A system for automatically measuring the mean cell-wall thickness in a user-defined area of plant tissue has been developed using image analysis. The digitized grey-level image of a tissue section is first segmented using a histogram-partitioning algorithm. The resulting binary image is then repeatedly thinned until the minimum connected set of pixels, or ‘skeleton’, remains. A nearestneighbour length estimator is used to calculate the total length of the skeleton which approximates to the location of the middle lamella in the original section. The length of the skeleton and the number of nodes it contains are used to estimate the mean cell radius, and mean cell-wall thickness using the area of cell-wall material in the segmented binary image. The method has been used to estimate mean cell-wall thickness along a newly extended Zea mays internode, and the results are compared to measurements obtained manually using a micrometer ‘line’. The techniques of rapidly assessing mean cell-wall thickness and cell dimensions using image analysis are needed to assess how much of the variation in nutritive value between forage cultivars can be ascribed to changes in cell-wall chemistry and how much to anatomical differences.

Seven-day-old leaves of two wheat cultivars, one resistant (Cruz Alta) and one sensitive (Leones) to water stress were subjected to 100% O2 and water stress in the light for 72 h. The aim of this work was to analyse the effects of both types of stress on the chloroplast antioxidant enzymes, glutathione reductase (GR) and ascorbate peroxidase (AP) and their relationship with stress resistance.

Both GR and AP increased following 100% O2 and water stress in the resistant cultivar Cruz Alta only. Sulphydryl (SH) groups increased in the resistant cultivar and decreased significantly in the sensitive one under both stress treatments. Measurement of stress parameters (chlorophylls, proteins, lipid peroxidation and conductivity) revealed that oxidations caused by stress treatments appeared to be higher in the sensitive cultivar Leones than in the resistant Cruz Alta.

It is suggested that there may be a link between GR, AP and oxidative protection. Some cross resistance between water and oxidative stresses in wheat leaves is also indicated.

Field studies were conducted in order to determine the components of yield and response of maizeto soil applied copper and sulphur in the rainforest-savannah transition zone and Guinea savannah zone of Nigeria. Five CuO treatments, 0, 1, 3, 6 and 9 kg/ha, were applied to maize in 1988–90, and grain yield was consistently and significantly increased by the 1 kg/ha CuO treatment. Five S treatments, 0, 10, 20, 40 and 80 kg/ha, were applied to maize in 1989–90, and all treatments increased grain yield significantly in 1989, but only the 10 kg/ha S treatment increased grain yield significantly in 1990. Higher amounts of applied S increased leaf S significantly in the Guinea savannah zone.

The morphology of independent plants of perennial ryegrass (Lolium perenne L.) in mixed swards under intensive sheep grazing was studied at Palmerston North, New Zealand in 1988/89. Intact plants of two cultivars, ‘Grasslands Nui’ and ‘Grasslands Ariki’, were sampled from pastures under rotational grazing, set stocking, and a combination of both systems, every 2 months for 16 months, by taking turves (250 × 250 mm) and washing out the plants. Characters measured for each plant were: number of flower heads, leaves and tillers; basal stem and internode stolon length; flower head, leaf blade, leaf sheath and stolon dry weight (DW). Additional pasture data on tiller density and dispersion and herbage DW to ground level were also collected.

Perennial rye grass exhibited a strong clonal growth pattern similar to that of white clover (Trifolium repens L.) but with a better balance between growth at the apex and death of old basal stem. Release of branch stolons to form new plants was regular, which maintained population stability. Formation of internode (I) stolon appeared to be a response of heavily shaded tillers for survival by elevation of the growing point to a more favourable position. The total DW of ryegrass stolon in pastures was greater than that of the companion white clover.

There was little seasonal variation in number of tillers or basal (B) stem length per plant. During the reproductive period (late spring/early summer) plants were heavier and had more leaves and internode stolon than at other times of the year. Grazing management had little effect on plant structure, but plants under rotational grazing had 75% greater DW, less basal stem and reduced probability of internode stolon formation than plants under set stocking. Nui plants had heavier but fewer tillers than Ariki did, resulting in little difference in plant DW. Ariki had fewer single-tiller plants and a higher proportion of multiple-tiller (> 7) plants than Nui had. The structure of the populations was not affected by season, management or cultivar and remained stable throughout the year, with a log-normal distribution of plant size. Because of the uniformity of plant structure, plant density in pastures paralleled tiller density, averaging 1900, 3360 and 2330 plants/m2 for rotationally grazed, set stocked and combined grazing treatments respectively.

In view of the strong influence that grazing management can have on ryegrass performance and persistence in pastures, the lack of response at the level of plant and population structure to grazing management suggests that some other level of organization within the ecology of the pasture is of greater importance.

The growth of the tree legumes Leucaena leucocephala, Gliricidia sepium, Sesbania sesban, Sesbania grandiflora, Albizia falcataria and Calliandra calothyrsus was evaluated at four sites in Indonesia between 1984 and 1986. Tree seedlings were planted at 10000 trees/ha and, after an establishment period of 9–12 months, harvested every 3 months for a 2-year period.

At Bambu Apus, West Java (2040 mm annual rainfall, 1 month dry period, lowland, latosol with pH 5·6 decreasing with depth), G. sepium and C. calothyrsus produced 13 and 10 t/ha per year of leaf dry matter, respectively. Other species did not grow well at this site and fewer than 60% of the trees of these species survived until the end of the experimental period. At Sei Putih, North Sumatra (1550 mm annual rainfall, 3 months dry period, lowland, podzolic with pH 5·5 increasing with depth), no species produced > 6 t/ha per year of leaf dry matter. The highest yielding species were L. leucocephala and A. falcataria. At Cisarua, West Java (3340 mm annual rainfall, no dry periods, 925 m altitude, latosol with pH 5–6 increasing with depth) only C. calothyrsus grew well and produced 9 t/ha per year of leaf dry matter. At Grati, East Java (1500 mm annual rainfall, 6 months dry period, lowland, alluvial with pH 6·6 increasing with depth) L. leucocephala produced > 8 t·ha per year of leaf dry matter, while none of the C. calothyrsus and A. falcataria trees survived the first dry season.

Although L. leucocephala has been the most widely grown tree legume species in the tropics, C. calothyrsus and G. sepium performed better at the wetter sites and at high altitude.

The rumen degradation and gas production characteristics (methane, carbon dioxide) of leaves of 20 accessions of multipurpose trees (MPTs) from six genera: Acacia, Cajanus, Chamaecytisus (L. fil.) Link, Erythrina, Leucaena and Sesbania and some poisonous plants were investigated in vitro and in sacco in rumen fistulated cows fed on a diet of grass hay ad libitum supplemented with cotton seed cake. The degradation constants (i.e. the soluble fraction (a), the slowly degradable fraction (b) and the rate of degradation (c) and the potential degradability (a + b) (PD)) were calculated. The gas production constants were estimated following the equation: Volume = bg(1—e-cgt) where bg is gas production and cg is the rate of gas production. Between and within genus comparisons of degradability and gas production constants were done.

The soluble fraction (a) was significantly higher for Sesbania (59) (P < 0·05) than the other genera, which had values between 45·18 and 40·38 units. There were no significant differences in the slowly degradable fraction (b) between genera. Sesbania was degraded significantly faster (P < 0·05) than either Acacia, Leucaena or Cajanus. Similarly, the potential degradability was significantly higher (P < 0·05) for Sesbania (92·7) than for the other genera. Acacia was the least degradable genus.

Degradation characteristics were similar between species within the genera Acacia, Erythrina and Leucaena. However, within the Leucaena genus, L. revoluta had the highest soluble fraction (50·02) and the cross L. leucocephala × L. diversifolia had the lowest (29·24). L. leucocephala had the highest slowly degradable fraction (57·32) and L. revoluta had the lowest (42·37). L. leucocephala × L. pallida had the highest rate of degradability (0·0626) and L. pallida had the lowest (0·0221). L. leucocephala had the highest potential degradability (92·23) and the cross L. pallida × L. diversifolia the lowest (84–81).

Between the genera, more gas was produced from Sesbania than from any other genus. The effect of genus was significant (P <0·0003). On the other hand, the rate of gas production (cg) was higher with the genus Chamaecytisus than with any other genera (P < 0·0001). Although the two methods used agree in the position of a forage of a high degradability like Sesbania, they fail to agree on the relative positions of the forages of lower degradabilities. For some genera, drying of the tree foliage reduced the volume of gas produced, but increased the rate of gas production.

Previous research has suggested that fry colour of processed potatoes is inversely correlated with tuber reducing sugar content, and agronomic practice should therefore be tailored to minimize amounts of tuber sugars at harvest and during storage as a means of maximizing processing quality. A total of 30 experiments from three sites in England from 1985 to 1988 examined this hypothesis for two cultivars using a wider range of husbandry than that used in practice and long periods of storage. No tuber sugar value was sufficiently well correlated with fry colour for the relationship to be interpreted as causal and of use predictively, irrespective of whether it was measured early in growth, at harvest or at the time of processing. Fry colour at harvest was not correlated with fry colour after storage. No agronomic practice (variables used were physiological age, date of planting, irrigation or date of harvest) consistently caused fry colours to be darker than the acceptable colour limit, whether at harvest or after long term storage. Crops producing unacceptable fry colours early in storage generally improved to produce acceptable fry colours after long term storage. Agronomic practices within the range normally found in commercial production are therefore considered to have little effect on long-term processing quality, although harvesting, handling and transport operations were not investigated.

Almond trees (Amygdalus communis L. cvs Garrigues and Ramillete) were grown in the field under non-irrigated conditions in Murcia, Spain. Seasonal variations in leaf water potential components were studied in 1989. Predawn leaf water potential showed high values in both cultivars, due to the absence of soil water stress. Pressure-volume curve analysis indicated that the leaf osmotic potential at full saturation (Ψo(sat)) for cv. Garrigues remained fairly constant throughout the season. Bulk modulus of elasticity (E) showed, in both cultivars, a tendency to decrease as the season progressed. E values were higher in Ramillete than in Garrigues. The relative water content at the turgor loss point (RWCtlp) seemed to be controlled by E values. The larger relative apoplastic water content (RWCa found in Ramillete might have allowed it to retain more water at low leaf water potentials than Garrigues. These facts would support the suggestion that Ramillete is a more drought-resistant cultivar than Garrigues.

Yields of dry matter, nitrogen, phosphorus and potassium in herbage and cereals from fields representing different stages of the rotation were recorded on two organic farms in 2 years. Amounts of N, P and K purchased and sold were also recorded on these farms.

Some additional data was obtained from three other organic farms. Herbage production was very satisfactory, whether fields were grazed or cut. The proportion of clover in sown swards was, in most cases, satisfactory to high, but the clover content was very low in a few fields. The yields of cereals were about equal to or below the average obtained on farms using fertilizer and other agrochemical inputs. Manure was normally applied to the leys, which were the fertility-building part of the rotation, rather than to the cereal crops. Leaching of K from manure heaps was considerable.

Purchases of N, P and K (mainly in manure) seemed excessive on one of the farms. On one of the farms studied in less detail, less P and K were purchased than were sold. More attention could be given to the balance between purchases and sales of N, P and K and to the efficient conversion of N into saleable produce.

On two organic farms, nitrate-N and ammonium-N in the surface layers of the soil of representative fields were recorded for 2 years. Nitrate-N was also determined in different soil layers down to 120 cm at the beginning, middle and end of two winters and at intervals after ploughing three fields, to seek evidence of leaching.

Nitrate-N and ammonium-N were both consistently low in the surface layers of fields in ley. Nitrate-N accumulated in arable soils on some occasions when there was little or no crop uptake of N, after ploughing, and after very heavy applications of manure.

There was some evidence of nitrate leaching in all five fields which were deep-sampled. In four cases, the loss by leaching appeared to be < 25 kg N/ha per winter. In the other case, in which a 4-year ley was ploughed on 5 October, the loss by leaching appeared to be c. 70 kg N/ha. Ploughing in winter, rather than early autumn, might have reduced the nitrate leached, but the drilling of the next crop might have been delayed.

The nitrate concentration of water draining from recently ploughed sandy soil in Shropshire was high, but it would have been diluted by water draining from unploughed fields.

Measurements of foetal head diameter (HD) and trunk diameter (TD) were made using ultrasonic scanning of 11 pregnant llamas (Lama glama). Each llama was scanned fortnightly to obtain measurements of HD and TD from c. 84–271 and 65–168 days since mating respectively. There were approximate linear relationships between TD and days after mating and between HD and the logarithm of days after mating.

Calibration equations for predicting the number of days after mating (d) from foetal measurements constructed using (i) the inverse method in which d is regressed on HD or TD and (ii) the classical method in which HD or TD are regressed on d. These calibration methods were assessed by crossvalidation, treating each animal in turn as the individual for which predictions were required. Analysis of the prediction errors showed bias in the classical method, which consistently underestimated d at low values. A components of variance analysis indicated substantial variation between individuals which must be taken into account in calculating standard errors of prediction (S.E.P.) and confidence intervals. S.E.P. of d from TD can be reduced from 12·5 to 10·4 days by increasing the number of observations on an individual from one to four at fortnightly intervals. For prediction from HD, the equivalent figures are size dependent: examples are from 8·3 to 5·6 days, and from 26 to 18 days, for HDs of 2 and 6 cm respectively. The effect of small positive correlations between residuals of successive fortnightly measurements on the same llamas had a negligible effect on S.E.P.S, increasing them by c. 0·2 days. Ultrasonic scanning is suitable for determination of stage of pregnancy of llamas providing S.E.P.S which are small in relation to their long gestation period (335–360 days).

Sixty-four multiparous Friesian cows were given one of eight diets from weeks 4–20 of lactation at the former National Institute for Research in Dairying, Shinfield, Reading in 1983–84. The diets consisted of 13·5 kg/day of experimental concentrates plus hay at 4·5 kg/day (fixed) or ad libitum. Concentrates were high-starch (S) based on cereal grains and cassava, high-fibre (F) based on highquality by-products, and two intermediate types containing 2:1 (SF) and 1:2 (FS) starch:fibre, all with a crude protein concentration of c. 180 g/kg DM. The diets were designed to provide similar intakes of digestible energy and crude protein at fixed hay intakes.

With ad libitum feeding, hay intake was lowest on S concentrates. With increasing fibre in the concentrates, the yields of milk, protein and lactose fell but fat concentration and yield were increased. These changes were linear and were unaffected by hay intake. Increasing hay intake to ad libitum had no effect on milk yield but increased the concentrations and yields of fat and protein. It also changed a net liveweight loss on fixed intakes to a gain on ad libitum intakes.

Diet digestibility was measured using sheep at about maintenance and cows at production intakes. Digestibility was higher in the sheep, probably because of the difference in level of intake. In the cows, increasing fibre in the concentrates reduced the digestibility of dry matter, organic matter, energy and nitrogen but increased the digestibility of fibre fractions and ether extract. Level of hay intake had variable effects on mean digestibility and on the relationship with concentrate type.

Increasing the fibre in the concentrates increased the molar proportions of acetate and n-butyrate in the rumen and reduced the proportions of propionate, n-valerate and n-caproate.

It is concluded that, with mixed diets of hay and relatively high proportions of concentrates, changes in the starch:fibre ratio of the concentrates by substitution of high quality by-products for starchy ingredients can induce linear changes in the yields of milk and the principal solids constituents and in milk fat concentration. Since changes in yields of fat and protein went in opposite directions, the optimal concentrate composition depends on the milk composition required by the market. These conclusions may not apply if poorer quality by-products are used.

The study investigated the effects of chronic elevation or suppression of circulating prolactin levels on seasonal wool growth in Romney sheep. Ewes (n = 10/group) were housed indoors under natural lighting (latitude 34 °S) and received either 50 mg bromocriptine i.m./ewe/28 days (Group B), 1 mg spiperone s.c./ewe/day (Group S) or no treatment (Group C) commencing in summer. Wool growth and liveweight were measured every 4 weeks and venous blood samples were collected for prolactin determination. Plasma prolactin levels (mean±s.E.) in Group C exhibited a gradual seasonal decline from 121±29 ng/ml to 35±9 ng/ml. Bromocriptine suppressed prolactin levels rapidly from a pretreatment value of 118±2 ng/ml to below 12±7 ng/ml for the duration of the study. Prolactin levels in Group S were not significantly higher than Group C, with the exception of the first 14 days following the initial treatment. A seasonal reduction in wool growth of c. 25% was observed in all groups; however, no significant treatment effect was evident. Mean liveweight of all animals increased from 50·4±0·8 to 56·8±0·7 kg during the study. These results indicate that perturbation of the annual cyclic secretion of prolactin does not affect wool growth in the Romney ewe.

Silages were prepared from the tropical grasses, pangola grass (Digitaria decumbens) and setaria (Setaria sphacelata), with the addition of molasses (4% w/w) and/or leaves (33%) from the leguminous trees leucaena (Leucaena leucocephala) and gliricidia (Gliricidia sepium). All forages were grown at the University of Queensland farm in south eastern Queensland during 1985. These silages, together with hays made from these grasses and sorghum silage (13 diets) were fed to sheep to assess their nutritive value. All silages were well preserved, as indicated by low pH (3·5–4·4), low ammonia N (26–57 g/kg total N) and high lactic acid (73–95% total acids) contents. The addition of legumes increased both the dry matter (DM) and total N (TN) contents of silages to the same extent as the addition of both legumes and molasses at ensiling. Sheep given silages prepared from pangola grass and legumes (±molasses) consumed similar DM intakes (22·9–25·4 g/kg0·75 per day) as sheep given pangola grass hay (23·9 g/kg0'75 per day). Silage made from pangola grass + molasses was of low palatability (16·1 g/kg0·75 per day). The digestibilities of silage DM (DMD) and its fibrous components were significantly (P<0·05) lower (DMD 53·3–60·6%) than that of pangola hay (DMD 64·7%). Silages and hay made from setaria, and sorghum silage, were of lower nutritive value than those from pangola grass. The addition of leucaena and molasses increased silage DM intakes (21·1 g/kg0·75 per day) above those for setaria hay and setaria + molasses silage (16·7 and 19·0 g/kg0·75 per day respectively). The intakes of silages made from gliricidia (17·1 g/kg0·75 per day) were significantly (P <0·05) improved when molasses was included at ensiling (21·8 g/kg0·75 per day). The digestibilities of silage DM were significantly (P<0·05) higher (DMD 53·6–60·4%) than that of setaria hay (DMD 40·6). Liveweight change in sheep was significantly (P<0·05) correlated with intakes of digestible DM (r2= 0·74) and with N intake (r2= 0·82). The inclusion of legumes in the silages increased N retention and, for setaria silages, also increased rumen ammonia concentration. It was concluded that tropical grasses can be effectively ensiled by the addition of legumes alone and, with the exception of setaria/gliricidia silages, the resultant silages were of sufficiently high quality to merit their use in tropical animal production systems.

Four silage diets were prepared from tropical grass and legume mixtures and fed to intestinally fistulated sheep to determine the sites and extent of digestion of the different silage components in the digestive tract. Pangola grass (Digitaria decumbens) was ensiled either alone or with the addition, 33% (w/w), of leucaena (Leucaena leucocephala cv. Cunningham), gliricidia (Gliricidia sepium) or cowpea (Vigna unguiculata cv. Caloona). All forages were grown at the University of Queensland farm in 1985. All silages were well preserved as indicated by low pH (< 4·1), ammonia N (< 9% total N), acetic acid (< 13 g/kg dry matter (DM)) and ethanol (< 19 g/kg DM) contents, and high DM (> 290 g/kg) and lactic acid (> 41 g/kg DM) contents. The inclusion of leucaena and gliricidia significantly increased the total N content of the silages. The addition of legumes at ensiling significantly increased rumen ammonia N (pangola 59 mg N/l, legume diets 110–115 mg N/l) and the proportion of propionic acid in rumen fluid. Sheep given pangola + leucaena silages had significantly higher DM intakes (66·3 g/kg W0·75 per day) than sheep given pangola and pangola + cowpea silages (52·4 and 53·2 g/kg W0·75 per day respectively). The inclusion of gliricidia significantly depressed silage intake (43·1 g/kg W0·75 per day). There were no significant effects of diet on DM (551–609 g/kg) and organic matter (550–612 g/rkg) digestibility. Sheep given pangola + leucaena silages had higher N intakes, N balances, rates and efficiencies of microbial N synthesis and total non-ammonia N (NAN) flows to the small intestine than did sheep given the other silages. Apparent degradabilities of silage N in the rumen were similar for all diets (0·491–0·559 g N/kg N intake), but sheep given pangola + leucaena silages had lower true (corrected for endogenous N) N degradabilities (0·648 g N/kg N intake) than those given the other diets (0·751–0·775 g N/kg N intake). The values obtained in this experiment were compared with those reported for temperate grass silages, and it was concluded that whilst the digestibility of tropical grass/legume silages was low, intakes and rumen fermentation characteristics were similar to those found for temperate grass silages.