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.

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 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.

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.

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.

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.

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.

Fat growth and distribution were studied by jointing and complete tissue separation of carcasses from 277 young bull progeny of eight sire breeds and two dam breeds, serially slaughtered at 300 kg live weight, 12 and 15 months of age. Growth impetus for fat in each joint was established from the allometric equation (Y = aXb). Differential growth of fat in different joints resulted in marked differences in percentage of fat in various joints as fattening progressed. Growth coefficients, b, for fat in each joint were homogeneous among breed groups, indicating similar fat development patterns over the weight range studied. Growth impetus for fat was lowest in the distal limbs and in the proximal hind limb. Fat growth in the proximal fore limb was proportional to total fat. Along the dorsal line, low impetus was found in neck and rump regions, increasing to a high impetus in the mid-back region. Ventrally the fat of the flank showed the highest growth impetus of all regions with fat in the brisket and flat ribs also showing an increasing proportion with increases in total fat.

Small but significant differences among sire breeds were found for the amount of fat in each joint at a standard amount of total fat in the carcass. Differences found among sire breeds in fat distribution were not associated with differences in maturity type.

Bone growth patterns and distribution were compared in joints of carcasses from 277 young bulls, progeny of eight sire breeds and two dam breeds, serially slaughtered at 300 kg live weight, 12 and 15 months of age. The growth pattern for bone in a joint was estimated from the allometric equation (Y = aXb). Growth coefficients (b) were homogeneous among breed groups for bone in each joint relative to total side bone indicating that the different breeds followed similar patterns of differential bone growth. Growth impetus of limb bones was lowest in the distal parts, increasing to the proximal regions, with the fore limb showing higher growth impetus than the hind limb. Bones of the whole thoracic region showed a high growth impetus and those of the lumbar region the highest. The cervical vertebrae showed only average growth impetus, maintaining a constant proportion of total bone. Significant sire breed differences were found in the proportion of bone in each joint when adjusted to equal side bone weight but the differences were rather small and probably commercially unimportant. Differences among sire breed groups reflected differences in maturity type, with progeny of Here-ford sires representing early maturity and progeny of Chianina sires the other extreme. Functional association between muscle and bone was not reflected in a similarity of growth patterns, except for the muscles and bones of the limbs.

1. The voluntary water intakes of eight housed lactating cows were measured. Four of them were subsequently deprived of 40% of this water intake for three weeks. Feed consumption, milk yield and quality, water, Na and K balances, and serum and urine osmolalities were measured. The cows were weighed weekly and their pulse, respiration and rumination rates and rectal temperatures were measured daily.

2. In deprived cows there was a decrease in the mean intake of dry matter by 24% and in milk yield by 16%. These changes were apparent after 24 h, but subsequently there were no further changes. Faecal water was reduced significantly and the percentage faecal dry matter increased significantly. Urine osmolality increased but the reduction in urine volume was not statistically significant.

3. Concentrations of urea and Na in serum and serum osmolality were significantly higher in deprived cows throughout the experimental period and increased slightly but significantly each day from the time the deprived animals were last offered water to appetite.

4. The deprived cows lost weight during the 1st week of deprivation but showed no further change until rehydration, after which normal body weight was regained within 4 days. The deprived cows had consistently lower mean rates of respiration and rumination than the control cows throughout the period of deprivation but they showed no signs of distress.

Five autumn-born British Friesian heifers were given a high-fat milk substitute ad libitum to 12 weeks of age followed by skim milk ad libitum to 20 weeks of age and were weaned at 26 weeks of age (Treatment 1). Nine heifers were offered the high-fat milk substitute to 8 weeks of age and were weaned at 12 weeks of age (Treatment 2). First oestrus was detected by a study of cervical secretions and plasma progesterone concentrations.

Heifers on Treatment 1 were significantly heavier at 12 weeks of age, but there was no difference between treatments in the mean age or weight of the heifers at first oestrus. Ten heifers conceived at their first or second oestrus (Group A) and four heifers required four to nine inseminations to establish pregnancy (Group B).

Age at first oestrus was inversely related to pre-pubertal progesterone concentrations, which tended to be higher in Group B heifers. All heifers showed a small peak in progesterone concentration before first oestrus, the height being significantly greater in Group B than in group A heifers.

Progesterone concentrations in cycles preceding a successful insemination tended to be lower in the 2 days before oestrus. Progesterone concentrations during pregnancy were significantly lower for the Group B heifers, and were significantly lower for all heifers during the middle 4 months of gestation than during the preceding or succeeding 2 months, with a marked dip at 140 to 160 days of gestation. Post-partum basal progesterone concentrations did not differ from prepubertal concentrations; small peaks of progesterone tended to occur before the first oestrus post partum.

Experiments in two successive years with 24 cattle compared a six-paddock grazing system with a simpler two-field system. In each system the whole area was cut for conservation once during the season. The two systems were stocked each at 3·9 or 6·5 cattle/ha. In the following winters the cattle were offered grass silage (1974) or dried lucerne pellets (1975) ad libitum with two levels of barley.

Daily gains on pasture were depressed by the higher stocking rate but there was no difference between grazing systems. The yield of conserved grass was least on the high stocking rate two-field system. The estimated output of utilized metabolizable energy per hectare was highest on the high stocking rate paddock grazing system but the output from the low stocking rate two-field system was almost as high. It was concluded that the latter system was valuable in many practical situations. Cattle that had been grazed at low stocking rates finished earlier in winter. There was some evidence of winter compensation in cattle weight gain on diets with dried lucerne pellets but not on grass silage diets.

The development of subcutaneous fat as measured by ultrasonics was determined in 28 Angus, 46 Hereford and 42 Charolais bulls, performance-tested on a barley/grass diet. The ultrasonic fat measurements were then examined for possible relationships with feed intake, growth rate and feed conversion efficiency. There were apparent breed differences in the rate of increase in subcutaneous fat thickness with changing live weight but ultrasonic measurements bore little relationship to performance parameters within any of the three breeds tested.

Since comparison of live-weight change of breeding cows is complicated by pregnancy and reproductive synchrony, possible analytical methods for overcoming these problems were reviewed. It was concluded that correction of cow live-weight by subtracting the weight of the gravid uterus and products of conception was biologically and practically meaningful. Two exponential models using polynomial coefficients were derived from published data to predict the fresh weights, at any time during gestation, of the foetus (calculated from calf birth weight) and the gravid uterus and foetal membranes and fluids.

The silage intake and growth rate of naturally suckled calves after weaning was less than that of similar groups of artificially reared animals that had received lower quantities of milk over the period to 8 months of age. Although the silage intake of all groups was linearly related to the level of herbage intake prior to weaning, those calves consuming least herbage had the higher rate of increase in silage intake. It was concluded that silage intake can be influenced for a considerable time after weaning by the level of herbage consumption achieved during the suckling period.

A Piétrain × Large White boar and a Large White boar were placed on each of 12 farms where the breeding females were crossbred white sows. Cooperators were requested to obtain 10 litters by each sire and record their performance to slaughter at 60 kg live weight. Breed of sire did not affect litter size or piglet body weight at birth or at weaning, age of progeny at slaughter, carcass mid-line fat depths or colour and condition of the ‘eye muscle’. Piétrain crosses had higher carcass yields (1·8%) and larger eye muscles in cross-section (13·2%) than Large White crosses. They also had less depth of fat above the eye muscle (14 %) but this did not confer any advantage in commercial evaluations.

Five samples from tested pig herds (Large White 1972, 1975, and 1976, British Landrace 1976 and Welsh 1976) were used to estimate the current rate of inbreeding in British pig testing herds. The annual rates of inbreeding (%) were estimated at 0·32, 0·19, 0·24, 0·33 and 0·34 respectively in the five samples. Overall average estimates of 0·49 to 0·52% per generation are similar to estimates from other pig populations reported in the literature. Coefficients of relationship within farms were calculated for various sib and non-sib groups and these were used to estimate the genetic contributions to the variance components in the analysis of variance of test records.

The nutritive value of wild oats has been examined in two trials with growing rats. Feed consumption was reduced with diets containing 50 % wild oats and dry-matter digestibility was lower (76 and 73 %) with two diets containing 25 and 50 % wild oats compared with diets containing 25 and 50% barley (80·2 and 81·1 %). Live-weight gain was depressed when diets contained more than 45 % wild oats and it can be predicted that growth and feed conversion ratios of mono-gastric animals fed on diets containing high levels of wild oats are liable to be affected adversely. Biochemical studies indicated that any reduction in growth rate could not be attributed readily to specific toxic effects.

ANIMAL PRODUCTION, Volume 25, part 2, pp. 193-208