Seasonal Effects on Body Condition and Characteristics of the Estrous Cycle in Captive Asian Elephants (Elephas maximus) in Thailand: A Retrospective Study.

Simple Summary: Thailand is in the tropics, with high temperatures, humidity, and long daylight hours. Seasons affecting estrous cycles have been discovered in the semi-captive Asian elephant in Thailand. In addition, seasonality in reproduction has been reported in sows and cows in the tropic environment. Despite the fact that measurements of the body condition score (BCS) have served as a disease diagnostic tool in terms of screening undernourishment and obesity in veterinarian practice and have been developed and applied in captive elephants, obesity is a growing concern today. The consequences of being overweight are typically not recognized until welfare-related reproductive dysfunctions, such as higher neonate weight, stillbirth, and acyclicity, are present. In captive-managed elephants, ovarian dysfunction and estrous cycling abnormalities are common, which are linked to a variety of issues such as obesity, reproductive tract pathologies, and metabolic derangements. These problems are most likely to contribute to poor reproductive health and then lead to undesirable reproduction. Thus, it is critical and urgent to identify the factors affecting reproductive health and ovarian patterns and thus facilitate fertility. The data for this study were collected from eight captive female elephants. During the rainy, hot, and cool seasons, their BCS was measured. Characteristics of the estrous cycle were studied, including the length of the estrous cycle and the lengths and starts of the luteal phase and follicular phase. The findings revealed that a higher BCS and the start of the follicular phase were highly frequent during the rainy season, which resulted in a longer luteal phase and estrous cycle and higher peak progesterone levels in the Asian elephant (Elephas maximus). The aim of this study was to investigate the effects of season on the body condition score (BCS), the characteristics of the estrous cycle (luteal phase [LPL], follicular phase [FPL], estrous cycle [ECL] lengths, and the start of the luteal phase [SLP] and follicular phase [SFP]), and progesterone levels (baseline and peak) of eight captive Asian elephants (Elephas maximus) in Thailand. From 2014 to 2019, blood samples were collected weekly for serum progesterone enzyme immunoassays (EIAs). Estrous cycles (n = 70), including the luteal and follicular phases, and BCS (n = 70) were recorded. Based on the BCS, the LPL, FPL, and ECL were assigned to the following two groups: normal (BCS = 3.0–4.0, n = 38) and overweight (BCS = 4.5–5.0, n = 32). The findings demonstrated that there was no difference in LPL between the groups. However, in the normal group, the ECL was one week longer (14.9 ± 1.7 vs. 13.9 ± 1.7 weeks; p < 0.05), and the FPL also tended to be one week longer (7.2 ± 1.7 vs. 6.4 ± 1.5 weeks; p = 0.06) than in the overweight group. The mean progesterone level during the rainy, hot, and cool seasons was not statistically different. Based on the yearly averaged BCS from three seasons, the baseline and peak levels of progesterone were classified into the normal (n = 16) and overweight (n = 12) groups. Females with a normal BCS tended to exhibit higher progesterone peak levels (p = 0.08). The majority of peaks appeared during the rainy season (53.57%). The BCS was highest during the hot (4.47) and rainy (4.38) seasons, but not during the cool (4.12) season. The LPL, FPL, and ECL were not affected by the season in which the luteal phase occurred. On the other hand, the rainy season had a significant effect on the SFP, resulting in a longer LPL (p < 0.05) and ECL (p = 0.01); both were the longest during the rainy season. In conclusion, the effects of season on BCS may be related to characteristics of the estrous cycle and peak progesterone levels. Ultimately, these findings provide ground knowledge to assist elephant managers and owners in planning breeding activities using seasonal effects and BCS measurements in tropical climates. [ABSTRACT FROM AUTHOR]