Wild Cats and White Tigers

Saturday we finished the Tiger Project with ‘Teja,’ an Indochinese tigress. Everyone is hopeful that in a few months, the HDZ will be crawling with tiger cubs!

Today we had a very busy morning. Five African Wild Cats out at the Wildlife Safari Park needed their annual physicals and vaccinations. Blood was drawn for routine CBCs, serum chemistry along with additional blood, feces and urine for a nutrition study. Then we looked at a swift fox that had gotten into a tussle with another swift fox. She had a torn ear and some bite marks that needed to be cleaned up. After that was done, she was put on some antibiotics and pain medication for the next few days. Then we had to vaccinate 5 pelicans and a raven against the West Nile virus. So, it was a busy day!

And it is high time I talked about yet another broad lesson I’ve learned so, here we go! This will be a long post, so bear with me (if you want to, that is :p)! (link to lesson 1, as a refresher)

Lesson 2: Conservation and Population Medicine (and the revelation that money is not green, but black and white)

There are two distinct forms of medicine within veterinary medical practice: population medicine and individual medicine. In the most basic sense, population medicine deals with animals in production situations (feedlots, cow/calf, swine farms, poultry farms, etc), but it can also deal with companion situations. An example would be vaccinating a pet dog against rabies to protect the dog, but also to reduce the incidence of rabies in the area, thereby making the entire population safer. Individual medicine more classically deals with individual companion animals of all shapes and sizes, but is applicable in production schemes as well. Individual dairy and beef cows, for example, routinely get individualized care for specific conditions from milk fever to bloat. Many veterinarians go into certain areas of practice, because they either like or dislike population medicine. In zoo medicine, I have found that you can’t have one without the other.

There are two main reasons that zoos exist: animal display and animal conservation. Some institutions are more heavily involved in one side or the other, but both have a place. At the HDZ, I’ve found that the split is fairly even. Yes, there are many animals on display, but many of them are a part of intensive conservation programs for their species. And there are many animals that are here but not on display, conservation being the primary reason they are here. One example of that would be the Wyoming Toads. Declared extinct in the 90s, an isolated population was later located and captured. Now there is a growing population of these toads (which, at one time, were the most numerous vertebrate in the state of Wyoming) in a handful of conservation institutions across the country, including the HDZ.

All of the endangered and threatened species here have an SSP (Species Survival Plan). These plans look at everything from conservation of the natural habitat of these species to breeding programs that will best maintain a genetically healthy population in the future. The SSP is one of the main cornerstones on which conservation stands. It is population medicine on an individual basis.

Now enter the white tiger. The white tiger is an anomaly in the tiger world; a man-made anomaly. Many have the mistaken notion that this is a unique, highly endangered species of tiger. Others think that all white tigers are actually Siberian tigers, the white coloring helping them to blend into their snowy environment. Both beliefs are actually wrong! In fact, all white tigers alive today can be traced back to one white Bengal tiger, Mohan, who was captured in 1951.

Before I continue, I should speak briefly about the inheritance of color in tigers and give you a basic genetics review. The ‘genotype’ of an animal is the genes it has. The ‘phenotype’ is how it expresses those genes; literally what it looks like. The normal color of all species of tigers is the characteristic orange and black that most of us think of first when we think of tigers. The white and black coloring is a simply inherited recessive trait. Without getting too technical, I’ll use ‘B’ for the dominant color gene (coding for orange and black) and ‘b’ for the recessive color gene. Simple dominant-recessive expression means that an animal will need to be homozygous (having two copies of the same gene) for the recessive gene, or a ‘bb’ genotype, in this example. A tiger that is homozygous dominant (BB) or heterozygous (Bb) will look normal, phenotypically. The Bb tiger, however, may produce a bb white tiger if it is bred to another Bb tiger (or, of course, a bb tiger).

Many people are familiar with the good old Punnit square from genetics. The Punnit square is used to predict the ratio of certain genotypes in a given breeding of two parents of a known genotype (or, conversely, to identify the genotypes of the parents, given the phenotypes of the offspring). Using a Punnit square, here are the likely outcomes of tiger breeding for color:

BB x BB = 100% BB offspring = 100% orange/black
BB x Bb = 50% BB + 50% Bb offspring = 100% orange/black
BB x bb = 100% Bb offspring = 100% orange/black
Bb x Bb = 25% BB + 50% Bb + 25% bb offspring = 75% orange/black, 25% white/black
Bb x bb = 50% Bb + 50% bb offspring = 50% orange/black, 50% white/black
bb x bb = 100% bb offspring = 100% white/black

Still with me? Excellent! I’ve gotten quite long today, so you’ll need to tune in tomorrow for what this all has to do with conservation and population medicine!