairy bulls in a group formed a restless community. Apart from dis turbances within the group, the presence of men, dogs, vehicles and bulls from other groups could disturb the group equilibrium. The signs of disturbance were bellowing, pawing and horning the ground, fighting and outbursts of sexual activity.

(3) No clearly defined order of social dominance could be detected and the bulls retained their individuality at all times.

In two trials with 48 pigs it was found that when algae supplemented with certain B-vitamins replaced fish meal on an equal-nitrogen basis in a diet based on barley and fish meal there was no decrease in rate of gain or feed conversion efficiency. When vitamin B12 was omitted from the algal diet, there was a decrease in rate of gain. There were no consistent differences in carcass characteristics between pigs fed on the algal diets and those fed ondiets containing fish meal. Digestibility studies indicated that algae are low in digestible energy, but their protein is 70% digestible.

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.

1. The voluntary feed intakes of pigs fed on diets having calculated digestible energy contents of 2,970, 3,356, 3,630 and 3,910 kcal/kg. dry matter were measured over four periods from 38 to 105 kg. live-weight.

2. The pigs achieved similar daily digestible energy intakes regardless of the digestible energy content of the diet.

3. When housed in metabolism crates pigs ate less than when housed in holding pens and the difference was greater than would be expected solely from the reduced exercise of the pigs in crates.

4. Daily digestible energy intake was 575 kcal/kg. live-weight 0.675 when the pigs were in holding pens. The daily digestible energy intake of pigs in metabolism crates increased less with live-weight.

5. The use of metabolism crates to obtain digestibility coefficients and values for nitrogen retention to be applied to animals housed under other conditions is discussed in relation to the differences found in apparent digestibility coefficients, feed intake and growth rates between pigs in crates and in holding pens.

1. Three experiments are reported, in which a total of seventy-two calves were weaned at 3 or 5 weeks of age and given concentrate mixtures containing either 19·2% or 11·9% crude protein, together with hay and water up to 12 weeks of age.

2. The performance of cross-bred calves weaned at 3 weeks of age and given concentrates ad libitum was significantly greater when the high-protein concentrate was used in Experiment 1.

3. In Experiment 2, in which Friesian heifer calves were weaned at 5 weeks and given concentrates ad libitum, the level of protein in the concentrates had no significant effect on live-weight gain from birth to 12 weeks. However, there was a tendency for the performance of calves given the concentrate containing 11·9% crude protein to be slightly inferior up to the age of 8 weeks.

4. When concentrate intake was restricted to 2 kg./day in Experiment 3, in which Friesian heifer calves were weaned at 5 weeks of age, the live-weight gain was significantly greater when the higher level of protein was given.

5. Daily increases in height at withers, heart girth and belly girth tended to be greater in all instances when the concentrate containing 19·2% crude protein was given, but significant differences between treatments occurred only in Experiment 3 for increase in heart girth and belly girth.

6. It is apparent from the results that the calf weaned at an early age needs to be given a concentrate containing more than 11·9% crude protein if maximum live-weight gain is to be achieved up to 8 weeks of age. The optimum protein content of the concentrate after this age seems to depend on the level of concentrate feeding. The relationship between energy and protein in determining production is discussed.

A genetico-nutritional experiment is described in which 22 Ayrshire twin cattle, both one-egg and two-egg, were reared and maintained for up to seven years on a standard all-pelleted ration. Six equally spaced constant levels of food intake ranging from 35 1b. to 140 1b. per week were used. Each twin was reared on nearly ad libitum feeding until it had grown sufficiently to be able to consume its pre-assigned level of constant food intake. Thereafter its weekly food intake remained unchanged until the end of the experiment. The number of animals on each of the six feeding levels varied from two to six.

On each constant level of food intake, animals continued to grow fairly rapidly for two or three years, but thereafter their growth tended to slow down and usually an equilibrium weight was eventually attained. The resultant mean weight curves constituted an apparently simple, regular and systematic family with each curve eventually separated from the next by a relatively constant weight difference.

Coefficients of variation were about 3% for unrelated animals strictly conforming to the design, but increased at later ages to around 6% when animals with different pre-treatment were included. Coefficients of variation, however, did not change over the ascending series of feeding levels.

The advantages of the design for exploring the triple relationship of gain, weight and food intake are outlined. The potential use of such results as an empirical feeding scale and the possibility of obtaining paths of maximum efficiency from such a controlled experiment are described.

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.

1. Voluntary feed intake, performance and carcass quality were studied with 20 individually housed pigs given isocaloric diets (2,770 kcal/kg. DM) containing either 8·9 % or 12·9 % crude fibre in the dry matter over the period of growth from 45 to 91 kg. live-weight.

2. There were no significant differences between diets in voluntary feed intake, rate of gain or carcass quality.

3. Apparent digestibility coefficients and rates of passage of the diets were determined in eight castrated male pigs. Rates of passage were not significantly affected by diet or live-weight when determined at 57 and 82 kg. live-weight.

1. Eighty-four Friesian heifer calves were used in two experiments (Experiments 4 and 5) to study the protein requirement of the ruminant calf to 12 weeks of age. The calves were weaned at 5 weeks of age and given a concentrate containing one of several protein levels, together with hay and water.

2. In Experiment 4, the effect of changing the protein content of the concentrates at 8 weeks of age under ad libitum feeding conditions was studied. A concentrate containing 20·6% crude protein (air-dry basis) tended to promote more rapid weight gains in calves to 8 weeks than a similar concentrate with 12·1% crude protein. Following the change in diet at 8 weeks, both groups of calves given the low-protein diet gained weight at similar rates in the period 8–12 weeks, irrespective of the protein level to 8 weeks. During the period 8–12 weeks calves given the high-protein diet, after receiving a low-protein diet to 8 weeks, tended to gain weight at a faster rate than those given the high-protein concentrate throughout. After adjustment for differences between treatment groups in mean concentrate consumption and mean live-weight at 8 weeks, the live-weight gain from 8 to 12 weeks was significantly greater in calves given the high-protein diet after 8 weeks.

3. In Experiment 5, a significantly lower growth rate was obtained when concentrate intake was restricted to a maximum of 2 kg./day than when given ad libitum. Calves given the concentrates containing 15·9% or 20·6% crude protein gained weight significantly faster than those given the concentrate containing 12·1% crude protein, at both levels of feeding, after live-weight gain was adjusted for differences between treatment groups in mean food consumption and live-weight at 1 week.

4. It is concluded that no advantage is obtained by giving a concentrate containing more than 15·9% protein to Friesian heifer calves weaned at 5 weeks of age. The results indicate clearly the importance of an adequate supply of energy in the diet of the ruminant calf if maximum live-weight gain is to be achieved.

This paper reports the second of two experiments which examined the possibility of improving pasture utilisation by restricting grazing and giving cows a supplement of concentrates. Two treatments (A and B) were continuously imposed, each on a group of 10 adult Ayrshire cows, for about 4 months. Cows received either pasture alone allocated daily by electric fence (B), or half this area of pasture plus 3 Ib. cubed concentrates per 10 lb. milk (A).

Herbage intakes were estimated by grass cutting techniques and also by faecal index methods, and animal performance was recorded. Over the whole experiment the two treatments gave similar levels of production per animal. Significant differences in milk yield and live-weight gain were detected only in periods 1 and 4, respectively, when the intended restriction was not completely achieved. While production per acre of grass was doubled by treatment a about 4,000 lb. grain was considered necessary to replace one acre of grazing.

The results are discussed in relation to the previous experiment. They suggest that the method of replacing half the normal grazing with barley or other concentrated feeds could be usefully employed to alleviate pasture shortage in parts of the grazing season and might therefore facilitate the maintenance of a high stocking rate.

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.

(1) Forty-five Ayrshire and Shorthorn bull calves were used in an experiment to study the ability of the calf weaned at 5 weeks on to concentrates, hay and water, to utilise urea added to a low-protein concentrate.

(2) Calves given the concentrate containing 20% crude protein gained weight significantly faster from 3 to 12 weeks than those given concentrates containing either 12% crude protein, or 18% crude protein of which 33% was in the form of urea. There was a tendency for calves given the urea supplement to gain weight at a slightly faster rate to 8 weeks than those given the low-protein diet, but this tendency was reversed between 8 and 12 weeks of age.

(3) At 15 weeks, the coefficients of apparent digestibility of dry matter, crude protein, crude fibre and nitrogen-free extract were significantly greater when an all-concentrate diet containing 19·6% crude protein was given, than with a concentrate containing 12·2% crude protein. When the lowprotein concentrate supplemented with urea was given (18·5% crude protein) the apparent digestibility of dry matter, crude protein and ether extract was significantly greater than on the low-protein concentrate. The digestibility of crude fibre in the urea-supplemented diet was intermediate between the values obtained on the high- and low-protein diets.

(4) Despite marked differences between treatments in the intakes of apparently digested nitrogen, similar amounts of nitrogen were retained, because of large differences in the amounts of nitrogen excreted in the urine. However, the amount of nitrogen stored per unit of body-weight gain was 27% higher in calves given the concentrate containing 19·6% crude protein than in those given either the low-protein concentrate or the urea-supplemented diet.

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.

Phenotypic variances within pairs of monozygotic and dizygotic twin heifers and also genetic variances and heritabilities were calculated for 12 linear body measurements at a sequence of eight ages up to two years old. The 60 pairs of fraternal and 60 pairs of identical twins used were reared as part of a larger uniformity trial in which feeding was effectively ad libitum throughout.

Size differences between members of DZ twin pairs were found to be approximately normally distributed with about the same variance for all breeds and crosses. The variance within DZ pairs increased strongly with age, with a marked increase between 9 and 12 months of age and with most body measurements showing a broadly similar trend. On a logarithmic scale DZ variances increased roughly linearly with degree of maturity and at about the same rate in each body measurement. Coefficients of variation within DZ pairs corrected for measuring error had an average value of 2%. They did not change greatly with age, and were roughly the same for most body measurements although width measurements tended to be more variable than average.

Coefficients of variation within MZ pairs had a corresponding overall average of 1·4%; they declined rapidly with age from 2·0% to 1·1%, were roughly the same for all body measurements, but at early ages tended to be greater in late than in early maturing body parts. However, they showed no association with the earliness of maturing of a body part provided variation was measured at the same degree of maturity for each body part.

Genetic variation increased rapidly with age in all body measurements. The rate of increase with age was greater for late than for early maturing parts. The rate of increase with degree of maturity, however, was about the same for all body measurements. Coefficients of genetic variation increased slowly with age; they had an average value of 1·6%.

Estimates of heritability are given at a sequence of eight ages for each of 12 body measurements. They increased strongly with age from 0·14 on average at three months of age to 0·67 on average at two years of age. At any fixed age, early maturing body parts tended to have higher heritabilities than later maturing body parts. However, if heritability was measured at the same degree of maturity in each body part, early and late maturing parts had about equal heritabilities.

The present results are compared with those obtained from twin cattle studies in New Zealand, Sweden and Wisconsin, U.S.A.

Inferences from twins about genetic variances and heritabilities for unrelated animals are discussed.

Regression equations relating the intake factor to the dissolved faeces fraction, faecal nitrogen and faecal cellulose contents were derived in a continous digestibility trial with cut herbage, and also with sheep fitted with oesophageal fistulae grazing the pasture from which the herbage was cut. In the grazing trial the intake factor was calculated from the in vitro digestibility of the fistula samples.

The relationships established in the digestiblity trial differed significantly (P<0·001) from those in the grazing trial. These differences may have arisen from selective grazing or from bias in estimating digestibility from fistula samples.

The digestibility of the diet selected in the grazing trial was estimated from the various faecal index relationships established. These estimates were very variable. In contrast there was reasonable agreement between estimates derived by the fistula technique and those predicted from a ‘general’ relationship between the intake factor and faecal nitrogen as established at this Laboratory with a wide range of herbages.

It is concluded that faecal index relationships must be derived with material similar to that selected by the sheep when grazing.

The growth and carcass characteristics of semi-intensively reared Charolais × Ayrshire and Beef Shorthorn × Ayrshire cattle were studied. Charolais × Ayrshires grew faster while grazing, achieved slaughter condition at a higher live-weight and age and had leaner carcasses than Beef Shorthorn × Ayrshires. The practical significance of these results is discussed.

Some possible sources of error when sampling oesophageally fistulated sheep at pasture were examined in eleven trials. Samples collected from sheep asted for varying periods of up to 22 hours did not differ significantly in nitrogen content from samples collected from unfasted sheep. There was no significant difference between the nitrogen content of extrusa collected at the start of a 30-minute period and that of extrusa collected at the end of the period. Sheep transferred from a perennial ryegrass/clover pasture to a native pasture for three months ingested herbage containing 3·80% nitrogen when returned to the original pasture. Control sheep which had remained on the ryegrass/clover pasture selected material containing 3·33% nitrogen. In a further trial sheep transferred from a ryegrass/clover pasture to a Phalaris/ clover pasture consumed herbage with an organic matter digestibility of 70·8 % which contained 3·44 % nitrogen. The material consumed by similar sheep which had grazed the Phalaris/clover pasture for 18 months was 71·5% digestible and contained 3·63% nitrogen.

Diurnal changes in the digestibility and nitrogen content of the diet of free-grazing sheep were observed in two trials. Diurnal changes in nitrogen content were similar on different days but changes in digestibility were relatively smaller and less repeatable between days.

Consistent differences in the composition of the diet selected by individual sheep and selected on different days were observed in a further five trials. Variation between sheep and between days in the nitrogen content of the diet was ±5·6% and ±7·4% respectively, both estimates being expressed as coefficients of variation. Corresponding estimates for digestibility, calculated as standard deviations, were ±1·6 and ±1·3 units. The implications of these results when sampling oesophageally fistulated sheep at pasture are considered.

Closely shorn Scottish Blackface female sheep aged 9–14 months, half on high plane and half on low plane nutrition, were subjected, in climate chambers, to two short acute cold exposures down to – 20° C. The exposures were separated by a period of two weeks in either a thermoneutral environment ( + 30° C.) or a subcritical environment ( + 8° C.). Thirty-seven out of 40 sheep showed a greater resistance to body cooling at the second exposure. The mean rates of fall of rectal temperature (in° C. per 100 min. exposure) were 0·42 at the first exposure and 0·22 at the second exposure. One group of sheep showed virtually complete resistance to cooling at second exposure under the specific test conditions used. The highly significant increase in cooling resistance was taken as a measure of acclimatisation.

The main conclusions were as follows:

1. Blackface sheep could acclimatise to cold as a result of one acute exposure to cold lasting about 8 hours.

2. Acclimatisation was slightly greater amongst sheep kept at a subcritical temperature (+8° C.) between acute exposures.

3. Additional data suggested that some acclimatisation resulted from 2 weeks prior exposure to +8° C. alone; but none was induced by 2 weeks prior habituation to the climate chamber environment at + 30° C.

4. Sheep on high plane nutrition showed greater initial cold resistance and slightly greater ability to acclimatise than those on low plane nutrition.

5. Cold resistance was more closely related to recent weight gain than to absolute body weight.

6. There was great individual variation in initial cold resistance and in ability to acclimatise.

7. Sheep kept at + 8° C. between acute cold exposures maintained significantly lower rectal temperatures than those kept at +30° C.

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.