Here goes:
We have seen them. The cats that are so fat they're practically the real life example of garfield, the dogs whose backs are so flat they're practically a coffee table. Some call them "fat and happy", but the reality is that pet obesity is a huge issue in the world nowadays. Many people simply love their pets and show their love through food. Rarely is obesity something forcibly inflicted upon their pets, but according to "Small Animal Clinical Nutrition", excessive intake of nutrients is considered to be malnutrition. So, it's not simply a simple "oh... he's just a happy fat dog/cat". Technically it's malnutrition, and can have numorous negative effects on the pet, just as a nutrient deficiency and starvation of an animal can.
So. First off. Is your dog/cat/horse/other pet overweight? There are many ways to tell, but one of the easiest is by looking at a simple body scoring chart:
Dogs and Cats-
http://vet.osu.edu/1851.htm
http://www.purina.com/dogs/health/bodycondition.aspx
http://www.purina.com/cats/health/BodyCondition.aspx
Farm Animals-
http://bedford.extension.psu.edu/agr...%20Scoring.htm
http://www.ces.purdue.edu/extmedia/as/as-550-w.pdf
If your pet fits the categories of "overweight" or "obese" or whatever they call it... you need to find a good diet plan!
First off... a visit to the veterinarian is in order. There are many things besides simply an excess of nutrients that could cause weight gain. I recommend this simply as a precaution, because changing diets or increased exercise could cause issues in an animal with a disease or imbalance. However, whether you follow this recommendation or not, proceed with care. Animals aren't made to handle drastic diet changes and extremely increased exercise like humans are.
The second thing one must look at is the diet. Here's a good website that explains some basic information about diet in dogs:
http://www.2ndchance.info/dogfood.htm
And in dogs:
http://www.2ndchance.info/catfood.htm
And if you have farm animals, consult your veterinarian and dietary handbooks. I know little about dietary information on them.
But, no matter what you're feeding, don't ever switch AND decrease at the same time. First, measure exactly what you are currently feeding. If your animal is on a free-fed schedule, take it off and measure approximately what you think is getting eaten on a regular basis. Then, if you're switching over to a new higher fiber food/higher quality food, mix in first 20% of the new food with 80% of the old food. Stay that way for one week. Then continue in 20% increments until you're feeding 100% of the new food. This way your pet's internal systems have been slowly adjusted to the new food.
Then, if you're on the new food (or you stayed on your old food), begin decreasing the amount. By 20% again. However, wait two weeks before decreasing again. Once you reach the amount that is recommended for your dog's size, age, and breed (not weight), stop decreasing the food. If you chose to wait on switching the food, do it now, however, you'll have to make some adjustments to the amount again with the 20% every two weeks rule. In the end, much easier to switch first, decrease afterwards.
Your pets may act like their starving. But, unless they lose more than 5% of their body weight in the first two weeks, he/she'll learn.
NO TREATS. If you feel you must give your pet something extra, green beans are excellent for dogs. Full of fiber, they fill the dog up. And an added plus, most dogs love them. Avoid prepackaged treats at this time. Avoid table scraps as well.
Mealtimes should be scheduled events. If your pet does not eat its food within thirty minutes of you setting it out, or doesn't finish, pick it up and either throw it out (if wet food) or put it away to use with the next meal (don't add it to the former amount, simply have this plus a little more be the amount needed). The dog will either learn that he'll have to eat at this time, or, it could be like people, that the dog/cat would simply eat because it had nothing better to do. (this won't work as well with farm animals).
Third tip. EXERCISE. Now, if your dog/cat has led a primarily sedentary lifestyle, which is to be expected if he/she is overweight/obese, do NOT begin on a suddenly extreme exercise routine. Not only could it unnecessarily tire out your pet, but your pet has a much higher likelihood of injury, and it is, for the most part, innefective.
Cats and dogs have a slightly different routine in the following two paragraphs:
A much safer and more effective route is to slowly build your dog up the way you did their food. For the first week, either begin walking for ten minutes at a brisk walk outside, or add ten minutes of a brisk walk to your normal walk. This should be daily, with maybe one day a week skipped if need be. After a week, bump it up to 15 minutes. Then after another week, 20 minutes. After another week, 25 minutes. And after another week, 30 minutes. After this, either begin adding running sessions to it, or get involved in a more strenuous activity. Sprinting is all good and fun, but for most dogs, will do nothing but tire them out, and cause them unnecessary stress. Fetch, as long as your dog isn't sprinting full out (which could possibly cause injury), IS a good way to work your dog without working yourself. If you have a dog with an active mind (border collies, some labs, terriers, etc), consider making everything fun and a job. Once you get down to their optimum amount at breakfast/dinner, begin either hiding their food in various places, or getting a feeder that makes the dog work for their food. Many can be found in various stores.
As for the cats, this can be much tougher, because many cats don't enjoy toys, won't exercise, etc. If you absolutely can't get the cat to move (either by walking, toys, etc), then make it work to get its food. Place it higher, or at the end of some kind of obstacle course. That is... if the pet is food motivated. Cats can be so varied, and hard to work with at times (due to their independent nature), that it might be hard to find something that works with yours.
And with the farm animals/other animals, simply increase their activity. Anything from riding to lunging to walking to getting them moving anyway anyhow.
And the fourth tip is this:
WEIGH YOUR PET. If this pet is more of a larger farm animal type of pet, then you might have a more difficult time with this. And if you can't, you can't. But with dogs and cats, you can weigh them. Your local vet might even be willing to let you come in once every two weeks to use their scale. I know that the one I worked at allowed this, even encouraged it.
Preferably check every two weeks. Not only will this help you stay on track with your dog/cat, but it can also help you know whether or not the animal is losing too much or nothing at all, and you can adjust your feeding and exercise plans accordingly. This is the most important part, because when you own the animal, you can't exactly see the progress as well as when you weigh them consistently.
So... if you have an overweight animal... it'll be hard work... and it'll take a LOT of time... but it can be done.
And you'll find yourself and your pet learning more and slimming down.