Oestrus synchronization of rabbit does at early post-partum by dam-litter separation or eCG injection: Effect on kit mortality and growth

Insemination of rabbit does at early post-partum combined with dam-litter separation (DLS) can increase prolificacy and decrease parturition intervals, but little is known about longer-term effects on kit survival and growth. In this study, does (n = 138) were artificially inseminated on day 4 post-partum (nine times over a period of 10 months, 35-day reproductive rhythm, kits weaned at 25 days), after DLS (for 48 or 24 h) or 48 h after 25 UI eCG injection. The litters from each group were adjusted to seven to nine kits per doe and then weighed at 2, 4, 16 and 25 days of age. Mortality was calculated in the pre-weaning period and development of the digestive system was quantified (length of intestinal villi). After DLS24 or DLS48, 4-day-old kits were lighter than eCG or controls of the same age. By 16 and 25 days of age, 48-h weaned kits had regained the same weight as the eCG and control groups (higher daily weight gain). The 24-h weaned kits weighed less, probably because their litter size was larger and daily weight gain was lower. Total kit mortality (day 2 to day 25) was highest in the DLS48 group but percentage mortality varied among treatments depending on the period considered (days 2–4, days 5–16 and days 17–25). In the first period, mortality was higher for DLS48; in the second, mortality was similar for all groups except eCG (which was lower). After 16 days of age, mortality was quite low and similar in all groups. There was a significant effect of the number of parturitions on the parameters considered. Intestinal villi were measured in 12 kits slaughtered at 4, 16 and 25 days of age (DLS for 24 or 48 h on days 3 and 2, respectively) and compared with controls (2, 4, 16 and 25 days old). At 4 days (immediately after separation), the stomach and whole digestive system were lighter in DLS48 than controls, due to the absence of the milk, but there were no significant differences among groups by days 16 and 25. Intestinal villi were shorter in 4-day-old DLS kits (24 and 48 h) compared to controls of the same age, longer at 16 days (possibly due to an intense cellular proliferation) and similar among all groups by day 25. In summary, both 24-h DLS and 48-h DLS can substitute hormonal treatments to synchronize oestrus in intensive rhythms, but kit mortality was higher after 48-h DLS in primiparous does, suggesting that results would improve if those females had a better body condition.