Effect of breeding system, cycle and cage size during fattening on rabbit doe and growing rabbit performance under heat stress

In order to evaluate heat stress and circadian rhythm 46 nulliparous rabbit does with a BW of 3.6760.05 kg (s.e.) were used. They were clipped once or not and rectal temperature, feed and water intake were recorded for 24 h. From this group, 43 rabbit does were mated 7 days after rectal measurements, and randomly assigned to one out of two breeding systems (including in both systems rabbit does that had been clipped or not). In the control one (C) rabbit does were mated 14 days after parturition and litter weaned at 35 days of age, and in the extensive one (E) they were mated 21 after parturition and weaned at 42 days of age. Rabbit doe and litter performance were recorded for 6 months (first three cycles). Two hundred twenty-eight weaned rabbits were divided into two cage sizes: 0.5 and 0.25m2 with eight and four rabbits per cage, respectively, to study growing performance. Farm and rectal temperatures were minimal and feed and water intake maximal during the night ( P,0.001). Unclipped rabbit does showed higher rectal temperature ( P50.045) and lower feed intake ( P50.019) respect to clipped does, which are symptoms of heat stress. Neither breeding system nor cycle number influenced fertility, total number of kits born, born alive or dead per litter (91.6%, 6.98, 5.80 and 1.19 on average, respectively). Kit mortality during lactation tended to increase in E compared with C group (48.5% v. 63.4%; P50.070), reducing the number of kits at weaning per litter by 33% ( P50.038). It also increased in the second and third cycles compared with the first ( P<0.054). It resulted that feed efficiency (g weaned kits/ g feed intake does1litter) tended to decrease in E respect C group ( P50.093), whereas it was impaired successively from the first to the third cycle by 48% ( P50.014). Growing rabbits from the E group were heavier at weaning (by 38%; P,0.001), showed a higher feed intake (17.4%) and lower feed efficiency (28.4%) throughout the fattening period ( P<0.056) respect to C group. However, age at slaughter was not different respect to C group (77.3 days on average). Cage size had minor influence in growing performance. In conclusion, rabbit doe and litter productivity impaired when lactation is extended from 35 to 42 days and along successive reproductive cycles.