The present work was planned to study the effects of mild and hot conditions on reproductive traits of male rabbits. The traits studied were libido (reaction time), semen quality characteristics (hydrogen-ion value, ejaculate volume, sperm motility, dead sperm, sperm abnormalities, acrosomal abnormalities, sperm-cell concentration and total sperm output), seminal biochemical traits (total protein, albumin, globulin, total lipid, cholestrol and creatinine), seminal enzymes (glutamic-pyruvate transaminase (GPT), glutamic oxalo-acetic transaminase (GOT), alkaline phosphatase and acid phosphatase), seminal hormones (tri-iodothyronine (T3) and cortisol), thermoregulatory parameters (respiration rate and temperatures of ear, rectum and skin), food and water consumption, blood metabolites (total protein, albumin, globulin, glucose, total lipid and cholesterol), kidney function (urea-N and creatinine), liver function (serum GPT, serum GOT and alkaline and acid phosphatase) and endocrine functions (T3 and cortisol hormones).
The estimated temperature-humidity index (THI) values were 20·2 during the mild and 30·1 in the hot period, indicating absence of heat stress in the first period and exposure of rabbits to very severe heat stress in the second one.
In semen characteristics, the effects of heat stress on reaction time, semen pH, sperm motility, percentages of dead sperm, sperm abnormalities and acrosomal damage, were not significant. However, ejaculate volume, sperm-cell concentration and total sperm output were significantly lower (P < 0·01) under heat stress than under mild conditions. In seminal plasma, effects of heat stress were not significant on total protein, globulin, total lipid, cholesterol, creatinine and alkaline phosphatase. Meanwhile, seminal plasma albumin, acid phosphatase, T3 and cortisol were significantly (P < 0·01 or P < 0·05) lower, while GPT and GOT were significantly (P < 0·01) higher in heat stress than in mild conditions.
Thermoregulatory parameters (respiration rate and temperatures of ear, rectum and skin) and water consumption were significantly (P < 0·01) higher, while consumption of food was significantly (P < 0·01) lower in heat stress than in mild conditions. Blood serum globulin was not affected, while serum total proteins, albumin, glucose, total lipid, cholesterol, acid phosphatase, T3 and cortisol were significantly (P < 0·01 or P < 0·05) lower and urea-N, creatinine, GPT, GOT and alkaline phosphatase were significantly (P < 0·01 or P < 0·05) higher in heat stress than in mild conditions, within the Egyptian subtropical climate.