Body composition in wild animals is regulated within a band that encompasses variations due to seasonal food supply and physiological state (e.g. that of the reproducing, lactating female and the growing juvenile). This body composition is characteristic of the genotype and is notable for the avoidance of obesity (Pitts & Bullard 1968). Urgent behavioural responses are also invoked to minimize weight loss. Figure 1 illustrates this homeostasis diagrammatically for the non-lactating, mature animal.

In this integrated complex, both food intake (quantity) and diet choice (quality) play a major role in achieving the required balance between food-energy intake and ‘net output’ of energy in its various forms such as activity, growth, lactation and change in body reserves. The development of such a system, through evolution, to achieve optimum reproductive fitness in a given environment, is consistent with the theory of optimal foraging which is characteristic of many animals in the wild. Newman (1991) has used such an approach in modelling diet selection by sheep.

Domesticated animals have inherited the complex genome of their progenitors, albeit modified in certain respects through natural and artificial selection, in their new circumstances. Many aspects of the physiology and behaviour of the domesticated animal still relate to the environment in which they evolved. For example Jensen & Redbo (1987) have demonstrated the complex nesting behaviour retained by the modern domestic pig, under free ranging conditions similar to those of its wild progenitor.

Two major non-genetic factors have emerged as major influences on the appetite of domesticated animals and man in modern times.

Nuclear magnetic resonance (NMR) micro-imaging techniques have been employed to study noninvasively the spatial distribution of mobile protons (1H) around the cotyledonary node of flax (Linum usitatissimum) plants of two differing growth morphologies. The gross anatomy of the tissues of the stem can be discerned as a result of differences in their mobile 1H contents. The technique produced excellent images of the complex changes in stem structure that occur at the point of origin of side shoots. Detailed structure within the xylem could be visualized and the presence of fibre bundles deduced as dark areas amongst tissues of higher 1H signal intensity.

As a result of the non-invasive and non-destructive nature of NMR-imaging, the images obtained have been compared to micrographs obtained by conventional histological techniques on the same plant tissue. In general, the two approaches produce comparable results, but the NMR images are influenced by the relaxation properties of the protons as well as their concentration. Paramagnetic species, such as Mn2+ ions, produce enhanced relaxation rates of protons in their vicinity and an apparent increase in proton density at short recycle times. Thus an NMR image can yield both chemical and structural information. Some of the advantages and disadvantages of this technique over conventional histological methods are discussed.

Field studies were conducted in 1989 and 1990 to investigate the effect of planting density on growth and yield of maize under irrigation in the Batinah Coast region, an arid zone in the Sultanate of Oman. Two maize cultivars, Eperon and Challenger, were grown at three densities (24000, 48000 and 74000 plants/ha). Grain yield was highest at 48000 plants/ha. Leaf area index (LAI) increased with increase in plant density but was not related to grain yield. Lodging was highly correlated with shelling percentage.

Under intermediate deepwater conditions (0–80 cm) at Cuttack, India, direct sowing of the semi-tall rice variety Utkalprabha with 200–800 seeds/m2 produced similar yields in 1989 when heavy rainfall (105 mm) after sowing resulted in more than 50% germination, followed by the gradual accumulation of water in the field. However, in 1990, which was characterized by drought in the initial stages, leading to poor germination (35–40%), followed by a sudden accumulation of water, the crops sown at 200 seeds/m2 produced a significantly lower grain yield than those sown at higher seed rates. Higher seed rates increased plant height, tillers/m2 and panicles/m2 but the associated decrease in panicle weight resulted in similar grain yield production. There was no decrease in the yield of crops sown at all seed rates in 1989 and at > 400 seeds/m2 in 1990 when clonal tillers were removed after 60 days to transplant either the equivalent of or double the uprooted plot area. The loss due to decrease in panicles/m2 with the removal of clonal tillers was compensated for by the resulting increase in panicle weight. The crop planted from clonal tillers produced a significantly higher grain yield than that planted from seedlings of equivalent age raised in a nursery seed-bed with or without fertilizer application. Furthermore, the clonal-propagated crop tolerated simulated flash-flooding better at the early vegetative stage, measured by less tiller mortality and relatively higher dry matter production than in the crop raised from nursery seedlings. Therefore, planting with clonal tillers uprooted from a well-established direct-sown crop is recommended under excess water conditions.

An assay was developed for assessing the potential for growth of shoot and root buds of white clover. This paper describes the technique and the experimental results on which it was based. The assay involved the incubation of nodes under standard conditions and the monitoring of bud activity at the nodes. Shoot buds were of primary interest but the assay was also used to investigate the activity of root primordia. Correlative influences were reduced by separating individual nodes and by removal of their subtending leaves and petioles. The optimal environmental conditions for incubation were: a constant temperature of 20 °C, a 24 h photoperiod of low irradiance (4 W/m2) and a high relative humidity (≥ 90%). The technique proved suitable for the monthly screening of 1000–2000 nodes sampled from field populations of white clover.

Factors influencing potato virus X (PVX)-induced resistance to Alternaria solani in potato leaves are reported. The inhibition of fungal infection was dependent on the time interval between viral and fungal inoculations, fungal inoculum load, age of the host, virus strain and host cultivar. The maximum reduction in fungal infection was observed when a gap of 120 h occurred between PVX and A. solani inoculations. The clearest interactive effect in terms of reduced susceptibility to A. solani infection was seen at a fungal spore concentration of 1000 spores/ml in 20-day-old plants. This effect was gradually reduced following an increase in inoculum load and age of the host.

The extent of pathogen interaction was also affected by different virus strains and host cultivars. Maximum inhibition of fungal disease occurred with the PVX-ring spot strain. Of five potato cultivar tested, the maximum inhibition occurred in Kufri Chandramukhi and Kufri Sindhuri, the cultivars most susceptible to A. solani.

In soil moderately infested with potato golden cyst-nematode, Globodera rostochiensis, nematicide treatments which lessened soil infestation when a susceptible potato crop was grown permitted a satisfactory second crop to be grown 3 years later without further treatment. In two experiments on heavily infested sandy loam on the same farm (Woburn Experimental Farm, Bedfordshire), aldicarb or oxamyl, incorporated in the seedbed in 1979 or 1980, greatly increased yields of Pentland Crown tubers and reduced the number of eggs left in the soil after harvest, but had little effect on a second crop of Pentland Crown potatoes grown 4 years later. Application of aldicarb or oxamyl to the seedbed before this second crop of potatoes increased yields and lessened nematode increase. The injection of 1,3-dichloropropene mixture (Telone II) into the soil in autumn at 224 kg/ha in one of these experiments did not enhance the nematode population control achieved by aldicarb or oxamyl alone.

The growth and yield of five cultivars of sunflower (Frankasol, Cerflor, Sunbred 246, Sokota 2057 and Sigco EX 10), sown from the end of March to the beginning of May, were studied in three experiments at Long Ashton Research Station, UK, during 1986, 1987 and 1988. The time from sowing to emergence and to maturity (as assessed by seed moisture content) was shortened by later drilling, although earlier sown crops were still ready for harvest slightly before the later sown ones. Cultivars differed in speed of development; Frankasol and Cerflor were the slowest to develop and Sigco EX 10 the fastest. Plant heights, head diameters and yields were all affected more by cultivar than by sowing date. The slower maturing cultivars produced the highest yields. Infection levels with Botrytis cinerea seemed to be related to the date of flowering, as early sown and fast developing cultivars became infected earlier. There were few benefits from early sowing and the optimum time appeared to be mid- to late April. Overall, Sunbred 246 was the most successful cultivar in these experiments, combining reasonable yields with moderately early maturity.

Leaves of olive trees (Olea europaea L.) of eight cultivars, Manzanilla, Picual, Hojiblanca, Edremit, Conservolia, Picholine-Marroqui, Chemlali and Frantoio, were collected in different seasons and years in Córdoba, Spain. Their chemical composition and in vitro organic matter digestibility values were determined. Differences in composition and nutritive value between cultivars, years and seasons were studied in Manzanilla, Picual and Hojiblanca, the three most important local cultivars. There were significant differences both between cultivars and seasons (P < 0·05) and a non-significant difference between years.

The effect of various drying procedures (fresh, oven-dried, air-dried indoors or air-dried outdoors) on chemical composition, in vitro digestibility and in vivo digestibility in sheep was also examined. The in vivo organic matter digestibility of fresh leaves was significantly higher than that of dried leaves. No difference was found between leaves air-dried indoors and oven-dried leaves. However, leaves air-dried outdoors were significantly less digestible. Quick drying in an oven reduced the digestibility of crude protein and acid detergent fibres compared to air drying indoors. There was a significant decrease in digestibility of 11% when leaves were dried separated from the branches as compared to leaves dried on the branches.

Field trials at the University of Nottingham, UK, in 1979 and 1980 investigated the effect of moisture stress on the growth and yield of the leafless dried pea Filby. In the absence of drought, the crop photosynthetic area was increased and maturity delayed. Seed yield was increased by the production of a greater number of reproductive nodes and a reduced abortion of flowers and pods.

In the second season, two sowing dates were also tested. Later sowing reduced the seed yield under the high and low moisture treatments by 14 and 33% respectively, due to an increased abortion of flowers and pods. The high moisture treatment reduced the water use efficiency (WUE) in this season and WUE was lower for the later sown crops, but there was no effect on WUE in the previous season.

The seed yield and water use of pot-grown leafless peas were lower than were those of a nearisogenic line of leafed peas. Moisture stress reduced the yield of both phenotypes but the effect on the leafless pea was greater. Moisture stress imposed at flowering reduced yields more than it did at pod filling and there was an additive effect of moisture stress at both times.

A field experiment compared the effects of urea, surface-applied either as a solid or liquid, at a rate of 100 kg N/ha, on ammonia volatilization from an established perennial ryegrass sward on three separate occasions during 1990 at the Agricultural Research Institute, Hillsborough, Northern Ireland. Total NH3 loss over 10 days from prilled urea for each of the three study periods was equivalent to 3.4, 9.1 and 4.4% of N applied. On two occasions, applying urea as a liquid significantly increased NH3 loss compared to prills, whereas on the third occasion there was no significant effect. Increasing the spray volume from 80 to 640 ml/m2 had no significant effect on NH3 volatilization.

Surface application of urea as a liquid compared to the prilled form did not lower NH3 volatilization and therefore is not a strategy that would improve the efficiency of urea as a nitrogen source for temperate grassland.

Four swamp buffaloes (Bubalus bubalis) and four crossbred Bos indicus x B. taurus cattle, fistulated at the rumen and abomasum or duodenum, were offered rice straw with mineral supplements in two experiments. In Expt 1, the straw was supplemented with 5% of leaf of Leucaena leucocephala, and in Expt 2 with either urea or urea with sunflower meal and rice grain. Intake of supplements of urea or urea/sunflower/rice respectively was 935 and 681 g/kg offered in buffaloes and 566 and 789 in cattle.

Buffaloes ruminated longer than cattle (Expt 1, 635 v. 452 min/day; Expt 2, 626 v. 466 min/day, P < 0·01). In Expt 1, voluntary intake and frequency of ‘A’ sequence forestomach contractions of both species was not affected by species, but buffaloes had a greater (P < 0·05) contraction force in the rumen and omasum, lower rate of ‘B’ sequence rumen contractions, and faster (P < 0·001) rate of gastrointestinal passage than cattle. In Expt 2, voluntary intake of both species was similar, and addition of concentrates did not affect voluntary roughage consumption, nor in situ rate of digestion of rice straw. Rate and predicted extent of digestion of dietary materials did not differ between species in Expt 1, despite lower concentrations of ammonia in rumen fluid in cattle than buffaloes; however in Expt 2, the rate of digestion of rice straw was higher (p < 0·05) and predicted extent of digestion was 14–20% (P < 0·05) lower in buffaloes. Digestibility of cell wall constituents was lower (P < 0·05) in buffaloes than in cattle in both experiments, but in Expt 2, provision of concentrates reduced (P < 0·01) the proportion of digestible cell wall constituents digested in the forestomach of buffaloes, but not of cattle.

Swamp buffaloes (Bubalus bubalis) and crossbred cattle (B. indicus x B. taurus) were offered two forages in two experiments. In Expt 1, four animals of each species were offered mature Rhodes grass hay (Chloris gayana) with a mineral supplement or with a supplement of minerals and urea (17·6 gN/d). In Expt 2, another group of four buffaloes and four cattle were offered mature spear grass hay( Heteropogon contortus) with mineral supplementation at intervals of 3 h. Four levels of urea (0, 5, 21 and 97 g/day) and 35S-sulphate were continuously infused in four periods.

Rhodes grass was consumed in greater amounts by cattle, whereas buffaloes ate more spear grass. Urea supplements increased intake of Rhodes grass by 12% in buffaloes and 22% in cattle, and of spear grass by 34% in buffaloes and 41 % in cattle. Digestibility of cell wall constituents and acid-detergent fibre of spear grass was lower (P < 0·05) in buffaloes than in cattle (417 v. 499; 471 v. 560 g/kg respectively). In Expt 2, dry matter digestibility progressively increased (P < 0·05) from 364 to 408 g/kg with increased urea infusion. Rumen dry matter pool increased by 11–21 % on infusion of 97 g urea/day, compared with no urea. Digestion of ground forages incubated in situ in the rumen was depressed below rumen ammonia levels of 30–60 mg N/l, while digestion of cotton thread was depressed below 60–80 mg N/l (Expt 1) or 150–200 mg N/l (Expt 2).

Patterns of N content in cotton thread suggested that more microbes attached in buffaloes and there was subsequently faster detachment than in cattle, particularly with increased urea infusion.

Using [14C]urea, the rates of urea synthesis in the body, excretion in the urine and degradation in the rumen and gut were compared in 20-month-old Kedah-Kelantan cattle and swamp buffaloes at the Universiti Pertanian Malaysia, Malaysia in 1987. The animals were fed rice straw or straw plus molasses.

The buffaloes were heavier than the cattle and had higher straw and nitrogen intakes, although these intakes did not differ significantly when compared on the basis of metabolic liveweight (W0·75).

Rumen pH in the buffaloes was lower, whereas ammonia and total volatile fatty acid (VFA) concentrations were higher than in the cattle. Total VFA concentration was lower when the diet contained molasses. Rumen bicarbonate kinetics did not differ significantly between species or diets.

There were no significant differences between species in plasma urea concentration, or urea synthesis rate per W0·75, or endogenous urea movement into the rumen per W0·75.

The buffaloes consumed more water and discharged twice as much urine as the cattle, but nevertheless excreted less urea per W0·75, and a larger fraction of their endogenously produced urea entered the gut. Movement of urea into the rumen per W0·75 was lower when the diet contained molasses.

Areas of sulla (Hedysarum coronarium) and pasture (Lolium perenne/Trifolium repens/Holcus lanatus) were grazed by young sheep (29·5–34·8 kg initial liveweight) in four experiments, and effects upon body growth, wool growth and rumen metabolism were measured.

Sulla contained 40–50 g condensed tannins (CT)/kg DM, whilst the pasture contained small amounts of CT (2–6 g/kg DM). After chewing during eating, a lower proportion of total CT was readily extractable and greater proportions were protein-bound and fibre-bound. Nutritional effects attributable to CT were assessed by oral administration of polyethylene glycol (PEG), which binds and inactivates CT, to half the animals grazing each forage. Rates of body growth were consistently higher for lambs grazing sulla than those grazing pasture, with the CT concentration in sulla being neither stimulatory or inhibitory to body growth or voluntary feed intake (VFI). The action of CT reduced carcass fatness in sheep fed both diets, in the one experiment where this was measured. CT present in both sulla and pasture decreased rumen ammonia concentration and decreased molar proportions of iso-butyrate and iso and n-valerate. During spring and early summer, when wool growth rates were highest, CT present in both pasture and sulla increased wool growth rate; when wool growth rates were low during winter, CT had no effect upon the wool growth of sheep grazing either forage. Numbers of protozoa and molar proportions of n-butyrate in rumen fluid were increased by CT in sheep grazing sulla but not pasture.

It was concluded that the higher rates of body growth and VFI in lambs grazing sulla was most likely to be due to its very high ratio of readily fermentable: structural carbohydrate.

Several previous studies have shown that the proportion of clover in sheep diets was greater than the proportion of clover in the mixed species swards being grazed. Various hypotheses have been put forward to explain this observation. One widely held hypothesis is that sheep prefer (actively select) clover to grass. This hypothesis was tested by offering 12 sheep, six that had been recently grazing perennial ryegrass and six that had recently been grazing white clover, the choice between foraging on grass or clover provided as turves. It was found that, rather than prefer clover, the sheep preferred the opposite species to the one they had previously grazed. From these observations, alternative hypotheses are proposed to explain the disparity in composition of the diet relative to the swards observed in previous studies, and the evidence for a constant preference for clover and its basis in grazing behaviour is reconsidered.