Published data are used in support of a hypothesis that equal amounts of digestible cell walls and digestible non-cell walls do not contribute equally to the energy value of forages. The relationship between the concentration in the organic matter of metabolizable energy (kcal/g organic matter) determined at the maintenance level of feeding, and the percentages of cell wall and digestible cell wall in the forage organic matter is defined by:

This equation derived from published data on 12 grasses appears to be applicable to both grasses and legumes.

Pregnant beef heifers allowed ad libitum access to oat straw were given 2·7 kg molassed sugar-beet pulp alone or with additional dicalcium phosphate or urea or a combination of both materials in a Latin square design involving four feeding periods each of 21 days. Supplementation with urea to increase the total daily intake of digestible crude protein from about 130 to 290 g/day increased straw consumption by 20%. This increased the total intake of metabolizable energy from about 13 to 15 Meal/day. Increasing the total intake of phosphorus from about 6 to about 17 g P/day did not increase straw intake or digestibility or the total intake of metabolizable energy in either the presence or absence of additional urea.

Supplementation with urea increased the concentration of urea and glucose in the blood plasma and the concentration of ammonia in the rumen liquor, but did not increase the concentrations or alter the proportions of rumen volatile fatty acids. Addition of urea tended to increase the digestibility of the dry matter and crude fibre of the straw. Phosphorus supplementation increased the concentration of phosphorus in the blood plasma.

Satisfactory comparisons of the incidence of virus yellows in sugar-beet fields or experimental plots with different amounts of N fertilizer can be made from visual symptoms early in the growing season, but not later because dressings of N fertilizer may then mask or delay the appearance of symptoms. Sugar-beet plants in the field infected with beet mild yellowing virus (BMYV) are less likely to show symptoms than those with beet yellows virus (BYV), and plants with BMYV in the glasshouse often fail to show clear symptoms.

Crop yield will be affected by the spread of viruses and colonization of plants by aphids, which in turn are affected by such factors as plant density, nitrogen supply and irrigation. The presence or absence of virus diseases and of aphids should therefore be considered during studies on the effects of these agronomic factors on the growth and yield of sugar beet. Where ample rather than little N fertilizer is used a small increase in the percentage of plants infected with yellows can be expected, and aphids will be more numerous, if plants are not treated with insecticide. Irrigation may also increase yellows incidence (e.g. from 16% to 20% of plants at Broom's Barn in 1967), but any loss of potential yield from increased virus incidence will be small compared with that gained from the use of fertilizer or irrigation. However, plant density can appreciably affect yellows incidence. For example, at Broom's Barn in 1972, 51% of plants in crops with 17500 plants/ha contracted BMYV but only 15 % of plants in crops with 126500 plants/ha. The less dense crop lost 3–4% more of its potential yield due to yellows than the dense crop; this represents a difference due to virus of about 0·25 t sugar/ha.

The amount of soil moisture used by sugar beet was determined weekly between May and October (1970–2) in plots testing 18500 and 124000 plants/ha with and without irrigation. When leaves covered more than 60% of the ground (after mid-June with the large density and after mid-July with the small density) the crop used water at the potential transpiration rate even with soil moisture deficits on plots without irrigation of up to 170 mm. Therefore as irrigation greatly increased sugar yield in 1970 and 1972, it probably did not do so simply by satisfying the crop's water need.

In 1970 irrigation appeared to act partly by decreasing the time taken to attain complete leaf cover but in 1972 irrigation had only a slight effect on leaf cover but greatly increased sugar yield, particularly of the large population. With little rainfall, the large density rapidly exhausted the available moisture from the plough layer. It seems likely therefore that irrigation increased yield by giving more leaf cover early and by improving nutrient supply but not by supplying extra water for transpiration.

Five successive trials were conducted using eight adult rams (Sudan desert sheep) to study the effect of restriction of water intake on some aspects of digestion and nitrogen metabolism. The feeds used in this study were berseem hay (Medicago sativa), lubia hay (Dolichos lablab), maize hay (Zea mais), a concentrate mixture, and dry desert grasses (hummra) (a mixture of Dactyloctenium aegyptium, Schoenefeldia gracilis, Eragrostis pilosa, Aristida funiculata and Aristida spp.).

Restriction of water did not affect the digestibility coefficients of organic matter, crude protein and crude fibre significantly. The digestibility coefficient of ether extract was significantly reduced whereas that of nitrogen-free extract was slightly higher when water was restricted.

The concentrations of ammonia and volatile fatty acids in the rumen and of urea in the blood were recorded before and 3 h after feeding. Increases in rumen ammonia and blood urea nitrogen concentration were reduced by water restriction except when hummra was fed.

Restriction of water intake also slightly increased the in vitro rate of fermentation of rumen contents which is taken as a measure of microbial activity in the rumen, and the retention of nitrogen. These results are interpreted as indications of more efficient nitrogen utilization under conditions of water restriction.

There were no significant effects of the treatments on changes in the concentration of volatile fatty acids.

The significance of these findings in relation to the management of desert sheep in the arid parts of the Sudan is discussed with special reference to the effect of the level of dry-matter intake on nitrogen balance.

The use of body weight, red cell volume and tritiated water space in the prediction of the body water, body-fat and soft tissue protein contents of hill sheep was investigated. Sixteen Blackface sheep, ranging in age from 2½ to 6½ years, were used before mating in November when in peak body condition and 21, of similar age distribution, were used in mid-lactation in June when in very poor body condition. Mean fat concentrations in the empty body were 188 and 28 g/kg in November and June, respectively.

Body weight alone accounted for 46 and 14% of the variation in body-fat content in November and June, respectively. The inclusion of red cell volume as a second independent variate did not improve the efficiency of the prediction equations. When tritiated water space and body weight were used 77% of the variation in body-fat content was accounted for in both November and June. Separate equations for the November and June groups gave the most accurate estimate of body-fat content, but it was concluded that for most practical purposes a single relationship would be sufficiently accurate. Soft tissue protein content was best described as a simple function of body weight.

The application of prediction equations from the literature to the present populations of sheep led to overestimates of body-fat content by up to 100%. It is suggested that prediction equations need to be specific to the experimental conditions operating or to the particular population under study.

A new mutant in maize with an unusual ear location is described. The condition was found to be controlled by a simple recessive gene located near the breakpoint on chromosome 3. The gene symbol, te, is proposed.

Three experiments are reported which investigated the effects of planting density and variety on the relationship between tuber dry-matter percentage and tuber size. In the first experiment dry-matter determinations were made on samples of tubers less than 3·8 cm and greater than 3·8 cm from different planting densities obtained at eight fortnightly harvests. Standard analysis of variance was used for each harvest date and apart from Maris Piper giving consistently higher dry-matter percentages than Pentland Crown for the same tuber sizes, effects were small and difficult to interpret. The reasons for the problems in interpretation, which were mainly due to differences in tuber size distribution, are discussed.

In the second and third experiments the effects of tuber-size distribution were removed by regression analyses of tuber dry-matter percentage on tuber size in definable grades and curves were fitted to the data. These curves revealed that tuber dry-matter percentage tends to show a quadratic response to increasing tuber size and is affected by variety and stem density. The significance of these results is discussed.

Specialized techniques, previously used in surgically prepared goats, which simultaneously measure udder metabolism (arteriovenous difference of milk precursors x udder blood flow) and the whole body turnover of the milk precursors, have been successfully transferred to dairy cows. Methods of obtaining representative samples of arterial and mammary venous blood and of measuring udder blood flow are described.

The rates of entry into the circulation, as determined by isotope dilution, of glucose, acetate and plasma free fatty acids were 3·3–4·0, 1·7–2·1 and 0·5 kg/day respectively. Acetate and glucose contributed 32–50 and 4–11% respectively of the total CO2output by the animal.

Measurement of the uptake of precursors of milk constituents and their transfer into milk showed that there were substantial arteriovenous differences of glucose, acetate, triglyceride and β-hydroxybutyrate which were not significantly different between breeds or related to milk yield. Isotopic and balance data confirm that glucose is the main precursor of lactose and that the oxidation and transfer of glucose into lactose accounted for 69–98% of the glucose entry rate. As in the goat, plasma triglycerides and blood acetate accounted for 35–80% and 25–50% of the milk triglycerides respectively. Propionate was extracted from plasma but the uptake was only about 8% of the value for acetate.

There was no net arteriovenous difference of phospholipids, cholesterol esters or free fatty acids, but the fall in specific radioactivity of free fatty acids across the mammary gland indicated there was an exchange of free fatty acids between plasma and mammary tissue. In agreement with previous findings, acetate contributed to all the milk fatty acids up to a chain length of C14 and part of the C16 fatty acid. Plasma triglycerides contributed to the remainder of the C16 fatty acid and all the milk fatty acids with a chain length of C18 or higher.

In contrast to the lactating goat, cow plasma contained very few chylomicrons. The majority of the triglycerides taken up by the udder were derived from the lowdensity lipoprotein fraction.

The essential amino acids were extracted from blood in amounts sufficient to account for the essential amino acids secreted into milk protein. Although the plasma level of methionine was low, 52–72% of the material reaching the mammary gland was taken up. The uptake of arginine was far in excess of the requirement for milk protein synthesis.

Data from experiments with spring wheat, variety Kolibri, were used to examine size gradients within the mature ear in relation to ear development. The greatest number of grains and florets per spikelet, and the heaviest grains, occurred in the lower-mid part of the ear. Within the spikelets in this region grain 2 > grain 1 > grain 3.

It is proposed that the timing and period of ear development and the number of spikelets can be described quantitatively in terms of (1) the rate of leaf initiation, (2) the number of leaves, (3) the rate of spikelet initiation and (4) the total number of primordia. Both leaf and spikelet initiation proceeded at more or less constant rates, but spikelet initiation was about three times as fast as leaf initiation. Differentiation of the spikelet primordia started at about the time the terminal spikelet was initiated, occurring first in the spikelets in lower-mid part of the ear. The rate of floret initiation was lower than that of spikelet initiation, but did not differ between spikelets. A maximum of nine florets per spikelet was formed and then, in all spikelets, some of the last-formed primordia died, leaving two to four potentially fertile florets.

Morphologically, primordia in the lower-mid part of the ear were always the most advanced. The more rapid development of the terminal primordia tended to synchronize events such as meiosis and anthesis, thus shortening the development period of the later formed florets. Changes in meristem size were such that both length and diameter were the greatest when the primordia of the lower-mid part of the ear were initiated.

The statistical model to describe primordium initiation and ear size is compared with other models describing primordium initiation rates. The analysis of ear development in quantitative terms is discussed in relation to analyses of ear development by morphological stages. A correlation between grain size and time of floret initiation is demonstrated and the significance of the size changes in the meristem is discussed.

Four samples each of Lolium perenne, Chloris gayana and Setaria splendida grown under similar conditions and having similar in vivo dry-matter digestibilities with sheep were used in a comparison of the chemical composition of tropical and temperate grass. L. perenne had less lignin, crude fibre, neutral-detergent fibre, acid-detergent fibre and cellulose than the two tropical grasses but more neutral-detergent solubles. In vivo digestibilities of the cell-wall polysaccharides of the tropical grasses were not reduced by their higher lignin contents. The digestibilities of the cell wall were generally higher than the digestibilities for the dry matter and neutral-detergent solubles. It is suggested that the effect of lignin on the digestibility of cell-wall polysaccharides is dependent on the area of protection, and better predictions may be achieved if the cell wall is divided into two fractions, an unlignified fraction that is completely digested and a completely indigestible fraction containing all the lignin.

It is concluded that differences may be found in the carbohydrate composition of temperate and tropical grasses but that these differences may not cause differences in the overall in vivo digestibility of the dry matter.

The effects of changing to a high starch: low roughage diet have been studied in two Friesian and two Jersey cows, surgically prepared for the simultaneous study of udder metabolism (arteriovenous difference x udder blood flow) and whole body turnover of milk precursors (isotope dilution).

In the Friesian cows milk fat concentration was lower on the high starch diet but in the Jerseys fell only slightly in one animal. In both Friesians and in the one Jersey these changes were accompanied by an increase in total rumen VFA concentration. Rumen acetate concentration did not change but propionate doubled. Thus this confirms that the usually reported fall in ‘acetate:propionate ratio’ is due to a rise in propionate production rather than due to a fall in acetate production.

There were significant falls in the blood concentrations of acetate and β-hydroxy-butyrate. The rate of extraction by the udder of acetate and β-hydroxybutyrate did not change but triglyceride extraction fell. Therefore since udder blood flow did not alter the uptake of all three fat precursors fell.

The entry rate of glucose into the circulation and its contribution to total body CO2 increased. The entry rate and contribution to CO2 of acetate decreased but this was probably mainly due to a fall in endogenous acetate production by the body tissues. Plasma FFA concentration showed little change but the entry rate of palmitate fell on the high starch diet. There was also an increased proportion of unsaturated and trans fatty acids in the plasma and milk triglycerides.

A number of herbicide treatments involving the use of trifluralin, preforan and igran were compared together with hand weeding as methods for the control of weeds in a cultivar of Phaseolus vulgaris sown on 19 January 1972.

Favourable increases in yield of beans were obtained by combinations of preforan and igran which were associated with an increase in the number of pods produced per plant. Hand weeding failed to give a significant increase in final yield.

Within 14 days from sowing there was an appreciable weed cover in the control and hand-weeded plots but little evidence of weeds in the herbicide-treated plots. At 41 days there were still no significant differences between the control and the plots to be hand weeded. There was, however, a considerable reduction in percentage cover of weeds on the herbicide treated plots. Trifluralin and preforan were equally effective in reducing weed cover.

A dynamic model was derived to predict crop response to nitrogen fertilizer under different soil and weather conditions. It combined formulae representing existing principles about important processes such as leaching of nitrate through soil and nitrate uptake by plant roots. Starting values were given for the initial plant weight and its nitrogen content and parameters were included for the crop's growth and rooting characteristics under optimum growing conditions. For each day the model re-calculated the distribution of water, nitrate and roots down the soil profile and the increment of growth.

The validity of the model was tested by using it to forecast the effects of different weather conditions and cultural practices on the nitrogen responses of a test crop, lettuce, when grown in experiments that were entirely independent of those used to obtain parameter values for the model. It successfully predicted the effects on the general shape of the response curve of the distribution of rainfall during the growing season, the age of the plant, the depth of fertilizer incorporation and the application of the nitrogen partly as a top dressing instead of entirely as a base dressing.

The model was used to develop a strategy for nitrogen fertilizer practice for lettuce in the U.K. which was found to be broadly in agreement with the results of fertilizer experiments on grower's holdings.

Lactation in ewes is associated with hypertrophy of the liver, due to cell proliferation and enlargement. The mean diameter of hepatic parenchymal cell nuclei increased after parturition to reach a maximum at 6 weeks, after which there was a decline.

The liver regressed in weight after weaning but total DNA declined less than liver weight and remained elevated in comparison with livers of unmated ewes, while DNA concentration increased. Total liver DNA remained relatively high for approximately 6 months. It is suggested that the final fall to control values was associated with cell death and disorganization of the hepatic parenchyma.

These results imply that the life span of one type of liver parenchymal cell may be at least 6 months.

Twenty-four Friesian bull calves purchased at 10 weeks old were reared in three groups to slaughter at 420 kg live weight. One group (BB) was fed on a barley-concentrate diet to grow rapidly at 1·41 kg/day, a second (GG) was fed on dried grass cubes to grow slowly at 0·97 kg/day and the other (BG) was fed to grow rapidly to a live weight of 250 kg and thereafter at a slow rate, overall 1–20 kg/day.

Efficiency of food conversion, energetic efficiency and efficiency of dissectible muscle production were best for BB animals, followed by BG and then GG. Changes in carcass composition mainly resulted from differential fat deposition, and bone/ muscle development was allometric in relation to fat-free empty body mass. The development of certain characteristics, the head, depth of forequarter, pelvic length and tibia length followed a time scale and may have reflected the priority for nutrients of some entire male characteristics irrespective of body size.

In addition to being most efficient, the fastest growing bulls yielded carcasses with sufficient fat deposition to meet grading requirements, whereas both the slower growing groups of bulls were penalized in this respect.

Sheep prepared either with a rumen cannula, or with a rumen cannula plus re-entrant cannulae in the duodenum and ileum were fed fresh ‘Ruanui’ perennial ryegrass (R), ‘Manawa’ short-rotation ryegrass (M) and white clover (C) at dry-matter intakes ranging from 450 to 1000 g/24 h.

The re-entrant cannulated sheep were given paper impregnated with chromic oxide (Cr2O3) once daily via the rumen fistula as a marker; recoveries of Cr2O3 at the duodenum, ileum and faeces were approximately 75, 69 and 100% respectively. Regressions of Cr2O3-corrected digesta constituent flows (g/24 h) on intake were constructed and from these were calculated the sites of digestion of OM, gross energy, readily fermentable carbohydrate, structural carbohydrate and lipid between the stomach, small intestine and large intestine.

There were differences between pasture species in partition of OM and energy digestion. With M, digestion in the stomach was significantly less (P < 0·01) and digestion in the small intestine was significantly more (P < 0·05) than with either R or C. These partitions of OM and energy digestion changed with level of feed intake. A substantial proportion (9–18%) of the digestible OM and energy was apparently digested in the large intestine with all three herbages.

With all three herbages approximately 93% of the digestible readily fermentable carbohydrate and 90% of the digestible structural carbohydrate was digested in the stomach region.

Reasons for differences in gross efficiency of utilization between the pasture species in the order C > M > R were examined.

A food preference trial was carried out in which 21 artificially reared lambs were offered ad libitum a choice of eight foods for a period of 4 weeks commencing at 28 days of age.

Growth rate and total food intake were highly variable but the lambs agreed substantially on what they liked and disliked. Soya-bean meal was the most preferred food throughout the experimental period. Flaked maize was very unacceptable for the first 12 days (up to 40 days of age) but after that its popularity rose steadily and considerably. Fish meal was quite popular at first but after 12 days had become the least preferred food and remained so for the remainder of the time.

In the latter part of the experiment the foods could be classified into a more popular group comprising soya-bean meal, rolled barley and two proprietary pelleted diets, and a less popular group comprising fish meal, flaked maize, whole oats and sugar-beet pulp.

It is argued that in order to be acceptable diets should not be coarse and either should not contain fish meal or have the flavour disguised.

Eight mature female sheep were offered a ration which maintained body weight constant during a 20-week period. During the final 10 weeks a comparison was made in each animal of the pattern of equilibration and urinary losses of tritiated water during 8 h after dosing by four different routes. These were intravenous, intraperitoneal, intraruminal and a combination of the intraperitoneal and intraruminal routes. Tritiated water spaces were calculated from (a) the 8-h plasma specific activity and (b) by extrapolation to zero time of the plasma specific activities during the 7 days after injection. At the end of the experiment the fat and water contents of the bodies of the sheep were determined directly.

Complete equilibration of tritiated water between plasma and rumen water was not achieved in all animals 8 h after intravenous or intraperitoneal injection but was when the rumen was primed by the combination of intraperitoneal and intraruminal dosing. After intraruminal dosing equilibration was not achieved in any animal within 8 h of dosing.

Urinary losses of marker were lower after intraruminal dosing but otherwise averaged 4–5 % of the dose/1 urine. This was equivalent to 0·3–6·7% of the dose for individual sheep.

Errors resulting from incomplete equilibration and urinary loss of marker did not influence the efficiency of prediction of total body water from tritiated water space. The multiple correlation coefficient relating body fat with empty body weight and its water content was very high (r = 0·99). Errors introduced into this relationship by the inclusion of gut water in the prediction equations were apparently of a similar magnitude to those resulting from the errors in the estimation of tritiated water space.

The extrapolation method for the determination of tritiated water space was shown to have the same accuracy as equilibration techniques under these controlled dietary conditions.

Experiments were conducted to study the effect of plant injection with growth regulators on the dormancy of onion bulbs cv. Elba Globe. Application of abscisic acid induced early senescence of the leaves and prolonged the rest period of the bulbs. This effect was partially overcome by subsequent applications of gibberellin, auxin or cytokinin and totally overcome with the application of a mixture of the three hormones. Maleic hydrazide application prolonged the rest period by inhibiting both sprouting and rooting of the bulbs throughout the storage period. This inhibitory effect was not overcome by the subsequent application of auxin, gibberellin, kinetin, or their combinations. Ethephon application increased rooting of bulbs and partially overcame the effect of abscisic acid on dormancy.