Since March 2024, H5N1 highly pathogenic avian influenza has been circulating among U.S. dairy cattle. Unlike the predominantly respiratory disease typically associated with influenza virus infection, this virus mainly infects the mammary gland and is shed in large quantities through milk, which can contaminate milking equipment and the farm environment. The infection leads to reduced milk yield, and the milk becomes thick and yellow. The virus transmission may occur via multiple routes, including milk contamination, milking equipment, and possibly air or wastewater on farms. However, the principal transmission pathway remains unclear. Notably, experimental evidence has shown that co-housed susceptible animals do not readily acquire infection, and intramammary inoculation of a single quarter does not consistently result in transmission to other quarters in the same animal, suggesting that within-herd transmission is likely multifactorial and cannot be attributed solely to milk-associated exposure. Farm workers who handle raw milk or sick cows are at risk, mostly through eye contact or breathing in virus particles. Control measures including isolation of sick cows, equipment disinfection, milk testing, and avoiding raw milk feeding to animals are necessary but challenging. Therefore, establishing an integrated One Health system is essential to effectively safeguard both animal and public health.