Impact of lighting regimes on reproductive performance and sperm ultrastructure in rabbit bucks under very severe heat stress conditions

Abstract

Lighting regimen is an important part of animal reproductive performance and physiological parameters, which can minimize the effect of high ambient temperature on semen quality and fertility of animals. The potential application of different light regimes in improving blood biochemicals, antioxidants capacity, reproductive hormones, semen quality, sperm ultrastructure alterations and fertility of rabbit bucks exposed to high ambient temperature was evaluated. Fifty bucks were allocated into five groups (10/group) according the lighting regimes. Bucks in each group were exposed to one of the following daily light-dark cycle (16L: 8D, 14L: 10D, 12D:12L, 10L: 14D or 8L: 16D) for four months (June to September). The ambient temperature, relative humidity and temperature–humidity index values during the experimental period were 34.25 ± 0.18°C, 63.68 ± 0.75%, 32.01 ± 0.33, respectively, indicating that the experimental bucks were under very severe heat stress conditions. Bucks exposed to 10L: 14D and 8L: 16D light regimes had significantly lower (P < 0.05) feed intake, rectal temperature, respiration rate, aspartate and alanine aminotransferases activities, and malondialdehyde level compared with their counterparts. Melatonin, testosterone, FSH, LH, and total antioxidants capacity levels were significantly increased (P < 0.05) by decreasing photoperiod, being the maximum for 8L: 16D regime. Bucks exposed to 10L: 14D and 8L: 16D light regimes exhibited significant improvement in sexual desire, semen quality (including: ejaculate volume, sperm progressive motility, vitality, intact acrosome and membrane integrity, sperm concentration and total sperm output) and fertility.The results indicate that application of short light period (8L: 16D) can be used as alternative and beneficial strategy to rabbit producers during heat stress months for improving semen quality, antioxidative capacity and fertility of bucks.