A quick online search regarding the US market for such products -
"The global pet supplements market size was valued at USD 637.6 million in 2019 and is expected to grow at a compound annual growth rate (CAGR) of 6.4% from 2020 to 2027. Key factors driving the market include changes in socio-economic aspects and inclination towards the humanization of animals. Pet supplements are used for dogs, cats, horses, birds, rabbits, and fishes in the form of multivitamins, minerals, prebiotics, antioxidants, and fatty acids such as Omega-3, 6, and 9."