The use of exogenous hormone treatment as a means of increasing the efficiency of animal production has, in general, been rather poorly received by both the public and government agencies. This antipathy towards hormone treatment has tended to direct research effort into finding less contentious ‘hormonefree’ methods of improving animal production. Over the last 10 years, immunological manipulation of the endocrine system has emerged as an attractive possibility in this search. In this review we briefly outline three approaches under current consideration, whereby growth hormone (GH) concentrations or activity are modified. These methods involve immunological manipulation of GH release, use of antibodies as GH mimics and antibody-mediated enhancement of GH action.

Dry matter production, transpiration and transpiration efficiency (DM production: transpiration) were studied during vegetative growth of oats over 4 years (1976–77 and 1982–83) in field experiments on loess-derived soils near Gottingen, Germany, under different weather conditions. Shoot and root dry matter and leaf area were measured or estimated regularly during the season. The rate of evapotranspiration including intercepted rain water by leaves (ET) was determined during five consecutive growth stages from the water balance in the 2 m soil profile. The rate of soil evaporation (E) and the rate at which rain water was intercepted by leaves (I) were estimated separately in order to attain T, the transpiration rate (T = ET–E–I), or IT, the rate of interception of rain water by leaves plus transpiration (IT = ET–E). The potential evapotranspiration rate (ETp) was derived from meteorological parameters.

During the early stages of oat development (seedling growth and tillering), T and IT, related to ETp, were higher than expected from crop growth rate (CGR), calculated for shoot and total dry matter including roots, respectively. It was concluded that, at a leaf area index (LAI) of < 3·4, part of the solar radiation was converted to sensible heat between plant rows, increasing ETp near the ground and hence T, but not CGR. Because of this, LAI influenced IT efficiency and the crop-specific constant m of de Wit's formula. IT efficiency was not only dependent on LAI but also on ETp. Grain yield was related to both cumulative IT (ITC), normalized by ET, and leaf area duration during the period from anthesis to harvest. Increased leaf area duration after anthesis may partly explain the higher yields obtained with modern high-yielding varieties of small-grained cereals.

Applications of nitrogen and a plant growth regulator (mepiquat chloride and ethephon) were used to manipulate stem structure and induce differing degrees of damage due to leaning and lodging in six cultivars of winter barley grown in Belfast, UK, in 1986/87. Weighted incidences of leaning and lodging were combined to give an index indicating damage susceptibility of the cultivars. The index was very high (70) in Pipkin and ranged between 1 and 18 in the other cultivars. Differences between cultivars in number of internodes, plant height and stem weight did not explain their differences in resistance to damage. However, dry weight per unit length ranged from 2·35 and 2·34 mg/mm in the strongest cultivars, Panda and Jennifer, respectively, to 1·75 mg/mm in the weakest cultivar, Pipkin.

Nitrogen application increased plant height but did not affect dry weight/main stem, so that dry weight/unit length of stem decreased. The growth regulator treatments reduced plant height and although dry weight/stem did not decrease significantly, dry weight/unit length of stem was similar in treated and untreated plots.

Dry weight/unit length has potential as an objective indicator of straw strength in winter barley cultivars and could be used in cultivar evaluation in the absence of damage in field trials.

Agronomic research was carried out on upland rice in Toledo District, Belize, in 1979–86, with the objective of improving returns from the traditional system of shifting cultivation and of examining the potential for reducing the demand for new land by cropping for more than one season. The rice was grown in the wet season on land cleared from forest by slash and burn, using a traditional planting technique, placing seed in holes made with a pointed stick.

In a series of fertilizer experiments, in which rice was grown for up to 7 consecutive years, urea and triple superphosphate both increased grain yield, whereas muriate of potash had no effect. Mean yield in the fifth year was 85 % of that in the first. Urea and triple superphosphate both increased the number of full grains/panicle.

A slash and mulch weed control treatment before sowing resulted in low yields of grain in the third year; yield after the use of propanil and 2,4-D (after sowing) was, on average, 77% of the yield after hand weeding; omitting weed control after sowing led to very low yields, particularly in the second and third years.

In the varieties Bluebonnet and C22, grain yield was increased by reducing the distance between stations, particularly where 6, rather than 15, seeds were sown per station. Reducing the distance between stations increased the leaf area index during crop development and the number of panicles/m2, which more than counterbalanced reductions in the number and area of leaf blades per plant, the number of panicles per plant and the number of full grains per panicle. However, the yield/kg of seed sown and per hour spent planting was greatest at the widest spacing. C22 produced more panicles per plant and a greater weight of grain per plant and per hectare than Bluebonnet.

It was concluded that returns from the traditional system can be improved and the demand for new land reduced.

The average yields of a 3-year field experiment (1985/86–1987/88) on a mollisol at Pantnagar showed that, at 87 kg N/ha, applying urea supergranules (USG) gave 0·47 t/ha more rice grain than split application of prilled urea (PU). The data also showed that, at this rate of N, one-third (29 kg N/ha) of inorganic N can be substituted by fresh straw (wheat or rice) applied at planting to give similar rice yields. However, at a total of 58 kg N/ha, 29 kg N/ha applied as straw with 29 kg N/ha of PU or USG reduced yield compared with 58 kg N/ha of PU or USG alone, except in 1986/87. Yield differences were attributed to differences in number of panicles/m2, N uptake by the crop and mean wet soil NH4+-N obtained at various stages of crop growth during 1986/87 and 1987/88. Wheat grown after rice in 1985/86 and 1986/87 showed significant residual effects in plots with straw application and these were correlated with the rate of hydrolysable organic N (HN) obtained after rice.

The nodal structure of white clover plants was studied in New Zealand in pastures stocked at 22·5 ewes plus lambs/ha and either continuously or rotationally grazed. Intact plants were sampled every month for a year (1988/89) by removing turves and washing out the plants. Plants were classified according to the degree of branching as first (unbranched, single-stolon plants), second, third or fourth order (plants with at least one quaternary branch). Where possible from each turf, four plants of each of the four branching orders were sampled and, for each stolon of each plant, nodes were ascribed positions numbered from the stolon apex, and the position of nodes with a live branch and the total number of nodes/stolon were recorded.

The mean number (and 5 and 95% quantiles) of nodes/plant was 15·7±0·26 (9, 24) for the firstorder, 42·2±0·90 (18, 81) for the second-, 91–4±2–13 (37, 163) for the third- and 163·7±7·49 (63, 367) for the fourth-order plants. Grazing management and month of sampling had minor effects on these values. The mean number of nodes/stolon within branched plants depended on the category of the stolon within a plant, the presence or absence of an apex and on the branching order of the plant. The first 10,.15, 20 and 25 node positions accounted for, respectively, 64, 79, 90 and 95% of total nodes in the field population and 39, 62, 79 and 90% of all branches. Successful branch initiation occurred at recently formed nodes at positions 3–10, emphasizing the significant contribution of such nodes in growth and persistence of white clover in grazed swards.

Where grazing management allows little consumption of stolon and there is adequate moisture, growth and fragmentation maintain the mean node composition of the branching orders reasonably constant throughout the year. Thus, any seasonal variation in the overall mean number of nodes/plant in a population must be driven by seasonal changes in the distribution of plants among the branching orders. However, there was evidence of mean number of nodes/plant decreasing in the third and fourth orders after dry conditions.

The assimilation and distribution of carbon in laterally spreading white clover plants was quantified in a controlled environment using CO2 exchange rate measurements and 14C as a tracer. Plants were restricted to three mature leaves on the main stolon apex, and the movement of 14C from these leaves (and one immature, but carbon-exporting, leaf) to meristematic zones throughout the plant was determined by detailed plant dissection.

Sinks throughout the plant drew small to moderate proportions (typically 1–8%) of the 14C exported by all mature leaves. The three mature leaves displayed similar export patterns, and no specific source-sink relationships involving any of these leaves were observed. However, 14C exported by the developing leaf moved predominantly to the main stolon apex, and to adjacent young stolon tissue. Estimated respiratory losses over 24 h accounted for 40–49% of the 14C fixed. Of the total amount of C exported by all four leaves and utilized in new growth or reserve storage, 22% moved to the main stolon apex, 16% to stolon tissue of the main stolon, 34% to adventitious roots on the main stolon (most of which was utilized in older, nodulated roots) and 29% to branches. The apex received the greatest amount of C/unit weight, reflecting its high sink activity, its proximity to the source leaves and, possibly, apical dominance. Subtending leaves provided 46–51% of the C utilized by young branches. Older branches continued to import significant quantities of C from parent stolon leaves despite having their own C sources, though parental support for branches was seen to decrease as branches aged, when the quantity of C they imported was expressed as a function of their weight.

Relative sink strength and distance between sources and sinks contributed to the observed patterns of C distribution. No apparent restriction on C movement was imposed by the vascular architecture of stolons.

Acid and neutral invertase activities in the stem of an early (CoJ 64) and a late cultivar (Col 148) of sugarcane were estimated by incubating stem slices in buffered sucrose solution and measuring the production of reducing sugars. High enzyme activity occurred in young tissue but the activity of both enzymes was considerably lower in the mature internodes. Acid and neutral invertase activity was highest in the midinternode position, corresponding to the region of cell expansion.

A trial of open-pollinated (OP) cultivars and hybrids of different origins was conducted in 1986–1988 at two sites in the central clay plains of Sudan, rainfed at one site and under supplementary irrigation at the other. Throughout this study, the patterns of growth of the OP cultivars differed greatly from those of the hybrids, despite differences amongst cultivars within each group. Differences in seed yield between OP cultivars and hybrids under irrigation were not significant; but, under rainfed conditions, the hybrids gave higher yields than the OP cultivars. Partitioning efficiency (PE; reproductive mass: total biomass) increased more rapidly during flowering and seed filling in the hybrids than in the OP cultivars; differences in PE between the two groups were significant. The higher leaf area index, leaf area duration and crop growth rate of the OP cultivars were compensated to some extent by the higher PE and leaf efficiency values of the hybrids, resulting in similar seed yields of all cultivars under irrigation. Overall, irrigation increased seed yield by 0·6–1·9 t/ha and increased oil content by 8–15%.

T-trellis apple trees treated with combinations of fungicides and insecticides applied with a boom sprayer had a lower percentage of fruit damage from diseases and insects than those treated with an airblast sprayer. With the boom sprayer, chemical deposit was uniform in distribution between outer and inner parts of the tree canopy, but with the airblast sprayer there was more than a threefold difference in deposit between parts of the canopy. The boom sprayer was inferior to the airblast sprayer in the control of apple aphids (Aphis pomi) when vertical top growth (watersprouts) had grown to 0·7–1 m. Management of aphids with a boom sprayer would probably require the control or periodic removal of watersprout growth, or the use of systemic insecticides.

Field emergence of 11 seed lots from six cultivars of long bean, all having laboratory germination of > 80%, ranged from 0 to 83%, indicating differences in seed vigour. Vigour differences occurred within and between cultivars, seed lots from cultivars with white or partly white testas having particularly poor emergence (0–21%) compared with those with brown or black testas (41–83% field emergence). The significant ranked correlations between field emergence and (i) solute leakage, measured by the electrical conductivity of seed soak water (r = –0·864), (ii) the percentage of cotyledons made up of completely living tissue, revealed by vital staining (r = 0·895), and (iii) the proportion of hard seeds (r = 0·916) indicated that lots with low vigour and potentially poor field emergence could be identified before sowing. Seed lots having low vigour imbibed water rapidly; the improved vital staining when seeds imbibed slowly indicated that damage occurred during imbibition and was a cause of low seed vigour. Rapid water uptake by low-vigour seed lots was partly explained by the incidence of seeds with cracked testas, but other factors could not be eliminated. The significance of differences in water uptake between cultivars differing in testa colour is discussed in relation to breeding for improved emergence.

A trial was set up in South Wales in 1980 on land replaced in 1972 after opencast coal mining, to assess the effects on soil rehabilitation of regular subsoiling, through an established sward, with and without incorporation of a ‘semi-organic’ fertilizer into subsoiling slots. Treatments were assessed on the basis of yield, soil structure indices, root and organic contents and earthworm population densities. Apart from yields, data are for the eighth year of the experiment (1987), 18 months after the fourth programme of treatments.

Treatments did not markedly affect productivity, although it tended to be higher with subsoiling and fertilizer incorporation. Subsoiling had little effect on root and organic content, but fertilizer incorporation increased the latter, particularly at depth. Earthworm population densities were markedly higher on subsoiled areas, the increase in the deeper burrowing species Aporrectodea caliginosa being largest. Fertilizer incorporation increased abundance of Lumbricus rubellus, but had little effect on other species. Subsoiling reduced surface wetness, but did not result in any significant improvement in structure. Fertilizer incorporation reduced clay dispersion at depth and, with subsoiling, also increased pore space.

Treatment responses in term of soil structure were not large, but the incorporation of fertilizer did markedly accelerate structure rehabilitation at depth. Subsoiling alone contributed to land rehabilitation by controlling surface wetness and encouraging an increase in earthworm populations.

Plant:soil ratios (CRs) of 85Sr concentration were studied in wheat, lucerne, lettuce, radish, string bean (Phaseolus vulgaris), and cucumber grown in pots in eight Greek soil types in a glasshouse pot experiment in 1989.

The CRs of the crops and of the plant parts studied differed according to soil type. They ranged from 0·034–1·39 for wheat grains to 7·6–36·5 for cucumber stems and leaves. The CRs of the edible parts were much lower than those of the other plant material.

The correlation between CRs and clay content was negative and, in most cases, significant (P = 0·05–0·01) or highly significant (P < 0·01). The negative correlation improved (higher absolute value of r, lower variability) if clay plus silt content or cation exchange capacity was used instead of clay content.

The correlation between CRs and soil properties was greatest for soil pH (r = –0·89) and decreased in the order: pH > total clay plus silt ≃ cation exchange capacity > total clay.

In laboratory studies, the amount of N mineralized under waterlogged conditions during 14 days at 30°C was significantly correlated (P < 0·001) with the activities of amidase, glutaminase and asparaginase in soil when these enzymes were assayed by either a nonbuffer or a buffer method using appropriate substrates. N mineralization under waterlogged conditions was also significantly positively correlated with N mineralization under aerobic conditions, especially at 25 and 35 °C (P < 0·001). Generally, the results indicate that the use of amidase, glutaminase and asparaginase activities in predicting plant-available N in soils deserves more attention.

Feeding studies were conducted in 1986 with penned sheep and cattle fed legume (C3) and grass (C4) hays mixed in different proportions. Large fluctuations in diet δ13C within or between days were associated with much smaller fluctuations in the δ13C of faeces. When the overall daily legume percentage in the diet was held constant, there was little variation in the δ13C of faeces irrespective of when during the day the legume, relative to the grass, was eaten.

Cattle set stocked on Stylosanthes/grass pastures in Queensland showed only minor variations in faecal δ13C within or between days in the short term. All animals within a group showed similar trends when the diet was changing. The changes in the δ13C of faeces from day to day reflected small but real changes in diet selection.

It was concluded that the δ13C of a single faecal sample reliably reflects the integrated diet over the previous 3–4 days of a free-grazing ruminant so that the frequency and pattern of faecal sampling for estimating diet composition may be determined by considerations other than reliability

Four experiments involving the two-stage in vitro digestibility technique of Tilley & Terry (1963) were undertaken to investigate whether cow rumen liquor could be replaced with effluent or extract from feed residue containing micro-organisms derived from the long-term rumen simulation technique (Rusitec) of Czerkawski & Breckenridge (1977).

In Expts 1 and 2, the dry matter digestibility (DMD) of hay was determined using either cow rumen liquor or Rusitec liquid effluent or extract from feed after 48 h of digestion in a Rusitec apparatus using various volumes of liquor and artificial saliva. Digestibilities determined with rumen liquor were c. 70% (c.v. 1·2%) while those determined with Rusitec effluent or extract were c. 62% (c.v. 1·8%). In treatments common to Expts 1 and 2, Rusitec effluent digestibilities were more repeatable than extract or rumen liquor digestibilities.

In Expts 3 and 4, Rusitec effluent was compared with cow rumen liquor for determining DMD of seven forages with DMD ranging from 33 to 70%. For a given feed there was good agreement between experiments in DMD values determined with Rusitec effluent, and for ten paired values there was a high correlation (r2 = 0·976) between DMD determined by the two methods. DMD determined using rumen liquor (y) was accurately predicted by Rusitec liquid effluent digestibility (x) from the equation y = 2·663 + 1·06477.x; R.S.D. 2·433.

The results show that Rusitec liquid effluent can be used instead of rumen liquor as a source of micro-organisms for the two-stage in vitro digestibility method. Routine use of Rusitec would obviate the need for using fistulated animals.

In an experiment conducted in the sheds of the Animal Nutrition Division of the Indian Veterinary Research Institute in 1988/89, eight adult Black Bengal goats were divided into two groups of four animals each. Animals in the control group were offered a conventional diet (concentrate and available roughage as per National Research Council standards) and those in the experimental group were fed exclusively on fresh leucaena foliage (young and newly developed leaves and shoots) for 300 days. Dry matter intake (DMI) and body weight of animals in the experimental group decreased in the first 6 weeks; daily DMI/lOOkg body weight was 306 ± 0·34kg in the control group and 2·40 ± 0·18 kg in the experimental group.

There were significant differences in the apparent digestibilities of crude protein and nitrogen-free extractives; contents of digestible crude protein (DCP) and total digestible nutrients were 5·2 and 20·3%, respectively, in the controls and 65·6 and 59·1 %, respectively, in the experimental group. DCP intake was significantly higher in the experimental group as a result of high protein content in foliage but it was not well utilized.

In the control and experimental groups, respectively, daily mean retention of nitrogen was 2·01±0·14 and 1·54±0·12 g/day, of calcium 1·60±0·08 and 2·92±1·69 g/day, and of phosphorus 1·12±0·25 and 0·24±0·07 g/day, the phosphorus balance being significantly lower in the experimental group. Blood calcium and serum glutamate oxaloacetate transaminase/serum glutamate pyruvate transaminase concentrations were statistically similar in both groups but the concentration of inorganic P was significantly lower in the blood of animals fed leucaena.

Two experiments were carried out to determine endogenous losses and the response of urinary purine derivatives to increased duodenal inputs of purine bases. Four ewes each fitted with a re-entrant cannula at the proximal duodenum, and conventionally fed, were subjected to full replacement of duodenal digesta followed by the administration of a solution either free of purines (Expt 1) or enriched with increasing amounts of purines, to supply 0·48–21·27 mmol/animal per day (Expt 2). Basal daily urinary excretions of allantoin, uric acid, hypoxanthine and xanthine were 11·5 ± 0·94, 9·9 ± 0·67, 6·9 ± 0·46 and 1·2 ±0·16 mg/kg W0·75. Allantoin was the only purine derivative which increased in response to incremental inputs of duodenal purines. The relationship between allantoin excretion and infused purines showed a urinary recovery of 0·8 for purines infused at > 220 μmol/kg W0·76. Lower rates of infusion did not alter allantoin excretion. The results show urinary allantoin to be a useful index to estimate duodenal input of purines when animals are fed close to or above their energy maintenance requirements.

Two experiments at Belclare, Co. Galway, in late autumn 1988, evaluated the use of herbage and dosed n-alkanes for estimating herbage intake by sheep. The first experiment examined faecal recoveries of dosed and herbage n-alkanes. The second experiment assessed the accuracy and precision of herbage intake estimates obtained using the n-alkane technique, and tested the effect of supplying n-alkanes to animals either in gelatine. capsules (containing different ratios of n-alkane: cellulose fibre) or in pellets prepared from shredded paper onto which the n-alkanes had been adsorbed. Individually penned wether lambs were offered freshly cut herbage ad libitum (+ 10%) and actual dry matter intake was recorded daily. Intake was estimated using the C31:C32 and C33:C32 (natural:dosed) n-alkane ratios.

There was no significant effect of n-alkane chain length on faecal recovery rate for either the dosed n-alkanes (C32 and C36), the herbage odd-chained n-alkanes (C29, C31, C33 and C36) or those used for the estimation of herbage intake (C31, C32 and C33). The accuracy and precision of the n-alkane technique for estimating herbage intake were unaffected by whether the dosed n-alkane was supplied in capsules or pellets or by the n-alkane:cellulose fibre ratio in the capsules. The bias in the estimated intake was – 8% (± 1·1%) and + 3% (± 1·2%) for estimates based on C31:C32 and C33:C32 ratios, respectively. The estimates based on C31:C32 and C33:C32 exhibited similar precision in the estimation of herbage intake, with a R.S.D. of 6% in actual intake when adjusted for variation in estimated intake and a correlation of +0·92 between actual and estimated herbage intake. The C.V. for actual herbage intake was 17%. The repeatability of actual dry matter intake over three consecutive 6-day periods was 0·54 while those of estimated intake were 0·57 and 0·60 for estimates based on C31:C32 and C33:C32, respectively. The results show that the n-alkane technique can provide an accurate and precise estimate of herbage intake.