METABOLIC DISEASES IN CATTLE

Transcription

1 Vet Times The website for the veterinary profession METABOLIC DISEASES IN CATTLE Author : PADY GORDON Categories : Vets Date : September 8, 2008 PADY GORDON describes the monitoring and treatment of metabolic disease during the periparturient period METABOLIC disease is the result of a mismatch between dietary requirements and production outputs. A wide spectrum of incidence and presentations may be seen, from clinical disease to suboptimal production, and it is a major focus for dairy herd production medicine. The periparturient period is a critical time, with most metabolic disease occurring within two weeks of calving. Other metabolic diseases, some infectious diseases and infertility can often be linked to metabolic disease during this period. Periparturient metabolic disease usually reflects an imbalance of energy metabolism, mineral metabolism or immune function. Common metabolic diseases are shown in Table 1. There are interrelationships between these diseases (for example, milk fever increases the risk of toxic mastitis). Therefore, it makes sense to look at the overall incidence of disease, as well as specific disease incidence. Secondly, mismanagement can create further metabolic problems, and these have been placed in a rumen dysfunction category (Table 1). Modern production systems have a profound influence on the incidence of diseases seen. This article will look at the approach to a herd with metabolic disease, considering the approach to 1 / 15

2 both treatment and to tackling the underlying metabolic condition. Case history In July 2007, a farmer in the practice asked us to identify reasons why his dairy cows were not producing as much milk as his neighbour's cows. The herd of 200 cows produced 8,000kg per lactation, with a predominantly autumn calving pattern. Initial investigation using NMR records and interherd analysis in the practice bureau identified that 53 cows were culled in the past 12 months. This is an acceptable culling rate of 25 per cent. However, 21 of these were premature or forced culls that is, cows culled within 150 days of calving. This was regarded as significant and likely to impact on milk production in early lactation, these culled cows should have been producing large volumes of milk. Cook (2006) gives a typical US figure of 25 per cent of culls by 60 days in milk. A variety of health problems, from downer cows and metritis to lameness (Table 2), were given as the reasons for culling. It appears that too many cows were culled for infertility, poor health and lameness. While the problems were likely to be multifactorial, the initial focus was on periparturient health, as change was achievable and likely to give a good financial return. Disease around calving was regarded as a cause of subsequent low production and culling. The incidence of dystocia and periparturient disease in the following two months was monitored and is shown in Table 3. As farmers increasingly carry out treatment of individual animals, it is essential they recognise disease presentations and administer appropriate treatments in a timely fashion, or, if not, recognise the limits of t heir skills and call for veterinary attention. Treatment protocols were reviewed on this farm to ensure they were both appropriate and that there were realistic expectations and recognised end points. The aim was to minimise premature forced culls in sick cows. Milk fever The milk fever incidence in this period was 14 per cent higher than the target of less than five per cent. Milk fever is a common presentation in dairy cows shortly before or after calving. The onset of lactation results in a sudden demand for calcium far in excess of normal blood levels. This increased demand is met by increased uptake from the intestines and bone. Cows that fail to adapt to this increased demand develop milk fever. This is typified by initial excitement followed by recumbency and unresponsiveness as skeletal and smooth muscle function declines. Death occurs in the absence of treatment as a consequence of bloat. 2 / 15

3 Optimal treatment of milk fever involves a slow, intravenous injection of 8g-12g of calcium, usually in the form of a 40 per cent calcium borogluconate solution, warmed to body temperature (Eddy, 2004). The rapid infusion of this solution results in a temporary hypercalcaemia, with levels returning to normal within 90 minutes (Braun et al, 2004). Calcium is potentially cardiotoxic and death can be an outcome. In the same paper, when 600ml of 40 per cent calcium borogluconate was used, a recurrence of hypocalcaemia was seen at eight and 24 hours in eight out of 15 clinical cases. Recurrence was based on a low blood calcium result and it is not clear from the paper whether there was a recurrence of clinical disease. Radostits et al (2000) indicate that 35 per cent of milk fever cases suffer from relapse and 15 per cent do not respond to treatment and are culled. While many culls may be due to secondary complications of milk fever, such as downer cow syndrome, these results suggest that standard treatments and infusion techniques should be reviewed. Prompt and appropriate treatment is the most important aspect, so we look to ensure that our farmers not only know how to recognise milk fever, but are capable of administering calcium injections effectively by intravenous injection. The use of sterile sharp needles is recommended. Selection of a clean injection site is important, and injection of a jugular vein is preferable to use of the milk vein. This advice was justified by a local VLA postmortem report indicating that septicaemia and death had resulted from abscess formation after poor injection technique. It is also essential that calcium is delivered intravenously to allow the opportunity for a rapid response to treatment. The high relapse rate is likely to be the result of calcium elimination before physiological processes adapt to the higher calcium demand. As a result, we now use oral calcium treatment in addition to our intravenous injections. These supplements provide calcium over a prolonged period and we believe this to be better practice than the use of subcutaneous calcium. Use of oral calcium supplements is particularly justified in herds with a high incidence of disease, as physiological responses are likely to be impaired, and in individual animals that are fat, thin or have had a long dry period. A number of commercially available oral treatments contain calcium as calcium chloride, calcium phosphate, calcium propionate and calcium formiate. Calcium chloride results in the most rapid uptake of calcium, but is a gastric irritant and, therefore, needs to be formulated as a gel. Calcium carbonate has the slowest uptake. Practices need to determine which available product meets their needs. 3 / 15

4 Uterine infections Almost all bovines will have a bacterial infection of the uterine lumen at two weeks after calving. The sloughing of caruncles at this time supports the growth of a wide spectrum of bacteria. Given the presence of both bacteria and a medium supporting growth, it may not be surprising that up to 40 per cent of cows will develop metritis. Metritis is defined as the presence of an enlarged uterus and purulent discharge within 21 days of calving. Puerperal metritis is a more severe form, where pyrexia and systemic illness occur. Interestingly, the presence of pyrexia is a highly variable finding, and not necessarily a good predictor for metritis. Treatment protocols need to ensure rapid recognition of disease, as metritis can rapidly progress to peritonitis. Antibiotic selection will depend on established farm policy. On this farm, the use of ceftiofur for mild cases was recommended, with tylosin used on cases with more severe clinical signs. Adjunctive treatment with NSAIDs was advised when necessary. Veterinary intervention could be called on if required. Further treatment can involve the siphoning of two to three litres of warm water, or dilute antiseptic solution, into the uterus and then draining again. This process can be repeated several times. However, care needs to be taken as the uterine wall can be friable. A major risk factor for uterine infection is retained placenta, along with calving environment, twins, dystocia and diet. These risk factors either contribute to the bacterial load or result in impaired immune function. Infection can occur after calving, presumably due to faecal contamination of the vagina, as well as around the time of parturition. In research carried out by Tim Potter at this practice, environment was found to be far less important than dystocia in the development of endometritis. On this farm, the need for a hygienic approach to calving was emphasised (Figure 1), along with raising awareness that parturition is a gradual process. Extracting the calf in great haste is not normal for the cow or calf, and likely to traumatise both (Figure 2). Metritis is likely to have longterm impacts on fertility through impaired ovarian function, as well as effects on the endometrium. Therefore, it is essential to have a plan in place to minimise the incidence of retained placenta and metritis when addressing poor herd fertility. The increasing incidence of twin births in Holstein cows does not help this situation (13 per cent in this period). Displaced abomasums The incidence of displaced abomasums was four cases in 2007 on this farm an incidence of two per cent. Left displaced abomasum (LDA) occurs in freshly calved cows when the abomasum distends with gas and becomes atonic. Its position shifts to the left side of the cow to sit between the rumen and ribs. Affected cows show a reduction in appetite, poor rumen fill and a tucked-up appearance, and frequently suffer from a secondary ketosis. We tend to see most LDAs within two 4 / 15

5 weeks of calving. Right displaced abomasum (RDA) has a slightly later presentation around peak yield. It is assumed that a similar disease process is involved, but RDAs require more urgent intervention. Our treatment of choice for LDAs is the Grymer-Sterner toggle approach. Keith Sterner presented a review of more than 800 cases at the 2008 World Buiatrics Congress (WBC) in Budapest. He concluded that success using the toggle approach was down to the operator. We have looked at our success rate and estimate that we carry out surgery due to recurrence on less than 10 per cent of our toggle cases. Surgical intervention in these recurrent cases is usually successful. There was some interest in laparoscopic approaches at the WBC, but given a high success rate with a simple, low-cost approach, this technique looks unnecessary. Herd assessment Considering each individual disease, the incidence of milk fever and retained foetal membranes was of greatest concern. Farmers often discount these problems as a poor run or attribute them to the incidence of twin births. This puts off the need to make changes, which can be countered by pointing out the overall proportion of cows with a problem. In this case, 16 out of 29 cows required attention (farmer or veterinary) for any reason (Table 3). This is a very expensive and time-consuming approach to managing dairy cows. The problems identified with calving health were regarded as being due to: Cows being turned away to graze distant fields after drying off. This approach can result in body condition score gain or loss, depending on the grazing conditions. Cows close to calving being housed on a transition diet aimed at delivering dry cow minerals and the milking cow forages. The time on this diet was variable and the ration was not controlling milk fever incidence. The calving yard was poorly ventilated with limited access to feed and water. This was regarded as contributing to poor feed intakes and a high incidence of metritis due to poor hygiene around calving. Preventive approaches revolve around promotion of improved efficiency of calcium uptake and calcium mobilisation. Efficient calcium metabolism is promoted by feeding magnesium salts to stimulate bone calcium mobilisation and activation of vitamin D3 though it can be ineffective due to high potassium levels in grazed grass. The use of sodium aluminium silicate (zeolite A) has been used experimentally to restrict calcium availability. The problem with this is that the volumes required are large more than 1kg with a 5 / 15

6 resultant drop in dry matter intake. Ammonium chloride and other salts can be fed to create a metabolic acidosis by dietary cation-anion balance manipulation. This helps to increase parathyroid hormone responsiveness. Experience is that DCAB diets are hard to maintain due to changes in forage mineral levels. Having considered the options with a nutritionist, a single dry cow diet across the dry period was proposed to take control of dry cow feeding. A high-fibre, low-energy approach involving a proportion of the milking cow diet and 4-5kg straw levels was introduced. Building modifications were made that involved the removal of a concrete wall along one side of the calving cow shed to improve both the area available and ventilation. A feed barrier was placed to increase the area available and to ensure all dry cows had access to feed. Following these changes, the results and reports from the farmer showed a reduction in the incidence of milk fever and displaced abomasum. In addition, the number of cows affected by periparturient disease has dropped from its initial 55 per cent (Table 4). SARA indications Energy status was assessed indirectly using fat:protein ratios (FPR). Elevation in fat and depression of milk protein indicates poor energy status, an increased risk of ketosis and negative energy balance. Conversely, milk fat depression to a level below that of milk protein is an indicator of sub-acute rumen acidosis (SARA). Data is available through milk recording websites (for example, CIS sites). Monitoring of trends can be helpful in identifying underlying energy status problems, backed up by strategic blood sampling. On this farm (Figure 3), average FPRs (blue line) appear largely acceptable as they remain in the green band, indicating acceptable energy status. The blue line dips in November and January 2006, and the yellow line indicating the proportion of cows with an abnormally low FPR increases. These peaks, and further peaks in December 2007, indicated an underlying acidosis problem. This was regarded as likely to be contributing to lameness (due to poor horn quality formation), and infertility (acidosis is likely to result in poor energy status). SARA was regarded as part of the problem by the nutritionist, who indicated increases in maize starch levels had not been allowed for in formulating rations. This was addressed by modifying starch inputs by ensuring starch sources were unlikely to create an acidosis, and where possible changing to digestible fibre sources of energy. This included: feeding caustic wheat rather than rolled wheat to avoid acidosis; minimising rolled wheat fed in-parlour; maintaining cows on established maize silage; avoiding opening new clamp for three weeks to avoid rumen upset (as seen on fresh maize); increasing levels of digestible fibre; and ensuring sufficient structural fibre in the diet. Further progress 6 / 15

7 Improvements in periparturient health have made another underlying problem with abortions in the herd more obvious to the farmer, who is tackling the causes of these problems BVD infection and iodine deficiency. He is also aware that most dystocia is due to the small stature of his heifers, so attention is being paid to serving heifers at the correct size rather than age. It is encouraging to see from the NMR Herd Companion Key Performance Indicator reports that efforts are achieving a reduction in culling rate and an increase in milk per cow per year (Figure 4 and 5 ). The farm performance is shown as a red line, compared with historical performance and a benchmark group in this case, NMR herds with similar yields. Summary In summary, it is the role of the veterinary surgeon involved with dairy herd production medicine to ensure systems are in place for effective treatment of metabolic disease, with established monitoring systems. Action can then be taken to promote both profitable milk production and improved animal welfare. This role revolves around training in the importance of disease processes and their influence on production, motivating farmers to give disease control priority, and ensuring management systems are directed towards health improvements health planning in action. 7 / 15

8 Figure 1. A hygienic approach to calving is essential a dry, well-ventilated cow shed is ideal. 8 / 15

9 Figure 2. Assistance at calving increases the risk of trauma and endometritis. 9 / 15

10 Figure 3. Monitoring of trends can be helpful. 10 / 15

11 Figure 4. NMR Herd Companion Key Performance Indicator reports. 11 / 15

12 Figure 5. NMR Herd Companion Key Performance Indicator reports. 12 / 15

13 Table 1. Common metabolic diseases of dairy cows 13 / 15

14 Table 2. Reasons for culling Table 3. Incidence of dystocia and periparturient disease 14 / 15

15 Table 4. Incidence of dystocia and periparturient disease from August until the following June 15 / 15 Powered by TCPDF (