In beef suckler herds, reproductive failure is a major cause of financial loss during a bovine viral diarrhoea (BVD) outbreak due to reduction in the numbers of calves, increased calving spread and the financial implications of dealing with infertile cows. These losses may be hidden and/or not fully attributed to BVD. A model of herd dynamics was built and combined with an epidemiological model to encapsulate the disruptions to reproduction that BVD may cause in beef suckler herds and to estimate the associated financial consequences of such disruptions.

Results from the model suggest that the average losses associated with BVD in Scottish beef suckler herds via impaired reproduction alone may vary between £43 and £22/cow/year during the course of a BVD epidemic. These results indicate that an outbreak can be costly and these losses may be hidden by the use of low risk management practices such as a long breeding season, not only in herds with no evidence of antibodies but also in herds where there are some antibody positive (immune) animals.

Descriptions of entire lactations were investigated using six mathematical equations, comprising the differentials of four growth functions (logistic, Gompertz, Schumacher and Morgan) and two other equations (Wood and Dijkstra). The data contained monthly milk yield records from 70 first, 70 second and 75 third parity Iranian Holstein cows. Indicators of fit were model behaviour, statistical evaluation and biologically meaningful parameter estimates and lactation features. Analysis of variance with equation, parity and their interaction as factors and with cows as replicates was performed to compare goodness of fit of the equations. The interaction of equation and parity was not significant for any statistics, which showed that there was no tendency for one equation to fit a given parity better than other equations. Although model behaviour analysis showed better performance of growth functions than the Wood and Dijkstra equations in fitting the individual lactation curves, statistical evaluation revealed that there was no significant difference between the goodness of fit of the different equations. Evaluation of lactation features showed that the Dijkstra equation was able to estimate the initial milk yield and peak yield more accurately than the other equations. Overall evaluation of the different equations demonstrated the potential of the differentials of simple empirical growth functions used in the current study as equations for fitting monthly milk records of Holstein dairy cattle.

Obtaining accurate estimates of the metabolizable energy (ME) intake (MEI; MJ/day) of individual grazing ruminants is an important requirement for effective nutritional management and genetic selection of energy efficient ruminants. Diet digestibility and the daily methane production rate (MPR; MJ/day) of ruminants can be closely linked with their MEI, so published data were examined to determine whether MEI could be accurately estimated from digestibility, MPR and other parameters able to be measured on grazing animals. Four modelling approaches were assessed or developed to estimate MEI: (i) a published fixed proportional relationship between the non-metabolizable losses of MPR and urinary energy (UE; MJ/day); (ii) the proportion of energy digestibility (EngDig); (iii) MPR and the ruminal factors that influence the stoichiometric relationships between MPR and MEI; and (iv) the calculated ME arising from rumen fermentation (MEf; MJ/day). Data to develop the models (n=61) were collected across three publications (Paper) where the Paper effect was treated as a random-effect variable. Each of the models (1–4) was challenged with an independent data set (n=19). The inclusion of MEf (P=0·01) to predict MEI [MEI=0·18 (2·03)+3·42 (0·36)×sqrt(MEf) (d.f.=57; residual log likelihood=173·6)] had the lowest mean square error of prediction (MSEP) when challenged with the independent data set; mean bias of −0·42 MJ/day (P<0·05), MSEP=0·68 MJ/day and the bias, slope and random components of the MSEP were, as a proportion, 0·26, 0·13 and 0·61, respectively. None of the models estimated MEI with sufficient accuracy to be useful for identifying individual animals with above average energetic efficiency. A critical limit to any model seeking to estimate MEI from MPR and fermentation traits appears to be the variation between animals and between diets, in the proportion of digested energy which is fermented relative to that which is made available by mammalian digestion, and this is evaluated.

During spring, perennial ryegrass tillers change from vegetative to reproductive growth in response to photoperiod and undergo irreversible morphological changes. The effect of latitude and meteorological factors on the timing of reproductive initiation and ear emergence (EE) were measured in the field on 40 vernalized spaced plants for each of eight cultivars. The measurements were made at two latitudes in Ireland (Moorepark 52°N, Crossnacreevy 54°N). There was a significant effect of site and cultivar on all the variables measured. Cultivar initiation responded to a specific photoperiod but detection through apical development incurred a small variation due to growing conditions affecting the time taken for a visible change in apical morphology to occur. When converted from photoperiod to initiation date this variance was minimal (±6 min). Timing of EE was dependent on growing conditions not photoperiod and so was specific to the studied conditions. As cultivar rank order for EE date was largely retained, there was a very strong correlation with published UK Plant Breeders Rights (PBR) heading dates for these cultivars, which in turn had a strong relationship with the ear initiation (EI) dates (R2=0·95). The latter relationship was sufficiently robust to allow estimation of photoperiod for any cultivar on the EU Common Catalogue based on its published heading date from Crossnacreevy, where the UK PBR trials are conducted. As photoperiod can be converted to calendar date by reference to latitude, this relationship can also be used to estimate the EI date for sites at latitudes other than those in the current study.

Seed composition in soybean [Glycine max (L) Merr.] has not been well investigated under charcoal rot infestation under irrigated and non-irrigated conditions. The objective of the present experiment was to assess seed composition and nitrogen fixation under these conditions. No significant differences in protein levels in the moderately resistant germplasm line DT97-4290 were observed under these conditions. Under irrigation, protein concentration was significantly (P⩽0·05) higher for the susceptible cultivars Egyptian and Pharaoh under non-infested than infested conditions. The opposite response for protein was observed under non-irrigated conditions for Pharaoh. Oleic acid concentration was significantly (P⩽0·001) higher in susceptible cultivars under infested conditions. The concentration of linolenic acid in susceptible cultivars was significantly lower under infested conditions. The enrichment of Delta 15N in susceptible cultivars under infested conditions indicated that nitrogen fixation was substantially inhibited, but soil nitrogen was used for compensating for atmospheric nitrogen inhibition. These results indicate that charcoal rot infection may alter seed composition and nitrogen fixation in soybean. The alteration in seed composition depended on cultivar susceptibility to charcoal rot and irrigation management.

The transition from conventional to organic farming is accompanied by changes in soil chemical properties and processes that could affect soil fertility. The organic system is very complex and the present work carries out a short-term comparison of the effects of organic and conventional agriculture on the chemical properties of a silty loam soil (Xerofluvent) located in the Guadalquivir River Valley, Seville, Spain, through a succession of five crop cycles over a 3-year period. Crop rotation and varieties were compared in a conventional system using inorganic fertilizer and two organic systems using either plant compost or manure. At the end of the study, organic farming management resulted in higher soil organic carbon (OC), N and available P, K, Fe and Zn. The available Mn and especially Cu values did not show significant differences. In general, treatment with manure resulted in more rapid increases in soil nutrient values than did plant compost, which had an effect on several crop cycles later. The present study demonstrated that the use of organic composts results in an increase in OC and the storage of nutrients, which can provide long-term fertility benefits. Nevertheless, at least 2–3 years of organic management are necessary, depending on compost characteristics, to observe significant differences. Average crop yields were 23% lower in organic crops. Nevertheless, only two crops showed statistically significant differences.

In Sub-Saharan Africa, cowpea is well known for its ability to survive under conditions of water stress and it plays an important role in regions where drought is the factor most limiting to crop yield. In the present study, the drought tolerance levels of 20 African cowpea accessions from three countries were evaluated. A number of the genotypes showed drought tolerance, the merits of stomatal behaviour and cell membrane stability to assess drought tolerance was demonstrated. Damage to the cell membranes caused by drought was less in tolerant accessions. Stomatal opening was also better regulated; the opening was smaller under drought conditions, thus reducing transpiration (T). The wide range of drought tolerance observed among the accessions suggests the possibility of breeding drought-tolerant cultivars in cowpea. Drought-tolerant accessions included Bafoussam 1, M.66, Bafoussam 3, Hluhluwa, Bafoussam 4, Balen, Makueni, Bafoussam 2 and Okhalweni and these could be recommended to breeders as valuable material for drought tolerance improvement in cowpea.

Watermelon is a crop with a high water demand and is frequently grown under conditions of higher than normal root-zone salinity. In the present study, seedlings of watermelon (cv. Fantasy, Citrullus lanatus (Thunb.) Matsum & Nakai) were grown either ungrafted or grafted on three rootstocks: Strong Tosa, S1 (both Cucurbita maxima×Cucurbita moschata), or Emphasis (Lagenaria siceraria). All the plants were exposed to an NaCl-induced salinity stress (electrical conductivity, EC=2·2, 4·0, or 6·0 dS/m). The vegetative growth of all the plants substantially reduced after 2 weeks of exposure to 6·0 dS/m; however, growth of the plants grafted on Strong Tosa reduced less than that of the others. The leaf water content and specific leaf area (SLA, m2/g) decreased with an increasing salinity in grafted plants, but not in ungrafted plants. Salinity induced an increase of superoxide dismutase (SOD) activity in grafted plants up to two-fold depending on the rootstock, whereas it had no effect on this enzyme activity in ungrafted plants. Leaf Na+ concentration increased with increasing salinity in ungrafted and S1 grafted plants, whereas there was no significant leaf Na+ accumulation in Emphasis and Strong Tosa grafted plants. Leaf K+ concentration was affected by the rootstock but not by salinity, thus, the ability to keep a high K+/Na+ ratio was achieved mainly by limiting leaf Na+ concentration. The rootstock determined the leaf Cl− accumulation, with lower overall concentrations found if plants were grafted on the S1 rootstock than on Emphasis or ungrafted plants. Salinity significantly decreased the leaf NO3− concentration on Emphasis grafted plants only, while the NO3−/Cl− ratio was reduced in all the rootstocks. The capacity of Strong Tosa to withstand salt stress better than other tested rootstocks was probably due to the ability to induce anatomical adaptation (SLA) and SOD activity in response to salt stress, and also to the efficiency of Na+ exclusion from the shoot.

A series of studies were carried out to measure the methane (CH4) production by Japanese goats fed 19 different diets (D1–D19) varying in nutritive composition in the open circuit respiration chamber (RC) and to compare them with CH4 estimated by the in vitro gas production test (IVGPT). Adult Japanese goats (>2 years old) with a mean body weight of 26±5·4 kg were used in these experiments. Each diet was fed to four randomly selected goats and feeding was carried out at 1·1 maintenance (M) as per National Research Council (NRC) (1981) for goats. Average CH4 emission by goats in the RC ranged from 0·23 to 0·39 (mean value 31 ml/g dry matter intake (DMI)); when it was expressed as a proportion of gross energy or, with methane conversion rate (MCR), it ranged from 5·0 to 8·2, with an average of 6·6. Incorporation of by-products like sweet potato vine silage (SPVS) (P=0·016), dried pumpkin (P=0·052) and brewers' grain in the diet suppressed (P<0·01) methanogenesis in goats, when compared with that of standard farm diet (D1). The CH4 output measured in the RC was very close to that estimated from the gas collected after 24 h and higher after 48 h of in vitro incubation. Although composition of the diets' acid detergent fibre (ADF) had a significant effect on methane emission, methane output estimated by IVGPT was very close to that measured in the RC demonstrating that this system could be used to estimate the CH4 production potential from diets in preparing a database and also in the planning of mitigation strategies in small ruminants to improve their performance as well as to reduce greenhouse gas emissions.

This group, which is concerned with the applications of mathematics to agricultural science, was formed in 1970 and has since met at approximately yearly intervals in London for one-day meetings. The fortieth meeting of the group, chaired by Dr John Thornley of Henley-on-Thames, UK and the Centre for Nutrition Modelling, University of Guelph, Canada, was held in the Kohn Centre at the Royal Society, 6 Carlton House Terrace, London on Friday, 11 April 2008 when the following papers were read.