Limiting factors for milk production in dairy cows: perspectives from physiology and nutrition.

With increasing milk yields in dairy cows, potential limiting factors are intensively discussed. The present review addresses physiological and nutritional constraints that are considered limiting for milk production. The limiting character can change depending on the stage of lactation. Especially after parturition, the limited availability of glucose and amino acids does not only restrict lactational performance but also immune function. Further limitations imposed by feed, intestinal absorption, intermediary metabolism, and nutrient uptake by the mammary gland are described. Moreover, the impact of environmental (heat stress, photoperiod length) and management-related factors (e.g., rearing intensity, dry-period length) on milk yield are elucidated. However, the physiological constraints addressed in this review give space for improvements. Of course, boundaries are set by the farming system, climate, etc. that cannot be overcome. Efforts in improving welfare, husbandry, feeding, and management are likely to further enhance milk production, but will simultaneously improve other traits like reproductive performance and animal health. The existing variation in metabolic adaptation to different environmental stimuli provides further potential for appropriately selecting cows fitting best to the respective conditions. However, increasing yearly milk yields must not be dismissed as driving forces worsening animal health. Only healthy animals can perform well and produce high amounts of milk.