Transition cows get a lot of attention in the herd, as the transition period brings significant challenges.
For dairy cows, the transition period is typically the last three weeks of gestation and the first three weeks of lactation, during which cows undergo a variety of metabolic and immunological changes that increase their susceptibility to metabolic disorders and infectious diseases. During this time, metabolic demands (i.e., nutritional requirements) increase so the cow can support fetal growth during late gestation and the subsequent onset and maintenance of lactation. However, cows are often unable to consume enough feed to meet increased nutritional requirements, so they enter a state of negative nutrient balance. More specifically, transition cows undergo a period of sustained negative energy balance that leads to losing bodyweight and body condition score.
While in negative energy balance, body fat is mobilized in the form of non-esterified fatty acids (NEFA). NEFAs can be used by most body tissues as a fuel source for cells; this helps the body to maintain blood glucose concentrations. When mobilization of body fat (i.e., bodyweight loss) is accentuated, the liver becomes unable to metabolize the massive amounts of fat arriving. Then, fat infiltrates the liver and gets accumulated in the form of triglycerides, leading to a metabolic disease called fatty liver syndrome. Also, when fat metabolism in liver is compromised due to increased body fat mobilization, β-hydroxybutyrate (BHBA) can be formed from the incomplete oxidation of NEFA. High BHBA concentrations in blood are associated with the appearance of metabolic diseases, including displaced abomasum, clinical ketosis and metritis, which could aggravate negative energy balance. It is well established that elevated concentrations of NEFA and BHBA in blood impair milk production and reproduction.
The relationship between negative energy balance and impaired immune function is concerning. For example, elevated concentrations of NEFA and BHBA in blood have been associated with systemic inflammatory conditions. Furthermore, immune dysfunction that happens during the transition period also favors the incidence of infectious diseases, such as mastitis. During infections, the process of killing pathogens includes generating free radicals. This can be affected in cows that are experiencing stressors (i.e., negative energy balance).
Cells produce free radicals as part of their normal metabolism, but accumulation of them is harmful to the body. Antioxidants play a role in neutralizing free radicals, so cells aren’t damaged. However, when levels of free radicals surpass the antioxidant capacity, oxidative stress occurs. Dairy cows in the transition period are known to undergo oxidative stress, mainly marked by the accumulation of free radicals, which may lead to impaired immunity and increased metabolic stress. In addition, inflammatory conditions, such as mastitis, can worsen oxidative stress by stimulating free radical production or decreasing antioxidant capacity.
The function of dietary antioxidants, such as plant-based polyphenols, is to protect lipids, nucleic acids, proteins and other molecules against oxidative stress. They work by increasing blood levels of enzymes that work as the first line of defense against oxidative stress, directly scavenging free radicals and enhancing antioxidant defenses, therefore reducing free radical accumulation. They can also increase blood levels of vitamin A and vitamin E. Feeding dietary antioxidants to cattle may support health of transition cows by reducing incidence of metabolic diseases, and improve nutrient digestibility and, ultimately, milk production and quality.
Another key consideration is trace mineral supplementation. Trace minerals are essential for vital processes of the body, which include functioning as antioxidants. Feeding adequate amounts of trace minerals may improve immune function, health and production, not just in dairy cows but also in other livestock species. As antioxidants, trace minerals can help the immune system to hunt free radicals and transform them into non-hazardous compounds. Interestingly, trace minerals may work in synergy with plant-based antioxidants, as both enhance levels of a same antioxidant enzyme, the first line of defense against oxidative stress. For example, copper and manganese are integral components of an antioxidant enzyme, whereas zinc acts as this enzyme’s cofactor, so the presence of these trace minerals is essential for the activity of this enzyme. Although these trace minerals play an important role in alleviating oxidative stress, they are also involved in other important processes:
- Zinc – bone formation, appetite control and energy metabolism
- Copper – regulation of iron availability, energy metabolism, cellular respiration and bone formation
- Manganese – tissue keratinization, energy metabolism, bone formation, reproduction and nervous functions
Controlling stress situations on the farm can be very challenging, especially when dealing with dairy cows during the transition period. Management options should always be considered to avoid or minimize negative effects of stress on cow health and production. Diets can be formulated to help cows fight against stress from inside out, enhancing their immune system and overall health. Meeting nutritional requirements for trace minerals and adding dietary antioxidants to diets can be important tools to keep your herd healthy and cows milking more.
