American Association of Zoo Keepers

Biggest Loser—Ape Style: How husbandry changes can result in significant weight loss

By Leslie Lurz, Animal Keeper
Maureen Leahy, Curator of Primates
Lincoln Park Zoo, Chicago, IL, U.S.A.
llurz@lpzoo.org

Overview

At Lincoln Park Zoo in Chicago, Illinois, several adult western lowland gorillas (Gorilla gorilla gorilla) were found to be overweight in 2008. Weight issues are of great concern since obesity in gorillas can result in a variety of health problems, including elevated cholesterol concentrations and premature cardiovascular disease (Gorilla SSP, 2008). In fact, cardiovascular disease is the leading cause of mortality in captive adult gorillas (Gorilla SSP, 2008; Lammey et al. 2008). Understanding that the maintenance of a gorilla’s optimal body weight may significantly reduce the health risks associated with progressive heart ailments—ranging from aneurism to valvular disease to cardiomyopathy—and Type 2 diabetes (Duffy, 2009; Tordiffe, 2008), animal care staff responded with both dietary and husbandry interventions.

This paper demonstrates how changes in husbandry, management, and diet (implemented over a two-year period) effectively promoted weight loss for targeted individuals within the gorillas housed at Lincoln Park Zoo (LPZ). This paper will highlight the case of “Kowali,” a 33-year-old gorilla and one of LPZ’s most significantly overweight adult females, who ultimately lost over 50 pounds [22.7 kg] over the course of two years.

Introduction

Body-weight management can be a challenging component of animal care. Some animals live a more sedentary lifestyle in zoological settings. Care must be taken to ensure that animals do not become overweight or obese as a result. Given their social nature and the need to provide group foraging opportunities, non-human primate species can be especially challenging. It is often difficult to manage dietary portion control when dominant animals hoard preferred foods and displace subordinate individuals from some foraging opportunities.

Because of the complexity of gorilla social structures, scientists theorize that dominant animals may be prone to excess weight gain (Ullery, et al. 2003). The dominant animal tends to determine the time that others spend feeding in any particular location, leaving the subordinate animals to eat only what is left over. This pattern of hierarchical behavior might result in excessive food intake by the dominant animals given their natural social dynamic. This dominant animal theory may explain one of the contributing factors for the weight gain of several gorillas housed at Lincoln Park Zoo in Chicago, Illinois, including the case of one adult female named Kowali.

Kowali resides in one of LPZ’s gorilla troops along with a silverback, two adult females, and her juvenile son. Kowali has a history of above-average weights compared with other LPZ females of similar age. She is also shorter in stature than the other adult female gorillas; as a result, weight increases tend to be more visible on her stout frame. In January 2008, Kowali (then 30 years old) topped the scale at more than 270 pounds, and the zoo’s veterinarians and nutritionist rated her body condition score as obese. A body condition score is defined as an assessment of the animal’s weight-for-age and weight-for-height ratios and its relative proportions of muscle and fat. Having Kowali identified as obese was a catalyst for the animal care staff to come up with creative and new ways to address weight for the gorillas housed at LPZ.

LPZ’s animal care staff devised a plan that would address diet management and activity for Kowali by focusing on five different goals: (1) incorporating scale training into the husbandry routine to obtain quarterly weights; (2) integrating additional exercise into her daily routine; (3) modifying diet content; (4) varying food presentation; and (5) increasing feeding schedules. The remainder of this paper describes the changes in husbandry practices made at LPZ in an attempt to reduce Kowali’s weight and the results seen from those modifications.

Methods

Monitoring weights with scale training

Prior to 2008, animal weights were obtained somewhat opportunistically and often solely during routine physical exams. Since then, keepers have made it a priority to monitor the apes’ weights more closely. Like the majority of LPZ apes, Kowali is now scale trained, meaning she will voluntarily sit on a scale and hold the position long enough to get an accurate weight. Other group members are stationed elsewhere while the focal individual is on the scale. The goal is to weigh each animal quarterly, but some individuals require variation depending on the individual’s health and body condition. Records are kept to monitor their weights, which are reported to other members of our animal care staff, including veterinarians and the nutritionist. Kowali is now typically weighed every three months to closely monitor her weight-loss progress.

Exercise

Operant-conditioning training sessions using positive-reinforcement techniques are integral to the husbandry practices at LPZ. The apes participate in individual operant-conditioning training sessions once daily in the morning, and ape groups are alternated to receive an additional afternoon training session. All the apes are trained to present various body parts to allow for visual inspection, hand-injections, and desensitization to other medical props. These sessions also provide an opportunity for keepers to encourage the apes to move about their exhibits and “exercise.”

In the case of Kowali, specific efforts were made to have her engage in behaviors that mimicked callisthenic-like exercises during these training sessions. Calisthenics are a dynamic form of exercise that consists of simple movements, often in repetition, to promote muscular and cardiovascular fitness. To facilitate this, her primary trainer devised a shaping plan to condition her to stand, sit, lift her legs, and repeat these movements. Reinforcements for offering a correct behavioral response were fruit, produce, and Mazuri® leaf-eater chow, which were already a part of her normal diet. As a result, there was an increase in her movement and activity level without increasing her caloric intake.

Initially, it was challenging to motivate an overweight animal like Kowali to exercise, so keepers started slowly with a simple “stand” and “sit” routine. She would stand; then the trainer would bridge, reinforce her, and ask her to sit. The trainer continued to work on this routine, increasing the number of repetitions over time. Next, the duration of her “stand” behavior was increased so that Kowali stood and the trainer asked her to “hold.” In the beginning, she would stand and then creep back down, but she learned quickly that she would not be reinforced if she sat before the cue, which usually terminated the exercise portion of her session. After she was comfortable standing for a longer duration, her established husbandry behaviors were incorporated while she remained standing, including leg lifts (“foot” presentation at various heights on the cage front), mouth, ear, shoulder, arm, chest, belly, etc. The trainer asked her to present these behaviors while she remained standing; Kowali was variably reinforced for her efforts. The sit-and-stand exercise portion remained part of her routine as well. Over time Kowali built up her endurance, so exercise portions of her training session were extended and included more repetitions. Later, the laser pointer was introduced to Kowali’s training routine. Once she learned to touch the laser dot, she locomoted around to follow the dot, touch it, and be reinforced. Once these behaviors were established, any ape keeper could ask her for them if her primary trainer was unavailable. This enabled Kowali to remain consistent with a daily exercise routine.

Kowali’s exercise training was not without its challenges, as she would sometimes appear frustrated when the number of exercise repetitions in her session began to increase. Kowali tried to swipe or bark at the keeper through the mesh barrier. As a result, her primary trainer developed some guidelines to curb her aggression. If she was minimally aggressive (e.g. hand flick directed toward keeper or slight barking), she would receive an LRS (least stimulus response, or three to five seconds with no response from the trainer) and then her session would continue. If she was aggressive a second time, her session would be ended. If she was unacceptably aggressive towards the trainer (e.g. attempted to grab her trainer), her session would be ended immediately. With all other keepers consistently following these criteria, her aggression quickly subsided.

Kowali’s Diet Modifications

Kowali quickly adjusted to the exercise portion of her weight loss program, but her diet needed to be addressed as well. At Regenstein Center for African Apes, individual diets are formulated by veterinarians and the nutritionist. Gorillas’ daily diet includes fruit, leafy greens, vegetables, starch, and Mazuri® leaf-eater chow. In 2008, with the exception of individual fruit rations, all other diet items were group fed, including Mazuri® leaf-eater chow, which is the most calorically dense item in their diet (See Figure 1, which shows Kowali’s daily diet amounts)…….