PSXII-10 Post-weaning energy balance in dual-purpose replacement heifers (Giroland-Brown Swiss cross) confined-raised and grazing-raised before and after rainy season in tropical systems livestock

Abstract Common management of dual-purpose (Giroland-Brown Swiss cross) cattle in the Mexican Tropical region is to rear heifer replacement post-weaning in group pens. It is assumed that placing post-weaning heifers in group pens has more access to higher energy reserves due to the reduced foraging behavior. This study compared β-hydroxy-butyrate (BHB), body condition score (BCS), and average daily gain (ADG) in the post-weaning barn-raised and grazing-raised calves. Giroland-Brown Swiss cross (n = 8) were divided into 2 groups: confined-group (CG; n = 4) and grazing-group (GG; n = 4) for 4 mo (June to September). Both groups had ad libitum access to the same pasture (star grass; Cynodon plectostachyus) containing 6.5 % and 12.4 % crude protein (CP) during 2 regional seasons (drought and rainy season). Commercial concentrate was offered daily (0.5 kg; 17.5 % CP and 1 881 Mcal/kg net energy) at 1000 h. CG bunk feeders were refilled with pasture when empty during the day and mineral salts and water were provided at libitum to both groups. BHB was estimated monthly using a test strip (Freestyle Optium Neo, Witney UK). Additionally, BCS and ADG were estimated twice per month. An analysis of variance (ANOVA) model with a factorial design was implemented to assess BHB, BCS, and ADG as dependent variables and group treatment (GG and CG), month (4 levels), and season (drought and rainy) as independent variables. BHB values were not significant in the 2 treatment groups (GG: 300 ± 40 and CG: 230 ± 20 µmol/L; P > 0.05). The ADG (LS Means ± SEM) did not differ between treatment groups during drought season (GG: 419 ± 115 g compared with CG 310 ± 15 g; P > 0.05). Nevertheless, the ADG was significantly different between treatment groups during the rainy season (GG 790 ± 131 g compared with CG - 110 ± 63 g; P < 0.05). In addition, BCS was significantly different at the end of the experiment among treatment groups (GG: 3.13 ± 0.22 compared with CG: 2.6 ± 0.19). Our conclusion is that both management (grazing and confined) were equal to rear calves after weaning during the drought season. However, grazing the calves performed better (> ADG, and BCS) than confined management during the rainy season.