PSV-8 - Differences in performance between Bos indicus versus Bos indicus cross Bos taurus when supplementing with calcium β-hydroxy-β-methylbutyrate in a subtropical environment

Abstract: The leucine metabolite, β-hydroxy-β-methylbutyrate (HMB), has been shown to affect protein and lipid metabolism. Differences in protein and energy metabolism between Bos indicus and Bos taurus breeds of cattle have been identified. Therefore, the objective of this study was to compare the efficiency of growth of Bos indicus (Nellore, NE) with crossbred Bos indicus x Bos taurus bullocks (CR) in a subtropical feedlot. A total of 96 bullocks (4 pens of 24, 12 NE and 12 CR each) were studied in a factorial 4 x 2 design with four levels of the calcium salt of HMB, CaHMB, (0 (control), 3, 5, or 7 g per head per day) and either NE or CR breeds. Treatments were fed during adaptation, growing, and finishing phases. Access to shade was provided and bullocks were radio frequency tagged with electronically monitored feed bunks and water troughs. The 5 g CaHMB daily group had greater DMI across the study in both breeds (P < 0.05). Daily DMI in CR was 10.40±0.08 kg versus controls at 9.60±0.09 kg and in NE DMI was 9.78±0.09 kg versus controls at 9.23±0.08 kg. Additionally, the 3 g CaHMB group had increased DMI during the growing period of 6.0% and 7.3% in CR and NE, respectively (P < 0.05). Ingestion rates, as a function of treatments and days of feeding, were analyzed using a Generalized Additive Model and CR supplemented with 5 g of CaHMB had the fastest ingestion rate (kg/min) during the first 60 days of experiment, while NE supplemented with 5 g of CaHMB had faster ingestion rates from 30 to 60 days on feed. The CR animals also had the greatest meal size (kg/meal) during the adaptation, growing, and initial days of the finishing period. In NE CaHMB treatments did not improve overall ADG. However, in CR 3 g CaHMB improved overall ADG versus controls (1.96±0.011 versus 1.88±0.013, respectively, P < 0.05). In the 3 g CaHMB group during the adaptation period NE had a 9.9% increase and CR had a 21.1% increase in ADG versus controls (P < 0.05). During the finishing period 5 g CaHMB increased ADG 4% versus controls in the CR breed (P < 0.05). In the NE breed CaHMB did not improve overall feed efficiency (FE), however, a numerical increase was noted with 3 g CaHMB during the adaptation period. Overall, FE was improved in the CR breed in the 3 g CaHMB group by 4.5% versus control (0.211±0.002 and 0.202±0.022, respectively, P < 0.05). In conclusion, we have identified breed differences in the effects of CaHMB in NE and CR. Feeding CaHMB to NE and CR increased DMI of both breeds; however, CR showed the most improvement in ADG and FE.