Patterns of oestrous cycle activity in the first breeding season were studied in 30 Suffolk × Mule ewe lambs, Twenty-eight reached puberty and the mean date of first oestrus was 27 November (s.d. 13·6 days). Mean live weight at first oestrus was 37·7 (s.d. 3·63) kg. The mean number of oestrous cycles was 3·3 (s.d. 1·6), 0·92 (65) being normal length single cycles (14 to 19 days), 0·03 (2) long single cycles (20 to 26 days) and 0·05 (4) multiple cycles (> 26 days).

Plasma progesterone profiles before and after the breeding season were studied in 10 randomly selected animals. All showed profiles suggesting one or two silent ovulations preceding the first oestrus but none showed any indication of silent ovulations following the last oestrus.

Plasma progesterone profiles were also studied on the four animals showing multiple cycles and on the two animals that did not reach puberty. These suggested that, in all four animals showing multiple cycles, one or two silent ovulations had occurred between the two overt oestrous periods. Of the two animals that did not reach puberty, one showed three abnormal silent cycles and the other showed no change in progesterone concentration from a low basal level.

1. Four experiments were performed to study the effects on the growth of lambs of extending natural daylength to 20 h with dim artificial light, under management conditions similar to those on commercial farms.

2. Thirty-six female lambs aged 6 months were given a concentrate ration at a restricted level in groups of nine; there was significantly faster live-weight gain in the two groups that received extra light but no effect on carcass weight or linear measurements.

3. Forty-eight castrated male lambs were fed either ad libitum or at a restricted level on a concentrate diet; half were given additional light. Feeding ad libitum gave faster growth than restricted feeding but there were no significant effects of daylength.

4. One hundred and fourteen lambs of mixed sex were offered silage ad libitum plus one of three concentrate supplements at an average of 0·25 kg per head per day. Half were exposed to 20·h daylength from mid-October until slaughter in mid-January. There were no effects of light treatment on growth or carcass weights.

5. The fourth experiment was a repeat of the third and again there were no effects of extended daylength.

6. It is concluded that this method of controlling daylength is not appropriate for commercial use.

The lysine requirement of the lactating sow was examined in two Latin-square experiments using multiparous sows, in mid lactation, each of which suckled a litter of 10 piglets. The lysine requirement was examined by the addition of supplementary synthetic lysine to a basal diet deficient in lysine, to give dietary lysine levels of 6·4 to 17·2g/kg dry matter. The adequacy of the lysine supply was judged by the responses of plasma lysine, plasma and urea-nitrogen, urinary urea-nitrogen and milk composition. Intersecting linear regression lines were fitted to the treatment means. The responses of urinary urea-nitrogen, in the two experiments, indicated that the lactating sow required approximately 48·5 g dietary lysine per day while the response of plasma lysine indicated a requirement of approximately 51 g lysine per day. Plasma urea and milk composition were less useful as indicators of the nutritional adequacy than were urinary urea-nitrogen and plasma lysine.

1. Two diets, containing either 400 g oat husks (OH) or 300 g straw (ST) per kg, given ad libitum during a 7-week lactation, were compared with a conventional control diet (C) given in restricted amounts. Eight sows per treatment were used in a randomized-block experiment.

2. Mean daily intakes of dry matter during lactation were 4·87, 7·79 and 5·80 kg for the C, OH and ST diets respectively (P>0·001).

3. There were no significant differences between diets in number or weights of piglets per litter either at 21 days of age or at weaning.

4. Mean changes in live weight during lactation were –9·8, +5 1 and –16·8kg for sows on the C, OH and ST diets respectively (P<0·01). Sows that gained weight during lactation tended to lose more in the 7 days following weaning.

5. There were no significant differences in either milk yield or composition. However, the fat content of milk tended to be higher for sows given the two fibrous diets.

6. Mean apparent digestibility coefficients for dietary dry matter were 0·82, 0·63 and 0·59, and for nitrogen were 0·81, 0·75 and 0·63, in the C, OH and ST diets respectively. The rate of passage of the ST diet through the gut was significantly faster than that of the other two diets (P>0·001), which were similar.

Four groups of 10 gilts were reared from an early age under four social conditions. The mating rate (the number of successful copulations as a proportion of oestruses) at the pubertal oestrus of gilts reared in isolation from boars was significantly lower than that of gilts reared near mature boars (P> 0·01). In addition, gilts isolated from boars during rearing had a significantly longer interval from the first mounting attempt by the boar until the display of the standing response (P<0·05) and a significantly higher proportion of these gilts were restless during copulation and terminated the copulation in comparison with gilts reared near mature boars (P<0·01). All gilts were ovariectomized after puberty or at 35 weeks of age and, following a standard oestrogen treatment, they were induced into a series of behavioural oestruses. There were no significant differences between the treatments in the mating rate at these oestruses. It is concluded that the social environment during rearing will influence the mating rate of the gilt at the pubertal oestrus.

Two studies were conducted at commercial farms on a total of 1117 sows to investigate the role of social environment on the weaning to mating interval of the sow. In one of the two studies, group housing and intense boar stimulation, achieved by daily introduction to a boar, were associated with significant reductions in the weaning to mating interval of the sow (P<0·05 and P<0·01, respectively): these two factors together produced increases of 0·18 and 0·22 in the proportion of sows mated within 10 and 28 days of weaning, respectively. In addition, parity and temperature during the week of weaning were significantly associated with the weaning to mating interval in both studies (P< 0·005 and P<005, respectively). It is concluded that the post-weaning social environment will influence the onset of oestrus in the sow.

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.

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.

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.

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.

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 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.

In two trials, three groups of eight dairy cows were fed for 2 months before calving to achieve condition scores at calving of 1·5 to 2 (low), 2·5 to 3 (medium) and 3·5 to 4 (high). For 16 weeks after calving, all cows were given a complete diet composed of silage, malt distillers' grains, barley, swedes and soya bean meal (metabolizable energy 12·25 and 12·35 MJ/kg dry matter in trials 1 and 2 respectively).

In both trials, significant differences were found between groups in dry-matter intake after calving. Cows that had higher condition scores at calving ate less and reached maximum intake of dry matter later than cows with lower condition scores (high, medium and low condition-score cattle attained maximum intakes in 14·5, 12·7 and 9·3 weeks in trial 1, and in 141, 9·6 and 7·9 weeks in trial 2). In trial 1, no difference was found in milk yield but, in trial 2, cows that had lower condition scores at calving produced slightly more milk. In both trials, cows that had higher condition scores at calving lost more body weight and condition, over a longer period, and started to regain the losses later than cows with lower condition scores. The biological efficiencies of milk production (energy output/energy input) from 8 weeks before calving until 16 weeks after calving were 0·302, 0·299 and 0·295 in trial 1, and 0·312, 0·290 and 0·306 in trial 2, for the low, medium and high groups respectively.

It was concluded that cows with lower condition scores at calving produced more milk directly from food rather than via body fat, were in positive energy balance earlier in lactation and over the total period were biologically more efficient than cows with higher condition scores. There appears to be no benefit from feeding cows to achieve a condition score greater than 1·5 to 2 at calving if high-energy complete diets are offered in early lactation.

In each of two trials, three groups of eight cows, with condition scores of 1-5 to 2, 2-5 to 3 and 3-5 to 4 at calving, were given a complete diet for the first 16 weeks of lactation. Food intake, milk yield, live weight and condition score were measured, and related to levels of plasma glucose and free fatty acids, serum insulin, prolactin and progesterone in weekly blood samples, in an attempt to explain differences in food intake.

In both trials, levels of plasma free fatty acids were high after calving for all cows and declined rapidly until week 8, after which they were fairly constant. Glucose and insulin levels increased after calving, producing curves similar to that for dry-matter intake in the first 8 weeks of lactation. Prolactin levels fluctuated too markedly to provide useful information. Progesterone levels increased until week 7 and then fluctuated at 3-week intervals coincident with oestrus. Dry-matter intake was negatively correlated with free fatty acid levels and positively correlated with insulin in trial 1, and with glucose and progesterone in both trials.

Measurements of the median diameter of all teats were recorded within 2 days of calving on 892 cows from eight breeding lines. Teats with a median diameter of ≥35 mm were classed as bottle teats. Their incidence varied from zero in a Hereford line to 0-55 in a Sahiwal crossbred line. In all lines, except the Hereford line, bottle teats were the most important single cause of mortality, up to 2 months of age, of calves that were born alive. However, mortalities became disproportionately high only when all four teats were classed as bottle teats.

Of calves that survived to weaning, those born to cows with at least one bottle teat had heavier live weights at weaning than those born to cows without bottle teats. Consequently, more calves were selected for high growth rate as potential sires from cows with bottle teats than from cows without bottle teats. This, combined with the observation that bottle teats occurred only after at least two calvings, is likely to reduce progress towards elimination of the defect through culling. However, indirect culling of the defect through any effect on calf performance is completely ineffective and uneconomic, and it is recommended that cows be culled directly for the defect in the year in which it first appears.

A study of 468 lactations in two herds of British Friesian cows sampled weekly between 1976 and 1979 was undertaken to investigate seasonal variations in milk yield and to compare four models of the lactation curve: (i) logey(n)=loge a + b logen—cn; (ii) y(n) = anbe-cn; (iii) y(n)= ae-pn—ae-qn; and (iv) y(n) = a—p'n—ae-q‘n.

Model (i) was fitted by unweighted linear regression and the remainder by maximum likelihood. Average peak yield was 29 kg/day and 305-day yield was 5720 kg.

Model (ii) fitted the data slightly better on average than models (iii) and (iv), and all were better than model (i). Compared with model (i), model (ii) reduced the average residual mean square proportionally by 0-10 in cows and 004 in heifers (first calvers). Model (iv) described the initial rise in milk yield up to week 5 better than models (i) or (ii) but reached a maximum value slightly early. Models (i), (ii) and (iv) slightly underestimated and (iii) slightly overestimated maximum milk yield, but model (ii) provided the best estimate of the position of maximum yield.

Peak yields for heifers occurred on average at approximately 10 weeks post calving compared with 7 weeks for cows. Mean persistency of lactation, calculated as s= -(b+1) logec, did not vary from the second lactation onwards, whereas the average rate of decline p' in model (iv) increased with parity.

When milk yields were adjusted for stage of lactation, significant variations were found that were related to the week of recording but this seasonal variation in milk production was smaller than that found nationally in the United Kingdom.

Three experimental diets (L, M and H) containing 135, 175 and 210 g crude protein per kg dry matter respectively were given to crossbred does in two experiments. Protein quality was constant throughout.

In experiment 1 a total of 18 does (six per diet) were given the diets during two successive reproductive cycles. Losses of nitrogen in faeces and urine were estimated for four successive 7-day periods in each 28-day lactation period. Litters were culled at birth to give ‘high’ and ‘low’ lactational loads with 8 and 4 pups respectively. Total 28-day milk yields on diets L, M and H were 3·89, 4·82 and 5·27 kg respectively with eight pups sucking, and 302, 400 and 400kg respectively with four pups. These differences in milk yield were directly reflected in the weights of the pups when weaned at 28 days of age. There was no effect of diet on milk composition, pup birth weight or litter size. Does given diet L did not always consume their allotted ration and this may have affected the results.

The proportion of digested nitrogen utilized for milk protein synthesis differed significantly between diets and lactational loads, and was at its maximum (0·72) when diet L was given to does with eight pups. Does suckling eight pups retained 005 of the nitrogen they digested in their body tissues and those with four pups 0·13; there were no differences between diets in this respect.

In experiment 2 the nitrogen retention of 18 does (six per diet) was measured during pregnancy. Nitrogen retention increased as pregnancy progressed, and overall 0·20 of digested nitrogen was retained for conceptus growth and doe body tissue accretion.

Poultry litter collected from a commercial broiler house, bedded with wood shavings, was used. The material was screened and ground before it was ensiled either alone or with other agricultural by-products, namely chopped barley straw, a mixture of weeds and grapefruit peels. The digestible organic matter in the dry matter value in vitro (0·39) for litter was comparable with that for straw and weeds. Of the total nitrogen (36·3 g/kg dry matter), 0·19 was ammonia-nitrogen and 0·77 protein-nitrogen. Digestible energy and crude fibre in the litter were 7·19 MJ and 334 g/kg dry matter, respectively. Addition of poultry litter at ensiling resulted in significant increases in nitrogen and ash content of the original mixtures. Inclusion of sodium hydroxide in fermented and non-fermented mixtures elevated digestible organic matter in the dry matter values in vitro by 0·19 and 0·13, respectively; the crude fibre concentration was lowered. All initial mixtures were free of lactic acid and were positive for the pathogen Proteus when tested. Unlike crude fibre, fatty acid and free ammonia, which were increased after fermentation, digestible organic matter in the dry matter and pH values were decreased. Ensiling killed the pathogen Proteus in the majority of the silages tested. The silages had a pleasant aroma and colour, and were consumed by Chios sheep.

The effect of monensin supplementation on suckling male dairy calves was studied on a commercial farm. Twenty-eight calves were given monensin supplements from the age of 1 week and compared with a similar group not given monensin. During a 52-day suckling period, the supplemented calves gained 0·12 faster, with little difference in the conversion ratio of metabolizable energy into live weight. During the subsequent 42 days, there was no difference in daily gain, but the supplemented animals were 0·064 more efficient in the conversion of metabolizable energy into live weight.