Growth analysis of cotton crops sown in the Sudan Gezira at monthly intervals between August and May revealed a marked seasonal pattern of growth. Irrespective of plant age and fruiting state growth of non-senescent plants was slowest during the cool winter months. Relative growth rates of young plants were highest in August, September and early October due to the high specific leaf areas and fairly high net assimilation rates found then. They were lowest when minimum temperatures were lowest. Net assimilation rates were also lowest in the coolest months, probably as a result of restricted growth. High temperatures in the spring reduced fruiting. It is concluded that low minimum temperatures and high evaporation rates are both associated with slow growth, and play a large part in determining the characteristic decline of growth rates of cotton sown at the usual date in August.

I wish to thank the Chief of the Research Division, Ministry of Agriculture, Sudan, for permission to publish this paper and to record my gratitude to the team of field and laboratory assistants, especially Salih Saad and Hassan Osman, who helped in the work.

1. Extremity skin temperature changes in British and Zebu cross cattle examined in moderate thermal environments followed a thermoregulatory pattern similar to that describedby Whittow (1962). At low environmental temperatures, ear and lower leg skin temperatures were usually only slightly above air temperature. At a variable time after air temperatures began to rise or the animals were fed, extremity skin temperatures increased suddenly to near trunk skin temperature.

2. In eight of the ten pairs of animals studied in rising ambient temperatures and during feeding after fasting for 36–72 hr, increases in ear temperature were measured in the British animal before similar changes occurred in its Zebu counterpart. Changes in lower leg skin temperature followed a similar pattern.

Trunk skin temperatures and respiratory frequencies were significant higher in British cross animals than in Zebu cross animals of similar thermal history. The mean rectal temperature of both British and Zebu cattle was 38·5 °C.

Seven Angus steers were reared under controlled conditions, slaughtered and their carcasses dissected. Muscles, fat, bones, connective tissues and samples of the steers' diet were measured by gamma spectrometry and the concentrations of potassium and caesium-137 determined. Significant variations in the concentration of each element were found both within and between tissues. Average potassium concentration was about four times greater in the muscle tissue than in the remainder of the carcass. Caesium/potassium ratios were similar in both Caesium/potassium ratios were similar in both bone.

The main conclusions reached were as follows:

(1) The variations of potassium concentrations in muscle may impose limitations on the potassium-40 technique for estimating muscle content of the living animal for scientific purposes, though not necessarily for estimating commercial value.

(2) Differences between animals in caesium-137 content of muscle were fairly consistent over the different muscle groups, and bore some relationship to caesium intake. This indicates that it may be possible to utilize caesium content of a representative muscle to monitor caesium-137 fallout in remote regions of Australia, where milk is not produced.

In factorial experiments covering a range of sowing dates and insecticide treatments the numbers of fleabeetle, jassid and whitefly on cotton in the Sudan Gezira were shown to be strongly influenced by the date of sowing and the age of the crop.

Attack by fleabeetle was most severe on cotton seedlings from July and early August sowings. Few fleabeetle were found on either more mature plants from these sowing dates or on seedlings from later sown cotton.

Whitefly numbers were highest on late July and early August sown cotton. Peak numbers were attained attained in late September and October and then fell to very low levels in November irrespective of date of sowing.

Jassid numbers were related both to plant age and to time of year, more being found on cotton sown, in July and early August early in the season and on later sown cotton later in the season. The highest numbers were found in November and December at which time populations were higher on cotton sown in mid-August or later than on earlier sown cotton.

The results of more than fifty estimates1 of herbage yield and ninety-seven analyses of chemical composition are presented in the first of several reports on nutritive evaluation studies of Panicum maximum (guinea grass). Effects of stage of maturity and season are discussed.

Herbage yield increased at an increasing rate with maturity, and was depressed by about 40 % in the dry season compared to the wet season. The most significant differences in chemical composition were a decrease in crude protein from 9·8 % to 6·6% and a corresponding increase in crude fibre from 32·1 % to 39·4% as the grass matured from about 2½ weeks to about 2½ months in age. An increased level of nitrogen fertilization resulted in crude protein content being nearly doubled and crude fibre somewhat reduced.

The histology of the skin follicles of a small group of Herdwick ewes was examined in midwinter and again in midsummer. In the primary follicles which remained active (about 9 % of the total follicle population) the ‘winter thinning’ in the fibre was accompanied by a thickening of the Huxley layer in the inner root sheath. In heterotype fibres (from primary follicles) a poorly defined crimp and a bilaterally differentiated cortex were present only in the thin length of fibre grown in winter.

The author is grateful to Dr. Marca Burns for permission to sample her Herdwick flock, and to Dr K. M. Rudall for helpful advice. This work was carried out while the author held a grant from the Agricultural Research Council.

Field experiments from 1959–60 to 1963–4 showed that when blackarm resistant strains of Egyptian type cotton were sown around the beginning of August and adequately protected from fleabeetle, the resultant crop was of higher yield and considerably better average quality than that from the normal mid-to-late August sowings. Effective length, maturity ratio, standard fibre weight, bundle strength and lea-count × strength product were all improved. Sowing in early July, tested in one season only, gave rather better quality but lower yield than sowing in early August. Sowing in late August or in September depressed both yield and quality. The importance of direct climatic effects and of blackarm, fleabeetle, bollworm, other insect pests and wilt in controlling the choice of, and response to, sowing date is briefly discussed.

Thanks are due to the Sudan Gezira Board for kindly supplying the results of the large-scale sowing date trials and for the grading of experimental cotton, to the Shirley Institute of Manchester for the fibre and spinning tests and to the Chief, Agricultural Research Division, Ministry of Agriculture, Sudan, for permission to publish this paper.

1. Fifty-one experiments on the nitrogen, phosphate and potash requirements of maincrop potatoes were carried out in Great Britain in 1956–62. Each experiment tested four rates of each nutrient in all combinations and both total and riddled yields and quality data were obtained.

2. Nitrogen requirement was influenced by previous cropping and the rainfall during the preceding winter. 50–80 lb/acre of N are recommended in mixed farming rotations depending on winter rainfall, and 120–150 lb/acre of N in arable rotations.

3. Yield increases from phosphate were usually larger on soils with low citric-soluble phosphate. Nevertheless, irrespective of soil phosphate status, optimum rates of application were at least 120 lb/acre of P2O5 which was the highest rate tested in most of the experiments.

Fifteen digestibility trials were conducted in the wet, early dry, and late dry seasons in the Philippines. Panicum maximum (guinea grass) was fed at growth stages of 1–4 months to Bos taurus (Holstein), Bos indicus (Red Sindhi), and Bos bubalis (water buffalo) bulls.

Significant differences were shown between digestibility coefficients from water buffaloes and those from Holstein cattle, the former having a 5–7 % advantage in most cases. Ratios of volatile fatty acids in rumen fluid from the two species were not different. Separate tables of digestible protein, TDN and digestible energy values for guinea grass were computed for cattle and water buffaloes.

1. Nine successive trials with three adult desert rams were carried out, with the aim of using ruminal ammonia or blood urea concentration as an index of the nutritive value of the proteins in the various types of forage grown in irrigated parts of the northern Sudan.

The change in the ruminal ammonia and blood urea concentration were considerably higher 3 h after feeding on leguminous forages than on the non-legumes. Among legumes, lubia and lubia hay produced the highest concentrations of both rumen ammonia and blood urea. Feeding the rams on berseem hay reduced the concentrations of ruminal ammonia and blood urea to levels below those given by feeding on fresh berseem.

3. Most of the nitrogen excretion from leguminous forages was in the form of urinary nitrogen whereas for grasses faecal nitrogen made up the bulk of the nitrogen excreted. Berseem hay gave the highest nitrogen retention, followed by the butterfly pea and fresh berseem. Lubia and lubia hay gave the lowest nitrogen retention. The desert grasses produced a negative nitrogen balance when offered to the desert rams.

Leaf tensile-strength measurements have been made at Grasslands Division, D.S.I.R., over several years on a number of pasture grasses (Evans, 1964; Wilson, 1965). These measurements were prompted by the work of Beaumont, Stitt & Snell (1933) and Kneebone (1961), who attempted to relate leaf tensile strength to animal production value, and Edmond (1960, 1964), who considered that the toughness of pasture species may be a factor determining their tolerance to animal treading. The following is a description of the apparatus developed for this work and of the techniques employed.

1. The effects of different levels of first winter nutrition over 3 years were studied from 18 months to maturity on the growth and development of groups of North and South Country Cheviot ewe hoggs (sheep between 6 months and 1½ years).

2. Differences in live weight amongst treatment groups within breeds and years were not significant at 30 months or any subsequent age. Live weight increase continued up to 54 months. Although leg growth had virtually ceased in all treatment groups by 18 months, body growth continued beyond 27 months and differences between treatments, although not always significant, were still present at that time.

3. The effects of first-winter treatment were also studied on the heavy and light hoggs (i.e. those above and below average weight) prior to treatment. Differences in weight and size between treatment groups were less persistent in the heavy animals, disappearing by 30 months, while in the light animals they were still present at that time. Regardless of treatment the within-group differences between heavy and light animals increased up to 54 months, the light animals showing relatively slower rates of gain.

4. The difficulty of interpreting data on liveweight change due to age, state of maturity, level of feed, and season interactions is commented on. The probable effects of differential productivity resulting from treatment on growth and development from 18 months onwards are discussed.

1. The effects of different levels of first-winter nutrition over 3 years were studied on the subsequent dental development of groups of North and South Country Cheviot ewe hoggs (sheep between months and 1½ years) by recording the time eruption of each of the four pairs of permanent incisors. High-plane first-winter feeding resulted earlier eruption of the first pair of permanent incisors. Later pairs were affected to a lesser extent, with low-plane/hill-wintered groups consistently the latest to erupt. Breed and year deviations from the general pattern were small and were largely due variations in growth rate both prior to and during treatment.

2. The effects of first-winter treatment were also studied on the heavy and light hoggs (i.e. those above and below average weight) prior to treatment. Although there was only a very limited difference the time of eruption of the heavy and light within each treatment group, the effects of treatment were greater in the heavy-weight class than they were the light.

3. The effects of first-winter treatment on dental efficiency and long-term persistence were also studied. There was little difference amongst treatments at 5½ years of age in the bite position, or looseness, wear, or condition of the teeth. Brokenmouth, i.e. the loss of one or more permanent incisors, did not appear in significant proportions until 7½ years of age, when considerable treatment, breed, and year differences were present. The incidence of broken-mouth was lowest in the high-plane and hill-wintered groups and highest in the lowplane and mid-plane/away-wintered.

1. The growth of lambs grazing tall fescue pastures, receiving high and low levels of nitrogen fertilizer, was studied.

2. fertilizer, was studied. final body composition was estimated. Rumen liquor samples were collected three times and herbage intake estimated five times during the 88-day experiment.

3. On clipped herbage samples, O.M. digestibility was estimated in vitro, and chemical composition was determined.

4. Live-weight gain, final body composition and D.o.m. intake did not differ significantly between treatments. Molar proportions of acetic acid were higher and n-butyric acid lower on the high nitrogen treatment.

1. Leaf strengths and cellulose contents of eight grasses grown as single spaced plants were compared over a period of 14 months. From some of the samples the proportion of sclerenchyma tissue in the leaves was compared with leaf strength.

2. The leaf strengths of individual plants were measured and the strengths of the six strongest and six weakest plants in each species compared with their cellulose contents.

3. There were significant differences between species, between seasons, and between regrowth ages within seasons in both leaf strength and cellulose content. There were also significant species × regrowth age interactions, particularly in leaf strength.

The effect of subsoiling an old arable clay-loam soil at Broom's Barn Experimental Station, Suffolk, was tested with a sequence of wheat, barley and sugar-beet crops, a lucerne ley and a sugar-beet test crop in the fourth year.

Subsoiling increased the yield of each crop each year, averages over 3 years were: wheat, 0·6 cwt/acre of grain; barley 0·4 cwt/acre; lucerne 0·6 cwt/acre of dry matter. Average increases of sugar beet over 4 years were 0·7 tons/acre of roots or 2·1 cwt/acre of sugar; the increase was greatest (2·9 cwt/acre of sugar) in the first year.

The relationship between milk production, blood glucose, blood ketones and free fatty acids (F.F.A.) were studied in lactating Awassi ewes. Increased milk production in ewes was associated with diminished blood glucose and increased serum F.F.A. Clinical cases of ketosis were not observed.

The ewes studied here could be divided into two metabolic populations depending on their blood ketone levels. Those with blood ketone levels of 11 mg % or more, did not show a significant increase in serum F.F.A. or a decrease in blood glucose values with increased milk production. The group of ewes with less than 11 mg % blood ketones showed a significant decrease in blood glucose and a significant increase in serum F.F.A. as milk production increased. Ketonemia of the high ketone group of ewes, was associated with relatively low serum F.F.A. levels. It is suggested that these ketones not originate from depot fat via serum F.F.A. These ketones and/or their precursors, acetic and butyric acids probably participate in caloric homeostasis and are associated with a glucose sparing serum F.F.A. suppressing mechanism.

The suggestion that ketones derived from rumen (R.D.K.) should be distinguished from those derived from adipose tissue (A.D.K.) is discussed.

The effect upon the onset of reproductive activity of exposure of ewe lambs of three British breeds (Border Leicester, Southdown, Suffolk) to constant long daylight hours (16 h light/8 h dark) was studied.

Oestrus, ovulation and conception were depressed but not inhibited; however, only the incidence of conception was significantly less than in the control group. Athough the treatment retarded the onset of oestrous activity, the age at first oestrus was still within the normal age range for puberty.

1. An improved artificial rumen apparatus of the dialysis type with multiple fermentation units was built and a method for its operation was evolved. Biochemical criteria of validity were used and particular reference was made to the molar percentage of the volatile fatty acids produced.

2. It was found that the apparatus was best used in a comparative manner, to measure treatment differences produced between individual fermentation units.

3. A series of experiments was carried out to measure the effects of a range of dietary treatments on rumen fermentation. In each case an in vivo comparison was also made using a cow with a permanent rumen fistula.

4. Correlation coefficients for treatment differences of 0·43 and 0·46 were found for ammonia T.V.F.A., and 0·73, 0·90 and 0·70 for the molecular proportions of acetic, propionic and butyric all the latter being significant.

5. The results were discussed with particular reference to the advantages and limitations of apparatus and the most suitable application of technique.

During the last ten years or so, the management of sheep for intensive lamb production has been studied on a considerable scale, and a variety of grazing systems have been investigated (Dickson, 1959; Cooper, 1959; Spedding & Large, 1959; Boaz, 1959). It is still too soon to specify precisely the place that any of these systems should occupy in sheep-production processes, in relation to breed, lambing percentage, weight of lamb at slaughter, stocking rate, botanical composition of the pasture, size of ewe and level of her milk yield. Quite apart from these biological considerations, the full economic implications are by no means clear. What has emerged most clearly, however, is that much higher stocking rates can be tolerated than had generally been regarded as safe and that, at these stocking rates, productivity can be extremely high.