Large-size fattening calves' lots fed with automatic milk feeders may have an increased risk for Mycoplasma bovis infection spread and for antibiotic use.

Bovine respiratory disease is the leading user of antibiotics (AB) in calf production. Mycoplasma (M.) bovis could lead to greater use of AB as it is a persistent and AB resistant causative agent for respiratory diseases. Two cross-sectional studies were set up to assess the effects of lot size and feeding system on M. bovis infection and the effects of M. bovis seroconversion, lot size and feeding system on AB use in calves' feedlots. Twenty-six lots in 22 fattening farms were monitored for 41-81 days, from all-in entry of calves until three consecutive weeks without using any collective antibiotics. M. bovis spread was estimated by measuring seroconversion at entry and at the end of study period in 10-15 calves randomly sampled in each lot. All AB treatments used in the meanwhile were recorded. The lots were selected according to feeding system, i.e. individual bucket (n = 7) vs. automated milk feeder (AMF, n = 19), and lot size (30-519 calves), less than 50 calves (n = 9) vs. more than 50 calves (n = 17). Statistical analysis was performed using multivariable generalised linear models with fattening farms as random effect. M. bovis spread increased with lot size (odds ratio (OR) 2.9[1.4; 5.8] per two-fold increase in lot size). This proportion of seroconverted calves was lower in bucket-fed lots compared to lots fed with the AMF using a shared nipple (OR = 0.03[0.003; 0.41]). The main risk factor for AB use was the lot size, with an increase of 1.5[0.94; 1.98] treatments per two-fold increase in lot size. For same size lots, the use of bucket can decrease AB consumption by up to 1.03[-2.18; 0.14] treatments per calf compared to AMF. Analysis of the association between seroconversion to M. bovis and AB use was inconclusive. We found that bucket feeding in small-size lots, i.e. up to a maximum of 50 calves in the same space, limits seroconversion to M. bovis and enables lower use of AB in veal calf production.

Prevalence of Mycoplasma bovis udder infection in dairy cattle: preliminary field investigation in southeast France.

AIMS: To update epidemiological data on Mycoplasma bovis infection in dairy herds from six departments in the southeast of France, in order to obtain a first estimate of the prevalence of M. bovis infection through bacteriological investigations on bulk tank milk, and estimate the prevalence of M. bovis in clinical mastitis in this population of cattle. METHODS: To estimate a prevalence of M. bovis of 2%, with 95% confidence, a sample of >270 herds was required. Bulk tank milk samples were collected from herds between January and February 2005 and milk samples from cows with clinical mastitis were collected between January 2007 and March 2008. Bulk tank milk and composite mastitic samples were analysed for M. bovis using culture and/or PCR. RESULTS: Mycoplasma bovis was not detected by either technique in any of the 345 bulk tank milk samples. The prevalence of M. bovis infection in this population of dairy herds was <1%, with 95% confidence. Mycoplasma bovis was not isolated from any of the 166 composite samples obtained from 828 samples of mastitic milk. The prevalence of M. bovis in clinical mastitis was <0.44%, with 95% confidence. CONCLUSIONS: These preliminary results suggest that the prevalence of udder infections with M. bovis is very low in dairy herds in the southeast of France. These two studies provide preliminary data, that can be used to derive working hypotheses for future statistically representative investigations at the national level.

A new chloramphenicol and florfenicol resistance gene flanked by two integron structures in Salmonella typhimurium DT104.

A new chloramphenicol resistance gene from Salmonella typhimurium DT104, designated floR, also conferring resistance to florfenicol, was characterized. Sequence analysis of the deduced FloR protein suggested that it belongs to the 12-TMS (transmembrane segments) multidrug efflux pumps family. The floR gene, and the downstream sequenced tetR and tetA tetracycline resistance genes, were surrounded by two class 1 integrons. The first one contained the resistance gene aadA2 and a deleted sulI resistance gene. The second one contained the beta-lactamase gene pse1 and a complete sulI gene. Thus, the floR gene is included in a multiresistance locus of at least 12.5 kb. Its particular organization and chromosomal location could be involved in the antibioresistance pattern stability of the DT104 Salmonella typhimurium strains.