Effects of forage allowance during growing phase of heifers for breeding and feedlot time of empty heifers

The study of pasture management associated with high supplementation [10 g/kg of body weight (BW)] is a strategy to reduce the age at breeding replacement Nellore heifers. Furthermore, to take advantage of the non-pregnant heifers (empty heifers) from this system, the feedlot time (FT) study is necessary to understand the carcass deposition and evaluate the feed efficiency of these animals. In this way, two experiments were carried out. In the first experiment (Exp. 1), the effect of two forage allowance (high and low forage allowance (FA); HFA and LFA, respectively) on canopy structure, forage nutritive value, supplement intake, performance, carcass characteristics and reproductive performance during the growing phase of weaned Nellore heifers (7 ± 1 months of age) receiving high supplementation on marandu grass pasture {Brachiaria brizantha (Hochst. ex A. Rich.) RD Webster [syn. Urochloa brizantha Stapf cv. Marandu]}, under continuous stocking, submitted to the breeding season at 14 months of age. In the second experiment (Exp. 2), the effect of three FT (45, 75 and 105 days) was evaluated on performance, carcass characteristics, intake, and feed efficiency of non-pregnant Nellore heifers (16 ± 1 months of age), from Exp 1. In Exp. 1, it was observed that the management of the canopy structure in two forage allowances affected the structural and nutritional characteristics of the pasture. The HFA treatment provided greater height (P < 0.01), a greater proportion of green stem (P < 0.01), a lower proportion of green leaves (P = 0.080), lower crude protein content (CP; P < 0.01) and lower CP:in vitro dry matter digestibility ratio (IVDDM; P < 0.01) compared to LFA treatment. There was no effect of forage allowance on supplement intake (P = 0.117), but greater average daily gain (P < 0.01) was observed in animals fed HFA. Higher stocking rate (P < 0.01) and gain per area (P = 0.035) were observed in the treatment of LFA. However, greater amounts of the supplement were offered per hectare (P = 0.016) in the same system. Regarding the measurements using ultrasound, the animals kept in the HFA had greater rib eye area (REA; P = 0.001), greater back fat thickness (BFT; P = 0.001) and rump fat (RF; P = 0.004) compared to animals in LFA treatment. Thus, heifers fed HFA had heavier (P = 0.004) and greater BFT during breeding. Thus, a higher cyclicity rate (P = 0.052) and proportion of pubertal heifers that became pregnant (P = 0.043) were observed in the HFA; however, differences in overall pregnancy rate (P = 0.223) and overall pregnancy loss rate (P = 0.221) among treatments were not detected. In Exp 2, BW and hot carcass weight increased linearly (P < 0.001). In addition, dry matter intake, BFT and REA increased over FT (linear effect; P < 0.01). The REA (P = 0.814) and BFT (P = 0.402) gains were similar among FT, but the rump fat gain increased (quadratic effect; P = 0.007). Feedlot time did not affect average daily gain (P = 0.807), carcass gain (P = 0.38) and carcass feed efficiency (P = 0.840). The total carcass gain (linear effect; P < 0.01) increased with FT. In conclusion, in Exp. 1, grazing management affected the structural and nutritional characteristics of the pasture, obtained better performance and carcass characteristics of heifers in the HFA treatment; however, both treatments were similar in the reproductive performance of breeding Nellore heifers at 14 months. Regarding FT in Exp. 2, it is concluded that Nellore heifers that received high supplementation during the growing phase did not vii reduce performance and feed efficiency until 105 days of confinement, increasing weight and carcass yield at slaughter. (AU)