Effects of Negative Energy Balance On Health and Milk Yield of Lactating Dairy Cattle

Selective breeding of dairy cattle has led to a dramatic increase in milk yield per cow where it has more than doubled in the past 40 years. This increase in yield has been accompanied by declining ability to reproduce, increased incidence of health problems and declining longevity in modern dairy cows. Cattle are at risk from diseases and disorders during early lactation. At this time, there is demand for energy for more milk production, but a lag in feed in take which leads to negative energy balance. Therefore, the cow draws from body reserves to support milk production. This release of free fatty acids results in the production of ketone bodies; acetone, acetoacetate and beta-hydroxybutyrate, which serve as a source of energy when carbohydrate levels are low. The accumulation of these compounds can lead to ketosis, a condition that has been found to reduce milk yields. A loss of 25% per lactation during clinical ketosis and 1-1.5kg/day of milk production for subclinical ketosis has been reported. Clinical ketosis occurs in the first six to eight weeks post calving and results in loss of body condition and decrease in milk production. The milk fat of ketotic cows increases due to the availability of beta-hydroxybutyric and fatty acids. Cows with clinical ketosis will show nervous signs, such as licking and blindness. Subclinical ketosis causes increased levels of circulating ketone bodies in serum, milk and urine. Cows are at risk of subclinical ketosis within two months postpartum with display of displaced abomasum. Negative energy balance has direct correlation to energy metabolism, which can be determined by measuring the amount of None- Esterified fatty acids in the blood and thus identify cows that are at risk. Dry matter intake is important in managing the degree and severity of the impacts of negative energy balance in the first 6 weeks of lactation. The stimulation of appetite to ensure adequate dry matter intake in normal, healthy cows is essential to provide nutrients for maximum milk production, follicular growth, ovulation, uterine involution, and the initiation of pregnancy. Keywords : Negative energy balance, Milk yield, cow disorder