Effect of different lighting schedules (16L:8D or 12L:6D) on reproductive performance and nursing behaviour of rabbit does

The objective of the experiment was to study the reproductive performance and nursing behaviour of rabbit does under two different lighting schedules: 24 h group ¼ 16L:8D ( n ¼ 54 does) and 18 h group ¼ 12L:6D ( n ¼ 54 does). There was continuous lighting between 0.00 and 16.00 h in the 24 h group, however the lighting periods were modified day by day in the 18 h group (between 0.00 and 12.00, 18.00 and 6.00, 12.00 and 24.00, 6.00 and 18.00, respectively). Rabbit does were first inseminated at 16.5 weeks of age (mean body weight: 3.69 kg). A single batch, 42 day reproductive rhythm was applied. Rabbit does could nurse their kits freely. Nursing behaviour of the does and reproductive performance of the first five consecutive reproductive cycles were evaluated. The body weight of the does, the kindling rate, the litter size (born total, born alive, stillborn, at 21 d and at 35 d of age), the mortality of the kits and survival of the does were similar in the two groups. The litter and the individual weights at 21 and 35 d were higher in the 24 h group than in the 18 h group (litter weight at 21 d:3.21 vs. 3.08 kg, P ¼ 0.004; at 35 d:7.99 vs. 7.66 kg, P ¼ 0.002; individual weight at 21 d:371 vs. 351 g, P o 0.001; at 35 d:931 vs. 883 g, P o 0.001, in groups 24 h and 18 h, respectively). Calculations of the numerical and overall productivity per 100 inseminations (kits born alive, number of kits at day 35, weight of weaned rabbits) were comparable. The frequency of nursing events was independent of the lighting schedule but the nursing events were shorter in the 24 h than the 18 h group (226 7 38 s vs. 247 7 42 s, respectively; P o 0.001). In the 24 h group, the most nursing events (87.5%) happened during the dark period and in the two hours after the lights were switched on. The same tendency was not observed in 18 h group. When the distribution of nursing events of the 18 h group was transferred to the 24 h lighting schedule (16L:8D) which had been applied until the does' age of 13 weeks, 57.3% of the nursing events happened during the dark period and in the two hours after the lights were switched on. Contrary to our hypothesis, the reproductive performance of the does did not differ between the lighting schedules. The 12L:6D lighting schedule did not increase the nursing frequency of the does. It seems, that 18 h rabbit does nursed their kits according to the former 16L:8D lighting schedule, under the control of a circadian clock that operates on a 24 h cycle.