Effects of melatonin on hematologic and biochemical changes and the effects of circadian rhythm on hematologic changes in donkeys (Equus asinus) subjected to packing during the hot-dry season.

Abstract

Melatonin is a hormone with antioxidant and anti-inflammatory properties and may alleviate the effects of stress on hematologic and biochemical analytes in working donkeys that pack (load-carry). We aimed to evaluate the effects of melatonin administration on hematologic and biochemical responses in donkeys subjected to packing during the hot-dry season. We also examined its effects on circadian rhythms. Ten male Nubian pack donkeys with (Packing + Melatonin; P + M) and without melatonin (Packing-Melatonin; P-M) administration were included. Blood samples were collected before, immediately after (15 min), and from 16 h to over 27-h postpacking at 3-h intervals for hematologic and total protein analyses. Serum from blood samples collected before and immediately after packing was analyzed for muscle enzyme activities and electrolyte concentrations. Student's t-test, one-way ANOVA, and online cosinor analysis were used for statistical analyses. Packed cell volumes (PCVs) of the P + M donkeys did not differ before and after packing. However, for the P-M donkeys, values before packing (30.20 ± 0.8%) were higher than those (26.87 ± 0.5%) after packing. The hematologic values recorded in the P + M donkeys were higher than those in the P-M donkeys, especially during the scotophase (P˂0.05). The mesor PCV, hemoglobin (Hb), and red blood cell (RBC) values for the P + M donkeys were significantly (P˂0.05) higher than those in the P-M donkeys. Lactate dehydrogenase (LDH) activity was not different before (289.40 ± 60.8U/L) or after packing (323.20 ± 36.0U/L) in P + M donkeys, but the activity was significantly (P˂0.05) higher postpacking than prepacking in the P-M donkeys (294.20 ± 66.9U/L and 513.40 ± 68.5U/L, respectively). The relationships between the meteorologic parameters and PCV, Hb, and RBC concentrations in the P + M donkeys were significantly negative (P˂0.05). Melatonin prevented a decrease in PCV and increase in LDH activity immediately after packing compared with non-treated donkeys. There was a marked effect during the scotophase on PCV, Hb, and RBC concentrations. The circadian parameters indicated a significant effect of melatonin on the rhythmicity of the PCV, Hb, and RBC concentration in the treated donkeys. Melatonin administration may reduce the risk of adverse effects of environmental stress and stress due to packing in donkeys during the hot-dry season.