High-producing cows are prone to oxidative stress in the same manner they are prone to having metabolic disorders. It is well recognized that the onset of events such as calving, rapid elevation of milk production, extreme heat conditions and unbalanced rations are factors that lead to the occurrence of metabolic disorders. These same conditions affect the level of oxidative stress.
Many dairy producers utilize special dry cow programs to give the cow a rest during the final period of calf growth. It is a time for properly conditioning the cow and replenishing body reserves for mobilization during the lactation. The use of effective forage particles appropriately balanced with quality concentrates, bioavailable trace minerals and vitamins helps maintain a healthy digestive system and proper body condition for the cow.
These management practices have been demonstrated to reduce the occurrence of metabolic disorders and also oxidative stress. They help the cow improve feed intake and reach peak production quicker. The net result is higher production, better breeding efficiency, shorter calving intervals and greater profitability.
Oxidative stress has been hypothesized to be related to metabolic disorders and antioxidant deficiency in dairy cows. Symptoms of lactating cows with oxidative stress include retained placenta, udder edema and mastitis. Other visible symptoms include delayed first estrus, delayed first breeding, repeat breeding resulting from failure to conceive or from early embryonic death. Symptoms of oxidative stress result in increased calving intervals, lowered production, and ultimate culling of cows. All of these symptoms are costly and reduce profitability for dairy producers. It has been estimated that more than 50% of health costs occur between calving and the first 30 days in milk. This is the same period that the majority of metabolic disorders and oxidative stress occur in high-producing cows.
It has been demonstrated that the level of alpha tocopherol is lowest during the periparturient period. Supplying antioxidants during this period could help protect the animal against lipid peroxidation, which is an indicator of oxidative stress.
Dietary ingredients have an effect upon oxidative stress. High quantities of fat are routinely supplied to high producing cows to increase the energy density of the diet. The effect of the fat on the animal is dependent on whether or not the fat has been stabilized with an antioxidant. Stabilized lipid supplements are less likely to contribute to elevating peroxides coming from the diet, therefore reducing the overall oxidative load on the animal. Peroxides cause damage to cellular membranes, internal cellular components and proteins. Dairy producers must consider all dietary sources of fat supplied to the cow. More than 50% of dietary fat can come from sources other than supplemental fat. Typical sources may include cottonseed (19% fat), distillers grains (5-15% fat), soybean meal (7-20% fat), and fish meal (10% fat). Thus, steps may be taken to include antioxidants in the diet to stabilize these ingredients and help manage oxidative stress prior to feeding.