The present experiment was conducted to quantify the net fluxes of both free and peptide amino acids across the mesenteric and stomach portions of the portal-drained viscera (PDV) of three yak cows (172·3±18·6 kg, BW) fed a straw-concentrate diet at maintenance level. Yaks had been fitted with sampling catheters in the portal vein, mesenteric artery and mesenteric vein prior to its convergence with the gastrosplenic vein. Blood flow was determined by measuring the dilution of para-aminohippurate (PAH) infused constantly into a distal mesenteric vein. Amino acids in the deproteinized plasma were analysed before and after acid hydrolysis. The increased amino acids after acid hydrolysis were considered as peptide-bound amino acids (PAA). The fluxes of free amino acids (FAA) and PAA across PDV and mesenteric-drained viscera (MDV) were calculated as the product of venoarterial differences and plasma flow. Flux across the stomach viscera (SDV) was calculated as the difference between portal and mesenteric fluxes. Portal blood flow was 389 l/h or 2·32 l/h kg BW, of which 37% was contributed by the mesenteric vein. There was net appearance of a large quantity of PAA across PDV, which accounted for 92% of the total nonprotein amino acid flux. Net release of PAA and FAA in SDV accounted for 78% and 42% of the net release in PDV, respectively. These results suggest that in yaks, peptide possibly is the primary form of amino acid absorption, and that the stomach area probably is the major site of peptide absorption.

A laboratory experiment was designed to determine the fate of 15N-labelled slurry ammonium (15NH4-N) and compare soil inorganic-N distribution following surface applied or injected pig slurry. A system of cylindrical volatilization chambers equipped to allow continuous trapping of ammonia (NH3) was used. Undisturbed soil columns were placed in the chambers prior to the application of slurry. A nitrogen balance including soil, air and plant analysis was established for both treatments, 8 days after application. Average cumulative emissions of NH3 were 15% and 11% of the total ammoniacal-N added with the surface and injected treatments, respectively. After 8 days 55% of the 15NH4-N applied through slurry injection was recovered in the soil inorganic-N pool: 37% as 15NH4-N and 18% as 15NO3-N. These figures compare with only 25% 15NH4-N recovered with the surface applied slurry treatment: 7% as 15NH-N and 17% as 15NO3-N. Immobilization into soil organic-N accounted for 8% of the 15NH4-N applied for the injected treatment and 6% of the surface applied slurry-15N. 15N uptake by the grass was 2% and 7% for the injected and surface applied treatments, respectively. The percentage of added 15N accounted for was 76% for the injected treatment and 53% for the surface applied slurry treatment.

An experiment was carried out from August to early November 1994 to examine differences in diet selection, herbage intake, grazing behaviour and animal performance between weaned lambs rotationally grazing swards of annual ryegrass (Lolium multiflorum)/white clover (Trifolium repens) and Yorkshire fog (Holcus lanatus)/T. repens with or without Lotus corniculatus. There were four replicate groups of six lambs per treatment. The effects of condensed tannins (CT) on lamb production were assessed by twice-daily oral administration of 10g polyethylene glycol (PEG; molecular weight 4000) to half the lambs on each sward. The Lotus content of all swards was very low, and results are presented here for main sward comparisons meaned over lotus treatments. Overall mean estimates of pre-grazing herbage mass and sward surface height for the annual ryegrass and Yorkshire fog swards respectively, were 5820 v. 4360±190 kgDM/ha (P<0·001) and 29 v. 21±0·6cm (P<0·001). The coefficient of organic matter digestibility (OMD) of the diet selected and herbage intake were higher on Yorkshire fog than on annual ryegrass (0·78 v. 0·74 ± 0·080g/kg; P<0·05, and 1070 v. 860±57g OM per lamb per day, P<0·05 respectively), reflecting the higher content in the diet of grass green leaf (980 v. 930g/kg±14g/kg, P<0·05) and the lower content of dead material (80 v. 110±15g/kg, P<0·08). Lambs grazing on Yorkshire fog swards had higher clean wool growth rate (1470 v. 1280±30mg/cm per day, P<0·01) and greater fibre diameter (31 v. 29±0·2μ, P<0·001), greater liveweight gain (152 v. 108±5·5g/day, P<0·001), final weight (42 v. 38±0·5kg, P<0·001), carcass weight gain (89 v. 69±2·5g/day, P<0·001), carcass weight (19 v. 17±0·3kg, P<0·001) and soft tissue thickness (GR value 11 v. 8±0·5mm, P<0·01), and lower faecal egg counts (FEC; square root transferred values 9·2 v. 11·0±0·4 eggs/g fresh faeces, P<0·01) than lambs grazing annual ryegrass swards. Similar dietary concentrations of condensed tannins (CT) between Yorkshire fog and annual ryegrass swards (4·2 v. 3·7 DM±0·2g/kg, P<0·08) increased clean wool growth (1440 v. 1310±32 mg/cm per day, P<0·05), fibre diameter (30·7 v. 29·5±0·21μ, P<0·01) and liveweight gain (141 v. 120±4·3g per lamb per day, P<0·01), although differences in carcass weight (17·9 v. 18·2±0·3kg) and FEC transformed values (9·6 v. 11·0±0·6 eggs/g fresh faeces) were not significant. The effects of CT on animal performance were greater in Yorkshire fog swards. CT had no significant effects on diet selection, herbage intake and grazing behaviour patterns.