PSXIII-15 Impact of forage allowance on performance and reproductive parameters in Nellore heifers

Abstract

Abstract The objective was to evaluate the effects of forage allowance on the performance and pregnancy rate of Nellore heifers submitted to the fixed-time artificial insemination (FTAI) at 14±1 months. The experimental period was divided into the growing phase (GP; 173d) and breeding season (83d). Ninety weaned Nellore heifers [169±19 kg of body weight (BW); 210±28 days of age] were blocked by initial BW and randomly assigned to receive different forage allowance: (1) High (HFA; 7.17 kgDM/kgBW; and (2) Low (LFA; 3.27 kgDM/kgBW); and divided into 6 paddocks (2.15 to 2.4 ha each one). The grazing method used was continuous stocking with a variable stocking rate where treatment conditions were established varying the stocking rate on pasture (put-and-take). The supplement consisted of corn, soybean meal, urea, monensin, sodium chloride and minerals mix (80% TDN and 24% CP) and was provided daily (ad libitum; expected intake around 1% of BW). The final pregnancy rate was determined after two FTAI (d256). Heifers BW at the end of the GP was greater (P < 0.01) for HFA vs. LFA (268 vs. 255 kg). The overall average daily gain (ADG) was greater 68 g/d for animals maintained in HFA than LFA (P < 0.01; 0.713 vs. 0.645 kg/d). Supplement intake (kg/animal/d) had no treatment effect (P = 0.117). On d173, forage allowance affected (P < 0.01) the backfat thickness obtained by real-time carcass ultrasound (HFA = 3.08 vs. LFA = 2.85 mm). The pregnancy rate had no treatment effect (P = 0.223; on average 61%). However, the pregnant heifers per hectare had treatment effect (P = 0.036; HFA = 3.78 vs. LFA = 2.72 pregnant heifers/ha). In conclusion, the low forage allowance reduces the animal performance and affects the carcass composition but provides a greater number of pregnant heifers per hectare.