Economic evaluation of puberty induction of nulliparian Nellore heifers using intravaginal device and melengestrol acetate

The present study evaluates the economic viability of puberty induction in nulliparous Bos taurus indicus Nellore breed heifers using an intravaginal device of fourth-use and melengestrol acetate (MGA®).  The experiment was undertaken in the Nossa Senhora Aparecida Farm, Terenos city, Mato Grosso do Sul, Brazil, and was utilized a completely randomized experimental design in a 2 × 3 factorial scheme.  Two age classes were included in the study, which were divided into 348 precocious (early-cycle) heifers, aging 16-18 months, weighting an average of 264.6 kg and 543 conventional-cycle heifers aging 24-26 months averaging 346.8 kg.  The three treatments were as follows:  control without the induction of follicle formation (treatment 1); treatment 2: induction with an intravaginal implant (intravaginal implantation with a fourth-use progesterone implant on Day 0, withdrawal on Day 12, and application of 1 ml of intramuscular estradiol cypionate [ECP®]); and treatment 3, 2.3 g of MGA® during 12 days with supplement followed by 1 ml of intramuscular ECP® at the end of the treatment.  Heifers induced via implantation had a higher rate of ovarian activity (presence of corpus luteum) during the early cycle (63.8% animals) while the conventional cycle (72.4%).  This effect influenced the frequency of early stage anestrus (56%).  Among the treatments evaluated, 72% of control heifers had no ovarian activity (absence of corpus luteum).  In the group with implant induction, the conception rates were 65.5% and 62.4% in early and conventional-cycle females, respectively.  Puberty induction in Nellore heifers provides a high economic return.  The protocol revealed the highest efficiency compared to the control group.