Sugarcane is an important forage resource in sub-tropical and tropical areas as it is used during the winter or dry season when the growth rate of pastures is significantly reduced. The current research study assessed the effect of four vertical sections of sugarcane in a pen trial and the level of sugarcane utilization in a grazing trial on the ingestive behaviour and forage intake of two age groups of steers (1 and 2 years old). The pen trial was comprised of two simultaneous 4 × 4 balanced Latin square designs (one for each age group of animals) of four periods, four animals and four feeding treatments, which consisted of four equal vertical sections of sugarcane. Dry matter (DM) and digestible DM (DDM) intake per kilogram of metabolic weight declined gradually from top to bottom of the sugarcane, with no significant differences between the age groups of steers. This difference in intake was associated with a decline in intake of neutral detergent fibre (NDF) as a proportion of the liveweight of the animal and an increase of total chewing time per kilogram of DM or NDF from top to bottom of the sugarcane. It was concluded that the toughness of plant material played a significant role regulating intake, which was higher for the top sections of sugarcane. In the grazing trial, steers of both age groups grazed down sugarcane in three plots over 9 days. Steers grazed up to four distinctive grazing strata. Digestible DM intake (DDM intake) was high at low levels of horizontal utilization of the top grazing stratum but DDM intake started to decline sharply when this stratum was removed in 0·92 of paddock area (i.e. equivalent to 0·08 of the pasture area remaining un-grazed). It was concluded that the proportion of un-grazed area of the pasture can be used as a grazing management strategy to control forage intake for sugarcane.

The four components of the synthesised sex pheromone of Spodoptera littoralis (Boisd.) are tetradecan-1-yl acetate (I); cis-9-tetradecen-1-yl acetate (IIA); trans-11-tetradecen-1-yl acetate (IIB); and cis-9, trans-11-tetradecadien-1-yl acetate (III). Dissolved in hexane they were dispensed in small polythene containers either singly or in combination over water-trough (WT) traps located in the potato-growing region of south-east Cyprus. Only III was necessary to attract male moths. Increased loadings of III resulted in an increased catch during the 20-day test periods; at a loading of 500 μg per dispenser the material was attractive for approximately 20 days, and at 5000 μg for up to 40 days. IIA combined with III in WT traps or with virgin females in the vane traps markedly reduced the catch of male moths. The level of inhibition induced by IIA on the attraction of female moths was related to the loading of this substance in the dispensers. An inhibitory effect on the attraction of female moths in vane traps was also shown for cis-11-tetradecen-1-yl acetate, although this substance was less active compared with IIA at the same loading. No marked attraction or inhibition was shown for I or IIB, neither was any synergistic action demonstrated for these substances when in combination with III. When 200 polythene dispensers each containing 500 μg of III were evenly distributed throughout a potato field of 2000 m2 during the test period of 19 days virtually no males were caught in a trap baited with virgin females located in the centre of the field. Using only 100 point sources of III at twice the loading, only a slight reduction in catch compared with control catches was noted.

The influence of a chronic subclinicael infection of Trichostrongylus colubriformis, 2500 larvae/day for 12 weeks, on gastrointestinal motility and digesta flow was studied in 12 sheep supplied ad libitum with food and water. Motility was recorded by X-radiography and electromyography from chronically implanted electrodes;abomasal volume and outflow were estimated by dilution of CrEDTA; small intestinal transit time was estimated by passage of Phenol Red. The findings were compared with measurements made prior to infection at restricted food intake and reported separately. The first effects of infection were seen after 3–4 weeks. No animal developed diarrhoea, but food intake was progressively reduced. Small intestinal transit time, abomasal volume and half-time of marker dilution increased while abomasal outflow decreased during infection. These changes occurred both in absolute terms and when compared with values predicted from the observed level of food intake. As the animals became resistant to the parasites abomasal volume and digesta flow returned towards control values (weeks 10–12). The migrating myoelectric complex (MMC) was disrupted in only one sheep, and only transiently. In all sheep the frequency of the MMC was increased during infection and there was a progressive inhibition of abomasal, duodenal and jejunal motility. X-radiography showed there was prolonged pooling of digesta in the proximal small intestine which was cleared only at the phase of regular spiking activity. Two sheep given an anthelmintic drench recovered normal motility and clearance of digesta. It is concluded that subclinical infection of sheep with T. colubriformis alters the normal pattern of gastrointestinal motility in the absence of any diarrhoea, and causes inhibition of abomasal and proximal small intestinal motility and digesta flow. The increased frequency of MMCs helps to maintain digesta flow through the proximal small intestine.

A series of metabolism experiments investigated the recovery of continuous-, intravenously infused chromium complexed with ethylenediamine tetra-acetic acid (CrEDTA) and lithium sulphate in the urine of cattle with a view to using the markers to estimate urine and metabolite output in grazing cattle. The recovery of Cr in urine from these infusions was similar (90%) in metabolism trials when cattle consumed three very contrasting diets: high-grain formulated pellet, lucerne hay (Medicago sativa) or low-quality native grass hay (predominantly Heteropogon contortus). By contrast, Li recovery in urine averaged 46.3 ± 0.40% and 72.6 ± 0.43% for native pasture and lucerne hays, respectively, but was not constant across days. There was negligible transfer of Cr from CrEDTA in blood serum to the rumen or faeces, whereas appreciable quantities of infused Li were found in both. The ratio of urine volume estimated by spot samples and marker dilution of Cr, to urine volume measured gravimetrically, was 1.05. In grazing studies using rumen-fistulated (RF) steers grazing seven different tropical and temperate grass and legume pastures, the ratio of concentrations of purine derivatives (PD) to Cr in spot samples of urine was shown to vary diurnally in the range of 49% to 157% of the average 24 h value. This finding indicated the need for regular sampling of urine to achieve an accurate average value for the PD : Cr ratio in urine for use in estimating urinary PD excretion and hence microbial protein production in the rumen. It was concluded that continuous, intravenous infusion of CrEDTA resulted in a constant recovery of Cr in the urine of cattle across diets and, provided an intensive sampling regime was followed to account for diurnal variation, it would be suitable as a marker to estimate urine volume and urinary output of PD in grazing cattle.

The quantitative partitioning of digestion between the stomachs, small intestine and large intestine was compared in kids and lambs offered a high quality meadow hay (organic-matter digestibility, 0·74; N, 23·9 g/kg D.M.) in amounts between maintenance and ad libitum.

Nutrient flow past the abomasum and terminal ileum and in the faeces was measured by reference to 51Cr-EDTA and 103Ru-phenanthroline. Digestion of D.M., neutral detergent fibre (NDF) and non-ammonia N (NAN) in the rumen (R), small intestine (SI) and large intestine (LI) was estimated from the regression of nutrient flow on nutrient intake.

No difference was observed between the species in digestion of D.M., NDF and NAN at any site. Approximately 0·60, 0·29 and 0·13 of the total in vivo D.M. digestion (0·74) occurredin the R, SI and LI, respectively, and approximately 0·94 of the total in vivo NDF digestion (0·79) occurred in the rumen of both species.

There was a gain of total N and NAN of 22 and 15%, respectively, in the rumen of both species whilst net disappearance of NAN in the small intestine and of N in the large intestine was approximately 0·62 and 0·27, respectively. All these characteristics varied slightly with level of feeding.

It is concluded that there may be little difference in the partitioning of digestion of D.M., NDF and NAN in the digestive tract of kids and lambs when consuming high quality forages.

It is increasingly being recognized that water intake in goats is considerably lower than in sheep on the same feed (Gihad, 1976; Gihad, El-Bedawy & Mehrez, 1980; Alam, Poppi & Sykes, 1983). It is, however, difficult to judge the significance of this difference for water transactions in the digestive tract. This paper describes the comparative water consumption and flow in the digestive tract of kids and lambs.

Twenty-eight male castrate kids and 28 male castrate lambs were assigned to a comparative slaughter experiment to compare energy and protein utilization. The experiment was conducted from January to March at Lincoln, New Zealand. Ten animals of each species comprised the initial slaughter group while the remaining 18 animals were randomly allocated to five feeding regimes. Animals were offered high-quality meadow hay for 13 weeks and then slaughtered. The energy retained in the body was regressed against metabolizable energy intake (MEI) to obtain estimates of maintenance energy requirement (MEm) and efficiency of energy utilization for growth (kg).

Kids tended to have a higher MEm (0·44 v. 0·37 MJ ME/kg W0·75 per day in kids and lambs, respectively) and a higher kg (0·28v. 0·22) though these differences were not significant. There was no difference between the species in the composition of gain of the fleece or hair-free body with a protein energy to gross energy ratio in the gain of 0·20. The fleece or hair-free body composition was similar for both species (initial 0·51v. 0·48; final 0·36 v. 0·32; protein energy:gross energy, kids and lambs, respectively). Overall, the values for kg in both species were low and could not be explained solely by the composition of the gain.

The efficiency of use of apparently absorbed amino acid (AA) for fleece or hair-free body protein deposition was higher for kids (0·52 v. 0·29) and, when the fleece or hair was included, the value increased markedly for lambs (0·50 v. 0·41, kids v. lambs, respectively). The protein energy apparently absorbed in the small intestine/MEI was not high or different between species (mean 0·18). The efficiency values for both species are low and not explained by the supply of protein relative to energy, which was not high.

It was concluded that, with high-quality forage used to promote live weight gain, there was little difference between kids and lambs in the utilization of forage energy, and that the efficiency of utilization of absorbed protein for protein deposition was lower than expected in both species.

Ninety 4-month-old wether lambs were allocated to an initial slaughter group (n =10) or to one cell (n= 5) of a 4 × 4 factorial treatment design involving four levels of infection with Ostertagia circumcincta (0, 1000, 2000 and 4000 larvae/day) and Trichostrongyluscolubriformis (0, 1000, 2000 and 3000 larvae/day). They were maintained indoors in individual pens and offered freshly cut ryegrass-white clover herbage during an 84-day period of infection after which they were slaughtered. Body protein, fat, water, Ca and P contents were determined. Feed digestibility was determined in all sheep during 5-day periods during weeks 2, 5, 8 and 11. Faecal egg counts were determined and blood samples obtained at intervals and total worm counts done at slaughter.

The effects of mixed infection on feed intake and body-weight gain were multiplicative. Mean D.M. intake of sheep infected simply with 3000 larvae of T. colubriformis or with 4000 larvae of O. circtimcincta was reduced by 10 and 8% respectively, but in those infected simultaneously intake was reduced by 30%. Energy retention was depressed mainly by reduction in gross efficiency of use of metabolizable energy in infections with T. colubriformisand by reduction in feed intake in infections with O. circumcincta. The additional effect of mixed infection occurred mainly through further depression in feed intake.

There was no interaction between infections in effect on deposition of Ca or P in the body, both species having significant effect. Infection with T. colubriformis caused hypophosphataemia and hypocalcaemia, but infection with O. circumcincta had no effect.

The number of worms established by the infections was generally low compared with previous studies with conserved and concentrate feeds. This was associated with relatively low pathogenicity in infection with O. circumcincta and normal pathogenicity with T. colubriformis.

Infection with T. colubriformis reduced the number of adult worms of O. circumcincta present at slaughter.

In a study of the effect of animal species on the threshold particle size leaving the rumen, two grasses cut at two stages of growth and one mature legume were separated into leaf and stem fractions and fed to cattle and sheep. Samples of rumen digesta and faeces were used to determine the validity of using a 1·18 mm porosity screen to separate the rumen particles into large and small pools when studying escape of particles from the rumen. Samples of rumen digesta and faeces were collected for the determination of particle size by wet sieving and the calculation of resistance of particles to passage from the rumen relative to small particles retained on a 0·15 mm sieve.

Particles < 1·18 mm but > 0·5 mm had a mean relative resistance to passage of 2·0 and 2·6 for cattle and sheep respectively, compared with resistance values of between 10·9 and 31·2 for particles between 1·18 and 2·36 mm. It is suggested that there is no justification for using different threshold particle sizes for sheep and cattle and that a 1·18 mm sieve may be used to divide the rumen contents of both cattle and sheep into two pools of particles with high and low relative resistance to passage from the rumen.

The voluntary food intake, in vivo digestibility and site of nutrient digestion was measured in 12 Polled Dorset ram lambs, from 6 to 24 weeks of age, offered clover hay. Lambs were weaned at 6 weeks of age. Six were fitted with a permanent T-shaped cannula in the abomasum and a temporary rumen catheter during the periods of digesta flow measurement.

Surgical modification of lambs did not influence intake (g/kg live weight (W) per day), in vivo digestibility or marker retention time in the rumen. However, intact lambs grew significantly faster than cannulated lambs (139 v. 109g/day, P < 0·05) apparently because of an overall higher cumulative intake over the whole experimental period rather than any change in efficiency of use of nutrients or maintenance requirement.

Relative to live weight, intake increased rapidly until c. 10 weeks of age and remained relatively constant at c. 37 g DM/kg W per day for the remainder of the experiment. Age had no effect on in vivo digestibility of organic matter (OM) or neutral detergent fibre (NDF) (average 0·69).

The proportion of digestible organic matter apparently digested in the rumen (DOMADR) decreased from 0·63 to 0·47 between 8 and 24 weeks of age whilst intake between these measurement periods increased. Nonammonia N (NAN) flow past the abomasum was similar at all ages in relation to digestible organic matter intake (55·1 g NAN/kg DOMI) but was higher at 16 and 24 weeks of age than at 8 and 12 weeks of age, respectively, in relation to organic matter apparently digested in the rumen (OMADR) (116 and 85 g NAN/kg OMADR, respectively, P < 0·05).

Fractional outflow rate of digesta markers from the rumen, when estimated from abomasal digesta, was significantly higher than when estimated from faeces (103Ru-p 0·121 v. 0·09; 51Cr-EDTA 0·169 v. 0·111/h; P > 0·05).

It was concluded that cannulation did not affect intake and digestion characteristics in these young lambs. The changes in the site of nutrient digestion as the animals aged may have been due to agerelated changes in digestive function but appeared to be associated with the increase in intake that occurred between measurement periods of the cannulated lambs.

Three grasses and two legumes, each at two stages of maturity, were fed to three fistulated sheep and samples of the feed, and faeces and contents of the reticulo-rumen, abomasum and ileum were collected for the determination of particle size by wet sieving. Modulus of fineness (MF) was calculated for all particulate matter that failed to pass a 0·15 mm screen. Resistance to flow from the rumen of feed particles of different sizes was also calculated.

The mean MF of the reticulo-rumen contents was 2·56 compared with 5·72 for the feed. Material leaving the rumen and found in the abomasum had a MF of 1·67 and subsequent changes were small and not significant; ileum 1·63, faeces 1·80. Particles greater than 1·18 mm passed out of the reticulo-rumen although the quantity was small (1–3%). The resistance to flow of particles of different sizes from the reticulo-rumen was closely related to particle size with no difference between grasses and legumes or between young and mature forages.

It was concluded that in modelling the flow of particles from the reticulo-rumen a non-compartmentalized approach should be adopted, but if a simple two-compartment model is required then a critical sieve size of about 1·18 mm may be useful, since less than 5% of the particulate material is retained on this sieve size.

The quantity of imbibed water that bypassed the rumen directly or rapidly effluxed from the rumen was investigated in four steers offered water marked with CrEDTA. Water was offered for short periods designed to simulate the drinking patterns that occur under extensive grazing conditions. Animals were fed either low quality pangola hay in the long form or a concentrate diet. Bypass of imbibed water was calculated by difference from marker imbibed and that present in the rumen on emptying after water had been imbibed. It thus represents the passage of marked water directly to the omasum/abomasum and that which rapidly effluxed from the rumen before emptying. Bypass of imbibed marked water was 19·0 and 25·3% for animals consuming pangola and concentrate respectively (significantly different from zero but no significant diet effect). Imbibed water entering the rumen mixed rapidly so that liquid from a posterior site in the rumen had a similar concentration of Cr to that from an anterior site in the proximity of the reticulum and cranial sac by about 1 h after drinking. There was no effect of rumen sampling site on the fractional outflow rate of CrEDTA (from imbibed marked water) from the rumen. It was concluded that most water which is drunk after a period of water deprivation will enter the rumen, mix rapidly and have a fractional outflow rate similar to other fluid in the rumen. The values derived may be used to calculate the amounts of supplement needed in drinking water if the target site is the rumen or intestines of cattle with intermittent access to water under extensive grazing conditions.

Large (>1600 μm), ingestively masticated particles of bermuda grass (Cynodon dactylon L. Pers.) leaf and stem labelled with 169Yb and 144Ce respectively were inserted into the rumen digesta raft of heifers grazing bermuda grass. The concentration of markers in digesta sampled from the raft and ventral rumen were monitored at regular intervals over approximately 144 h. The data from the two sampling sites were simultaneously fitted to two pool (raft and ventral rumen–reticulum) models with either reversible or sequential flow between the two pools. The sequential flow model fitted the data equally as well as the reversible flow model but the reversible flow model was used because of its greater application. The reversible flow model, hereafter called the raft model, had the following features: a relatively slow age-dependent transfer rate from the raft (means for a gamma 2 distributed rate parameter for leaf 0.0740 v. stem 0.0478 h-1), a very slow first order reversible flow from the ventral rumen to the raft (mean for leaf and stem 0.010 h-1) and a very rapid first order exit from the ventral rumen (mean of leaf and stem 0.44 h-1). The raft was calculated to occupy approximately 0.82 total rumen DM of the raft and ventral rumen pools. Fitting a sequential two pool model or a single exponential model individually to values from each of the two sampling sites yielded similar parameter values for both sites and faster rate parameters for leaf as compared with stem, in agreement with the raft model. These results were interpreted as indicating that the raft forms a large relatively inert pool within the rumen. Particles generated within the raft have difficulty escaping but once into the ventral rumen pool they escape quickly with a low probability of return to the raft. It was concluded that the raft model gave a good interpretation of the data and emphasized escape from and movement within the raft as important components of the residence time of leaf and stem particles within the rumen digesta of cattle.

Brahman Shorthorn steers (213±4·6 kg initial weight) were grazed on a pangola (Digitaria eriantha cv. Steudel) pasture interplanted with leucaena (Leucaena leucocephala cv. Cunningham) in rows 1·8–2·7 m apart in the Ord River Irrigation Area (ORIA) in north-west Western Australia. The leucaena comprised a mean of 46% of the diet but ranged from 100% of the diet on day 1 to c. 18% on day 7 of a 7-day grazing period, within the rotational grazing system. It was suggested that the low herbage allowance of leucaena may have restricted the intake of the steers, reducing the quantity and quality of the herbage consumed.

The steers were also supplemented with maize during the dry and wet seasons (1992 and 1992/93). The maize supplement was offered at 0, 0·5, 1·0, 1·5 and 2·0 kg/head per day, over a 168-day period. Maize supplementation at 1·5 kg maize per head per day resulted in an increase in the liveweight gain of the steers grazing leucaena/pangola pastures in the dry season from 0·73±0·05 kg/day (mean±S.E.) for no supplementation to 1·1±0·05 kg/day for 1·5 kg/head per day of maize. Maize supplementation up to 2·0 kg/day did not further increase the liveweight gain. A high rate of substitution of leucaena and pangola intake for the maize supplement occurred.

There was a large seasonal difference in liveweight gain (mean 0·89 v. 0·63 kg/day for the dry and wet seasons respectively; P<0·001) irrespective of the level of maize supplementation. This seasonal difference in liveweight gain was not primarily a function of the herbage on offer, but was most probably a direct function of the effect of the seasonal temperature and humidity influencing the feed intake and growth rate of these Brahman crossbred cattle.

This system produced some of the higher liveweight gains recorded per hectare for a grazing system (1570–2110 kg/ha per year), as a result of the very good individual liveweight gains (250-340 kg/head per year) and high stocking rate (6·25 head/ha).

Two experiments were carried out at Mt. Cotton, The University of Queensland, from November 1992 to July 1993, to study the effect of extent of digestion or feed type (grass or legume) on particle kinetics in the rumen. Small (0·5–1·18 mm) Yb-labelled grass or legume particles, either digested or undigested, were injected into the rumen of sheep fed on different diets, and their retention time in the reticulo-ruminal compartment measured. In Expt 1, four intact wethers were fed on either pangola grass hay, chaffed lucerne hay, pelleted lucerne hay or commercial pelleted concentrate. Digested particles from the faeces of animals fed on pangola or lucerne and undigested material from the same diets were wet-sieved and the fraction 0·5–1·18 mm collected, labelled with Yb-acetate and injected into the animals together with a solution of Cr-EDTA. Faecal samples were taken and analysed for marker concentrations. In Expt 2, four similar animals, fitted with duodenal and ruminal cannulae, were fed on different proportions of pangola grass hay and lucerne hay, and Cr-EDTA and the above mentioned labelled particles were injected through the rumen cannula. Samples were taken from the duodenum and analysed for marker concentrations.

The results indicated that diet characteristics rather than extent of digestion or particle type had the greatest influence on rates of passage of both liquid and particulate phases. Different proportions of pangola and lucerne did not result in marked differences in either the volumes of rumen contents or the rates of passage of the solid phase marker but altered the rates of passage of Cr-EDTA. Increasing the proportion of legume increased intake and decreased retention time markedly, with no additive effects on digestibility.

Particles of the same small size escaped with the same fractional passage rate within each diet, irrespective of type (grass or legume) or status (undigested or digested), indicating identical kinetics within each rumen type.

It was concluded that rumen conditions as influenced by diet type have most influence on water and particle kinetics and that extent of digestion of the small particles used in our experiments was not important. Particles of legume or grass of the same size behaved similarly within a diet type.

Sixty-four intact lambs and twenty-four lambs fitted with a duodenal cannula were weaned at 6 weeks of age and grazed pure species swards of either lucerne (Medicago sativa), white clover (Trifolium repens), ryegrass (Lolium perenne) or prairie grass (Bromus catharticus) for 6 weeks. Intake and duodenal digesta flow were estimated when lambs were 8 and 12 weeks of age. Lambs grazing the two legume species grew at a similar rate, as did lambs grazing the two grass species. Legumes promoted a 38% higher growth rate than grasses. The higher growth rate of lambs grazing legumes was associated with a 36% higher digestible organic matter intake (DOMI; 29.5 and 21.7 g/kg body-weight per d for legume and grass respectively) and a 33% higher duodenal non-ammonia-nitrogen (NAN) flow (1.22 and 0.92 g/kg body-weight per d respectively). There was no species difference in the site of organic matter digestion; on average 0.56 of DOMI was apparently digested in the rumen and 0.77 of DOMI was truly digested in the rumen. There was no difference in duodenal NAN flow, relative to DOMI (average, 43 g/kg) or to organic matter apparently digested in the rumen (80 g/kg). Similarly, there was no difference in microbial N flow relative to duodenal NAN (0.50 g/g) and organic matter apparently (41 g/kg) or truly (29 g/kg) digested in the rumen. It was concluded that the higher growth rates achieved by lambs grazing legumes were due to higher intakes which increased the total quantity of nutrients supplied despite more protein being lost in the rumen of lambs consuming legumes.

Twelve lambs, paired on the basis of live weight, were cannulated in the abomasum, in the proximal jejunum approximately 4 m distal to the pylorus and in the terminal ileum. Six were infected with 3000 Trichostrongylus colubriformis and 3000 Ostertagia circumcincta larvae each day for 18 weeks and the remainder were pair-fed to individual infected lambs. All animals were offered ryegrass (Lolium perenne)–white clover (Trifolium repens) pasture, cut daily. Dry matter (DM) intake, live weight, faecal egg concentration, plasma pepsinogen and plasma protein concentrations were measured weekly. During weeks 7 and 17 after commencement of infection, the flow of digesta along the gastrointestinal tract was measured together with enteric plasma loss and true digestion and absorption of 125I-labelled albumin in the small intestine. DM intake was depressed by parasitism, being 1331, (se 70), 423 (se 32) and 529 (se 52) g/d during weeks 3, 7 and 17 respectively. The flow of nitrogen at the proximal jejunum and in faeces was increased by parasitism during week 7 and at the abomasum and ileum during week 17. Plasma protein-N loss (g/d) into the gastrointestinal tract was 0.68 (se 0.091) and 1.97 (se 0.139) during week 7, and 0.85 (se0.158) and 1.96 (se 0.396) during week 17, in control and infected sheep respectively. True digestion and absorption of albumin in the proximal small intestine, the site of infection, was very low (mean 0.08) and was not affected by parasitism. Between the abomasum and terminal ileum absorption of albumin was high (mean 0.87) and again was not affected by parasitism. It was calculated that of the total increase in endogenous protein passing from the ileum tract as a result of infection, plasma protein comprised only a small percentage (10–36%). The major proportion of digestion and absorption of protein occurred in the distal small intestine beyond the site of infection and was not affected by infection.

Previous experiments with early weaned lambs at pasture have indicated the large protein losses which occur in the rumen (prairie grass 3%, ryegrass 22%, white clover 29% and lucerne 42%) (Cruickshank et al. 1985). Growth appeared to be related to duodenal protein supply and these were similar for the grasses and for the legumes (grasses 228 g/d liveweight gain and 0.92 g duodenal NAN/kg W/d, legumes 314 g/d and 1.22 g duodenal NAN/kg W/d). Efficiency of use of absorbed amino acid also appeared to be low (0.43). These results suggested that growth of lambs grazing these high quality pastures could be increased by increasing duodenal protein supply and/or by amino acid supplementation. Because of the large protein losses which occur in the rumen of animals grazing legume pastures in particular there is scope for manipulation of this aspect either through supplementation or plant breeding.

The objective of this experiment was to examine the liveweight gain response of lambs grazing grass or legume pastures to fishmeal supplementation and also the response of lambs grazing legume pastures to two forms of protected amino acid supplements designed to supplement first limiting amino acid(s).

1. Ten 5-month-old lambs (29 (SE 1.2) kg), reared parasite-free and prepared with rumen duodenal and ileal cannulas, were paired and given rations of Ruminant Diet AA6 (90 g/kg live Weight0.75) by means of continuous feeders. From 6 months of age one of each pair was dosed daily with 2500 Trichostrongylus colubriformis larvae for 14 weeks. Untreated animals received the amount of ration consumed by their infected pair-mates the previous day.

2. During three periods, ((1) the week before and the first 2 weeks of dosing with infected larvae, (2) during weeks 5–7 and (3) during weeks 11–13 of dosing) all lambs underwent a series of experiments to determine their nitrogen balance, the amounts of N leaving the small intestine, the amount of 51CrC13-labelled plasma protein leaking into the small intestines, and the disappearance of 35S-labelled bacteria from the small intestine.

3. The infection caused varying degrees of feed refusal in all infected animals. As a result the values for N balance and for the flow of N at the ileum during the latter two periods were regressed against dry-matter intakes for each group in each period.

4. The infection caused a reduction (P < 0.05) in N retention and increased (P < 0.05) flow of N at the ileum. The increase in N flow at the ileum of infected lambs was greater (P < 0.01) at weeks 11–13 of dosing (infected–control 3.6 g N/d (standard error of difference (SED) 0.57), P < 0.01) than at weeks 5–7 of dosing (infected–control 1.5 g N/d (SED 0.57), P < 0.05).

5. There were no between-treatment or between-period differences in the disappearance of 35S-labelled bacteria from the small intestines of infected or control lambs, but the infection did cause an increase in plasma N leakage during both periods. During weeks 5–7 and 11–13, plasma N leakage in infected lambs was 1.1 g N/d (P < 0.01) and 1.7 g N/d (P = 0.056) respectively higher than that in the control lambs.

6. A proportion of the endogenous secretions which enter the small intestine is likely to be resorbed before the ileum. It was calculated that to account for the extra non-ammonia-N (NAN) flow at the ileum up to 3–5 g NAN/d during weeks 5–7 of dosing and 15–20 g N/d during weeks 11–13 of dosing could have entered the small intestine as mucin and sloughed cells.

7. The results seem to indicate that the nutritional penalty associated with the development of resistance to infection is greater than that associated with the primary infection.