Prepartum application of internal teat sealant or intramammary amoxicillin on dairy heifers: Effect on udder health, survival, and performance

Intramammary infusion of antimicrobials (IA) and application of an internal teat sealant (ITS) at the end of the lactation is a common strategy to prevent and treat intramammary infections during the dry period. In heifers, precalving IA has been reported to improve udder health and milk quality; however, the effect of ITS in heifers housed in freestall barns is still unknown. The objective of this study was to investigate the effect of prepartum application of ITS or IA on udder health of dairy heifers. A total of 886 heifers were randomly allocated into 1 of 4 treatment groups when they were 245 ± 3 d pregnant. Control heifers (CON) did not receive any treatment. Heifers in the ITS group received the application of ITS containing 2.6 g of bismuth subnitrate. Animals in the IA group received intramammary administration of 62.5 mg of amoxicillin. Heifers in IA+ITS group received intramammary administration of amoxicillin followed by ITS application. The follow-up period was 270 d in milk (DIM). Clinical mastitis was diagnosed and treated by trained farm personnel throughout the study period. Composite milk somatic cell counts (SCC) were determined monthly for the first 9 mo of lactation by Dairy Herd Improvement Association. Subclinical mastitis was defined as a cow having a SCC >200,000 cells/mL for at least 1 test day and not diagnosed with clinical mastitis during the study period. At 7 ± 3 DIM, composite milk samples were collected for bacteriological analysis for a subset of the study animals. The presence of pathogens in milk at 7 ± 3 DIM was more frequently detected in the CON heifers compared with animals enrolled in the treatment groups. Heifers in IA+ITS group had a decreased incidence of clinical mastitis compared with CON heifers (12.9 vs. 21.4%). Additionally, the incidence of subclinical mastitis was decreased for IA+ITS heifers compared with CON counterparts (20.1 vs. 43.8%). During the first 9 mo of lactation, IA and IA+ITS heifers had lower SCC linear scores compared with ITS and CON counterparts. Although IA+ITS treatment successfully improved udder health, it did not result in better milk yield, fertility, and survivability. In conclusion, ITS alone was not effective in improving udder health; however, the combination of ITS and IA decreased the incidence of clinical and subclinical mastitis during the first 9 mo of lactation. Additionally, IA+ITS had a long-term effect on the SCC linear score throughout the study period.