First report of the use of mucosal swabs of the palatine tonsillar crypt for detection of Mycoplasma bovis in naturally infected calves

ABSTRACT

Aims: To compare detection by real-time PCR of DNA from Mycoplasma bovis on mucosal swabs taken from the palatine tonsillar crypt and the mainstem bronchi of clinically asymptomatic calves after slaughter.

Methods: We compared the sensitivity of mucosal swabs taken from two sites: the palatine tonsillar crypt and the mainstem bronchi. Paired samples were taken post-mortem at slaughter from 55 clinically well calves from an infected herd and were tested by real-time PCR for the presence of M. bovis-specific DNA.

Results: Mycoplasma bovis DNA was detected in 51 palatine tonsillar crypt swabs (92.7 (95% CI?=?82.4–98.0)%) and seven mainstem bronchial swabs (12.7 (95% CI?=?5.3–24.5)%). All seven calves with positive mainstem bronchial swabs also had positive palatine tonsillar crypt swabs.

Conclusions: When compared to mucosal swabs of the mainstem bronchi, mucosal swabs of the palatine tonsillar crypt were seven times more sensitive for the post-mortem detection of M. bovis DNA. The viability of detected M. bovis was not assessed, because any cattle carrying viable or non-viable M. bovis DNA were determined to be a potential risk to eradication. Palatine tonsillar crypt mucosa may be a useful anatomical site for real-time PCR detection of M. bovis DNA in naturally infected calves. More work is needed to define the persistence and viability of M. bovis at this anatomical site.

Clinical relevance: The results of this study helped form the basis of surveillance tools used in M. bovis control and eradication efforts. Familiarity with these results may help veterinarians better communicate with their clients about the science behind the eradication efforts.     

An overview of dropped hock syndrome cases in New Zealand cattle

ABSTRACT

Case history: Data were collected from 47 outbreaks of dropped hock syndrome (DHS) that were reported by veterinarians in New Zealand to the Ministry for Primary Industries between October 2012 and August 2017. There were 181 affected dairy cows from 44 farms. Of those with records, all 86 were aged between 2–3 years-old, and 4/94 (4%) were Friesian, 56/94 (60%) were Jersey and 33/94 (35%) were Jersey/Friesian cross. Of the 47 outbreaks, 45 (96%) occurred during winter and 37 (79%) in the South Island.

Clinical findings: Of 151 cases with records, hindlimb weakness (117 cows), shortened gait (112 cows) and dropped hocks (106 cows) were most commonly reported, with 110 cases being bilaterally affected. The level of diagnostic work-up and the data recorded by veterinarians for each outbreak were highly variable. Creatine kinase and aspartate aminotransferase activities were reported for 22 cases and were within normal ranges for cows with mild disease but increased in cows with severe disease. Concentrations of Cu in serum and liver were below normal for 13/22 and 9/10 cows, respectively, from six outbreaks. Of 41 cows with records for clinical outcomes, 12 had complete resolution, 18 had partial resolution, and 11 had no resolution.

Pathological findings: Post-mortem data were available from 26 cases. Muscle necrosis and haemorrhage of the origin of the gastrocnemius muscle were the key gross findings. In 14 cows with records for muscle histopathology, myodegeneration and recent haemorrhage were observed, and connective tissue pathology was reported to predate muscular pathology in seven cases.

Diagnosis: DHS appeared to be a degenerative rather than inflammatory condition primarily affecting the connective tissue of the hind limb, especially at the dense collagen interfaces of the gastrocnemius. Although no evidence of neuropathy was found, this cannot definitively be ruled out as a potential cause.

Clinical relevance: A more standardised and systematic approach to investigating cases and recording case data is required to make robust inferences about the aetiology, risk factors, and treatment interventions for DHS.     

First report and histological features of Chlamydia pecorum encephalitis in calves in New Zealand

CASE HISTORY: Between September and October 2013, 40 of 150 crossbred Friesian dairy calves on a farm in the Manawatu region of New Zealand developed neurological signs when between 1 and 3 months of age. Calves were grazed in multiple mobs and calves from each mob were affected. A variable response was observed to initial treatment with thiamine, fluoroquinolone antibiotics and non-steroidal anti-inflammatory drugs.

CLINICAL AND PATHOLOGICAL FINDINGS: Affected calves exhibited a range of neurological signs that included generalised depression, hind limb ataxia with a stiff gait, and knuckling of the fetlocks. In advanced cases, calves became recumbent with opisthotonous. Over a 4-week period, 13 calves died or were subject to euthanasia and a thorough necropsy was performed on three of these calves. Necropsy findings included fibrinous peritonitis, pleuritis and pericarditis, with no gross abnormalities visible in the brain or joints. Histology of the brain was possible in seven of the affected calves, with lesions ranging from lymphocytic and histiocytic vasculitis and meningoencephalitis, to extensive thrombosis and neutrophilic inflammation. Immunohistochemistry using an anti-chlamydial lipopolysaccharide antibody revealed positive immuno-staining in all seven cases, with no brain samples exhibiting immunostaining for Histophilus somni. DNA was extracted from a sample of fresh brain from one case and chlamydial DNA sequences were amplified by PCR and found to be identical to Chlamydia pecorum. PCR was also performed on formalin-fixed brain tissue from three of the other cases, but no chlamydial DNA was amplified.

DIAGNOSIS: Chlamydia pecorum meningoencephalomyelitis (sporadic bovine encephalomyelitis).

CLINICAL RELEVANCE: This is the first time that C. pecorum has been confirmed as a cause of clinical disease in New Zealand. Practitioners should be aware of this disease as a differential in calves with neurological signs, and submit samples of formalin-fixed brain as well as fresh brain to enable confirmation of suspected cases using PCR analysis. Furthermore, these cases illustrate that the histological lesions in the brains of calves with C. pecorum are more variable than previously reported, and pathologists should be aware that histological features may overlap with those traditionally ascribed to other organisms, such as H. somni.     

Supplementation with Calcium Salts of Linoleic and trans-Octadecenoic Acids Improves Fertility of Lactating Dairy Cows

Objectives were to evaluate effects of feeding a calcium salt rich in linoleic and trans -octadecenoic acids (LTFA) on synthesis of prostaglandin F_2α based on its metabolite (PGFM), uterine involution and pregnancy rates in lactating dairy cows. Five hundred and eleven Holstein cows were blocked according to parity, body condition score and milk yield in the previous lactation. Primiparous and multiparous cows were randomly assigned to one of the two treatments consisting of calcium salt (2% diet dry matter) of either palm oil (PO) or LTFA from 25 days prepartum to 80 days of lactation. Cows were time-inseminated at 70 ± 3 days postpartum. Feeding LTFA tended (p = 0.08) to decrease the incidence of puerperal metritis (15.1% vs 8.8%). Primiparous cows supplemented with LTFA showed larger increase in plasma PGFM concentration at day 1 postpartum (17018 vs 6897 p m ). Pregnancy rate after first insemination tended (p = 0.07) to be greater at 27 days after insemination (37.9% vs 28.6%), and was greater (p = 0.05) at 41 days after insemination (35.5% vs 25.8%) for cows fed LTFA compared with PO. These results indicate that unsaturated fatty acids fed in a rumen inert form have the potential to modulate reproductive events and improve pregnancy rates in lactating dairy cows.