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.

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.

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.

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.

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.

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.

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.

The performance of two flocks of crossbred Masham ewes (Tees-water × Dales Bred) was measured for 6 and 4 years respectively. The ewes in Flock 1 were mated with Dorset Down rams and the ewes in Flock 2 with Suffolk rams.

The overall mean mating weight of each flock was 68-0 kg with no consistent year-to-year variation. The mating weight repeatability values for ewes entering the flocks as 2-year-olds were 0·532 (±0·0681) and 0·524 (±0·1118) for Flocks 1 and 2 respectively.

Mean litter size increased with age, but repeatability was low. Over- all litter weights for singles, twins and triplets were 5·89, 9·88 and 12·43 kg respectively. Two-year-old ewes had lighter litters than mature ewes. Repeatability for litter weight in Flock 1 was 0·337 (±0·0755).

Lamb growth rate to 4 weeks of age was lower for 2-year-old ewes in both flocks and the repeatability was 0·322 (±0·0947) in Flock 1. For ewes having twin lambs, significant correlations (P < 0·01) were found between mating weight and birth weight and between birth weight and lamb growth rate to 4 weeks of age.

Perinatal mortality was higher for lambs with a birth weight below 3·9 kg, but overall lamb mortality was only 8%: this low figure was probably due to the relatively high birth weight of the twin and triplet lambs.

Changes in body composition during lactation were measured in 12 Border Leicester × Scottish Blackface ewes by serial slaughter at 12, 41 and 111 days of lactation. Ewes suckled twin lambs and were given daily 1·6 kg dry matter of a complete diet containing 151 g crude protein and 10·2 MJ metabolizable energy/kg dry matter.

Live weights of ewes averaged 60·2, 58·9 and 55·8 kg at 12, 41 and 111 days of lactation respectively. There were no significant changes in weights of stomach, small and large intestine and liver.

The weight of body fat averaged 9·19, 2·28 and 1·19 kg at 12, 41 and 111 days respectively (P < 0·001) and weight of ash increased from 1·72 kg at 12 days to 2·30 kg at 111 days (P < 0·001). Water to protein ratios at the three stages of lactation were 2·94, 3·36 and 3·18 (P < 0·10). The energy value of weight loss varied from 68 to 17 MJ/kg, depending on the relative changes in total body water and fat. Live-weight change was therefore a poor indicator of change in body energy during early lactation.

Body fat could be predicted from its combined relationships with live weight and total body water (residual s.d. ±0·70 kg), but when deuterium oxide space was used to estimate body water separate equations were necessary for early and later stages of lactation. This was apparently due to differences between stages of lactation in the time required for deuterium oxide to equilibrate with water in the reticulo-rumen.

1. Seven experiments involving 191 calves and 40 cows were under- taken over a 2-year period into the effect of copper treatment of hypocupraemic calves on their subsequent performance.

2. Significant increases in mean live-weight gain of copper-treated calves ranging from 19·9 to 34·3 kg/head relative to untreated control groups were obtained in three cases.

3. The frequency of copper injection required to maintain plasma copper levels above 0·60 mg/1 varied from 6 to 12 weeks.

4. The live-weight gain and plasma copper concentration responses are discussed in relation to the pasture herbage concentrations of copper, molybdenum and sulphate.

Linear y = a′ + b′x and gamma type y = ea−cx xb models for the lactation curve (y = daily production on day x of lactation) were adjusted to daily production records of 870 lactations. Within- lactations pooled R2 = 0·71 and R2 = 0·74 were respectively obtained for the linear and gamma type models, the latter being preferred for further analyses on account of its general validity under varied circumstances.

The parameters a, b, c of individual gamma type lactation curves were analysed by least squares within a subset of 634 lactations from Holstein-Friesian (HPB), 1/2 HPB: 1/2 Gir (F1) and 3/4 HPB: 1/4 Gir (B1) cows. Crossbreds had both higher initial production and higher persistency of lactation than purebred cows. F1's had higher initial production than B1's, both groups having similar persistency of lactation. Cows calving during the rainy season had higher initial production than cows calving in the dry season, which, however, had more persistent lactations. Parity affected only the initial production a parameter, which was lower for first calvers, while the other parity classes had similar a values.

The effects of days-open on milk yields in current lactations and in following lactations were estimated from 71 911 current and 68 693 following lactation records. Yields were expressed as 305-day, total and annual records, where annual record = 365 × (total yield/days between calvings).

The data were grouped according to current days-open, corrected for initial yield differences and analysed separately for heifers and cows in Moshav (moderate-yielding) and Kibbutz (high-yielding) herds. Current 305-day records increased by 15 to 18 kg milk/day-open up to 90 days-open, and 2 to 3 kg/day-open thereafter. In contrast, the effects of increasing days-open on annual yields were generally small and negative, being positive only for heifers up to 90 days-open. Thus 305-day records heavily under-rated annual yields of fertile cows. For current lactations, 70 to 100 days-open for heifers and 30 to 50 days-open for cows resulted in the highest annual production. Yields in following lactations were positively associated with days-open in the previous lactation. The effect was highest in high-yielding herds, suggesting that high-yielding cows respond positively to some rest between calvings.

Combining the effects of days-open on current and following lactation yields and on the calf crop: in high-yielding herds heifers had the highest productivity when mated not earlier than 70 days post partum, while in moderately-yielding herds days-open did not affect productivity. Cows in high-yielding herds achieved highest productivity at 41 to 90 days-open, while cows in moderately-yielding herds were most productive when mated as early as possible.

A comparison of the economic value of sire fertility and sire transmitting ability for milk production showed that fertility may often be over-rated.

Hays varying from 58 to 75% organic matter digestibility (OMD) were offered ad libitum to steers weighing approximately 400 kg, together with concentrates at rates varying from 0·0 to 8·5 g organic matter (OM)/kg live weight per day. Total digestible OM intake (DOMI) increased linearly by 0·75 g/g concentrate OM intake (OMI) for a hay of 58% OMD, but by only 0·26 to 0·36 g/g concentrate OMI for hays above 70% OMD. With hays above 70% OMD, supplementary feeding had little effect on the overall OMD of the diet but significantly depressed the cellulose digestibility of the diet. With the hays of lower digestibility, supplementary feeding increased the OMD of the diet by an average of 0·90% units/unit concentrate OMI, and had no significant effect on the cellulose digestibility of the diet. Live-weight gain increased with increasing digestibility of the hay and with increasing level of supplement.

In multiple regression equations, variations in hay digestibility and concentrate intake accounted for from 77 to 91% of the variation in hay intake, diet digestibility and total DOM intake.

1. One-hundred-and-ten British Friesian, British Friesian × Ayrshire or successive backcrosses to British Friesian heifer calves were allocated to three groups. Groups A and B were rapidly reared and fed a barley-beef diet which resulted in mean body-weight gains exceeding 1 kg/day (13 to 39 weeks) and group C was normally reared on summer grazing and hay plus concentrates in winter at a mean body-weight gain never exceeding 0·74 kg/day. Animals in group A were first mated at an average age of 42·9 weeks (body weight, 302 kg). Groups B and C were mated later at average ages of 78·4 and 78·1 weeks (average body weights, 443 and 353 kg respectively). After the first calving all animals were fed and managed as a single group.

2. There were no significant differences between the proportion of heifers conceiving at first service in groups A (55·5%), B (66·7%) and C (72·4%).

3. There were no differences in the incidence of dystocia at first calving in heifers served by an Aberdeen Angus bull but 12 out of 19 heifers in group A served by a British Friesian bull had dystocia.

4. Average 305-day fat-corrected milk yields in the first four lactations in group A (18 animals) were 1959, 2918, 3545 and 3210 kg and in the first three lactations in group B were2450,3216and3310kgand in group C 3863,4694 and 4813 kg. Thus milk yield was significantly lower in all lactations for rapidly-reared animals irrespective of the age at breeding and was further significantly lowered in the first lactation of animals mated early.

5. There was a high incidence of laminitis and bloat in heifers reared on the barley-beef diet, but during lactation, there was a lower incidence of mastitis in the lower-yielding, rapidly-reared groups.

A study was undertaken to compare the chemical composition of Texas No. 2 hybrid yellow sorghum with that of a traditional brown-seeded variety and also their digestibility and nitrogen retention in the growing pig. Dry matter, crude protein and gross energy contents and amino acid composition were similar in the two varieties but brown-seeded sorghum had a markedly higher tannin content. In diets containing 70% of either yellow or brown sorghum, N retention was marginally higher on the yellow sorghum diet and apparent digestibility of dry matter, nitrogen and gross energy was improved (0·07, 0·06 and 0·12 units respectively). The improvements in digestible energy and crude protein content of the yellow sorghum diet over the brown-seeded one were 10% and 6% respectively. In a subsequent trial 16 pigs were individually and scale-fed each of the diets over the live-weight range 28 to 81 kg. Growth rates and feed conversion ratios were better on the yellow sorghum diet (10%) but sorghum variety did not influence killing-out percentage, deposition of backfat or area of eye muscle in cross-section.