DEAR READERS: Attorneys in California, Minnesota, Georgia and North Carolina filed a class action lawsuit against the leading manufacturers and sellers of pet food: Mars, Nestle Purina, Hills, PetSmart and several veterinary hospital chains in California on Dec. 7. The four main pet food brands involved in the suit include Hill's Prescription Diet, Purina Pro Plan Veterinary Diets, Royal Canin Veterinary Diet and Iams Veterinary Formula.

Mars, the biggest seller of pet food, sells two of the four prescription pet food brands and is also the owner of the largest veterinarian hospital chain the United States, BluePearl Vet Hospital. Mars also partners with the largest specialty pet retailer, PetSmart, in the ownership of the largest veterinarian clinic chain, Banfield Pet Hospital.

The suit concerns prescription pet foods that cost more, but that plaintiffs contend are no different than any other kind of pet food. Some highlights in this complaint:

-- "Defendants' prescription pet food contains no drug or other ingredient not also common in nonprescription pet food."

-- "Defendants' marketing, labeling and/or sale of prescription pet food is deceptive, collusive and in violation of federal antitrust law and California consumer-protection law."

-- "Defendants are engaged in an anticompetitive conspiracy to market and sell pet food as prescription pet food to consumers at above-market prices that would not otherwise prevail in the absence of their collusive prescription-authorization requirement."

As documented in the book "Not Fit for a Dog: The Truth About Manufactured Cat and Dog Food," which I co-authored with two other veterinarians in 2009, the claims being made by the providers of overpriced, often unpalatable and nutrient deficient prescription-only manufactured pet foods are generally questionable and often lacking in sound clinical and scientific evidence of being of any benefit.

DEAR DR. FOX: I have a 13-year-old beagle-shepherd-Lab mix named Nibbles. At her last vet appointment, her tests showed kidney problems.

Up until that point, she had always been eating Nutro Max dog food, and was on the senior formula. The vet, who I've gone to for years and do trust, put her on new food, Hills Prescription Diet k/D Kidney Support, which has "less phosphorus, protein and salt" -- or so he said. Looking at this food's ingredients and comparing them with Nutro Max, it seems to me like this new food has a lot more junk ingredients in it, and more fat.

Now, if this diet works despite all the crap ingredients, then fine! The issue is, prior to the diagnosis, I had seen no sign of kidney issues. Now, after about a month on this food, she seems very antsy and anxious; she pees more than she used to, drinks more than she used to and seems hungrier. The main reason I am writing is that last night, she wet the bed (she released her whole bladder). This has never happened before!

The reason she went to the vet in the first place was merely for a senior exam, during which I mentioned her recently insatiable appetite, and her weight loss (she's lost about 5 pounds). Her whole life, she's received a half-cup of food in the morning and a half-cup at night. We upped it to an extra half-cup in the past year, and now with the new kidney support diet, we upped it to 2 full cups a day.

Is this recent bed-wetting and altered behavior part of the kidney cleansing process? Or is this making her issue worse? To me, it seems like the less I feed her, the better (for example, go back to only 1 cup of food per day), but she is so hungry, and that also seems kind of mean. She also takes a kidney-support vitamin (VetriSCIENCE). -- H.P., Washington, D.C.

DEAR H.P.: Dogs with chronic kidney disease, when accurately diagnosed, need careful monitoring of blood pressure, dietary phosphate, potassium and blood urea nitrogen, as per my article on kidney disease posted on my website, DrFoxVet.net.

The ingredients in the special prescription diet are of dubious value, possibly harmful and certainly not providing your dog with sufficient nutrients if she is constantly hungry.

This is no way to go. Chronic kidney disease can lead to sarcopenia -- wasting of muscles due to the kidneys passing out more protein. So your dog needs some good-quality protein in her daily diet.

Dogs with kidney disease drink more, so take your dog out more frequently to urinate. But this, coupled with the increased appetite, could be related to diabetes, which I would have your dog checked for, along with a blood test to see how her kidneys are functioning.

Do keep me posted on the outcome, and good luck.

BIRD INFLUENZA VIRUS INFECTS CATS

Avian influenza H7N2, identified by the Wisconsin Veterinary Diagnostic Laboratory at the University of Wisconsin -- Madison, infected at least 45 feline residents of the Animal Care Center shelter in Manhattan, marking the first documented instance of infection and transmission of H7N2 among domestic cats.

Most affected cats exhibited mild symptoms, but one elderly cat with other health problems died, and testing is underway to ensure no humans or other species of animal at the center have been infected.

(Send all mail to animaldocfox@gmail.com or to Dr. Michael Fox in care of Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106. The volume of mail received prohibits personal replies, but questions and comments of general interest will be discussed in future columns.

Visit Dr. Fox's website at DrFoxVet.net.)

DEAR DR. FOX: I have what is supposed to be a male German shepherd-Labrador mix. I got him as a 3-month-old pup, and he is now approximately 3 years old. He is extremely hyper and vomits on car rides that exceed 20 to 30 minutes. He is a good eater and weighed as much as 56 pounds a few months ago.

Over the summer, his weight decreased to 50 pounds. He has always been skinny, but he looks almost uncared for due to his thinness. He doesn't have any physical ailments or parasites, sleeps well and is happy and loving.

I was wondering if a supplement exists that I could add to his diet that might calm him. I feel if he was calmer, he might be able to ride in the car better, be generally calmer, walk easier and possibly gain enough weight to look healthy. -- E.M.T., Clinton, Maryland

DEAR E.M.T.: A change in diet may indeed help your dog become somewhat less hyperactive and anxious, as could some supplements and essential oil therapy.

I would avoid all cereals in your dog's diet, at least until there is some behavioral change, and increase the fat content by including 1 teaspoon of organic butter and coconut oil with each meal, feeding him three times daily and monitoring his body weight until satisfactory. My home-prepared dog food recipe (posted on my website) along with a good-quality commercial dog food may be the best solution.

Many dogs "on the edge" of being unstable can benefit from a high tryptophan diet, found in turkey, and supplements that increase brain serotonin, such as the product NutriCalm, which can be prescribed by vets. Over-the-counter options include Animal Health Options' ProQuiet and PetzLife's @-Eaze.

A few drops of organic lavender oil on a bandanna around your dog's neck and a spritz of equal parts lavender oil and warm water in the car could make a big difference. A thimble-size portion of chopped ginger root in a ball of cream cheese may calm the stomach from motion-induced nausea.

U.K. INVESTIGATION OF GENETIC HEALTH PROBLEMS IN DOG BREEDS

Launched in January 2016, the Kennel Club Genetics Center at the Animal Health Trust's initial survey of health issues prevalent in various breeds, epilepsy was the top concern voiced by most dog breeders in the United Kingdom.

The second most commonly listed health concern identified through the breed health summary was hereditary cataracts, listed by seven of the breeds. The Kennel Club Genetics Centre at the AHT has had success launching DNA tests for hereditary cataracts in the Staffordshire bull terrier, Boston terrier and French bulldog, and is currently investigating hereditary cataracts in several more breeds, including the Labrador retriever.

Overall, 80 different disorders were reported with the following conditions listed by multiple breeds: progressive retinal atrophy (PRA), hypothyroidism, hip dysplasia, lymphoma and patella luxation (listed by six breeds) as well as autoimmune disorders and dilated cardiomyopathy (listed by five breeds). For more details and updates, visit aht.org.uk/gdg.

This is important for American dog owners and breeders of these particular breeds whose burden of disease of genetic origin is both costly and often a cause of much suffering.

(Send all mail to animaldocfox@gmail.com or to Dr. Michael Fox in care of Universal Uclick, 1130 Walnut St., Kansas City, MO 64106. The volume of mail received prohibits personal replies, but questions and comments of general interest will be discussed in future columns.

Visit Dr. Fox's website at DrFoxVet.net.)

DEAR READERS: According to the American Veterinary Medical Association, in 2011, 21.5 percent of cat owners and 29.3 percent of dog owners did not visit a veterinarian because they could not afford it. The percentage of cat and dog owners not taking their animal to a veterinarian has since increased, raising the serious issue that a growing segment of the companion animal population is not receiving any veterinary attention.

An estimated 23 million pets live in poverty alongside their human families, lacking access to veterinary care, proper nutrition and basic supplies. All animals should have access to veterinary care, which is now the rule of law in the United Kingdom. The good news is that this serious issue is recognized by many veterinary colleges and nonprofit organizations, which provide affordable, basic veterinary care in low-income communities and to financially challenged individuals, many burdened with their own unaffordable health care concerns.

Michael Blackwell, DVM, chief veterinary officer with the Humane Society of the United States says: "We have a large sector of the American population who, frankly, are poor and can't afford private care. The model the profession built (this robust private veterinary industry, in all of its glory) is not a panacea. It is not complete in its ability to address the needs of all animals." Dr. Blackwell's organization is part of a coalition that is advocating for shelters and nonprofit veterinary clinics to supplement and complement the veterinary industry by addressing unmet needs in the companion animal sector. For more information, visit jav.ma/accesstovetcare and jav.ma/moneytipsforpetowners.

DEAR DR. FOX: I adopted a pair of kittens six months ago, and I love them. I am at work all day, and I hate for them to be bored. I read an article about using puzzles with food treats inside for pets, similar to what zoos use for enrichment for their animals. I got a couple, and my cats love them. They spend time fishing out a pellet and chasing it around for hours. They've stopped chewing on my furniture -- a bonus!

I'm wondering if it's a problem that I use dry food pellets in the puzzles. They still eat a can of good wet food every day, and I bought dry food that is supposed to be grain-free, but do I need to worry about them eating the dry food from the puzzles? I would guess they eat only about a half-cup a day, and they are nearly adult-size at this point. -- B.M., St. Louis

DEAR B.M.: I am glad that you found your cats to be responsive and engage with the cat puzzles as a source of stimulation and food reward. Not all cats engage with these "environmental enrichment" toys, but when they do, it certainly does add something to their lives, especially when they live alone with no other animal in the home and no windows to look out of, ideally overlooking a bird feeder and bath.

We should all consider what quality of life we are providing our indoor cats, and for a start, having more than one cat, ideally a littermate or mother can make a big difference. Boredom, depression and obesity are all-too-common consequences of cats living boring lives.

I would purchase freeze-dried meat treats as well as good-quality dry cat food that is free of corn and soy, and ideally with organically certified ingredients.

DEAR DR. FOX: My 2-year-old Saint Bernard won't eat.

I'll find a food she will eat for a couple days and think I've found something she likes, but on day three, she sniffs the food and puts her nose in air and won't eat. She is healthy, but I'm wondering if she is playing with me because she knows I'll find a different food every time. What should I do? -- P.S., Forked River, New Jersey

DEAR P.S.: You may be turning your dog into a finicky eater, or rather, your dog is playing you in a game that needs to end. Cats are better at this kind of caregiver training and manipulation, and they often make themselves sick from eating mainly canned tuna or raw beefsteak.

So ignore your dog. Put the food down and sit quietly close by. Leaving her alone could make her anxious. See how she eats.

Other things to consider:

-- An elevated platform for the food bowl may make eating easier, since big dogs have to bend low and may have difficulty swallowing.

-- Dry food can be difficult to swallow, so moisten with hot water or give canned or raw food.

-- Schedule a vet checkup to rule out a broken tooth or other pain-related oral issue that could make eating unpleasant for your dog.

DOG FOOD RECALL

Blue Ridge Beef is voluntarily recalling two of its frozen products due to the potential to be contaminated with salmonella and/or listeria monocytogenes. Salmonella and listeria can affect animals eating the product. For details, visit truthaboutpetfood.com/blue-ridge-beef-recalls-product-because-of-possible-health-risk.

(Send all mail to animaldocfox@gmail.com or to Dr. Michael Fox in care of Universal Uclick, 1130 Walnut St., Kansas City, MO 64106. The volume of mail received prohibits personal replies, but questions and comments of general interest will be discussed in future columns.

Visit Dr. Fox's website at DrFoxVet.net.)