In laboratory studies, the amount of N mineralized under waterlogged conditions during 14 days at 30°C was significantly correlated (P < 0·001) with the activities of amidase, glutaminase and asparaginase in soil when these enzymes were assayed by either a nonbuffer or a buffer method using appropriate substrates. N mineralization under waterlogged conditions was also significantly positively correlated with N mineralization under aerobic conditions, especially at 25 and 35 °C (P < 0·001). Generally, the results indicate that the use of amidase, glutaminase and asparaginase activities in predicting plant-available N in soils deserves more attention.

A total of 52 individually penned pigs (mean initial and final live weights (LW) of 31·7 and 81·5 kg, respectively) was used in a randomized block experiment at the Agricultural Research Institute of Northern Ireland, Hillsborough, in 1984. The treatments were based on dietary regimes which comprised a control diet in which meal was offered at 86 g dry matter/k W0·75 per day or diets in which silage effluent was substituted for part of the allowance of meal of the control diet at 125, 175, 225 and 275 g/kg on a dry matter basis to give 0·125, 0·175, 0·225 and 0·275 effluent diets. There was also a negative control diet in which meal was offered at 850 g/kg of the rate of feeding of the control diet. Each of these dietary treatments included water available ad libitum. In a further treatment, effluent was substituted for 225 g/kg of the meal allowance of the control treatment on a dry matter basis, but additional water was not offered. The treatment based on the 0·275 effluent diet was omitted from the first four replicates.

Some refusals of diet occurred at the higher rates of effluent feeding, with mean refusals of 7, 11 and 21 g/kg, respectively, for the 0·175, 0·225 and 0·275 effluent diets on a dry matter basis. Significant linear and quadratic contrasts (P <0·01) were found for daily LW gain, feed conversion ratio and total liquid intake. The quadratic response curves for daily LW gain and feed conversion ratio had relatively flat peaks, optimum values occurring at concentrations of effluent in the diet of 95 (S.E. 17) and 99 (S.E. 15) g/kg, respectively. From the response curves, performance in terms of LW gain and feed conversion ratio was equal, or superior, to that obtained with the control diet at concentrations of effluent of up to 190 (S.E. 33) and 199 (S.E. 30) g/kg, respectively, but deteriorated at higher concentrations of effluent.

Additional water was consumed at all rates of inclusion of effluent. However, from the quadratic equations, the total consumption of liquid was lower with diets containing effluent at up to 161 g/kg of diet than with the control diet.

Feeding studies were conducted in 1986 with penned sheep and cattle fed legume (C3) and grass (C4) hays mixed in different proportions. Large fluctuations in diet δ13C within or between days were associated with much smaller fluctuations in the δ13C of faeces. When the overall daily legume percentage in the diet was held constant, there was little variation in the δ13C of faeces irrespective of when during the day the legume, relative to the grass, was eaten.

Cattle set stocked on Stylosanthes/grass pastures in Queensland showed only minor variations in faecal δ13C within or between days in the short term. All animals within a group showed similar trends when the diet was changing. The changes in the δ13C of faeces from day to day reflected small but real changes in diet selection.

It was concluded that the δ13C of a single faecal sample reliably reflects the integrated diet over the previous 3–4 days of a free-grazing ruminant so that the frequency and pattern of faecal sampling for estimating diet composition may be determined by considerations other than reliability

Two experiments were carried out in Scotland 1984 to study the efficiency of energy utilization by Suffolk × Blackface lambs. In the first experiment, a digestibility trial, the lambs were fed three diets: roughage (R) consisting of chopped dried grass; concentrate (C) containing 700 g whole barley, 225 g ground barley and 75 g fishmeal/kg dry matter (DM); and a mixed diet (M) containing 500 g of roughage and 500 g of concentrate/kg DM. The DM and organic matter digestibility coefficients of diet M were lower than the ‘expected’ values calculated by summation of the separately determined digestibility coefficients of the component feeds. Similarly, the metabolizable energy (ME) value was 4·0% lower than expected.

In the second experiment, 40 lambs of c. 20 kg live weight (LW) were offered 50 kg roughage DM (ME 9·74 MJ/kg DM) and 50 kg concentrate DM (ME 12·21 MJ/kg DM) either as a mixture (treatment M) or sequentially (treatment S). Lambs on treatment S took 33 days longer to consume their allocation of food than those on treatment M, but achieved a similar final empty body weight and empty body composition. This contrasts with results predicted by a feeding standards model for lambs of a similar LW offered diets of the same ME content. The longer feeding period, and hence greater overall maintenance requirement, of lambs on treatment S was partly offset by associated effects causing a reduction in the total ME available to lambs on treatment M, and partly to improved efficiency of energy utilization for gain and/or a lower daily maintenance requirement of lambs on treatment S. Allowing for associated effects and the adoption of a variable maintenance requirement in current feeding standards would result in a more accurate prediction of animal performance.

One hundred and fifty-four, March-born, lowland ewe lambs, on the Lyons Estate farm, were allocated to a 2×2 factorial experiment. In September 1987, half were shorn and 1 month later the lambs were treated with intravaginal sponges, containing either 60 mg medroxyprogesterone acetate or 40 mg fluorogestone acetate, for 12 days. Following sponge removal, ewes were mated to fertile rams at a ram: ewe ratio of 1:6. There was no significant difference in reproductive performance between the two progestagen treatments (P > 0·05). Premating shearing increased (P < 0·01) conception rate and reduced the percentage of barren ewes (P < 0·01) but there was no effect on litter size. Time of gestation following shearing was increased (P < 0·01) by 1·24 days. Lamb growth rate up to weaning was not affected by the shearing treatment. The results of this trial indicate positive advantages of premating shearing of ewe lambs.

Four experiments involving the two-stage in vitro digestibility technique of Tilley & Terry (1963) were undertaken to investigate whether cow rumen liquor could be replaced with effluent or extract from feed residue containing micro-organisms derived from the long-term rumen simulation technique (Rusitec) of Czerkawski & Breckenridge (1977).

In Expts 1 and 2, the dry matter digestibility (DMD) of hay was determined using either cow rumen liquor or Rusitec liquid effluent or extract from feed after 48 h of digestion in a Rusitec apparatus using various volumes of liquor and artificial saliva. Digestibilities determined with rumen liquor were c. 70% (c.v. 1·2%) while those determined with Rusitec effluent or extract were c. 62% (c.v. 1·8%). In treatments common to Expts 1 and 2, Rusitec effluent digestibilities were more repeatable than extract or rumen liquor digestibilities.

In Expts 3 and 4, Rusitec effluent was compared with cow rumen liquor for determining DMD of seven forages with DMD ranging from 33 to 70%. For a given feed there was good agreement between experiments in DMD values determined with Rusitec effluent, and for ten paired values there was a high correlation (r2 = 0·976) between DMD determined by the two methods. DMD determined using rumen liquor (y) was accurately predicted by Rusitec liquid effluent digestibility (x) from the equation y = 2·663 + 1·06477.x; R.S.D. 2·433.

The results show that Rusitec liquid effluent can be used instead of rumen liquor as a source of micro-organisms for the two-stage in vitro digestibility method. Routine use of Rusitec would obviate the need for using fistulated animals.

In an experiment conducted in the sheds of the Animal Nutrition Division of the Indian Veterinary Research Institute in 1988/89, eight adult Black Bengal goats were divided into two groups of four animals each. Animals in the control group were offered a conventional diet (concentrate and available roughage as per National Research Council standards) and those in the experimental group were fed exclusively on fresh leucaena foliage (young and newly developed leaves and shoots) for 300 days. Dry matter intake (DMI) and body weight of animals in the experimental group decreased in the first 6 weeks; daily DMI/lOOkg body weight was 306 ± 0·34kg in the control group and 2·40 ± 0·18 kg in the experimental group.

There were significant differences in the apparent digestibilities of crude protein and nitrogen-free extractives; contents of digestible crude protein (DCP) and total digestible nutrients were 5·2 and 20·3%, respectively, in the controls and 65·6 and 59·1 %, respectively, in the experimental group. DCP intake was significantly higher in the experimental group as a result of high protein content in foliage but it was not well utilized.

In the control and experimental groups, respectively, daily mean retention of nitrogen was 2·01±0·14 and 1·54±0·12 g/day, of calcium 1·60±0·08 and 2·92±1·69 g/day, and of phosphorus 1·12±0·25 and 0·24±0·07 g/day, the phosphorus balance being significantly lower in the experimental group. Blood calcium and serum glutamate oxaloacetate transaminase/serum glutamate pyruvate transaminase concentrations were statistically similar in both groups but the concentration of inorganic P was significantly lower in the blood of animals fed leucaena.

Oestrous activity in local Rahmani and Ossimi sheep and imported subtropical Awassi sheep at different times of the year in Upper Egypt and the effect of continuous exposure to long-day conditions from July till December on this activity was studied in 1986. The three breeds differed substantially in oestrous activity but differences did not seem to be directly related to latitude of origin. Rahmani ewes from the Nile Delta were mostly cyclic all year round; the percentage coming to oestrus each month never fell below 70%. Ossimi ewes originating from mid-Egypt had a very long breeding season; 74% had an anoestrous period of 68·8 days (v. 27% for Rahmani ewes). All Awassi ewes, except one, had an anoestrous period of 96·5 days on average.

Awassi ewes also showed more response to continuous exposure to long days (14 h) than Ossimi ewes, seen in a shorter reaction interval and a greater decrease in the percentage of ewes coming into oestrus (27 and 90% in control and treated Awassi ewes, respectively). The results indicated that changes in daylength, although small in subtropical regions, may be a major factor controlling seasonal changes in reproductive activity in subtropical sheep breeds, the more seasonal breed being more responsive to changes in daylength. The possibility of selection within these breeds for continuous reproductive activity is also indicated.

Two experiments were carried out to determine endogenous losses and the response of urinary purine derivatives to increased duodenal inputs of purine bases. Four ewes each fitted with a re-entrant cannula at the proximal duodenum, and conventionally fed, were subjected to full replacement of duodenal digesta followed by the administration of a solution either free of purines (Expt 1) or enriched with increasing amounts of purines, to supply 0·48–21·27 mmol/animal per day (Expt 2). Basal daily urinary excretions of allantoin, uric acid, hypoxanthine and xanthine were 11·5 ± 0·94, 9·9 ± 0·67, 6·9 ± 0·46 and 1·2 ±0·16 mg/kg W0·75. Allantoin was the only purine derivative which increased in response to incremental inputs of duodenal purines. The relationship between allantoin excretion and infused purines showed a urinary recovery of 0·8 for purines infused at > 220 μmol/kg W0·76. Lower rates of infusion did not alter allantoin excretion. The results show urinary allantoin to be a useful index to estimate duodenal input of purines when animals are fed close to or above their energy maintenance requirements.

Simulation modelling was used to investigate interactions between forage degradation characteristics, rumen processes and body weight, and to predict the voluntary food intake and digestion of a range of forages. Predicted voluntary intake and digestion agreed well with empirical data, explaining 61 and 70%, respectively, of variance in observed values. Since the data covered a wide range of animal weights and forage qualities, these results suggest that the model is a useful means of integrating the effects of animal and forage variables. Interactions were examined between animal weight and diet quality, as defined by the proportion of potentially digestible cell contents and cell walls and their rates of digestion. Retention time of food in the digestive tract was shown by regression to scale with W0·27. The time taken to comminute large fibre particles also scaled with W0·27. Longer retention of digesta by large ruminants increases digestive efficiency compared with small animals and would permit them to survive on lower-quality foods. The model showed that maximum intake of metabolizable energy scales with c. W0·87, greater than the scaling of maintenance with W0·73.

A rumen simulation device (Rusitec) was used to compare the effects of autoclaved and γ-irradiated Aspergillus oryzae fermentation extract (AO) with those of untreated AO on rumen fermentation. Each vessel received daily 18 g of a basal diet consisting of 500 g hay, 299·5 g rolled barley, 100 g molasses, 91 g fishmeal and 9·5 g of a minerals and vitamins mixture/kg dry matter. AO preparations (0·25 g/day) were added with the feed. Dry matter digestion increased at 24 h, but not at 48 h, after adding AO, suggesting that AO stimulated the rate of digestion but not the extent. AO increased the numbers of total and cellulolytic bacteria by 90 and 50%, respectively. Irradiated AO stimulated numbers of bacteria in the same way as AO, although to a slightly lesser extent. Autoclaved AO had no effect. Thus, the mode of action of AO on rumen fermentation depends on a heat-labile component, possibly a nutrient or an enzyme, or metabolic activity. Viable AO cells are not required to stimulate bacterial growth and activity.

Two experiments at Belclare, Co. Galway, in late autumn 1988, evaluated the use of herbage and dosed n-alkanes for estimating herbage intake by sheep. The first experiment examined faecal recoveries of dosed and herbage n-alkanes. The second experiment assessed the accuracy and precision of herbage intake estimates obtained using the n-alkane technique, and tested the effect of supplying n-alkanes to animals either in gelatine. capsules (containing different ratios of n-alkane: cellulose fibre) or in pellets prepared from shredded paper onto which the n-alkanes had been adsorbed. Individually penned wether lambs were offered freshly cut herbage ad libitum (+ 10%) and actual dry matter intake was recorded daily. Intake was estimated using the C31:C32 and C33:C32 (natural:dosed) n-alkane ratios.

There was no significant effect of n-alkane chain length on faecal recovery rate for either the dosed n-alkanes (C32 and C36), the herbage odd-chained n-alkanes (C29, C31, C33 and C36) or those used for the estimation of herbage intake (C31, C32 and C33). The accuracy and precision of the n-alkane technique for estimating herbage intake were unaffected by whether the dosed n-alkane was supplied in capsules or pellets or by the n-alkane:cellulose fibre ratio in the capsules. The bias in the estimated intake was – 8% (± 1·1%) and + 3% (± 1·2%) for estimates based on C31:C32 and C33:C32 ratios, respectively. The estimates based on C31:C32 and C33:C32 exhibited similar precision in the estimation of herbage intake, with a R.S.D. of 6% in actual intake when adjusted for variation in estimated intake and a correlation of +0·92 between actual and estimated herbage intake. The C.V. for actual herbage intake was 17%. The repeatability of actual dry matter intake over three consecutive 6-day periods was 0·54 while those of estimated intake were 0·57 and 0·60 for estimates based on C31:C32 and C33:C32, respectively. The results show that the n-alkane technique can provide an accurate and precise estimate of herbage intake.

Bentonite (2 g/day) was added to four vessels in the rumen simulation technique (Rusitec) and the effects on the fermentation were compared with four control vessels over a 21-day period. Vessels in both groups were supplied with 20 g/day of a diet containing, per kg, 500 g hay, 299·5 g barley, 100 g molasses, 91 g fishmeal and 9·5 g of mineral/vitamin mix. Numbers of ciliate protozoa were reduced by 69% (40 v. 12·8 ×103/ml) in vessels receiving bentonite. The viable count of bacteria was increased by one-third in these vessels (4·8 v. 3·6 × 108/ml), and ammonia production was 54·7 and 76·7 mg/day in the bentonite and control vessels, respectively. Other effects on fermentation products and metabolic activities were minor, except that the rate of breakdown of [14C]leucine-labelled Selenomonas ruminantium protein was 47% lower in fluid taken from vessels receiving bentonite. Bentonite did not affect the rate of bacterial breakdown by protozoa immediately when it was added to rumen fluid in vitro, although a decline in activity was becoming apparent after 4 h incubation. Microscopic examination of rumen fluid to which bentonite was added indicated that some bentonite was ingested by protozoa, but that its main toxic effect was at the cell surface, causing interference with the motion of cilia and thereby preventing motility of protozoa, particularly the holotrichs.