Diverse cultivars of winter wheat (Triticum aestivum L.) were grown in the field in 1993/94 and 1994/95 at Reading UK in temperature gradient tunnels at normal atmospheric (c. 370) or elevated CO2 concentration (c. 700 μmol CO2 mol−1 air). In 1993/94, grain yield of cv. Avalon was insensitive to mean temperature (between 8·8 and 10·9°C), while elevated CO2 increased yield by 1·3 t ha−1 (12·6%). In all other cultivars, warming reduced grain yield and CO2 increased grain yield. In 1993/94, in cvs Galahad and Mercia the effects of CO2 and temperature on yield were additive. However, for cv. Hereward in both years and for cv. Soissons in 1994/95, there were negative interactions between the effects of CO2 and temperature on yield: the maximum benefit of doubling CO2 to grain yield, 4·5 and 2·7 t ha−1 (65 and 29%) respectively, occurred at cooler temperatures; there was no benefit from doubling CO2 (i.e. 0%) once the temperature had increased above the seasonal mean by 2·2–2·6°C in cv. Hereward and by 1·3°C in cv. Soissons. The beneficial effect of doubling CO2 on grain yield in cvs Galahad, Hereward, Mercia and Soissons was negated by an increase in mean seasonal temperature of only 0·7–2·0°C. Warming decreased root dry mass at anthesis in 1994/95 while it increased at elevated CO2 (49 and 186%, coolest and warmest regime, respectively). Carbon partitioned to roots declined progressively with warming, while at elevated CO2 there was an average of 56% increase in allocation to roots. The relative impacts of both CO2 and temperature were greater on root dry mass than on either grain yield or total above-ground biomass, while the effects on grain and biomass yield varied considerably between cultivars, suggesting that the impact of rising CO2 and temperature are likely to be dependent on cultivar.

The dipping of sheep and cattle, as a means of eradicating ‘scab,’ lice, ticks, etc., and the diseases which it is now known the latter may transmit, has met with such success, that compulsory dipping is now in vogue in most pastoral countries. Where compulsory dipping obtains, there must of necessity be some system of the standardisation of dips. In Queensland and South Africa, the respective Governments issue official formulae from which the stockbreeder can prepare his own dipping fluid. Only such proprietary dips, as are duly recognised by the Government, may be employed. In the United States, the regulations for the sale of proprietary dips are still more stringent. The quantity of active substance, usually sodium arsenite, nicotine or cresylic acid, is defined within very narrow limits. Further, no proprietary dip is now recognised, unless the manufacturer can furnish a ‘Field Tester,’ by means of which the stockbreeder can himself determine, in a simple and fairly trustworthy manner, the percentage of active constituent in his bath.

Yields from five of the plots on the Park Grass Continuous Hay experiment at Rothamsted, started in 1856, were examined to see if any long-term trends could be detected over the last 100 years. Three of the plots examined are unfertilized; two receive inorganic nutrients every year; all are harvested twice a year. In 1959 the harvesting procedure was changed: yields for the periods before and after this change were examined separately and together. On none of the three unfertilized plots was the slope of the regression of total yield (i.e. first and second cutscombined) on time significantly (P < 0·05) different from zero in either the 1891–1958 or 1960–1992 periods. On both the fertilized plots, there were significant declines in yield with time over the 1960–92 period, assuming that the effects of autocorrelation are sufficiently small to be ignored; there were no consistent changes between 1891 and 1958. There were some significant trends on the five plots when the two cuts were considered separately.

A linear regression model was fitted to the data in an attempt to separate the effects of meteorological variables (rainfall and sunshine hours over selected parts of the year) on total yield from possible long-term effects brought about, for example, by the increasing concentration of CO2 in the atmosphere. On four of the five plots this model accounted for between 12 and 21% of the yield variance in the pre-1959 period and between 45 and 63% after 1960. On the fifth plot, which received the highest level of N, the model accounted for 29% of the variance in the first period but only for 16% in the second period. When a linear trend with time was included in the model, this was not significant on any of the plots over the entire 1891–1992 period, although some significant trends appeared when the two periods were considered separately. The model was also fitted with the atmospheric CO2 concentration in place of the linear trend with time: again there were no consistent trends.

Neither changes in the concentration of CO2 in the atmosphere over the last century nor increasing inputs of combined N in rainfall or in dry deposition have had any detectable effects on yield in these plots.

Volatilization of ammonia (NH3) from slurry applied in the field is considered a risk to the environment and reduces the fertilizer value of the slurry. To reduce volatilization a better understanding of the slurry–soil interaction is needed. Therefore, the present study focuses on measuring NH3 volatilization as affected by differences in infiltration. Livestock slurries with different dry matter (DM) composition and viscosity were included in the experiments by using untreated cattle and pig slurry, pig slurry anaerobically digested in a biogas plant and pig slurry anaerobically digested and physically separated. NH3 volatilization was measured using dynamic chambers and related to infiltration of the livestock slurries in the soil by measuring chloride (Cl−) and Total Ammoniacal Nitrogen (TAN=ammonium (NH4+)+NH3) concentrations in soil at different depths from 0·5 to 6·0 cm from the soil surface. The slurries were applied to sandy and sandy-loam soils packed in boxes within the chambers. There were no significant differences in relative volatilization of NH3 from untreated cattle and pig slurries, but anaerobic digestion of pig slurry increased volatilization due to increases in pH. However, physical separation of the digested slurry reduced the volatilization compared with untreated slurry, due to increased infiltration. In general, the volatilization decreased significantly with increased infiltration. The present study shows that NH3 volatilization from applied slurry can be related to infiltration and that infiltration is related to slurry composition (i.e. DM content and particle size distribution) and soil water content. The infiltration of liquid (measured by Cl− infiltration) was affected by soil water potential, therefore, Cl− infiltrated deeper into the sandy loam soil than the sandy soil at similar gravimetric soil water values. Dry matter (DM) and large particles (>1 mm) of the slurry reduced infiltration of liquid. A high proportion of small particles (<0·025 mm) facilitated infiltration of TAN.

Hailed as the single most important paper published on crop protection in the 20th century, Stern et al. in 1959 formed the conceptual basis for modern integrated pest management (IPM) worldwide. The ecological foundation for IPM envisioned by its authors is as valid today as in 1959. However, adoption by developing country farmers has been low and its advances short-lived. The present paper examines the concept of integration in IPM and criteria for determining whether its control tactics have been integrated harmoniously. The effects of local and regional landscape patterns on pests and on the design of IPM are reviewed, arguing that the agroecosystem must be understood and managed as a living system with the goal of enhancing and conserving agrobiodiversity and keeping ecosystem services intact. Key to IPM adoption is convincing farmers to integrate non-chemical alternatives (e.g. biological control, plant diversification) as primary management components and to apply pesticides judiciously and only after non-chemical components fail to manage pests effectively. Research, extension and policy changes are identified to increase the efficiency, adoption and sustainability of IPM on resource-limited farms. The over-arching challenge is devising communication and support systems that allow resource-limited farmers to try, adopt and sustain IPM that enhances yields and profits in light of the many uncertainties and challenges. Use of information technology, media development, crowdsourcing and rural sociology is advocated to connect farmers to the technical sources required to enhance yields and profits and reduce risks to them, the farming community and the environment.

1. The length of oestrus in mares varied from 3 to 54 days, although in most cases it was 7–8 days.

2. The length of dioestrus varied from 5 to 30 days, but in most cases was 11–16 days.

3. Ovulation occurred in most cases on the last day of oestrus, but a considerable number of ovulations occurred on the 1st and 2nd days before the end of oestrus, and in a few cases from the 5th day before the end of oestrus to 1 day after the end of oestrus.

4. Artificial insemination of mares was equally effective in the intervals of 24, 48 and 72 hr. before ovulation but was unsuccessful in intervals of 2 and 4 hr. after ovulation.

5. Pregnancy was diagnosed in all mares by rectal palpation on the 23rd day and in one mare as early as the 16th day.

6. The foetus developed in the opposite horn of the uterus to the ovary which ovulated at the onset of pregnancy in five out of seven mares.

7. Ovulation occurred in one mare on the 23rd day of pregnancy.

8. Gonadotrophic hormones had no effect when given in the anoestrous period (November to March).

9. Ovulation was induced in 20–40 hr. in most cases after the intravenous injection of 1000–2000 mouse or rat units of pregnancy urine extract intravenously, provided a fairly mature follicle was present in the ovary at the time of injection.

When this ovulation occurred, the duration of oestrus was shortened.

1. Cereal plant density affects yield and growth parameters of fundamental importance. An experiment is described in which growth and development, and yield and yield components of barley grown over a wide range of density were examined.

2. Four varieties of barley—Proctor, Plumage-Archer, Domen, and Moore—were grown at densities approximately equivalent to 35, 70, 140 and 280 lb/acre. Density was found not to affect seedling establishment or plant survival, but there was a variety effect on seedling establishment.

3. Varietal differences were seen in maximum tiller number, and the percentage of tillers surviving to form ears. These differences were most marked between the six-row variety and two-row varieties. The effect of increasing density was to increase the maximum tiller number, but this was followed by different rates of tiller death until early June, after which there was no further compensation for tiller number. Ear emergence and ear number were affected both by variety and density.

It is predicted that climate change will increase not only seasonal air and soil temperatures in northern Europe but also the variability of rainfall patterns. This may influence temporal soil moisture regimes and the growth and yield of winter wheat. A lysimeter experiment was carried out in 2008/09 with three factors: rainfall amount, rainfall frequency and soil warming (two levels in each factor), on sandy loam soil in Denmark. The soil warming treatment included non-heated as the control and an increase in soil temperature by 5°C at 100 mm depth as heated. The rainfall treatment included the site mean for 1961–90 as the control and the projected monthly mean change for 2071–2100 under the International Panel on Climate Change (IPCC) A2 scenario for the climate change treatment. Projected monthly mean changes in rainfall compared to the reference period 1961–90 show, on average, 31% increase during winter (November–March) and 24% decrease during summer (July–September) with no changes during spring (April–June). The rainfall frequency treatment included mean monthly rainy days for 1961–90 as the control and a reduced frequency treatment with only half the number of rainy days of the control treatment, without altering the monthly mean rainfall amount. Mobile rain-out shelters, automated irrigation system and insulated heating cables were used to impose the treatments.

Soil warming hastened crop development during early stages (until stem elongation) and shortened the total crop growing season by 12 days without reducing the period taken for later development stages. Soil warming increased green leaf area index (GLAI) and above-ground biomass during early growth, which was accompanied by an increased amount of nitrogen (N) in plants. However, the plant N concentration and its dilution pattern during later developmental stages followed the same pattern in both heated and control plots. Increased soil moisture deficit was observed only during the period when crop growth was significantly enhanced by soil warming. However, soil warming reduced N concentration in above-ground biomass during the entire growing period, except at harvest, by advancing crop development. Soil warming had no effect on the number of tillers, but reduced ear number and increased 1000 grain weight. This did not affect grain yield and total above-ground biomass compared with control. This suggests that genotypes with a longer vegetative period would probably be better adapted to future warmer conditions. The rainfall pattern treatments imposed in the present study did not influence either soil moisture regimes or performance of winter wheat, though the crop receiving future rainfall amount tended to retain more green leaf area. There was no significant interaction between the soil warming and rainfall treatments on crop growth.

A grazing experiment, conducted for 55 days (from 4 March to 29 April) in the late summer/autumn of 1997, at Massey University, Palmerston North, New Zealand, compared the reproductive efficiency and wool growth of ewes grazing Lotus corniculatus (birdsfoot trefoil) or perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) dominant pasture (pasture). Half the ewes grazing each forage were given daily oral polyethylene glycol (PEG: molecular weight 3500) supplementation to inactivate the condensed tannins (CT) in lotus. A rotational grazing system with 200 mixed age ewes (54·2±0·88 kg/ewe; 50 ewes/treatment) was used.

The effect of forage species and PEG supplementation upon voluntary feed intake (VFI), concentration of plasma metabolites, reproductive efficiency, wool production and wool characteristics was measured during two synchronized oestrous cycles. The ewes were restricted to maintenance feeding for the first 12 days of each oestrous cycle and then increased to ad libitum for the 6 days prior to and including ovulation. Lotus contained 17 g total CT/kg dry matter (DM) in the diet selected. There were only trace amounts of total CT in pasture. In vitro organic matter digestibility (OMD) was higher for lotus (0·82 v. 0·74) than for pasture, whilst lotus contained less nitrogen (N; 37·8 v. 44·5 g/kg OM).

Mean ovulation rates (OR) for CT-acting and PEG sheep grazing pasture and lotus were respectively 1·33 v. 1·35 and 1·78 v. 1·56, with corresponding lambing percentages being 1·36 v. 1·36 and 1·70 v. 1·42. Fecundity (number of corpora lutea/ewe ovulating) was greater for ewes grazing lotus than pasture (P<0·01), and tended to be greater for CT-acting than for PEG sheep grazing lotus (P=0·06). In unsupplemented sheep, ewes grazing lotus had increased plasma concentrations of branched chain amino acids (BCAA; 57%) and essential amino acids (EAA; 52%) compared to ewes grazing pasture.

In ewes grazing pasture, PEG administration had no effect on plasma concentrations of urea and free amino acids, VFI, reproductive efficiency and wool production. However, in sheep grazing lotus, plasma concentrations of urea were significantly lower and concentrations of most amino acids were significantly higher for CT-acting than for PEG supplemented ewes (CT not acting); there was no difference in VFI between these two groups. Compared to ewes grazing pasture, ewes grazing lotus had similar VFI but produced more wool with longer staples and thicker fibre diameter, with there being no effect of PEG supplementation.

It was concluded that feeding lotus increased the efficiency of both reproduction and wool production without an increase in VFI, and that a possible cause was the action of CT in increasing plasma EAA and especially BCAA concentration.

In situ and in vitro rumen incubations were used to determine the effect of condensed tannins (CT) on the solubilization and degradation of the plant protein from white clover (Trifolium repens) and Lotus corniculatus. These forages contained, respectively 0·3 and 22·1 g CT/kg dry matter (DM). The sheep used for the experiments were also fed either white clover or L. corniculatus. Effects of CT were determined by making measurements in the presence and absence of polyethylene glycol (PEG; molecular weight 3500), which binds and inactivates CT. The loss of DM, neutral detergent fibre (NDF), total nitrogen (N) and Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase; EC 4.1.1.39; fraction I leaf protein) from polyester bags suspended in the rumen of sheep was measured. The loss of these constituents from polyester bags suspended in the rumen was used as a measurement of their solubilization. Degradation was defined as the disappearance of Rubisco from white clover and L. corniculatus added to in vitro incubations with rumen fluid obtained from the same fistulated sheep fed either white clover or L. corniculatus.

In the absence of PEG, the in situ loss of Rubisco from L. corniculatus was less rapid than the loss of this protein from white clover when each forage was incubated in the rumen of sheep fed the same diet. Addition of PEG tended to increase the loss of Rubisco from L. corniculatus, suggesting that CT slowed the rates of solubilization of Rubisco from this forage. Effects of rumen fluid were small, but there was some evidence that the rumen fluid in sheep fed L. corniculatus reduced the solubilization of Rubisco from white clover. The action of CT did not inhibit the in situ loss of NDF from either white clover or L. corniculatus.

In the absence of PEG, the in vitro degradation of Rubisco from L. corniculatus was slower when compared to the degradation of this protein from white clover; PEG addition increased the degradation of Rubisco from L. corniculatus, but not from white clover, showing that CT was the causal agent. The addition of CT extracted from L. corniculatus markedly depressed the degradation of Rubisco from white clover, with the effect being completely reversible by PEG. The large subunit (LSU) of Rubisco was consistently degraded at a faster rate than the small subunit (SSU) and added CT had a greater effect in slowing the degradation of the LSU compared to the SSU. There was little difference in the degradation of Rubisco when rumen fluid from sheep fed either white clover or L. corniculatus was used for in vitro incubations.

It was concluded that the action of CT from L. corniculatus reduces the digestion of protein in the rumen of sheep. This effect is predominantly due to the action of CT reducing the degradation of plant protein, although CT also reduced the solubilization of plant protein. The main effects of CT on protein solubilization and degradation seemed to be produced locally by CT present in plant tissue; transfer of these effects through rumen fluid was small in magnitude.

A total of 140 British Friesian cows in their second or later lactation and with a mean calving date of 27 October (s.D. 18 days) were used in a randomized-block experiment over a 3-year period. The experiment was designed to examine the effects of level of concentrate given during the winter period, in addition to ad libitum access to grass silage, on total lactation performance. The silage had a mean dry-matter content and digestible organic matter in the dry matter of 206 and 698 g/kg respectively and the mean inputs of concentrates on the five treatments were 0–64, 0–89, 1–14, 1–38 and 1·59 t/cow (treatments 1–5 respectively). Sixteen replicates per treatment were housed in individual stalls during the winter period in order to facilitate the measurement of silage intake and the remaining animals in each year were maintained as a single group.

All animals in each year grazed together as a single group at pasture at a mean stocking rate of 6–0 cows/ha and without supplementary concentrates.

Level of concentrate supplementation had a significant linear effect on the intake of silage dry matter with the relationship between total intake of silage dry matter over the winter period (kg, y) and concentrate dry matter input (kg, x) being described by equation (1)

The challenge for the next 50 years is to increase the productivity of major livestock species to address the food needs of the world, while at the same time minimizing the environmental impact. The present review presents an optimistic view of this challenge. The completion of genome sequences, and high-density analytical tools to map genetic markers, allows for whole-genome selection programmes based on linkage disequilibrium for a wide spectrum of traits, simultaneously. In turn, it will be possible to redefine genetic prediction based on allele sharing, rather than pedigree relationships and to make breeding value predictions early in the life of the peak sire. Selection will be applied to a much wider range of traits, including those that are directed towards environmental or adaptive outcomes. In parallel, reproductive technologies will continue to advance to allow acceleration of genetic selection, probably including recombination in vitro. Transgenesis and/or mutagenesis will be applied to introduce new genetic variation or desired phenotypes. Traditional livestock systems will continue to evolve towards more intensive integrated farming modes that control inputs and outputs to minimize the impact and improve efficiency. The challenges of the next 50 years can certainly be met, but only if governments reverse the long-term disinvestment in agricultural research.

Despite the successes of the Green Revolution, about a billion people are still undernourished and food security in the developing world faces new challenges in terms of population growth, reduced water resources, climate change and decreased public sector investment. It is also becoming widely recognized that poverty is a cause of environmental degradation, conflict and civil unrest. Internationally coordinated agricultural research can play a significant role in improving food security by deploying promising new technologies as well as adapting those with well-established impact.

In addition to the genetic challenges of crop improvement, agriculturalists must also embrace the problems associated with a highly heterogeneous and unpredictable environment. Not only are new genetic tools becoming more accessible, but a new generation of quantitative tools are available to enable better definition of agro-ecosystems, of cultivar by environment interactions, and of socio-economic issues, while satellite imagery can help predict crop yields on large scales. Identifying areas of low genetic diversity – for example as found in large tracts of South Asia – is an important aspect of reducing vulnerability to disease epidemics. Global strategies for incorporating durable disease resistance genes into a wider genetic background, as well as participatory approaches that deliver a fuller range of options to farmers, are being implemented to increase cultivar diversity.

The unpredictable effects of environment on productivity can be buffered somewhat by crop management practices that maintain healthy soils, while reversing the consequences of rapid agricultural intensification on soil degradation. Conservation agriculture is an alternative strategy that is especially pertinent for resource-poor farmers.

The potential synergy between genetic improvement and innovative crop management practices has been referred to as the Doubly Green Revolution. The unique benefits and efficiency of the international collaborative platform are indisputable when considering the duplications that otherwise would have been required to achieve the same impacts through unilateral or even bilateral programmes. Furthermore, while the West takes for granted public support for crucial economic and social issues, this is not the case in a number of less-developed countries where the activities of International Agricultural Research Centres (IARCs) and other development assistance organizations can provide continuity in agricultural research and infrastructure.

Increasing the efficiency with which crops use supplied nitrogen (N) can minimize the impact on the environment. In the growing seasons 1990/91 to 1992/93, the effects of different cropping systems on yield, N uptake by the grain and apparent N-use efficiency (NUE) of the grain of winter wheat and winter barley were investigated in a factorial field experiment at Hohenschulen Experimental Station near Kiel in NW Germany. The crop rotation was oilseed rape–winter wheat–winter barley, and soil tillage (conservation tillage without ploughing, conventional tillage), application of pig slurry (none, autumn, spring, autumn+spring), mineral N fertilization (0–240 kg N ha−1) and application of fungicides (none, applications against pathogens of the stems, leaves and ears) were all varied. Each year, the treatments were applied to all three crops of the rotation and were located on the same plots.

Averaged over all factors, wheat yield was >7 t ha−1 dry matter in all years and N uptake of the harvested grain varied between 140 and 168 kg N ha−1. Pig slurry application in autumn increased grain yield and N uptake more than spring slurry in two out of three years. Mineral N unfertilized wheat yielded only 5·3–6·3 t ha−1 depending on the year, mineral N fertilization increased wheat yield up to 8 t ha−1. Barley yield was lower than wheat yield, ranging from 4·5 t ha−1 in 1993 to 6·3 t ha−1 in 1992. Unlike wheat, spring slurry N affected barley yield and N uptake more than autumn slurry.

Wheat apparently utilized 12–21% and barley up to 13% of the applied slurry N for its grain development. In 1991, the highest apparent slurry N-use efficiency (SNUE) of wheat and barley occurred after the late spring slurry application. However, in the following years, autumn SNUE of wheat was similar to (1992) or higher than (1993) spring SNUE, presumably because of vigorous tiller growth before winter. Additionally applied mineral fertilizer N decreased SNUE.

Apparent mineral fertilizer N-use efficiency (FNUE) was higher than SNUE and ranged in wheat from 40 to 59% and in barley between 19 and 37% of the applied mineral fertilizer N. FNUE decreased with increasing N fertilization.

To improve the N-use efficiency of both slurry N and mineral fertilizer N, more information is needed about the combined use of both N sources, with special emphasis on split applications of slurry as is common practice for mineral N fertilizer.

Barley (cv. Beecher) was grown at two sites (Jindiress and Breda) in northern Syria, chosen for their contrasting edaphic and climatic conditions. At both sites, three fertilizer treatments were applied zero (Z), 60 kg P2O5/ha (P), and 60 kg P2O5/ha with 60 kg N/ha (NP) and measurements made of shoot and root growth, and water use.

The growth of crops not given fertilizer was similar at both sites and early growth was increased by the application of fertilizers. However, at maturity, yield was increased at Jindiress by giving N and P together, but not by P alone, while at Breda P alone increased yields but additional N produced no additional yield. There were marked effects of fertilizer on crop development at Jindiress; anthesis and maturity were about 14 days earlier in the NP treatment than in the Z treatment.

Root growth was also affected by fertilizer applications and there were small but significant differences in growth between the sites. The proportion of root weight: total plant weight was greater than commonly observed in temperate cereals and there were substantial differences between the sites in the pattern of root distribution within the soil profile.

The total amount of water used by the crops differed between the sites but was largely unaffected by fertilizer treatment at each site. Evapotranspiration during the winter when the soil was recharged with water was about 50% of the seasonal total. At Jindiress, the pattern of water extraction from the profile and the root distribution were similar before flowering but at Breda, there was no correspondence. Rates of water inflow varied with both site and time.

Crop characteristics that may be associated with increased yields are discussed. Deeper, more extensive rooting is unlikely to be useful in such regions but rapid early growth of both shoots and roots may allow water to be used more efficiently.

A method is proposed for correcting for competition effects in yield trials by joint regression of plot yields on to the yields of neighbours. Estimation of the variety effects and competition coefficient along with tests of significance are described for a sugar-beet trial with single-row plots where competition effects are assumed to extend only to plants in immediately adjacent rows. For designs which are balanced for neighbouring varieties it is feasible to estimate separate varietal competition coefficients which may be partitioned into components for sensitivity and aggressiveness. An example is given of this extended model fitted to a competition diallel of seven species. While species differed in their sensitivity to competition there was no essential difference between inter- and intra-species behaviour. The model is used to assess comparative varietal performance in monocultures from performance in small plot trials.

(Note that the general term ‘variety’ is used throughout this paper to refer to progenies at any stage in a selection programme.)

Seventy-eight Finnish Landrace × Dorset Horn ewes in lamb to Suffolk rams were slaughtered serially between 50 and 145 days of gestation. The mean litter size was 2·7. The daily feeding regime aimed to provide each ewe with 15 MJ of metabolizable energy (ME) in the first month of gestation and 9·4 MJ in the second and third. Thereafter the ewes were provided with a basal intake of either 9·6 MJ (low plane, LP) or 13·4 MJ (high plane, HP) plus 1·3 MJ for each foetus.

For ewes with 2, 3 and 4 foetuses the mean percentage changes in maternal body weight over pregnancy were respectively — 5, — 10 and — 14 (LP) or + 3, — 2 and — 6 (HP). Changes in weights of blood, liver and the empty gastro-intestinal tract through gestation varied with the plane of nutrition but not with number of foetuses. In contrast, udder weight at parturition was dependent on number of foetuses but not on plane of nutrition.

Increased hydration of the maternal tissues in late pregnancy tended to mask concurrent losses of body fat. For example, over the last 2 months, HP ewes carrying quadruplets lost on average 1·0 kg in body weight but 5·5 kg of (chemically determined) fat. The latter was lost at a rate which increased up to an average of 170 g/day over the last 2 weeks of pregnancy. Net changes in body protein were estimated to be relatively small, but there was some redistribution, including loss from muscle and gain by the udder. There was no evidence of any demineralization of the maternal skeleton.

The practical significance of the changes in body composition is discussed, in particular that of the increasing rates of loss of body fat with increasing litter size. It is suggested that the dangers implicit in these rates of fat loss must be taken into consideration when deciding on dietary regimes and the timing of breeding cycles for highly prolific ewes, or indeed when embarking on a programme of increased prolificacy.

Experiments were carried out on oil-seed rape, variety Zollerngold, to determine the effects on flower and pod development when (1) the supply of carbon assimilates was reduced by shading or leaf removal at different stages of development or (2) the supply of assimilates to the more apically positioned flowers or pods on the terminal raceme was increased by removing 15 of the most basal flowers or pods.

A decrease in the production of carbon assimilates led to fewer flowers and pods developing to maturity and when the stress continued over most of the period of pod development the pods were smaller and had fewer seeds which were also lighter in weight.

Removal of the 15 basal flowers or pods led to more of the apically positioned flowers developing into mature pods and the other pods becoming heavier with bigger husks, heavier seeds and sometimes a greater number of seeds.

The results of a shading experiment in a controlled environment cabinet suggest that stresses in the supply of carbon assimilates around the time of anthesis are particularly harmful since in addition to reducing the number of pods which develop they appear to restrict the capacity for compensatory growth in the pods that remain when the supply returns to normal.

Three wheat experiments are described in which a range of plant populations were shaded during different periods of development; in two of the experiments plant thinning was also carried out at a number of growth stages. Shading during the period of ear development caused an appreciable decrease in grain yield by decreasing the number of grains per ear. Shading during the grain filling period also reduced grain yield, this being brought about by decreased grain size. Thus in contrast to the barley experiments reported earlier (Willey & Holhday, 1971), these particular results gave no indication of a potential surplus of carbohydrate for grain filling and an associated limited ear capacity. However, when plant thinning was carried out at anthesis to make more carbohydrate available for grain filling in the remaining ears, grain yield per ear did not increase. It is argued, therefore, that grain yield probably was determined at least partly by a limited ear capacity. Plant thinning at earlier stages showed how the development of competition during the ear development period progressively reduced the potential capacity of the ear; the greater competition of higher plant populations accelerated this reduction in ear potential.

From an examination of the effects of plant population, it is suggested that the number of grains per ear is the component having greatest influence on the decline in grain yield at above-optimum populations. The possible importance of the number of grains per unit area as an indicator of ear capacity on an area basis, and as a determinant of grain yield per unit area, is emphasized. A close relationship between grain yield per unit area and number of grains per unit area is illustrated for a number of plant-population response curves, and it is suggested that the decrease in grain yield at high populations is probably determined by a decrease in the number of grains per unit area. Evidence is presented to substantiate the idea put forward in the barley paper that this decrease in the number of grains per unit area may be attributable more to a lower production of total dry matter by the high populations during the later stages of ear development, than to an unfavourable partitioning of such dry matter between the ear and the rest of the plant.

Teat orders were determined for 76 litters of Large White and Large White × Landrace pigs. Regression analysis within litters revealed a relationship between suckling position and weight both at birth (P<0·01) and at 3 weeks of age (P<0·001), with the heavier piglets tending to occupy the more anterior teats. The correlation coefficients, however, were very small (r = –0·16 and –0·22 respectively). The correlation between birth weight and 3-week weight was much larger (r = +0·47); and a comparison of pairs of litter-mates showed that a difference in birth weight of 0·25 kg or more persisted at 3 weeks in the majority of cases, regardless of which piglet suckled the more anterior teat. Birth weight accounted for much more of the variation in 3-week weight than did teat number, and, when the effect of birth weight had been taken into account, teat number accounted for only an additional 2·3% of the variation. Even so, the anterior teats did appear to confer some advantage which was independent of that of the birth weight of the piglets suckling these teats. From the results of this and other studies it is concluded that there is only a weak relationship between suckling position and weight at birth and 3 weeks. Other unidentified factors are probably of more importance for the within-litter variation in weight gain of suckling pigs.