Milk production and composition in warm-climate regions: a systematic review and meta-analysis

Milk production is a key component of the agriculture sector in the tropics and subtropics, contributing 47.32% to global milk production. This study aimed to quantify milk production and composition (fat and protein) in warm-climate regions located between 30 degrees north and south of the equator. A meta-analysis was conducted using the standardized mean (SM) for milk production, fat percentage, and protein percentage, all adjusted for dry matter intake (DMI), focusing on lactating ruminants. A total of 42, 11, 15, and 16 research papers were selected for cows, buffalo, sheep, and goats, respectively, encompassing 2421 animal records from experiments published between 1992 and 2024. The SM for milk production was 10.38, 9.77, 0.79, and 1.13 kg/day/animal for cows, buffalo, sheep, and goats, respectively. Due to the significant variance between different cow breeds, the study divided the cows into three main groups based on breed type crossbreds, foreign, and local breeds. The SM for milk production per animal was 11.49 kg/day for crossbreds, 22.95 kg/day for foreign breeds, and 7.13 kg/day for local breeds. The effect of DMI on the SM of milk production for cows, sheep, and goats was highly significant. For milk fat, the SM was 3.95, 6.64, 4.70, and 3.56% for cows, buffalo, sheep, and goats, respectively. Regarding milk protein, the SM was 3.36, 3.91, 4.34, and 3.45% for cows, buffalo, sheep, and goats, respectively. The results of this meta-analysis highlight that warm-climate regions are significant contributors to global dairy production. Furthermore, improving ruminant milk production and quality in hot climates need further efforts.