Sewage sludge applications were made to two freely draining grassland sites of contrasting rainfall in SW England in 1991/92 and 1992/93. Applications were made in autumn, winter and spring (following first silage cut), with raw sludge applied by injection and digested sludge both as a surface application and injection at application rates of 140 m3/ha and 125 m3/ha for raw and digested sludge respectively. A tine-only treatment and an untreated control were also included. Nitrate leaching was measured following autumn and winter applications using porous ceramic cups. Average NO3--N concentrations in drainage water exceeded the EC limit for potable water of ll·3 mg/l following autumn injection of digested sludge at one site for both years. Average concentrations in drainage water for all other sludge treatments were below this limit. Up to 24, 11 and 6% of the applied total N was leached from injected digested, surface-applied digested and injected raw sludge respectively. Autumn applications resulted in greater leaching losses than winter application. Leaching losses were greater from digested than from raw sludge when both were applied by deep injection. Injection of digested sludge as compared to surface application exacerbated nitrate leaching losses. Herbage yields and N recoveries were better from later sludge applications, with the exception of injection treatments, where spring sludge injection during a prolonged dry period resulted in yield reductions as compared to autumn injection.

Milled grass particles were coated with n-alkanes and suspended in a xanthan gum solution. Experiments snowed that grass particles could be coated uniformly with alkanes by means of a rotary evaporator. Further experiments showed that the grass particles, in stable xanthan gum suspension, could be accurately dispensed. The coefficients of variation of the alkane content per dose delivered by means of a dosing gun and syringe were 2·6 and 2·3%, respectively. There was no significant difference between the concentration of faecal alkanes derived from alkanes dosed in suspension-form and alkanes placed directly into the rumen.

Experiments were designed to assess the effects of cover crops, compared with bare stubble, on the establishment and yield of a following crop of vining peas sown in March. The cover crops of winter wheat (to simulate self-sown wheat) or winter rye, and bare stubble, were ploughed in on different dates: 1 December, 1 February or 1 March. Cover crops were destroyed with or without the use of herbicide. The three experiments in 1990/91, 1991/92 and 1992/93 were sited on a free-draining, sandy loam soil at Thornhaugh, Cambridgeshire.

The cover crops, sown as soon as possible in September following a winter wheat crop, had low dry matter (DM) production and nitrogen uptake in the dry autumns of 1990 and 1991, but in the third experiment (1992/93), autumn rainfall was higher than the long-term average and DM production and N uptake were greater. Cover crops reduced the overwinter soil mineral nitrogen (SMN) content in all 3 years compared with bare stubble. However, in spring, SMN increased where cover crops had been incorporated, due to the mineralization of the cover crop residues. Rye captured more nitrogen than wheat.

Vining pea vigour and maturity at quick-freezing harvest stage were not affected by cover crop, destruction date or method in any of the three seasons.

On the light soil, satisfactory seedbeds were achieved after ploughing at all three timings for experiments in 1990/91 and 1992/93 and vining pea yields were not reduced by cover crops or by destruction date or method. However, delayed ploughing in February and March in the 1991/92 experiment resulted in lower vining pea yields compared with ploughing in December. This was due to poor seedbeds after late ploughing rather than cover crop, stubble treatment or method of destruction.

The hyperinsulinaemic euglycaemic clamp technique was used to determine the effect of recombinant bovine growth hormone on the response to insulin in castrate male Corriedale sheep. Saline or growth hormone (6·3 μg/min/animal) was infused into four sheep from the beginning of each experiment for 9 h, such that eight clamp experiments were performed, four with growth hormone and four controls. After a basal period of 3 h, insulin was sequentially infused at 1, 3 and then 6 mU/kg/min for 2 h each and the plasma glucose concentration was maintained at the value noted during the basal period by a variable rate of glucose infusion. Short-term growth hormone infusion decreased the glucose infusion rate (GIR) required to maintain eugylcaemia as well as the rates of glucose appearance and disappearance. The glucose metabolic clearance rate (MCR) was also decreased by the growth hormone treatment at all rates of insulin infusion, the average decrease ranging between 20 and 30%. The insulin concentration causing half maximal stimulation of glucose MCR and GIR was unchanged by growth hormone treatment. Endogenous glucose production was not consistently affected by either the growth hormone or insulin treatments. The results of this experiment demonstrate that growth hormone decreases the responsiveness of peripheral tissues to insulin, possibly at a site beyond the receptor.

This group, which is concerned with the applications of mathematics to agricultural science, is sponsored by the Biotechnology and Biological Sciences Research Council. It was formed in 1970, and has since met at approximately yearly intervals in London for one-day meetings. The twenty-seventh meeting of the group, chaired by Professor D. E. Beever of the Department of Agriculture, University of Reading, was held in the Wellcome Meeting Room at the Royal Society, 6 Carlton House Terrace, London on Friday, 13 October 1995, when the following papers were read.

A grazing experiment was conducted for 8 weeks in the spring/summer of 1993 at Palmerston North, New Zealand, to study the effects of condensed tannins (CT) in Lotus corniculatus (birdsfoot trefoil cv. Grasslands Goldie) upon the lactation performance of ewes rearing twin lambs. Effects of CT were evaluated by studying the responses of ewes to twice daily oral supplementation with polyethylene glycol (PEG; MW 3500), which binds and inactivates CT. A rotational grazing system with restricted feed allowance was used. Measurements were made of pre- and post-grazing herbage mass, the composition of the feed on offer and diet selected, voluntary feed intake (VF1), milk yield and composition, liveweight gain and wool production. The concentration of metabolites in rumen fluid and in blood plasma was also measured. Lotus contained 35–5 g total nitrogen and 44–5 g total CT/kg dry matter in the diet selected, with an in vitro digestibility of 73%. At peak lactation (weeks 3 and 4) milk yield and composition were similar for control (CT-acting) and PEG-supplemented (CTinactivated) ewes but, as lactation progressed, the decline in milk production and in the secretion rates of protein and lactose were less for control than for PEG-supplemented ewes. In mid and late lactation (weeks 6–11), control ewes secreted more milk (21 %), more milk protein (14%) and more lactose (12%) than PEG-supplemented ewes. Milk fat percentage was lower for control than for PEG-supplemented ewes, but secretion rates of fat were similar for the two groups. VFI, liveweight gain and wool growth were similar for both groups. Plasma urea and glucose concentrations were lower for control than for PEG-supplemented ewes, but concentrations of non-esterified fatty acids (NEFA), growth hormone and insulin were similar for the two groups. The concentrations of ammonia and molar proportions of iso-butyric, iso-and n-valeric acids in rumen fluid were lower for control than for PEG-supplemented ewes; molar proportions of acetic, propionic and H-butyric acids were similar for the two groups. It was concluded that for ewes rearing twin lambs grazing L. corniculatus, the action of CT increased milk yield and the secretion rates of protein and lactose without affecting VFI, thereby increasing the efficiency of milk production. The increased milk production did not appear to be mediated by effects on plasma concentrations of growth hormone or insulin.

Twelve red deer (Cervus elaphus) hinds from a research facility in Eastern Scotland were randomly divided into two groups between June and September to study the physiological response to three management practices, given sequentially, which were expected to cause increasing levels of stress (herding; herding and handling; and herding, handling and a veterinary procedure). One group of animals received a long-acting neuroleptic (LAN; perphenazine enanthate and zuclopenthixol acetate) on three occasions at 4-week intervals. Automatic blood sampling equipment (ABSE) was used to obtain blood samples remotely before, during and after the application of each of the stressors. The plasma concentrations of cortisol, creatine phosphokinase (CPK), aspartate aminotransferase (AST), total protein (TP), 3,5,3'-triiodothyronine (T3), thyroxine (T4) and testosterone (T) were measured and heart rates recorded. The ABSE provided a useful means of collecting blood samples without the superimposition of stress factors associated with conventional sampling. Increases in plasma concentrations of cortisol (P <0·01), CPK (P <0·01) and AST (P <0·05) were observed in all animals in response to all three management practices. There were smaller increases in plasma cortisol concentration (P <0·05) in those animals treated with LAN. The results suggested a degree of habituation of the hinds to some procedures common to all treatments, in agreement with previous analysis of the behavioual response of these animals. Peaks of heart rate were recorded over the 30-min period stressors were applied. Higher heart rates and T3 and T4 concentrations were observed in LAN-treated animals. Heart rates returned to baseline more rapidly in the LAN-treated animals. Higher plasma concentrations of testosterone were recorded in the first week of the study (P <0·001). Physiological and behavioural evidence supports the view that LANs are effective long-term tranquillizers in red deer.

Ammonia volatilization and denitrification were measured in a ryegrass field in Denmark after direct injection and application with trail hoses of an untreated cattle slurry and an anaerobically digested slurry in late May-early June 1993 and 1994. Ammonia volatilization was measured using a windtunnel system for a period of 8 days after slurry application. Denitrification was measured for a period of 21 days after slurry application. In an adjacent field experiment, nitrogen-uptake (N-uptake) was determined in the first two cuts of the ryegrass harvested after slurry application. N losses through ammonia volatilization were larger in 1993 than in 1994 due to differences in climatic conditions. Ammonia volatilization was lowered substantially (47–72%), when slurry was injected compared with surface application. In 1993 the loss from surface-applied digested slurry was only 35% of total ammoniacal nitrogen (TAN), while the loss from the raw slurry was 47%. There were no significant differences in ammonia volatilization from the two slurry types in the other experiments. N losses through denitrification were low (< 2% of TAN), but there were clear differences in the losses, depending on slurry type, application method and experimental year. Injection of the slurry gave a larger N-uptake in the first cut of grass compared to the trail-hose application. In 1993 N-uptake from the digested slurry treatment gave significantly larger N-uptake compared to the raw slurry in the first cut.

The pre-natal and post-natal development of wool follicles in sheep of five genotypes with contrasting wool types was examined to provide data on which to base studies of physiological factors affecting wool type via follicle development. This study was conducted following Autumn mating in 1992 at Palmerston North, New Zealand (40° S, 176° E). The rate and timing of follicle development in midside skin samples from Romney, Merino, Merino × Romney (M × R), Drysdale and Wiltshire foetuses and lambs collected at weekly intervals from days 76 to 143 of gestation and 1, 3, 7, 12 and 32 weeks after birth were examined.

Primary (P) follicle density had a similar pattern of development in each of the genotypes, although the Merino had a significantly greater density of P follicles than the other genotypes. There was a difference in the rate of P follicle maturation between genotypes with the Drysdale, Wiltshire and M × R completing P follicle maturation before the other two genotypes. However, the majority of P follicles in all genotypes were producing fibres by 111 days of gestation. It was concluded that the small differences in the density and time of development of the P follicles could not cause the differences in wool type between genotypes.

The pattern of development of the secondary (S) follicle population was examined by comparing S: P ratios. The initiation of S follicles began at similar ages in the five genotypes, but initiation was completed earlier in the Romney, Drysdale and Wiltshire than in the Merino and M × R, as indicated by a significant genotype by age interaction (P < 0·001). There was no difference between genotypes in S:P ratio from 90 to 104 days of gestation. The S:P ratio of the Romney, Drysdale and Wiltshire did not change significantly from 104 days of gestation until the end of the study, indicating that few S follicles were initiated in these genotypes after 104 days of gestation. The M × R data showed a significant increase in S:P ratio until 119 days of gestation and the Merino S:P ratio increased until 126 days of gestation.

The period between days 90 and 125 of gestation was identified as being the critical period for the development of different follicle populations in Merino and non-Merino genotypes and it is this period which should be the focus for studies to determine physiological factors controlling secondary follicle development.

An experiment to measure the effects of cold conditions upon heat production in young sambar (Cervus unicolor) and red deer (Cervus elaphus) was conducted during winter 1994, at Massey University, Palmerston North, New Zealand (NZ), using four young animals of each species. Animals were fed a pelleted concentrated diet (total N 29g/kg DM; 11·9MJ metabolizable energy (ME)/kg DM) at approximately maintenance ME intake (MEI). Hair coat characteristics were measured on samples cut from a patch on the mid-side of the body. Pairs of animals (one sambar and one red deer) were confined in two open circuit calorimetry chambers (one deer in each chamber) for 18-day periods, and oxygen consumption was measured at 20 and 5 °C, with and without simulated wind (6 km/h). Heat production was calculated as 20·5 MJ/1 oxygen consumed.

Hair coats of sambar deer were less deep, lighter in weight (g/m2) and contained a lower proportion of undercoat than those of red deer. Fibre length of both guard hairs and undercoat were shorter in sambar deer than in red deer, whilst fibre diameter of both guard hairs and undercoat was greater in sambar deer. Heat production (HP) at 20 °C was lower in sambar than in red deer (P <0·05; 0·46 v. 0·48-0·53 MJ/kgW0·75 per day). Increases in HP from 20 to 5 °C and from 20 °C to 5 °C W (i.e. with wind effect) were greater in sambar than in red deer (P < 0·01; 34 v. 16% and 44 v. 20%, respectively). Calculated lower critical temperatures (LCT) were higher for sambar than for red deer (P < 0·10) both in the absence (0 km/h; 11·6 v. 8·9 °C) and in the presence of wind (6 km/h; 140 v. 11·1 °C). Under field conditions, young sambar deer are likely to require more shelter and better feeding during cold weather than do red deer.

In a 15-week animal-house experiment, 24 steers were offered one of six diets based on molasses and ad libitum barley straw. Three levels of dietary nitrogen (N) and three levels of dietary phosphorus (P), in factorial combination, were formulated by the addition of urea, formaldehyde-treated wheat gluten and monosodium orthophosphate. Food intake, liveweight gain, plasma metabolites and P kinetics were measured under dietary regimens similar to those experienced by cattle grazing Australia's northern semi-arid rangelands.

The adverse effect of the low dietary N on both liveweight change and feed intake was greater and more immediate than that of the dietary P deficiency. The reduction in feed intake due to the P deficiency approached that caused by the N deficiency after 10 weeks. Under conditions of adequate dietary N, there was a trend for the effects of P deficiency on liveweight gain to be exacerbated. Dietary N and P deficiency reduced the concentrations of plasma urea-N and inorganic P respectively. Dietary N deficiency had no effect on cortical rib bone thickness but P deficiency markedly decreased bone thickness. Faecal endogenous loss of P and P absorption efficiency ranged from 9 to 21 mg/kg LW and 0·63 to 0·82 respectively for P intakes from 6 to 41 mg·kg LW. Faecal endogenous losses were closely related to dry matter intake and plasma inorganic P together. Dietary N deficiency affected the efficiency of absorption of P.

The results of this experiment indicate that cattle consuming diets containing low levels of N and P require supplementary N and P in combination to avoid severe depletion since an increase in N intake alone exacerbated the P deficiency. The results are also discussed in relation to the published findings regarding P metabolism and the implications for the calculation of P requirements.

The results of six experiments on growing cattle weighing 140–480 kg, and with liveweight gains of —0·46 to 1·11 kg/day, were reanalysed to provide estimates of their phosphorus (P) requirements. The 158 data sets were from individually penned cattle offered barley straw-based diets ad libitum with dry matter digestibilities of 0·53–O·65, or from cattle grazing tropical pastures with in vitro dry matter digestibilities ranging from 0·50 to 0·62. Various concentrations of dietary energy, nitrogen (N), calcium (Ca) and P were imposed during the course of the experiments with the penned cattle and various rates of application of P fertilizer changed the botanic and nutrient composition of the forages available to the grazing cattle. The P balances and P kinetics of the cattle were studied using 32P as a tracer.

Over the range of P intakes normally observed in cattle consuming forage diets (10–60 mg/kg LW), the coefficient of P absorption was high and not affected by age or liveweight. The regression coefficient relating P intake to P absorption was 0·77 for unsupplemented grazing cattle and 0·82 for penned supplemented cattle. When the plasma inorganic P concentrations were < 50 mg/1, urinary P excretion of the penned cattle was low, as were the endogenous faecal P losses of both the penned and grazing cattle. These losses were concluded to represent obligatory losses and were related to dry matter intake (r = 0·73) in the range 9–17 mg P/kg LW.

The total P requirements of growing cattle were estimated as g/day and g/kg DM intake from this data. The requirements of cattle consuming forage diets were 40–50% lower than those published by the Agricultural and Food Research Council (AFRC 1991), even though the same equation for the net requirements for growth was utilized.

Measurements of grazing, ruminating and idling time and number and duration of bouts of these activities were made on cows grazing a perennial ryegrass-white clover sward on a number of different occasions between 8 May and 10 July 1990 at the North Wyke Research Station, Devon, UK. Repeatabilities, calculated using the residual maximum likelihood method, were low for all measurements, the highest being for idling time. Coefficients of variation were generally lower between periods than between animals for total activity times and ruminating and idling bout duration but were higher for the number of bouts of all activities and for meal duration. Grazing time and meal duration increased significantly as the season progressed, while the number of bouts of all activities declined. Behaviour was not significantly correlated with meteorological conditions. There were no significant correlations between production traits and mean behaviour of cows across periods.

This study (conducted in Debre Zeit, Ethiopia in 1993) examined (i) the effect of source of inoculum on in vitro dry matter (DM) digestibility (1VDMD) and gas production (GP) and (ii) the IVDMD, GP and in sacco degradability as predictors of in vivo DM digestibility (DMD) and intake. Six ruminally cannulated male sheep (used in the degradability studies and from which rumen fluid was harvested for the in vitro studies) and six intact sheep (from which faeces for reconstitution was obtained) were given teff straw ad libitum supplemented with 200 g/day of concentrate (1:1 mixture of noug (Guizotia abyssinica) cake and wheat middlings). In determining IVDMD on 26 feeds, pepsin-HC1 digestion was replaced with neutral detergent extraction. Microbial GP was measured on these feeds incubated with rumen fluid or reconstituted faeces inocula at various time periods. The degradability of each feed was determined by the nylon bag technique in three sheep. Eighty-eight intact male Ethiopian Menz type sheep (mean liveweight 256 (S.D. = 1·98) kg) were used in a randomized complete block experiment to determine intake and digestibility.

Gas production using faeces inoculum (GP-F) was strongly related to GP using rumen fluid inoculum (GP-R) particularly at 48 h (R2 = 0·85; P <0·001) of incubation. The IVDMD obtained with reconstituted sheep faeces inoculum (IVDMD-F) had a strong positive relationship (R2 = 0·88; P <0·0001) with IVDMD measured using rumen fluid (IVDMD-R). The IVDMD values obtained by centrifugation were positively related to those obtained by filtration for the rumen fluid (R2 = 0·61) and reconstituted faeces (R2 = 0·47) inocula.

The relationship between degradability and in vivo DMD was generally poor for roughages but improved with the length of incubation for forage legumes, being strongest at 24 h (R2 = 0·54). The in vivo DMD had the strongest relationship with GP-R at 24 h of incubation for roughages (R2 = 0·64) and legumes (R2 = 0·84). Dry matter degradability was poorly related to DM intake for roughages (R2 <0·10), while these were closely related for legumes particularly at 6 h of incubation (R2 = 0·55). The relationship between GP-R and intake was strongest at 12 h of incubation for roughages (R2 = 0·41) but was generally weak for legumes. The IVDMD accounted for a very low proportion of the variation in intake of roughages and legume forages. The gas production method was the best among the methods tested in predicting voluntary roughage intake, but not the intake of legumes. The nylon bag technique gave the best predictors (solubility, rate constant ‘c’ and Lag phase) of legume intake (R2 = 0·98).

The discussion suggests explanations for why the nylon bag technique predicted performance from forage legumes better than from roughages, why the technique was much better as a predictor of intake than of in vivo DMD, and why the gas production technique predicted in vivo DMD and not the intake of legumes. Reconstituted faeces inoculum may replace rumen fluid inoculum in in vitro procedures. The IVDMD method is a less accurate predictor of in vivo DMD than GP and rumen degradability constants. Both feed factors and practices inherent in the methodologies may modify the predictiveness of indirect digestibility methods.

Four lambs (mean 27 kg liveweight) offered 900 g/day lucerne chaff were prepared with catheters in the portal vein (PV), cranial mesenteric vein (CMV), femoral artery (FA) and abomasum. L-[2,6-3H]phenylalanine (Phe) and 14C-(Phe)casein were infused into the abomasum in separate experiments. Concurrent samples of blood from the PV, CMV and FA were prepared as four fractions: plasma, deproteinized whole blood, free Phe in deproteinized whole blood, and whole blood. Ratios of net label uptakes in different blood fractions indicated that red blood cells and blood proteins were unlikely to contribute to net Phe uptake into the PV or CMV. Small peptides may have contributed up to 20% to total appearance of Phe in the PV and CMV. However, net uptake of peptides from the lumen was probably zero. It was concluded that the Phe uptake and, by implication, total amino acid uptake from the lumen of the small intestine into the PV and CMV were as free amino acids.