Acta veterinaria Scandinavica. Supplementum最新文献

In 1986, a new progressive neurological condition similar to scrapie of sheep and goats was recognised in cattle in the United Kingdom (UK), and was named bovine spongiform encephalopathy (BSE). There is an ongoing discussion whether BSE should be classified as infectious, contagious, or zoonotic, and if it fits the definition of a production disease. The objective of this work is to briefly describe the main characteristics of transmissible spongiform encephalopathies (TSE), to review the epidemiology of BSE, and to address the question of how to classify BSE. TSEs are characterised as chronic wasting diseases with spongiform vacuolation and the accumulation of infectious prion protein (PrP(Sc)) in the central nervous system. TSE infectivity is very difficult to inactivate. Cattle BSE most likely originated from sheep scrapie, although this will remain to be an issue for debate. The disease can be transmitted from cattle to a range of species, and has resulted in smaller TSE epidemics in domestic cats, zoo cats and zoo ruminants, and in humans. Transmission in the field occurred through feed containing ruminant-derived protein, and measures to prevent the recycling of infectivity have proven effective to reduce the number of new infections. Mandatory reporting of clinical suspects combined with targeted screening of risk populations is needed to assess the BSE status of a country. Infection studies and the transmissibility to other species classify BSE as infectious and zoonotic. Absence of excretion of the agent, and therefore of horizontal transmission, categorise BSE as non-contagious. However, BSE is a multifactorial infectious disease that is dependent on management factors (mainly feeding), and therefore fits into the broader definition of production diseases.

The hypocalcemia associated with the clinical disease known as milk fever is due to a failure of the calcium homeostatic mechanisms in the cow to restore normal blood calcium concentration in a timely manner at the onset of lactation. The defect in calcium homeostasis appears to reside in the sensitivity of bone and kidney tissues to parathyroid hormone (PTH) stimulation. Evidence suggests the acid-base status of the cow dictates the sensitivity of the tissues to PTH stimulation, and that metabolic alkalosis is responsible for blunting tissue PTH responsiveness. Hypomagnesemia can also reduce tissue PTH responsiveness but hypomagnesemia can be corrected in most rations. Excessive dietary potassium is very common and is the most important factor causing metabolic alkalosis in dairy cows. Formulation of rations to reduce metabolic alkalosis and/or induce a compensated metabolic acidosis in the pre-partal cow has proved a useful strategy for prevention of milk fever. The concept of dietary cation-anion difference manipulation and the physiologic effects this can have in the cow are presented, with special emphasis on the Strong Ion Difference theory of acid-base physiology.

A restriction in energy intake during the final weeks pre-calving is believed to depress milk production post-calving. The requirements of the non-lactating periparturient cow for energy, and in particular for glucose, have been shown to increase dramatically as parturition approaches. However, a decline in precalving dry matter intake has also been measured during this period. One solution to this problem has been to reduce the forage to concentrate ratio, thereby substituting feeds that are greater in energy density for feeds that are less dense. However, the pre-calving decline in dry matter intake appears greater as the amount of concentrates in the diet increases or alternatively as the fibre concentration of the diet declines. Previous reviews of transition cow nutrition have largely dealt with the nutrition of cows offered a total mixed ration or diets containing primarily lucerne or maize silage, and have not accounted for differences in farming systems, the base diet offered, or differences between cows within breeds. In this paper the effect of nutrition during the transition period on the metabolism of the periparturient cow offered a pasture-based diet was examined.

A large emphasis on precalving magnesium supplementation has substantially reduced the incidence of clinical hypocalaemia in pasture-based systems. Survey data in the major pasture-based systems suggest a 2 to 4% incidence of parturient paresis, although this can vary considerably between farms. Detailed blood measurements under research conditions suggests that approximately 5% of cows are clinically hypocalcaemic (blood calcium < 1.4 mmol/l) and between 30 and 40% of cows are subclinically hypocalcaemic (plasma calcium < 2.0 mmol/l). Systems of control have traditionally been based on preventing the paretic cow, with more emphasis of late being placed on preventing hypocalcaemia. Preventative measures vary, but largely involve either supplementation with magnesium oxide pre-calving, supplementation with calcium carbonate during the colostrum period or a combination of magnesium supplementation precalving and calcium supplementation post-calving. In New Zealand, the use of commercial products that bind calcium is increasing precalving, but is still only practiced by a small percentage of farmers. The dietary cation-anion difference (DCAD) of pasture is so high and so variable that changes in DCAD sufficient to change blood pH are not practical and very difficult to achieve with consistency. The use of magnesium chloride and magnesium sulphate in preference to magnesium oxide, as precalving magnesium supplements, is increasing.

Medication is used in all intensive animal productions. However, the increasing problems with resistant bacteria in all animal productions and in humans are supported by a number of reports. Special attention is given to the risk for transmitting food-borne (multi) resistant zoonotic agents to humans due to failure in antibiotic treatment resulting in lower cure rates or higher case fatality rates. The use of medication in humans per se is capable of selecting for resistance in human pathogens. Nevertheless, the amount of used medication/antimicrobials in treatment of Danish production animals goes far beyond the amount used for human consumption. The increase in consumption has not been followed by a similarly increased mortality, e.g. illustrated by the number of rendered animals, increased use of injection medicine for veterinary treatments of diseased animals, or increased number of remarks on the carcasses from the slaughterhouses. Medication in animal production is facing its limits and relevant economic alternatives have to be developed. The strategy for the future must concentrate on using medication only for clinically diseased animals and not as a strategic treatment of the whole herd in order to maximise growth and camouflage of suboptimal production systems and insufficient management.

Health is an important part of animal welfare. This implies that measures for the protection against disease will also affect animal protection. In most instances, efforts to improve disease protection act synergistically with efforts to promote animal protection, and vice versa. In the context of farm animal transport, however, infectious disease protection and animal protection may not always be mutually beneficial. Examples of contradictions are: Logistic perturbations; Current farm animal production is increasingly sensitive to logistic perturbations. Control and prevention of epizootic diseases involve extraordinary transport precautions that rapidly result in overcrowded stables. Transhumance; The practise of transhumance is compromised when control measures are taken to prevent spread of epizootic diseases. Travel sickness; Travel sickness is a problem particularly in pigs. Starvation before transport prevents vomiting but result in hungry animals. Lack of experience; Animals that are kept under conditions estranged from situations associated with transport alike are more prone to transport induced stress. Flooring; A non-slip flooring is a prerequisite for firm footing but demand more careful cleaning and disinfection to prevent spread of infectious agents.