Description
The estrous cycles of Limousin heifers (n = 30) were synchronized by insertion of a controlled internal drug release (CIDR) device (1.94 g progesterone; Pfizer Animal Health) placed into the vagina for 8 days. A 0.5 mg intramuscular injection of a prostaglandin F2a (PG) analogue (PG, Estrumate, Shering-Plough Animal Health, Hertfordshire, UK) was administered 1 day before CIDR removal.  Heifers were checked for standing  estrus  and only those exhibiting  estrus  (Day 0) were used. All animals were expected to come in heat between 48 and 72 hours after CIDR removal. Cervical tissues were collected at slaughter from heifers 12h after CIDR removal (Group 1: CIDR + 12 h, n = 6), 24h after CIDR removal (Group 2: CIDR + 24 h, n = 6), at the onset of  estrus  (Group 3: Estrus, n = 4), 12 h after the onset of  estrus  (Group 4:  estrus  + 12 h, n = 5), 48 h after the onset of  estrus  (Group 5: Estrus+48h, n = 4) and on day 7 after the onset of  estrus  (Group 6: Luteal phase, n = 5). Overall design: Cervical tissue from 30 animals taken at 6 timepoints in the peri-oestrus period. +12hrs post CIDR, Onset of Oestrus,+12hrs post Oestrus, +48hrs post Oestrus, Luteal phase