Characteristics of boli formed by dairy cows upon ingestion of fresh ryegrass, lucerne or chicory.

This study examined the comminution of fresh herbage, subsequent nutrient release, and the characteristics of swallowed boli from three physically and chemically contrasting forages during ingestive mastication by dairy cows. The extent and pattern of nutrient release will determine their availability to rumen microflora, and potentially influence their efficiency of use. The forages evaluated were perennial ryegrass (ryegrass, Lolium perenne L., cv Alto AR37), lucerne (Medicago sativa L., cv Torlesse) and chicory (Cichorium intybus L., cv Choice). Experimental design was a 3×3 cross-over with three forages and three consecutive 1-day measurement periods, conducted twice. Six non-lactating, pregnant, multiparous Holstein-Friesian×Jersey cows (Bos taurus) were used, with the first cross-over applied to three mature (10.1±0.61 years old; BW 631±64 kg) cows, and the second to three young (4.8±0.02 years; BW 505±19 kg) cows. Fresh cut forage was offered to the cows following partial rumen evacuation. Swallowed boli were collected directly at the cardia at the commencement, middle and end of the first feeding bout of the first meal of the day. Forage species did not affect the fresh weight of ingested boli (mean 169 g, P=0.605) but the proportion of saliva in boli varied between forage. Boli of chicory contained the greatest amount of herbage material and least amount of saliva, whereas ryegrass boli were the opposite. Boli fresh weight tended to increase as time in the meal progressed, but the age of the cow was not shown to affect any boli characteristics or nutrient release. Particle size reduction was affected by forage, with 31%, 38% and 35% of chicory, lucerne and ryegrass herbage reduced to <2 mm. There was little evidence of relationship between comminution and any physical or chemical characteristic of the forage, except in ryegrass where extent of comminution was moderately correlated with herbage strength. Proportional release of herbage soluble carbohydrate exceeded that of N during mastication. Differences in loss of N were moderately correlated with the amount of N in the herbage (R 2=0.53) but herbage comminution was not strongly correlated with release of either N or carbohydrate. These findings illustrate the complex animal×forage interactions that occur during mastication, and that it is not possible to infer nutrient loss from herbage based on herbage characteristics as the driver for this differ between species.

Forage-based dairying in a water-limited future: use of models to investigate farming system adaptation in southern Australia.

The irrigated dairy industry in southern Australia has experienced significant restrictions in irrigation water allocations since 2005, consistent with climate change impact predictions for the region. Simulation models of pasture growth (DairyMod), crop yield (Agricultural Production Systems Simulator, APSIM), and dairy system management and production (UDDER) were used in combination to investigate a range of forage options that may be capable of sustaining dairy business profitability under restricted water-allocation scenarios in northern Victoria, Australia. A total of 23 scenarios were simulated and compared with a base farm system (100% of historical water allocations, grazed perennial ryegrass pasture with supplements; estimated operating surplus $A2,615/ha at a milk price of $A4.14/kg of milk solids). Nine simulations explored the response of the base farm to changes in stocking rate or the implementation of a double cropping rotation on 30% of farm area, or both. Five simulations explored the extreme scenario of dairying without any irrigation water. Two general responses to water restrictions were investigated in a further 9 simulations. Annual ryegrass grazed pasture, complemented by a double cropping rotation (maize grown in summer for silage, followed by either brassica forage crop and annual ryegrass for silage in winter and spring) on 30% of farm area, led to an estimated operating surplus of $A1746/ha at the same stocking rate as the base farm when calving was moved to autumn (instead of late winter, as in the base system). Estimated total irrigation water use was 2.7ML/ha compared with 5.4ML/ha for the base system. Summer-dormant perennial grass plus double cropping (30% of farm area) lifted operating surplus by a further $A100/ha if associated with autumn calving (estimated total irrigation water use 3.1ML/ha). Large shifts in the forage base of dairy farms could sustain profitability in the face of lower, and fluctuating, water allocations. However, changes in other strategic management policies, notably calving date and stocking rate, would be required, and these systems would be more complex to manage. The adaptation scenarios that resulted in the highest estimated operating surplus were those where at least 10 t of pasture or crop DM was grazed directly by cows per hectare per year, resulting in grazed pasture intake of at least 2 t of DM/cow, and at least 60% of all homegrown feed that was consumed was grazed directly.

Metabotropic glutamate receptor 5 antagonist-induced stimulation of hypothalamic-pituitary-adrenal axis activity: interaction with serotonergic systems.

The mGluR5 antagonist 2-methyl-6-(phenylethynyl) pyridine (MPEP) produces anxiolytic or antidepressant effects in several rodent models through incompletely described mechanisms. Anxiolytics and antidepressants share several neuroendocrine features, including acute activation of the hypothalamic-pituitary-adrenal (HPA)-axis, desensitization of neuroendocrine responses with repeated dosing, and desensitization of the HPA axis to 5-HT1A agonist stimulation. We characterized these neuroendocrine parameters in rats treated systemically with MPEP and compared them to those induced by the anxiolytic buspirone. Acutely, MPEP dose-dependently (0.1-10 mg/kg i.p.) increased plasma corticosterone concentrations. These responses were blocked by 50% with the 5-HT1A antagonist WAY100635. The corticosterone responses to both 3 mg/kg MPEP and buspirone were decreased by 80% after 5 days of twice-daily injections. Repeated injection with MPEP decreased HPA-axis sensitivity to buspirone challenge by 75%. This desensitization was not associated with changes in mGluR5 or 5-HT1A receptor binding properties, expression of G-protein subunits coupled to these receptors, or in 5-HT-stimulated binding of [(3)H]-GTPgammaS to membranes. We conclude that MPEP acutely disinhibits the HPA axis, in part through uncharacterized changes in serotonergic signaling. Desensitization of 5-HT1A responses after repeated MPEP administration may indicate that, like other anxiolytics and antidepressants, plasticity in 5-HT signal transduction pathways has occurred.

Comparison of TNK with wild-type tissue plasminogen activator in a rabbit embolic stroke model.

BACKGROUND AND PURPOSE: Tissue plasminogen activator (tPA) is an effective treatment for stroke, but its utility is limited by fear of cerebral hemorrhage. Tenecteplase (TNK), a genetically modified form of wild-type tPA, exhibits a longer biological half-life and greater fibrin specificity, features that could lead to fewer cerebral hemorrhages than wild-type tPA in stroke patients. METHODS: We injected radiolabeled blood clots into the cerebral circulation of New Zealand White rabbits. One hour later, we administered tPA (n=57), 0.6 mg/kg TNK (n=43), 1.5 mg/kg TNK (n=27), or vehicle control (n=37). A blinded observer examined the brains for macroscopic hemorrhage using a semiquantitative score. We estimated thrombolysis by assessing the amount of radiolabel remaining in the cerebral vessels postmortem. RESULTS: Both wild-type tPA and TNK caused thrombolysis in most subjects. Hemorrhage was detected in 26% (6/23) of the control group, 66% (27/41) of the wild-type tPA group, 55% (16/29) in the 0.6-mg/kg TNK group, and 53% (9/17) in the 1.5-mg/kg TNK group (P:<0.05, chi(2) test). The tPA group was statistically significantly different from the control group, but the TNK and tPA groups did not differ from each other. Neither TNK nor tPA affected the size of the hemorrhages. CONCLUSIONS: TNK shows comparable rates of recanalization compared with wild-type tPA in a model of embolic stroke. While tPA increases hemorrhage rate, the hemorrhage associated with TNK treatment is not statistically different compared with controls or the tPA group. These findings suggest that TNK shows promise as an alternative thrombolytic treatment for stroke, but we could not demonstrate improved safety compared with wild-type tPA.

Pharmacological effects of the spin trap agents N-t-butyl-phenylnitrone (PBN) and 2,2,6, 6-tetramethylpiperidine-N-oxyl (TEMPO) in a rabbit thromboembolic stroke model: combination studies with the thrombolytic tissue plasminogen activator.

BACKGROUND AND PURPOSE: It has been proposed that spin trap agents such as N:-t-butyl-phenylnitrone (PBN) may be useful as neuroprotective agents in the treatment of ischemia and stroke. However, to date, there is little information concerning the effectiveness of spin trap agents when administered in combination with the only Food and Drug Administration-approved pharmacological agent for the treatment of stroke, the thrombolytic tissue plasminogen activator (tPA). Thus, we determined the effects of PBN when administered before tPA on hemorrhage and infarct rate and volume. We also compared the effects of PBN with those of 2,2,6, 6-tetramethylpiperidine-N:-oxyl (TEMPO), another spin trap agent that has a different chemical structure and trapping profile, on the incidence of infarcts and hemorrhage. METHODS: One hundred sixty-five male New Zealand White rabbits were embolized by injecting a blood clot into the middle cerebral artery via a catheter. Five minutes after embolization, PBN or TEMPO (100 mg/kg) was infused intravenously. Control rabbits received saline, the vehicle required to solubilize the spin traps. In tPA studies, rabbits were given intravenous tPA starting 60 minutes after embolization. Postmortem analysis included assessment of hemorrhage, infarct size and location, and clot lysis. RESULTS: In the control group, the hemorrhage rate after a thromboembolic stroke was 24%. The amount of hemorrhage was significantly increased to 77% if the thrombolytic tPA was administered. The rabbits treated with PBN in the absence of tPA had a 91% incidence of hemorrhage compared with 33% for the TEMPO-treated group. In the combination drug-treated groups, the PBN/tPA group had a 44% incidence of hemorrhage, and the TEMPO/tPA group had a 42% incidence of hemorrhage. tPA, PBN/tPA, and TEMPO/tPA were similarly effective at lysing clots (49%, 44%, and 33%, respectively) compared with the 5% rate of lysis in the control group. There was no significant effect of drug combinations on the rate or volume of infarcts. CONCLUSIONS: This study suggests that certain spin trap agents may have deleterious effects when administered after an embolic stroke. However, spin trap agents such as PBN or TEMPO, when administered in combination with tPA, may improve the safety of tPA by reducing the incidence of tPA-induced hemorrhage. Overall, the therapeutic benefit of spin trap agents for the treatment of ischemic stroke requires additional scrutiny before they can be considered "safe" therapeutics.

Dehydroepiandrosterone sulfate is neuroprotective in a reversible spinal cord ischemia model: possible involvement of GABA(A) receptors.

BACKGROUND AND PURPOSE: Dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) may function as neurotrophic or neuroprotective factors to protect central nervous system (CNS) neurons against a variety of insults, including excitotoxicity. The present study evaluated the pharmacological effects of DHEAS in a reversible spinal cord ischemia model. METHODS: DHEAS was administered (50 mg/kg IV) 5 or 30 minutes after the start of occlusion to groups of rabbits exposed to ischemia induced by temporary (15 to 60 minutes) occlusion of the infrarenal aorta. The group P(50) represents the duration of ischemia (in minutes) associated with 50% probability of resultant permanent paraplegia. RESULTS: The P(50) of the vehicle-treated control group, when behavioral analysis was assessed 18 hours after aortal occlusion, was 28.8+/-2.0 minutes. Neuroprotection was demonstrated if a drug significantly prolonged the P(50) compared with the vehicle-treated control group. Treatment with DHEAS at 5 minutes significantly (P<0.05) prolonged the P(50) of the group to 36.8+/-3.9 minutes. In addition, the DHEAS effect appeared durable, because a significant difference between the control and DHEAS-treated groups was still measurable at the 4-day time point. At 4 days, the P(50) of the control group was 26.1+/-2.2 minutes, whereas the P(50) for the DHEAS-treated group was 38.6+/-5. 9 minutes. DHEAS was not neuroprotective if administered 30 minutes after occlusion. In addition, the GABA(A) antagonist bicuculline abolished the neuroprotective effect of DHEAS. CONCLUSIONS: The present study suggests that neurosteroids may have substantial therapeutic benefit for the treatment of ischemic stroke.

Metalloproteinase inhibition reduces thrombolytic (tissue plasminogen activator)-induced hemorrhage after thromboembolic stroke.

BACKGROUND AND PURPOSE: A potentially dangerous side effect associated with tissue plasminogen activator (tPA) use is cerebral hemorrhage. We have focused on developing drugs that could be administered with tPA to reduce the rate of hemorrhage. Since recent studies suggest that various matrix metalloproteinases (MMPs) are important in tumor necrosis factor-alpha production and membrane and vessel remodeling after ischemia, we investigated whether MMP inhibition affected the rate of hemorrhage and infarct production in the absence or presence of tPA treatment. METHODS: We occluded the middle cerebral artery of New Zealand White rabbits with radiolabeled blood clots. Five minutes after embolization, we administered either the MMP inhibitor BB-94 (30 mg/kg SC) or its vehicle. Additional groups received BB-94 or vehicle in combination with tPA, administered 60 minutes after embolization (3.3 mg/kg tPA). After 48 hours, the rabbits were killed and brains were removed, immersion fixed for 1 week in 4% paraformaldehyde, and then cut into 5-mm coronal sections that were examined for the presence of hemorrhage, infarcts, and recanalization. RESULTS: Hemorrhage after embolic stroke was detected in 24% of the control group. tPA induced macroscopically visible hemorrhage in 77% of the tPA-treated group. The rabbits treated with BB-94 had an 18% incidence of hemorrhage (P:>0.05 compared with control). However, when the combination of BB-94 and tPA was administered to rabbits, there was only a 41% incidence of hemorrhage (compared with 77% in the tPA group; P:<0. 05). Both tPA and BB-94/tPA were similarly effective at lysing clots, at 49% and 35% (P:<0.05), respectively, compared with the 5% rate of lysis in the control group. There was a trend for a reduction in the number of infarcts, but it did not reach statistical significance. CONCLUSIONS: Our data suggest that MMP inhibition attenuates mechanisms involved in tPA-induced hemorrhage. This novel form of combination therapy may show promise as a treatment strategy for acute stroke.

Physiological integration in the clonal perennial herb Trifolium repens L.

Translocation of 14C-labelled carbohydrates between the parent stolon and branches, and among branches, of Trifolium repens plants was investigated in two glasshouse experiments to determine patterns of physiological organisation in this clonal species. Differential defoliation treatments were applied to the parent stolon and/or branches to test the sensitivity of translocation to the short-term carbon needs of defoliated sinks. Strong reciprocal exchange of carbohydrate between the parent stolon and branches was observed, with 18 41% of the 14C exported from leaves on the parent stolon moving to branches, while branches simulta-neously exported 25% (for old source branches) to 54% (for young source branches) of the 14C they assimilated to the parent plant, including translocation to other branches. Branch-to-branch translocation occurred both acropetally and basipetally. Parent-to-branch, branch-to-parent and branch-to-branch carbon fluxes all increased in response to defoliation of the sink, at the expense of carbon supply to stolon tissue or roots of the source module. Reduced export to stolon tissue of the parent axis played a major role in facilitating C reallocation from leaves on the parent stolon to defoliated branches. The observed patterns of C allocation and translocation could be adequately explained by accepted source-sink theory, and are consistent with a high degree of intra-plant physiological integration in resource supply and utilisation. This information provides mechanistic explanations for aspects of the growth dynamics and ecological interactions of T. repens in the patchy environment of a grazed pasture.

The physiological role of old stolon material in white clover (Trifolium repens L.).

Clonal plants of white clover (Trifolium repens L.), consisting of a single stolon plus roots and either three fully unfolded leaves or one fully unfolded leaf at the stolon apex, were grown in a controlled environment and sampled three times (after 7, 49 and 85 d growth) to examine the effects of increasing respiratory demand imposed by an increasing mass of old stolon material upon carbon allocation patterns and plant morphology. Where the total pool of available carbohydrate remained more-or-less constant over time, greater C allocation to stolon tissue was associated with reduced allocation to new leaf growth between d 7 and d 49. Rapid death of old stolon material began about d 70, perhaps as the result of withdrawal of C previously supplied to stolon tissue by leaves at the apex. Current assimilate no longer needed to maintain this old stolon material was, in part, reallocated to the apex region. Stolon death was greater when stolons were covered rather than fully illuminated, reflecting the elimination of direct CO2 assimilation by stolon tissue (estimated to be 12-22% as efficient as leaves in assimilating CO2 , on a surface area basis) and accentuation of the carbohydrate deficit. Respiration accounted for an estimated 32% of C fixed by leaves on d 85 when stolons were covered, compared to 25 % when stolons were fully illuminated. The relevance of these results to the seasonal changes in plant morphology in pastures, and the effects of stolon burial, are discussed.

Three-year follow-up (1983-1986) of children undergoing bilateral grommet insertion in Sheffield.

A retrospective study with review, after 3 years, of 43 children between the ages of 4 and 13 years, who had bilateral otitis media with effusion treated surgically purely by the insertion of grommets is described. The results shows that the younger the child at initial grommet insertion, the greater the likelihood of more than 1 grommet insertion being required (P less than 0.05). A younger patient is likely to make a greater number of outpatient visits (P less than 0.05), and the number of outpatient visits correlates with the number of grommets inserted (P less than 0.01). At 3 years, 49% of children remained on regular outpatient follow-up, while 34% of children had persisting effusion in 1 or more ears. Whilst grommets are in place, otorrhoea is not adversely influenced by swimming. The role of adenoidectomy in the management of otitis media with effusion is not assessed by this study.