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.

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.

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. 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.

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.

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.

1. The carcass composition, the composition and characteristics of the subcutaneous and longissimus dorsi muscle fats, the volatile fatty acids of the rumen-reticulum fluid and the degree of flavour and odour of the cooked 12th rib chops of two groups each of fifteen Southdown–Romney cross ewe and wether lambs fed respectively white clover and perennial ryegrass have been determined. The lambs had been on treatment for 5 months and were slaughtered when about 9 months of age.

2. The white clover-fed lambs had a mean live weight at slaughter of 94 lb ± 9 lb compared with 67 lb ± 7 lb for the perennial ryegrass-fed lambs. The carcasses of the white clover-fed lambs had greater (P < 0·01) amounts of fat.

3. The iodine values of the subcutaneous fats of the white clover-fed lambs were highly significantly greater than those of the ryegrass-fed lambs and this result was consistent with the greater deposition of endogenous fat.

4. The extra fatness of the white clover-fed lambs was consistent with their greater production of rumen-reticulum volatile fatty acids.

5. The maj or differences in fatty acid composition of subcutaneous and intramuscular fats between pasture treatments were the highly significant increases in shorter-chain saturated and C15 branched-chain acids of the ryegrass-fed lambs. In addition, the subcutaneous fat of the ryegrass group contained highly significantly more octadecadienoic and octadecatrienoic acids while the 1. dorsi fat of the ryegrass group was highly significantly richer in stearic and oleic acids.

1. A study was made of the voluntary intake hay, of low nutritive value, by heifers of two breeds of African cattle when given four different amounts concentrate foods (9, 18, 27 and 36 g/kg W0.73/day) each providing three levels of protein (1·3, 2·6 and 3·9 g DCP kg W0.73/day). The trial was designed two incomplete Latin squares, one for each breed, with thirteen treatments, thirteen heifers and four replicates.

2. Voluntary intakes of low-protein hay by Africander and Mashona heifers were similar and these increased as levels of supplementary protein were raised and intakes of hay were reduced amounts of concentrate provided to them became more liberal. Inter-relationships of food intake and dietary composition were, however, very complex.

3. Increased allowances of dietary protein and concentrate generally corresponded with higher intakes of total food and digestible energy. But this was not true at the lower levels of protein input where there was evidence that food and digestible nutritient intakes were depressed when liberal amounts of concentrate were fed to the cattle.

1. A study was made of the voluntary intake of hay of low nutritive value by sheep when given four different amounts of concentrate foods (9, 18, 27 and 36 g/kg W0.73/day) each providing three levels of protein (1·3, 2·6 and 3·9 g DCP/kg W0.73/day). Hay alone was offered as a separate treatment. The trial was designed as an incomplete Latin square with thirteen treatments, thirteen sheep and four replicates.

2. Voluntary intake of low-protein hay by sheep was invariably lowered when they were given increasing amounts of concentrates. Hay consumption was also affected by level of supplementary protein; intakes increasing sharply from the lowest level provided (1·3 g DCP/kg metabolic body weight) to maximal intakes when about 3 g DCP/kg W0.73 were given to the sheep.

3. Total food and digestible energy (DE) intakes were similarly affected by changes in dietary protein level. Successive increments in concentrate allowances, except at the highest level of concentrate input, caused corresponding reductions in hay intake so that total food consumption remained similar (when protein level was kept constant). In consequence, DE intakes rose to maxima when approximately 30 g concentrate/kg W0.73/day were fed to the sheep.

1. Dry-matter and nitrogen yields were recorded from perennial ryegrass-white clover associations which were defoliated 2, 4 or 6 times a year during the period 1963 to 1965.

2. The average yearly output of dry matter was approximately 4000, 7000 and 6000 lb/acre for 1963, 1964 and 1965 respectively. Nitrogen harvested amounted to 132, 184 and 179 lb N/acre.

3. The mean annual dry-matter yields from 2, 4 and 6 defoliations were 5300, 6100 and 6000 lb/acre and the corresponding figures for nitrogen yields were 112, 166 and 217 lb N/acre.

4. Both segregation of the species below ground and increasing the defoliation frequency were responsible for higher contributions towards drymatter and nitrogen yield from the clover component.

5. A comparison of the nitrogen yields between the plots with species segregated rather than integrated below ground suggests that the effects of underground nitrogen transference from 30–31 lb N/acre could first be demonstrated in the spring of the third year.

1. A study of grazing intake and efficiency was carried out on eighty-one ewes suckling twin lambs during early lactation.

2. A method of estimating comparative grazing intake is described involving the administration of Cr2O3 and sampling from the pasture with the minimum of labour. The results indicated that reasonable precision was achieved with a method suitable for studying large numbers of animals. 3. The efficiency of production of lamb up to 5 weeks of age was not associated with the body weight of the ewe nor with the wither height. It was, however, negatively associated with grass intake by the ewe and to some extent with the gain in body weight by the ewe during lactation. Only in two of the four experiments was efficiency associated with lamb production up to 5 weeks.

1. Two experiments with 52 lambs are described investigating the use of reconstituted cold milk for rearing lambs and comparing full cream dried milk with a milk substitute.

2. The use of cold milk resulted in high growth rates and few health problems.

3. Satisfactory food conversion efficiencies were obtained by feeding of cold reconstituted whole milk and cold milk substitute.

4. During the first 3 weeks of rearing, the growth rates and food conversion efficiencies on the milk substitute were similar to those obtained on the full cream milk.

Wool-growth rates were measured at monthly intervals on eight free-grazing Cheviot wethers. Nutrient intakes provided by the upland environment were measured at the same intervals during the 2½ years. Analysis of periodic regression disclosed that both intake and wool growth had similar seasonal cycles but were slightly out of phase. It was concluded that the similarity was largely due to the relationship of both characters with some independent seasonal variable. The seasonal cycle of efficiency of wool growth depends on the time relationship between its two components, but it was found that variation amongst sheep in wool production was greater in the summer months and this depended more on variation in overall efficiency than on variation in grazing intake.

1. Data on the fresh weight, mineral and fat composition of foetuses from Border Leicester / Cheviot ewes were obtained for seven singletons, fourteen sets of twins and four sets of triplets. The age of the foetuses ranged from 80 to 144 days. The foetuses were dissolved individually in concentrated nitric acid and the mineral composition of the resultant solution determined.

In a factorial experiment on a mixed grass/clover sward, continued over 13 years, D.M. yields were strongly affected by N and K, which showed a marked interaction. P had very little effect on yield. There was evidence of a depressing effect on yield of continued application of KC1 at low rates of N input: this is thought to be due to excess Cl. It may be associated with the effect of Cl on clover growth, since it did not occur in predominantly grassy swards heavily dressed with N, in spite of high Cl content in the herbage.

The botanical composition of the herbage was strongly affected by the fertilizer treatments.

The effects of Nitro-chalk, superphosphate and potassium fertilizers on the chemical composition of grassland herbage and the removal of major plant nutrients have been traced over 14 years.

Without fertilizer N, but with adequate K, clover supplied a yearly average of up to 87 lb Nsol;acre. With an annual application of 348 lb N and adequate K, 237 lb of N was recovered annually.

Without applied P, herbage P concentration fell with time especially under heavy N treatment. When P was applied, herbage P concentration did not fall, irrespective of N treatment: K depressed P concentration irrespective of P application. Maximum removal of P occurred with annual applications of 348 lb N, 43 lb P and 280 lb K: at these rates gain and loss of P approximately balanced.

Herbage K concentration was greatly increased by K fertilizer. It was reduced by N when no K was applied but applying K counteracted this effect. Removal of K slightly exceeded the 280 lb of K applied when 348 lb N was also applied.

1. The lengths and weights of 241 pig embryos, aged 26–109 days, were recorded; the pregnant sows were from a mixed herd of Landrace, Large White and Wessex stock and some of their crosses.

2. An empirical linear regression of length on age was estimated (equation 1); the relation between weight and age was represented by a polynomial weight and age was represented by a polynomial (equation 2).

We thank Mr A. S. Cray and the other directors of Unigate Ltd. for giving us the pigs; Mr P. Sedgewick of that Company gave us excellent co-operation. Prof. C. W. Ottaway and Dr P. Radford helped us throughout the investigation.

(1) Nine Scottish Blackface and four Merino × Cheviot ewes were shorn and given an acute cold exposure (at approximately −18 °C) in climate chambers. Individual exposures lasted up to 10 h. Because they were shorn, the sheep subsequently received 4 weeks of mild cold exposure, although kept indoors at an ambient temperature between + 8 °C and +15 °C. Skin and wool samples were taken before and after treatment. Twelve unshorn control ewes were also sampled.

(2) Wool production in the Blackface sheep was depressed following the treatment, and this was accounted for by a reduction in both the mean length and the mean diameter of the wool fibres.

1. Investigations of individual soyabean families over a 5-year period showed in some famines that the strain compounded in the F5 generation had a more stable environment × genotype interaction than the daughter strains compounded in the F6 generation.

2. Regression of each strain yield on an ‘environmental’ mean gave values for the slope of the regression line (bi), and the mean square of the regression (s2d) gave a value of deviations from the regression line. The values bi and s2d were used as estimates of stability.

3. Groups of F5 and F6 compounded strains were compared. Analysis of variance for yield over 5 years for twenty-four F5 compounded strains and twentyfour F6 compounded strains gave s2d value of 166·4 for the former and 289·1 for the latter. With 72 degrees of freedom for each group they differed from each other at the 1 % level of P.

4. Multiple correlation analyses were also done on the two groups of strains. It was concluded, all else being equal, that the F5 strains over a period of years would be less liable to give low yields in a bad year than the F6 strains.