Infusion of an internal teat sealant into the mammary gland of the dairy cow at drying off has been claimed to reduce the incidence of clinical mastitis over many months in the subsequent lactation, despite the absence of any ingredient of the sealant remaining for that long. However, these claims have been poorly substantiated, often by lack of identification on when the infection occurred in the period from calving to disease, if the infection was present at post calving sampling and if the pathogen causing the disease was that causing an earlier infection. Moreover, no hypothesis on how any effect on clinical mastitis might occur has been advanced in any of the publications claiming the effect. That the effect might occur is only reported in a minority of publications, and the possibility that this is relatively specific to Gram-negative pathogens is reviewed.

The internal teat sealant OrbeSeal® (Zoetis, Berlin, Germany) is intended to prevent new intramammary infection (IMI) throughout the dry period. The aim of this field study was to determine new infection rates in udder quarters applied exclusively with the sealant at dry-off and untreated ones (control group). For that, the new infection rate of udder quarters treated with the sealant was evaluated in a split-udder design (front right and rear left udder quarters treated, the other ones untreated) in 128 cows from nine dairy farms in North Germany that were healthy in all four udder quarters (i.e. <100 000 cells/ml, bacteriologically negative). After calving, duplicate quarter milk samples were collected twice at DIM (days in milk) 5–12 and 7 d later for culture. The new infection rates for treated and untreated groups were 3·4 and 10·5%, respectively. The results showed that applying a standardised study design with very few confounders under field conditions, using internal teat sealants reduced the new infection rate on quarter level to a third of that of the control group. Thus, internal teat sealants represent a viable option for dry-off treatment of udder-healthy cows.

The objective of this field study was to compare the udder health status as well as the clinical mastitis rate during the first 100 d of lactation in cows that received long-acting dry cow antibiotic alone (group AB) or in combination with an internal teat sealant (group AB + OS). The study was conducted during a 9-month period and included 136 Holstein cows from 12 dairy farms in Hessia, Germany. Between days 1 and 5 after calving a California mastitis test (CMT) was performed. Milk-samples were collected for bacteriological culture before drying off, between days 6 and 14 and days 35 and 56 of lactation. Additionally the cows were monitored for the occurrence of clinical mastitis events until 100 d post partum. Within the 12 herds cow-pairs were formed on the basis of age, milk yield and SCC. A cow-pair consisted of one cow from group AB and one cow from group AB + OS. For statistical analysis within every cow-pair one quarter that has been dried off with internal teat sealant and dry cow antibiotic (group AB + OS) was compared with one quarter that has been dried off with dry cow antibiotic (group AB) alone. As criterion for the matching process of udder quarters the cytobacteriological udder health status before drying off was used. A total of 544 quarters (136 cows) were used in this analysis. In the first 5 d after calving, group AB had significantly more quarters with a positive CMT reaction than group AB + OS (85 vs. 57; P <0·001), and in the first 100 d of lactation, group AB had more quarters with clinical mastitis than group AB + OS (25 vs. 15; P = 0·03). In the time periods 6–14 and 35–56 d of lactation, there were fewer quarters in group AB + OS populated with Corynebacterium spp. (days 6–14, P = 0·05; days 35–56, P = 0·02) and aesculin-positive streptococci (days 35–56, P = 0·02). The internal teat sealant was a promising tool for the prevention of new intramammary infections (IMI) of dry cows with environmental udder pathogens as expressed during early lactation.