Infusion of [35S]-labelled cysteine into the jugular of Romney sheep of different ages was used to estimate the extent of combined cysteine and cystine (cyst(e)ine) and glutathione (GSH) interchange in various tissues, including skin, and to measure whole body irreversible loss rates (1LR) for cyst(e)ine. The studies were undertaken at Palmerston North, New Zealand during 1990 and 1991.

Reverse phase HPLC using a fluorigenic reagent, 7-fluoro-2,1,3-benzoxadiazole-4-sulphonate (SBD-F) was used for the simultaneous determination of thiols (cysteine and GSH) in whole blood (bound and free fractions), liver, kidney, small intestine, muscle, pancreas and skin. The appearance of [35S]-label in thiol compounds and their oxidation products was determined by ion-exchange HPLC. Specific radioactivities (SRA) for cyst(e)ine and GSH derived from this data showed equivalence for cysteine and GSH SRAs in all tissues, except for whole blood, indicating rapid withintissue interconversion between these thiols. In whole blood, however, the very low SRA for GSH (< 4 DPM/nmol) compared to cyst(e)ine (250 DPM/nmol) indicated markedly slower or negligible exchange with red blood cell GSH, and hence little inter-organ transport of [35S]-label as GSH.

Close infusion of [35S] cysteine into a defined patch of skin and collection of the venous outflow permitted direct in vivo measurement of the proportional uptake of cysteine by the skin. Results indicated considerable variation in the uptake of cysteine per se (20–40%) but no, or very little, oxidation of cysteine in the skin and no net export of GSH.

The combination of whole body, tissue and skin specific studies of [35S]-labelled cysteine metabolism quantitatively confirmed the very high proportion of circulating cyst(e)ine in sheep which is directed to skin and wool protein synthesis alone, and highlighted those aspects of this metabolism which are of most importance to wool production.

The effects of dietary deficiencies of phosphorus (P) and nitrogen (N) were studied in 28 lambs allotted to seven treatments for 18 weeks. The lambs in four treatments were offered roughage-based diets ad libitum containing high (H) or low (L) levels of P (4·13 or 0·98 g/kg dry matter (DM)) and N (108 or 68 g crude protein/kg DM). The lambs in the remaining three treatments were fed the same quantities of DM of the HNHP diet as the lambs receiving the three deficient diets (HNLP, LNHP and LNLP). A dietary deficiency of P caused a reduced DM intake and liveweight gain, lower yields of N and DM in carcass muscle and reduced DM, N and P contents of bone. A dietary deficiency of N resulted in reductions in DM intake, liveweight gain, DM digestibility, N balance, and in carcass muscle and bone DM and N. The deficiencies of N and P were not additive in lowering food intake but were additive in reducing the mineralization of the bones. The DM intake of the lambs offered their diets ad libitum was closely correlated to the log of the plasma inorganic P and urea N concentrations (R =0·72). Feeding lambs with restricted quantities of diet HNHP resulted in higher liveweight gains and DM and N digestibilities than when any of the deficient diets were offered. Measurement of the N content of the lambs by a neutron capture gamma ray analysis technique showed that the changes were occurring progressively over the experimental period. The P content of the metatarsal bone, measured by a neutron activation technique, showed progressive changes. Although the faecal endogenous losses of P were related to P intake, high urinary losses were observed in those lambs which had their food intake limited by low dietary N alone, or had their food intakes restricted. The total endogenous P losses of the lambs were most closely dependent upon the DM intake and plasma inorganic P together. The efficiency of P absorption was high (> 0·75) in all lambs except for those given the HNHP diet ad libitum. The glucose entry rate was reduced in the lambs offered diets deficient in either N or P. Mechanisms by which the N and P deficiencies reduce DM intake are discussed.

The effect of rumen fermentation on the relationship between urea and glucose kinetics was examined in sheep fed chopped lucerne hay with intraruminal infusions of water, urea, sucrose, or urea plus sucrose at Palmerston North, New Zealand in 1986. Sheep were fed hourly and infused intraruminally with water (1200 m1/day), or a similar volume containing either urea alone (13·7g/day), sucrose alone (178·2 g/day) or urea (14·6 g/day) plus sucrose (175·0 g/day). The added sucrose resulted in a lower rumen ammonia concentration (P < 0·05), lower plasma urea concentration (P < 0·05) and reduced urinary urea excretion (P < 0·05). Urea recycled to the gut tended to increase with the sucrose, urea or sucrose plus urea treatments compared with the water treatment. The fermentation of sucrose in the rumen resulted in decreases in ruminal pH (P < 0·05) and in the ratio of acetate to propionate (A:P) (P < 0·05). The infusion of sucrose also increased the concentration of propionate in rumen fluid (P < 0·05), tended to increase the plasma glucose level and increased plasma glucose irreversible loss (P < 0·05). The infusion of urea resulted in an increase in the plasma urea level (P < 0·05), urea pool size (P < 0·05) and urea irreversible loss (P < 0·01). However, urea infusion did not affect glucose metabolism or volatile fatty acid (VFA) fermentation. The effects of sucrose infusion on glucose and urea kinetics were broadly similar when given alone or with urea, apart from changes in the urea degradation rate. It was concluded that the additional fermentative activity resulting from sucrose increased propionate production which, in turn, was available for glucose production, thus ‘sparing’ amino acids for tissue protein utilization and reducing urea excretion.

Two experiments were conducted at the Massey University Deer Unit, New Zealand in 1990 and 1991 to evaluate the performance of lactating red deer hinds and their calves grazing conventional perennial ryegrass-based pastures, red clover or chicory. In both experiments, hind and calf performance was evaluated from 1 month post-parturition over a 2½ month summer period to weaning at 3½ months of age.

In Expt 1, hinds and calves were grazed on low (5·4 kg dry matter (DM)/hd/day), medium (10·8) or high (16·4) allowances of red clover, or on a medium allowance of a conventional ryegrass/white clover sward (9·9 DM/hd/day). In Expt 2, hinds and calves grazed equal DM allowances (12 kg DM/hd/day) of perennial ryegrass/white clover, chicory or red clover.

Red clover generally had higher organic matter digestibility (OMD) and higher total N than ryegrass/white clover, and when grazed at equal DM allowances, promoted higher voluntary food intake in the hinds, increased calf growth (430 v. 330 g/day) and increased hind liveweight change. Although decreasing the red clover allowance in Expt 1 slightly but non-significantly decreased hind voluntary food intake and decreased both calf and hind liveweight change, all low red clover values were still consistently higher than all ryegrass/white clover values (P < 0·05). In Expt 2, chicory was of higher OMD and ash content than red clover but N content was lower and similar to ryegrass/white clover. Chicory promoted lower levels of calf liveweight change than red clover but higher than ryegrass/white clover. Hind liveweight change on chicory was lower than on red clover and was similar to ryegrass/white clover. It was concluded that red clover offers potential as a special purpose forage for deer production and that further experimental work is needed with chicory.

Broiler chicks reared under three environmental temperatures (7·2, 23·9 and 35 °C) in the Southeastern United States of America in 1988/89 were precision-fed to levels which were c. 70, 90, 110 and 130% of the consumption observed in ad libitum-fed controls at 23·9°C, in order to examine the limitations imposed by feed intake upon growth rate, feed efficiency and survival. Ad libitum-fed birds that were housed at 7·2, 23·9 and 35 °C consumed feed at 12·1, 9·4 and 8·5% of body weight, respectively. Liveweight gain of birds consuming feed ad libitum was depressed by 26 and 46% in the 7·2 and 35 °C environments respectively. Increasing feed intake by precision feeding exceeded ad libitum consumption in the 23·9 and 35 °C environments, but not at 7·2 °C. Consumption of feed above thermoneutral ad libitum levels failed to increase (p <0·l) liveweight of carcass gain. Ration digestibility and dressing out percentage declined (P < 0·05) at the higher feed intake levels in the 7·2 °C environment.

The Agricultural and Related Industries Study Group of the Operational Research Society held a one-day meeting on ‘Decision Support Systems for Profitable Livestock Production’ on 18 November 1992 at the Meat and Livestock Commission, Milton Keynes, UK. The Group promotes the use of the scientific method in solving management problems. The aim of the meeting was to look at the contribution of advances in modelling towards improving management and hence profitability in livestock production. The first four papers concerned feeding and the remaining two breeding. A large part of the discussion could perhaps best be summed up by the regression equation which related dry matter intake and waste output from a cow. When the output was zero, the intake was reduced by 50%!

The hulls (seed coat) of tannin-free, white-flowered and tannin-containing, coloured-flowered faba beans (Viciafaba L.) were used in three experiments (1989–90) to investigate the effect of tannins on the apparent metabolizable energy corrected to zero nitrogen retention (AMEN) and apparent metabolizable nitrogen (AMN) of broiler chick diets.

In Experiment 1, the effects of four rates of hull inclusion from one white- and one colouredflowered cultivar (0, 28, 56 and 84 g/kg) on dietary AMEN and AMN were studied. There was a significant response of AMEN to hull inclusion rate (P <0·001) but no inclusion rate × cultivar interaction. For dietary AMN there was a significant effect of hull inclusion rate (P <0· 001) but no inclusion rate x cultivar interaction.

Experiment 2 consisted of two parts. In both, the total concentration of hulls was 227 g/kg but the ratio of white- to coloured-flowered hulls was varied in five increments; initially over the range 0·42–16·58 g/kg dry matter (DM) and subsequently, with another cultivar, 0·44–7·85 g/kg DM. Synthetic lysine and methionine were added to ensure that the basal diet was not limiting in these amino acids. A significant effect of tannin intake on dietary AMEN and AMN was detected across the greater range of tannin concentrations (P <0·001) but not across the smaller one.

Experiment 3 evaluated three pairs of near-isogenic faba bean lines differing only in the gene governing tannin content and flower colour. Diets were formulated using three bean inclusion rates; 200, 400 and 600 g/kg. At each rate the white- and coloured-flowered lines were mixed in the ratios 100:0, 75:25, 50:50, 25:75 and 0:100. The response in carcass nitrogen retention (CNR) to tannin intake was assessed at each bean inclusion rate and for each pair of lines.

There was a significant effect of tannin intake on CNR in only one of the nine comparisons and in that case CNR increased as dietary content increased.

It was concluded that faba bean tannins can have a negative effect on the dietary AMEN and AMN for chicks when present at a sufficiently high dietary concentration. However, the highest dietary concentration of faba bean tannins in Expt 3 was 10·52 g/kg DM, giving a maximum daily intake of 1·03 g tannins for the two-bird experimental unit. At concentrations and intakes up to this there was no evidence to suggest that faba bean tannins had a significant adverse effect.

A study of growth and venison production from weaner red deer grazing pure tetraploid red clover (RC) or conventional perennial ryegrass/white clover (PRG) pasture was conducted in 1990, with the objective of attaining a minimum slaughter liveweight of 92 kg (50 kg carcass) by 12 months of age in the stags. Ten weaner red deer stags and ten weaner red deer hinds were randomly selected and rotationally grazed on either RC or PRG forage. In autumn and spring, forage allowances were 7 kgDM/hd/day and 8 kgDM/hd/day respectively. In winter, the animals from both groups were grazed together on PRG pasture, at a residual dry matter (DM) of 1100 kgDM/ha. Total nitrogen (N) concentration was higher in RC on offer than in PRG on offer (autumn 3·4 v. 3·1 %DM; spring 3·8 v. 3·1 %DM), whilst organic matter digestibility (OMD; autumn 80·5 v. 76·5%; spring 82·1 v. 80·3%) was also higher for RC on offer. Diet selected showed similar differences in total N concentration, but there were negligible differences between forages in OMD.

Liveweight gains of RC and PRG stags were respectively 263 v. 192 g/day, 101 v. 106 g/day and 354 v. 341 g/day during autumn, winter and spring, with the corresponding values for hinds being 198. 173 g/day, 52 v. 53 g/day and 242 v. 218 g/day. At one year of age, stags grazing RC were 7 kg heavier and hinds 3 kg heavier than animals grazing PRG pasture. Animals grazing RC forage had higher voluntary feed intake (VFI) in both autumn (P < 0·10) and spring (P < 0·001), than animals grazing PRG pasture.

All stags grazing RC forage reached the minimum slaughter liveweight by one year of age, compared to 75% of those grazing PRG pasture. At slaughter, stags that had grazed RC produced heavier carcass weights (59·9 v. 54·5 kg, P < 0·01), had higher carcass dressing percentage (55·3 v. 53·2 %; P < 0·01), and tended to have slightly greater carcass subcutaneous fat depth than stags grazing PRG pasture, but this effect disappeared when the data were corrected to equal carcass weight. All stags grazing RC produced velvet antler, relative to 75% of those grazing PRG; in stags producing harvestable velvet antler, there was no difference in antler weight between those grazing RC and PRG. It is concluded that RC offers potential as a special-purpose forage for the growth of weaner red deer.

Sambar deer (n = 8) and red deer (n = 8) fawns were successfully artificially reared to 70 days of age, using ewe milk replacer, at Flock House Agricultural Centre, New Zealand, during 1991. Sambar deer fawns had a lower overall milk consumption than red deer fawns (312 v. 359 g DM/day; P < 0·05), and showed an earlier peak in milk consumption, a faster rate of decline and earlier self weaning. Birth weight as a proportion of dam liveweight was lower for sambar than for red deer, but liveweight gains to weaning (347 v. 330 g/day) and 70 day weaning weights (300 v. 30·4 kg) were similar. The age at which deer commenced a range of activities, including eating forage and ruminating, was similar for both species, except that jumping activities commenced 5 days later in sambar than in red deer (P < 0·01). Following milk feeding, sambar fawns were less active than red deer fawns. It was concluded that sambar deer fawns can be successfully artificially reared using ewe milk replacer, but that extra precautions are needed to avoid scouring and abomasal bloat, which were more prevalent in sambar than in red deer fawns.

This group, which is concerned with the applications of mathematics to agricultural science, is sponsored by the Agricultural and Food Research Council. It was formed in 1970, and has since met at approximately yearly intervals in London for one-day meetings. The twenty-third meeting of the group, chaired by P. H. Nye of the Department of Plant Sciences at the University of Oxford, was held in the Wellcome Meeting Room at the Royal Society, 6 Carlton House Terrace, London on Friday, 7 May 1993, when the following papers were read.