Dietmar Holm and Martin van der Leek
Department of Production Animal Studies,
Faculty of Veterinary Science, University of Pretoria
From Southern Cape Proceedings 2018
Ketosis or acetonaemia
Ketosis in dairy cows can broadly be classified into either type I or type II ketosis, based on the underlying pathophysiology, with some similarities to that of type I and type II diabetes.
Type I ketosis is a metabolic disorder of high yielding lactating dairy cows caused by an imbalance in the energy metabolism. It is characterized by ketonaemia, ketonuria, hypoglycaemia, depression and anorexia. It is most often seen from the third to the sixth week of lactation.
The key factor in the occurrence of ketosis in dairies, is sufficient intake of a properly balanced ration (Dry Matter Intake). Feedbunk management, as mentioned before in the case of hypocalcaemia, is of particular importance.
Type I ketosis can be sub-classified into primary and secondary, where primary ketosis occurs due to a severe negative energy balance (NEB) that leads to a substrate (oxaloacetate) deficiency in the absence of any other disease. Secondary ketosis is the accumulation of ketone bodies in the body due to anorexia secondary to a disease process. Any disease process that reduces dry matter intake (DMI) in early lactation may cause secondary ketosis.
The prevalence of primary ketosis is relatively low in southern Africa. Subclinical ketosis can often be detected in cows from high producing dairy herds if body fluids are tested for ketone bodies. Most cases occur between the 3rd and 6th week of lactation.
Many cases (50%) will spontaneously recover within days and mortalities are rare loss of production is more important, especially where cows do not respond well to treatment.
High producing cows and cows in their 3rd lactation and older have an increased risk for type I ketosis.
Carbohydrates and fibre compounds in the feed are broken down in the rumen by rumen microbes. The end products of rumen digestion are the volatile fatty acids acetate (average 70%), propionate (average 20%) and butyrate (average 10%).
Propionate can enter the citric acid cycle (CAC) directly and its carbon atoms can move through the cycle to enter the gluconeogenic pathway to form new glucose (propionate is thus glucogenic).
Acetate may also enter the CAC through acetyl CoA (small amounts) but only if there is enough C4 atoms (oxaloacetate) available in the CAC. Most of the acetate will, however, be used in fat synthesis, or if the body is in a catabolic state with fat being broken down, acetate will be used to form ketone bodies (aceto acetate, ß hydroxy butyric acid and acetone). Aceto-acetate and ß hydroxy butyrate have 4-carbon atoms, but they cannot be interchanged with the C4 units in the CAC. Acetone is a C3 compound that is formed slowly and spontaneously from aceto-acetate. Ketone bodies form an important energy source. They can enter the CAC via acetate and be oxidized for energy in heart, kidney, skeletal muscle and lactating mammary glands if there is sufficient C4 units (oxalo-acetate) available. If the C4 units concentration of the mitochondria becomes sufficiently depleted, there will not be enough C4 units to condense with C2 (acetyl CoA) to allow the initiation of the CAC. When this occurs, C2 units accumulate in the mitochondria and are removed via the production of ketone bodies.
Butyrate will also enter the ß oxidation pathway and be transformed into triglycerides or ketone bodies. Most of the butyrate will in fact already be converted to β hydroxy butyrate by the rumen epithelium as it is absorbed from the rumen. Acetate and butyrate are thus ketogenic in nature.
As ruminants cannot rely on a dietary glucose source of any magnitude, they need to produce large amounts of newly formed glucose (gluconeogenesis). This happens mainly in the liver through the gluconeogenic pathway. Skeletal muscle acts as an amino acid depot. Most amino acids from muscle are not transported directly to the liver but rather are first converted in the muscle to the transport amino acids alanine, glutamine and aspartate. They form an important part of the substances contributing to gluconeogenesis. The substances used to form glucose through the gluconeogenic pathway (i.e. propionate, lactate, glycerol alanine, aspartate and glutamine) enter the energy pathways in several positions.
The glucose formed through the gluconeogenic pathway is mainly used to manufacture lactose in lactating animals. Milk contains about 4.5 % lactose i.e. 50 kg of milk will contain 2.25 kg of lactose, nearly all of which must come from glucose provided by gluconeogenesis.
Protein breakdown for gluconeogenesis from amino acids plays an important role in energy metabolism in cows, and it has recently been suggested that cows with an insufficiency of this pathway, or rather an imbalance between lipolysis and proteolysis, may be at an increased risk of ketosis.
Diagram illustrating the pathways of energy metabolism in lactating dairy cows.
Pathogenesis of type I ketosis
The clinical manifestations are caused by:
- hypoglycaemia the brain needs glucose for normal functioning,
- hyperketonaemia it is speculated that the isopropyl alcohol formed from ß hydroxybutyrate is toxic and may cause the nervous symptoms seen,
- suboptimal liver function – detoxification function of liver affected,
- distension of liver-abdominal pain,
- acidosis – there is usually a mild metabolic acidosis (ketone bodies are acids) – Compare with pregnancy toxaemia in sheep where there may be a more severe acidosis.
The key underlying factor leading to type I ketosis is a deficiency in glucose due to a severe negative energy balance (NEB). The loss of glucose through milk production is not hormonally regulated, and will thus carry on despite causing harm to the health of the cow. Glucose in the ruminant has three main sources.
Firstly it can be absorbed directly from the small intestine in the form of sugars or starches, and secondly it can be metabolised from propionic acid, one of the most common volatile fatty acids produced in the rumen through microbial fermentation. In the third place it can be synthesised from acetyl-CoA, a metabolite of two other volatile fatty acids (butyric and acetic acid) or of fat break-down. Acetyl-CoA is an important fuel in ruminants, and apart from being a glucose precursor, it can be metabolised further into ketone bodies (acetone, aceto-acetate and beta-hydroxy butyric acid) that can also act as fuel in many tissues. The brain however requires glucose as energy source and cannot function on ketone bodies.
Ketone bodies enter the Krebbs cycle, a carbon cycle that utilises Acetyl-CoA and other substrates for glucose production, in the liver as well as many other tissues in the body to form glucose for energy production. This is the most important mechanism of energy production in the udder of lactating dairy cows, and is a unique property of ruminants. A very severe depletion of glucose stores, however, leads to a deficiency of 4-carbon substrate (oxaloacetate) needed to combine with Acetyl-CoA in order to enter the Krebbs cycle. This leads to failure of the Krebbs cycle to utilise all the available Acetyl-CoA, the excess being metabolised into excessive levels of ketone bodies.
Hormone sensitive lipase is the enzyme that causes break-down of fat, and is stimulated by low insulin, somatotropin, prolactin and other hormones. In type I ketosis, large amounts of fat is broken down and transported to the liver as Non-esterified fatty acids (NEFA), where it is metabolised into Acetyl-CoA. During a glucose shortage, insulin levels are low, indirectly leading to high levels of Acetyl-CoA in the liver where it forms ketone bodies. All lactating dairy cows have a certain level of ketone bodies in circulation as fuel for milk production, but when oxaloacetate becomes depleted glucose can not be formed from ketones anymore and the organ mostly affected by this is the brain. This leads to anorexia and other clinical signs.
Ketones are actively excreted in the urine (beta-hydroxy butyrate) and milk, or excreted through the lungs (acetone), while high levels are toxic to the brain.
Diagram illustrating how a negative energy balance (NEB) leads to Type I Ketosis
Predisposing factors of type I ketosis
Insufficient Dry Matter Intake (DMI) is key:
– high milk production High producing dairy cows are genetically programmed to produce milk even to the detriment of other bodily needs.
– high producing dairy cows just cannot physically eat enough food for their energy needs in early lactation and depend on the mobilization of their fat reserves to prevent an energy deficiency. Rumen size and activity are also diminished in the peripartum period.
– change of diet: a sudden change over from dry cow diet to a lactation diet may disturb rumen function, as well as reduce DMI
– type of diet: ratio between volatile fatty acids produced: Increased intake of fodder types that will generate proportionally more acetic and butyric acid and less propionic acid, e.g. grass, maize silage, high protein diets will predispose to ketosis. The body uses energy to excrete excessive nitrogen and the production of butyrate (ketogenic) will increase with a high percentage protein in the diet,
– butyrate is formed in certain types of silage (especially silage made from plants with a high moisture content). This butyrate from external sources is ketogenic,
– lack of exercise has been incriminated as a predisposing factor,
– in some herds a deficiency of cobalt and phosphorus seems to play a role – cobalt is needed for the formation of Vit B12 which is needed as a co factor where propionate enters the CAC – also review the effect of cobalt deficiency on rumen microbe activity,
– stress plays a role in limiting dietary intake and increasing energy needs,
– certain breeds and certain families within breeds are susceptible, indicating a possible genetic link – the prevalence of ketosis has decreased since the Holstein has become the dominant dairy breed in the world. Recently it has been suggested that the heritability of ketosis is not necessarily linked to milk production level, but that variation in ketone levels exist within groups of animals under the same management with similar milk production levels.
Note: Maize kernels contain a glucose polymer that can bypass the rumen microorganisms and be directly absorbed from the intestines and will thus have an antiketogenic effect.
Pathophysiology of type II ketosis or fat cow (fatty liver) syndrome
Type II ketosis is a peripartum (compare with type I ketosis) syndrome in high producing dairy cows where fat droplets will accumulate in liver cells to the extent that normal liver function is disturbed. This will lead to an exaggerated response of the animal to common postpartum illnesses.
The onset of type II ketosis is earlier during the production cycle of the cow, and in actual fact the factors leading to the condition occur some time before the syndrome is seen. Over-feeding of cows in the time before calving leads to high levels of glucose, continually stimulating the secretion of insulin, the hormone responsible to maintain glucose levels. Insulin normally inhibits hormone sensitive lipase, but due to the constant high levels, hormone sensitive lipase becomes refractory to the inhibitory stimulus of insulin. This is called insulin resistance, and reminds of the pathogenesis of type II diabetes mellitus in humans, from there the term type II ketosis.
Recent research indicates that Chromium possibly plays an important protective role against insulin resistance. Due to insulin resistance, hormone sensitive lipase becomes over-sensitive to other hormonal stimuli such as somatotropin, placental lactogen, prolactin and other hormones that are secreted at the time surrounding calving. This is called adipose sensitivity, and together with the fact that these obese cows have large fat stores, leads to the sudden very fast break-down of fat stores and transportation of non-esterified fatty acids (NEFA) to the liver. In the liver an enzyme called carnitine palmitoyltransferase-1 (CPT1) is responsible for the transport of NEFA into the mitochondrium, where it can be metabolised into Acetyl-CoA for gluconeogenesis or ketogenesis. CPT1 is inhibited by high levels of Malonyl CoA, a glucose substrate in the hepatocyte cytoplasm, leading to the formation of fat droplets containing esterified fats (macro-vesicles) in the hepatocyte cytoplasm.
The formation of macro-vesicles is a normal physiological mechanism of the cow to store excess energy, and only becomes a problem when these vesicles become large enough to impair normal liver function. This happens when about 60% of the liver cell is occupied by fat.
The liver would normally utilise the stored fat by excreting it in the form of very low density lipoproteins (VLDL), once again a fuel source for tissues elsewhere in the body. VLDL’s are formed by combining triglycerides (fat in macro-vesicles) with phospholipids, proteins and cholesterol, after which it forms micro-vesicles in the liver cytoplasm which excrete the VLDL’s directly into the blood. This can only happen in the presence of adequate phospholipid, cholesterol and protein. This pathway is not well developed in ruminants. A shortage of especially phospholipid compounds seems to be responsible for the accumulation of triglycerides in liver cells. Therefore total serum cholesterol indirectly measures the presence of VLDL in blood and consequently measures the liver’s ability to produce VLDL.
If VLDL production is compromised, fatty infiltration will ensue Cholesterol levels are decreased in ketosis, while dietary choline is required for the formation of phospholipid. It has further been shown that the secretion of micro-vesicles into the blood is inhibited by a decreased ratio of Poly-unsaturated fatty acids to saturated fatty acids (PUFA:SFA). This holds promise as a possible way through which the liver’s ability to excrete fat can be improved by manipulating the dietary PUFA:SFA ratio.
Diagram illustrating how constant high energy levels before calving leads to the formation of large fat droplets in the liver cells
Normal liver function plays a role in many crucial physiological processes like:
– detoxification of toxic and potentially toxic substances – i.e. the breakdown of certain hormones,
– storage area for food substances like glycogen, vitamins (A, D, K and certain B vitamins) and minerals,
– synthesizing of essential substances like vitamin A, albumin, globulin and other plasma protein
The disturbance of normal liver function will have a severe impact on the immune status of the body in general and certain organs in particular, i.e.;
– the uterus may become more prone to infection due to a failure of the liver to break down certain hormones,
– a reduction in the formation of immunoglobulins may generally affect the immune status of the body.
The immediate post partum period is a critical period for the dairy cow and in this period the prevalence of certain conditions is relatively high. The common postpartum diseases of dairy cows are metritis, mastitis, milk fever, displaced abomasum, retained placenta and ketosis. A cow with TYPE II KETOSIS will be more likely to contract one or more of the above mentioned conditions and will usually respond poorly to treatment for the specific condition. Cows with TYPE II KETOSIS also will manifest a reduced breeding efficiency as evidenced by both a prolonged calving to first oestrus period and an increased number of services per conception.
Predisposing factors of type II ketosis
Poor reproduction performance results in extended lactations, which gives the cows time to become overconditioned on the lactation ration towards the end of their lactations.
During the last half of the lactation period, when the hormonal regulation of lactation still results in cows to be very efficient in their ability to utilise feed, the ration and intake may far exceed the nutritional requirements of the cow. In obese cows there is a greater adipose tissue mass ready to be broken down and this predisposes them to excessive adipose mobilization and a fatty liver. It must also be remembered that fat cows tend to have a reduced feed intake in late gestation and early lactation, which will exacerbate the lipolysis.
Post partum disease
Type II ketosis may occur as either a predisposing cause or as an effect of postpartum disease. It is not always possible to say which came first.
A sudden change to an inadequate or inferior ration in especially the steam-up period will encourage lipolysis and predispose to type II ketosis.
Pre- and postpartum stress
Will lead to lypolysis (adrenergic stimulation) and poor feed intake
Clinical findings of ketosis
- Rapid loss of weight/mobilization of s/c fat reserves (“Woody” appearance).
- Marked drop in production (milk yield) over 2 – 4 days. Inappetance – first refuse grain and later may refuse silage and hay.
- Cow is dull and listless, depressed and reluctant to move or eat.
- Ruminal movements decreased, hollow, empty rumen. TPR normal, but Pulse and Resp may be marginally increased
- Faeces are firm; mild constipation.
- Ketotic odour of breath and milk (smells like acetone).
- Ketone strip test positive in milk and urine (ketostix): good sensitivity and specificity
- Death occurs rarely.
Seldom encountered. Shivering, depression, staggering gait, walking in circles and head tilt, aimless movements, crossing of legs, head pressing, leaning against wall, partial “blindness”, vigorous licking of skin of the fore limb, chewing and salivation, hyperaesthesia and bellowing.
Usually the patient will not show such classic symptoms, therefore a thorough clinical examination is necessary to identify the primary cause and allow rapid therapy thereof.
Manifestations of type II ketosis
There is an increase in the prevalence of common peripartum conditions: Mastitis, Metritis, Displaced Abomasum, Ketosis, Foot problems, retained foetal membranes.
The response to therapy for the concurrent peripartum conditions is characteristically poor in type II ketosis outbreaks.
Breeding efficiency will decline in herds with a high prevalence of type II ketosis: this is thought to be due to the toxic effect of NEFA’s on the follicle and the oocyte.
In a herd with a high prevalence of type II ketosis a high proportion of the dry cows are excessively fat (in excess of a body condition score of 3,5) and many of the cows four weeks after calving are thin (BCS of less than 2).
Herd surveillance to determine the prevalence and risk of ketosis
Type I ketosis surveillance
Post-partum beta-hydroxybutyrate (BHB) is currently the test of choice for herd surveillance of ketosis. Please note that this will not distinguish type I from type II ketosis. Ideally 15 cows should be sampled in the first few days post-partum, and BHB levels over 1.0mmol/l indicate subclinical ketosis while levels over 1.2mmol/l indicate clinical ketosis. A hand-held device is available on the market (designed for human diabetic patients) that has been validated as a cow-side test on blood (similar to the hand-held glucometers). It is important to use a central blood sample as the level of ketones can vary significantly at the peripheral level.
Urine ketone tests (detecting acetoacetate) have a sensitivity and a specificity of 78 and 96% respectively, translating to false positive and false negative rates of 4% and 8% respectively when the true herd prevalence is 30%.
Tests designed to detect acetoacetate in milk have relatively poor sensitivity, and are not commonly used any more.
Type II ketosis surveillance
Currently the best way to do herd surveillance to determine the risk of Type II ketosis developing, is to take serum samples of multiparous cows for NEFA evaluation between 2 and 14 days prepartum of 5-15 cows. NEFA levels above 0.3mEq/l are indicative of an increased risk of Type II ketosis.
Although high NEFA levels in heifers is also associated with the risk of Type II ketosis, it has also shown correlation with high milk production, which may be due to the genetic ability of high producers to utilise NEFA as energy source. Care should be taken with the interpretation of these results.
Carrier J et al 2004 Evaluation and use of three cowside tests for detection of subclinical ketosis in early postpartum cows J Dairy Sci 87(11):3725-3735
Clark CEF, Fulkerson WJ, Nandra KS, Barchia I and Macmillan,KL 2005 The use of indicators to assess the degree of mobilisation of body reserves in dairy cows in early lactation on a pasture-based diet Livestock production science 94:199-211
DeGaris PJ, Lean IJ 2008 Milk fever in dairy cows: A review of pathophysiology and control principles The Veterinary Journal 176:58-69
Goff JP 2006 Major advances in our understanding of nutritional influences on bovine health J Dairy Sci 89:1292-1301
Goff JP 2008 The monitoring, prevention, and treatment of milk fever and subclinical hypocalcaemia in dairy cows The Veterinary Journal 176:50-57
Grummer RR 2008 Nutritional and management strategies for the prevention of fatty liver in dairy cattle The Veterinary Journal 176:10-20
Herdt TH 2000 Ruminant adaptation to negative energy balance: Influences on the etiology of ketosis and fatty liver Veterinary clinics of North America: Food animal practice 16(2):215-230
Kurosaki N et al. 2007 Biomarkers for the activation of Calcium metabolism in dairy cows: elevation of tartrate resistant acid phosphatase activity by lowering dietary cation-anion difference is associated with the prevention of milk fever, J Vet Med Sci 69(3):265-270
LeBlanc SJ et al 2006 Major advances in disease prevention in dairy cattle J Dairy Sci 89:1267-1279
Leroy, J., G. Opsomer, A. Van Soom, I. Goovaerts, and P. Bols. 2008. Reduced fertility in High‐yielding dairy cows: Are the oocyte and embryo in danger? Part I the importance of negative energy balance and altered corpus luteum function to the reduction of oocyte and embryo quality in High‐yielding dairy cows. Reproduction in domestic animals 43: 612-622.
Leroy, J., A. Van Soom, G. Opsomer, I. Goovaerts, and P. Bols. 2008. Reduced Fertility in High‐yielding Dairy Cows: Are the Oocyte and Embryo in Danger? Part II Mechanisms Linking Nutrition and Reduced Oocyte and Embryo Quality in High‐yielding Dairy Cows. Reproduction in domestic animals 43: 623-632.
Leroy, J., T. Vanholder, A. Van Knegsel, I. Garcia‐Ispierto, and P. Bols. 2008. Nutrient prioritization in dairy cows early postpartum: mismatch between metabolism and fertility? Reproduction in Domestic Animals 43: 96-103.
Murray R D et al 2008 Historical and current perspectives on the treatment, control and pathogenesis of milk fever in dairy cattle, Vet. Record 163:561-565
Stewart A P 1983 Modern quantitative acid-base chemistry. Canadian Journal of Physiology and Pharmacology 61:1444-1461
Van der Drift SGA, Houweling JT, Schonewille JT, Tielens AGM and Jorritsma R 2012 Protein and fat mobilisation and associations with serum beta-hydroxybutyrate concentrations in dairy cows J Dairy Sci 95:4911-4920
Van der Drift SGA, Hulzen KJE, Teweldemedhn TG, Jorritsma R and Nielen M 2012 Genetic and nongenetic variation in plasma and milk beta-hydroxybutyrate and milk acetone concentrations of early-lactation dairy cows J Dairy Sci 95:6781-6787
Waage S 1984 The relationship between packed cell volume and the course of disease in milk fever in dairy cows. Nord Vet Med 36(1-2):19-25