Impact of the nutritional reserves and body development on the cyclicity of Nelore heifers of 13 months of age

The aim of this study was to evaluate different parameters of corporal and reproductive development at the sexual precocity in Nelore heifers. Between October and December 2013, 740 Nelore heifers aged 13.0±0.85 months were enrolled from three commercial farms located in the cities of Camapua, Tres Lagoas and Agua Clara – MS. The following parameters were evaluated: age, weight, body score condition (BCS, 1 to 5 scale), subcutaneous fat thickness of rump (SFTR), height/depth of rib (PROF). Subcutaneous fat thickness was measured by ultrasound examination (Aloka SSD500, Aloka, Japan) on the gluteal muscle biceps. The cyclicity was evaluated by two ultrasound exams within 10 days, using a device with a 7.5-MHz transducer (Aloka SSD-500, Aloka, Japan). Heifers with luteal tissue in one of the examinations were considered cyclic. The body condition score was assessed during the ultrasound examination. Cutoff values for the variables previously described were determined through the ROC curve (Receiver Operating Characteristic). The variables were analyzed using the GLIMMIX procedure of SAS 9.3. Heifers were classified into categories: ≤ 13.0 months (≤ 13m) and > 13 months of age (> 13m); ≤ 248 kg of body weight (LIGHT) and > 248 kg of body weight (HEAVY); low BCS (LBCS; ≤ 3.0) and high BCS (HBCS; > 3.0); low SFTR (LSFTR; ≤ 2.47 mm) and high SFTR ( HSFTR; > 2.47 mm), low (LPROF; 44%). There was relationship only between cyclic heifers and BCS [LBCS = 9.59% (45/469) vs. HBCS = 16.97% (46/271); P 13m = 13.86% (61/440); P = 0.35], body weight [LIGHT = 9.64% (30/311) vs. HEAVY = 14.21% (61/429); P = 0.69], SFTR [LSFTR = 8.60% (27/314) vs. HSFTR = 15.09% (62/411); P = 0.45] and PROF [LPROF = 8.93% (31/347) vs. HPROF = 15.27% (60/393); P = 0.49]. Therefore, it was possible to conclude that the body condition score was positively correlated with cyclicity in Nelore heifers aging 13 months.