Avoiding Fatty Liver
Paying attention to body condition score, feed intake and energy metabolism can help minimize the risk of your transition cows falling prey to a common condition known as fatty liver. Even moderate cases of this condition can result in decreased milk production, poorer reproductive performance and reduced overall well-being of these animals-factors that can lower your income.
Recent research related to body condition score during this period has shed new light on just how complex the transition is for cows as they go from dry to milking. Too much body condition during the few weeks before and after calving can lead to fatty liver but we're just now starting to understand the reasons.
A dairy cow often reduces feed intake before calving. After calving, milk production requires her to use a lot of energy. She can't eat enough to meet her energy needs, so she offsets that deficit-known as negative energy balance-by using her own body reserves.
You notice the effect of this negative energy balance as a loss in body condition score during early lactation. It's normal for the cow but, in some cases, it leads to fatty liver, estimated to affect half of mature dairy cows to a moderate or severe extent during the transition period.
Most of the cow's energy reserve is in her body fat. When she needs this energy, her body breaks down the fat into non-esterified fatty acids [NEFAs]. They're released into her bloodstream and processed by her liver.
In excess amounts, however, NEFAs can be toxic. Excess breakdown of body fat causes high NEFA levels in the blood. When levels exceed the liver's capacity to process NEFAs, they start accumulating in the liver as fat. Fat deposits in the liver interfere with this organ's function. Remember that these problems originated with the degree and duration of negative energy balance and the amount of body fat metabolized.
New research has shown that more than just NEFAs are released into the bloodstream when body fat is broken down. A variety of substances, including hormones in the fat cells, are released with NEFAs. These hormones signal other parts of the cow's body that she's experiencing a negative energy balance.
The important sites for fat metabolism in a lactating cow are the mammary gland, where she makes butterfat, the liver and body fat. Well-known hormones like insulin and growth hormone help co-ordinate fat metabolism in these locations.
Dr. Richard Vernon, a British dairy researcher, recently reviewed the interactions between fat tissue and liver in the development of fatty liver. His review identified the role of the hormones released from fat, collectively called adipocytokines, as an important new factor in fatty liver development.
These hormones signal the brain, resulting in reduced appetite. That increases or prolongs the negative energy balance as the cow continues to draw on her body fat reserves.
The role of adipocytokines to control appetite is a relatively new field in dairy research. Using this knowledge about hormones from fat cells on farm isn't practical yet, but it underlines the complexity of feeding the transition cow.
The illustration on page 30 shows many interactions among fat, the liver, the brain and the mammary gland. Eventually, this knowledge will improve the ability of dairy nutritionists to avoid energy metabolism problems like fatty liver by developing nutritional and feeding strategies to achieve better transition cow health.
Currently, the best recommendations to avoid energy-related health issues during the transition period are to dry off cows at a recommended body condition score of 3.5 to 3.75-not 4.0. Also, you have to manage the two biggest details of feeding transition cows: optimizing feed intake and improving energy metabolism.
Optimize feed intake by:
Improve energy metabolism with feed additives: rumen-protected choline and Rumensin.
You can't manage the hormonal signals that may control appetite by nutritional means yet. By paying attention to nutrition and management details during the transition period, however, you can avoid fatty liver and other health issues associated with excessive negative energy balance. You'll see that benefit on both the revenue and cost sides of the ledger.
Vernon, R.G. 2005. Lipid metabolism during lactation: a review of adipose tissue-liver interactions and the development of fatty liver. J. Dairy Res. 72: 460-469.
This article first appeared in the Ruminations column of The Milk Producer Magazine, April, 2006.
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