Investigating body condition and metabolic hormones in relationship to reproductive cyclicity in zoo female African elephants, Loxodonta africana
Date
2013-08
Authors
Morfeld, Kari Ann
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Abstract
African elephants (Loxodonta africana) in U.S. zoos generally appear heavier than wild counterparts, and there are claims that obesity-related health and reproductive problems may be contributing to population non-sustainability. A previous study found a high body mass index (BMI) was positively correlated with ovarian inactivity in African elephants, suggesting reproductive problems may be caused in part by metabolic derangements associated with excessive body weight. To determine whether obesity and related metabolic conditions are a problem in zoo-managed African elephants, body condition, insulin, glucose, and leptin levels, and the glucose-to-insulin ratio (G:I) were compared between breeding-aged cycling (n=23) and non-cycling (n=23) females. Body condition scoring (BCS) is the assessment of subcutaneous fat stores based on visual or tactile evaluation of muscle tone and key skeletal elements, and provides an immediate appraisal of the degree of fatness of an individual. An objective of this study was to develop a visual BCS index for female African elephants and validate it using ultrasound measures of subcutaneous fat. To develop the index, standardized photographs were collected from zoo (n=50) and free-ranging (n=57) female African elephants to identify key body regions and anatomical sites, which were used to visually assess body fat deposition patterns. The visual BCS method consisted of a list of body regions and the physical criteria used for obtaining an overall score on a 5-point scale, with 1 representing the lowest and 5 representing the highest levels of body fat. Significant correlations were found between the visual scores and ultrasound measures of subcutaneous fat thickness at all anatomical sites, but were highest in the backbone (r = 0.748, P < 0.01) and pelvic bone (r = 0.745, P < 0.01) regions, indicating that BCS adequately reflects the amount of actual fat reserves. The new BCS index proved to be a reliable and repeatable evaluation method, with a high percentage agreement (73 % to 95%) and an overall "substantial" strength of agreement determined by the weighted k statistic (κw = 0.62 to 0.91) between and among three assessors. In comparing photographs of wild vs. captive elephants, the median BCS in the free-ranging individuals (BCS=3, range 1-5) was lower (P = 0.0001) than that of the zoo population (BCS=4, range 2-5). When comparing, BCS, insulin, glucose, and leptin levels, and the glucose-to-insulin ratio (G:I) between cycling and non-cycling females, the mean BCS of non-cycling elephants was higher than that of cycling elephants [4.39 (SD 0.58) vs. 3.73 (SD 0.93), P = 0.009]. There were differences in the serum concentrations of leptin [4.03 ng/mL (SD 1.63) vs. 3.16 ng/mL (SD 0.88); P = 0.041] and insulin [0.65 mg/mL (SD 0.31) vs. 0.48 mg/mL (SD 0.18); P = 0.032] for non-cycling females in the BCS=5 category. Serum glucose did not differ between cycling and non-cycling elephants (P = 0.892); however, the G:I was lower in the non-cycling group [69.82 (SD 53.21) vs. 227.18 (SD 96.23); P = 0.019]. Using "non-cycling" as the outcome variable in regression models, we examined BCS, leptin, insulin, and the G:I ratio as predictors, and found that BCS showed the strongest predictive power (P = 0.01). The odds ratio for the BCS coefficient is 3.15 with a 95% confidence interval of [1.36, 7.26], which suggests that with each 1 point increase in BCS, an elephant is approximately 3 times more likely to be non-cycling. These results demonstrate that ovarian acyclicity is associated with a high BCS and perturbations in markers of metabolic status. Thus, monitoring BCS, insulin, glucose, and leptin may assist in identifying elephants at risk for developing metabolic health conditions, including fertility problems. This would allow for management interventions to be implemented to improve body condition and metabolic status with the goal of reinitiating ovarian activity and promoting a healthier zoo population.
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Keywords
Endocrinology, Zoology, Physiology, African elephant, Body condition, Insulin, Leptin, Metabolic hormones, Reproductive cyclicity