Effect of Melatonin Supplementation from Mid- to Late- Gestation on Hair Growth and Skin Temperature of Beef Cattle

Melatonin has been previously shown to increase distal skin temperature and decrease core body temperature in humans. However, limited research is available on the impact of melatonin on skin temperature in cattle. Therefore, the objective was to examine effects of supplemental melatonin treatments on core body temperature, skin temperature, and hair growth during mid to late gestation in cattle. Commercial beef heifers (n = 32) and cows (n = 25) were artificially inseminated and delegated to receive melatonin implants (MEL) or non-implant control (CON). Animals in the MEL (n = 29) treatment group received two 24 mg melatonin ear implants at d 180, 210, and 240 of gestation. Maternal BW, rectal temperature, ambient temperature, humidity, thermal images, and hair weight were collected on d 180 (baseline) and 240 of gestation. Thermal imaging was collected using a Flir ThermaCAM S60 (FLIR Systems, Boston, MA, USA) infrared thermography camera. A sample of hair was collected from a 5.08 x 10.16 cm area on the left thoracic region right behind the shoulder and images taken. Temperatures of both the shaved and unshaved areas were analyzed using ThermaCAM Researcher PRO 2.7 Software (FLIR Systems). Data were analyzed using MIXED procedure of SAS. The model statement included melatonin treatment, parity, and breed. Maternal BW was not different between MEL vs. CON on d 180 (P = 0.92) or d 240 (P = 0.95). Similarly, rectal temperature was not different between MEL vs. CON on d 180 (P = 0.34) or d 240 (P = 0.54). The ambient temperature was not different (P = 0.27) and averaged 31 ± 1°C; however, average humidity was increased on d 240 (82 ± 4%) vs 180 (67 ± 5%). Temperature of the shaved areas on d 180 (P = 0.92) and 240 (P = 0.28) were not different between treatments. Temperature of the unshaved area was not different on d 180 (P = 0.75); however, on d 240 temperature of the unshaved area was decreased (P = 0.05) in MEL (32.7 ± 0.4°C) vs. CON (33.5 ± 0.3°C). Hair weight of the shaved areas on d 180 (P = 0.91) and d 240 (P = 0.63) were not different between treatments. In summary, melatonin supplementation did not alter BW, rectal temperature, or temperature of the shaved area. However, temperature of the unshaved area was decreased during melatonin supplementation.