Hormonal protocols with progesterone on puberty induction in Nellore heifers

• Grant number: 21/12451-3
• Support Opportunities: Regular Research Grants
• Start date: April 01, 2023
• End date: March 31, 2025
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Animal Reproduction
• Principal Investigator: Alexandre Vaz Pires
• Grantee: Alexandre Vaz Pires
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil
• Associated researchers: Marcos Vinicius de Castro Ferraz Junior

Abstract

There is a scientific gap about the use of hormonal protocols for inducing puberty in Nellore heifers exposed to reproduction from 12-14 months of age. The main objective of the study is to demonstrate that inducing puberty with progesterone may not be enough for heifers to actually enter puberty (continuation of estrous cycles) and that many ovulate only by hormonal induction and return to the anestrus. In addition, it is intended to evaluate the effect of EPD bulls for age at first partum on the induction of puberty in heifers. A total of 220 Nellore heifers with an average age of 11 months and 200 kg will be used, confined in collective pens in the experimental facilities of the Animal Nutrition and Reproduction Laboratory (LNRA/ESALQ/USP). The experiment will last 8 months and will be carried out in randomized blocks according to the heifer's paternity. The study consists of 4 treatments to assess the rate of natural puberty and the rate of puberty induced by hormonal protocol: Control (CO): heifers not induced to puberty (no hormonal treatment); Induction (IN): heifers will be submitted to an induction protocol (Pind) at 14 months of age; Induction + 1 IATF protocol (IN + 1): heifers will be submitted to a Pind at 14 months of age and will be submitted to one IATF protocol (Piatf), without insemination; and Induction + 2 IATF protocols (IN + 2): heifers will be induced to puberty at 14 months of age and will be subjected to two Piatf, without insemination. There will be measurement of the daily consumption of the pen. The heifers will be submitted to reproductive ultrasound and will also be weighed weekly throughout the experimental period. Carcass ultrasound data will be collected at the beginning of the experimental period, at the time of Pind application and at the end of the study. Also, at the beginning of the study there will be body measurement of the height and depth of rib of the heifers. Blood samples will be collected for P4 analysis when a CL is detected in the period before the application of hormonal protocols. Statistical analyzes will be performed using the MIXED and GLIMMIX procedures of the SAS software. (AU)