The descriptive aspects of hepatic fatty acid metabolism, and of ketogenesis in particular, have been extensively described for ruminants. There is, however, a distinct lack of information on the more mechanistic aspects of the subject. The biochemical profile of the livers of ruminant species shows both similarities to, and striking differences from, that of simple-stomached animals. Consequently, it may not always be valid to extrapolate from the situation in, say, rat liver to that in ruminant liver in order to interpret experimental observations in ruminants. Of perhaps greater interest is the recognition that the adaptations in the ruminant system are important not only in enabling us to rationalize the physiological changes observed in ruminants, but are in themselves of interest in the analysis of metabolic regulatory strategies. Consequently, this review deals with the peculiarities of the regulation of hepatic ketogenesis in ruminants, and the biochemical mechanisms that may explain their existence.

Experiments were conducted in wheat planted in microplots at Hisar and Sirsa in Haryana state, India, to observe and simulate the depth distribution of moisture content, electrical conductivity in 1:2 soil-water extract (EC 1:2), and exchangeable sodium percentage (ESP) of soils after irrigation with water of high electrical conductivity (12–19 dS/m) and sodium adsorption ratio (20–80 (mmol/1)0·5). The three simulation models used differed in the procedure of estimation of evapotranspiration (models I and II, Reddy 1983; model III, Arora et al. 1987). In general, the means of the experimental moisture content profiles decreased and those of EC 1:2 and ESP increased with irrigation at both locations. Statistical analysis showed an overall good agreement between the experimental and simulated values of moisture content, EC 1:2 and ESP; the accuracy of simulation of the models followed the order model II = model III > model I, for moisture content and EC 1:2, but was identical for ESP.

In 12-year (1975–87) fertilizer trial on a pearl millet-wheat rotation, there were no responses to applied K and exchangeable K decreased from 620 to 200 kg/ha. In spite of progressively diminishing exchangeable K, removal of K by crops was independent of soil K status, indicating that exchangeable K had no relation to K uptake in this soil. Thus, nonexchangeable K made a major contribution to plant K, up to 90% in untreated plots and > 70% in K-treated plots. A significant (r = -·708) relationship between nonexchangeable K and K fixation capacity was found. Nonexchangeable K was also significantly but negatively correlated (r = -0·583) with free energy exchange (ΔGr). Potassium supply values, expressed by pK-½p (Ca + Mg), were positively and significantly correlated with K removal by crops in 1987 and with the K saturation values of the exchange phase, so that both these measures can be successfully used to test soil K availability. The results of this study suggested that on this soil, under a pearl millet-wheat crop system, inclusion of K in the fertilizer programme may soon be needed.

The response of an old, unimproved mixed-species pasture to fertilizer nitrogen was examined under 4-weekly cutting or continuous grazing with young beef cattle. Five N fertilizer rates were applied: zero, 100, 200, 400 or 800 kg/ha per year. The investigation was carried out in Devon, on a heavy clay soil in a region of high winter rainfall in 1984, 1985 and 1986.

Annual total herbage dry-matter (DM) production, live weight gain (LWG) and utilized metabolizable energy (UME) output all increased with successive increments of fertilizer N up to 400 kg N/ha per year. Under 4-weekly cutting, the response per kg applied N fell below 10 kg DM at an application rate of 268 kg N/ha per year, giving a yield of 10·6 t/ha per year. Under grazing, the overall response during the grazing season per kg applied N fell below 300 kg live weight carried per ha at a fertilizer rate of 248 kg/ha per year, giving a UME output of 78 GJ/ha over the grazing season. High available soil N contributed to the high productivity from these swards. Animal output at moderate (200 kg N/ha per year) N application rates did not appear to be constrained by the initial botanical composition of this unimproved sward. Repeated high N applications in the 400 kg N/ha per year treatment reduced output in 1986 under grazing and cutting, compared with treatments which had received the lower N applications.

The DM yield from the 4-weekly cutting study gave a satisfactory prediction of UME output from this pasture. Climatic conditions, particularly high rainfall, appeared to be an important constraint on animal performance at pasture.

The high UME output achieved from this pasture at 200 kg applied N/ha was well above the average UME for commercial farms.

In a field trial at Rukuhia, New Zealand, ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) seed was direct drilled into pasture (i) without herbicide suppression of the resident sward, (ii) with banded application of glyphosate or paraquat herbicide at drilling to remove 50% of the resident sward and (iii) after complete removal of the grass and weed components of the old sward with glyphosate or paraquat before drilling. These treatments were compared with the untreated old swards. Where the old sward was removed by herbicide before drilling, pests moved onto the drilled seedling rows, but, where herbicide was sprayed in bands over the drill rows, the pests remained in or moved into the residual bands of the old sward. Significant beneficial interactions between herbicide use and in-furrow applications of molluscicides and insecticides resulted in reductions in the numbers of pests on the seedling rows. The influence of vegetation control on the pest burden is discussed in the context of current pasture renovation practices.

In field and wind tunnel experiments in 1988 at the Scottish Centre of Agricultural Engineering, moisture loss in the 24 h after cutting increased when grass swaths were mixed, spread or turned and was positively related to the number of mixings. In the field trials, dry matter loss from conditioned swaths increased when the swaths were mechanically mixed or spreadafter cutting.

The effects on a winter wheat test crop of a preliminary year of winter or spring field beans (Vicia faba), winter oats, winter oilseed rape, winter or spring peas (Pisum sativum), winter wheat, spring lupins (Lupinus albus), spring sunflowers (Helianthus annuus) or a cultivated fallow were compared in three 2-year experiments on clay-with-flints soil at Rothamsted from 1986 to 1989. In one experiment, autumn-sown ryegrass (Lolium perenne) and an uncultivated fallow, given weedkiller, were also included in the first year. Plots of test-crop wheat were divided to compare no N fertilizer with an optimal amount estimated from a predictive model.

Amounts of take-all (Gaeumannomyces graminis) in the test crop of wheat following wheat were very slight in the first experiment, but large in the second and third. All the break crops reduced takeall to none or very slight amounts.

Amounts of NO3-N in the soil in autumn after the first-year crops ranged from 7 to 95 kg N/ha. On average, they were least after oats, and most after cultivated fallow. In autumn 1988they were least after autumn-sown ryegrass. In early spring, amounts of NO3-N were generally less, ranging from 7 to 55 kg N/ha, depending on preceding crops, sowing date of the wheat and the weather. Amounts of NH4-N in soil were little affected by preceding crops or weather and were generally smaller in spring.

The estimated average N fertilizer requirement of test-crop wheat following winter wheat was 230kg N/ha. This was increased by 10 kg N/ha following winter oats, decreased by 40 kg N/ha after spring peas and by 30 kg N/ha after winter rape, winter peas, spring beans and cultivated fallow. Other preliminary crops not represented every year had effects within this range.

Grain yields of test-crop wheat given optimal N averaged 7·2 t/ha after winter wheat, c.1·5 t/ha less than the average after most of the break crops. The yield after oats was limited by self-sown ‘volunteers’ and that after ryegrass by limited soil N after ploughing.

Of the break crops tested, winter and spring beans, winter oats, winter rape and spring peas all gave satisfactory yields. A farmer should choose between these on the basis of local farm circumstances and current economics of the break crops. Differences between effects on take-all and savings on fertilizer N were too small to influence this decision.

The distribution of dehydrogenase activity (DHA) and the activities of phosphatases were studied in the rhizosphere of four varieties each of clusterbean (Cyamopsis tetragonoloba (L.) Taub.), mung bean (Vigna radiata (L.) Wilczek), moth bean (Vigna aconitifolia (Jacq.) Marechal) and pearl millet (Pennisetum americanum (L.) Leeke) grown in pots containing soil low in available P. Activities of dehydrogenase and phosphatases were greatest 25 days after sowing and remained constant from 50 days after sowing until crop maturity. Rhizosphere soils showed higher activities than other soils: 26–158% for acid phosphatase, 66–264% for alkaline phosphatase and up to 292% for DHA. Dehydrogenase and alkaline phosphatase activities were significantly higher in the rhizospheres of legumes than in those of P. americanum.In general, the rhizospheres of C. tetragonoloba ‘HFG314’, V. radiata ‘PDM62’, V. aconitifolia ‘IPCMO344’ and P. americanum ‘RCB2’ had higher activities than those of other varieties of the same species. Acid phosphatase activity was lower than alkaline phosphatase activity and differences between species and varieties were small and nonsignificant. The results suggest that the higher phosphatase activities in the rhizospheres of some crops may increase P availability and utilization from arid soils.

Field trials were conducted in 1988 at the University of Ibadan to determine the effects of cypermethrin + dimethoate (Sherpa Plus®), the oil extract from ripe seeds of Piper guineense Schum & Thonn and the aqueous extract of ripe seeds of Azadirachta indica A. Juss on the pests and yield of cowpea. Cypermethrin + dimethoate was consistently superior to all other treatments in substantially reducing the population densities of Megalurothrips sjostedti Trybom and of Maruca testulalis Geyer, which are serious pests on flowers and buds, and in reducing the densities of four pod-sucking bugs. Pest population densities were also reduced by foliar sprays with A. indica or P. guineense extracts.

Seed yield after treatment with cypermethrin + dimethoate was 0·99 t/ha, more than double the yield from other treatments. A marginal increase in seed yield compared with the control was achieved by foliar spraying with A. indica extract.

Two-year-old tea bushes were given NPK fertilizer on 12 November 1986 and 14CO2 on 22–23 December 1986 and 9–10 January 1987. Late-autumn fertilizer dressing stimulated photosynthate accumulation in the whole bush, especially in overwintering leaves and roots. Large amounts of photosynthates in overwintering leaves provide the nutrition required for early spring budding. Lateautumn dressing also accelerated the transport of photosynthates from leaves to roots in winter, where photosynthates, with absorbed nitrogen, synthesized more animo acids, especially theanine and phenylalanine. The re-use of photosynthates stored in the roots of the dressed bushes during shoot growth the following spring was also facilitated by late-autumn dressing. The contents of amino acids and caffeine in the shoots of dressed bushes were much higher than those in the control, whereas the content of polyphenol was lower than in the control. The results indicate that late-autumn dressing improves the quality of spring green tea.

Growth, yield and incidence of lodging of poppies were studied in Tasmania at 10–200 plants/m2 and at nominal rectangularities (within-row: between-row spacing) ranging from 1:1 to 10:1. In 1983/84 and 1988/89, there were asymptotic relationships between plant population density and both total dry-matter production and total head (capsule plus seed) yield at maturity. In 1983/84, a season with above-average wind, the incidence of lodging increased as density increased to > 50 plants/m2; morphine concentration decreased as density increased to > 100 plants/m2. This resulted in parabolic relationships between yield of erect (machine-harvestable) heads and yield of morphine from erect heads with plant density, the maximum morphine yield from erect heads being achieved at 70 plants/m2. In 1988/89, a season with below-average wind, the effects of lodging were less severe at high densities and the components of ‘erect’ yield were adequately fitted by an asymptotic function. Rectangularity of 1:1 gave higher total dry matter production, total head yield, yield of erect heads and morphine yield from erect heads than 4:1 and 10:1. Since calm conditions similar to those of 1988/89 occur only once in every 4 years, growers should be encouraged to establish c. 70 plants/m2. As most commercial crops in Tasmania are drilled in 150–175 mm rows, growing at 70 plants/m2 to maximize the effect of plant density would also approximate to the ideal rectangularity (2:1 in this case).

Field experiments were conducted during 1983–85 and 1984–86 on an entisol at Lucknow, India. Dry herbage, essential-oil yields and nutrient uptake increased significantly with the application of 83 kg K/ha. Considering the means from both experiments over a two-year cropping cycle, the application of 41·5 kg K/ha in four splits exceeded the zero K control by 6·8 t/ha (dry matter) and 233 kg/ha (oil), and exceeded a basal application of 83 kg/ha K by 2·8 t/ha (dry matter) and 109 kg/ha (oil). Amounts and methods of K application showed no effect on oil quality. Application of 41·5 kg K/ha in four splits, one after each harvest, is recommended to obtain maximum yields in this perennial grass.

Eighty autumn-calving (A) and 82 spring-calving (S) British Friesian cows were divided during the grazing season into two groups: one group received silage overnight indoors and grazed herbage during the day (partial storage feeding, P) and the other was conventionally set-stocked (C). The effects of the four treatments (AC, AP, SC and SP) on reproductive performance and herd health are reported for the 27-week grazing season and the subsequent 25-week housed period in 1985/86 in North Wales. Calving to conception interval was not affected by treatment but, in treatment SP, pregnancy rate to all services was lower and number of barren cows was greater than in the other treatments. Partial storage feeding increased the incidence of under-run heel and laminitis in the early part of the grazing season, and this was reflected in poorer locomotion. Treatment SC resulted in an increased incidence of punctured sole with pus later in the grazing season. Both autumn-calving treatments resulted in a large decrease in lameness and poor locomotion at drying off, but these increased in the autumn before housing. The mean duration of each lameness incident was 1·88 months and, in 40 out of 97 incidents, lameness was preceded by uneven gait. The incidence of lameness and poor locomotion was low for all treatments throughout the housed period. It is concluded that a high standard of buildings and reproductive and herd health management is necessary for partial storage feeding to be practised successfully.

This study sought to determine whether increases in live weight (LW) of steers implanted with Compudose 200®, a growth promotant that contains 17β-oestradiol, arose in part from increases in resistance of those steers to cattle ticks and gastro-intestinal nematodes (worms) to which the steers were exposed while they were growing. Half of a group of interbred Hereford × Shorthorn (HS) and interbred Brahman × HS (BX) steers was implanted with Compudose 200 on two occasions 200 days apart. Half of each of the implanted and nonimplanted groups in each breed was treated every 3 weeks to control cattle ticks and worms. All animals grazed together and were regularly monitored for parasite burdens and LW changes. Both breeds responded positively to Compudose 200, to which BX responded most, and to treatment to control parasites. Resistance to either ticks or worms was unaffected by the presence of the implant so that, within each breed, increases in LW gain in response to the implant were similar regardless of parasite control. Thus the increases in LW gain resulting from the use of Compudose 200 arose directly from the action of the implant on metabolism, not indirectly through any effect on resistance to parasites.

Acetyl-CoA hydrolase which is stimulated by adenosine-5′-triphosphate is present in the cytoplasm of ovine liver and, unlike in certain others species, is not inactivated by cold. It is suggested that this enzyme is involved in a substrate cycle between acetate and acetyl-CoA. The heat produced as a result of such cycling may be as much as 2·5% of basal heat production and may be partly responsible for the increased heat increment that often follows the ingestion of diets that provide large quantities of acetate.

A feeding trial was performed during 1986, in Townsville, Australia, to describe alterations in nutrient metabolism, and the coincident gross changes in rumen microbiology, when a sulphurdeficient diet was supplemented with inorganic sulphur. Eight Merino sheep were fed ad libitum a spear grass (Heteropogon contortus) hay of low sulphur content (0·4 g/kg DM), supplemented with all other essential minerals. Upon supplementation, daily sulphur intake was increased to c. 0·75 g and four animals continued to be fed ad libitum (group A) whilst the remaining animals were restricted in feed intake (group B). Sulphur supplementation caused a twofold increase in the feed intake of group A (P < 0·05). In both groups of animals, sulphur supplementation increased the fermentation of cotton thread cellulose (P < 0·05), as well as of ground plant dry matter (P < 0·05), suspended in the rumen in nylon bags for 24 and 48 h. The apparent digestibility of organic matter (AOMD) was also increased by sulphur supplementation; from 30·6 to 39·3% in group A (P < 0·05) and from 35·1 to 41·5% in group B (P > 0·05). The difference in AOMD between groups with sulphur supplementation was not significant, despite group B maintaining a longer retention of fluid digesta in the rumen (20·7 v. 25·3 h) with a significantly lowered rumen volume (4·68 v 3·67 litres, P < 0·05) and outflow of fluid digesta from this site (5·31 v 3·58 litres/day, P < 0·05). Sulphur supplementation increased the molar proportion of acetic acid in rumen fluid (P < 0·05) but lowered propionic and butyric acids in group A (P < 0·05). Only the molar proportion of propionic acid in rumen fluid was significantly lowered in group B (P < 0·05). In both groups of animals, counts of fluid-borne rumen bacteria, protozoa and sporangia of rumen anaerobic fungi (RAF) all increased significantly with sulphur supplementation (P < 0·05 in all instances), but no significant differences were observed between groups in microbial counts, despite the different feeding regimes. The increase in sporangial forms of RAF was most marked; no sporangial forms were detectable until the diet was supplemented with sulphate and measurable concentrations of rumen sulphide were observed. This is the first account of nondetectable concentrations of RAF brought about by the nutritional status of the diet.

Five sheep were fitted with rumen cannulas and fed once daily ad libitumat 09.00 h with a low-quality mixed-grass hay or a good-quality lucerne hay. The effects of a second amount of the same hay or of the second hay distributed at the end of the large meal following the morning distribution, when rumen fill reaches its daily maximum, were investigated for feed intake, alimentary behaviour and rumen fill. The second distribution induced a true meal (200–400 g dry matter intake), except in the case of mixed grass offered after lucerne. On the basis of initial eating rate and the amount ingested, the highest palatability was for lucerne offered after mixed grass, and the lowest for mixed grass offered after lucerne. Diet selection was more pronounced with lucerne than with mixed grass, as indicated by the larger decrease in the neutral detergent fibre content of the fraction ingested. The true meals following the second distribution were associated with an increase in rumen fill up to 10% of the daily maximum observed without the second distribution. However, rumen fill with lucerne remained 1 kg lower than with mixed-grass hay, even after a second meal. It is concluded that the sensory response induced by a distribution of a sufficiently palatable hay is able to override the satiety signals due to rumen fill, and that there is a permanent balance between the stimuli related to the characteristics of the food available and those related to reticulo-ruminal digesta.

Ionophores and inhibitors of bacterial energy metabolism were added to mixed rumen bacteria prepared from sheep receiving grass hay plus concentrate diets, and their influence on the rate of metabolism of alanine (Ala) peptides was determined. Dicyclohexylcarbodiimide (DCCD) had no influence on the rate of breakdown of Ala2, Ala3, Ala4 or Ala5, indicating that the metabolism of these peptides did not require ATP. The protonophores tetrachlorosalicylanilide (TCS) and carbonyl cyanide m-chlorophenyl-hydrazone (CCCP) inhibited peptide breakdown to a minor extent (< 15%), whereas the ionophores monensin and tetronasin had greater, but still small (12–31%), inhibitory effects. Toluene stimulated peptide breakdown, consistent with a permeability barrier having been removed. Thus, at least some peptide metabolism depends on transport into bacteria; transport appears not to be ATP-linked, and may well be coupled to the uptake of mineral cations rather than protons. Rumen fluid from sheep receiving a similar diet with added monensin (33 mg/kg) or tetronasin (10 mg/kg) hydrolysed Ala3 and Ala4 at rates that did not differ significantly from controls. Nevertheless, the peak concentration of free peptides in rumen fluid after feeding was more than doubled in ionophore-fed sheep, and peptides persisted for longer than in control animals.

The effect of 200, 400 and 600 mg dietary copper sulphate/kg was studied in 64 Japanese quail (Coturnix coturnix japonica) in 1987. The results indicated that addition of 200 or 400 mg/kg to conventional diets of quail 7–42 days old significantly increased (P < 0·05) body weight gain and significantly decreased (P < 0·05) feed intake. There were significant (P < 0·05) increases in carcass, breast and leg weights in some cases; the first two characters had the highest values in the quail fed the diet containing 200 mg Cu/kg. The addition of 600 mg Cu/kg to the diet had an adverse effect on liver weight compared with the addition of 200 and 400 mg/kg. Copper concentration in the liver was not influenced by any rate of copper supplementation.