T J Potter

Risk factors for clinical endometritis in postpartum dairy cattle

Bacterial contamination of the uterine lumen after parturition occurs in most dairy cattle. The presence of clinical endometritis beyond three weeks post partum depends on the balance between microbes, host immunity, and other environmental or animal factors. The present study tested the hypothesis that clinical endometritis is associated with animal factors, such as retained fetal membranes, assisted calving and twins, as well as fecal contamination of the environment. The association between selected risk factors and the lactational incidence risk of clinical endometritis was examined in 293 animals from four dairy herds. Multivariate analysis was used to identify risk factors and quantify their relative risk (RR) and population attributable fraction (PAF) based on the proportion of cows exposed to each factor. The lactational incidence of clinical endometritis was 27% and significant risk factors for clinical endometritis were retained fetal membranes (RR=3.6), assisted calving (RR=1.7), stillbirth (RR=3.1), vulval angle (RR=1.3), primparity (RR=1.8), and male offspring (RR=1.5) but not the cleanliness of the environment or the animal. The highest PAF was associated with male offspring (0.6) so the use of sexed semen has the greatest potential to reduce the incidence of clinical endometritis. The dominant association between retained fetal membranes and clinical endometritis was supported by an expert panel of clinicians. The risk factors for clinical endometritis appear to be associated with trauma of the female genital tract and disruption of the physical barriers to infection rather than fecal contamination.

Pharmacokinetic/pharmacodynamic integration and modelling of amoxicillin for the calf pathogens Mannheimia haemolytica and Pasteurella multocida

The antimicrobial properties of amoxicillin were determined for the bovine respiratory tract pathogens, Mannheima haemolytica and Pasteurella multocida. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill curves were established. Pharmacokinetic (PK)/pharmacodynamic (PD) modelling of the time-kill data, based on the sigmoidal Emax equation, generated parameters for three levels of efficacy, namely bacteriostatic, bactericidal (3log10 reduction) and 4log10 reduction in bacterial counts. For these levels, mean AUC(0-24 h) /MIC serum values for M. haemolytica were 29.1, 57.3 and 71.5 h, respectively, and corresponding values for P. multocida were 28.1, 44.9 and 59.5 h. Amoxicillin PK was determined in calf serum, inflamed (exudate) and noninflamed (transudate) tissue cage fluids, after intramuscular administration of a depot formulation at a dosage of 15 mg/kg. Mean residence times were 16.5 (serum), 29.6 (exudate) and 29.0 h (transudate). Based on serum MICs, integration of in vivo PK and in vitro PD data established maximum concentration (Cmax )/MIC ratios of 13.9:1 and 25.2:1, area under concentration-time curve (AUC0-∞ )/MIC ratios of 179 and 325 h and T>MIC of 40.3 and 57.6 h for P. multocida and M. haemolytica, respectively. Monte Carlo simulations for a 90% target attainment rate predicted single dose to achieve bacteriostatic and bactericidal actions over 48 h of 17.7 and 28.3 mg/kg (M. haemolytica) and 17.7 and 34.9 mg/kg (P. multocida).

Pharmacokinetic and pharmacodynamic integration and modelling of marbofloxacin in calves for Mannheimia haemolytica and Pasteurella multocida

The pharmacokinetics (PK) and pharmacodynamics (PD) of marbofloxacin were established in calves for six strains of each of the pneumonia pathogens Mannheimia haemolytica and Pasteurella multocida. The distribution of marbofloxacin into inflamed (exudate) and non-inflamed (transudate) tissue cage fluids allowed comparison with the serum concentration-time profile. To establish the PD profile, minimum inhibitory concentration (MIC) was determined in Mueller-Hinton broth (MHB) and calf serum. Moderately higher MICs were obtained for serum compared to MHB. An initial integration of PK-PD data established C(max)/MIC ratios of 45.0 and AUC(24h)/MIC values of 174.7 h, based on serum MICs, for both bacterial species. Using bacterial time-kill curves, generated ex vivo for serum marbofloxacin concentrations, PK-PD modelling established three levels of growth inhibition: AUC(24 h)/MIC ratios for no reduction, 3 log(10) and 4 log(10) reductions in bacterial count from the initial inoculum count were 41.9, 59.5 and 68.0 h for M. haemolytica and 48.6, 64.9 and 74.8 h for P. multocida, on average respectively. Inter-strain variability for 3 log(10) and 4 log(10) reductions in bacterial count was smaller for P. multocida than for M. haemolytica. In conjunction with literature data on MIC(90) values, the present results allowed prediction of dosages for efficacy for each organism for the three levels of growth inhibition.

Reliability of quantitative echocardiography in adult sheep and goats.

BackgroundEchocardiography is a non-invasive method for assessment of the ovine and caprine heart. Complete reference ranges for cardiac dimensions and time indices for both species are not currently available and reliability of these measurements has not been evaluated. The objectives for this study are to report reliability, normal cardiac dimensions and time indices in a large group of adult sheep and goats.Fifty-one adult sheep and forty adult goats were recruited. Full echocardiographic examinations were performed in the standing unsedated animal. All animals underwent echocardiography four times in a 72-hour period. Echocardiography was performed three times by one author and once by another. Images were stored and measured offline. Technique and measurement repeatability and reproducibility and any differences due to animal or day were evaluated. Reference ranges (mean ± 2 standard deviations) were calculated for both species.ResultsMajority of the images obtained were of good to excellent quality. Image acquisition was straightforward with 5.4% of animals demonstrating a small scanning window. Reliability was excellent for majority of dimensions and time indices. There was less variation in repeatability when compared with reproducibility and differences were greater for technique than for measurements. Dimensions that were less reliable included those for right ventricular diameter and left ventricular free wall. There were many differences in cardiac dimensions between sheep and goats.ConclusionsThis study has demonstrated that specific reference ranges are required for these two species. Repeatability and reproducibility were excellent for the majority of cardiac dimensions and time indices suggesting that this technique is reliable and valuable for examination of clinical cases over time and for longitudinal research studies.

Pharmacodynamics of florfenicol for calf pneumonia pathogens

The antimicrobial properties of florfenicol were investigated for the bovine respiratory tract pathogens, Mannheimia haemolytica and Pasteurella multocida. Three in vitro indices of efficacy and potency were determined; minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and in vitro time-kill curves for six pathogenic strains of each organism. Each was monitored in two matrices, Mueller Hinton broth (MHB) and calf serum. MBC:MIC ratios were low, 1.8 : 1 for M haemolytica in both MHB and serum and 2.4 : 1 and 2.1 : 1 for P multocida in MHB and serum, respectively. The killing action of florfenicol had the characteristics of concentration dependency against M haemolytica and codependency (on time and concentration) against P multocida. Modelling of the time-kill data after 24 hours exposure was undertaken to quantify three levels of activity for the ratio, area under concentration-time curve over 24 hours (AUC24h)/MIC; bacteriostatic action (no change in bacterial count), 3log10 reduction and 4log10 reduction in bacterial count. Mean AUC24h/MIC values for P multocida in MHB (and serum) were 22.0 (23.3) hour, 34.5 (39.9) hour and 45.8 (50.4) hour, respectively. Similar numerical values were obtained for M haemolytica. For both bacterial species, interstrain variability was low; coefficients of variation ( per cent) in serum for 3log10 and 4log10 reductions in count were, respectively, 14.3 and 24.1 for P multocida and 7.8 and 11.4 for M haemolytica. These data form a rational basis for dosage selection for treatment of calf pneumonia caused by M haemolytica or P multocida.

Pharmacodynamics of marbofloxacin for calf pneumonia pathogens

The pharmacodynamic (PD) properties of the fluoroquinolone, marbofloxacin, were determined for the bovine respiratory tract pathogens Mannheima haemolytica and Pasteurella multocida. For six pathogenic isolates of each organism, three in vitro indices of efficacy and potency were determined, namely, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill curves. Each parameter was determined in two matrices, Mueller Hinton Broth (MHB) and calf serum. For serum, MBC:MIC ratios were 2.7:1 (M. haemolytica) and 2.4:1 (P. multocida). The killing action of marbofloxacin had the characteristics of concentration dependency against M. haemolytica and co-dependency (on time and concentration) against P. multocida. To confirm the characteristics of the time-kill profiles, growth inhibition produced by marbofloxacin was also established ex vivo in three biological fluids, calf serum, exudate and transudate, harvested from a tissue cage model. The in vitro time-kill data were modelled with pharmacokinetic properties of marbofloxacin, established by intramuscular administration in calves at a dose of 2 mg/kg; three levels of activity, namely bacteriostatic, 3 log10 reduction and 4 log10 reduction in bacterial counts were determined. Mean AUC(24h)/MIC values (with percentage coefficients of variation indicating inter-isolate variability) for M. haemolytica, based on serum MICs, were 31.3 (41.6), 57.7 (42.4) and 79.2 (44.6) h, respectively. Corresponding values for MHB were 20.5 (58.0), 40.5 (51.8) and 51.2 (24.30) h, respectively. When allowance was made for binding of marbofloxacin to serum protein, the AUC(24h)/MIC values for serum were similar to those for MHB. Numerical AUC(24h)/MIC values for P. multocida were slightly lower than those obtained for M. haemolytica. These data establish for the first time inter-isolate variability in AUC(24h)/MIC values required for three levels of bacterial kill for two pathogenic species and thereby provide an indication of variability in serum concentration that might be required to achieve efficacy in clinical subjects.

Labial fusion causing urinary tract obstruction in an alpaca cria.

CONGENITAL vulval deformities have been reported in many species, including human beings (Klein and others 1989, Norbeck and others 1993), camels (Ramadan 1997), cattle (Oettle and Coubrough 1985), llamas (Lopez and others 1998) and marmosets (Isachenko and others 2002). Wilkins and others (2006) reported six cases of congenital vulval abnormalities in alpacas seen in the USA. To the authors’ knowledge, this short communication describes the first case reported in alpacas in Europe. A six-hour-old female alpaca cria was presented at the Royal Veterinary College as an out-of-hours emergency due to a vulval swelling. The referring veterinary surgeon suspected an imperforate vulva, and the owners reported that they had not seen the animal urinate. The cria had had an uneventful birth and had behaved normally. It came from a large commercial establishment, where other congenital anomalies, such as cleft palate, had been reported, but not ones involving the urogenital system. Physical examination was unremarkable, other than the swollen vulva and no identifiable vulval opening. The cria was bright, alert and responsive, in average body condition, and weighed 8 kg. At admission, haematology was unremarkable. Serum biochemistry revealed an increased lactate concentration (3·6 mmol/l; normal range <1·5 mmol/l), reduced total protein (40 g/l; normal range 58 to 70 g/l) and increased urea (10·2 μmol/l; normal range 3·5 to 8·9 μmol/l) and creatinine (327 μmol/l; normal range 136 to 205 μmol/l) concentrations. The cria had partial failure of passive transfer (IgG concentration 2·5 g/l; normal range >10 g/l). Abdominal ultrasonography revealed dilation of the left renal pelvis and ureter and an enlarged bladder, but no other abnormalities were noted. At this stage, a diagnosis of labial fusion was made with secondary azotaemia and partial failure of passive transfer. A 16 G catheter (Mila International) was placed in the right jugular vein using aseptic technique. The cria was then sedated with 0·3 mg/kg midazolam (Hypnovel; Roche), administered intravenously, and positioned in ventral recumbency. The vulval skin was aseptically prepared with a weak solution of chlorhexidine scrub and surgical spirit. Local analg esia was provided by infiltrating the fused labia with 2 ml mepivicaine (Intra-epicaine; Arnolds Veterinary Products). The imperforate tissue was opened surgically using a number 11 scalpel blade by incising through the midline of the fused labia. Artery forceps and digital palpation were used to ensure that only vulval tissue was incised. At this stage, urine was passed. Urinalysis revealed a specific gravity of 1·023 with 1+ protein and 4+ blood (MultiStix SG; Bayer). Digital palpation of the vestibule revealed no other anomalies. The cria received an infusion of plasma from the dam, and was treated with 10 mg/kg trimethoprim-sulfadiazine (Norodine; Norbrook Laboratories) administered intravenously every 12 hours, and 6·6 mg/kg ranitidine (Zantac syrup; GlaxoSmithKline), administered orally every eight hours. Once the sedation had worn off, the cria was united with its dam and was allowed to nurse. Repeat ultrasonography, 24 hours after admission, revealed that both kidneys had a normal appearance. Serum biochemistry revealed a reduction in blood urea (6·5 mmol/l) and creatinine (165 mmol/l). At this stage, the level of IgG was deemed adequate (>10 g/l). Urinalysis revealed no blood or protein and a specific gravity of 1·008. The animal was seen to urinate normally and was discharged three days after presentation with a further three days of oral trimethoprim-sulfadiazine (10 mg/kg every 12 hours) and ranitidine (6·6 mg/kg every eight hours). No further problems were reported with the animal, and eight weeks later it was doing well. To the authors’ knowledge, this is the second reported case of azotaemia secondary to labial fusion. In the other reported cases of labial fusion in alpacas, two of six animals developed urometra, which was not present in this case. However, the bladder was dilated and backflow of urine causing dilation of the renal pelvis was present. It is likely that increased pressure within the bladder, and then further proximally within the urogenital tract, resulted in a decreased glomerular filtration rate due to increased pressure within Bowman’s capsule. There was likely prerenal involvement, as the blood lactate concentration was increased, but the degree of azotaemia seems too severe to be completely explained by this. It was also interesting to note that at no point had the cria been straining, even though its bladder was distended. The only reason that the animal was noted to be abnormal was the marked vulval swelling. Other causes of postrenal obstruction generally cause stranguria, as was reported by Wilkins and others (2006). The authors speculate that stranguria would have developed had the problem not been noticed so promptly. Labial fusion is thought to be heritable in other species (Wilkins and others 2006), and the owner was therefore advised not to breed from the affected animal or to use the same dam and sire combination again.

Medical support for cattle and small ruminant surgical patients

While the initial assessment of cattle and small ruminants presented for surgery is similar to that in other species, it can be more challenging because farm animals are often sicker than they appear to be. This article outlines how to identify and manage potential medical problems in large animal surgical patients, including practical fluid therapy, analgesia, sedation, anaesthesia and rational antimicrobial use.

Head and ocular surgery in farm animals

Head surgery is commonly undertaken in large animal practice and there are a number of procedures that can be accomplished in the field. This article covers some of the commonly performed ocular and head surgeries along with the appropriate local anaesthetic techniques.

Practical guide to ocular ultrasonography in horses and farm animals

ULTRASONOGRAPHY is an underused imaging modality in practice for the examination of the large animal eye, especially in food-producing animals. It can be performed easily using ultrasound equipment that is readily available to the large animal veterinary surgeon and can provide valuable diagnostic and prognostic information quickly and cheaply. It allows visualisation and examination of the eye or its internal structure that would otherwise be difficult to assess due to eyelid swelling or eyelid closure following trauma, opacification of the cornea or anterior chamber, or because of lens and vitreal opacities. It also allows investigation of exophthalmos and the extent of tumour progression, particularly squamous cell carcinoma in cattle. This article describes how to carry out ocular ultrasound examination in horses and farm animals, and highlights normal findings and some commonly encountered abnormalities seen in these species.