Ram novelty and the duration of ram exposure affects the distribution of mating in ewes exposed to rams during the transition into the breeding season

摘要

This study compared the affect of short-term and continuous exposure to rams during the transition between anoestrus and the breeding season on the distribution of mating and subsequent lambing. Further, within ewes continuously exposed to rams we investigated the effect of replacing these rams every 17 days with 'novel' rams. During August (late anoestrus, Northern Hemisphere), multiparous, North of England mule ewes were allocated to one of four groups: SVR ewes were exposed to vasectomised rams for 24h on Day 0 (short term; n =109), RVR ewes were exposed to vasectomised rams for 24h on Days 0, 17 and 34 (short term; n =113); PVR ewes were exposed to vasectomised rams on Day 0 and remained with the same rams for the duration of the pre-mating period (continuous; n =104); NVR ewes were continuously exposed to vasectomised rams from Day 0 with the rams replaced with 'novel' rams every 17 days (continuous; n =113). Blood samples were collected from a subset of ewes (n =22 per group) to monitor progesterone. On Day 50, harnessed, entire rams were introduced for mating and raddle marks recorded daily for the first 17 days. The median date of mating occurred 1 day earlier in NVR ewes than PVR ewes (P <0.05). A synchrony score calculated from the blood sampled ewes showed that the distribution of mating was more synchronised in PVR and NVR ewes than SVR and RVR ewes (P <0.001). PVR and NVR ewes had an earlier onset of cyclic activity than RVR ewes (P <0.01). However, only NVR ewes differed from SVR ewes in this variable (P <0.05). Within ewes lambing to first service, the median date of lambing of PVR, NVR and SVR ewes occurred at least 2 days earlier than RVR ewes (at least P <0.05). Further, PVR and NVR ewes had a more compact distribution of lambing than SVR and RVR ewes (P <0.05) and lambing was more compact in NVR ewes than PVR ewes (P <0.05). In conclusion, ewes in continuous contact with rams prior to mating had a more synchronised distribution of mating and lambing than ewes given only short-term exposure to rams. This distribution of mating in continuous ram exposed ewes can be further enhanced by periodic exposure to novel rams.