Health

should actually not be a fussy theme - now, I'll try to explain here some of the general aspects: 

Keeping a dog in a proper environment, corresponding alimentation and regularly maintenance are surely the best preconditions to conservation of the general healthiness. Dogs metabolism is more fast expiring as in humans, dogs breathe faster and more often, a dog's heart beats faster and more often and also the average body- temperature of the healthy dog is with 38,5°C higher as with humans.

Important are regularly annual vaccinations and booster-shots against the known infectious diseases, as well as deworming. hereby your veterinary will help you ; the data for vaccainations and booster-shots are shown in the health-certificate, medication for deworming (paste, or tablets) can be obtained also by the veterinary (dosage is weight dependent) and if your four-legged darling despite all the care given should itself captured one time a flea - which could happen even for the perfectly cared dog -, there are products to fight against this "unwanted guests"; such as spray's  - ointments - tablets etc.

The ears - even with regularly done cleaning ( 1 X weekly) - should be watched:  increased shaking of head and scratching at ear could allude an inflammation; inflammation obstructing ointments will be prescribed by your veterinary - ear control with otoscope (auditory canal to interior ear) procured articulateness. The eyes, if there should be an irritation of conjunctiva, or inflamed conjunctiva,could be treated with with eye drops or eyes ointment - prescr. by veterinary - .
Please do not work with any obscure things.

generally keep in mind:

See the veterinary better once more than one time too less !!!

First aid - already difficult most by humans; we have learned that once but are all very glad, if never had to use it. The most cities have animal hospitals, where partly around the clock service is provided, if one need help immediately.Still we want give some basic advices: 

skin injuries (smaller abrasions etc.) can be treated with special gel or spray. Wound must be watched, should it suppurate, treatment with an antibiotic-containing ointment is required.
All deep open wounds by cutting through of the skin and evtl.risk of injured tendons, nerves etc. need immediate veterinarian examination and supply (lacerated and bite-wounds etc. ). Tetanus is a very rare condition in dogs. But I know from one case where a friends dog died from Tetatnus. Still - vaccinations against aren't usual.

injuries of bloodvessels (symptoms are strong continued and spraying bleedings, often intensive red bloodstream etc.) require as a first - emergency-measure a pressure-bandage; this will be applied like with humans also, so the blood stream above the wound has to be tied off and then directly bring the dog to the veterinary. 

at accidents is the risk of interior injuries / or cerebral comm. (concussion) given and worse of skull basis fracture. carefully the animal turn in side-position, head-down-positure, tongue taken out (to avoid danger of suffocating) and on a transportation-carriage directly transport to the veterinary resp. veterinary / animal hospital.

lameness can have various causes - often of more harmless type -. Mostly the dog has either a foreign body in the paw (thorn, splinter etc.), or has itself sprained. Still don't take this easy as for the giant breeds and above all during the growing-period monitoring of lameness is adviseable. If you can't find effects such as foreign body in the paw, toes (undersite), toes spaces-inbetween, see as a precaution the veterinary, s/he can clearify, whether a sprain, or contusion, dislocation, exists. Unfortunably it must be mentioned that growth disorders, periosteum inflammations etc. at large - and giant breeds more often get observed. 

Poisonings are most unlucky incidents.The dog should be kept under control during the walks; some dogs tend thereto, to rankle all, to lick everywhere around, whereas others not so interested. Often are in parks and other areas bait with rat poison found - caution, danger of interior bleedings -; the highly toxic effect of pesticides is everywhere acquainted. directly to the veterinary, s/he will provoke vomiting - fastest method to get the poison out from the body.
Do not self-experimentalize in such cases. Poisonings are always an emergency-case, as the ingested toxins are different quick in circulation and reaching the metabolism; only the specialist = veterinary knows the exact therapy.

Besides this there are diarrhoe, obstipation,vomiting, which doesn't always indicate a disease, often the dog had eaten something wrong or too much eaten, which caused a purging effect or obstipation.
If there are no other pathological symptoms, for example. fever, coughing, blood in ordure, or uric, immoderate salivating etc.,already 1 - 2 fasting days, or diet-food can be helpful. 
attention: the dog must always be provided with fresh clear water to drink. 

Although "smaller incommodations" could surely be self-treated,I want you absolutely advise, to ask at least advice of the veterinary by phone - with as far as possible exact description of the symptomatology - and in case of any doubt go and see the vet, because diagnostics are even for the expert not always simple and, if the veterinary visit was not necessary, you can at least go home reliefed.
That's at any rate better than to displace sickness and to deal after with chronical devolution or an animal must be put to sleep, because  treatment is delayed. 

At this point I allow myself the generally notic, that at giant breeds by reason of the enormous growth-episode in the first life age, as well by reason to the final size and weight a somewhat higher risk for skeletal disorders and growth disorders.

From breeders you can admittedly expect, that matches are done due "to the best of one's knowledge and conscience" - but guarantees can't be given - and those who "guarantee, that ....." - well, they must have clairvoyant abilities (or they are maybe not to be taken totally serious). Guarantee on the health-status of the parent-dogs (and previous litters out of this dogs) is what you should ask for - as this can be proven.

I add at this point some tables from the book "genetics in dog breeding" , those give a good overview on breed-specific dispositions for determined diseases. 

tables 14 -17 to in extracts 

Basic care - besides cleaning ears weekly (with a tissue, spec. wet tissues from pet-store or vet, baby-cleaning-tissues will do as well) - consists in regularly grooming and from time to time a shower (don't use too much shampoo and only use pet-products). As the Leo's are usually love to swim think of rinse with clear water in case of swimming in the sea as the salt-water might damage the coat.

Dental care - there are several products (teethpaste, fluids, brushes) available - but a bone will do it's purpose too. Elderly dogs have more problems with plaque - therefor dental care and examination of mouth should be included in the basic care. I use a tissue, wet with fluid and wrapped around my finger to "brush" the doggie's teeth.

Twice a year - during the periods of "sheding lots of hair" - daily grooming is required. For the "feathered" parts of the legs you might use a comb to untangle. The coat of a healthy dog is always rich in colour and shiny.
A dull coat or unusual sheding of hair could be first signs of an intolerance of metabolism.

For extensive health-info pls. visit either

healthsite of www.leonberger.150m.com

or

  or  

There you find the Health-Site (bilingual) with additional info.