Concentrations of larval blood protein and blood lipid and density of blood in relation to the silk yield of Bombyx mori L. were estimated under the action of sublethal treatments (to give 0·0% kill of larvae) with the insect growth regulator Altozar, ZR-512.

Results indicated that there was an inverse correlation between Altozar dosage and both weights of larvae and of the resulting cocoons, larval blood-protein and blood-lipid concentrations and density of blood. The decline in these attributes compared with the controls may indicate that a considerable proportion of the inhibitory effect of the growth regulator compound occurred during the development from larva to pupa.

Considering the relationship between larval blood-protein or blood-lipid concentrations and wet weight of the resulting cocoons under the sublethal dosages of Altozar used, the present results confirm our findings concerning the strong relationship between the larval protein content and silk formation. There was a positive increase in the mean wet weight of the resulting cocoons as the protein and lipid concentrations increased.

These experiments suggest that the sole source for the synthesis of silk protein is the protein present in the haemlymph of silkworms and dependent on the larval diet.

In field trials conducted over 8 years the effect of sowing depth on plant establishment, tillering capacity, plant height, grain yield, top growth weight and patterns of root development of wheat and barley was studied. Establishment, number of grainbearing tillers per established plant, plant height at maturity and grain yield and top growth weight per plot as well as per plant were reduced with increase in sowing depth from 2 to 20 cm. Seedling emergence started earlier from large seeds and from shallow sowing. Establishment from large seeds of two varieties was better, especially for deep sowing and in clay soils. Several patterns of root and tiller development were observed at various sowing depths. Varietal differences in stand establishment under field conditions were not related to plant height. It was concluded that deep sowing beyond around 10 cm should be avoided because stand and plant vigour are adversely affected.

Six early maturing inbreds from maturity group I of Indian cauliflowers were selected and diallol crosses were made to study the combining ability of inbreds and identify the desirable parent(s) for hybridization. Seven characters, i.e. curd weight, curd size index, maturity, plant height, number of leaves, leaf size index and plant spread were studied both in F1 and F2 generations. Though the estimates of both general and specific combining ability variances were highly significant for all the characters, the magnitudes of general combining ability variances were higher than that of specific combining ability variances. The performance of the inbreds was in general associated with their general combining ability effects. The inbred 103 was found to be best combiner for all the characters and the cross 105 x 108 showed maximum yield potential.

A digestibility and metabolism experiment was carried out to study the effect of two levels of feeding Rhodes grass-concentrate mixed diets when the grass had been preserved as hay or as frozen grass. Twenty Awassi lambs were used.

The method of preserving the Rhodes grass did not affect the digestibility of dry matter, crude protein or nitrogen-free extract. However, the digestibility of energy and crude fibre was lower with the hay treatments.

A consistent trend towards higher digestibility of the diets' constituents was observed with the high level of feeding.

Acetic acid concentration in the rumen was lower with the hay than with frozen grass. Feeding the high level resulted in higher concentrations of volatile fatty acids in the rumen.

A highly significant effect of the level of feeding on the C2/C3 ratio was observed; the high level of feeding resulted in a lower C2/C3 ratio

Rumen fermentation characteristics were studied using sheep fitted with rumen cannulae. Diets of 100% hay and 20% hay:80% cooked flaked maize (concentrate diet) were fed at the maintenance level of energy intake as two equal portions per day. Both the gas and liquid phases of the rumen were continuously sampled over 33-h periods.

Concentrations of O2 and N2 in rumen gas inoreased during feeding, whilst concentrations of CO2 and CH4 decreased. Thereafter the concentrations of both CO2 and CH4 rapidly increased. The CO2: CH4 ratio increased rapidly following feeding; it declined to baseline levels 2–4 h after feeding the hay diet, but with the concentrate diet the decline took longer. O2 concentration declined rapidly following feeding and was stable within the range 1–3% for long periods. At no stage was O2 absent from the rumen gas phase. H2 comprised 100–1500 μ1/1 and 100–6000 μ1/1 of the gas phase in sheep fed the hay or concentrate diets respectively and its concentration increased very rapidly with the onset of eating. CO concentration varied between 2 and 16 μ1/1 in the rumen gas of hay-fed animals and was not related to time after feeding. In concentrate-fed animals CO comprised 0—130 μ1/1 of rumen gas and increased very slowly after feeding.

Eh and rH values ranged between —150 and —260 mV and 8·0 and 5·0 units respectively for rumen contents from animals fed the two diets. A diurnal cycle was evident, with the most oxidizing state being attained just before feeding, and the most reducing state just after feeding. The diurnal cycles were better denned by rH than by Eh. The magnitude of the decrease in rH (and pH) during feeding was greater for animals fed the concentrate than the hay diet. At no stage during feeding did Eh or rH change towards more oxidizing conditions. Changes in the concentration of H2 in rumen gas were related to changes in the rH of rumen contents.

VFA molar proportions showed no changes during the 24-h cycle with hay-fed animals but showed erratic variation with concentrate-fed animals. When two sheep fed the concentrate diet were sampled daily for 21 days, it was shown that VFA molar proportions were not constant.

It was concluded that the gas phase of the rumen was never completely O2-free, and that whilst a stable rumen fermentation existed in sheep fed the hay diet the fermentation appeared to be continuously changing in the concentrate-fed sheep, and on this last mentioned diet abnormal values for rumen gas composition and VFA proportions were produced from time to time.

An impermeable continuous-culture artificial rumen was constructed and rumen microbial populations were cultured in vitro for periods of up to 23 days. Diets of hay and 20:80 hay:cooked flaked maize (concentrate diet) were fed to the in vitro cultures and also to sheep, and the performance of the in vitro fermentation compared with that of the in vivo fermentation.

With the hay diet, changing the initial inoculum from strained rumen liquor to unmodified rumen contents (containing solid ingesta) reduced the time required to attain a steady-state fermentation in vitro from 13 to 4 days. VFA molar proportions and the CO2: CH4 ratio indicated that the type of fermentation taking place in vitro was remarkably close to in vivo fermentation. However, rates of cellulose digestion, CH4 production and number of bacteria/unit volume (as judged by DNA concentration) were much less in vitro than in vivo, showing that the rate of fermentation was reduced in the artificial rumen. Total VFA concentration and the osmotic pressure of fermentor liquor were slightly higher than the maximum values found in vivo, and it was concluded that these were responsible for the reduced rate of fermentation.

Regardless of the duration of culture, a satisfactory steady-state fermentation was never attained when the concentrate diet was administered. DNA concentration in fermentor liquor declined to very low levels after 4 days; CH4 production rapidly declined and was replaced by H2 production after 5 days. VFA molar proportions bore little resemblance to those found in vivo. Both the osmotic pressure of fermentor contents and total VFA concentration rapidly increased with time, and by day 3 were approximately 2·5 times the values found in vivo. It was concluded that high VFA concentration, and the associated increase in osmotic pressure, were the main factors responsible for the unrealistic in vitro fermentation, and that this problem was much greater than encountered with the hay diet due to starch being digested at a faster rate than cellulose and hemicellulose.

Methods of regulating VFA concentration in continuous culture in vitro rumen systems are discussed and some improvements suggested.

Studies on 59 first four completed lactations of 37 imported Jersey cattle in Western Nigeria showed that their mean lactation length (248·4 days) and average milk yield (1257·4 kg) were inferior to those of their counterparts in other tropical countries. Lactation length following the birth of female calves was longer and milk production greater than those subsequent to male births but the differences were small (P > 0·05). Peak milk production was reached at the third lactation. Influence of season of calving on lactation length was slight; mean milk yield was significantly highest (P < 0·05) among October-December calvers, while the July-December period appeared to be more propitious for milk production. The regression coefficients of lactation length and milk yield on age of dam at calving were negative and unimpressive (P > 0·05), being −2·108 ± 2·661 and −19·106 ± 17·130 respectively. Analysis of variance for weight of milk with lactation length as a covariate revealed that although lactation length was a major (P < 0·001) determinant of milk production, both the period of calving and lactation number had recognizable bearing on milk yield. All interaction effects were trivial (P > 0·05). The period of study was 1968–74.

Using continuous infusion techniques the entry rate of linoleic acid and its contribution to carbon dioxide production has been studied in fed and fasted sheep. The entry rate of linoleic acid in fasted sheep (0·052 mg/min/kg) was considerably less than that of stearic acid (0·432 mg/min/kg), and the percentage of total carbon dioxide production derived from the oxidation of linoleic acid (0·4%) was also markedly less than that from stearic acid (10·13%).

On starvation there was a preferential mobilization of palmitic, stearic and oleic acids relative to linoleic acid.

The infused 14C-labelled linoleic acid was initially incorporated into plasma phospholipids, with maximal radioactivity at about 1 day post-infusion, and subsequently into plasma cholesteryl esters with a maximum at 2 days post-infusion. The incorporation of 14C-labelled stearic acid into plasma phospholipids was only 25–30% that of linoleic acid, with negligible incorporation into cholesteryl esters.

Possible explanations for ruminant animals being able to exist on a very low intake of linoleic acid are discussed. In essence, there is a discrimination against the use of linoleic acid as an energy source, but the mechanisms involved do not appear to be unique to ruminant animals.

Sugar beet bolting in the root crop was studied during nine growing seasons, under the extreme climatic conditions in which the autumn-sown crop grows in Southern Spain.

Bolting is positively correlated with the number of days with minimum air temperatures ranging from 2 to 8 °C or with the number of days with mean temperatures between 8 °C and 13 °C.

The occurrence of bolting is also affected by rainfall distribution in so far as it determines the date of seedling emergence.

All flowers were removed daily on soya-bean plants (cv. Hampton) for 1, 2, or 3 weeks and all pods developed on the plant were removed after 1, 2 or 3 weeks of pod development, in two field trials, in order to evaluate the effects of removing flowers or pods on the growth, development and yield of the cultivar. Removal of flowers or pods led to less dry-matter accumulation, longer leaf area duration and delayed maturity of the plants and these became more pronounced with the severity of the removal.

Number of mature pods per plant, number of seeds per plant, pod yield per plant and seed yield both per plant and per hectare, were significantly reduced when flowers were removed for 1 week or pods removed after 2 or 3 weeks of development in the early season crop. Yield was reduced by 27%, 35% and 40% respectively both per plant and per hectare. In the late season crop, removing flowers for 3 weeks or removing pods after 3 weeks of development led to significant reduction in number of mature pods per plant, number of seeds per plant, number of seeds per pod, pod yield per plant and seed yield both per plant and per hectare. The magnitudes of yield reduction were 40% and 49% respectively.

The ability of the variety of soya bean used in this study to prevent significant reduction in seed yield by compensatory development, following flower or pod removal, depends on the severity of the removal vis-d-vis the stage of development of the plant and its vigour.

Two systemic fungicides, benomyl and thiabendazole, were more active than the non-systemic fungicide Drazoxolon in inhibiting fungal growth in vitro. A similar pattern was obtained in glasshouse trials with benomyl and thiabendazole giving adequate protection at low concentrations while Drazoxolon was ineffective unless applied at 50% the commercial product concentration. A field trial using thiabendazole, Drazoxolon and a mixture of benomyl and thiram confirmed the glasshouse results.

Some phytotoxicity was noticed with high concentrations of both benomyl and thiabendazole, but satisfactory disease control was achieved using fungicide concentrations which did not induce phytotoxicity.

This paper presents the results of analyses of yield variability in more than 500 trials of varieties of spring oats, spring wheat, spring barley and winter wheat. A table of critical percentage yield differences has been constructed for guidance in planning future series of trials.

The evaluation of the genetic potential of cereal varieties in variety trials will be accurate only if compensation can be made for all the variables known to influence the results, or if those variables are controlled. The influence of one such variable, seed size, on subsequent performance of crop plants, is well documented (wheat, Kittock & Law, 1968; beans, Ries, 1971; barley, McDaniel, 1969). McFadden (1963), working with barley, felt that seed size was such an important determinant of subsequent plant performance that he suggested that seed used in comparative testing systems should all be processed to the same seed range.

Previous work has shown that the technique of laparoscopy in anaesthetized ewes is a practical and reasonably accurate method for the diagnosis of pregnancy between 17 and 28 days after conception and for estimating numbers of foetuses (Phillippo et al. 1972). This method in common with other reported endoscopic techniques for sheep positions the animal on its back, necessitating the use of either general anaesthesia (Roberts, 1968; Boyd & Ducker, 1973) or tranquillization and local anaesthesia (Kelly & Allison, 1976). These methods have the disadvantages of the necessity to withhold food and water for up to 24 h prior to surgery and the risk associated with general anaesthesia and the positioning of the animal. A new procedure with the sheep standing was therefore developed from the method used in cows (Mariana, 1969; Wishart & Snowball, 1973).

Whole barley grains were soaked in dilute sodium hydroxide solutions or sprayed with concentrated solutions, then incubated in bags in the rumen of sheep. Rate of digestion was increased by the alkali, and spraying with 35 g NaOH/kg was concluded to be the optimum treatment. Whole barley treated in this way was as well consumed and digested by cattle as rolled barley, and better digested than untreated whole grain, but promoted a rumen pH one unit higher. Oats, wheat and maize were also treated successfully, as judged by digestion in bags. Urea added with NaOH remained stable; treated grain could be stored at 19% moisture without deterioration.