A major problem for all animals kept in zoos is obesity. Even when recognised as such and correctly treated, animals with a history of obesity often have a poor reproductive record and many health problems, including arthritis, diabetes and coronary heart disease.
In addition, reproductive problems result from obesity such as infertility, overlarge infants resulting in problems giving birth, or larger than natural litter sizes. For example, wild Red Ruffed lemurs produce one offspring every other year, whereas in captivity they can produce triplets or even quads annually. As a result there is a moratorium in European zoos on breeding them, as there are too many closely related offspring about.
The purpose of this post is to explore the causes and possible remedies for this, and hopefully enable any visitors to zoos to think about the deeper issues of the welfare of captive animals beyond the more obvious concerns of the average zoo visitor, who is mostly concerned with the animal’s housing. I should add that these are my own opinions and do not necessarily reflect those of Bristol Zoo itself.
It has been said that almost all slimming advice can be boiled down to four words – “eat less, move more”, and this is also true for captive animals. I will cover the “move more” part on another post, in this one I would like to consider the effects of captive diets compared to wild diet.
1) Large carnivores
Large carnivores such as lions are adapted to a few large meals at unpredictable intervals, interspersed with periods of rest and strenuous hunting activity. Just as importantly, the food they eventually get is usually fairly low in fat and includes the internal organs and gut contents of their prey, which is a major source of their vitamins and other essential nutrients. Captive predators are usually given mostly muscle meat from cattle, horsemeat, or similar, and so they need additional vitamins – usually supplied as powder rubbed into the meat.
The ideal way to feed a lion or a leopard would probably be with a whole carcass, but this would obviously be messy to clear up and probably distress visitors or their children. We used to have leopards at Bristol, and gave them whole rabbits sometimes, but even this caused some adverse comments. Some zoos have constructed an artificial carcass out of fibreglass and put meat in that, but this limits the method of food presentation.
One variable zoos can use for feeding is not to feed at the same time every day. Most large carnivores have at least one “hunger day” per week – not always the same one – and are also fed different size meals at different times. The concept of “feeding time” is not usually followed at most zoos these days. In fact, you could probably get away with feeding a lion or tiger only once or twice per week if the meal was sizable enough, but the animals would then spend most of the week sleeping and be difficult to get to move from their outside to their inside quarters by offering titbits.
2) Large omnivores
The classic examples of these are bears. Here the problem is that a bear’s diet changes throughout the year depending on availability. In captivity by contrast, the diet is constant. This means that the animal’s physiology does not receive the correct cues for behavioural changes and so the activity patterns become unnatural. According to the September 2008 edition of International Zoo News, Ouwehands zoo in the Netherlands has recently implemented a seasonal diet plan for their polar bears, with the summer diet comprising nuts, berries, eggs and vegetables – to replicate the summer diet when polar bears subsist on what they can get on land before the sea ice returns -, and a winter diet of lamb, beef fat, fish and chicken. A similar seasonal regime has been used for some years for their brown bears, and as a result their brown bears now hibernate naturally.
3) Small carnivores and omnivores
Small carnivores are much easier to get to maintain activity levels. Most hunt daily, or even constantly, looking for insects of various sizes, small mammals, birds’ eggs etc. These a re fairly easy to replace in zoos, but the quantities need to be strictly controlled as they are not ranging over as wide an area and are consequently burning up less energy.
4) Large herbivores
Large herbivores are bulk feeders of vegetation, but here the issue is how much of this is supplied as fresh vegetation and how much as artificial diets. Historically, most large herbivores have been fed a diet which is a modified form of that given to domestic livestock. The problem here is that the diets of domestic animals are designed to maximise growth rates and fertility, not necessarily long life. Why should a farmer care that the diet he is feeding his beef cattle cuts their potential lifespan in half? – They will be sent for slaughter before two years of age anyway. This means that zoo herbivores usually need to be fed strictly limited quantities of pony nuts, stock feed and the like, even if they eat it readily.
The other problem is that hay given to zoo herbivores is often grass based. Given to a natural grazer like a zebra or an African elephant this is no problem, but given to an animal which naturally feeds by browsing on broad-leaved plants such as trees or shrubs this can result in unnatural patterns of tooth wear and poor digestion. For such animals alfalfa hay is far better.
Best of all however is fresh plant material. This comprises cut branches of shrubs or trees, fresh cut herbaceous fodder, and the like. Many zoos have “browse gardens” where they grow such food for their animals. Such food has to be carefully checked however - some plants can be toxic to some species but harnless to others.
5) Small herbivores
Most small herbivores select carefully the leaves and fruit they eat, which has resulted in them being termed “concentrate selectors” in ecological studies. The problem is that further research has shown that the plants they select are not that different in composition from those they avoid, and indeed many wild fruits have very little difference in nutrient and sugar content to foliage. What these selective browsers are probably choosing is not high nutrient content but low toxicity. Many plants, especially evergreen ones, protect themselves with a variety of distasteful or downright lethal compounds, and small herbivores have to be very careful in choosing what to eat.
In captivity, this has unfortunately resulted in many animals being fed cultivated fruits as a direct substitute for the wild diet. However, cultivated apples, bananas etc almost invariably have a far higher content of sugar and water, and a far lower content of protein and fibre, than wild fruits. As a result, there are a great many overweight primates (in particular) in the world’s zoos.
We have had here at Bristol several animals which had to be put on a diet. Our oldest female gorilla Salome was rather overweight when she first arrived (she is still portly) and has to be kept on a strict diet. Our male Mongoose lemur in our walk through became very obese by grabbing all the bananas in the daily meal, and has had to be kept on a calorie controlled diet. Lemurs are particularly prone to obesity, as they have a very low metabolic rate compared to other animals of similar size – up to 50% lower in some cases. Although now back to a wild weight, he has kept the “stretch marks” in the form of loose skin around his neck, which can be seen in the picture at top. You can meet him in the Lemur Walk Through, which he shares with a female and a family of Ring Tailed lemurs.
Obesity is particularly a problem with animals which spend long periods of time waiting for prey to come to them, and this covers in particular crocodilians and many snakes. People usually see a large python or boa remaining very still when they visit, but this is because their activity period is after dark. In the wild they would be quite wide ranging, and many species would be climbing extensively. The fairly limited space they are supplied with in most collections does not give the giant snakes much room for exercise, and in addition the domestic rodents which are their main food in captivity have a much higher fat content than wild rodents. The effect is that they turn into couch potatoes, and because people are used to thinking of them as fat they do not realise they are much wider bodied than they should be. Snakes store excess fat attached to their intestines, and as a result just about the commonest cause of ill-health in snakes is excessive fat causing damage to the internal organs.
To some up, here are some questions for any zoo visitor to ask themselves:
Is that animal overweight?
Is it being treated for obesity?
Is it being fed at times and in quantities that are similar to what it would get in the wild?
Is it fed a diet which changes seasonally?
What kind of hay is it getting?
How is the food presented? – In one or two meals or scattered so it has to spend the whole day searching for it?