Abstract The optimization of the nutritional program of calves is essential for the sustainability and profitability of dairy companies. The use of additives such as Monensin allows to improve growth efficiency; however, concerns about the use of antibiotics in animal feed are growing. Therefore, the use of alternative products that can replace antimicrobial feed additives is necessary. Our objective was to evaluate the use of a combination of saponins and tannins in rearing stage of Holstein calves. A total of 36 female calves (BW, 114 ± 11 Kg; age, 86 ± 6 days) were distributed in 3 groups (n = 12/group) in a completely randomized design, using BW as criteria for assignment to each treatment (diet): 1) CON: without additives, 2) MON: Sodium Monensin (MON, 60 mg/kg DM, Elanco, Indianapolis, IN), 3) BXS: (900 mg/kg DM, a mixture of saponins and tannins, Silvafeed BXS, Silvateam, Argentina). The animal was used as the experimental unit. The calves were fed individually during an adaptation period of 10 days to the diet and a measurement period of 62 days. Body weight assessments were performed at the beginning and end of the measurement period with 12 previous hours of fasting. The feed intake was determined daily by measuring offer and rejection, and the conversion efficiency was determined using the quotient between the average daily gain and dry matter intake. Data were analyzed using PROC GLM of SAS, considering treatment as a fixed effect. Means differences were compared using Tukey's test, considering significance when P value ≤ 0.05. BXS and MON had increased final BW than CON (181, 181, and 174 kg respectively, P = 0.03). ADG was greater in BXS and MON than CON (1.075, 1.080, and 0.958 kg/d respectively, P = 0.03). BXS had similar DMI than MON but greater than CON (5.29, 5.13, and 4.62 Kg/d respectively, P = 0.03). The G:F was similar between treatments (0.208, P = 0.69). In conclusion, a combination of saponins and tannins can be used as an alternative additive to improve the performance of Holstein calves in rearing stage.
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