1. An experiment designed to investigate the growth and yield of lucerne over a wide range of plant populations is described and the results discussed.

2. The mean yields of lucerne per plant were fitted to three different equations relating yield per plant to plant population, and the ‘goodness-of-fit’ of these equations was compared.

3. As plant population increased, the yield of lucerne per acre increased very rapidly up to a certain level, but further increases in plant population led to much smaller increments in yield. It is argued from theoretical considerations that the yield per acre would reach a maximum only when the plant population is infinite.

1. In the course of a 2-year field trial (1959–60) conducted in mid-Wales, 525 cattle were entered by 317 co-operating farmers for treatment with p.m.s. in the induction of multiple-pregnancy. Most animals were commercial, non-pedigree cattle maintained in accord with local custom. The cattle were of mixed ages and included some milking cows as well as animals used in calf rearing.

2. The method of hormone treatment tested consists of a single subcutaneous injection of a freeze-dried preparation of p.m.s. administered in the follicular phase of the oestrous cycle. Most cows were injected 16 or 17 days after a previous oestrus and bred by a.i. at the heat period following injection.

3. Of the 525 cattle injected 416 provide comprehensive data on factors affecting ovulatory response; seventy cattle, which had a ‘silent heat’ after injection, provide additional but partial information. In thirty-nine cattle, it was not possible to obtain reliable evidence of response. Data on ovulation and pregnancy were obtained by examinations per rectum conducted during the early weeks of pregnancy.

4. Ovulation data relate to 416 cows which were injected, came in oestrus shortly afterwards and inseminated, then examined for evidence of fresh corporea lutea at the following mid-cycle stage. Five dosage levels of p.m.s. were employed (800, 1000, 1200, 1600 and 2000 i.u.). The normal process of ovulation did not appear adversely affected by any of the doses employed. 173 of the 416 cows (41·6%) produced more than one egg.

5. There is clear evidence of a dose-response relationship over the dosage range employed. The mean number of ovulations varies from 1·43 at 800 i.u. to 3·97 at 2000 i.u. The percentage of cattle shedding additional eggs rises from 33 at 800 i.u. to 56–6 at 2,000 i.u., but increasing dosage level leads to considerable variability in ovulatory response: range of ovulations at 800 i.u. is 1–5, and at 2000 i.u. is 1–25.

6. Little affect was observed in ovulatory response according to the stage of p.m.s. administration. At low dosage levels, an interval of at least 2 days between injection and oestrus was necessary to allow response to occur. Among factors affecting response to a standard dose of p.m.s., lactation and state of normal ovarian activity appeared to have some importance. There was no evidence of an effect on cycle length. Treatment did not give rise to abnormal mating behaviour and the incidence of adverse side-effects following p.m.s. injection was negligible. The occurrence of large unovulated follicles occurred more frequently following treatment with 2000 i.u. than with lesser dosage levels. 59·1% of all ovulations occurred in the right ovary and 40·9% in the left. In examinations made prior to injection, the incidence of spontaneous double ovulations was 4·1%.

7. With the p.m.s. approach, it is found that one problem in cattle is that of silent heat, the condition where ovulation is not accompanied by the usual symptoms of oestrus. In 486 animals for which information was obtained, silent heat occurred in 70 (14·4%). There is some tendency for the condition to occur more frequently where low dosage levels are used or where p.m.s. is administered very late in the oestrous cycle. Lactation appears to affect the incidence of the defect. The lowest incidence (4·8%) occurs in ‘dry’ cows and the highest (22·7%) in cattle rearing three to four calves. Superovulation occurred less frequently at silent heat than at normal oestrus. There is no evidence that p.m.s. injection is the direct cause of the condition. It appears that time of ovulation in animals showing silent heat is comparable with that for cattle showing the normal symptoms.

8. Of the 416 cattle put to a.i. shortly after p.m.s. administration, 317 (76·2%) were pregnant when examined some 6 weeks after first insemination. This compares closely with the normal 30–60 day non-return figure for the mid-Wales area (78·5%). Cattle conceived as readily after injection with 2000 i.u. as after treatment with 800 i.u. Even where animals shed many eggs (e.g. more than six) the conception percentage (84·0) was high. It is clear that this form of therapy does not adversely affect the processes of ovulation, fertilization and implantation. There is some suggestion that p.m.s. aided conception in repeat-breeder cattle. Examinations in the mid-cycle stage following a.i. did not adversely affect conception.

9. Data on the number of eggs surviving (as foetuses) in the 6th week after mating, in relation to the initial number of ovulations, clearly show a heavy loss in eggs in early pregnancy. 41·6% of cattle shed additional eggs but only 23·1% possessed multiples in early pregnancy.

10. Reduction to a single foetus seemed particularly liable to occur in cattle producing two eggs-only. Of sixty-seven double-ovulating animals that conceived, thirty-two possessed twins at the 6th week (47·7%). The survival of both eggs in such cows was better when one egg was shed by each ovary (61·5%) than where both ovulations occurred in the one ovary (28·6%). Analysis of data on egg survival according to factors such as age, breed, time of treatment did not reveal differences.

11. Trans-uterine migration of eggs was rarely (1 case in 197 examinations) noted. The ability of a single uterine horn to sustain more than two foetuses was limited. In cattle where three to six eggs were shed by an ovary, the survival of twins in the associated uterine horn was observed in a majority (57%) of cases. Where many eggs (ten to fifteen) were shed by an ovary, twins were rarely sustained by the associated uterine horn.

12. A steady increase in the percentage of cows carrying multiples (at 6 weeks) was noted over the dosage range employed. 20·8% of cows injected with 800 i.u. carried multiples, the figures for doses of 1000, 1200 1600, and 2000 i.u. being 25·2, 31·3, 41·7 and 42·7, respectively. Multiples in the form of triplets and quadruplets occurred more frequently at the higher dosage levels than at 800–1000 i.u. of all cows with multiples considered, 36·5% possessed more than two foetuses at examination in the 6th week.

13. Pregnancy diagnosis examinations were conducted over a period ranging from 35 to 101 days after mating, with most falling in the period 41–44 days. It appeared that the most appropriate time for diagnosing multiples was at the end of the 6th week of pregnancy. The need to conduct diagnosis at a specific time after mating, and the fact that the examination may lead to total litter loss in many animals, makes the procedure unsuitable for any widespread practice. Partial litter loss (loss of one foetus) was observed in 12·5% of cows carrying twins at 6 weeks and in 20·0% of those with triplets.

14. In nineteen cows, each possessing either three or four foetuses, an attempt was made in the 6th week of pregnancy to control litter size to two. This was by rupture of excess amniotic vesicles by manipulation per rectum. Two of those so treated eventually produced calves, the others either aborting or returning in oestrus soon after the control procedure. The method is unsuitable for farm application for reason of the delay in returning to normal breeding after such cases of failure of pregnancy.

15. A substantial proportion (32·5%) of those cows which were subjected to pregnancy diagnosis lost the conceptus a short time afterwards. Foetal loss in cows with twins was greater (43–46%) where foetuses were both in the one horn than where distributed between both horns (31%). The various factors which were possibly involved in foetal loss are discussed. Evidence was obtained that total foetal loss occurred more frequently in animals shedding many eggs than in those shedding few.

16. Information is recorded for 147 injected cattle which produced single calves following conception at the oestrus immediately following hormone treatment. Additional data on single calvings are provided by 200 untreated cattle which were studied in the area of the trial. These data show birth weight of single calves to be 78·6 lb., and the incidence of calf mortality, retention of foetal membranes and difficult calvings to be 4·9, and 6·0%, respectively. The mean duration of the gestation period was 283·4 days.

17. The outcome of multiple calving was observed in forty-four cattle (thirty-five sets of twins, eight sets of triplets and one set of quintuplets). As a result of earlier examinations, farmers were usually alert to the fact that cows were carrying twins. Herd owners were encouraged to provide such cows with an additional 2 cwt. of a suitable concentrate feed during the final 2 months of pregnancy. Although a number of herd owners followed the recommended feeding programme, in a number of instances the most appropriate pre-calving preparation was not given. The outcome of calvings in relation to the level of additional feeding is considered under three headings, high, moderate and low plane.

18. Given good feeding (high plane) the outcome of twin calvings was satisfactory. Results suggest that the problems often associated with twins (low-weight calves, high rate of mortality, retained foetal membranes, loss of conditon and poor subsequent breeding of the dam) may largely be overcome by an adequate ‘steaming-up’ policy. In cows adequately prepared, birth weight ranging from 59 to 89 lb. were recorded (mean 73·9 lb.) Mean gestation was a little less (280·6 days) than for singles. The incidence of retained foetal membranes (18·2%) was greater than that for single-bearing cows, but did not constitute a serious problem in any animal.

19. Less satisfactory results were noted in cows not given adequate preparation for twins. Where triplets were carried, the outcome for cow and calves, regardless of the feeding attention given, was unsatisfactory. Triplet-bearing cows calved earlier, and the incidence of retained foetal membranes, difficult calvings and calf deaths was much above that noted for the twin-bearing animals. The single set of quintuplets was born prematurely, all calves being dead.

20. Problems in the field application of the p.m.s. technique are considered in the light of the results obtained in the trial and from discussion with farmers in the area of work.

21. Information was obtained on the incidence of natural twins in 3826 calvings in the mid-Wales area. The figure of 2·82% compares closely with that noted in other surveys in the United Kingdom. Literature on the incidence is reviewed.

22. It is clear, from the results obtained in this trial, that the technical problems facing commercial usage of p.m.s. are too numerous to allow any practical recommendation to be made. While none seems to be of such a nature as to make the eventual development of a twinning technique unlikely, there is little hope of immediate solution to many of them. The lines of work which may lead to more satisfactory results are discussed in the final section of the paper.

1. Investigations on the fats from different tissues of forty-eight Romney ewes have shown that the iodine numbers of the fats cover a wide range from 32·7 for a perinephric fat to 83·7 for the fat from a metacarpal bone, while the percentage fat varies from as low as 3·8 in a longissimus dorsi muscle sample up to as high as 95·5 in a perinephric fat sample.

2. The mean iodine values of the fat and percentage fat respectively in the tissues examined were as follows: perinephric, 39·8, 88·1; loin subcutaneous, 41·7, 80·9; loin intermuscular, 44·4, 71·4; longissimus dorsi muscle, 53·1, 7·7; femur, 45·1, 39·8; tibia-tarsus, 54·3, 30·6 and metacarpus, 79·9, 24·3.

3. In the carcass tissues the muscle fat was significantly higher in iodine value than the fat from the fatty tissues. In the long bones analysed, the fats from the metacarpus had a highly significantly greater iodine value than was found for the other bones or carcass tissues. The fat from the tibia-tarsus was comparable in iodine value to that of the muscle tissue while the iodine value of the fat from the femur approached that from a fatty tissue.

4. A distinctive feature of the fats examined was their variability in iodine value. The values varied between animals by 15·3 units for perinephric fat, by 13·0 units for subcutaneous fat, by 16·9 units for intermuscular fat and by 12·4 units for muscle fat.

5. The present results for the iodine values of the fats of Romney ewes generally agree with those obtained by Callow (1958) for Suffolk lambs. However, whereas in Suffolk sheep in accordance with the temperature theory of Henriques & Hansen (1901) the subcutaneous fats have higher iodine values than do the intermuscular fats, in the Romney sheep studied the reverse holds.

1. Data on the crude-protein content and crudeprotein production of five grass species (each sown with white clover) over the period 1954–56, at six levels of compound fertilizer application, are reported. Perennial rye-grass (S. 101), meadow fescue (S. 215), timothy (S. 48), cocksfoot (S. 26) and bent (N.Z. Browntop) were sown in 1953 at appropriate seed rates, each with 2 lb./acre S. 100 white clover. The fertilizer treatments were 0, 1, 3, 5, 7 and 9 cwt./ acre of a compound of composition 10% N, 4%P2O5, 9·5% K2O applied in the early spring of each of the years 1954–56. The swards were cut three times a year in 1954 and 1956, but only two cuts were possible in 1955.

2. Bent mixtures had a higher crude-protein content than any other mixture in all years and (with one exception) at every cut within years. Differences between other mixtures were smaller and often erratic, though timothy invariably had the lowest crude-protein content at the second cut and cocksfoot at the third. Application of the fertilizer raised the crude-protein level of the herbage at the first cut, but depressed it in subsequent cuts.

3. The bent mixture gave the highest yield of crude-protein per acre followed by the timothy mixture, while the lowest yield was produced by the perennial rye-grass mixture. The bent mixture differed from all others in its distribution of crudeprotein production over the season, producing less at the first cuts and more at the second and third cuts. This reflects its pattern of production of dry-matter. Response to spring application of fertilizer in terms of crude-protein yield declined rapidly from cut to cut. Over the whole period of the experiment 1 cwt./acre/ annum of fertilizer containing 10% N gave a response of about 0·5 cwt. crude-protein/annum.

1. Data on the dry-matter production of five grass species (each sown with white clover), over the period 1954–56, at six levels of compound fertilizer application, are reported. Perennial ryegrass (S. 101), meadow fescue (S. 215), timothy (S. 48), cocksfoot (S. 26) and bent (N.Z. browntop) were sown in 1953 at appropriate seed rates, each with 2 lb. per acre S. 100 white clover. The fertilizer treatments were 0, 1, 3, 5, 7 and 9 cwt. per acre of a compound of composition 10% N, 4% P2O5 and 9·5% K2O, applied in the early spring of each of the years 1954–56. The swards were cut three times a year in 1954 and 1956, but only two cuts were possible in 1955.

2. The timothy mixture gave the highest total production of dry-matter over the 3 years, the bent and perennial rye-grass mixtures giving the lowest total productions. Differences between mixtures in annual yield varied in sign and in magnitude from year to year. For example, bent gave the lowest yield in 1954, but outyielded the meadow fescue and the cocksfoot mixtures in 1955, and the perennial rye-grass mixture in 1956. As regards the distribution of dry-matter production over the season, it was found that bent differed from the other mixtures in that a higher proportion of its annual yield was produced at the second and third cuts.

3. There were significant linear relationships of dry-matter yield to fertilizer application rate in most of the data. On average over the 3 years, 1·6 cwt. of dry-matter were produced for each cwt. of spring applied fertilizer in the first cut, 0·7 cwt. per cwt. of fertilizer in the second cut, while very small and non-significant responses were found in the third cut. There was no evidence of systematic differences between grass mixtures in response to fertilizer level.

4. The yield of clover dry-matter in 1956 (the third harvest year) was least from the cocksfoot and timothy swards, and was significantly and linearly depressed by fertilizer application in all three cuts.

Efficiency of food utilization from 2 to 18 weeks of age has been examined in 12 MZ and 7 DZ pairs of twin calves fed standard rations. Mean efficiency reached a maximum at about 6 weeks of age; weaning brought about a rapid decline followed by a recovery. Animals became more alike in efficiency as their ages increased.

Those animals least efficient shortly after birth were most adversely affected by weaning, although they tended to be relatively more efficient when fully established on either milk or solid food.

Relative to the fairly closely replicated age-efficiency trends of identical twins, different pairs followed different trends. These trends, which primarily reflected the variable success with which the calves adapted to new diets, were subject to some genetic control.

The nitrate-nitrogen contents of herbage at the first cut of 1956, and at a first cut in 1957

Herbage samples from two replicates of the first cut of 1956, and from two replicates of a first cut taken in 1957 in the present experiment, were analysed for nitrate-N. The 1957 results are included here as illustrating the influence of season on nitrate-N accumulation, although data from that year have not been reported in the two papers of the present series. Attention has been limited to first cuts, as nitrate-N accumulation is normally greater the shorter the interval between, the application of nitrogen fertilizer and sampling, and in addition the spring flush of growth is usually conducive to high nitrate-N contents (ap Griffith, 1961).

The relationship of efficiency to weight and feeding rate has been studied in 38 twin calves from 2 to 18 weeks of age. Following birth or weaning heavier animals were more efficient, but tended to be slightly less efficient when fully established on a diet. On balance, they possessed an advantage.

Heavier twins and heavier pairs were also on average more efficient. The increase in mean efficiency for contemporary animals was about 1% for each 1 lb. superiority in weight over the 4-month period. These results contrast with the well-known decline in efficiency as animals increase in weight. Different pairs declined in efficiency with increasing live weight at distinctly different rates judged by the resemblance of twin and co-twin, but evidence for genetic control was slight.

More efficient animals were associated with a relatively more rapid decline in efficiency, leading to a general convergence in efficiency as animals grew heavier.

The relationship of efficiency to feeding rate was very similar to the relationship with weight.

The effect of fertilizers in increasing the yield of clover seed was examined by a series of manurial trials. The initial mineral status of the crop and the extent of the uptake of the applied nutrients were determined by analyses of the leaf. The techniques for sampling and analysing leaves to determine mineral status are described.

The high yields of seed and lack of response to fertilizers in trials at Cambridge led to their being repeated at Saxmundham on land known to be extremely deficient in minerals. Even then there was a response only to phosphate which although significant was small.

Leaf samples were also collected from commercial crops of red clover in 1955, 1956 and 1957. The analyses of these samples indicted that none of them was as deficient as the crops at Saxmundham, and no relationship was found between mineral status and seed yield.

It is concluded that yields of red clover seed in Eastern England are not likely to be increased materially by the application of fertilizers.

1. Pure swards of S. 48 timothy and S. 215 meadow fescue receiving approximately 52 or 156 lb. N per acre over a period of 8 months were cut (a) at anthesis and twice thereafter or (6) every 4 weeks. The number and weight of tillers and leaves and annual plot yields were determined.

2. Tiller numbers rose to their highest in spring and then declined throughout the summer. The higher rate of nitrogen increased tillers in the meadow fescue more than in the timothy; the system of frequent defoliation resulted in enhanced production of tillers in the low nitrogen swards of both species, so that maximum populations within a species were similar under the two levels of nitrogen.

1. The object of the experiment was to make a detailed investigation of the carcass composition of Large White hogs at 68, 91 and 118 kg. live weight (i.e. 50, 68 and 92 kg. carcass weight). Ten hogs were dissected at each stage.

2. A dissection technique suitable for this investigation is described, involving the dissection of one side into individual bones and muscles, subcutaneous and intermuscular fat deposits, skin, tendon, glands and blood vessels. Some possible modifications of the method for future investigations are also discussed.

3. The complete dissection of one side took approximately 110 man-hours and the average weight loss in dissection was 0·798%.

1. The habits of five Tanganyika Shorthorn zebus and their suckling calves were studied during periods of 72 consecutive hours at monthly intervals in each of the first 6 months of the calves' lives, during the ‘dry’ season of the year.

2. Cows grazed for 7·16 hr. per day while grass was green and plentiful, but, as grazing became dry and sparse, they ate silage at night for up to 3 hr., and reduced their grazing time by about 2 hr. The ratio of rumination time to eating time tended to increase as grazing became drier and as silage eating increased. The average ratio was 1·01 to 1.

3. All calves were actively grazing for 4·0 hr. per day by the second month, and for 5·6 hr. per day by the fifth month. They ate silage diffidently in the second month, but they were eating silage for 1·7 hr. per night at 6 months. Rumination was observed in a calf at 18 days of age, but was consistently observed in the second month when calves ruminated for 6·1 hr. per day. The ratio of rumination time to grazing time for calves declined from 1·5 to 1 in the second month to 1·1 to 1 in the fifth month. Rumination time among calves was more closely related to silage eating than to grazing time.

4. The calves acted as individuals in the first month, and thereafter their eating habits were determined more by their dam than by their age. Day-time rumination pattern was a characteristic of the age of calf, but night-time rumination by calves was more closely correlated to that of their dams.

5. Calves suckled for an average period of 9·2 min. per suckle. There was very little variation with age, but frequency of suckles decreased from 9·5 times per day at 1 month to 5·6 times per day at 6 months. The fastest-growing calf suckled less frequently for shorter periods, suggesting readier availabilty of more milk.

6. Suckling intensity was evenly spread over the 24 hr. during the first 2 months, but thereafter suckling became increasingly confined to nighttime while the cattle were yarded.

7. It was concluded that artificial feeding divided into three equal feeds per day at 05.00, 13.00 and 21.00 hr. for the first 2 months, followed by two equal feeds per day at 05.00 and 18.00 hr., would be reasonably consistent with natural suckling activities if restrictive feeding has to be applied. But further work is required to determine the cost, in terms of reduced efficiency of milk utilization, incurred by concentration of intake to restricted feeding times.

1. Results are presented concerning the gross composition of pig carcasses at 50, 68 and 92 kg. carcass weight in ten litters. They show that during the periods under consideration the proportion of muscle in the carcass exceeded that of the other tissues. However, while the rates of growth of muscle and bone were similar the growth rate of fat was markedly greater. The result was that at 92 kg. the proportions of muscle and fat in the carcass were 43·53 and 41·37%, respectively.

2. Results are also presented dealing with the relative development of the different parts of the skeleton. Of the five major anatomical regions of the skeleton the sacrum grew relatively fastest between 50 and 68 kg. carcass weight while the cervical vertebrae grew fastest in the second period. In both periods the bones of the thorax and loin grew at rates intermediate between the fastest and slowest growing regions.

1. Between 1955 and 1961 nineteen experiments were carried out on Majestic potatoes in various parts of England comparing muriate and sulphate of potash at three rates of application, in the range 75–336 lb./acre of K2O. Most of the experiments were on light soils.

2. Total yield of tubers was on average the same from both sources at all rates of application, and this similarity was not affected by environmental conditions.

3. Muriate of potash consistently gave a higher yield of large tubers than sulphate, with an average difference of 0·6 ton/acre. Conversely, muriate gave a lower yield of medium tubers than sulphate, again with a mean difference of 0·6 ton/acre.

4. Muriate of potash significantly depressed tuber dry-matter content in eleven of the experiments, particularly at the higher rates, while sulphate had this effect in three experiments. Muriate gave a small increment in two experiments, at low rates only, while sulphate had this effect in five, most markedly at low rates. Sulphate gave a higher dry-matter content than muriate in most of the experiments. The mean difference was 1·0% at 300 and 336 lb./acre of K2O and 0·4 to 0·5% at lower rates.

5. Sulphate of potash gave a more floury texture to the boiled tubers than muriate in three experiments, but otherwise no difference in texture was detected between the sources.

6. The degree of off-flavour was not appreciably affected by rate or source of applied potash.

7. After-cooking blackening was more marked at low than at high rates of applied potash in seven of the nineteen experiments. Muriate and sulphate of potash had similar effects.

8. Farmyard manure ploughed down in winter was tested in three experiments and did not influence to any important extent the relative effects of muriate and sulphate of potash on tuber yield and quality.

9. Application of the two sources on the flat before ridging and in the open drills was compared in the same three experiments, but did not alter the relative effects of the sources on yield or dry-matter content.

Bovine spermatozoa aged for 6–7 days at room temperatures (18–30° C.) in a coconut milk extender retained their fertilizing capacity. However, their fertilizing ability appeared to be impaired by environmental hazards in the form of oxygen damage, exposure to visible light, and temperature shock. Protective measures developed and used in the preparation and in the storage of the sperm suspensions to minimize premature loss of sperm function involved the addition of catalase and egg yolk to the extender and the maintenance of cell suspensions in the dark in vials containing a minimal air space. The experimental evidence obtained with this improved coconut milk extender established its ability to support and sustain the fertilizing capacity of bovine sperm for 6–7 days at room temperatures at a level comparable to the fertilizing capacity of refrigerated sperm in milk-glycerol or egg yolk-citrate-glycine extenders. The economic importance of this room temperature diluent is suggested by the fact that it eliminates the costly refrigeration required to maintain stored and shipped bovine semen at 5° C.

Coconut milk extender modified by the addition of 5% egg yolk also proved to be a satisfactory storage medium for sperm at low temperatures. It was found to be superior to both egg yolk-citrate and skim-milk extenders in conserving motility at 5° C. The fertilizing capacity of Ayrshire and Brown Swiss sperm stored at 5° C. in coconut milk extender which contained 15% coconut milk and 5% egg yolk compared favourably with the fertilizing capacity reported for sperm stored at 5° C. in other more widely used diluents. The number of motile sperm recovered from this extender after freezing to −79° C. was comparable to the number of motile sperm recovered from the egg yolk-citrate and skim-milk test diluents. The results of this study indicate that coconut milk extender is a versatile, easily prepared medium which can be used to preserve functional sperm over a wide temperature range.

1. An experiment has been carried out to compare the results of feeding the B-group diets of Parts II and III of this series to ewes during pregnancy and lactation.

2. The ewes fed a diet containing maize in place of dried molassed sugar beet pulp again maintained better bodily and skeletal condition.

3. The basis for other experiments in this series is discussed.

1. Three groups of twenty, 3½ to 4-year-old zebu steers, replicated four times in each quarter of the year, were used to examine the effects of 30 and 45 mg. hexoestrol implants on their beef production, under ranch conditions in Tanganyika.

2. Significant advantages in mean live-weight gains of 20·8–47·3 lb. for 30 mg., and 9·8–47·3 lb. for 45 mg., were obtained when treated at any time of the year; but during the dry-season implantation is contra-indicated as initial response is adverse although followed by pronounced recovery when pasture conditions improve.

3. There was no significant difference between dosage rates in growth response, but on smaller steers, and as the pasture deteriorated, 45 mg. showed signs of being excessive.

4. Duration of significant response was about 3 months during the period of adequate grazing, but was delayed to 5 months, and probably longer, during the dry season.

5. Steers were slaughtered 6–9 months after implantation and at that time showed: no significant difference in dressing percentage, shrinkage in store, proportion of bone, or carcass grade; there was significantly less fat, and more lean, but increased proportion of moisture in the muscle accounted for the extra proportion of lean in the sample joints.

Treated carcasses were significantly longer by 1·0% and highly significantly larger in circumference of hind quarter by 2·0%.

1. The ‘availability’ of the magnesium of diets consisting solely of roughage or succulent feeds, including herbages cut at different seasons and at different stages of growth, and of diets of hay supplemented with various concentrate feeds, was assessed in metabolism trials conducted with two non-pregnant, non-lactating Shorthorn cows.

2. The highest daily intakes of magnesium (1720 g./day) were provided by a diet of red clover: grasses and hays generally gave a considerably lower intake of magnesium (8–10 g./day), and most of the other diets provided intermediate amounts. However, with timothy hay and barley straw, intakes of 5 and 2 g./day, respectively, were recorded. Supplements to a diet of hay of dairy cubes or of oilcakes rich in protein gave a massive increase in magnesium intake but a supplement of flaked maize provided little additional magnesium.

3. The ‘availability’ of the magnesium of the diets was generally low, within the range of 5–30%. With diets of single feeds no clear distinction between the various roughages and succulents in the ‘availability’ of their magnesium was established, though within the group of herbages the lowest values tended to occur with grasses cut at an early stage of growth and the highest values at the mature stage. A supplement of flaked maize increased the ‘availability’ of dietary magnesium and one of protein-rich oil cakes decreased the ‘availability’ of dietary magnesium.

4. The results are discussed in relation to the development of hypomagnesaemia in cattle grazing spring pasture.

1. Effects on productivity and skeletal mineralization of high as opposed to moderate levels of protein and, or, energy intake by the ewe during pregnancy and lactation in the presence of adequate calcium, phosphorus and vitamin D have been studied.

2. Two experiments were undertaken. One experiment used 4½-year-old Cheviot ewes and the other used 3½- and 4½-year-old Scottish Blackface ewes. Weight records, blood samples and in vivo and flesh-free radiographs were obtained, and bone ash determinations were carried out.

3. The results showed that contrary to indications from earlier experiments in this series superiority in ewe weight, lamb growth, and mineralization of the ewe skeleton did not necessarily result from raising the protein and, or, energy values of the feed above the ‘moderate’ level.

4. Discrepancies between the in vivo and flesh - free radiological assessments were noted for consideration.

The practice of supplementary feeding of concentrates has been the subject of much investigation and also the centre of considerable controversy during the last decade. The latter is perhaps not hard to explain as so many variables are present; first and foremost there is the cow which at all times must be considered an individual whether it be milk yield, time of calving or dry-matter intake. In addition, one must always take into account the quantity and quality of grass, both of which are dependent on sward management and the system of grazing.