The performance of traditional Border Leicester × Blackface cross- breds (Greyfaces) was compared with Blackface crosses from a synthetic Dam Line developed from four breeds; Finnish Landrace (47%), East Friesian (24%), Border Leicester (17%) and Dorset Horn (12%). The Dam Line crosses were lighter (−10%), showed earlier sexual maturity, were more prolific (+12%) and weaned more lambs (+13%) than the traditional crosses but had similar litter weights and flock survival. The lambs from the Dam Line crosses grew more slowly (−5%) (comparing twins with twins and singles with singles) but their carcass composition and carcass grades were similar to those from the traditional crosses.

An assessment of the relative biological efficiency for meat production of the two crossbred types indicated an advantage of about 10 to 12% in favour of the Dam Line crossbred type.

Grass silage with a dry-matter content of 19·4% and containing 16·7% crude protein was offered ad libitum to 42 first lactation British Friesian cows during the first 75 days post-calving. In addition the animals received supplementary concentrates containing either 10·3, 13·6, 17·3, 21·1, 25·2 or 30·3% crude protein on a fresh weight basis, with extracted soya bean meal being used as the main protein source. All concentrates were offered at an equal level of 8·0 kg per day. The relationship between milk yield and protein content of the supplement was curvilinear and was described by the following equation:

Y= 8·95+ 1·0×–0·0205×

where Y = milk yield per day in kg, and × = percentage protein in the supplement. This equation indicated that maximum milk yield was obtained with a concentrate containing 24·4 % protein on a fresh weight basis. The protein content of the milk was also curvilinearly affected by the level of protein in the supplement, and it was calculated that maximum milk protein (nitrogen × 6·38) would be obtained with a supplement containing 23·9% protein. Plasma blood urea levels increased linearly with increasing protein intake. The effects on live-weight change and blood components were also recorded.

Sixty-four lactating dairy cows (Ayrshire, British Friesian and Shorthorn × Ayrshire) were offered grass silage with a dry-matter content of 258 g/kg, and containing 75 g/kg digestible crude protein and 64·6% digestible organic matter in the dry matter for an average period of 16·7 weeks. The control and supplemented groups, each of 32 cows, received concentrates containing on a fresh basis 14% and 18% crude protein respectively which were offered at the rate of 0·4 kg/kg milk for yields above 2·3 kg/day. The mean daily yields of milk were 17·4 and 19·5 kg/cow, silage dry-matter intake 8·16 and 9·00 kg/cow per day and concentrate dry-matter intake 5·36 and 5·94 kg/cow per day on the control and supplemented treatments respectively and these differences were highly significant. The treatments had no significant effects on milk yield and composition in the post-experimental grazing period.

In two experiments over 2 years, 113 North Country Cheviot and 132 South Country Cheviot hill ewes were differentially group-fed over a 10-week period to achieve either good or moderate body con- dition. Ewes were maintained in these levels of condition over the 5 weeks prior to mating. After mating, ewes were killed either on return to service or between days 23 and 85 for counts of corpora lutea and viable embryos.

Ovulation rate in each breed was positively related to body condition at mating. Embryo mortality, as ova loss, was not influenced overall by breed, type of ovulation, year of recording, or body condition. Although comparisons of loss were partly confounded by a differen- tial distribution in the number of ova shed in each breed and body condition group, there was an apparent breed difference in loss of single- and multiple-shed ova. Potential lambing rate therefore showed greater response to improved body condition at mating in the North Country Cheviot breed than it did in the South Country Cheviot.

A computerized mathematical model was used to test the economic effect of changing calving intervals under typical high-yielding (63701 per 305 days for mature cows) herd conditions at 1976 prices. The effect of month of first calving was also tested in a herd where four lactations are assumed to follow at equal calving intervals.

Under the prescribed conditions, cows should calve at 320-day to 360-day intervals (with two exceptions) to maximize the annual margins over concentrates, but the month of the initial calving affects the absolute level of margins over concentrates markedly (maximum £382·10 for 365-day interval for November calving, minimum £318·10 for April). This means that complete knowledge of the main input-output factors is required before recommendations can be made for an individual cow. The change in margin over concentrates for each day's delay in conception varies widely, with rates of loss as high as £1·80 per day's delay occurring.

Twenty-one mature autumn-calving Blue Grey cows were divided into three groups for a 3-year change-over experiment, and each group was allocated to one of three planes of nutrition for the first 150 days of lactation during each year. Milk yields were recorded by machine milking twice daily. The three planes of nutrition corresponded to 1·63, 1·21 and 0·89 of the cow's maintenance allowance 12 h post partum. Increasing the plane of nutrition significantly (P<0·05) increased 150-day cumulative milk yield, but had no significant effect on milk composition. The extent of live-weight loss decreased significantly (P<0·001) as plane of nutrition increased and was reflected in cows maintaining better condition, measured as condition score, through the experimental period.

The small 150-day cumulative milk yield response (32·8 kg per additional 10 MJ metabolizable energy and 62 g digestible crude protein/day) demonstrated the limitation of feeding beef cows for increased milk production in comparison with feeding the calf directly. However, the possible relationship between plane of nutrition, live-weight loss and fertility suggests an important limitation of under-feeding cows during the mating period. Within the constraints imposed, the medium treatment (64 MJ metabolizable energy and 516 g digestible crude protein/day) resulted in levels of cow performance similar to those currently recorded in commercial units. One of the major constraints in the present investigation was the high level of body reserves available in the cows at the start of lactation.

Four groups of 14 3-month-old Israeli Friesian male cattle were each given monensin supplement in their concentrates at the following rates: between 3 and 6 months of age, 0, 0, 25 and 35 p.p.m.; and between 6 months and slaughter, 0, 35, 35 and 35 p.p.m. They were offered hay at approximately 0·3 % of their live weight and concentrates ad libitum.

Daily gain between 3 and 6 months was 1·36, 1·40, 1·50 and 1·57 kg/day, respectively; between 6 months and slaughter it was 1·22, 1·32, 1·33 and 1·24 kg/day, respectively. Differences in intake of concentrates were small. There were no significant differences in slaughter data.

Daily carcass gain throughout the experiment was 0·71, 0·74, 0·77 and 0·76 kg/day, respectively.

Monensin-supplemented animals were approximately 9% more efficient in the conversion of metabolizable energy into live weight or carcass weight than the control animals.

Production of propionate in the rumen was significantly increased in response to monensin supplementation, and the acetate to propionate ratio was significantly reduced.

1. Thirty lactating British Friesian heifers and cows were individually given maize silage ad libitum containing 331 g dry matter/kg, 13 g nitrogen and 11·2 MJ of metabolizable energy per kg dry matter. Urea or aqueous ammonia was mixed in at the time of feeding to give 7·0 g nitrogen per kg silage dry matter. Urea-treated silage was given with concentrates at a high (mean 6·6 kg dry matter/day: treatment HU) or a low (mean 3·3 kg:treatment LU) level of feeding; the lower level only was given with ammonia-treated silage (treatment LA).

2. The addition of ammonia raised silage pH values from 3·9 to 4·4. Silage dry-matter intakes in lactation weeks 7 to 22 for treatments HU, LU and LA were 8·8, 11·1 and 10·7 kg/day.

3. Digestible organic matter content in the dry matter of the diets measured in vivo was not significantly affected by treatment. However, digestible organic matter intakes were significantly greater for treatment HU than for LU in weeks 7 to 10, and for LU than for LA in weeks 11 to 22.

4. The yields of milk and the contents of protein, lactose and energy did not differ between treatments. The milk yields for treatments HU, LU and LA in weeks 7 to 22 were 20·2,19·2, 18·8 kg/day respectively. Fat content of milk was significantly depressed with the HU treatment for heifers in weeks 7 to 10. The live-weight changes of the cows in weeks 7 to 22 for treatments HU, LU and LA were +0·10, −0·07 and −0·37 kg/day; the live-weight loss by cows given treatment LA was significantly greater than for LU. The live-weight change of the heifers was not affected by treatment.

In two experiments over 2 years, 57 North Country Cheviot and 82 South Country Cheviot hill ewes were differentially group-fed indoors over a 2-month period to achieve either good or moderate body con- dition. Over 5 weeks prior to mating, ewes in good condition were brought down in condition by restricted feeding and ewes in mod- erate condition were raised in condition by a high level of feeding. The ewes were thus in moderately-good condition at mating. After mating, ewes were maintained in this condition until killed either on return to service or at 29 ± 8 days for counts of corpora lutea and viable embryos.

Ovulation rate in each breed was positively related to the level of pre-mating food intake at the condition level studied. Embryo mortality, as ova loss, was not influenced overall by the level of pre-mating food intake but loss of multiple-shed ova was greater than that of single-shed ova in ewes which had been on restricted feeding before mating. Although a greater proportion of ewes in the North Country Cheviot breed were not pregnant at slaughter, this could not be identified as a breed difference since the breeds were studied in different years.

Three groups of five male pigs (boars) were reared from an early age under various social conditions. The sexual and social behaviour of the boars was studied from 31 to 56 weeks of age. Boars individually reared from 3 to 12 weeks of age in adjacent wire-mesh pens had similar copulatory performance to that of group-reared boars. However, an apparently important component of courting behaviour, ‘nosing activity’, was significantly reduced (P<0·05) amongst those boars individually reared from 3 weeks of age in adjacent wire-mesh pens. Social behaviour appeared to be unaffected by the rearing treatment.

One hundred and twenty South Country Cheviot hill ewes were differentially group-fed indoors over a 2-month period to achieve either moderately-good or poor body condition. Over 5 weeks prior to mating, ewes in moderately-good condition were brought down in condition by restricted feeding and ewes in poor body condition were raised in condition by a high level of feeding. The ewes were thus in moderate condition at mating. During the first 4 weeks after mating, half the ewes from each original condition group were fed at a high level and the other half were fed at a low level. Ewes were killed either on return to service or at 30 ± 10 days forcounts of corpora lutea and viable embryos.

Ovulation rate was not significantly related to the level of pre-mating food intake at the condition level studied, although the trend was positive. Embryo mortality, as ova loss, was reduced by a high level of post-mating food intake but was increased by a high level of pre-mating intake. This latter result, however, may be influenced by the experimental confounding of high pre-mating food intake and very low initial body condition. The greatest loss was incurred by ewes, originally in poor condition, which were fed at a high pre-mating level and a low post-mating level. Potential lambing rate at slaughter was not affected by the level of food intake either before or after mating although the trend was for a low level of post-mating intake to be associated with an increase in the proportion of barren ewes.

Measurements of the m. longissimus and overlying fat at the last rib were taken on the live pig using ultrasonic machines of differing complexity: Sonatest (simple A-mode machine), Scanogram and His Observer (modified linear scanners), and Danscanner (‘real time’ scanner). These measurements were examined as predictors of the corresponding carcass measurements and percentage lean in the carcass.

Sonatest and Scanogram were compared using 143 purebred and crossbred pigs of different types. The analysis was pooled within breed-type and sex. The standard deviation for percentage lean was 3·94. Residual standard deviations for predicting percentage lean from live weight and best fat thickness were 2·72 (Sonatest) and 2·56 (Scanogram). Addition of m. longissimus depth (Sonatest) and m. longissimus area (Scanogram) reduced these to 2·69 and 2·29 respectively. The use of two or more fat measurements provided no extra precision over a single fat measurement.

Scanogram and His Observer were compared using a subset of 38 pigs. Scanogram was a better predictor of percentage lean using a single fat measurement but when a combination of measurements was used, there was little difference between the machines.

Scanogram and Danscanner were compared using a subset of 27 pigs. The standard deviation of percentage lean was 3·57. Residual standard deviations for predicting percentage lean from live weight, best fat depth and m. longissimus area were 2·18 (Scanogram), and 2·03 (Danscanner). Fat areas had similar predictive precision to fat thickness measurements.

Observations were made on a pig herd where sow service in lactation had been practised for 2 years. Sows and their litters were grouped and a boar later introduced. Of the 49% of sows mated in lactation 78% conceived. Sow and litter data were subjected to multiple regression analyses which indicated that lactational oestrus was more likely to occur for sows farrowing at the end of the calendar year, and for sows with smaller litter sizes. Sows mated in lactation showed a smaller weight change from the end of the previous pregnancy to weaning than those first showing oestrus after weaning. It is suggested that these weight changes in lactation and the seasonal relationship to lactation oestrus may be related to weight gain achieved by the sow in the previous pregnancy. Sows mated early in lactation had piglets with lower weaning weights and sows mated in late lactation had greater weaning weights than piglets whose dams showed oestrus after weaning.

Two field trials were conducted with 138 and 123 bacon-weight pigs respectively from one farm to determine the effect on bacon yield of feeding the animals sugar solutions prior to slaughter. Three treatments were tested: immediate slaughter on arrival at the abattoir; lairage overnight with access to water only (15 h); and overnight lairage with access to a sugar solution (6 h) followed by water only (9 h) prior to slaughter. A glucose syrup solution was used in one trial and a sucrose solution of similar hexose-equivalent concentration (550 g/kg) in the other. Access to either of the sugar solutions, relative to water only or immediate slaughter, increased bacon yield. This was entirely due to glucose-fed pigs having a higher carcass yield (2·3 % and 1·5 % respectively) and a trend in this direction for the sucrose-fed animals (0·9% and 1·0% respectively). Carcasses of glucose-fed pigs actually gained less weight than those of their counterparts during the curing process, but this did not occur with the sucrose solution. Access to sucrose relative to water only and immediate slaughter increased liver weights by 32% and 42% respectively. Lower hepatic responses were obtained with glucose syrup (18% and 12%). Both sugar solutions reduced muscle ultimate pH (0·1 to 0·2 unit) relative to water only in overnight lairage.

Two experiments were carried out with crossbred lambs which had been weaned in July when 16 weeks old. From early September they were kept in a light-proof building with 12 h artificial light per day for 3 weeks and then half were exposed to 16 h and half to 8 h light per day for a further 16 weeks.

Experiment 1 included 72 lambs (48 castrated males and 24 females) and half in each daylength were fed on a concentrated ration ad libitum; the other half were restricted to 70 g/kg live weight0·75 per day. Half of each group were shorn. Lambs kept in 16 h light per day grew significantly faster than those in short daylength at both levels of feeding. Food conversion ratio was best in the 16 h restricted sheep. Unshorn lambs had heavier carcasses than shorn lambs. Long daylength stimulated general growth of the animal without markedly affecting carcass composition, irrespective of level of feeding, whereas ad libitum feeding resulted in much fatter carcasses than did restricted feeding. Gut fill was significantly greater in long-daylength sheep.

Experiment 2 included 24 individually penned castrated male lambs, 12 of which were sired by Suffolk rams and 12 by Oxford rams; all were fed at the restricted level. Long daylength significantly stimulated weight gain, especially in the Oxford-cross lambs, but the increase in carcass weight was not significant in this experiment due to the large effect on gut fill.

It was concluded that long daylength stimulated growth and gut fill by some central control mechanism and not merely by encouraging more eating.

Failure to recycle after weaning and the interval from weaning to oestrus were studied using sows representing 28 crosses from eight breeds at three stations. Of the sows farrowing their first litter, 12·9% failed to recycle within 50 days. The least squares mean for weaning to oestrus interval for all crosses was 13·5 days. Hampshire × Landrace, followed by Hampshire × Yorkshire sows had the shortest intervals (8·0 and 8·7 days respectively) whereas Large Black × Lacombe sows had the longest interval (22·1 days). Crosses involving the Yorkshire, Hampshire, Berkshire and Tamworth breeds had shorter intervals than those involving Landrace, Duroc, Large Black and Lacombe. Season of farrowing had significant effect (P < 0·05), with the shortest interval (11·4 days) occurring in autumn and the longest (15·1 days) in spring and summer. Weaning to oestrus interval increased with the increase in litter size. The interval was longer (15·7 days) at Lennoxville but similar at the other stations. There was a steady increase in size in the following litter with the increase in the weaning-oestrus interval. The heritability estimate (full-sib analysis) for the weaning-oestrus interval was 0·25 ± 0·10. Repeatability based on limited data was calculated at 0·28.

Ten sows were each infected with 300 000 larvae of Oesophagostomum dentatum after weaning their second litter, and subsequent per formance over one parity was compared with that of 10 ‘worm free’ controls. Mean worm burden in the sows when slaughtered immediately after weaning, was 13 480 ±2377. From service to weaning of the litter the mean body weight of worm-free sows increased (+11·3 kg) whereas that of infected sows declined (—13·1 kg) and at slaughter the carcasses of infected sows had lower depths of backfat. Worm-free sows averaged 12·8 pigs born of which 11·3 were born alive, corresponding values for infected sows being 12·4 and 9·5. Worm infection reduced birth weights by 15% but differences were not significant. Litters were equalized at eight pigs shortly after birth, and subsequent weaning weights were 10·5 % lower in those of infected sows despite a 29 % higher consumption of creep feed. Clinical disease was never observed in the infected sows, and no parasitic infection was found in the piglets. It is concluded that sub-clinical infections of O. dentatum in sows may be of economic significance.

1. The levels of four hormones which might be involved in the control of growth have been measured in the blood of lambs kept in 16 or 8 h daylengths for 4 months in each of two experiments. Under the conditions of these experiments long daylength stimulated growth.

2. Prolactin concentration was significantly increased by long day-length and by ad libitum feeding, compared with short daylength and restricted feeding, respectively.

3. Growth hormone, insulin and thyroxine concentrations were unaffected by daylength. Ad libitum feeding caused lower growth hormone and higher insulin concentrations than restricted feeding, and growth hormone levels fell after the morning feed.

4. Of the hormones measured, prolactin is most worthy of further study as a possible mediator of the effects of long daylength on growth.

Sixty-four growing pigs, with equal numbers of females and castrated males, were fed diets containing from 10 to 17·6% crude protein but in which lysine was maintained at 0·95%. Over the 25 kg to 55 kg live-weight range studied, growth performance was unaffected by a reduction in crude protein level from 17·6 to 14·5%. Below 14·5% crude protein, daily live-weight gain and feed conversion ratio deteriorated linearly. Percentages of lean meat and fat in the middle joint showed similar trends. Significant sex effects were confined to carcass characteristics which indicated that the females produced leaner carcasses. It was concluded that below 14·5% crude protein a deficiency of the next limiting amino acid to lysine, or possibly non-essential nitrogen, depressed growth performance.

Fifty-three lambs were artificially reared from 1 day old. From 14 days of age they were either housed and offered cut herbage or grazed at pasture.

Five milk feeding treatments were allocated to both the housed and the grazing lambs; these were a total of 50, 70, 90 and 110 kg of ewes' milk given over 12 weeks and milk substitute for 4 weeks. Three additional lambs were housed and offered milk ad libitum.

Digestibilities of the dietary components, herbage and milk intakes and lamb growth rates were measured.

Similar digestibility coefficients were obtained for milk and for herbage when consumed together compared with individually.

Milk intake was negatively correlated with herbage intake and positively correlated with growth rate.

Under conditions permitting ad libitum intake, lambs at pasture had higher intakes of herbage than lambs offered cut herbage indoors. Equations are given which enable herbage intake at a particular age to be predicted from total milk intake.