The use in dairy cattle improvement of loci associated with quantitative effects that might be found by genetic analysis is discussed. These methods can make a significant contribution only if they result in the identification of quantitative loci whose inheritance can be followed in a simple Mendelian manner. Another possibility, the identification of genetic components of production having a higher heritability than overall production, would make only a minor contribution to increased genetic progress. Selection of young males, according to the estimated breeding value associated by linkage with particular marker alleles in their sire, will not make a detectable contribution to genetic improvement.

Two experiments were conducted to determine whether the depression in fibre digestion caused by inclusion of fat in diets could be alleviated by addition of urea and whether the physical incorporation of fat in itself caused a reduction in rate of fibre digestion.

Early-weaned lambs were given dried grass containing either 65 or 130 g/kg of tallow with or without 15 g/kg of urea. Fat inclusion caused a linear depression in intake and fibre digestibility. The depression in intake was partly alleviated by urea inclusion, but urea did not affect fibre digestibility.

The physical incorporation of fat into dried grass did not in itself appear to depress rate of digestion. It is suggested that if coating of feed particles is important then this would be due to non-esterified fatty acids in the rumen and not to triglycerides.

1. Using 12 castrated Large White pigs, the way in which the size and number of recognizable fat cells (i.e. > 6·0 μm) increases during growth from 26 to 109 kg live weight, and the relationships between fat cellularity and body fat content were determined.

2. Fat biopsy samples were taken at 87, 145 and 188 days of age from the shoulder region. This region grew rapidly in volume but was early maturing since its relative growth during the period of the experiment was low compared with other regions, particularly the mid-back to loin region.

3. The growth of fat that occurred during the experiment was due to increases in both the size and number of recognizable cells. There was no indication that the number of cells had become constant even at 188 days of age.

4. Subcutaneous or total fat expressed as a percentage of total dissectible tissue weight was related quite closely (r = 0·6 to 0·7, residual s.d. about 8% of mean fat percentage) to average fat cell size measured at 145 and 188 days. The number of cells at these times, defined as the number in a cylinder whose depth was known and whose cross-sectional area was 1 mm2 on day 1, was not significantly correlated with whole body fatness.

5. Appetite was strongly linked to the rate of fat deposition and to the weight of fat at 188 days, but not to fat expressed in percentage terms. This was, however, closely related to the corrected food conversion ratio (r = 0·90, residual s.d. 2% of mean total fat percentage).

6. Fat thickness measured by ultrasonics before slaughter was no better as a predictor of percentage fat than average fat cell size.

Two pairs of uniformly treated identical twins were weighed four times daily for 16 days. In addition, daily growth rate was analysed for 10 pairs of identical twins kept on high and low planes of nutrition over a 16-week period.

Identical twins fluctuated in body weight from hour to hour and day to day in a significantly more similar manner than did unrelated animals. The greater similarity found when all animals were uniformly treated still persisted when identical twins were placed on different planes of nutrition.

In two trials, male Suffolk sheep were weaned at birth and reared artificially. Animals were ranked on weight at about 90 days and groups comprising the fastest- and slowest-growing animals were selected. The selected rams were subsequently progeny-tested to the same age, with some progeny reared with their dams in normal field conditions and others reared artificially.

In Trial I, performance tests were obtained on 35 rams and progeny tests of seven of these (three low and four high), with records on 34 artificially reared and 144 naturally reared progeny on one farm. The regressions of progeny on sire 90-day weight were 0·29 ± 0·12 and 0·19±0·09, respectively.

In Trial II, performance tests were obtained on 86 rams, sampled from five source flocks. Rams were selected in pairs of high and low performance from each source, and both members of the pair sent to the same one of seven farms for progeny testing. Ten pairs had progeny tests, comprising 62 artificially reared and 567 naturally reared progeny. The regressions of progeny on sire weight were, respectively, 0·05 ± 0·06 and 0·13 ± 0·03 if source of sire was fitted in the model, and little different, 0·06 ±0·05 and 0·14 ± 0·03 if source of sire was ignored. Progeny from a 2nd year from some sires in Trial II gave rather smaller regression coefficients: 0·06 or 0·09, with source of sire fitted or ignored, respectively.

Taking the two main trials together the pooled estimates (ignoring source of sire) of doubled progeny-on-sire regression for 90-day weight were 0·20 ± 0·10 for artificial rearing (a heritability estimate) and 0·30 ± 0·06 for natural rearing. These results suggest that early weaning is an effective method of selecting sires for growth rate.

Ten Landrace × (Landrace × Large White) young female pigs were allocated to each of four treatments. The experiment was arranged as a 2 × 2 factorial design, the variables being oestradiol benzoate v. ethyl oleate and boar v. visual testing. The oestradiol benzoate (or ethyl oleate) was administered at 140 days of age, the treatment consisting of six injections, over a 3-day period, of 0·5 ml of either ethyl oleate or a solution of 0·4 mg/ml β-oestradiol-3-benzoate in ethyl oleate. Subsequently the gilts were either inspected visually each day or taken to a vasectomized boar for oestrus detection. All gilts were mated at the second oestrous period, and slaughtered on the 20th day of gestation. Those gilts receiving exogenous oestrogen attained puberty significantly earlier (P<0·01) than the control gilts. Of the 20 gilts treated with oestrogen, 12 (60%) attained puberty within 5 days of the start of treatment. No significant difference was found between boar testing and visual testing, although receptivity to mating appeared to be lower for visually tested gilts. There are no significant differences between treatments in ovulation rate, conception rate or embryo survival.

The effects of breed type and season on semen quality and libido were examined. Tests were carried out in autumn, winter, spring and summer using 47 rams of five breeding groups, namely the the Fleisch Merino, the Ossimi, the first cross and the two parental backcrosses. All the rams were born and reared locally.

Except for the percentage of abnormal sperm cells and time to first mount, semen quality and libido were not affected by breed type. There was little consistent evidence of heterosis in any of the traits examined. All traits except time to first mount were significantly affected by season. Semen was of better quality in autumn and spring than in winter and summer. With one exception all aspects of libido were depressed in winter.

Breed × season interactions were significant in six of the 10 traits studied but showed no consistent trends.

The reproductive performance of Merino rams was not adversely affected by the environment. This indicates the feasibility of introducing new breeds so far as semen quality and male libido are concerned.

The effect on genetic improvement of a policy of sequential selection, in which breeding animals are retained for differing times, is investigated for a closed herd of pigs. Selection is practised for traits of the growing animal, either on phenotype or on predicted breeding value with account taken of parental age.

The following scheme gives near to maximum response over a wide range of values of parameters such as litter size, mating ratio and farrowing interval and of heritability. One out of every three or four females should be retained fora second litter and with continuous use of males about three out of every seven males should be retained after 3 months of use for a further 3 months. Such a scheme gives an improvement of only up to 3% over a procedure where all females are kept for two litters and all boars for 6 months, and progeny are selected without regard to parental age. The advantage of sequential selection becomes greater if sows are kept for more litters.

Two fibrous roughages, wheat straw (WS) and cotton hulls (CH), were either untreated or treated with 30 g/kg or 60 g/kg of sodium hydroxide (NaOH), the residual NaOH was either unneutralized or neutralized with sulphuric acid, and the materials were then pelleted. The effects of these treatments on the nutritive value of the two roughages were examined in an arrangement that differed from the factorial 2 × 3 × 2 = 12 in that only one control group was included for each roughage. Digestibility trials, in vitro and in vivo, and a 7-month feeding trial were carried out. Concentrates were limited in the feeding trial to 6 kg/head per day, and roughages were offered ad libitum.

Dry matter digestibility in vitro was significantly higher on CH than on WS and was significantly increased by NaOH treatment. Level of NaOH and neutralization of residual alkali had no significant effect. Intake of WS was increased by treatment with 30 g NaOH/kg in the digestibility and feeding trials. Increasing the level of NaOH to 60 g/kg reduced intake of both roughages. Digestibility of organic matter of WS was increased by NaOH treatment at both levels, by 25 to 30%, while that of CH was improved significantly only by the higher level. Neutralization had no effect. The actual intake of roughages was 30 to 35% of the entire ration. The rate of gain of animals offered roughages treated with 30 g NaOH/kg was non-significantly increased, and that of animals offered roughages treated with 60 g NaOH/kg was reduced significantly in comparison with the control. Animals offered NaOH-treated roughages had a significantly higher dressing percentage, and those offered treated WS had a greater fat trim than the control animals. Efficiency of conversion of metabolizable energy into live or carcass weight for both roughages was improved only with the neutralized 30 g NaOH/kg treatment. Comparing the performance in this study with that of a former study of similar design in which the same roughages were offered wet, revealed no marked advantage from pelleting.

Progeny tests of three Hampshire × Duroc, three Hampshire, three Duroc and five Landrace boars were performed to compare the use of crossbred and purebred boars producing pigs, intended for slaughter. Boars were double-mated to Landrace sows, and 830 sire-identified pigs from 92 double-mated litters were farrowed. Significant (P < 0·05) breed of boar effects were observed for birth weight, 21-day weight, daily gain from 56 days to slaughter and age at slaughter, but breed of boar differences for 56-day weight, backfat depth, killing-out percentage and carcass index were not significant. Progeny of the Hampshire × Duroc crossbred performed similarly to pigs sired by purebred Hampshire and Duroc boars. Progeny performance of the Hampshire × Duroc and Duroc boars was almost identical for daily gain, age at slaughter, backfat depth and carcass index. Hampshire-sired pigs grew slightly faster, but progeny of Hampshire × Duroc boars had higher killing-out percentages than either Hampshire- or Duroc-sired pigs. Purebred Landrace pigs were slower growing, had more backfat and lower carcass indexes than crossbred pigs sired by either the Hampshire × Duroc, Hampshire or Duroc boars.

Sixty-four British Friesian castrated male cattle (steers) with an average starting weight of 292 kg and an average slaughter weight of 460 kg were used to compare compound diets containing 0, 10, 20 or 30% NaOH-treated straw. A basic diet of 1·8 kg hay, 1·8 kg barley straw and sugar beet pulp, on a scale rising from 1·4 to 2·8 kg according to live weight, was given throughout the trial. Compound diets were individually offered on a scale starting at 3·8 kg rising to 5·8 kg with an average intake of 4·9 kg/day. Treatments did not differ significantly in respect of live-weight gain, which ranged from 0·94 kg/day with the control to 0·97 kg/day with the 30% NaOH-treated straw compound. The grading of the animals, based on the Meat and Livestock Classification scheme, also showed no significant difference.

A second trial with a further 64 British Friesian steers tested inclusion levels of 0, 30,45 and 60% treated straw in a compound diet. At the start of the trial, the cattle averaged 328 kg live weight and were slaughtered from 450 kg live weight. Animals were yarded in store condition and were given a combination of grass silage and compound diets according to a scale, based on live weight and a predicted performance of 1 kg live-weight gain per day. There were no significant differences between treatments in live-weight gain, which ranged from 0·97 kg on the control to 1·02 kg/day on the 45% NaOH-treated straw diet. There was some refusal on the 60% NaOH-treated straw diet in respect of twice daily allocations, with a few cattle on occasions not being able to consume the allowance in the 30 min provided. However, each feed allocation was always consumed before the next meal. There were no significant differences between treatments in respect of fat class, but cattle on the 45% treated-straw diet had statistically superior conformation compared with the control.

The coefficients of inbreeding and the degree of relationship for British Friesian bulls used for artificial insemination by the Milk Marketing Board in sample years between 1955 and 1972 and for random samples of registered females from the same years have been calculated. The average coefficient of inbreeding was lower in bulls (0·5%) than in registered females (2·7%). The average degree of relationship was 0·7% for bulls and 2·6% for heifers.

A system of time-controlled feeding has been developed to give a considerable degree of control over the food intake of animals without eliminating individual variation.

The system is based on the Calan-Broadbent electronic feeding doors and animals are conditioned by certain electrical and sound stimuli to use the doors only during prescribed periods. Clock mechanisms control the time intervals when electric power to the doors is on or off.

Times and durations of feeding can be adjusted so that a predetermined level of intake is obtained, and a heavy demand on labour is avoided.

In the present trial, British Friesian and Jersey cattle on a time-controlled feeding regime were compared with animals given access to food ad libitum. A significant reduction in food intake due to time-controlled feeding was detected in both breeds over a 6-month period.There was no evidence to suggest that the particular time-controlledfeeding regime restricted one breed more than the other.

Data from 675 litters were used to study the effects of type of service, number of services, parity, year, season, breed of sire, sire, type of dam (purebred or crossbred), breed of dam, dam, breed of sire × type of dam and breed of sire × breed of dam on litter size (live births), number of males, number of females, sex ratio (percentage of males) and length of gestation. Yorkshire, Landrace and Lacombe breeds and their crosses were represented. Artificial insemination significantly reduced litter size and the number of females and increased sex ratio. Parity had a significant effect on all traits except sex ratio. Lacombe-sired litters were approximately one-half pig smaller than Yorkshire- and Landrace-sired litters. Landrace-sired litters had gestations of one-third day shorter than Yorkshires. On average, crossbred dams farrowed 0·65 more pigs per litter than pure-bred dams. Litters from Yorkshire dams, however, were more than one pig larger than Landrace and Lacombes, and did not differ significantly from crossbred dams. Gestation length of Lacombe sows was 1·34 days shorter than Yorkshires. Repeatabilities of litter size, number of males, number of females, sex ratio and gestation length were 0·15, 0·08, 0·06, 0·05 and 0·32 respectively.

An experiment was conducted with 72 male British Friesian calves between 5 and 11 weeks of age. The major treatments were the inclusion of 0, 20 or 40% wheat straw or 20, 40 or 60% lucerne in a complete pelleted diet. The roughage was either ground or chaffed. A methane inhibitor was included in the diets given to 36 of the calves. The weight gains of the calves were greater with diets containing lucerne than with those containing wheat straw. Grinding increased the intake of wheat straw but depressed intake of lucerne. The apparent digestibility of dry matter and acid detergent fibre, which was greater for the diets containing lucerne than for the diets containing wheat straw, was reduced by grinding both roughages.

Inclusion of the methane inhibitor in the diets increased the feed intakes and weight gains of the calves given the all-concentrate diet and the diets containing wheat straw, but not those given the diets containing lucerne.

1. Eight-one British Friesian and 44 Jersey steers was slaughtered at 1. 12, 24, 48 or 72 weeks of age. Those aged 24 weeks and over were reared on a standard complete diet offered ad libitum, and individual food intakes were recorded until slaughter when carcasses were dissected on an anatomical basis.

2. From 1 to 72 weeks British Friesians were on average 50% heavier than Jerseys and consumed 47% more food. Total lean tissue (L) increased 11-fold to 137 + 6·4 kg in the British Friesians and 16-fold to 84 ± 4·7 kg in the Jersey. L as a percentage of live weight rose to 32% ±0·6 in the British Friesians and to 29% ±0·8 in the Jerseys. Breeds did not differ significantly in average efficiency of growth of lean tissue in any period.

3. From 24 to 72 weeks, an allometric relationship held between L and total food consumed postnatally, F. The two breeds had the same allometric coefficient of 0·61. Current efficiency, 0·61 L/F, was thus proportional to cumulated efficiency, L/F. Allowance was made for the prenatal input, Fo, required to produce the newborn calf. An optimum slaughter point at which overall efficiency, L/(F+F0), reached a maximum occurred in each breed when postnatal input was 58% higher than prenatal input (F = 1·58F0). When the breeds had equal maximum efficiency the British Friesian: Jersey ratios for prenatal input, total food consumed and total lean produced were all 2·6:1.

1. Twenty-two Scottish Blackface, 51 Welsh Mountain and 22 Tasmanian Merino lambs aged between 6 and 75 h were tested for resistance to body cooling in a climate chamber. Blackface lambs had long birthcoats, Merinos were short-coated. Welsh lambs were from two strains with long (L) and short (S) types of birthcoat. Some lambs were clipped before cold exposure.

2. Clipping reduced cold resistance in Welsh (S) and (L) lambs by factors of 3 and 13 respectively.

3. Undipped lambs showed significant breed differences, Welsh (L) and Blackfaces having the greatest cold resistance and Merinos the least. Long-coated lambs (Blackface and Welsh (L)) were on average six times more cold resistant than the average of Welsh (S) and Merino lambs; and Welsh (L) lambs were four times more resistant than the Welsh (S) type. Birth weight and age did not significantly influence cold resistance.

4. In clipped lambs there was a significant positive linear regression between cold resistance and birth weight. Breed differences in cold resistance were still significant if no adjustment was made for the effect of breed differences in birth weight.

5. Cold resistance was strongly influenced by breed differences in birthcoat morphology and probably by other physiological factors partly attributable to the different genetic backgrounds associated with birthcoat type. The breed differences in cold resistance were generally consistent with field data on mortality and body temperature regulation of lambs in severe weather, suggesting that climate chamber tests might be used to evaluate potential viability in the field.

From July 1975 to January 1977, 225 cows in three autumn-calving dairy herds were condition-scored, weighed and milk-recorded at monthly intervals. The condition score at calving was related to the ability of the animal to achieve potential milk yield. This potential milk yield was denned by the lactation curve prediction. Animals below condition score 2 at calving did not achieve their predicted milk yield, and those above condition score 2½ yielded more than their predicted milk yield. Cows in poor condition at calving gave low, late peak milk yields with a high persistency, and those in good condition at calving gave high, early peak milk yields with a lower persistency. A positive relationship of 25 ± 1·6 kg live weight per unit of condition score was established within cows in months 1 to 7 of lactation. After month 7 of lactation foetal development caused changes in live weight without changes in score.

Muscle weight distribution was compared by jointing and complete tissue separation of carcasses from 277 young male progeny of eight sire breeds and two dam breeds, serially slaughtered at 300 kg live weight, 12 months and 15 months of age. The sire breeds were Simmental, Charolais, Danish Red and White, Romagnola, Chianina. Hereford, Blonde d'Aquitaine and Limousin; the dam breeds were Danish Red and Danish Black Pied.

Growth impetus for muscle in each joint was established from the allometric equation (Y = aXb). Growth coefficients, b, were homogenous among breeds, indicating similar muscle development patterns over the range of weights studied. Growth impetus waves increased centripetally on the limbs, caudocephalically on the whole of the body (being more marked dorsally) and dorsoventrally on the trunk.

There were small but significant breed differences in the proportion of muscle in different joints at similar total muscle weight. They probably reflect differences in maturity and other minor functional influences. Chianina and Hereford crosses were the two extremes for muscle distribution with many of the remaining breed groups being very similar. Differences were already established by 300 kg live weight and muscle growth patterns were similar among breeds over the range of the experiment.

High (1·31 kg/1) or medium-density (1·17 kg/1) dried grass pellets of 9, 12 or 18 mm diameter were given to British Friesian male calves of 7 to 14 weeks of age as supplements to chopped hay (Experiment 1). Pellets were given ad libitum but with access limited to two periods of 1½ h per day, and hay was given ad libitum for the remaining 21 h. In Experiment 2, high (1·34 kg/1) or medium-density (1·14 kg/1) dried grass pellets of 18 mm diameter were given to British Friesian male calves of 26 to 30 weeks of age. Pellets were given as supplements to chopped hay as in Experiment 1.

There was no effect of pellet size or density on total intake of organic matter or live-weight gain by calves in either experiment. With the exception of animals given pellets of 12 mm diameter in Experiment 1, animals in both experiments consumed less pellets of high density than of medium density, but they were able to compensate for low pellet intake by eating more hay.

The coefficients of variation for intake were higher in Experiment 1 than in Experiment 2, and higher for the intake of pellets than for total intake. There was a progressive increase in the intake (g organic matter/kg M0·75 per day) by calves in Experiment 1, whereas in Experiment 2 intake increased for the first 10 days and then remained constant. On average the proportion of pellets and hay consumed did not change in Experiment 1, but in Experiment 2 the proportion of pellets in the feed consumed increased from 53·5 to 60·6%.