Sixty-six multiparous hybrid Camborough female pigs and their litters were housed in groups of five or six at day 20 post partum. A boar was added to each group on day 21. Four groups (a total of 22 sows) were fed to appetite (TA), to requirement (R) or to 0·70 of requirement (RO·70). Average daily sow food intakes were 8·2, 61 and 4·5 kg for TA, R and RO·70 respectively. Significant differences occurred in live-weight changes between grouping and weaning (TA>R>RO·70; P<0·001). TA sows were heavier at weaning than either R or RO·70 sows (P< 0·001).

Oestrus occurred during lactation in 0·68, 0·73 and 0·18 of sows, on average 11·3, 13·4 and 8·0 days following grouping respectively, for TA, R and RO·70 sows but these differences were statistically non-significant. The average non-return rate at day 21 was 0·69, with no differences between treatments.

Estimates of the economic returns from pig improvement in Great Britain are substantial. Genetic improvement in the national pig improvement scheme from 1970 to 1977 was estimated, using two control herds, to be 76 (s.e. 10) pence per pig per year. Stocks from breeding companies were of a similar merit from 1975 to 1980, so both groups were combined in the economic evaluation. Annual costs were estimated at €2 × 106 and annual benefits at approximately €100 × 106. The use of crossbreeding in commercial production was also estimated to contribute approximately €16 × 10 per year. These substantial figures are the best estimates available for the benefits, but some of the deficiencies are discussed.

An auto-immunization procedure selective for boar 5α-androstenone is described. Immunization of boars with a conjugate of androstenone and bovine serum albumin as a carrier protein significantly reduced the accumulation of androstenone in adipose tissue from a mean value of 0·77 (s.e. 0·19)mg/kg fat for untreated boars to 0·24 (s.e. 0·06) mg/kg fat for treated animals. No detrimental side-effects were observed in the immunized animals, and the advantages of male-type growth and carcass characteristics were preserved.

An experiment was performed to determine whether quality differences between boars and castrates when used for bacon production are true castration effects or due to the greater leanness of boars. Sixty-four commercial hybrid male pigs, half of which were castrated at 10 days of age, were given different levels of feeding so that at 87 kg live weight there was a 2-mm difference in P2 fat thickness between two groups of 16 boars and two groups of 16 castrates. The leanest group of castrates and the fattest group of boars had similar fat thickness and carcass composition. This design allowed the separation of castration and feeding treatment (carcass composition) effects. Skin thickness and weight (boars greater) and kidney weight (boars heavier) were much more influenced by castration than feeding treatment. Other effects that were more influenced by castration, although less strongly, were killing-out proportion (boars lower because of testes), leg and loin length (boars shorter), joint weight distribution (boars lighter in flank) and lean weight distribution (boars slightly less lean in leg, and more in foreloin and belly). Lean to bone ratio in the side was influenced less by castration than by feeding treatment but boars had more intermuscular fat in relation to subcutaneous fat than castrates. The lean content of the leg was closely related to that of the side, and there were different relationships in boars and castrates.

Ultrasonic measurements, using a Danscanner, were taken of the m longissimus dorsi and overlying fat at the 10th and 13th ribs, and 3rd lumbar vertebra, of 50 Hereford bulls with ages ranging from 400 to 600 days, just prior to slaughter and side dissection.

The analysis adjusted the data for live weight and day of slaughter, and the precision of carcass lean and fat prediction was examined. The standard deviations of total fat and lean in the carcass at constant live weight were 40 and 33 g/kg respectively.

The best single measurement of fat depth for predicting fat proportion was fat depth taken 125 mm from the midline at the 13th rib (residual s.d. = 21·8g/kg). The best combined predictors of both total fat and lean proportions in the side were fat depth 125 mm from the midline at the 13th rib, fat depth 75 mm from the midline at the 3rd lumbar vertebra, and fat area at the 10th and 13th ribs, and 3rd lumbar vertebra, with residual s.d. of 20·5 and 19·6 g/kg for fat and lean proportions respectively.

The results confirm that ultrasonic scanning is now able to give a useful indication of the body composition of live cattle.

Sixty-four commercial hybrid male pigs given different levels of feeding between 27 and 87 kg live weight were used to determine whether quality differences between boars and castrates, when used for bacon production, are true castration effects or due to the greater leanness of boars. At the same carcass composition as castrates, boars had: a higher proportion of water in m. longissimus; a higher proportion of water and lower proportion of lipid in both layers of backfat at last rib; and slightly lower curing gain as the result of a greater loss of tissue water during curing. A separate study on the composition of backfat in lighter weight pigs also revealed a higher proportion of water and lower proportion of lipid in boar backfat compared with that of castrates or gilts, and in both studies a higher proportion of fat-free dry matter in boar backfat indicated greater synthesis of connective tissue protein. Subjective assessment of backfat firmness and whiteness revealed no important castration effects that were independent of carcass composition. The leanest group of boars (average 12 mm P2) had the lowest score for firmness. Fatty acid composition of outer and inner backfat layers was determined more by the rate of fat deposition than by castration.

In a previous paper, pig improvement in Great Britain was assessed for the value of genetic improvements in growth-carcass traits. The benefits are substantial, estimated at €100 × 10 per year. Here, several factors that possibly affect these estimated benefits are examined. These include: 1. comparisons in production systems optimal to improved and to unimproved stocks; 2. interaction of station and farm performance; 3. changes in correlated traits, especially sow weight; and 4. uncertainty about future husbandry and marketing needs.

The conclusion is that, despite appreciable documentation and evaluation, and although the overall benefits are certainly large, there is room for uncertainty about the actual value of past pig improvement work in Great Britain.

The age at which the four pairs of permanent incisors emerged, and the interval between first emergence and the attainment of full size, was recorded from observations taken every 2 weeks on 332 female cattle of a herd comprising the Ayrshire, Friesian and Jersey breeds, and the reciprocal crosses among them.

The 1st pair of incisors emerged at a mean age of 101 weeks of age and later pairs at approximately 30-week intervals, with the s.d. increasing proportionately from 7 to 14 weeks. Full size of the incisors was attained, on average, 4·0, 2·4, 3·0 and 5·6 weeks after the initial observations on incisor pairs 1 to 4 respectively.

Breed (or cross) and season of birth significantly affected the age at emergence of the 1st and 2nd pairs of teeth, and breed also affected the age for the 4th pair. Relative to the Friesian breed, an Ayrshire parent delayed emergence of both 1st and 2nd incisor pairs by approximately 4 weeks, and a Jersey parent delayed emergence of all four pairs. The maternal effect was opposite in sign to the effect of breed substitution; in particular, a Jersey dam caused a reduction in the age at emergence. There was no evidence of heterosis in the crosses. On average, each pair of incisors erupted approximately 4 weeks earlier for cows born between October and December than for those born in the period April to June.

Age at calving, lactation length, milk yield, body weights and the ratio of 18-month body weight to that at 42 months (as an estimate of proportion of maturity) were not significantly correlated with the dental traits. Correlations between age at emergence of adjacent incisor pairs were approximately 0·7, a value higher than that between pairs separated by longer time intervals.

The ‘flight distance’ of Merino sheep was examined in three experiments. In experiment 1 a man moved towards flocks of sheep confined at the end of a 2-m wide laneway, and the speed of approach, flock density and flock size were varied. In experiment 2, single sheep were tested and, in experiment 3, the width of the laneway was doubled.

The critical distance at which sheep started moving past the man was proportional to the width of the laneway. In the 2-m wide laneway the flight distance was 5·7 (s.e. 0·3) m compared with 11·4 (s.e. 0·6) m in the 4-m laneway. Flight distance was not affected by flock size, density or speed of approach, except for individual sheep, who had a greater flight distance than flocks, but this was reduced at fast approach speeds.

Analysis of head orientation showed that the proportion of the flock facing towards or away from the handler could be a useful predictor of the flight distance of confined flocks. On the edge of the flight zone approximately half the flock was facing towards the handler and half was facing to either side or away from him.

Sixty-four commercial hybrid male pigs, half of which were castrated at 10 days of age, were fed in four groups from 27 kg live weight to 87 kg on different feeding scales so as to produce carcasses of different fatness. After curing by the Wiltshire process, there was no difference in the water or curing salt levels in the lean bacon from the different groups, although the boar bacon had a higher water content in the adipose tissue. 5a-androst-16-en- 3-one was found in the boar fat (mean 0-89mg/kg) but levels were not related to carcass composition or growth rate. Taste panellists, all of whom were sensitive to boar taint, did not give the boar bacon lower scores for flavour or overall acceptability and found it more tender.

Consistent age differences at around 27 kg live weight have been found between control (C) and selection (S) line boars of the Large White breed in a coordinated breed improvement programme (89·8 v. 94·6 days, P<001). After 10 generations of index selection on feeding ad libitum, a sample of 20 boars from the programme, 10 C and 10 S, were slaughtered at 27·6 (s.e. 0·48) kg live weight for a more comprehensive examination of this finding. Physical dissection of the carcass and whole body chemical analysis were carried out. Differences between C and S boars were apparent even at this light weight: S boars were older than C (92·7 v. 83·5 days, P<0·01), contained less dissected fat (2·93 v. 3·58kg, P<005) and chemical lipid (315 v. 3·59kg, P<0·05), and had a higher lean proportion (0·477 v. 0·458, P<0·01). There was no significant difference between lines in weight of dissected lean or whole body protein. Index selection has clearly affected early growth and body composition, which questions current assumptions underlying pig testing methods.

Results of two fattening trials, with 49 crossbred ram lambs fattened on an all-concentrate diet given ad libitum with toasted soya bean meal as the main protein source, are presented.

In the first 84-day trial (January to March 1979) there were 32 twin- and triplet-born ram lambs of five genotypes, i.e. Finn-Awassi F2 (FAF 2), Romanov-Awassi F2 (RAF2), Assaf × Finn-Mutton Merino (AsFMM), Suffolk × Finn-Awassi (SuFA) and Suffolk × Finn-Mutton Merino (SuFMM). The overall means ( + s.d.) of the parameters investigated were: initial age, 64·6( + 4·5) days; initial weight, 17·6(±3·0)kg; final weight, 52·2(±4-l)kg; daily gain, 411( + 38)g; food intake, 1·5(±0·3)kg dry matter per day; and food conversion, 3·6( + 0·8)kg dry matter per kg gain.

In the second 56-day trial (August to September 1979) there were 17 single-, twin- and triplet-born FAF2 and Assaf × Finn-Awassi (AsFA) ram lambs. The overall means (±s.d. ) of the parameters investigated were: initial age, 64·1(±8·7) days; initial weight, 24·3(+ 3·6)kg; final weight, 48·5(±5·6)kg; daily gain, 431(±24)g; food intake, l-5(±0·3)kg dry matter per day; and food conversion, 3·5( + 0·7)kg dry matter per kg gain.

In both trials the differences between genotypes in daily gain, food intake and food conversion were not statistically significant and the performance of the progeny of Australian Suffolk and Assaf rams was similar to that of the progeny sired by Finn-Awassi and Romanov-Awassi rams.

Food intake and food conversion were highly correlated with weight of lambs, i.e. r = 0·8864 and r = 0·8857 (d.f. 36), respectively.

In both trials the relationships between daily gain and the pre-fattening performance of the lambs (birth weight, type of birth, weaning age and weight, rates of growth to weaning and from weaning to the start of the trials, as well as the initial age and weight) were not statistically significant.

An experiment was conducted using two batches of 40 purchased male Hereford × Friesian calves, reared conventionally with weaning after 5 weeks. Five diets were offered ad libitum for 9 weeks: a basic concentrate pellet A offered alone, or with additional chopped or long straw; a diet incorporating 35 g sodium bicarbonate per kg in the basic pellet; and a complete diet with the inclusion of 176g chopped straw (20 mm) per kg in the concentrate pellet.

Concentrate intakes and live-weight gains tended to increase with voluntary intake of roughage and the inclusion of buffer in the diet; giving a complete diet, however, gave the best results, with total intake increased to 1 -6 of that for diet A and also significantly increased weight gains.

Rumen acidity was decreased by roughage consumption or by buffer inclusion in the diet. Increasing roughage consumption tended to promote an increase in the molar proportions of acetic and butyric acids in the rumen liquor, and a decrease in the molar proportion of propionic acid.

Results suggested that chopping the roughage into 20-mm lengths did not obviously alter the rumen-buffering characteristics of long roughage, provided that a greater quantity was included in chopped form.

Two experiments were conducted to compare the effects of single and double suckling on the performance of Hereford × Friesian and Friesian cows at pasture. Double-suckled cows each fostered a Friesian male calf in addition to their own calf. Cows were housed from calving to turnout for 57 and 35 days in experiments 1 and 2 respectively, with corresponding grazing seasons lasting 152 and 146 days. During the grazing season the two suckling treatments were stocked on a series of adjacent plots of equal area, with the occupancy of each plot pair being reversed daily. Live weights, milk yields, herbage intakes, and daylight grazing times and nursing activities were recorded on three occasions 28 days apart.

Double-suckled cows lost significantly more weight than single-suckled cows from calving to turnout in both experiments (39·5 v. 3·3 kg and 45·7 v. 20·6 kg), gained more weight from turnout to weaning in experiment 1 (58·4 v. 23·3 kg) but gained less in experiment 2 (17·5 v. 32·3 kg). Double-suckled cows produced significantly more milk than single-suckled cows: 10·1 v. 8·3 and 13·5 v. 9 1 kg/day in experiments 1 and 2 respectively. Differences in daily milk yield in experiment 2 were apparent 28 days after calving.

Suckling treatments did not influence herbage intakes or daylight grazing times and nursing frequencies. Mean nursing intensities were 1·0 calves per single-suckled cow, compared with 1·8 calves (experiment 1) and 2·2 calves (experiment 2) per double-suckled cow. Double-suckled cows nursed significantly more ‘foreign’ calves than single-suckled cows. Total calf weight at weaning from double-suckled cows in experiments 1 and 2 was respectively 364·6 and 344·4 kg, which was 1·64 of the corresponding weights weaned by single-suckled cows (221·1 and 209·4 kg).

Live-weight growth and efficiency of food utilization of purebred Galloway, Luing and Welsh Black steers, and crossbred steers out of Blue-Grey and Hereford × Friesian dams by Aberdeen-Angus, Charolais, Devon, Hereford, Limousin, Lincoln Red, Simmental, South Devon and Sussex sires, were examined in two suckled calf fattening systems. In one system, autumn-born calves were purchased at 1 year of age and fattened during their second winter; the other system involved late winter-born calves, which were purchased at 7 months of age, overwintered on a cheap growing diet and fattened during their second summer. The trial involved a total of 1430 cattle and extended over 5 years (winter system) and 6 years (summer system).

Cattle were slaughtered as close as possible to a standard carcass subcutaneous fat concentration.

The data for crossbred and purebred cattle were analysed separately within the fattening system using least squares models, which included effects for year, sire breed and dam breed, and with regression on the age at beginning of the trial and carcass subcutaneous fat concentration estimated by visual appraisal.

Breed differences in live weight at slaughter were similar to those recorded in the Meat and Livestock Commission's on-farm recording work. Among crossbreds, the larger sire breeds consumed more food per day, generally grew faster and were older at slaughter.

They did not differ significantly in the efficiency with which food was converted into live-weight gain. Among the purebreds, the Luing had a relatively high daily food intake in relation to its growth rate and, together with the Welsh Black in the summer fattening system, was less efficient than the Galloway (P<0·05).

A randomized-block experiment has been carried out over 2 consecutive years to examine the effects of frequency of harvesting grass for silage, and level of concentrate supplementation, on the intake and performance of beef cattle. Swards of S24 perennial ryegrass were harvested at 6-, 9- and 12-week intervals throughout the growing season, commencing on 14 May, 4 June and 25 June respectively. The three silages were offered ad libitum with 0, 1, 2 or 3 kg per head per day of cereal-based concentrates to 84 Hereford-cross suckled calves (mean initial live weight 313 kg) in a 3 × 4 factorial design experiment in each year. The treatments were imposed for a mean period of 100 days. The digestible organic matter in the dry-matter values of the silages harvested at 6-, 9- and 12-week intervals were 0·684, 0·646 and 0·607 respectively. The mean silage dry-matter intakes and live-weight gains for the silages harvested at 6-, 9- and 12-week intervals were 4·75, 4·70 and 4·74 (s.e. 0·08) kg/day, and 0·75, 0·67 and 0·52 (s.e. 0·020) kg/day, respectively. The mean silage dry-matter intakes and live-weight gains for the supplement at 0, 1, 2 and 3kg/day were 5·23, 4·79, 4·72 and 4·17 (s.e. 009)kg/day, and 0·38, 0·57, 0·75 and 0·88 (s.e. 0·023) kg/day, respectively. There was a significant interaction between cutting interval and level of supplementation for live-weight gain, the response to supplementation declining as silage digestibility increased.

Ninety-two British Friesians and 62 Jersey castrated male cattle were slaughtered serially in five age groups at 13, 89, 170, 339 and 507 days, and dissected fully into lean, bone, intermuscular fat, subcutaneous fat, perirenal-retroperitoneal fat (kidney knob and channel fat), omental fat and mesenteric fat. The aim was to investigate the partition of body fat in these dairy breeds and the role of the partition of fat in determining carcass value.

Relative to live weight, Friesians had more lean, subcutaneous fat and carcass fat (subcutaneous and intermuscular) at most ages, and Jerseys had more kidney knob and channel fat, and intra-abdominal fat. Friesians had a higher killing-out proportion and lean:bone ratio, and thicker subcutaneous fat.

The order of increasing relative growth of fat depots with total body fat as the independent variable was, for Friesians: intermuscular < mesenteric < kidney knob and channel fat < subcutaneous < omental. In Jerseys the order was: intermuscular < mesenteric < subcutaneous < kidney knob and channel fat < omental. There were only small breed differences in the distribution of subcutaneous fat between eight regions. t I is suggested that, between breeds, there is a physiological link between the capacity for milk-fat production and the partition of fat within the body, with relatively high milk-fat producers depositing proportionately more fat intra-abdominally.

Since the timing of slaughter is often determined by level of external finish in beef production, the breed difference in the partition of fat, which caused Jerseys to have a higher proportion of kidney knob and channel fat, and intermuscular fat, at the same proportion of subcutaneous fat, would reduce carcass value in Jerseys compared with Friesians.

Two experiments were conducted to compare the effects of single and double suckling on the performance of calves at pasture. In association with their own (status 1) calf, each double-suckled cow fostered a Friesian male (status 2) calf during the post-partum housing period. Calf live weights, milk intakes, and daylight grazing times and suckling activities were recorded.

Single-suckled calves were significantly heavier at weaning (221 and 209 kg) than either status 1 (185 and 170 kg) or status 2 (180 and 175 kg) double-suckled calves in experiments 1 and 2 respectively. Daily gains of the single- and status 1 and 2 double-suckled calves were 0·87, 0·69 and 0·61 kg/day in experiment 1, and 0·94, 0·72 and 0·70 kg/day in experiment 2. Single-suckled calves consumed significantly more milk per day during three 28- day periods at pasture than did either status 1 or status 2 double-suckled calves (7·9, 5·2 and 50kg/day, and 90, 7·2 and 6·5 kg/day in experiments 1 and 2). Status effects in the double-suckled calves were not significant for live weights, weight gains or milk intakes.

Double-suckled calves spent more time grazing and sucked their own or assigned foster dams less frequently than did single-suckled calves. Status 2 double-suckled calves spent more time grazing (experiment 1) and sucked for significantly shorter periods from more foreign dams than did their status 1 contemporaries.

It was concluded that double suckling increased annual total weight of calf output per cow but that it was achieved at the expense of individual calf growth performance. Reduced milk intake appeared to be a major factor in limiting live-weight gains in the double-suckled calves.

A comparison was made of the carcass characteristics of purebred Galloway, Luing and Welsh Black steers, and crossbred steers out of Blue-Grey and Hereford × Friesian dams by Aberdeen-Angus, Charolais, Devon, Hereford, Limousin, Lincoln Red, Simmental, South Devon and Sussex sires, in winter and summer fattening systems. A total of 1430 cattle were involved and the trial extended over 6 years.

The cattle were slaughtered when their fatness was estimated, using the Scanogram ultrasonic machine, to be in fat class 3L of the Meat and Livestock Commission Beef Carcase Classification Scheme. Carcasses were evaluated using a standardized commercial cutting technique.

The data for crossbred and purebred cattle were analysed separately within the fattening system using leastsquares models, which included effects for year, sire breed and dam breed, and with regression on age at the beginning of the trial and carcass subcutaneous fat concentration estimated by visual appraisal.

Limousin and Charolais crosses killed out best. Their carcass weights were, on average, 20g/kg live weight heavier than those of Aberdeen-Angus, Devon, Hereford and Lincoln Red crosses. There was a range of 20 to 30 g/kg carcass weight between sire breeds in carcass saleable meat yield: the highest values were recorded for the Limousin crosses (evaluated on winter fattening only) followed by Charolais and Aberdeen-Angus crosses; Lincoln Red crosses had the lowest values among the crossbreds and Luing cattle among the purebreds. These differences were more a reflexion of differences in fat trim than of differences in meat to bone ratio.

Continental sire breeds had significantly more of their total saleable meat in the higher-priced cuts (P<0·05), although the range between sire breeds was only 15 g/kg.

Rectal temperatures of breeding cows at the National Cattle Breeding Station, ‘Belmont’, Rockhampton were recorded in each of 2 years. The data analysed represented two Bos taurus (Hereford × Shorthorn) and four B. indicus × B. taurus half-bred lines, and 800 to 900 cows in each year. Rectal temperatures averaged 39·8°C, and were 0·5°C higher in British breed than in zebu-cross cows and 0·3°C higher in lactating than in dry British cows (no effect in zebu cross).

Fertility, measured as success or failure in producing a calf at term, was affected by rectal temperature (P<0·0001 in both years). The relationship was curvilinear, the reduction in calving rate due to 01°C increment in temperature being 0009 at 39°C, 002 at 40°C and 0035 at 41°C. Response of fertility to a given change in rectal temperature was the same in different breeds. The average depression of fertility due to heat susceptibility was 015 to 0·25 in British-breed and approximately 010 in zebu-cross herds.

Even in relatively heat-tolerant zebu crossbreds and in a relatively mild environment on the Tropic, both the mean rectal temperature and its genetic variability within a herd had quite large effects on reproduction. The heritability of rectal temperature was 0·25 (s.e. 012) and its genetic correlation with fertility was −0·76 (s.e. 0·35). There was a parallel effect of rectal temperatures of cows on the birth weights of their calves.