Ketosis and Fatty Liver
Mary Beth de Ondarza,
Ph.D., Technical Services Nutritionist
F.A.R.M.E. Institute, Homer, NY
What Is Ketosis?
Ketosis is caused by the incomplete metabolism of body fat which has been mobilized to supply energy demands. The characteristics of ketosis include: reduced milk yield, loss of body weight, loss of appetite, and occasionally, signs of nervousness. Sometimes these signs are clearly recognized (clinical) but, often, they are not easily seen (subclinical). By nature of their high energy demands, most of today's high-producing dairy cows experience some sub-clinical ketosis during the first 5 to 7 weeks of their lactation. In general, fatter cows (BCS > 3.75) will experience more ketosis.
A Little Biochemistry......
In the rumen, grains are generally broken down by the microbes to form propionate. Fiber is mostly converted to acetate or butyrate. All three of these volatile fatty acids are absorbed through the rumen wall and transported to the liver.
Propionate is used by the liver to make glucose. Glucose is used by the cow to make lactose, the sugar in milk. For this reason, total milk production is very closely related to the total glucose supply at the udder.
Propionate's second function involves the cow's fat metabolism. When the cow's energy demands for milk production exceed the amount of energy she is eating, she begins to break down some of her body fat stores. Fats are first broken down into smaller pieces, called non-esterified fatty acids (NEFA's), and carried to the liver. At the liver, they are broken down to form acetate and through this process, energy is generated. Acetate must then be broken down to carbon dioxide and water to yield more energy, however, this process requires some propionate. If there is not enough propionate available (which is often the case when cows are making a lot of milk sugar), the excess acetate builds up in the liver, then acetate molecules combine to make acetone, acetoacetate, and beta-hydroxybutyrate. These products are released from the liver into the cow's bloodstream, causing the ketosis symptoms.
What is Fatty Liver?
Fatty liver syndrome is the accumulation of fat within the cow's liver. Excessive fat stores in the liver do not occur while the cow is putting fat on her back but instead, they are the result of her taking fat from her back and trying to process that fat through her liver generally during the prefresh period and early lactation. The liver becomes fat when the cow is loosing weight. Fatty liver syndrome (> 20% fat) impairs the function of the liver, increases disease incidence, reduces fertility, and sometimes leads to death. Once deposited in the liver, fat levels are not reduced until the cow achieves a state of positive energy balance about 5 to 10 weeks after calving. As with ketosis, fatter cows (BCS > 3.75) are more likely than thinner cows to experience fatty liver syndrome during early lactation.
Causes of Fatty Liver --
First, negative energy balance can cause fatty liver. This is simply a situation in which a cow's energy needs exceed her dietary energy supply. When cows are presented with this situation, they take fat from their backs and process it at the liver to make energy. Second, stress can cause fatty liver. When a cow is stressed at calving time, her hormones trigger a rise in blood fat concentrations. Poor environmental and handling conditions can upset the cow and contribute to her stress.
Prevention of Ketosis and Fatty Liver --
1. Energy Density of the Prefresh Diet
Research at the University of Wisconsin, has shown that cows dramatically reduce their dry matter intake during the final week prior to calving. At the same time as her dry matter intake is decreasing, fetal growth and mammary tissue growth are increasing, causing an increase in her total nutrient requirements. Cows carrying twins actually start to reduce their dry matter intake even earlier than other cows, plus they have higher fetal requirements.
When formulating a ration for a prefresh group, we assume that they will consume, on average, about 1.75% of body weight, or about 23 lbs of dry matter for a Holstein cow. The diet needs to contain about 0.70 Mcal/lb NEl. If we don't account for this reduction in dry matter intake prior to calving and increase energy density, we can expect cows to begin to mobilize excessive amounts of fat from their backs and to have high levels of NEFA's prior to calving. This sets the cow up for reduced dry matter intake, ketosis and fatty liver syndrome following calving.
2. Non-Fiber Carbohydrate of the Prefresh Diet
Since propionate is used by the cow to derive energy from body fat, non-fiber carbohydrate (NFC) levels need to rise to about 32% of the dry matter during the prefresh period. Higher NFC levels also help to transition the rumen microbes towards a lactating ration again and to increase the absorptive ability of the rumen papillae. Both of these processes will reduce rumen acidosis and "off-feed" problems once the cow calves. Of course, increased dietary NFC will also increase the energy density of the diet.
3. Effective Fiber of the Prefresh Diet
As we increase dietary grain in the prefresh diet and dry matter intake is reduced, we increase the likelihood of a displaced abomasum (D.A.). A cow with a D.A. is likely to become a cow with ketosis (or vice-versa). Therefore, it is important to maintain adequate levels of effective fiber (> 32%) in the prefresh ration. About 5 lbs of high-quality (below 65% NDF) grassy hay can go a long ways towards meeting the effective fiber requirement.
4. Protein of the Prefresh Diet
There is some research from Cornell that suggests that if we meet the DIP needs of the rumen microbes and then meet the amino acid deficits from the microbial flow to the small intestine by supplying a high-quality bypass protein, we can reduce the incidence of ketosis. For this reason, we recommend that the prefresh diet contain about 14.5% CP with about 30% of that protein being in the form of soluble protein (SIP), 60% in the form of degradable protein (DIP), and 40% as undegradable protein (UIP). The inclusion of some processed soy proteins and animal proteins is recommended to improve the amino acid quality of the UIP.
5. Mineral Balance of the Prefresh Diet
If a cow goes down with milk fever or downer cow syndrome and doesn't eat well for a period of time, she is more likely to get ketosis and fatty liver syndrome. Watch calcium (0.50 - 0.65% DM), phosphorus (0.35 - 0.45% DM), magnesium (0.25 - 0.31% DM), and potassium (<1.2% DM).
6. Palatability of the Prefresh Diet
The prefresh cow is the fussiest eater on the farm. The forages in the ration must be fresh and mold-free. Do not use the sweepings from the milking cows as part of the prefresh ration. Do not feed the prefresh TMR every other day. Have fresh TMR available at least once per day, better yet, twice per day. Never let the prefresh bunk get empty during the day. Be careful to minimize and gradually introduce anionic salts, bypass fats, and animal proteins which are not very palatable. Include forages to be fed in the milking ration in the prefresh ration to minimize adjustment after calving.
7. Niacin Inclusion in the Prefresh and Fresh Diet
Niacin is a water soluble vitamin which is normally produced in the rumen by the microbes. Often during the prefresh and early lactation period, the demand for niacin exceeds its production in the rumen. Niacin aids the liver in its metabolism of fats and therefore, an additional 6 to 12 grams of niacin added to the diet can reduce beta-hydroxybutyrate levels in the blood and increase blood glucose.
8. Calcium Propionate Inclusion in the Prefresh and Fresh Diet
Inclusion of 0.25 lb of calcium propionate in the prefresh and fresh ration, provides a extra daily dose of propionate which reduces both subclinical and clinical ketosis. Propionate is used as a glucose source to make milk lactose (or milk sugar). Propionate is also used at the liver to convert acetate (from mobilized fat) to energy. Some researchers believe that calcium propionate mainly spares dietary protein from being metabolized to glucose. Thus, with the addition of calcium propionate in the diet, more amino acids are available for conversion to milk protein and total milk production increases.
9. Environment of the Prefresh Cow
Reduce stress and the blood NEFA levels associated with stress by providing a well-ventilated, clean, dry, well-bedded calving stall.
10. Prevent Over-Conditioning of Cows
Ideally, cows should calve in at a BCS of 3.25 to 3.75. A fat cow is more prone to take fat off her back and to have a depressed appetite. Watch cows from 200 DIM to 305 DIM. The goal is to have cows dry off at the BCS that you want them to calve in at and to maintain that BCS throughout the dry period. Don't put cows on a diet during the dry period because fat can be deposited in the liver at that time.