Milk Fever – an Overview Milk Fever Or Periparturient Hypocalcaemia, Is a Metabolic Disease of Dairy Cows That Occurs Around the Time of Calving
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LARGE ANIMAL | METABOLIC DISEASE ONLINE EDITION Milk fever – an overview Milk fever or periparturient hypocalcaemia, is a metabolic disease of dairy cows that occurs around the time of calving. During the dry period, calcium requirements are relatively low; but at calving there is a sudden increase in calcium requirement as lactation begins. If this demand is not met quickly enough, the concentration of calcium in the blood drops below a critical threshold, resulting in either clinical or subclinical milk fever. Jenny Bellini BVSc MRCVS A cow can lose 23g of calcium 10 in 10 litres of colostrum in Jenny qualified from the one milking; yet, typically, only has 12g of free calcium 9.0 University of Bristol in 2014 8 available to her. This huge and started working soon 8.0 after for Friars Moor Livestock demand for calcium must be Health – a member practice met from elsewhere to prevent of XLVets*. Jenny works milk fever developing. The 6 primarily in dairy practice, average incidence of clinical with particular interests in milk fever in the UK dairy herd 4.8 nutrition, heifer rearing and is four to nine per cent, while 4 block-calving systems. the incidence of subclinical milk fever is estimated to be between 25 to 50 per cent. Times more likely 3.0 *XLVets is a community 2 2.6 The average cost of a case of of independently-owned, 2.0 progressive veterinary milk fever is approximately 1.7 practices that work together to £200 (Husband, 2005). achieve the highest standards 0 of veterinary care. As plasma calcium is required LDA 30d) for neuromuscular function, Mastitis Ketosis www.xlvets.co.uk Metritis Dystocia Retained milk fever is characterised placenta by decreased feed intake, Culling (1- decreased heart rate, Figure 1. The incidence of other conditions associated with milk inhibition of urination and fever (Source: EBVC, 2011). defaecation, rumen and intestinal stasis and reduced rectal temperature. If it is left untreated, cows progress to lateral recumbency, and eventually coma and death. Reduced feed intake leads to greater fat mobilisation, and one study (Reinhardt et al, 2011) has shown cows with low blood calcium levels post calving (<2mmol/L) have higher concentrations of non- esterified fatty acids (NEFAs). 0.75 As muscle contraction is hours* inhibited, the teat sphincter relaxes; which leads to an increased risk of mastitis. Hypocalcaemia post calving also directly impairs immune *Suggested Personal & Professional cell response to an activating Development (PPD) stimulus, therefore making these cows more susceptible to disease. ™ As shown in Figure 1, the METABOLIC DISEASE incidence of mastitis and Figure 2. A cow with milk fever and metritis. ™ ketosis in cows recovering from 46 VETERINARY PRACTICE TODAY | VOLUME SEVEN | ISSUE ONE | 2019 WWW.VETCOMMUNITY.COM | ONLINE EDITION ™ ™ ™ ™ ™ ONLINE EDITION METABOLIC DISEASE | LARGE ANIMAL Mechanisms involved in calcium metabolism Low calcium High calcium + Parathyroid - hormone + 1-a-hydroxylase Kidney Activated 1,25(OH) D Inactive 25-OH-D3 2 3 Bone Gut Steps enchanced by induction of mild metabolic acidosis Figure 3. The mechanisms involved in calcium metabolism in the Figure 4. Milk fever is a disease that can largely be prevented and cow (Husband J, 2005). controlled through careful transition cow feeding. milk fever is eight and nine within minutes. Although the first month of lactation. 1,25 that there are fewer intestinal times greater, respectively. The amount of calcium available (OH)2 D3 also increases renal receptors for 1,25 (OH)2 D3 in incidences of dystocia, retained for recovery from the urine is tubular reabsorption of calcium these breeds. foetal membranes, displaced small, this process may still and stimulates active transport abomasum and uterine be sufficient to compensate of dietary calcium across the The risk of milk fever also prolapse are all greater in cows for small decreases in plasma intestinal wall. increases with age, rising by nine with milk fever (Figure 2). calcium. However, in many per cent per lactation. (DeGaris cases this mechanism alone These mechanisms take et al, 2009). There are several During the dry period, is insufficient and continued between 24 and 48 hours reasons for this – there is usually calcium requirements for PTH secretion stimulates to correct the negative an increasing milk yield and, skeletal development and calcium resorption from bone. calcium balance and both are therefore, demand for calcium maintenance are low – at less The bones are the source of 95 magnesium dependant. The with increasing age. Older cows than 30g/day. At calving, the per cent of the cow’s calcium, nadir in blood calcium occurs are also less able to mobilise demand for calcium is much which is available to the cow at 12 to 24 hours post calving. calcium from the bone, and increased – 2.3g Ca/L of in two forms. Normal blood calcium for an have reduced active transport colostrum produced and 1.2g adult cow is 2.1-2.8mmol/L, of calcium from the intestines Ca/L milk produced. Calcium There is a soluble, readily with clinical or subclinical owing to reduced production quantity in milk increases as available pool of calcium in the milk fever occurring below this of the steroid hormone, 1, 25 butterfats increase. The cow fluid surrounding bone cells. (Merck Veterinary Manual). (OH2)D3 and reduced receptors does not have enough calcium PTH acts on bone lining cells on target tissues. in her bloodstream to meet to transfer this soluble calcium Certain breeds are more these increased demands, into the extracellular pool. susceptible to milk fever, Prevention of milk fever and so it must be replaced by There is approximately 6-10g of including Jerseys, Channel Milk fever is a disease that the activation of homeostatic calcium available here, which Islands and Swedish red and can largely be prevented and mechanisms to increase its can be increased by 6-8g in whites. It is thought this is a controlled through careful intestinal absorption, reduce cows under metabolic acidosis. consequence of the increased transition cow feeding (Figure renal excretion and increase loss of calcium in their milk 4). Some of the key principles resorption from the bone PTH also activates the renal with increasing butterfat, and are discussed overleaf. (Figure 3). enzyme responsible for producing the vitamin D Low blood calcium causes the metabolite, 1,25 (OH)2 D3. This “A cow can lose 23g of calcium in 10 parathyroid glands to secrete stimulates osteoclastic bone parathyroid hormone (PTH). resorption activity to mobilise litres of colostrum in one milking; yet, This hormone increases renal more calcium from the skeleton typically, only has 12g of free calcium re-absorption of calcium – cows typically lose nine to 13 from glomerular filtrate per cent of skeletal calcium in available to her” WWW.VETCOMMUNITY.COM | ONLINE EDITION @VPTODAY | WWW.VETERINARYPRACTICETODAY.COM 47 LARGE ANIMAL | METABOLIC DISEASE ONLINE EDITION 7.0 DCAB Feed component (mEq/kg Comments DM) 6.0 Grass silage (2003 +390 Extremely variable (up to +1,000), season to date) 5.0 higher with legumes Grass silage +391 4.0 (2002 season) Maize silage +194 Less variable than grass silage 3.0 Whole crop silage +158 Consistently low DCAB 2.0 Straw +139 Milk fever incidence (%) 1.0 Barley +25 0.0 Brewer's grains -220 Can be useful to 'dilute' high -40 -20 0 20 40 60 80 100 120 DCAB silages DCAD (meq/100 g DM) Fodder beet +300 Figure 5. The linear relationship between DCAB and milk fever Kale +806 incidence (DeGaris PJ and Lean IJ, 2009). Maize gluten +137 Molasses Dietary cation anion two cations in the DCAB +681 balance (DCAB) equation, sodium and Potatoes +343 The transition diet can be potassium must be kept at Rape extract -201 manipulated to push the cow low levels to achieve a low into mild metabolic acidosis, DCAB. Potassium in UK diets Wheat -6 which has been shown to is usually the most difficult to Sugar beet pulp -123 reduce the risk of clinical control. Grass, grass silage Soya extract +203 milk fever. Reducing the and hay can all be very high DCAB reduces the risk of milk in potassium, while maize, Wheat feed +177 fever – the two have a linear whole crop silages and straw Data supplied by Thomson & Joseph, Norwich. relationship (Figure 5). are usually low in potassium. DCAB (meq/kg DM) = It is crucial to have all forages Figure 6. The DCAB of common feedstuffs (Husband J, 2005). (sodium + potassium) - fed to dry cows analysed (chlorine + sulphur) for their mineral content, diet and the cow too much. of PTH in response to Feeding a dry cow diet higher because there can be great If high levels of anionic salts hypocalcaemia and increases in anionic salts, chloride and variation (Figure 6). As a rule, are fed, palatability is reduced the tissue sensitivity to PTH. sulphur, reduces the DCAB, potassium must be kept <1% and, therefore, so is dry Magnesium is primarily making the cow acidotic DM. Potassium in grass can matter intake (DMI). absorbed from the rumen and and the blood and urine pH be reduced by having dry cow cows need a constant supply decrease. These acidotic paddocks with no manure Urine pH is a good indicator of it in the diet. As the rumen conditions increase the tissues’ spread on them and using of whether the dry cow diet is pH increases above 6.5 – responsiveness to PTH as the just N fertiliser at moderate acidified enough or too much. and on higher forage diets, receptors for PTH on bone to heavy applications. Target urine pH is 6.2-6.8. If conditions common to dry and kidney cells function Potassium levels in grass are average urine pH is 5-5.5, the cows – magnesium solubility better, as well as increasing the highest in spring and autumn, diet is too acidic and DMI will declines sharply.