Effects of Oral Vitamin D3 Supplementation on Growth, But Not on Development of Shell Deformities in Juvenile Eastern Spiny Softshell Turtles (Apalone spinifera spinifera)

Abstract The eastern spiny softshell turtle (SST: Apalone spinifera spinifera ) is listed as endangered within its range in Canada and, since 2014, has been the focus of a head-start program aimed at increasing the juvenile survival rate over their first winter. From 2017 to 2020, shell deformities have been observed among the SSTs in this program, raising concerns about the potential underlying risk factors for musculoskeletal disease, including vitamin deficiencies. This study aimed to assess the impact of dietary vitamin D 3 (cholecalciferol) levels on shell deformities in captive-raised juvenile SSTs. Twenty-two juvenile SSTs from four distinct nests were selected and divided into two groups. Both groups experienced identical environmental conditions, and their diets differed only in vitamin D 3 content. The control group received standard dietary levels (low: LVD) at 1,980 IU/kg/ration, and the other received an added dietary supplementation (high: HVD) at 6,000 IU/kg/ration. Morphometric measurements and shell deformity severity assessments were conducted at 2-wk and 12-wk intervals, respectively, over the course of 1 yr. The HVD group exhibited significantly greater increases in body weight ( P < 0.001) and carapace width ( P = 0.004) than the LVD group by the conclusion of the study. Specifically, HVD females gained the highest body weight ( P = 0.001), with LVD males displaying the lowest weight gains. Shell deformities were more prominent in females ( P = 0.043) but were not different between the treatment groups. Although these findings suggest a role for oral vitamin D 3 in the growth and development of juvenile SSTs, it appears that the occurrence of shell deformities in these turtles is more closely associated with sex and growth rate, rather than oral vitamin D 3 supplementation. Further investigations are warranted to understand the nutritional needs and potential risk factors influencing shell deformity development in this endangered species comprehensively.