Effect of a second infusion of an internal teat sealant 4 weeks after drying off

Mastitis continues to be a major financial and animal welfare concern for dairy producers globally. Interventions at the end of lactation (drying off) including internal teat sealants (ITS) and antibiotics, which reduce the risk of new intramammary infection over the dry period, resulting in reduced clinical and subclinical mastitis incidence in the subsequent lactation. However, some ITS-treated cows are diagnosed with clinical mastitis over the dry period or early in the subsequent lactation, and loss of ITS may be a contributing factor. This study tested the effect of infusion of ITS (Interseal, Elanco New Zealand) at ∼4 wk following drying off at reducing the risk of subsequent subclinical and clinical mastitis in cows >4 yr old with an SCC of <250,000 cells/mL at the last DHI test of lactation. Cows from 23 spring-calving herds in the Waikato region of New Zealand were randomly assigned to ITS or antibiotic dry cow therapy (DCT) at dry-off (dry-off treatment) and ITS or no treatment (negative control) at 4 wk after drying off (wk 4 treatment) in a 2-by-2 factorial design. Cows were monitored until 30 d after calving for clinical mastitis, and the SCC from the first DHI test of the season for each cow were retrieved for analyses. Treatment groups were balanced for age, breed, previous SCC, milk yield, and lactation length. Cows treated with ITS at dry-off were 2.1 (1.1-4.1) times more likely to get clinical mastitis first 4 wk of the dry period than DCT treated cows. Internal teat sealant administration at wk 4 reduced the cow-level clinical mastitis incidence in the first 30 d of lactation compared with negative control (odds ratio = 0.59 [95% CI = 0.38-0.91]). We found no effect of dry-off treatment on clinical mastitis incidence in the first 30 d of lactation. The geometric mean DHI SCC for DCT-treated cows was 34 (95% CI = 31-53) versus 48 (95%CI = 43-53) × 1,000 cells/mL for ITS-treated cows, with subclinical prevalence (i.e., SCC >200,000 cells/mL) being 10.3% (95% CI = 8.3%-12.7%) versus 14.9% (95% CI = 12.3%-17.9%) for DCT and ITS treated cows, respectively. We found no effect of wk 4 ITS administration on first DHI test SCC or subclinical mastitis prevalence. We found no interaction between dry-off treatment and wk 4 treatment for any of the outcomes. We conclude that administration of ITS 4 wk after drying off in low SCC, older cows following drying off with ITS or DCT alone resulted in a decrease of ∼40% in cow-level early lactation clinical mastitis. Antibiotic DCT administration at dry-off resulted in fewer cases of clinical mastitis in the first 4 wk of the dry period, and a 31% relative reduction in subclinical mastitis prevalence at the first DHI test. Week 4 ITS administration is an intervention to reduce clinical mastitis in herds or subpopulations deemed at higher risk of clinical mastitis.