Premilking teat disinfection: Is it worthwhile in pasture-grazed dairy herds?

Abstract

A controlled trial was conducted in 5 pasture-grazed commercial dairy herds in Australia in 2012 to determine whether premilking teat disinfection and drying of teats reduces clinical mastitis incidence during early lactation by at least 50%. A 50% reduction was estimated to be the minimum required to justify additional costs of labor, disinfectants, and other resources if premilking teat disinfection was implemented in a 500-cow herd averaging 8 clinical cases per 100 cow-months. A secondary aim was to determine whether this premilking teat disinfection routine reduces incidence of new udder infections. Treatment was applied in each herd for approximately 60 d (range of 59.5 to 61 d), commencing in each herd soon after the start of the herd's main or only calving period. Within each herd, cows were allocated to either the treatment (premilking disinfection) or the control (no premilking disinfection) group based on their herd identity number. During the trial period, any cow having a new case of clinical mastitis or an individual cow cell count greater than 250,000 cells/mL of milk (when preceded by individual cow cell counts of 250,000 cells/mL of milk or below) was deemed to have had a new infection. Overall, neither clinical mastitis incidence nor new infection rate differed significantly between treatment and control groups. Over the whole study period, 98 of the 1,029 cows in the premilking disinfection group and 97 of the 1,025 cows in the control group had clinical mastitis. Total cow-days at risk of clinical mastitis were similar in each group. However, clinical incidence rates were markedly lower in treatment cows in one herd (herd 3; incidence rate ratio=0.34) and there was some evidence that new infection incidence rates were lower in treated cows in this herd (incidence rate ratio=0.42). Rainfall during the study period was below long-term district average in all 5 study herds. Cows' teats were less dirty than in previous, wetter years for the 4 herds where no significant clinical mastitis response was detected but some teat soiling was observed in herd 3 during the study period. Routine application of premilking teat disinfection in pasture-grazed herds is unlikely to produce a worthwhile (economic) reduction in the number of clinical mastitis cases when teats are relatively clean and dry and the clinical mastitis incidence is low. However, premilking disinfection might be worthwhile during periods when teats are heavily soiled and the incidence of clinical mastitis due to environmental pathogens is high.

Effect of pre‐milking teat disinfection on clinical mastitis incidence in a dairy herd in Northern Queensland, Australia

“…Our finding that PMTD was not a cost‐effective practice is consistent with the two largest studies conducted to date . Our failure to find a significant benefit is also consistent with the findings from cross‐sectional studies of PMTD, most of which show either a positive association or no association between the practice and clinical or subclinical mastitis …”

“…This herd met many of the criteria for a herd that should benefit from PMTD. Firstly, udder contamination was common . Although the rainfall during the trial period was below average, it was sufficient in both frequency and volume to cause shady areas of the farm to remain muddy when over‐crowded by heat‐stressed cows.…”

“…In addition, the environmental mastitis incidence was 360% higher in multiparous animals. It is thus very clear that, in this season and on this farm, PMTD did not result in a cost‐effective (> 50%) reduction in clinical mastitis incidence. In first‐lactation heifers, the 95% CI for clinical mastitis (0.52–3.29), although broad, was sufficient to support this conclusion.…”

“…This is the first trial to date that has demonstrated a statistically significant increase in clinical mastitis in cattle treated with PMTD. Other intervention studies have demonstrated a significant reduction, non‐significant reductions, 12–14,17–19 no effect or a non‐significant increase …”

“…The primary objective of this trial was to determine if PMTD would reduce clinical mastitis incidence by more than 50% (the break‐even point for herds with >8 cases/100 cow‐months) during periods of increased udder and teat contamination from environmental sources.…”