www.roanoke.com

Paws & Claws

Jill Bowen has practiced veterinary medicine in England and Texas. She lives in Blacksburg now, and answers local pet owners' questions every week in The Roanoke Times and roanoke.com.

Recent columns

• Bacteria can cause ear infections in cats
• Chiari is a malformation of the back for some spaniels
• Your plant smells like a great spot to ...
• Sting salve: meat tenderizer

Q We just got a new kitten (free in the newspaper), and we were told that as it is a calico color, it is a female. Why?

A Calico-colored cats are a mixture of orange, black and white and are almost invariably female, as are black and orange tortoiseshell cats.

All cats have 38 pairs of chromosomes, half of which the cat inherited from the mother and half from the father. Each chromosome contains many different genes. Every female cat gets one X chromosome from the mother and one X chromosome from the father, while male cats get an X chromosome from the mother and a Y chromosome from the father.

The X chromosome carries the gene for coat color. In calico and tortoiseshell cats, one X chromosome has a gene for black coat color and the other X chromosome has the gene for the orange color (the white coat color is carried on a totally separate gene.)

In female cats with two X chromosomes, one X chromosome will become inactivated at some point during development in the uterus. Since there is no way of predicting when the second X chromosome will become inactivated in each individual cat, the color patches will vary. If both X chromosomes carry the same color gene then the calico or tortoiseshell color will not appear.

Male cats have only one X chromosome, and it is never inactivated. Whatever color gene is on this chromosome will determine the color of the cat. Rarely males are either calico or tortoiseshell, but only if they are born with two X chromosomes and a Y chromosome (XXY). The extra X chromosome allows for the occasional male cat to be either tortoiseshell or calico. The XXY is an extremely rare genetic defect and the resulting male is usually sterile.

It is very difficult to breed specifically for a calico or tortoiseshell cats. Breeding a black cat to a ginger cat may increase the chances if the resulting kitten is a female, but it also depends on what stage of development the second X chromosome becomes inactive. It is not possible to predict or force an X chromosome to become inactive at a specific point in the developing embryo.

Q Is it OK to make my dog a vegetarian? My dog eats grass all the time so I figured he was halfway there.

A Dogs are primarily carnivores, but they can survive on a well-balanced vegetarian diet and probably should more correctly be called omnivores, as the majority are not fussy eaters and are happy to eat table scraps, garbage, as well as regular dog food and, in many cases, grass.

Cats, on the other hand, are strictly carnivores and will die without animal protein in their diet.

Dogs need a combination of protein, fats, carbohydrates and trace amounts of vitamins, minerals and access to fresh water.

There are a number of theories as to why dogs like to eat grass. Wolves and wild dogs eat their entire kill, which are usually herbivores; they usually eat the stomach and intestines first, which contain grass as well as plants and berries, so maybe dogs are genetically programmed to like grass.

Many people think dogs eat grass to make themselves vomit when they are not feeling well, but it could be that the grass acts as an irritant and causes the vomiting and the dog is not smart enough to use the grass medicinally. Perhaps dogs eat grass because their diet is lacking in greens, or maybe they just like it.

The bottom line is that the habit of dogs eating grass is quite normal. Just be careful that your pet does not eat any grass that has been treated with fertilizer, pesticides or herbicides because those products could cause a serious stomach upset. A vegetarian diet for a dog must have a source of readily digestible protein, fats and carbohydrates.