The Merck Veterinary Manual 12th Edition
Liliane Hubright
The Merck Veterinary Manual is a reference manual of animal health care. It was first published by Merck & Co., Inc. in 1955.[1] It contains concise, thorough information on the diagnosis and treatment of disease in a wide variety of species.[2] The Manual is available as a book, published on a non-profit basis.[3] Additionally, the full text can be accessed for free via the website, or downloaded in its entirety via an app.[4] In January 2020, the website was redesigned with a more helpful search function without advertising.[5] Interactive features on the website include quizzes, case studies, and clinical calculators. In addition, there are animal health news summaries and commentaries.
The Merck Veterinary Manual was first published in 1955.[1] It was based on the Merck Manual of Diagnosis and Therapy, which was first published in 1899 as a reference for physicians.[1] The first edition of the Veterinary Manual included contributions from over 200 authors, with 389 chapters divided into sections on public health, toxicology, and diseases of domestic animals, zoo and fur animals, and poultry.[1] The first five editions were edited by Otto H. Siegmund.[6] The fifth edition was published in 1979.[6] The sixth and seventh editions were edited by Clarence M. Fraser.[7]
The eighth edition, edited by Susan Aeillo, was published in 1988 with contributions from 317 authors.[8] A review in the Canadian Veterinary Journal declared it to be an 'excellent veterinary handbook'.[8] The ninth edition was published in 2005, and included chapters by over 350 authors.[9] New subjects included Hendra virus infection in the horse, and biosecurity.[9] The tenth edition, published in 2010 and edited by Cynthia M. Kahn, was the first to contain images.[2] It included radiographs, illustrations, and photomicrographs, as well as new chapters, including one on African hedgehogs.[2]
The eleventh edition, published in 2016, had over 400 contributing authors.[10] New topics in the eleventh edition included backyard poultry and smoke inhalation.[11] In 2018, a free app version was made available which included a 57 megabyte download of all the information from the eleventh edition.[12]
The Avian Disease Manual has become the best selling publication of the AAAP. Its success is likely due to its ability to deliver at a reasonable cost, concise yet complete information on commonly encountered diseases affecting poultry. Not surprisingly, it has become an educational staple to North American veterinary and poultry science students, to those interested in avian diseases, but also a most useful reference in developing countries.
The world of commercial poultry production is a rapidly evolving one, new pathogens regularly emerge, microorganisms are reclassified and renamed, discoveries are being made, hence the need for regular re-edition of this manual. Putting together a new edition, presented this new editor with the challenges of keeping the great teaching qualities of past editions while updating the information and improving the format. This was made possible through a great team effort. The current editorial committee is made up of newcomers and experienced members. They all have extremely busy professional life, but all generously accepted to answer my call and share their knowledge and expertise. I would like to thank them for their timely diligence in reviewing and updating their chapters. Naturally, we are also indebted to a number of esteemed colleagues who, since the first edition in 1980, initially written by C.E. Whiteman and A.A. Bickford, provided us with a solid heritage on which we keep building.
Under the editorial guidance of Dr. Bruce Charlton, the previous edition incorporated the addition of electronic photos available on a CD. The 7th edition has now included them in the text while enhancing its library content. After all, an image is worth a 1000 words! Photos referenced in the text can be found after each disease section. The editorial committee is deeply indebted to all the authors of the photographs for the exceptional quality and historic significance of the photos in their collection. Special recognition needs to be offered to Dr. HL Shivaprasad (CAHFS, UC Davis) and Dr. HJ Barnes (North Carolina State University) for their passion and amazing photo collection, and also to the numerous colleagues who spontaneously accepted to go through their slides and photos to provide the readers with the highest quality images. We also used select photos from the AAAP Slide Sets and want to extend our gratitude to their authors. Readers of this manual are encouraged to investigate these sets and the book Diseases of Poultry for further excellent photos and information. Although every attempt has been made to correctly credit authors and institutions of the photographs, we apologize for any mistake that might inadvertently occur.
On a final note, I would like to thank the AAAP Board for their continuous support and willingness to endorse the editorial committee suggestions, as well as recognize the hard work of Mr. Bob Bevans-Kerr, AAAP Executive Director. His patience, availability and expertise in Photoshop and the editing process has made the whole process an enjoyable experience.
Every veterinarian will tell you that essential instruments are the thermometer and stethoscope, all, but the poultry veterinarian. In this case, a knife will be more useful. But an acute sense of observation, the ability to collect good information when talking to the owner/animal caretaker and logical reasoning are as important, whatever the field of practice, to determine the necessary course of action.
A flock visit can be done either because there is a problem and the owner has requested your presence, or as part of a routine health check. Compared to the other fields of veterinary practice, there is no real emergency in poultry medicine i.e., rare are the after hour calls. However, in the case of a marked increase in mortality, or in case of a suspicious reportable disease, the veterinarian should visit the affected flock as soon as possible.
In the case of an increased mortality, a greater number of birds than the usual expected daily rate die. This expected daily mortality does vary according to the age of the flock, the type of birds, the type of production and housing. For example, a certain number of chicks/poults/ducklings unable to find feed and water in the barn where placed will die of starvation/dehydration once their yolk sac, hence nutrient reserve, is exhausted.
Mortality is also expected in breeding/laying flocks, from reproductive-related conditions (often associated with obesity), or again from lameness. Cannibalism is another cause of death observed in many flocks.
Depending on the housing system, birds should be able to stand, walk, even run, scratch and sit only for short periods. Turkeys and ducks do not scratch the litter and birds in cage cannot unless provided with a sand box. Chickens will quickly walk away from the unusual visitors while turkeys will follow them. Young broiler chickens will often be found fighting i.e jumping at each other with spread wings. Turkeys can show a belligerent behaviour to their mates but will be hissing, walking slowly in the crowd with fluffed up feathers, a blue colored head with an elongated snood. Breeder birds should be also found mating during a visit. Many birds but not all will be drinking and eating at the time of your visit once the stress caused by your presence has decreased.
Clinical signs will vary according to the disease and affected system(s) and will vary in severity. Not all birds in a flock will exhibit clinical signs. Early in the course of the disease only a few individuals might be affected and care should be taken to find them.
In general, sick birds are listless, will sit for long periods, their head held close to the body, tail and possibly wings dropping. Comb and wattles may be paler and shrunken. Eyes will be dull and sometimes closed. They might not drink nor eat, hence slowing/stopping growth and eventually losing weight. Anorexic chickens will often have green colored feces (due to bile stain) which might stain the feathers of the pericloacal area. Dehydrated birds will show darker and thinner looking legs, they will feel lighter and the skin will not move freely over the keel. If cold or pyrexic, feathers will be fluffed, and birds will huddle in corners or with others to keep warm. Uncomfortable chicks will initially be chirping loudly before becoming depressed if source of discomfort is not corrected.
If an enteritis is suspected, some birds might have dirty feathers around the vent that might be even soiled with blood or sulphur colored feces depending on the infectious agent. These blood or sulphured colored feces will also be found on the litter.
Lame birds will spend more time sitting, and will walk with difficulties, spreading their wings. Traumatic lesions will be observed on the ventral aspect of the carpo-metacarpal joint as well as a sternal bursitis in chronically recumbent birds. Depending on the cause, joints might or might not be swollen and hot. The plantar surface of the feet might be dirty, crusted, cracked and/or reddened.
When investigating a loss in performances, a reduced body weight, a higher feed conversion, a drop in egg production, a decreased hatchability, flock results should be carefully examined and compared to expected result in order to define the problem perceived by the flock manager and answer the basic questions: who, what, when, where, how?
Light. The lighting schedule and light intensity are very important parameters in laying birds, since light stimulates egg production. In many meat type birds, daylength will be shortened early in life to control the growth rate.
Litter. The litter is a mixture of feces and bedding material. The latter should be made of absorbent material and in enough quantity for comfort. If too dry, respiratory problems will arise while a too humid litter might trigger intestinal and skeletal pathologies. A litter is too humid if it keeps its shape once you have squeezed a handful in your fist.
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