Herd characteristics and cow-level factors associated with Prototheca mastitis on dairy farms in Ontario, Canada

Abstract

Prototheca spp. are algae that cause incurable acute or chronic mastitis in dairy cows. The aim of this case-control study was the identification of cow- and herd-level risk factors for this unusual mastitis pathogen. Aseptically collected composite milk samples from 2,428 milking cows in 23 case and 23 control herds were collected between January and May 2011. A questionnaire was administered to the producers, and cow-level production and demographic data were gathered. In 58 of 64 isolates, Prototheca spp. and Prototheca zopfii genotypes were differentiated using PCR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. All isolates were identified as Prototheca zopfii genotype 2. The mean within-herd prevalence for Prototheca spp. was 5.1% (range 0.0-12.5%). Case herds had a significantly lower herd-level prevalence of Staphylococcus aureus and a higher prevalence of yeasts than did control herds. The final logistic regression model for herd-level risk factors included use of intramammary injections of a non-intramammary drug [odds ratio (OR) = 136.8], the number of different injectable antibiotic products being used (OR = 2.82), the use of any dry cow teat sealant (external OR = 80.0; internal OR = 34.2), and having treated 3 or more displaced abomasums in the last 12 mo OR = 44.7). The final logistic regression model for cow-level risk factors included second or greater lactation (OR = 4.40) and the logarithm of the lactation-average somatic cell count (OR = 2.99). Unsanitary or repeated intramammary infusions, antibiotic treatment, and off-label use of injectable drugs in the udder might promote Prototheca udder infection.

Mastitis associated with Prototheca zopfii - an emerging health and economic problem on dairy farms

“…Excessive usage of antibiotics and consequent elimination of the competitive natural udder flora can give rise to the development of algal infections. Interestingly, specific farm management practices or milking hygiene deficiencies were not identified as risk factors for occurrence of Prototheca mastitis in the aforementioned study (24).…”

“…Contrary to infections caused by other mastitic pathogens, the initial mammary immune response to protothecal infection is very mild, and the somatic cell count (SCC) usually remains unchanged during the initial stages of the disease (31). In cows infected with P. zopfii, the SCC in quarter and composite milk samples can be lower than 100,000 cells/mL (24). The infection is commonly subclinical and is discovered only after significant increase of the SCC (8).…”

“…Moreover, intermittent shedding of the algae in milk may prevent detection of the agent during one single testing or examination of lactating cows. Pieper et al (24) established that unsanitary or repeated intramammary infusions and antibiotic treatment can contribute to the development of Prototheca infection of the mammary gland. Similarly to other pathogens manifesting natural resistance to antibiotics, inadequate intramammary administration of antibiotics (contaminated applicator or inadequate teat disinfection before administration) is an important risk factor for direct introduction of the organism into the mammary gland.…”

“…Pieper et al (24) have conducted extensive research aimed at identifying cow-and herd-level risk factors for the occurrence of Prototheca mastitis. The research encompassed 23 Holstein-Friesian farms in Ontario (Canada).…”

“…Identification of relevant risk factors is of major importance in the control of the disease; however, causal relationships between various factors in each individual case are still difficult to establish. Poor hygiene practices, excessive antibiotic use, and inadequate milking hygiene are most commonly considered the major risk factors for mastitis development (10,13,17,24,26,31).…”