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.

1. The heat tolerance and walking performance of bulls, steers and heifers exposed to moderate heat stress have been compared, following the method of Yeates & Murray (1966). Hereford cattle aged 14–16 months were used in the experiment. Two speeds of walking were employed and the effect of clipping the coats of both exercised and stationary cattle was studied.

2. In the undipped state, at both speeds of exercise (1⅔ and 2⅔ m.p.h.), the heifers performed best followed by the steers and bulls in that order, judged by their ability to preserve normal body temperature.

1. Thirteen experiments were made with spring barley from 1963 to 1965 on soils overlying chalk. They compared yields at ear emergence and of ripe grain from ammonium sulphate and from calcium nitrate, from sodium nitrate or sodium chloride or both, and from potassium nitrate or potassium chloride. Two rates of seedbed N were tested, though they were different each year, and in 1964 and 1965 N top-dressings were also applied. The amounts of N, K, Na and Mg in the green barley, and of N in the grain, were measured.

greatly increased grain yields in all but one experiment, where the barley followed sugar beet. Calcium nitrate gave larger grain yields than ammonium sulphate in three-quarters of the comparisons, but gave much smaller yields than ammonium sulphate on one light soil in 1964 when much rain fell after the fertilizers had been applied. Grain yields from calcium, potassium and sodium nitrates were nearly the same.

3. Na slightly increased grain yields in three and K in two experiments, but combine-drilled P or PK fertilizers increased them in every experiment.

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.

Field experiments of modern design that included carrots were first made at Woburn in 1934, to compare the value of nitrogen in dried poultry manure with ammonium sulphate. The experiments were repeated at several centres and continued until 1939. Most other crops responded well to nitrogen but in only one of the five experiments containing carrots did ammonium sulphate at 3 cwt/acre increase the root yield, and in two it significantly depressed yield. Ammonium sulphate tended to lessen plant numbers, but it increased the yield of tops (Rothamsted Experimental Station, 1934)

1. In a 2×3×3 factorial experiment a total of seventy-two female or castrated pure Friesian, Charolais × Friesian and Welsh Black × Friesian cattle were fed individually and ad libitum on three diets from 200 lb to slaughter at 800 or 900 lb, depending on sex. The diets were ground barley (87%) and protein-mineral-vitamin supplement (13%) given with or without 1 lb of hay per animal daily, or ground maize (87%) and supplement (13%) given with 1 lb of hay daily.

2. The three breed-types differed significantly in growth rate and feed conversion efficiency. Gaining at 2·66 lb/day and converting 4·56 lb of meal into 1 lb live-weight gain, the Charolais crosses grew 7·7 % faster than pure Friesians and consumed 14·1% less meal per unit gain. Welsh Black crosses made 9·3% less rapid gains and required 7·7 % more meal per unit gain than pure Friesians. The disparity between the three breedtypes increased with increasing liveweight.

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.

In a series of five irrigated cotton sowings (T2, T7, T9, T11, T14) evapotranspiration (Et) was determined for the period between October 1961 and October 1962 by observing frequently the changes in soil moisture storage, calculating through drainage, and solving for evapotranspiration in the water balance equation. Thus a water balance was obtained for each sowing extending over the entire crop.

The average evapotranspiration in wet season sowings was of the order of 6·5 mm day−1 and in dry season sowings of the order of 4·5 mm day−1. The highest evapotranspiration values ranged between 10 and 12 mm day−1 in T2, T7 and T9 and between 7 and 9·5 mm day−1 in T11 and T14.

1. The object of the experiment was to determine the effects on the diet and production of grazing dairy cows of providing different quantities of herbage over a relatively long period.

2. Three groups of five Ayrshire cows were strip grazed on areas supplying (A) 25, (B) 35 or (C) 45 lb D.M. per cow per day, for a total of 11 weeks. Three swards were used in succession, and measurements of herbage intake, milk production and live-weight changes were made over the last 10 weeks.

3. Mean intakes for treatments A–C, respectively, were 23·9, 25·6 and 26·4 lb organic matter per cow per day, and milk yields were 30·4, 30·8 and 32·8 lb. Differences in digestibility between treatments were small, even when the cows grazed poor herbage in which the organic matter was only 68 % digestible.

4. The treatments had no significant effects on milk composition or live-weight gain, although the latter was less for treatment A.

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. The effect of seed rate on yield of grain and its components in four contrasting oat cultivars, Maldwyn, Milford, Victory and Marvellous, was investigated over 3 years. At the high (206 lb/acre) and medium (137 lb/acre) seed rates, the final grain yield was similar within each of the three seasons. The low seed rate (69 lb/acre) gave significantly lower yields than the medium or high rates in 1955 and 1957, and in the latter year there was a significant cultivar × seed rate interaction.

1. Plants of S.48 timothy were established on a 1 ft square pattern for production of seed. Two series of plots, one irrigated and one not irrigated, were treated with three levels of applied nitrogen: 0 (NO), 87 (Nl) and 261 (N2) lb N per acre (0, 97·5 and 292·5 kg N/ha) per annum, for 3 years. In this, the first of two papers, only vegetative aspects of growth are considered. Since the irrigation treatment started only 2 weeks before most of the data were recorded, effects of irrigation on vegetative growth were generally small.

2. The number of tillers per plant was increased by application of nitrogen; the lower increment was more effective than the additional nitrogen in the higher dose.

3. The weight of tillers per plant was increased by nitrogen at both levels of application. The mean weight of each tiller was increased by nitrogen after the first year, predominantly in the N 2 treatment. In the second year, irrigation also increased the weight per tiller.

4. The weight of roots per plant was significantly affected by application of nitrogen. In the first year, the weight was increased by nitrogen in irrigated plots; in the second year the roots were significantly heavier in the Nl treatment than in N0 and N2 treatments, where weights were similar; the same situation existed in irrigated plots in the third year, but in non-irrigated plots the weights of roots were similar in N1 and N2 treatments and were heavier than in the N0 treatment. Irrigation had positive effects on the weight of roots in the first and second years.

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. Plants of S.48 timothy were established on a 1 ft square (30 cm × 30 cm) pattern for production of seed. Plots at three levels of applied nitrogen, 0 (N0), 87 (Nl) and 261 (N2) lb N/acre (0, 97·5 and 292·5 kg/N ha) per annum were either irrigated to field capacity from 1 week before initiation of spikelets until 2 weeks before harvest, or not irrigated, during each of three years.

2. Application of nitrogen caused earlier initiation and emergence of inflorescences each year, and earlier general anthesis in the first and third years. Irrigation generally had no effect on the date of initiation, but it prolonged the period of reproductive development and delayed the date of harvest by 2–5 days.

3. The number of ears per plant was increased by the N1 treatment above the number produced by plants in the N0 treatment. In the N2 treatment the number of ears per plant was between the number in the N0 and N1 treatments in non-irrigated plots; in irrigated plots, plants in the N2 treatment sometimes had a lower number of ears than plants in the N0 treatment. The length of ears increased with the rate of application of nitrogen.

The growth and development of five winterwheat varieties and of random selections from hybrids between them were compared. Successive sampling demonstrated varietal differences in orthogonal polynomial regression coefficients fitted to data for tiller number, shoot weight and leaf area. The correlation coefficients between these parameters and yield were statistically significant, but when polynomial regression equations of yield on them were determined, only the terms relating to shoot weight and leaf area duration after anthesis were significant.

The heritabilities of these parameters in each of 2 years were determined from measurements of genetic and environmental variance. The results obtained were compared each year with estimates of yield derived from parameters determined in the other year. The correlation between successive estimates of yield was found to be closer than that of of yield was found to be closer than that of yield with any of the growth parameters.

Separate analyses of crosses involving each of the parental varieties showed seasonal and varietal differences in the usefulness of the growth parameters for predicting yield.

The value of this approach to the choice of parents is discussed in view of these findings.

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.

The plasma lipid concentrations of newborn lambs, kids and calves and of adult ruminants in 0various physiological states have been reported. In newborn ruminants plasma lipid concentrations were 20–40 % of those found in their dams at parturition.

The concentrations of blood lipids have also been estimated in five lambs from birth to weaning at 90 days post partum. The plasma free fatty acid concentrations rose to a maximum at about 45 days post partum and then declined. Possible reasons for this elevation in plasma free fatty acids have been discussed with reference to published data on age changes in lambs of plasma glucose and volatile fatty acid concentrations. The concentration of plasma esterified lipids, mainly phospholipids and cholesterol esters, were very low at birth and rose to reach maximum values at about 20 days post partum before declining to adult values at weaning. These changes have been discussed in relation to diet and rumen development.

1. Plant nutrients, N, P and K, were applied to the soil surface or injected at a depth of 18 in. or 30 in. in perennial ryegrass swards, when the upper horizons of the soil profile were dry.

2. When the surface soil was dry and a soil water deficit of 2 in. existed there was no response to surface applied N but injection of N into moist soil at a depth of 18 in. produced a marked increase of growth. At this depth of injection there was a significant positive interaction between N and PK.

3. There was a substantial recovery in the herbage (59–80%) of the nitrogen applied to the subsoil, provided water was available in the soil horizon in which the nitrogen was applied.

4. Failure of a grass sward to regrow after cutting when the water available to the plant has been removed from the uppermost soil horizons is largely due to a deficiency of plant nutrients in the subsoil. The major deficiency is that of nitrogen.

1. Seven experiments with main-crop potatoes on heavy soils from 1962–5 measured yields from 0, 5, 10 or 15 cwt/acre of 13–13–20 fertilizer; (1) broadcast and worked into the soil by seed bed preparations; (2) broadcast on the final seed bed; (3) placed in bands 3 in. from the seed centre. Wheat followed the potatoes and was manured with 0, 5, or 10 cwt/acre (of the equivalent) of 13–13–20 fertilizer, in all combinations with the four amounts of, and the three ways of applying, the fertilizer given for the potatoes.

2. Fertilizer greatly increased potato yields and 15 cwt/acre of 13–13–20 was justified, provided it was broadcast. Both methods of broadcasting gave similar yields with 5 or 10 cwt/acre, but working the fertilizer into the seed bed was usually the better method with 15 cwt/acre of the fertilizer. Placing in bands beside the seed was the best method in four experiments with 5 cwt, in two with 10 cwt, but never with 15 cwt/acre of fertilizer.

3. Yields of green wheat, and of grain and of straw, were increased by residues of fertilizer applied for the potatoes, but were increased much more by freshly applied fertilizer. The residues increased wheat yields by the same amount as one quarter as much freshly applied fertilizer. The residues had smallest effects when the winter rainfall was largest, and were the same however the fertilizer had been applied.