Relationship of body maturation with response to estrus synchronization and fixed-time AI in Nelore (Bos indicus) heifers

• Published in: Livestock science Vol. 251; p. 104632
• Main Authors: Freitas, B.G., Mingoti, R.D., Monteiro, B.M., Guerreiro, B.M., Crepaldi, G.A., Ramos, L., Vasconcellos, G.S.F.M., Sá-Filho, M.F., D'Occhio, M.J., Baruselli, P.S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2021
• Subjects: Fixed-time AI; Heifer; Nelore; Pregnancy; Puberty; Subcutaneous adipose; Subcutaneous adipose; Pregnancy; Nelore; Puberty; Heifer; Fixed-time AI
• ISSN: 1871-1413; 1878-0490
• DOI: 10.1016/j.livsci.2021.104632

•Subcutaneous adipose tissue has an important bearing on puberty and P/AI in young Nelore heifers.•Chest depth, which is indicative of adipose-muscle maturation, also influences P/AI.•Nelore heifers selected and managed for body maturation can achieve a pregnancy rate to FTAI at around 14 months that is similar with pregnancy rates in older heifers.•Heifers subjected to assisted breeding must have an appropriate body maturation which is reflected in subcutaneous adipose tissue. The relationship between body maturation at puberty and pregnancy after fixed-time AI (FTAI) was investigated in young Nelore (Bos indicus) heifers. Heifers (n = 650; 13.9 ± 0.03 months; 252 ± 0.99 kg LW) were assessed for body condition score (BCS, scale 1–5), withers height (hWITHERS, cm), chest depth (cDEPTH), subcutaneous fat thickness (SCFT, mm), and the presence of a corpus luteum (puberty). Heifers then underwent a progesterone-based estrus synchronization protocol with FTAI, and pregnancy rate to AI (P/AI) was recorded. Data were analyzed by univariate and multivariate logistic regression using the GLIMMIX procedure of SAS 9.3 and Receiver Operating Characteristic (ROC) curves were used to ascertain the effects of variables on puberty and P/AI. BCS and hWITHERS were not related (P > 0.05) to either puberty or P/AI. cDEPTH had no relationship (P = 0.56) with puberty but influenced (P < 0.02) P/AI. A greater (P = 0.002) proportion of heifers with SCFT > 3.4 mm attained puberty and the P/AI was greater (P = 0.0003) for heifers with SCFT > 2.5 mm. The findings were interpreted to indicate that both puberty and the response to estrus synchronization-FTAI in young Nelore heifers are dependent on the acquisition of subcutaneous adipose tissue that is sufficient to support reproductive function. It was concluded that Nelore heifers selected and nutritionally managed for body maturation can achieve a pregnancy rate to FTAI at around 14 months of age that is similar with pregnancy rates in older heifers.