Lamprey GnRH‐III Releases Luteinizing Hormone but not Follicle Stimulating Hormone in Pigs

The effect of exogenous administration of lamprey GnRH‐III (IGnRH‐III) on gonadotropin secretion was evaluated in pigs. Six crossbred barrows (82.4 ± 3.5 kg body weight) were assigned randomly to a replicated 3 × 3 Latin square design to evaluate the effect of 0.1, 1.0 or 10.0 μg/kg body weight of exogenous IGnRH‐III on LH and FSH secretion. To facilitate blood collection and infusion of IGnRH‐III, barrows were catheterized in the jugular vein 1 day before initiation of experiments. Blood samples were taken at 10‐min intervals for 6 h, starting 2 h before treatments were applied. Relative concentrations of LH and FSH were calculated by obtaining the ratio of the average concentration of each hormone 2 h after infusion divided by the average concentration during the 2 h before infusion. Relative concentrations of FSH after IGnRH‐III infusion did not influence mean concentration of FSH at any of the doses; yet 10.0 μg/kg body weight had a significant effect on LH secretion (p < 0.01). Relative concentrations of LH averaged 1.2, 1.0 and 3.0 ng/ml (for doses of 0.1, 1.0 and 10.0 μg/kg body weight of IGnRH‐III respectively). Only a dose of 10 μg/kg body weight elicited a significant LH increase that was associated with exogenous IGnRH‐III infusion. We conclude that IGnRH‐III is a weak GnRH agonist and at high doses, IGnRH‐III has the ability to release LH but not FSH in barrows.     

Effects of methadone on the minimum alveolar concentration of isoflurane in dogs

ObjectiveTo investigate the effects of methadone on the minimum alveolar concentration of isoflurane (ISO_MAC) in dogs.Study designProspective, randomized cross-over experimental study.AnimalsSix adult mongrel dogs, four males and two females, weighing 22.8 ± 6.6 kg.MethodsAnimals were anesthetized with isoflurane and mechanically ventilated on three separate days, at least 1 week apart. Core temperature was maintained between 37.5 and 38.5 °C during ISO_MAC determinations. On each study day, ISO_MAC was determined using electrical stimulation of the antebrachium (50 V, 50 Hz, 10 mseconds) at 2.5 and 5 hours after intravenous injection of physiological saline (control) or one of two doses of methadone (0.5 or 1.0 mg kg^?1).ResultsMean (±SD) ISO_MAC in the control treatment was 1.19 ± 0.15% and 1.18 ± 0.15% at 2.5 and 5 hours, respectively. The 1.0 mg kg^?1 dose of methadone reduced ISO_MAC by 48% (2.5 hours) and by 30% (5 hours), whereas the 0.5 mg kg^?1 dose caused smaller reductions in ISO_MAC (35% and 15% reductions at 2.5 and 5 hours, respectively). Both doses of methadone decreased heart rate (HR), but the 1.0 mg kg^?1 dose was associated with greater negative chronotropic actions (HR 37% lower than control) and mild metabolic acidosis at 2.5 hours. Mean arterial pressure increased in the MET1.0 treatment (13% higher than control) at 2.5 hours.Conclusions and clinical relevanceMethadone reduces ISO_MAC in a dose-related fashion and this effect is lessened over time. Although the isoflurane sparing effect of the 0.5 mg kg^?1 dose of methadone was smaller in comparison to the 1.0 mg kg^?1 dose, the lower dose is recommended for clinical use because it results in less evidence of cardiovascular impairment.     

The effect of temperature on the spring growth of perennial ryegrass at three contrasting sites

The effect of temperature on the spring growth of perennial ryegrass swards was studied at three contrasting sites. Two of these were situated on land restored after opencast coal mining, one of which had been drained. The third was on undisturbed land of the same soil type. Rates of leaf extension were measured in an attempt to give an early indication of differences in plant growth in the spring of 1982.
Spring growth started earliest on undisturbed land. On the restored land drainage proved beneficial, for although the onset of growth was delayed compared to the undisturbed site the subsequent rates of growth were similar. Both the onset and the rate of growth were slower on the undrained site. Highly significant relationships existed between leaf extension rate and soil temperature at each site. However, when sites were compared, differences in soil temperature could only partly explain observed differences in growth rate between sites.
It was concluded that some factor other than soil temperature was responsible for the difference in spring growth between the undisturbed site and the undrained opencast site in this experiment.     

Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals

Background  

Determining the relative contribution of intrinsic and extrinsic factors to fluctuations in population size, trends and demographic composition is analytically complex. It is often only possible to examine the combined effects of these factors through measurements made over long periods, spanning an array of population densities or levels of food availability. Using age-structured mark-recapture models and datasets spanning five decades (1950–1999), and two periods of differing relative population density, we estimated age-specific probabilities of survival and examined the combined effects of population density and environmental conditions on juvenile survival of southern elephant seals at Macquarie Island.     

The efficacy of a high magnesium grass cultivar in controlling hypomagnesaemia in grazing animals

A cultivar of Italian ryegrass (Bb 2067), specifically bred for high magnesium content, was assessed for its efficacy in alleviating the incidence of hypomagnesaemia in lactating ewes. Pasture and animal management was regulated to maximize the potential for the development of hypomagnesaemia. The incidence of clinical hypomagnesaemia in ewes grazing the control pasture (cv. RvP) was 21% within the first 10 days and this was accompanied by a significant fall of 35% in serum magnesium concentration. The incidence in ewes grazing the high magnesium cultivar was only 2·5% and there was no significant change in the serum magnesium concentration.
The mean magnesium content of Bb 2067 herbage (1·45 gkg DM^-1) was 48% higher than cv. RvP (0·93 g kg DM^-1) while calcium and phosphorus were 15% and 30% higher. The mean dry matter intake of ewes grazing Bb 2067 was higher than that of ewes grazing RvP, and although the difference was not statistically significant there were significantly increased intakes of magnesium, calcium and phosphorus for ewes grazing Bb 2067 compared with RvP. Ewes grazing Bb 2067 ingested more than the recommended allowance of magnesium and were close to sufficiency for calcium and phosphorus, while those grazing RvP were in serious deficit for all three minerals.
There was no significant difference in the ewe body weight loss between the treatments but lamb liveweight gain was significantly greater on the Bb 2067 pastures compared with those on cv. RvP.
It was concluded that the high magnesium grass provided an effective means of controlling hypomagnesaemia under grazing despite the extreme predisposing conditions imposed in this trial.     

Factors affecting the leaf extension rate of perennial ryegrass in spring

The effects of soil temperature and other factors on the early spring growth of perennial ryegrass (Lolium perenne) swards were studied in 1983, 1984 and 1985. Leaf extension was used as the measure of growth and soil temperature was recorded at 10 cm depth below bare ground. Measurements were taken before the first nitrogen dressing had been applied each spring on swards that had received annual dressings of 0, 200 or 400 kg N ha^-1 since 1982.
On the pooled data temperature alone accounted for 604% of the variation in leaf extension rate, with an average increase of 0·4 mm d^-1 for each 1°C increase in temperature over the range studied. Considering the data for each year separately did not greatly improve the correlation but did indicate that leaves extended more rapidly in 1985 for each degree increase in temperature whereas the smallest response was recorded in 1984. A better correlation was achieved by grouping data according to the nitrogen rates previously applied to plots and there was evidence of residual effets of this nitrogen. It seems likely that the differences between years can be explained in terms of differences in radiation and other environmental parameters over the measurement period, whereas the effects of previously applied nitrogen may be more closely related to physiological changes in the sward.     

Hemodynamic effects of sevoflurane in spontaneously breathing cats

Sevoflurane has recently been introduced in feline anesthesia. However, its cardiovascular effects have not, to our knowledge, been reported in this species. Six healthy cats, aged 1.81 ± 0.31 years (mean ± SEM) and weighing 3.47 ± 0.11 kg, were studied. Anesthesia was induced and maintained with sevoflurane in oxygen. Body temperature was maintained between 38.5 and 39.55 °C. After instrumentation, end‐tidal sevoflurane concentration was randomly set at 1.25, 1.5, and 1.75 times the individual minimum alveolar concentration (MAC), determined in a previous study, according to a Latin Square Design. Thirty minutes of stabilization was allowed after each change of concentration. ECG and heart rate, systemic and pulmonary arterial pressures, central venous pressure (CVP), and core body temperature were continuously monitored and recorded. Inspired and end‐tidal oxygen, carbon dioxide, and sevoflurane concentrations were measured using a Raman spectrometer, calibrated every 80 minutes with three calibration gases of known sevoflurane concentration (1, 2, and 5%). Moreover, at selected times, pulmonary artery occlusion pressure and cardiac output (thermodilution) were measured, and arterial and mixed venous blood samples were collected for pH and blood gas analysis, hemoglobin concentration, hemoglobin oxygen saturation, packed cell volume (PCV) and total protein determination, and lactate concentration measurement. Cardiac index (CI), stroke index (SI), systemic and pulmonary vascular resistance indices, rate‐pressure product, left and right ventricular stroke work indices (LVSWI and RVSWI, respectively), arterial and mixed venous oxygen contents, oxygen delivery, oxygen consumption, and oxygen utilization ratio were calculated. Data were analyzed by a Repeated Measure Latin Square Design followed by a Tukey's test for 2 × 2 comparisons. Arterial pH significantly decreased from 7.40 ± 0.05 to 7.29 ± 0.07 with the administration of increasing concentrations of sevoflurane. Similarly, LVSWI decreased from 3.72 ± 0.60 to 2.60 ± 0.46 g m^?2. Mean arterial pressure, PaO₂, mixed venous pH, CI, SI, and oxygen delivery tended to decrease dose‐dependently, whereas CVP, PaCO₂, Pv CO₂, PCV, and arterial and mixed venous hemoglobin concentrations tended to increase dose‐dependently with the administration of sevoflurane. However, these trends did not reach statistical significance, possibly because of the limited number of animals studied. Sevoflurane seemed to induce dose‐dependent cardiovascular depression in cats.     

Heterozygote detection for maple syrup urine disease in cattle

SUMMARY The clinical, pathological and biochemical manifestations of maple syrup urine disease (MSUD) are similar in Poll Hereford and Poll Shorthorn X Poll Hereford calves. No significant differences were observed in branched-chain amino acid concentrations in plasma, or of branched-chain keto acid dehydrogenase activity in fibroblasts, between Poll Herefords homozygous normal and heterozygous for the mutation responsible for MSUD. Haemopoietic chimerism resulted in incorrect diagnosis of the MSUD genotype in 30% of non-identical twins when blood DNA was analysed using allele-specific amplification. Hair roots are shown to be a suitable source of target DNA for genotyping Poll Hereford cattle for the MSUD mutation. Twelve of 203 (5.8%) aged Poll Hereford bulls, sampled at saleyards during the last 4 months of 1993, were found to be heterozygous for the mutation. In contrast, the mutant sequence was detected in only 1 of 150 (0.7%) 2- and 3-year-old Poll Hereford bulls offered for sale at 2 stud sales held during 1993, suggesting that the prevalence of the disease may decline over the next few years.