Delivery frequency of loose mineral mixtures for grazing cattle: Physicochemical changes of the supplement and animal responses

ABSTRACT The objective was to evaluate the effect of delivery frequency of loose mineral mixtures (LMM) offered to grazing steers on the physicochemical characteristics of the mixture and animal performance. Two experiments were carried out both during the wet-to-dry transition period (March 2021 to June 2021) and during the rainy season (November 2021 to March 2022). Brangus steers (n = 120, distributed in 24 paddocks) were used in experiment 1 and Nellore steers (n = 96, distributed in 20 paddocks) in experiment 2. The LMM contained 8% phosphorus and was delivered at two different frequencies: weekly (DF7d) and every 21 days (DF21d). The paddock was considered the experimental unit, with 12 experimental units in experiment 1 and 10 experimental units in experiment 2. The LMM disappearance was assessed as the difference between LMM delivered mass and orts. Assessments included the chemical characteristics of the LMM orts, the rainfall drained water mineral content and its electrical conductivity, fecal and plasma mineral content, and animal performance. Data were analyzed for outliers and subjected to analyses of maximum restricted likelihood. In experiment 1, drained rainfall water was higher for DF21d. There were differences in plasma and fecal mineral concentrations due to homeostatic balance. There were no significant differences in average daily weight gain (ADG) between treatments during the wet-to-dry transition period (P>0.05); however, the ADG of animals supplemented weekly was 60 g higher than ADG of animals in the DF21d treatment (P<0.04). During the rainy season, there was a greater demand for force to penetrate the mass of the mixture for the DF21d treatment (2.14 vs. 1.63 kg/cm2; P = 0.01). The delivery frequency of loose mineral mixtures changes the physicochemical patterns of the supplement, affecting animal performance, which is more evident during the rainy season.