The relationship between variations in in vitro microbial biomass production and microbial protein supply to the host animal was examined in 13 Malawian goats fed on stover leaves from two varieties of maize at Bunda College, Malawi, in 1995. The in vitro parameters were analysed based on the concept of the partitioning factor (PF) which is obtained by the combination of gas volume measurements with determinations of the amount of substrate truly degraded. The PF reflects substrate-dependent variation in the in vitro partitioning of degraded substrate between short chain fatty acids (SCFA), gases and microbial biomass. The in vivo microbial protein synthesis was estimated by the urinary excretion of the purine derivatives (PD) allantoin, uric acid and xanthine + hypoxanthine. For the two types of stover leaves examined, the higher microbial efficiency of one variety in vitro was reflected by different PD excretions on practically identical digestible dry matter intakes in vivo. It is concluded that substrate-dependent variations in microbial efficiencies as detected by the PF are also evident and relevant for in vivo microbial protein synthesis.

In order to learn more about some of the reasons for differences between forage plant species in nutritive value, plant parts of three contrasting species, Onobrychis viciifolia Scop., Spergula arvensis L. and Lolium multiflorum Lam., were examined. In vitro digestibility was recorded in milled and in chopped (1 cm lengths) material, neutral detergent fibre (NDF) and lignin were recorded in milled material and the proportions of thick-walled, thin-walled and epidermal cells and the thickness of the cell walls were recorded in cross-sections. Early harvesting was compared with later harvesting in each of two years. The plants were grown in a heated glasshouse in spring-summer.

In O. viciifolia the petioles had much higher concentrations of NDF and lignin, a higher proportion of thick-walled cells and generally thicker cell walls than the leaflets, but the petioles were, if anything, slightly more digestible than the leaflets. The leaflets of O. viciifolia had cell walls of similar thickness to those of Trifolium repens and Medicago sativa. The leaves of S. arvensis had generally thin cell walls and a high proportion (0·84) of thin-walled cells. The stems of S. arvensis had high concentrations of NDF (633 g/kg) and lignin (94 g/kg) and a high proportion of thick-walled cells, but the walls of these cells were not particularly thick (1·4 μm). The leaflets and petioles of O. viciifolia and the stems of S. arvensis were much less digestible than the leaf blades or leaf sheaths of L. multiflorum. L. multiflorum leaf blades and leaf sheaths were low in lignin (16–18 g/kg) and had rather thin cell walls; the sheaths were lower in NDF than the blades and tended to be more digestible than the blades, despite thicker epidermal cell walls.

The air quality in 82 German livestock buildings was investigated, using ammonia as a gaseous indicator. The ammonia concentrations were measured hourly and a 24 h mean was calculated. In cattle houses the mean ammonia measurement ranged between 3·7 ppm in calf houses (n = 16), 4·7 ppm in beef units (n = 10) and 6·4 ppm in dairy cattle houses (n = 8). In pig buildings the highest mean concentrations of 15·9 ppm were found in fattening pig livestocks (n = 8). In sow (n = 16) and weaner livestock buildings (n = 8) the averaged ammonia concentration varied between 13·4 ppm and 9·1 ppm, respectively. Within poultry houses, broiler flocks (n = 8) were associated with ammonia concentrations of 21·2 ppm. On the other hand, livestock buildings containing laying hens (n = 8) showed the lowest ammonia concentrations of all, namely 2·7 ppm. A significant positive correlation between temperature, relative humidity and ammonia concentrations could be found in poultry houses. Assuming an ammonia threshold limit value of 15 ppm, although no cattle house in this study exceeded this recommended limit, 31% of all the pig and poultry units investigated did, indicating a need for improved housing conditions in the future.

This experiment examined the effect of feeding a concentrate diet ad libitum for two periods of time in two breeds of contrasting mature size cattle, on the activity of the components of the calpain system and the association between components of the calpain system and tenderness as determined by shear force in the longissimus muscle. Nine-month-old Angus and Simmental steers were either fed ad libitum on a feedlot from 9 months of age (F9) or on pasture until 25 months of age (F25) and then fed on the same ad libitum ration as the F9 steers. Groups within a breed were killed at mean liveweights of c. 800 kg for the Angus and 950 kg for the Simmental. Steers were slaughtered in a commercial abattoir and muscle samples collected from the longissimus muscle at the 13th rib within 60 min of slaughter. The activities of the components of the calpain system were determined 2 and 24 h post-slaughter. The length of time on the feedlot diet had the largest effect on shear force of the longissimus muscle and the activity of μ-calpain. The steers growing fastest prior to slaughter (F25) had the highest μ-calpain activities two h post-slaughter and produced the most tender meat, even though they were slightly older at slaughter. The best component of the calpain system for predicting shear force over all the treatments was the activity of calpastatin 24 h post-slaughter. This association between shear force 21 days post-slaughter and the activity of calpastatin 24 h post-slaughter was weak and varied between the treatments. The strongest associations occurred in the F9 Angus steers who also had the toughest meat and the slowest growth rates prior to slaughter.

Two experiments were conducted at Palmerston North, New Zealand during 1997, to investigate the effects of wilting chicory to reduce its bulkiness upon voluntary intake of fresh feed and dry matter (DM), apparent digestibility and voluntary water intake. In Expt 1 fresh chicory was cut and wilted for 48 h to determine the drying rate; wilting for 24 h increased DM content from 87 to 173 g/kg, reduced in vitro organic matter digestibility (OMD) by 0·016 (P<0·05) and was selected for use in Expt 2. In Expt 2, chicory was fed either fresh (113 g/kg DM) or wilted (250 g/kg DM) to castrated male red deer kept indoors over two time periods, late autumn and early spring. Chemical analyses showed that wilting slightly lowered the concentration of water-soluble carbohydrate from 185 to 158 g/kg DM, but did not change any other aspect of composition. There were no significant differences between fresh and wilted chicory in apparent digestibility of DM, organic matter (OM), hemicellulose and cellulose. Wilting significantly lowered voluntary intake of fresh feed (P<0·01), but significantly increased voluntary DM intake from 49 to 57 g DM/kg W0·75/day (P<0·05). Wilting chicory lowered feed water intake (P<0·01) but increased drinking water consumed (P<0·001), with total water intake still being slightly lower (P<0·05) for deer fed wilted chicory.

It was concluded that wilting chicory increased DM intake by reducing its bulkiness, without seriously affecting digestibility, and it is suggested that the feasibility of breeding forage chicory for higher leaf DM content should be investigated. A comparison with literature values showed that DM contents of fresh forages < c. 150 g/kg are likely to restrict the voluntary DM intake of ruminants.

Sixteen sheep were continuously fed diets based on straw, straw and barley grain, or NaOH-treated straw, each with adequate minerals and with or without additional urea (7·3 g N/day for the straw and straw and barley diets; 14·4 g N/day for the diet containing NaOH-treated straw) infused intra-ruminally. [14C] tracers were used to measure the rate of irreversible loss (i.e. synthesis) of plasma urea and its transfer to the rumen and to the remainder of the gastrointestinal tract in 4–6 sheep per treatment. [15N] tracers were also used to make these measurements in four sheep fed the straw, straw and barley and straw and barley with intra-ruminal urea infusions. Inclusion of the barley grain in the diet increased digestible organic matter intake by c. 70%. Replacing the straw with a greater amount of NaOH-treated straw increased digestible organic matter intake by 43% in the absence of additional urea, and by 65% when urea was infused intra-ruminally. Rumen ammonia concentrations were 37 and 31 mg N/l when straw or straw and barley diets respectively were provided and were reduced to 3 mg N/l when treated straw was given to the sheep. These concentrations exceeded 223 mg N/l when urea was infused intra-ruminally. Rate of irreversible loss of plasma urea measured using [14C]urea ranged from 3·7 g N/day in sheep given the treated straw diet to 16·8 g N/day when urea was infused intra-ruminally, while this rate was correlated with plasma urea concentration. In the three diets where it was measured, rate of irreversible loss of [15N]urea was on average 0·73 of the rate of irreversible loss of [14C]urea. Measurements made with 14C and 15N tracers of plasma urea transfer to the rumen were similar. This transfer measured with 14C tracers ranged from 1·4 to 2·4 g N/day for the three diets without additional urea, while providing urea by intra-ruminal infusions reduced the transfer to 1·1–1·4 g N/day. Transfer of plasma urea to the rumen was not changed by the higher digestible organic matter intake associated with either inclusion of barley grain in the diet or provision of a greater amount of more highly digestible NaOH-treated straw. These studies indicate that plasma urea transfer to the rumen is not always increased by greater organic matter fermentation in the rumen.

Two experiments were conducted, at ADAS Drayton in the autumn and winter 1996/1997, to compare methane (CH4) emissions from sheep housed either in a polytunnel system or in open-circuit respiration chambers. In each system, the sheep received maintenance levels of either cut grass or high temperature dried grass pellets (HTDG). All experiments in the tunnel were conducted on concrete to avoid any interactions of the CH4 with the soil/plant environment. The results suggested that CH4 production from the open-circuit chambers was greater than from the tunnel system (26·9±0·46 v. 31·7±0·35 l/kg dry matter intake (±S.E.) for open circuit respiration chambers and tunnel, respectively). Recovery tests gave similar results for both systems (95·5–97·9% for tunnels and 89·2–96·7% for chambers), and confirmed that both methods give good quantitative recovery of added CH4, and can therefore be assumed to provide reliable estimates of emissions from animals. There is no technical explanation, therefore, for the different estimates of emissions provided by the two systems. Further studies are required to understand the reasons for the differences and in particular, the possible links between animal behaviour induced by the two systems and CH4 emission rates.

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 thirty-first meeting of the group, chaired by Professor M. Gill of NR International, Chatham, was held in the Kohn Centre at the Royal Society, 6 Carlton House Terrace, London on Friday, 16 April 1999 when the following papers were read.

Twelve female desert goat kids and an equal number of males were used to study meat production potential of desert goats at Kuku Research Station, Khartoum North, Sudan. The kids were kept in two separate groups according to sex. Kids were fed ad libitum a complete diet (a concentrate mix and green lucerne) for 147 days from 12 July to 10 Oct 1997.

Male kids consumed more dry matter, had significantly greater liveweight gain and had heavier slaughter weight and superior feed conversion efficiency than females. Carcass weight was significantly greater in males than females but females dressed out heavier than males. Male carcasses had more muscles and bone while female carcasses had more fat and trimmings.

Male goat kid carcasses yielded significantly (P<0·001) heavier wholesale cuts as single short forequarter and neck while female kid carcasses yielded heavier wholesale cuts as leg and chump, best end of neck as well as significantly (P<0·01) heavier loin and breast.

Methods to alleviate the toxicity of Acacia angustissima (acc. no 15132) were evaluated in vitro and in vivo at ILRI Debre Zeit Research station in Ethiopia in 1997–1998. In an in vitro evaluation, A. angustissima leaves were incubated for 120 h with rumen fluid from Borana steers consuming native hay and cotton seed cake or from free ranging goat and sheep. Addition of polyethylene glycol (PEG, molecular weight (MW) 4000) increased gas production (4·9 v. 13·9 ml/100 mg dry matter (DM)), ammonia concentration (5·2 v. 9·7 mmol/l) and neutral detergent fibre (NDF) digestibility (380 v. 540 g/kg DM). In an in vivo experiment, Ethiopian highland sheep fed native hay and A. angustissima as a supplement (200 g/d) were inoculated with mixed rumen content from sheep gradually adapted on A. angustissima or were given PEG (MW 4000, 100 g/kg supplement) as methods to alleviate toxicity induced by A. angustissima. Sesbania sesban (acc. no 10865) with and without PEG were fed as a control. Effects on intake, apparent digestibility and nitrogen balance were studied in a 5×5 Latin square experiment. DM intake was increased by all the supplements (P<0·001) even though hay intake was slightly reduced compared to hay only (P<0·05). PEG increased intake of A. angustissima compared to inoculation. There were no significant differences in apparent DM or OM digestibility. Apparent nitrogen digestibility tended to be higher with S. sesban than with A. angustissima (P<0·10) and addition of PEG increased it with A. angustissima (P<0·05). Supplements increased ammonia and VFA concentrations and molar proportion of propionate (P<0·05). Supplements tended to increase microbial nitrogen supply (P<0·10) but there were no significant differences in efficiency of microbial synthesis. Supplements increased nitrogen retention (P<0·01) but due to short periods there were no significant differences in the live weights of sheep. All the animals remained healthy during the experiment suggesting that both methods used alleviated the toxicity of A. angustissima. Addition of PEG was more effective than inoculation in increasing intake and nutritive value of A. angustissima.

The Agricultural and Related Industries Study Group of the Operational Research Society held a one-day meeting on ‘Operational Research, Agriculture and the Environment’ on 27 November 1998 at Silsoe Research Institute, Bedfordshire, UK. The group promotes the use of the scientific method in solving management problems. The aim of this meeting was to look at models concerned with the effects of management of the environment in agriculture. Two looked at decision support systems – one for land use balancing different interests and one from the point of view of biodiversity. Andrew Moxey however highlighted the difficulties of interdisciplinary projects and the risk of the ‘illusion of technique’ in decision support systems. Three other papers were more specific – concerned with livestock and climate change, nitrogen fertilizer rates and slurry application.

Maternal serum hormones (progesterone, oestradiol, triiodothyronine and cortisol) and blood metabolites (β-hydroxy butyric acid [BHBA] and blood urea nitrogen [BUN]) concentrations at weeks 0, 4, 8, 12, 16 and 20 of pregnancy were measured in 39 pregnant Javanese thin-tail ewes (20 and 19 carrying single and multiple [2–3] foetuses, respectively), and six non-pregnant ewes as controls, to evaluate their correlations with lamb birth weight at parturition. All hormones and metabolites changed with the advance of pregnancy. Regression analyses showed that concentrations of triiodothyronine, cortisol, BHBA, and BUN in the maternal circulation during pregnancy had lower correlations with lamb birth weight at parturition than those of progesterone and oestradiol. Progesterone and oestradiol concentrations in the maternal circulation at week 8 of pregnancy had the greatest correlations with lamb birth weight at parturition. The higher the concentrations of progesterone and oestradiol in the maternal circulation at week 8 of pregnancy, the higher the lamb birth weight at parturition. The results suggested that raising maternal serum progesterone and oestradiol concentrations during early pregnancy in sheep, either by exogenous administration or superovulation, might improve prenatal growth and lamb birth weight.

The intake and digestion of fresh and dried Digitaria decumbens grass by rams was compared using a 2×2 factorial design. The experiment took place in Guadeloupe (French West Indies) in 1996. Eight rams (mean liveweight: 45·7±3·1 kg) were maintained in metabolism cages. Digitaria decumbens grass was cut daily and distributed to four of them, the other four were fed the following day with the equivalent forage which had meanwhile been dried for 20 h at 60°C. Chemical composition (g/kg of dry matter (DM)) of the two diets based on neutral detergent fibre (NDF, 713, S.E. 18), acid detergent fibre (ADF, 361, S.E. 13) and crude protein (CP, 90, S.E. 4) was similar. The DM intake (61·0 and 53·2 g/W0·75, S.E. 2·0, P<0·05), the NDF (0·753 and 0·727, S.E. 0·004, P<0·011) and CP (0·588 and 0·544, S.E. 0·014, P<0·09) total tract digestibility of fresh and dried herbage were different. Nylon bag estimates of effective DM degradability and fractional degradation rates (per h) in the rumen were 0·436, 0·414 (S.E. 0·005, P<0·004) and 0·048, 0·038 (S.E. 0·002, P<0·02) for fresh and dried grass, respectively. Rumen digestibility of organic matter and NDF were 0·516, 0·541 (S.E. 0·021) and 0·763, 0·692 (S.E. 0·019), respectively. The rumen turnover rates of particles (per h) were 0·024 and 0·015 (S.E. 0·001, P<0·05) for fresh and dried forage respectively. The efficiency of microbial protein synthesis (g microbial nitrogen/kg organic matter apparently degraded in the rumen) was similar with the two diets : 33·5 and 33·0 (S.E. 3·3, P<0·9) for fresh and dried forage respectively. In conclusion, fresh Digitaria decumbens was nutritionally superior to dried. This is probably due to a faster degradation rate and a lower rumen retention time of the fresh forage.