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An experiment was carried out in which simulated swards of ryegrass (cv. S23) were grown in boxes. In the first instance the swards were cut at weekly intervals to maintain five levels of leaf area index (LAI) from LAI 1 to 4–5 in simulation of continuous grazing. Measurements were made of growth, senescence and net growth rate and of net canopy photosynthesis at constant irradiance. The results showed that the swards adapted to the defoliation regimes mainly by changes in tiller population density and pseudostem length. When the swards had equilibrated to the cutting regime growth rate increased with LAI but, since tiller density and the partitioning of growth between herbage harvested and that lost by sensecence also changed with LAI, net growth rate was constant over the LAI range 2–4·5. Maximum weight of herbage harvested was obtained between LAI 2 and 3.
After 10 weeks of weekly cutting all the swards were cut back to LAI 1 and allowed to regrow. Growth rate showed almost no response to the previous culling treatments. The relationship of net canopy photosynthesis to LAI was linear for the frequently defoliated swards and curvilinear for regrowing swards. The reasons for this difference were examined. 相似文献
After 10 weeks of weekly cutting all the swards were cut back to LAI 1 and allowed to regrow. Growth rate showed almost no response to the previous culling treatments. The relationship of net canopy photosynthesis to LAI was linear for the frequently defoliated swards and curvilinear for regrowing swards. The reasons for this difference were examined. 相似文献
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LYNNE I. KUSHNER DVM CYNTHIA M. TRIM BVSc Diplomate ACVA SILUVERU MADHUSUDHAN BPharm CAROLYN R. BOYLE PhD 《Veterinary surgery : VS》1995,24(2):180-187
The hemodynamic effects of interpleural (IP) bupivacaine were studied in six halothane-anesthetized dogs. On four separate occasions, each dog received IP saline (S), or bupivacaine at a low dosage of 1.5 mg/kg (L), high dosage of 3.0 mg/kg (H), or high dosage of 3.0 mg/kg with epinephrine 5 μg/mL (HE). Heart rate, systolic and mean arterial pressures, and base excess were significantly lower in the H dosage group than in the other treatment groups. Cardiac output, expressed as a percentage of change from baseline, was significantly higher in the L group than in the H and S groups. Pulmonary arterial pressure and respiratory rate were significantly higher in the HE group than in the other three groups. Mean plasma concentrations of bupivacaine peaked between 5 and 15 minutes after IP injection. Maximum plasma concentrations in individual dogs were variable; however, mean maximum plasma concentrations in the H and HE groups were not significantly different. Clinically significant hypotension occurred in one dog in the H group and in one dog in the HE group. No pulmonary complications were detected. 相似文献
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Components of regrowth in grazed and cut Lolium perenne swards 总被引：1，自引：0，他引：1
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Sward management, lamina turnover and tiller population density in continuously stocked Lolium perenne-dominated swards 总被引：2，自引：0，他引：2
S. A. GRANT G. T. BARTHRAM L. TORVELL J. KING H. K. SMITH 《Grass and Forage Science》1983,38(4):333-344
Measurements of rates of growth and senescence of leaf lamina per tiller and of changes in tiller population densities were made in three experiments designed to investigate the influence of sward slate on leaf turnover and net production under continuous stocking. In each experiment initially uniform swards were fenced to provide four plots on which animal numbers were adjusted twice weekly to give a series of swards maintained as nearly as possible in a steady state with respect to sward surface height (range 1.1–6.4 cm) and herbage mass (range 440–2690 kg OM ha?1). Two experiments were carried out in July–September on vegetative swards and one in May–June on a reproductive sward. Measurements were begun 3–7 weeks after treatments were started and were repeated weekly during 3–4 week measurement periods. In all three experiments the rate of lamina growth per tiller increased linearly with an increase in sward surface height and herbage mass. In the two experiments conducted in July–August this relationship was partially offset by a linear increase in the rate of senescence per tiller but net production per tiller also increased linearly in relation to sward height and mass. In the experiment conducted in May–June the rates of growth and senescence per tiller increased in parallel so that net production per tiller showed no relationship with sward condition. Tiller population densities in the July–August experiments were highest in swards maintained between 2 and 3 cm surface height and declined in swards maintained above and below this height. In the experiment in May–June tiller numbers were similar in all treatments prior to the summer solstice but diverged in a manner similar to the other experiments later in the year. The rate of lamina growth per unit area increased in a manner consistent with an asymptotic relationship and the rate of senescence increased linearly with increasing sward height and mass in all three experiments. Net production per unit area was reduced on swards below about 2.5 cm in height but was insensitive to variation in sward surface height between 2.5 and 6.0 cm (approximately 1000–2500 kg OM ha?1 herbage mass). The effectiveness of adjustments in tiller numbers and production per tiller and of changes in the balance between growth and senescence as mechanisms of sward homeostatis, together with their implications in the scope for manipulating herbage production by grazing management are discussed briefly. 相似文献
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LYNNE A. SNOW DVM RICK WHITE DVM SCOTT GUSTAFSON DVM MS Diplomate ACVS LIN XIE BS GISELLE HOSGOOD BVSc MS PhD Diplomate ACVS W. TODD MONROE PhD PE JOHN P. CASEY BS MANDI J. LOPEZ DVM MS PhD Diplomate ACVS 《Veterinary surgery : VS》2010,39(2):195-207
Objective— To quantify and compare canine stifle stability after 3 stabilization techniques. Study Design— Randomized controlled study. Sample Population— Adult canine cadaveric pelvic limbs. Methods— Total craniocaudal (CrCa) tibial translation quantified in stifles with the cranial cruciate ligament (CrCL) intact, transected, and stabilized with 1 of 3 techniques: (1) hamstring graft (HG); (2) modified retinacular imbrication (MRIT); (3) anatometric fascia lata translocation (AFLT). Tibial translation was quantified from radiographs generated during application of cranial and caudal forces to the tibia. After removal of all soft tissues except periarticular ligaments and fixation, CrCa tibial translation, as before, and medial–lateral rotation, via torsional loading, was quantified with an active motion analysis system. Total tibial translation was evaluated for effect of technique and cruciate status using mixed effect linear model with significance considered at P‐value <.05. Results— CrCa translation was not significantly different across stabilization techniques with CrCLs intact, transected, or after stabilization. Poststabilization translation was significantly less than posttransection for all techniques. Compared with the intact CrCL, CrCa translation poststabilization after HG was significantly greater whereas poststabilization after MRIT and AFLT was not significantly different. Tibial rotation exceeded instrumentation limits in 62.5% HG limbs, 20% MRIT limbs, and 60% AFLT limbs. Conclusions— All 3 stifle stabilization techniques confer comparable CrCa translational stability after CrCL disruption with that provided by the MRIT and AFLT techniques comparable to the intact CrCL. Clinical Relevance— The extra‐ and intracapsular techniques evaluated in this study reduced CrCa tibial translation in CrCL deficient stifles to varying amounts. 相似文献
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A factorial pot-experiment was carried out to investigate the effect of burial of stolons (stolons unburied or buried to a depth of 0·5–1 cm at day 0), with and without defoliation (plants uncut or all unfolded laminae removed at weekly intervals) on the growth of two varieties of white clover (cv. Kent or cv. Milkanova) harvested on three dates (14 d, 28 d and 42 d after burial). The soil used was a 3:2:1 mixture of clay loam:peat:sand, and there were three replicates of each variety for each treatment at each harvest date. Burial of stolons in the absence of defoliation had no effect on stolon extension, leaf appearance, or the concentration of water-soluble carbohydrate in the stolons. The number of axillary buds developing (new branches plus flowers) was increased on the new surface-growing tips of primary stolons but was reduced on branch (i.e. secondary) stolons. The proportion of branches to flowers was largely unaffected by burial. Defoliation caused substantial reductions in the concentration of water-soluble carbohydrates in stolons and stolon extension growth, a reduction in number of axillary buds developing, and in the proportion of buds which were floral, but had only a small effect in reducing leaf appearance. The combination of stolon burial and defoliation resulted in the death of secondary stolons; 42% of all secondary stolons had died by day 42, and stolon extension, leaf appearance and numbers of axillary buds developing on secondary stolons were severely reduced. The numbers of axillary buds developing on primary stolons was increased owing to more buds developing on the resurfaced stolon tips, but the increase was inadequate to compensate for the reduced growth, and death of secondary stolons. Differences between clover varieties in response to treatments were small. In general, the smaller variety, cv. Kent, was more adversely affected by burial than the larger variety, cv. Milkanova. A variety x defoliation interaction occurred for senescence of leaves; petiole senescence of cut leaves was reduced or similar to that of intact leaves for cv. Kent, but was increased for cv. Milkanova. The results are discussed in relation to treatment effects on carbon sources and sinks, and in relation to climate-soil interactions. 相似文献
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LYNNE P. HARRISON R.J. HEITZMAN B. F. SANSOM 《Journal of veterinary pharmacology and therapeutics》1983,6(4):293-303
Twenty wether sheep were allocated to seven groups and received implants near the base of one ear with pellets containing: for group 1, (OE) 20 mg oestradiol-17 beta alone; for group 2, (TBA/OE) 20 mg oestradiol-17 beta intimately mixed with 140 mg trenbolone acetate; for group 3, (T/OE) 20 mg oestradiol-17 beta mixed with 200 mg testosterone; for group 4, (P/OE) 20 mg oestradiol-17 beta mixed with 200 mg progesterone; for group 5, (TBA/OE2) 20 mg oestradiol-17 beta in one ear and 140 mg trenbolone in the other ear; for group 6, (TBA/OE1) 20 mg oestradiol-17 beta and 140 mg trenbolone as separate pellets in one ear; group 7 sheep received implants of carrier material and served as controls. The concentrations of steroids were measured in plasma samples collected from both jugular veins during the 16-week period after implantation. The absorption of oestradiol-17 beta was slower and more sustained from the pellets in which it was mixed with other steroids (groups 2, 3 and 4) than from the pellets containing oestradiol-17 beta alone (groups 1, 5 and 6). The concentration of each steroid in plasma was higher in the jugular vein ipsilateral to the implant than in the vein on the opposite side. The difference between the concentrations in the two veins was used to calculate the biological half-lives of the steroids; for oestradiol-17 beta and trenbolone the mean values ranged from 1.8 to 6.8 min and from 3 to 4 min, respectively, and for testosterone and progesterone the mean values were 4.7 and 3.5 min, respectively. 相似文献
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Photosynthetic potential of ryegrass pastures when released from continuous stocking management 总被引：1，自引：0，他引：1
The relationship between the rate of canopy gross photosynthesis and LAI was investigated for ryegrass swards released from grazing after a period of continuous stocking to maintain the pasture at LAI 2–3. The regrowing swards were allowed to increase to about LAI 5 over a period of about 2 weeks while the rate of photosynthesis was measured and compared with that for continuously stocked swards maintained at LAI values between 2 and 6. Gross photosynthesis was found to increase more rapidly than LAI on the regrowing swards than on the steady-state control pastures. However, this response appeared to be influenced by seasonal factors. The potential increase in net COi uptake was estimated to range from 0 to 22%. The response was attributed to an increasing proportion of young photosynthetically-efficient leaves near the top of the canopy, modified by seasonal changes in the rate of tillering. The agronomic implications of the results are iscussed. 相似文献
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SHEILA A. GRANT G. T. BARTHRAM LYNNE TORVELL J. KING D. A. ELSTONJ 《Grass and Forage Science》1988,43(1):29-39
The possibility of increasing the herbage utilized over a grazing season was investigated in a study comparing continuously stocked steady-state swards maintained at optimum height (3.5 cm) with intermittently grazed swards. The intermittent systems were designed (a) to allow periodic increase in leaf area and hence growth rate, (b)to ensure that the accumulated herbage was eaten before it senesced, and (c) lo retain high tiller density by alternating periods of herbage accumulation with periods of continuous stocking. Two treatments (no animals or animal numbers reduced to half those on the 3.5 cm steady-state treatment) were used during the 17-18-d periods of herbage accumulation. Grazing down was completed in 3–4 d, after which two treatments (14 d or 28 d) were used for the intervening periods of continuous stocking when sward height was maintained at 3.5 cm. Herbage production was estimated using the tissue turnover technique, with tiller population densities and rates of growth, senescence and net production per tiller measured at frequent intervals. Intermittent grazing treatments where animals were removed during herbage accumulation resulted in changes in tiller size and number, and in growth rates, but not senescence rates, per tiller such that short-term deviations in the net rate of herbage production occurred compared with the continuously stocked control. The periods of advantage during phases of herbage accumulation were counterbalanced by those of disadvantage during the subsequent steady-state phases. Where animal numbers were reduced during herbage accumulation, sward conditions differed little from those of the continuously stocked control, implying that intake per individual animal was increased. It was concluded that intermittent grazing systems offered no advantage over simpler continuous stocking systems, provided that a flexible approach to conservation was incorporated to allow control of sward conditions on the grazed area. 相似文献
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