Reproductive performance of Bos indicus and Bos taurus X Bos indicus heifers submitted to a synchronization of ovulation protocol

The aim of this dissertation was to evaluated the reproductive performance of Bos indicus (BI) and Bos taurus x Bos indicus heifers submitted to a synchronization of ovulation protocol. In Chapter 2, pubertal and prepubertal BI and CR heifers were submitted to the reproductive program proposed by Rodrigues et al. (2014) and a group of pubertal heifers were synchronized with the standard TAI protocol. In Chapter 3, pubertal and prepubertal BI and CR heifers were submitted to the reproductive program at the age of 12 months. In Chapter 4, was evaluated the effects of progesterone concentration at Day 9 of the TAI protocol and treatment with eCG in BI and CR heifers. In the experiment of Chapter 2 a greater number of BI heifers were pubertal at the beginning of the experimental period than CR heifers. The induction rate did not differ between BI and CR heifers. Breed of the heifers impacted pregnancy rate to TAI in Farm 1, but not in Farm 2. Heifers that did not respond to the induction protocol had lower pregnancy rate when compared to the others experimental groups. In the experiment of Chapter 3, the CL presence on D0 did not differ between breeds. Independent of the genetic group heavier heifers were more likely to have a CL on D0. There was an effect of CL presence at D0 on P/AI vs. Without CL. The interaction between CL presence on D0 and genetic group did not affect P/AI, and BI heifers had lower P/AI in comparison to CR heifers. An interaction between CL presence on D0 x weight was detected for P/AI. In heifers with CL, the weight did not have effect on P/AI; however, in heifers without CL, heavier heifers were more likely to become pregnant. In the experiment of Chapter 4, the progesterone concentration that has more sensibility and specify for pregnancy at Day 9 was 2.03 ng/mL. Follicle diameter at D9 was greater for CR heifers than BI heifers and in Low P4 compared to High P4. The follicle diameter at D11 tended to be greater for Low P4 than High P4. Probability of pregnancy was negatively associated with P4 level at Day 9. Ovulation rate was greater for eCG compared to Control. Crossbred heifers had greater conception rate and greater pregnancy rate than BI. LOW P4 heifers have greater conception and pregnancy rate than HIGH P4. In conclusion, it is possible to induce first ovulation in BI and CR heifers followed by the TAI protocol with satisfactory pregnancy rates in heifers from 12 to 27 months old, after puberty induction, if the nutritional requirements are achieved. (AU)