In Bedouin goats maintained outdoors during the summer, fed lucerne hay and watered once daily, drinking was followed by a 35% increase in rumen fluid volume, with a concomitant drop in osmolality from 300 to 150 m-osmol/kg. When water was provided to these goats only once every 4 days, a three-fold increase in the rumen fluid volume was recorded and osmolality dropped from 360 to 80 m-osmol/kg.

Feeding, which was depressed during the hot hours of the day, resumed in the afternoon and was followed by an expansion of rumen fluid volume. This expansion occurred irrespective of drinking and was sustained throughout the night. On the 1st day of water denial it amounted to 40% of the noontime rumen fluid volume and was less pronounced during the rest of the water deprivation period. An evening increase in the concentrations of volatile fatty acids, along with a compatible increase in the osmolality and a drop in the pH, also followed the afternoon resumption of feeding.

In goats maintained on wheat straw, drinking as well as feeding time affected the physico-chemical conditions in the rumen to a lesser degree than in goats maintained on lucerne hay.

Since the early studies of Jones & Tisdale (1921), temperature has been recognized as influencing symbiosis and as affecting both nodule formation and nitrogen fixation (Roughley & Dart, 1969).

Phosphate adsorption on Narrabri medium clay loam soil followed a four-region Langmuir isotherm equation, i.e. the plot showed four distinct linear portions. These four regions corresponded closely to saturation with respect to hydroxyapatite, β-tricalcium phosphate, octacalcium phosphate and dicalcium phosphate dihydrate, shown by a calcium phosphate solubility diagram. The differential isosteric heat of adsorption, AH, of P adsorption on soil between 4 and 22 °C, plotted against phosphate sorbed, revealed discontinuities corresponding to the breaks in slope found on the Langmuir plot.

In recent years, processors in Tasmania have introduced Russet Burbank as the most desirable potato cultivar for processing into French fries. Malformed tubers, collectively known as second growth, have been observed in some commercial Russet Burbank crops with the main defect being knobby tubers. Second growth of potato tubers has been shown to occur when the plant suffers a period of stress during the growth of the tubers such as drought, high and low temperatures, restricted soil aeration, interference with water and carbohydrate translocation and fertility imbalance (Sparks, 1958; Bodlaender, Lugt & Marinus, 1964; Iritani, 1981; Holder & Cary, 1984) or a combination of both drought and high temperature stress (Ohms, 1968). If stress from these factors is relieved, the renewed growth of the tuber is often confined to the eyes, producing knobby tubers (Moorby, 1978). Moderate water stress during early tuber bulking can lead to pear-shaped tubers (pointed at the basal end) whilst water stress during the latter part of the season can lead to tubers pointed at the apical end (Iritani, 1981). Knobby tubers are undesirable because knobs are easily broken off leading to yield loss and the exposure of tissue to infection. Severely pointed tubers cannot be processed efficiently into French fries.

J. agric. Sci., Camb. (1988), 110, 261–270

The authors regret that there is an error in Fig. 1 of this paper. The values on the x-axis should be reversed to read from left to right: 200, 150, 100 g ADF/kg diet D. M.

Depth accumulation of exchangeable Na+ was measured in Ca-saturated sandy loam soil columns (length 50 cm; diameter 5 cm) after percolating 500, 1000, 1500 and 2000 ml of 013 M Na+, as NaCl, NaHCO3, Na2SO4 and Na2CO3 solutions. The values of exchangeable sodium percentage (ESP) increased gradually with the increase in the volumes of the solution percolated. Two conceptual layer models, based on whether solutions were added to the topmost soil layer in one lot (M-I) or in splits equal to the saturation deficit (M-II), were used to predict the depth distribution of ESP of soil. The chemical processes considered in the models were the formation of ion pairs and the exchange equilibria of Na+ and Ca2+. The predicted values of ESP were considerably higher for model M-II than model M-I. The consideration of ion-pair formation and the accompanying anion had only negligible effect on the predicted ESP. The model M-II over-predicted the experimental ESP throughout the soil columns, whereas the model M-I under-predicted it for the upper layer(s) and over-predicted for the lower layers. On the basis of average ESP of the whole columns, the less realistic model M-I predicted experimental results better than model M-II. This was attributed to the presence of mobile and immobile zones for the flowing solutions.

O'Kelly (1985) has presented evidence which suggests that at the same feed intake Brahman cross cattle synthesize more microbial lipid than British cattle with a resultant increased efficiency of utilization of metabolizable energy for maintenance. The lipid content of bacteria associated with both liquid and solid fractions of rumen contents is also higher in Brahman than in Hereford cattle (J. C. O'Kelly & W. G. Spiers, unpublished). The reasons for these breed differences are unknown. A step in investigating the problem could be to determine whether microbial lipid content in Hereford cattle can be increased by altering rumen fermentation patterns in association with changes in the microbial population. Ionophores alter rumen fermentation by increasing the production of propionic acid relative to other volatile fatty acids and also inhibit Gram-positive bacteria by facilitating the formation and transport across cell membranes of lipid-soluble complexes with various cations (Bergen & Bates, 1984). However, there are no reports on the effects of ionophores on microbial lipid metabolism in cattle on restricted feed intakes typical of those in tropical areas.

J. agric. Sci., Camb. (1988), 111, 171–177

The Editors regret the omission from the paper of the explanation for Plate 1, facing p. 172, as follows:

EXPLANATION OF PLATE

Example of visual lesions used to evaluate winter injury: (a) viable buds (arrow) are white, turgid, and may be pink tipped; (b) injured buds (arrows) are dry, discoloured, limp, or Shrivelled and dry; (c) bark is more easily peeled from injured roots; (d) injured roots are soft and easily squeezed; also note white fungal mycelium; (e) non-injured (left) root interiors are white, whereas injured (right) root interiors may be discoloured; note that discoloration from disease (left arrow) must be separated from that caused by winter injury (right arrow). The extent of leaf development at the time of sampling is demonstrated in (e).

The effect on live-weight gain from dosing cattle with rumen bacteria capable of degrading 3-hydroxy-4(l H)-pyridone (DHP) was measured on cattle grazing leucaena and native grass pastures in south-east Queensland. Dosing increased the growth rate of cattle grazing only leucaena pasture: from 0·52 kg/head per day when not dosed, to 1·03 kg/head per day when dosed, in the period 6·19 weeks after treatment. Dosing did not affect the growth rate of cattle either grazing leucaena with native pasture, or grazing only native pasture. The introduced bacteria spread naturally to untreated cattle after 19 weeks post-dosing.

The response to dosing occurred when untreated cattle grazing only leucaena pasture had high urinary concentrations of DHP (maximum 0·28%) and low concentrations of serum thyroxine (< 30 nmol/1). The results show that DHP-induced depressions in growth rate may occur in this environment when cattle graze mainly on leucaena-based pasture. Dosing with DHP-degrading bacteria will overcome this problem.

Birth weight and pre-weaning performance are recognized as important components in determing economic returns from beef cattle. The accuracy of ranking animals based on their breeding values, and hence the effectiveness of selection, will be increased when allowance is made for non-genetic sources of variation. Furthermore, the proper evaluation of identifiable sources of variation in calf weaning weight aids in more accurate appraisal of genetic differences in mothering ability among beef cows.

Following a winter with low temperatures during a period with no snow cover, lucerne (alfalfa; Medicago sativa L.) plants were dug from the field and various root and crown lesions were identified and rated according to severity. The plants were then put into pots of soil and grown for 6 weeks to determine if they would live or die. The relationship between lesions present at the time of digging and survival was then studied to see if the lesions could be used to predict survival. Injuries to several characteristics were found to be associated with plant death: bud vigour, leaf vigour, resistance of root bark to peeling, resistance of root to squeezing, root interior colour and, depending on site, the presence of fungi on the root surface. A model combining injury ratings for three characteristics (bud vigour, root colour, and root resistance to peeling) was developed and survival probabilities based on this model are presented. Use of this model will allow for an early evaluation of low-temperature injury without having to wait for aerial growth to occur.

Between weeks 3 and 16 of lactation 191 British Friesians received a basal ration ad libitum of either grass silage (GS), grass and maize silage (GS/MS) blended in a ratio of 1:2 or grass silage and 4% NaOH-treated barley straw (GS/TS) blended in a 4:1 ratio. The grass silage, which was not well preserved, had an estimated metabolizable energy (ME) content of 9–9 MJ/kg D.M., while corresponding values for the GS/MS and GS/TS mixtures were 106 and 9–5 MJ/kg D.M., respectively. A conventional concentrate (CC) based on barley and soyabean meal was fed at three levels (9, 6 and 3 kg fresh weight/day). Although the 9 kg level was only used in conjunction with GS, the two lower levels were fed with all three forage types. Concentrate composition was also varied at the 6 and 3 kg levels by replacing, in each case, 2 kg CC with a special concentrate (SC) which, in addition to barley, wheat and soyabean meal contained, on an air-dry basis, 25 % fishmeal and 25 % protected fat in the form of Megalac

In many areas of the world grazing cattle lose weight for part of the year because the dry standing pasture on offer is of poor quality and animals are unable to eat enough to meet their maintenance energy requirements. In countries where growth promoting anabolic agents are used, a perod of liveweight loss may coincide with the functional life of an implanted agent. There is evidence to suggest that diethylstilboestrol, a xenobiotic with oestrogenic activity, may increase maintenance energy requirements (Rumsey, Tyrrell & Moe, 1980). This has the effect of increasing the rate of live-weight loss under restricted submaintenance feeding conditions (Oltjen et al. 1973). One of the most common anabolic agents currently in use is the naturally occurring oestrogen, oestradiol-17β. However, its effects on energy requirements of animals either gaining or losing weight are unknown.