In this issue – December 2009

Results of a field survey suggest that if the Australian dairy industry continues the current trend of intensification, coliform intra-mammary infections may become more important. The prevalence of contagious mastitis pathogens has decreased because of mastitis control programs, but environmental mastitis has increased. The aim of this study was to assess the prevalence of mastitis pathogens in five high-producing intensive dairy herds in New South Wales.1 A total of 820 milk samples were collected from 686 cows with clinical mastitis, and were cultured using standard microbiological culture techniques. Bacteria or fungi were isolated from 83.3% of primary samples and enrichment cultures that were used to increase sensitivity showed single colony type bacterial isolates from 36.5% of the remainder. Most were environmental pathogens, including coliforms, (especially Escherichia coli), environmental Streptococcus and Staphylococcus spp. Contagious pathogens were only found in 2.5% of the total isolates. The authors discuss the differences between the relatively high prevalence of coliform mastitis in the intensive high-producing herds and the low incidence reported in surveys of pasture-based herds in Victoria. Specific ultrasonographic teat measurements may be useful for identifying cows with a predisposition to mastitis, as well as for evaluating in-herd cows in terms of udder or teat deformities. The results of a study that assessed the role of teat morphology, as measured by ultrasound, in the aetiology of mastitis suggest that extensive studies are needed to establish standard criteria for such measurements.2 The anatomy of the udder does not allow mastitis bacteria to enter the udder, and the incidence of mastitis is reported to be closely related to teat and udder measurement. Ultrasound can be used as a non-invasive and easy to use technique to identify intramammary abnormalities. Ultrasonographic measurements were taken from 190 teats from 100 dairy cows of different breeds. Mastitis was diagnosed by the California Mastitis Test (CMT) and microbiological tests. Breed, age and CMT scores were found to have significant effects on teat and teat cistern diameter. The number of lactations, pregnancy, the lactation period and the udder lobe (rear, front) were not found to have a significant effect on any of the measurements. The teat cistern diameter was significantly smaller in CMT-positive udder lobes than in CMT-negative lobes, but no difference was detected in other measurements between the CMT-positive and -negative lobes. This historical and histological review of field and experimental cases of an ovine disease attributed to the consumption of Lythrum hyssopifolia (lesser loosestrife) concludes that there is compelling circumstantial evidence of plant chemicals that are toxic to ovine hepatocytes and renal tubular epithelial cells.3 Disease outbreaks occurred in summer on nine farms across Victoria, between 1974 and 2002. Photosensitivity or liver damage occurred on six of the farms. Histologically, liver damage occurred in all nine outbreaks, with kidney damage in at least eight. There was between 1% and 20% mortality in sheep flocks grazing paddocks where L hyssopifolia was the predominant green vegetation. The paper also reports results of a feeding trial in two lambs that ate little of the L. hyssopifolia plants, but still had biochemical and histological evidence of liver and kidney damage. The authors conclude that the poisoning is likely to be sporadic because the plant is not usually eaten in large amounts. Staphylococcus capitis should be included in the differential diagnosis of ovine genital infections, according to the authors of this case report.4 This case report describes a massive unilateral scrotal pyocele caused by Staphylococcus capitis in a 6-year-old ram. An irregular hyperechoic mass in an anechoic fluid was found using ultrasound. The right testis was completely atrophied. Coagulase-negative S. capitis was isolated in pure culture from the dense extensive greenish purulent exudate that was collected from the scrotum. To the author's knowledge, this is the first report of genital infection by S. capitis in rams. Surgical placement of polyurethane tubes designed for percutaneous endoscopic gastrostomy is a useful method of cannulating the third compartment in alpacas, and the authors suggest that it could be used for nutritional support and fluid therapy in sick camelids that might need long-term care. New world camelids have a three-compartment forestomach, the third of which is analogous to the abomasum of ruminants, and is the primary site of enzymic digestion. Enteral supplementation requires daily intubation, which is stressful, and other methods of long-term nutritional support would be useful. The aim of this prospective study was to develop a simple and effective surgical technique for third-compartment cannulation in alpacas.5 General anaesthesia was induced in six adult male alpacas and a polyurethane gastrostomy tube was surgically implanted into the distal portion of the third compartment. Three of the alpacas retained their cannulas for 100 days but three cannulas were dislodged during the study. Two of the three dislodged cannulas were replaced during a second surgical procedure. The authors report that the cannulas were well tolerated by the alpacas and all animals remained clinically healthy during the study period. Third compartment contents did not leak from the cannulation site. The tubes were manually removed following the completion of the study and the small defect in the body wall quickly healed over in all animals. A new form of toxicity, called equine fescue oedema, has occurred in horses grazing varieties of Mediterranean tall fescue (Festuca arundinacea) that carry the endophyte known as Max P or Max Q.6 It has affected 48 of 56 horses on six farms and 4 horses have died. The clinical signs included inappetence, depression, and subcutaneous oedema of the head, neck, chest and abdomen. Affected horses had very low plasma albumin values. The authors propose that a pyrrolizidine alkaloid, N-acetyl norloline, which is produced by the Max P endophyte, may be responsible for this new toxicity in horses, and that more studies are needed. Foot pain is a common cause of lameness in horses, and the aetiology can be difficult to diagnose. In this case, a 12-year-old show-jumping mare presented with a chronic hindlimb lameness of 16 weeks duration.7 The lesion was localised to the medial collateral ligament of the distal interphalangeal joint of the left hindlimb using perineural anaesthesia and ultrasonography. Collateral ligament desmitis of the distal interphalangeal joint is a commonly diagnosed condition of the forelimb; however, hindlimb collateral ligament desmitis has been rarely reported. Immobilisation of the foot by means of a heavily padded distal limb cast for 6 weeks, with strict box rest and a strictly regulated hand walking program allowed excellent healing of the ligament. Serial ultrasonographic examinations were performed throughout the rehabilitation period. The authors suggest that this is a novel treatment for collateral ligament desmitis. At the time of writing the mare had returned to her previous level of exercise and was showing no signs of lameness. This case report is the first to highlight this potentially life-threatening manifestation of sulfonamide-induced hypothyroidism. Sulfonamide combinations are widely used antimicrobials in veterinary medicine and early recognition of this syndrome is critical, the authors suggest.8 The case report describes a sulfonamide-induced hypothyroid crisis in a 4-year-old Labrador Retriever bitch. Empirical therapy with high-dose trimethoprim-sulfamethoxazole for 10 days produced signs of weakness, ataxia and mental depression and the clinicopathological results supported hypothyroid-induced central nervous system depression. The differential diagnosis included encephalitis, intracranial space-occupying lesion, toxicity, vascular accident, as well as iatrogenic sulfonamide-induced hypothyroidism. Short-term levothyroxine sodium therapy led to complete resolution of all clinical signs and follow-up thyroid hormone assays ruled out underlying thyroid pathology.

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