519 Late-Breaking: Evaluation of the 7 & 7 Synch and Bee Synch II protocols for control of the estrous cycle among cows of varying percentage Bos indicus influence. (8th October 2021) - Andersen, Carson M
Abstract: The 7 & 7 Synch and Bee Synch II protocols for control of the estrous cycle were compared among cows with varying percentages of Bos indicus influence. Angus (n = 48), ⅛ - ¼ Brahman-influenced (n = 90), Brangus (n = 11), and ½ Brahman-influenced (n = 56) cows were blocked based on breed, age, and days postpartum and randomly assigned to treatment. Cows treated with 7 & 7 Synch (n = 104) received prostaglandin F2α (PG; 25 mg dinoprost tromethamine) and insertion of an intravaginal progesterone-releasing insert (CIDR; 1.38g progesterone) on Day -17, gonadotropin-releasing hormone (GnRH; 100 μg gonadorelin) on Day -10, and PG coincident with CIDR removal on Day -3. Cows treated with Bee Synch II (n = 101) received PG coincident with CIDR insertion on Day -8 and PG coincident with CIDR removal on Day -3. Fixed-time artificial insemination was performed on Day 0 at 66 h. Ovarian ultrasound was performed on Day -3 to assess presence of corpora lutea (CL) and diameter of the largest ovarian follicle (LFD), and color Doppler was used on Day 7 to assess CL blood perfusion. A greater proportion of 7 & 7 Synch cows (P < 0.0001) had CL on Day -3 (83%; 86/104) compared with Bee Synch II cows (48%; 48/101). On Day -3, LFD did not differ among Bos indicus-influenced cows treated with Bee Synch II (12.5±0.3 mm), Bos indicus-influenced cows treated with 7 & 7 Synch (12.2±0.3 mm), or Angus cows treated with 7 & 7 Synch (12.1±0.6 mm); however, greater LFD was observed among Angus cows treated with Bee Synch II (15.4±0.8 mm). Brangus cows had greater periphery signal percentages (P = 0.02) when treated with 7 & 7 Synch compared with Bee Synch II. In conclusion, across cow of varying percentage Bos indicus influence, 7 & 7 Synch resulted in a greater proportion of cows with CL on Day -3.