Equine castration: review of anatomy, approaches, techniques and complications in normal, cryptorchid and monorchid horses

Complications associated with equine castration are the most common cause of malpractice claims against equine practitioners in North America. An understanding of the embryological development and surgical anatomy is essential to differentiate abnormal from normal structures and to minimise complications. Castration of the normal horse can be performed using sedation and regional anaesthesia while the horse is standing, or under general anaesthesia when it is recumbent. Castration of cryptorchid horses is best performed under general anaesthesia at a surgical facility. Techniques for castration include open, closed and half-closed techniques. Failure of left and right testicles to descend occurs with nearly equal frequency, however, the left testicle is found in the abdomen in 75% of cryptorchid horses compared to 42% of right testicles. Bilateral cryptorchid and monorchid horses are uncommon. Surgical approaches described for the castration of cryptorchid horses include an inguinal approach with or without retrieval of the scrotal ligament, a parainguinal approach, or less commonly a suprapubic paramedian or flank approach. Laparoscopic castration of cryptorchid horses has recently been described but the technique has limited application in practice at this time. A definitive diagnosis of monorchidism can only be made after surgical exploration of the abdomen, removal of the normal testis and hormonal testing. Hormonal assays reported to be useful include analysis of basal plasma or serum testosterone or oestrone sulphate concentrations, testosterone concentrations following hCG stimulation, and faecal oestrone sulphate concentrations. Reported complications of castration include postoperative swelling, excessive haemorrhage, eventration, funiculitis, peritonitis, hydrocele, penile damage and continued stallion-like behaviour.     

Osmium isotopic evidence for ancient subcontinental lithospheric mantle beneath the kerguelen islands, southern indian ocean

Upper mantle xenoliths found in ocean island basalts are an important window through which the oceanic mantle lithosphere may be viewed directly. Osmium isotopic data on peridotite xenoliths from the Kerguelen Islands, an archipelago that is located on the northern Kerguelen Plateau in the southern Indian Ocean, demonstrate that pieces of mantle of diverse provenance are present beneath the Islands. In particular, peridotites with unradiogenic osmium and ancient rhenium-depletion ages (to 1.36 x 10(9) years old) may be pieces of the Gondwanaland subcontinental lithosphere that were incorporated into the Indian Ocean lithosphere as a result of the rifting process.     

A COMPARISON OF FIELD ESTIMATES AND LABORATORY ANALYSES OF THE SILT AND CLAY CONTENTS OF SOME WEST MIDLAND SOILS

Field estimates of silt and clay contents were compared statistically with the silt (2-60 μm) and clay (<2 μm) contents determined by the pipette method of 184 soil horizons from a large range of west Midland soils (clay contents 1–81 per cent and silt contents 3–71 per cent). Regression equations were calculated (a) for each of four surveyors using combined topsoil and subsoil data and (b) for surface and subsoils separately using combined data for the four surveyors. There is slight evidence of ‘operator bias’ and a tendency for all four surveyors to underestimate clay in surface horizons though these conclusions have limited significance because of the small number and the distribution of some of the sample populations. Single equations for the combined data from all operators and all horizons explained 75.5 per cent of the variation in field estimates of silt content and 85.4 per cent of the variation of clay estimates. For silt, the regression line almost passes through the origin with a slope not significantly different from unity, whilst for clay, the line intercepts the y-axis close to zero and has a slope of 0.904. The results show that, with experience and adequate reference samples, surveyors can confidently estimate the particle-size distribution of a wide range of soils. These studies were done during soil mapping in Staffordshire, Hereford and Worcester, and Salop using the newly introduced soil classification (Avery, 1973) and revised Handbook (Hodgson, 1974) of the Soil Survey of England and Wales.     

The effects of change in herbage mass on rates of herbage growth and senescence in mixed swards

A study was conducted to determine the influence of a change in herbage mass on rates of herbage growth (G), senescence (S) and net production of green herbage (NP) in swards of Lolium perenne L., Poa annua L. and Trifolium repens L. under continuous stocking with sheep. Swards were maintained at either high (1700–1900 kg OM ha⁻¹; H) or low (700–900 kg OM ha⁻¹; L) herbage mass from April to 20 August. From 20 August to 13 September half of the L sward was permitted to grow until a herbage mass similar to that of the H sward was achieved (LH), and at the same time half of the H sward was grazed down until a herbage mass similar to that of the L sward was achieved (HL). The other half of each sward was held at constant mass (LL and HH). Estimates of G, S and NP were obtained for each plant species over a 2-week period from 17 September to 1 October and estimates of species population densities were also made.
The combined species rates of G and S per unit area were highest in treatment LH and lowest in treatment HL, whilst the rates for the LL and HH swards were intermediate. The rate of NP was similar in the LL, HH and LH treatments (34.5, 29.3, 33.6 ± 6.2 kg DM ha⁻¹d⁻¹) but was lower in the HL sward (100 ± 6.2). The effects of alteration of herbage mass on individual tiller or stolon G and S rates were rapid but population density changes were slower.
Within the limited conditions of this trial it was not possible to increase NP by manipulation of herbage mass under continuous stocking management but the results indicate that NP can be reduced in the short term if a sward of high herbage mass and low population density is grazed hard.     

Modification of a Nonrebreathing Circuit Adapter to Prevent Barotrauma in Anesthetized Patients

Barotrauma, pneumothorax, and pneumomediastinum occurred in two anesthetized cats in which the waste gas outlet of a nonrebreathing circuit was occluded. To prevent any similar cases of barotrauma, we have modified our nonrebreathing circuit adapters by inserting a 15 cm H₂O PEEP valve into the gas pathway of the nonrebreathing circuit adapter. This PEEP valve prevents the circuit and airway pressures from exceeding 15 cm H₂O if the pop-off valve of the nonrebreathing circuit adapter is inadvertently left closed.