Sward growth under cutting and continuous stocking managements: sward canopy structure, tiller density and leaf turnover

The change in structure of continuously grazed versus infrequently cut swards of perennial ryegrass ( Lolium perenne L), cv. S23, was investigated during their first full harvest year. Measurements were made from early May until late September. The intensity of stocking by sheep in the grazed sward was adjusted in an attempt to maintain a high level of radiation interception and the cut sward was harvested at approximately monthly intervals.
The herbage mass, lamina area index and radiation interception of the cut sward varied in a cyclic pattern between harvests but in the grazed sward these parameters showed considerably less variation, although they all increased early in the season and then declined later. The proportion of dead material above ground increased throughout the season in both sward types but was more marked in the grazed sward.
There were major differences between the grazed and cut swards in the number of tillers per unit ground area; the difference became more marked throughout the season and by September the tiller densities in the grazed and cut swards were 3·20⁴ m^-2 and 6·20³ m^-2 respectively. Divergence in tiller density was associated with differences in specific stem weight and leaf area per tiller.
Rates of appearance and death of leaves on tillers in the grazed sward were determined. During May, leaf appearance exceeded leaf death but this was reversed in June. During the rest of the season as a new leaf appeared on a tiller so the oldest leaf died.     

PULMONARY ANGIOGRAPHY USING 16 SLICE MULTIDETECTOR COMPUTED TOMOGRAPHY IN NORMAL DOGS

We report a canine computed tomography (CT) pulmonary angiography technique using multidetector CT (MDCT). CT pulmonary angiography using a 16 slice MDCT was performed on five healthy, anesthetized beagles. A helical acquisition with pitch of 1.4 was used. The time delay for the angiographic study was determined using a bolus‐tracking program. A dose of 400 mg I/kg of nonionic contrast medium (Iohexol 300 mg I/ml) was administered to each dog via a cephalic catheter using an angiographic power injector at a rate of 5 ml/s. In two dogs a second study, using a contrast medium dose of 200 and 600 mg I/kg was performed. Arterial enhancement of transverse and reformatted images was classified subjectively as excellent, good, or poor, and assessed objectively by measuring Hounsfield units at the right main pulmonary artery. Angiographic studies were evaluated by two radiologists to determine the number of subsegmental arterial branches visualized. The median number of subsegmental arterial branches identified was five (range: 2–7). Based on the time attenuation curve obtained by the bolus‐tracking program, there was consistent enhancement of the right main pulmonary artery beginning at 6 s and peaking at 8 s in 4/5 dogs. The contrast medium dose of 400 mg I/kg produced good to excellent vascular enhancement in the same 4/5 dogs. A dose of 200 mg I/kg resulted in poor enhancement. CT pulmonary angiography using MDCT and an automated bolus‐tracking program allows rapid, consistent evaluation of the pulmonary vasculature using a single dose of 400 mg I/kg of contrast medium.