A scheme is described for the genetic improvement of milk yield in a large population of dairy cows, based on half-sister selection of young bulls, as an alternative to the normal procedure of progeny testing. The results indicate that the suggested scheme would lead t o an eventual rate of genetic progress very similar to the progeny testing scheme. However, the annual cost of the new scheme is less than a progeny testing scheme, largely because the ‘laying off’ of candidate bulls, to await selection, is completely eliminated. In addition, improvement of the dairy cows shows up sooner in the new scheme; by the 10th year from the start the cumulative genetic improvement is four times greater than for progeny testing.

Thirty one-year-old Charolais × Holstein-Friesian (CH) and Hereford × Holstein-Friesian (HH) steers averaging about 268 kg live weight were used to study the effect of increasing slaughterweight from the traditional 454 kg (1000 lb) to 544 and 635 kg (1200 and 1400 lb) live weight. The steers were fed a growing ration of grain, silage and hay until they weighed 68 kg (150 lb) below the assigned slaughter weight, followed by a finishing ration of grain mixture and maize silage given ad libitum. Average daily gain on the growing ration was 0·91 kg in CH, 14% higher than that in HH steers, while on the finishing ration HH steers, finished at 544 and 635 kg, made higher gains. CH steers were 7·9% more efficient than HH steers in feed conversion. Feed conversion efficiency (total dig. nutrients (kg) per kg live-weight gain) decreased by 10% and 19% respectively as slaughter weight increased to 544 and 635 kg. Live measurements showed that CH steers were generally longer, taller and wider at the hip, whereas HH steers had a greater depth of chest and width of shoulder. CH steers, slaughtered at different weights, had a higher percentage of round and shank, while HH steers had a higher percentage of all other wholesale cuts. Carcass measurements were generally higher in CH than in HH steers. CH steers had a higher percentage of muscle and bone, and lower fat, in the 12th rib. They also had larger areas of m. longissimus thoracis. Fat deposition over and in that muscle was much higher in HH than in CH steers. Under the conditions of this study, 544 kg was found to be the optimum slaughter weight for both groups. Slaughtering steers at 635 kg was found to be economically disadvantageous.

Maternal performance of female sheep of three hill breeds, Scottish Blackface, Cheviot and Welsh Mountain, and the crosses among these breeds has been studied in terms of lifetime production and some of its components. The data are based on 193 ewes, which were given the opportunity of having four annual lamb crops, and their lambs.

There was no significant variation among the breeds and crosses in ewe survival or in the proportion of barren ewes at each lambing. There was significant variation among the breeds and crosses in the number of lambs born per ewe lambing, in lamb survival and in weights of lamb at birth and at weaning. Crossbred ewes (producing crossbred lambs) had more and heavier lambs than expected from the average of the pure breeds contributing to each cross, but the three crossbred types differed in the amount of heterosis shown. Over their lifetime in the flock there were significant breed differences in the total weight of lambs weaned, with crossbred ewes producing about 9% more than the average of the parent breeds involved. The crossbred ewes produced more weight of lambs over their lifetime than pure Cheviot or pure Welsh Mountain ewes, but not as much as pure Scottish Blackface.

Effects of parity of dam and of sex, birth type, and type of rearing of lamb are given.

Data werfe analysed of litters from Large White and Landrace herds which were tested at central stations in Great Britain for growth and carcass traits. Information on reproductive performance of young females was combined with data on their relatives at central stations in order to calculate genetic relationships of reproduction with growth and with carcass traits. Progeny testing of boars for both sets of traits was the most efficient of the methods considered for this analysis.

In general, the estimated genetic correlations of reproductive performance with growth and with carcass traits were alike in sign for the two breeds, and the signs of the matrix of values were internally consistent. For example, combining data for litter sizes in the Large White breed, genetic correlations were −0·15 (food conversion ratio), 0·06 (daily gain), −0·18 (average backfat depth), −0·63 (killing-out percentage) and −0·41 (hind quarter percentage). When the growth and carcass traits were combined as total points score in a selection index, the genetic correlation between this score and reproductive performance was very small, with a range from −0·04 to 0·02. Calculations showed that inclusion of reproductive performance in the index would increase the rate of genetic improvement by only 0·55%.

Half carcasses of 18 Pietrain and 18 Large White female pigs were dissected into 10 bone units. An allometric analysis of the weights of these units relative to total bone revealed increasing craniocaudal and distoproximal growth gradients. No differences in bone distribution were observed between the two breeds. Because of a difference in muscle distribution, the muscle: bone ratio in the femoral region of the Pietrain was greater than that of the Large White breed.

1. Pig growth hormone (PGH) concentrations were measured in plasma samples from piglets of 3–4 to 7–8 weeks of age.

2. Plasma PGH concentrations decreased significantly with age. No difference was observed between the hormone concentrations of gilts and barrows.

3. Correlation coefficients were calculated between mean plasma growth hormone concentration over a 4-week period and several carcass characteristics and measures of growth rate. Plasma PGH over this period showed significant negative correlations with several measures of carcass backfat thickness at bacon weight. In barrows only, PGH concentrations showed a significant direct correlation with relative growth rate from 3 to 7 weeks.

The rate of cutaneous evaporation was highest in the White Fulani (Bos indicus) followed by the N'Dama and German Friesian (Bos taunts). The lowest rate of evaporation was recorded in the Muturu (Bos taurus brachyceros). In all breeds, the rate at 15.00 hr was significantly higher than at 18.00 hr.

For the sites sampled, evaporation rate was highest on the hump and mid-side, followed by the neck and lateral thigh and lowest on the dewlap and navel flap.

The possible correlation of these results with the size and distribution of the sweat glands on various sites of different cattle breeds is discussed.

1. A total of 33 energy balance trials was conducted with veal calves offered a high-fat milk replacer diet containing 10, 20, 40 or 100 mg iron/kg DM.

2. There were no significant differences in weight gain, food conversion or energy retention between calves receiving 20, 40 or 100 mg iron/kg DM in their diet. Calves receiving only 10 mg iron/kg gained weight and retained energy at significantly lower rates than those in the other groups.

3. The metabolic heat production of calves receiving the liquid diet was greater than that of calves given the same amount of gross energy from a barley diet. The recommended air temperature of about 20°C for veal calf houses is therefore unnecessarily high.

1. Weanling male rats were used in three experiments to evaluate the sequence of limiting amino acids for maximum growth with diets based on wheats containing 10, 13 or 17% crude protein (N×5·71).

2. Lysine was the first-limiting, threonine the second-limiting, and valine or methionine the third- or fourth-limiting amino acid for growth rate and feed-conversion ratio of rats offered the diet based on wheat containing 10% crude protein. A further four amino acids (isoleucine, histidine, tryptophan and tyrosine) were limiting for feed-conversion ratio only.

3. For the diet based on wheat containing 13% crude protein the sequence of limiting amino acids was lysine, threonine and methionine.

4. Only lysine was limiting in the diet based on wheat containing 17% crude protein.

5. Plasma-free amino-acid concentrations were found to be a valuable criterion for prediction of the first-limiting amino acid in diets.

6. Improvement of growth and feed-conversion ratio was observed with diets based on wheat containing 17 or 13% crude protein when the limiting amino acids were supplemented to provide the recommended allowance. Further improvement in feed-conversion ratio was obtained when lysine and threonine were provided in excess of the recommended allowances.

7. There was a lysine-threonine interaction affecting growth rate and feed-conversion ratio, and a lysine-me.thionine interaction affecting feed-conversion ratio.

An experiment was conducted with 60 male Friesian calves between 5 and 11 weeks of age. The experiment was a 5×2×2 factorial design. The five major treatments were the inclusion of 20 or 40% ground wheat straw or 20, 40 or 60% ground lucerne in a pelleted diet. A methane inhibitor was included in the diet given to 30 of the calves. The diets were given alone or with a chaffed wheat straw supplement ad libitum. All diets contained 2% sodium bicarbonate.

The weight gain of the calves was greater with the diets containing ground lucerne than with those containing ground wheat straw, but in both cases weight gains were reduced with increasing roughage content of the diets. The efficiency of feed conversion showed a similar trend. The supplementation of the diets with chaffed wheat straw did not affect the performance of the calves. The inclusion of the methane inhibitor in the diets improved the weight gains and efficiency of feed conversion. The daily retention of nitrogen in the calves showed a similar trend to the growth rates.

The molar percentage of acetate in the rumen increased as the roughage content of the diets increased while the proportions of propionate, butyrate and valerate decreased. The inclusion of the methane inhibitor in the diets decreased the concentration of total volatile fatty acids (VFA) in the rumen and increased the molar percentage of propionate, butyrate and valerate.

1. Pelleted grass and a concentrate containing 90% rolled barley and 10% soya bean meal were offered to cows in three combinations, 25: 75, 50: 50 and 75: 25 respectively, together with a constant low level of coarse roughage.

2. The experiment was carried out in two stages, in early lactation as a randomized block design involving 18 Jersey cows fed to appetite and in mid-lactation as a 3 × 3 Latin square change-over design involving 12 cows, rationed according to milk yield.

3. There were no significant between-treatment differences in either milk yield or milk fat content in either stage of the experiment.

Twenty-seven groups of Finnish Landrace × Dorset Horn lambs each of 2 castrated males and 2 females were offered daily quantities of 180, 248 or 343 g of milk substitute dry matter (DM) for 21, 29 or 40 days. Concentrate pellets were available ad libitum and from 22 days of age 150 g of hay per week was offered. When the mean live weight of a group reached 35 kg two castrates and one female from each group were slaughtered and the carcasses appraised.

The growth rate and daily concentrate intake of lambs from 48 days of age until slaughter (reported -in this paper) were not affected by previous treatment, but lambs weaned at 40 days had a higher food conversion efficiency in this period (0·266 kg gain/kg feed DM) than those weaned at 21 days (0·244) or 29 days (0·232).

Delaying weaning from 21 to 29 and 40 days reduced overall concentrate DM intake from birth to slaughter (from 88·15 to 81·09 and 73·39 kg) but increased growth rate (261, 276 and 288 g/day) and the conversion of total DM consumed to live weight (0·300, 0·311 and 0·350 kg/kg). Increasing the daily allowance of milk substitute from 180 to 248 and 343 g/day also reduced total concentrate intake (84·18, 80·74 and 77·71 kg). Growth rate and food conversion efficiency tended to increase and concentrate DM intake to decrease when the same total quantity of milk substitute was given over a longer period. Castrated males grew faster than females (290 v. 260 g/day).

Weaning age generally had a greater effect than daily allowance of milk substitute on carcass measurements. Fat in the carcass tended to increase with increasing weaning age and significant interactions between daily allowance of milk substitute and weaning age were found for some carcass measurements.

The carcass characteristics of young adult female pigs (gilts) slaughtered after weaning their first litters have been investigated using three groups of 19 Landrace × (Landrace×Large White) gilts. In two treatment groups gilts were mated at their pubertal oestrus and suckled their piglets for 5 to 11 and 35 to 42 days respectively. These gilts were slaughtered on average 10 days after weaning. A third control group consisted of unmated gilts slaughtered at 118 kg live weight.

There was no significant difference in the killing-out percentage for the three groups. The carcasses of the gilts which farrowed contained significantly less fat (P<0·001) than those of the unmated controls. The carcasses of the farrowed gilts had significantly lighter middle sections (P<0·001) and significantly heavier shoulders (P<0·001) than the controls.

Despite the variations in tissue yield and distribution, the yield of prime joints for the gilts which had farrowed was only 0·62 percentage units less than that of the controls.

No commercially significant variations between groups in meat quality were observed.

One hundred and twenty-eight Landrace and Large White pigs were allocated on the basis of sex, litter origin and initial weight to one of 16 treatments, made up of four basal 16, 18, 20 and 22% protein diets, each supplemented with either 0·00, 0·10, 0·15 or 0·20% synthetic DL-methionine, at a common digestible energy level of 3740 kcal/kg. Pigs were reared between 8 and 50 kg live weight. Growth rate of pigs and efficiency of feed conversion were significantly improved as the protein levels were increased up to the 20% protein level, optimal performance being on the 20% protein diet, with added 0·15% methionine, giving a total methionine+cystine level of 0·65% and a lysine level of 1·07%. Addition of synthetic methionine to the diets resulted in significant improvement in the rate and efficiency of gain only at the 16 and 18% protein levels.

Carcass leanness and fatness increased and decreased respectively over the whole range of protein levels. Graded addition of DL-methionine within each protein level did not influence carcass characteristics.

Nitrogen retention showed optimal utilization of dietary nitrogen to be at the 18% protein level, with a total dietary methionine + cystine level of 0·61%, which was at variance with the levels indicated by both growth and feed efficiency.

One hundred and twenty-eight Landrace and Large White pigs were allocated on the basis of sex, litter origin and initial weight to one of 16 treatments made up of four basal 16, 18, 20 and 22% protein diets, each supplemented with either 0·00,0·05,0·10 or 0·15% synthetic L-lysine; methionine was added to meet the levels earlier found to be optimal. All diets had a common energy level of 3740 kcal/kg DE and pigs were fed from 8 to 50 kg live weight.

Growth rate and feed efficiency improved as the protein levels were increased from 16 up to 20%. Only the 16 and 18% protein diets showed significant responses to additional lysine. Best overall gains and efficiency of gain was achieved on the diet with 20% protein and total dietary lysine and methionine+cystine levels of 1·17 and 0·66% respectively. Carcass leanness increased and fatness decreased as protein and lysine levels were increased, being best at the highest level (1·41%) of lysine studied.

Nitrogen retention indicated slightly lower protein and lysine requirement, efficiency of utilization being best on the 18% protein diet with added 0·15% lysine, giving a total dietary lysine level of 1·1% at the equalized methionine and cystine level of 0·66%.

It is indicated that diets providing between 18 and 20% protein in the diet, provided proper amino acid balance is maintained, would be optimal for pigs between 8 and 50 kg live weight.

Three experiments are described in which castrated male (steer) calves previously reared to 6 to 7 months of age on dried grass ad libitum gained weight faster, following turnout to pasture, than calves previously reared on a cereal/protein concentrate ad libitum. Rate of gain at pasture was found to be more an effect of previous rate of gain than of diet per se. There were indications that calves whose growth rate had been previously restricted ate more herbage per unit live weight than calves whose growthrate had not been restricted.

Twenty-four cows were used in a randomized block, continuous feeding trial to examine the effects of including 0, 25 or 50% of dried grass in a concentrate given to cows receiving grass silage ad libitum. The concentrates also contained barley, and soya bean meal to maintain the crude protein content at 16%, and were given at the rate of 0·4 kg/kg of milk. The treatments were imposed for a 6-week period after a preliminary feeding period of 4 weeks. At the beginning of the experiment the cows had, on average, calved 39 days previously. The mean intakes of silage dry matter were 7·60, 8·28 and 8·39 kg/day with the concentrates containing 0, 25 and 50% dried grass, respectively, and were significantly greater when dried grass was included in the concentrate. The mean milk yields of 200, 18·2 and 19·6 kg/day for the three treatments respectively were not significantly different. Body-weight change and milk composition were not significantly different between treatments.

1. In two experiments the nutritive value for the growing pig of wheat which had been micronized at temperatures of 155°, 190° or 220°C, flaked (rolled) and then ground was compared with wheat which had either been ground, or rolled and then ground.

2. In the first experiment 60 pigs offered individually, restricted amounts of feed were used in a growth and efficiency of conversion study. In the second experiment 15 pigs were used in digestibility and nitrogen retention studies.

3. The highest micronization temperature gave a significant depression in growth rate and in efficiency of conversion of dietary dry matter as compared with the other treatments for which there were no significant differences.

Two-way selection for muscle fibre diameter in mice was practised for four generations. The response was small and did not differ significantly from zero.