PSVII-26 - Follicular growth in beef cows when using a low dose of FSH and hCG at the time of CIDR removal in a 7-day Co-synch + CIDR protocol.

The aim of the study was to compare the growth of the periovulatory follicle in crossbreed cows receiving either a low dose of hCG (150 IU; Chorulon®, Merck) or a low dose of FSH (20 mg)Folltropin®, Vetoquinol) vs. a control group when applied at CIDR removal during an estrus synchronization protocol. At d0, a CIDR (Eazi-Breed CIDR®, Zoetis) was placed, a dose of GnRH (Factrel®, Zoetis) was applied i.m. and transrectal ultrasound was conducted to evaluate cyclicity status. On d7, cows (n = 79) were randomly assigned to three treatments (Control n = 27, FSH n = 26, and hCG n = 26) according to body condition score (1 to 9 scale) and cyclicity status. On the same day, CIDR was removed, a dose of prostaglandin analog (Lutalyse HighCon Injection®, Zoetis) was administered i.m. and an Estrotect™ patch was placed between the hip and tail head. Transrectal ultrasound was conducted to evaluate the diameter of the preovulatory follicle (DPF) at d7 and every 12h from d8 until ovulation was detected. Five cows that did not ovulate were removed from the study. Data were analyzed using GLIMMIX and LIFETEST procedures (SAS). The diameter at ovulation was not different among treatments (Control: 13.02 ± 0.53 mm; FSH: 12.38 ± 0.54 mm; hCG; 11.69 ± 0.47 mm; P = >0.10). Also, the time to ovulation was not different among treatments (P = 0.65; Figure 1a). However, cows of the control group presented estrus signs earlier than FSH and hCG groups (P = 0.02, Figure 1b). In conclusion, the use of a low dose of hCG or FSH at the time of CIDR removal did not increase the DPF or the time to ovulation.