The three core physiological adaptations of dairy cows during transition

Milk production of dairy cows has increased dramatically over the last decades and continues to increase. During the last 30 years, it almost doubled in many countries of the world. This increase is mostly driven by genetics and improvement of feed conversion. The challenge modern dairy cows are facing at calving is huge, due to their genetic potential. At the beginning of lactation, energy demand to support lactogenesis increases by about 300% and calcium requirements increase by more than 65%. The metabolic requirements of the mammary gland that are a priority at the onset of lactation.

Physiological adaptation refers to the metabolic or physiological adjustment within the cell or tissues of an organism in response to an environmental stimulus. It results in the enhancement of that organism's ability to cope with its changing environment and to maintain homeostasis. Understanding the interactions that occur between nutrient demand, feed intake capacity and immune function during the transition to lactation is key to optimize health and welfare of cows. This enables them to produce according to their genetic potential, improving sustainability of dairy farming.

The three core physiological adaptations

During the transition to lactation, dairy cows undergo 3 core physiological adaptations. There is a strong connection between these three physiological adaptations, one is not independent from the other.

Moving from a non-lactating to a lactating state is a challenge for the metabolism of dairy cows. The explosive demand of nutrients and energy by the mammary gland needs complex adaptation processes to prioritize metabolic requirements. When a cow fails to adapt to this metabolic challenge, several metabolic disorders occur and considerably affect the immune system, reproductive performance, milk quality as well as animal welfare. Is normal that cows metabolically adapt to negative energy balance (NEB) by mobilizing adipose tissue. When this mobilization is adequate and regulated, the release of NEFA is limited to concentrations that can be fully metabolized for energy needs. When this process is disrupted as consequence of a reduced dry matter intake due to wrong diets formulation, minerals unbalance, bad management and animal stress between others, the cow fails to adapt and this situation becoming a source of systemic immune activation and inflammation.

Inflammation is the result of an immune response and is beneficial in recruiting innate immune cells to defend against pathogens, but it comes at a high energy cost to the animal. Macrophages and neutrophils require considerable energy to support their antimicrobial functions, and glucose serves as a primary fuel source, but they are competing with other processes related to milk production and fertility.

Changes to high-energy diets in early lactation can affects ruminal kinetics and the digestion of nutrients across the gastrointestinal tract (GIT). A high flow of soluble carbohydrates to the hindgut can lead to excessive fermentation and accumulation of organic acids. This will reduce the hindgut pH, shifting the microbiota population and damaging the gut epithelium. The primary role of the gastrointestinal epithelium is to protect the cow from pathogens, toxins and chemicals in the lumen and to prevent unregulated transport of these into the portal circulation. When the acidotic insult damages the epithelium, systemic inflammation occurs in response to hindgut permeability (“leaky gut”).

Supporting hindgut integrity is key to ensure a better transition to lactation. This prevents immune activation, decreasing the energetic and nutrient needs for inflammation and improving their availability for milk production and fertility.

Digestive adaptation and metabolic adaptation will influence the immune system.Poor digestive adaptation will increase the risk of leaky gut which an cause systemic immune activation. Prevention of excessive inflammation will support the immune function and improve the energy partition to milk production.

Calcium homeostasis is an important aim of metabolic adaption. The relation between hypocalcemia and the risk of infectious diseases is well documented. Calcium plays a central role in the activation of the immune system because T cells require a sustained calcium flow for regulation, survival, activation and proliferation. Another metabolic adaptation during the transition period is related to the intense lipolysis as a result of negative energy balance. When dairy cows are unable to adapt successfully, dry matter intake is reduced and increased lipolysis will cause oxidative stress and systemic inflammation.

These three key adaptations will influence longevity and milk production by enhancing resilience to the transition period. Supporting cows with these three core adaptations will reduce the impact of metabolic diseases and the involuntary culling in the first 100 DIM. It will improve nutrient partition, milk production and reproduction.