Milk protein is well accepted for nutritional value compared with other sources of protein. Detailed understanding of the natural factors that can determine milk protein subcomponent (i.e., casein) not only fulfill the knowledge of protein synthesis but also provide the potential idea to improve milk quality. The variation in milk protein content from dairy cows and goats fed in tropical areas may determine the added value of milk from this region. Under prolonged high ambient temperature (HTa), dairy cows and goats are at the stage of heat stress. This physiological condition produces a negative effect on dairy cows and goats, i.e., food intake and milk yield. However, the higher milk protein content during summer is demonstrated in dairy goats in our condition. Likewise, an increase in heat shock protein 70 (Hsp70) gene expression from mammary epithelium cells isolated from either in vivo (summer and winter periods) and in vitro conditions suggests the direct effect of HTa on mammary gland and perhaps on milk protein synthesis. The intracellular effect of Hsp70 on milk protein synthesis has been proposed in regard to the endoplasmic reticulum and Golgi apparatus protein transportation and with the subcomponent of casein micelle. The present information reveals the molecular mechanism of HTa on milk protein synthesis.