Rations for dairy cows are often formulated using predictions of voluntary feed intake calculated from regression equations. The accuracy of the predictions of dry-matter intake by seven equations is investigated. Comparisons are made when live weight is taken to be the observed weekly mean (MLW), the observed live weight after calving (CLW) or an estimated breed weight accompanied by a notional pattern of live-weight change (BLW). Data recorded on a British Friesian dairy herd at the Grassland Research Institute fed mostly silage ad libitum and various supplements are used. The mean square prediction error (MSPE) is calculated for each week and summarized over the whole experimental period.

The least MSPE's are 2·1, 2·8 and 2·4 (kg D.M.)2 for comparisons using MLW, CLW and BLW respectively. The Ministry of Agriculture, Fisheries and Food (1975) equation involving only live weight and milk yield performs well and would be useful when only the limited measurements of live weight and milk yield are available, but the more complex equations of Vadiveloo & Holmes (1979) and of Lewis (1981) give consistently the best predictions. The importance of using the original definitions of the variables when applying a predictive equation is illustrated. Even so, the large errors found in the predictions of intake points to the need for further research.

Working rules for determining plot size and number of plots within a block in field experiments are proposed based on the value of the intrablock correlation (ρ), which can be obtained from the analysis of variance of a randomized-block experiment. The method uses Binns' (1982) equation to relate this correlation to Smith's (1938) empirical law. The rules are: (1) if ρ is greater than 0·5, use an incomplete block design or reduce the plot size in order to increase the number of replications; (2) if ρ is less than 0·1, an increase in plot size is effective; (3) if ρ is between 0·1 and 0·5, an increase in plot size and a decrease in the number of plots per block may be helpful in combination.

Chemical compositional (protein, fat, ash and water) changes in the fleece-free empty body, carcass, viscera and ‘remainder’ components of Corriedale wether sheep were measured by serial slaughter of animals following five different growth paths.

The composition of sheep, after losing up to 34% of body weight over 18 weeks at 125 g/day, was significantly different from a continuously growing control group at the same body weight, but the actual differences in the weights of tissues were small. At the end of weight loss all treatment sheep contained more fat and protein, and less water than controls.

The different growth paths followed during weight loss led to differences in the proportions of protein, fat, ash and water lost and to differences between the three body components in the relative contribution made by each.

The periods of weight loss led to changes in the relative growth coefficients for chemical constituents during realimentation, particularly those of fat and ash which were reduced, and of water which was increased.

The response to realimentation differed between body components, particularly the carcass and viscera. Above the body weight at which weight loss was imposed the realimented sheep did not differ in chemical composition from the continuously ad libitum fed controls when compared at the same weight.

Metal contents are reported of the soils from a field experiment in which two rates of various organic manures, including sewage sludge and sludge compost, were applied from 1942 to 1961. Changes in the concentrations of some elements in the sludges during the 20 years are also presented.

The percentage recoveries of the added metals Zn, Cu, Ni, Pb, Cd and Cr in the topsoil varied from 71 to 96%. In 1960, extractability of the metals from the soils by 0·05 M-EDTA was 50% of the aqua regia-soluble total metals. This figure did not vary greatly with metal or with the type of organic manure that was applied.

The ruminal metabolism of lactic acid was investigated in vivo under normal feeding conditions in four sheep each adapted to one of the following diets: high-concentrate, intermediate, high-roughage containing 65, 43 or 10% maize meal and molasses respectively, or lucerne hay. A continuous basal turnover of ruminal lactate (0·01–0·02 mmol/1/min) was found which increased 10- to 40-fold immediately after feeding when production exceeded utilization and lactate accumulated in the rumen. This was followed by an increase in utilization rate which removed the accumulated lactate. Both lactate and glucose turnover were related to the amount of readily fermentable carbohydrate in the diet. Approximately 8, 6·5, 5 and 2·5% of the total VFA was formed through lactate on the high-concentrate, intermediate, high-roughage and lucerne hay diets respectively.

Rumen microbial counts of total culturable, glucolytic, amylolytic and lactateutilizing bacteria, and of ciliate protozoa were also performed on the four sheep. Numbers of micro-organisms in all groups were highest on the high-concentrate diet and lowest on the two roughage diets. The proportions of the predominant genera from the different metabolic groups of bacteria differed, although in most cases the same organisms were present in the rumen on all diets. The succinate pathway was found to be quantitatively more important in the conversion of lactate to propionate in the rumen. Although the numbers of lactate-utilizing bacteria increased as the amount of RFC in the diet increased, their metabolic activity was actually lower. Reasons for this finding are discussed, together with factors influencing the regulation of lactate production and utilization in the rumen.

Sixty families of each of two tomato triple test crosses (S 120 × EC 61747 and EC 31513 × Pusa Ruby) were raised in completely randomized blocks in two replications with two fertilizer levels. Perkins & Jinks' (1971) analysis was used to detect and measure the interactions of additive, dominance and epistatic effects of genes with micro- and macro-environments for flowering time, maturity period, number of branches, final height, number of locules, number of fruits per plant, yields per plant and weight per fruit. Additive and dominance gene effects were almost equally sensitive to micro- and to macro-environments. The j and l type epistasis was more sensitive to the environments than the i type epistasis.

The effect of sowing date on root growth of high-yielding crops (8–1 It grain/ha, 85% D.M.) of winter wheat (Triticum aestivum L. cv. Hustler) was measured at Rothamsted and Woburn in 1980 and 1981. Roots were sampled by coring on five occasions and changes in root dry weight and length were determined. The average growth rate between March and June was about 1 g/m2/day (200 m/m2/day), over 5 times that measured between December and March. Increases in root weight or length with time were generally exponential to anthesis when the crops had 101–172 g root/m2 (20–32 km/m2). September-sown wheat had more root than October-sown wheat at all times, but whereas early differences in length were maintained throughout the season, root weights converged between March and June. Overall, there was no significant difference in root dry-matter production between sites at anthesis, but there was a substantial difference between years. Differences in root growth between crops were reduced by plotting the amount of root against either the number of days from sowing or accumulated thermal time. Using che latter, root growth between December and June was reasonably linear although there was some indication of a lag below 500 °C days. Regression equations obtained for the relationships between root growth and accumulated thermal time also fitted previously published data and may provide general descriptions of root growth with time.

Roots of September-sown crops reached 1 m depth by December but those of October-sown crops were not detectable at this depth until April. For most crops the distribution of roots with depth was reasonably described by an exponential decay function, with over 50% of the roots in the top 20 cm of soil at all times. At Woburn in 1981, a plough-pan restricted roots to the upper soil horizons for most of the season but apparently had little effect on the total amount of root produced. For one of the experimental crops an empirical mathematical function describing the distribution of roots with depth and time is presented.

Using the data from this and previously published studies, the relationship between grain yield and the amount of root at anthesis was investigated. Total root length was positively correlated with grain yield but nonetheless similarly yielding crops could have different-sized root systems. Total root dry weight was poorly correlated with grain yield.

Field experiments were conducted for 2 years in Peshawar, North West Frontier Province of Pakistan, to study the effect of three levels of boron (1, 2 and 3 kg/ha) on the amino acid composition of wheat protein. The soil was clay loam, alluvial in nature, with a pH value of 7·8, and hot-water-soluble boron content of 0·58 mg/kg.

Positive linear and negative quadratic effects of boron were observed on the protein and ash contents of wheat grain. Most of the essential amino acids were linearly increased with increasing supply of boron. There was a negative linear relationship of boron with all non-essential amino acids, except histidine and tyrosine.

Lysine was the most deficient amino acid in wheat protein. Chemical score based on this amino acid was positively affected by boron. There was also an improvement in the amino acid profile due to boron.

Four repletion experiments were carried out to clarify the roles of molybdenum, sulphur and iron in the inhibition of copper absorption by ingested soils. In each experiment, groups of four to six hypocupraemic Scottish Blackface ewes were repleted for 21 days with diets containing CuSO4 and/or soil Cu and the responses in plasma Cu used to assess the availability of the Cu supplied.

In Expts 1 and 2, three soils varying in Mo but high in Fe content and derived from Lower Lias Clay, Namurian Shale and Weald loam were added at 100 g/kg D.M. to diets of low (1·0) and high (4·1 g/kg D.M.) S contents: they provided 3·1, 2·8 and 0·1 mg Mo/kg D.M. respectively. When compared with groups given no soil, each soil increased plasma Cu repletion in the low S experiment and decreased it in the high S experiment. Inhibition was thus not completely dependent on soil Mo but dependent upon dietary S.

Soils varying in Fe content were compared in the manner of the above experiments in Expts 3 and 4. Two Fe-rich soils, developed from the Upper Chalk and a Barton Clay and providing 2·8 and 1·5 g Fe/kg D.M., impaired Cu repletion on the high S diet but not on the low S diet. A soil, developed on a sand from the Bagshot Beds and providing only 0·15 g Fe/kg D.M., did not impair repletion but FeSO4, providing 0·8 g Fe/kg D.M. did so, irrespective of dietary S content. Ingestion of Fe-rich soils in a high S diet caused three-fold increases in rumen sulphide concentrations 5 and 24 h after feeding. It is suggested that soil ingestion impairs Cu absorption in sheep by trapping S as heavy metal sulphides such as FeS and releasing sulphide in the acid abomasum.

Soil water content affected the nodulation and N2 fixation of Phaseolus vulgaris by Rhizobium phaseoli and the utilization of mineral N by plants. Plants grown in wet soil produced twice as much as those grown on dry soils. Nodule weight and activity were five to ten times greater than those from dry soils. At 45 days, N additions inhibited nodulation, but this effect was partially diminished in wet soils.

The maximum N utilization from fertilizer to produce dry matter did not correspond to maximum N utilization by pods.

An examination of the effects of adding phosphorus to the soil on nodulation and P utilization in Phaseolus vulgaris L. showed a positive response in plant weight to increasing rates of phosphorus (32P) when water tension was low in the pots.

The efficiency of the utilization of fertilizer-P was directly influenced by the water content of the soil, showing increasing P accumulation after flowering.

A highly positive interaction between P addition, water content and nodulation was observed. Nodules were shown to have a high P requirement, with phosphorus (32P) contributing to an increase in the number and size of nodules.

The field experiments were conducted at the Indian Agricultural Research Institute, New Delhi in summer-rainy seasons of 1980 and 1981 to study the effect of different sorghum-legume intercropping systems and weed control methods on growth, yield and nutrient uptake by different crops and on weeds. The intercropping of legumes increased growth, uptake of N, P and K and yield of sorghum compared with sole sorghum. However, maximum increase was obtained when it was grown in association with fodder cow pea. All intercrops smothered the weeds but maximum suppression was by fodder cow pea. The total uptake of nutrients (N, P and K) was also greater in intercropping systems. Pre-emergence application of fluchloralin at 0·5 kg/ha was most effective in all intercropping systems followed by nitrofen at 1·0 kg/ha. Hand weeding and fluchloralin application also led to higher nutrient uptake by sorghum and the whole system than the unweeded control. Application of fluchloralin and nitrofen controlled most of the weeds and reduced nutrient removal compared with the control but was less effective than hand weeding.

Mulching polybag oil-palm seedlings with bunch refuse, shredded polythene, sawdust, grass, wood shavings and kernel shells ‘all-year’ or throughout the nursery period (May–May), in the ‘wet-season only’ (May-November), and in the ‘dry-season only’ (November–May) resulted in soil temperature differences which did not exceed 1 °C at 5 cm polybag depth. This was attributed to the high rainfall which reduced considerably the soil temperature differences between mulched and unmulched soil in the wet season and to the enhanced leaf canopy in ‘all-year’ and ‘wet season only’ mulchings which shaded soil in polybags in the dry season.

The mulch materials and times of their application significantly influenced growth variables like number of leaves, plant height and stem girth, and number of blast-affected seedlings at 6 months after sowing (wet season). By 12 months after sowing, all growth characters measured were similar in the various treatments, indicating compensatory growth at the latter half of the growing period (dry season).

N, P, K, Mg and Ca contents of seedlings were not significantly affected by either mulch materials or times of their application. The results emphasize that mulching for at least 6 months during the early or late nursery period and the use of various mulches may be beneficial to oil-palm seedling growth.

Gabriel (1971) proposed a technique for displaying the rows and columns of a twoway table as a two-dimensional biplot so that any element of the table can be approximated by the inner product of vectors corresponding to the appropriate row and column. The technique is useful for investigating the pattern of response of varieties over different environments, and substantially increases the information available from the more familiar methods of regression and principal component analysis without need for additional computation.

Calves from three breeds, Brahman, Hereford × Shorthorn (HS) and Brahman × HS (BX), were divided equally into two groups, one of which was treated every 3 weeks from birth onwards to control ticks and gastrointestinal helminths, and one of which was untreated. Mortalities, growth rates and levels of resistance to environmental stresses that affected both mortality and growth under grazing conditions were recorded for all animals up to weaning (6 months) and for all males up to 15 months of age. The Brahmans were the most and the HS were the least resistant to environmental stresses, each of which was shown to depress growth in proportion to its magnitude and to contribute to the high mortalities of the HS. All breeds responded positively to parasite control with the greatest response in both survival and growth in the HS breed and the least response in the Brahman breed.

Samples of males from the various breed-treatment groups were taken into pens where they were protected from environmental stresses and fed both low-quality pasture hay and high-quality lucerne hay ad libitum. Measurements were made of fasting metabolism, maintenance requirement, voluntary food intake and gain, variables related to the growth potential of each animal. The HS animals had the highest whilst the Brahmans had the lowest values for each variable.

However, despite their low growth potential, the Brahmans had the highest growtli rate, and the HS, despite their high growth potential, had the lowest growth rate, when growth was measured in the presence of all environmental stresses. When parasites were controlled, growth rates were highest for the BX, the breed with intermediate growtli potential, and did not differ between the HS and Brahmans. These interactions arose because of the different contributions of resistance to environmental stresses and growth potential to growth rate measured at the different levels of environmental stresses. The relevance of these interactions to breed evaluation and cross-breeding is considered.

Growth potential and resistance to environmental stresses were negatively correlated both between and within breeds, though the latter was biased by the effects of compensation. The influence of these relationships on the likely outcome of selection for increased growth rate, both between and within breeds, is discussed.

The seasonal and post-partum oestrus occurrence and ovarian activity, assessed by the plasma progesterone concentrations, were studied in Finn-cross ewes following autumn and winter lambings.

The last seasonal oestrous cycle was followed by a silent ovulation in C0% of the Finn × Awassi ewes. Silent ovulations during midanoestrus occurred in 50% of the ewes, and in 90% of the animals a silent ovulation preceded the normal resumption of the seasonal sexual activity.

The first post-partum oestrus occurred within C0 days after October lambings in about 90% of the ewes. Silent ovulations before the first post-partum oestrus were evident in 70% of the recycling ewes.

It is suggested that breeding ewes with ovarian activity after oestrus induction during anoestrous periods might increase the reproductive performance of the flock in a frequent lambing system.

Two experiments were conducted with milking cows on continuously stocked perennial ryegrass pastures. In each a control group, T0, received 1 kg/day of a concentrate supplement and treatment groups T1 and T2 received 4 kg (Expt 1) or 5 kg/day (Expt 2) of a low quality T1 or a high quality T2 concentrate. In Expt 1 treatments were applied continuously for 14 weeks to a total of 30 cows. In Expt 2 a Latin square design for 9 weeks was conducted with 18 cows. The stocking rate of the pasture declined from 9·6 to 5·1 cows per ha (mean 6·7 cows/ha) from May to August (Expt 1) and was maintained at 3 cows/ha in August-October (Expt 2).

Supplements increased total intakes by 0·92 and 0·77 kg organic matter (OM)/kg OM supplied in the concentrates respectively for Expts 1 and 2. Milk yields increased by 0·6 and 0·5 kg/kg concentrate supplied and supplemented cows showed small increases in live weight. Differences in lactation milk yield just approached significance. Grazing times were only slightly reduced by supplements and bite sizes were lower than normal. There was no important difference in animal performance between the two concentrates. The total output from the pasture was 19·6t milk and 115 GJ of utilized metabolizable energy per hectare.

Reasons for the high supplementary effect of the concentrates and its implications for stocking rates are discussed.

One hundred and ninety-four lactating British Friesian cows were used over a 2-year period to determine the effects of mixing diet ingredients on dry-matter (D.M.) intake, animal performance, digestibility coefficients, rumen fermentation and efficiency of food utilization. Four treatments were imposed in both years and were complete diet and separate ingredients at ad libitum and restricted levels of feeding.

In Expt 1 a complete diet at ad libitum and restricted levels of feeding was compared with separate ingredients. The diet consisted of 60% concentrates and 40% forage and contained 20, 20, 10 and 50% on a D.M. basis of maize silage, lucerne silage, dried sugar-beet pulp and dairy compound, respectively. Method and level of feeding were the same in Expt 2; however, the diet in the 2nd year consisted of 50% concentrates (40% dairy compound, 10% dried sugar-beet pulp) and 50% grass silage.

In Expt 1 cows fed the complete diet ad libitum consumed 16·5 kg D.M./day which was significantly more than the 14·3 kg/day consumed by those offered the separate ingredients ad libitum. Intakes in Expt 2 were not significantly affected by method of feeding. Much of the difference in Expt 1 was attributed to the fact that many cows rejected lucerne silage when fed in an unmixed form and therefore to keep the concentrate to forage ratio constant other diet ingredients were reduced proportionately.

Mixing diet ingredients did not significantly affect milk yields, which were for the complete diet ad libitum and restricted and the separate ingredients ad libitum and restricted 22·2, 22·2; 22·1 and 20·7 kg/day in Expt 1 and 23·6, 20·8; 24·2 and 21·5 kg/ day in Expt 2, respectively. In Expt 1 when the concentrate to forage ratio was 60:40, cows fed the complete diet ad libitum produced milk with a significantly higher milk fat concentration (39·2 g/kg) than those fed the separate ingredients (31·6 g/kg). Similar effects were not recorded in Expt 2 when the concentrate to forage ratio had been reduced to 50:50. Changes in milk protein concentration were more closely related to changes in intake rather than method of feeding. Mixing diet ingredients tended to decrease live-weight loss in early lactation and accelerate live-weight gain in midlactation.

In vivo digestibility coefficients determined in lactating dairy cows showed that in Expt 1 the D.M. and organic-matter digestibility coefficients for the complete diets fed ad libitum (0·689 and 0·713) were lower than those recorded (0·712 and 0·732) for the unmixed diet ad libitum. Although the digestibility coefficient of the acid-detergent fibre of the complete diet was markedly higher at 0·519 compared with 0·478 for the separate ingredients, the difference was not significant. In Expt 2 the only difference in digestibility coefficients was that for nitrogen, which for the complete diet was significantly higher than that of the separate ingredients at both levels of feeding.

At an ad libitum level of feoding in Expt 1, the molar proportions of acetate and butyrate were 620 and 116 mM/l for the complete diet which were slightly higher than 602 and 95 mM/1 for the separate ingredients ad libitum. This diet also had a slightly higher molar proportion of propionate, 249 compared with the 221 mM/l for the complete diet ad libitum. In Expt 2 there wore no significant differences between treatments for either molar proportions of rumen volatile fatty acids or the ratio of lipogenic to non-lipogenic acids.

An experiment to compare the effect of diverse ratios of 0–6 h old Microplitis rufiventris Kok. progeny within Spodoptera littoralis (Boisd.) larvae is described and the results discusssed. Five to 21% of parasite progeny was eliminated during the egg stage. Surplus parasite larvae were eliminated mainly by physical attack, physiological suppression and perhaps by encapsulation. Parasite larvae which escaped competition during their first instar were subjected to physiological suppression. Some of the super-numerary parasite larvae other than the winners survived competition mechanisms and developed in the host haemocoele. Nevertheless, most of these parasites suffered from moulting failure and emergence problems at the end of their endoparasitic development. The development of the winning parasite was retarded by 1–2 days during its egg-larval stage while the duration of its pupal stage was about the same as parasites from singly parasitized hosts.

In each of the years from September 1977 to July 1982 winter wheat was grown on one or more of three clay soil sites (clay content 35–55%) in Oxfordshire where the climate is close to the average for the area of England growing winter cereals.

The effects on crop water use of different soil management practices, including ploughing, direct drilling and subsoil drainage, are compared. Cultivation treatment had little effect on the maximum depth of water extraction, which on average in these clay soils was 1·54 m below the soil surface. Maximum soil water deficit was also little affected by cultivation; the maximum recorded value was 186±7·6 mm. Subsoil drainage increased the maximum depth of water extraction by approximately 15 cm and the maximum soil water deficit by about 17 mm.

Generally soil management had little effect on either total water use by the crop which was found to be close to the potential evaporation estimated by the method of Penman, or water use efficiency which for these crops was about 52 kg/ha par mm water used.

Results are discussed in relation to limitations to potential yield.