Utilization of fortified cubes to deliver trace minerals and monensin in forage-based diets

Abstract

The potential benefits of mineral or monensin delivery through forage cubes vs. free-choice were investigated in Simmental × Charolais pregnant cows and their calves. Thirty-six mid-gestation cows (615 ± 21 kg) placed in 18 pens were initially depleted of liver Cu reserves by feeding a TMR containing 100 mg Mo kg^-1 DM and 4 g S kg^-1 DM for 42 d, allowed to stabilize on a low Mo, Cu and S diet for 42 d and were then used in a mineral uptake study. Experimental diets containing chopped grass-hay were fed ad libitum with one of the following three alfalfa-barley grain cubes at 2 kg head^-1 d^-1: (1) no addition of mineral and ionophore (Free Choice); (2) addition of mineral and no ionophore (+M Cube); and (3) addition of mineral and ionophore in the form of monensin (+M+I Cube). Mineral intake and mineral status (through liver biopsy and blood sampling) were monitored over a 16-wk feeding period, which included the first 6 wk post-calving. Dry matter intake by Free Choice cows prior to calving was higher than that by +M Cube and +M+I Cube fed cows (P < 0.05). Pre- and post-calving mineral intake (g pen^-1 d ^-1) by Free Choice cows was 31.6% higher than +M Cube and +M+I Cube fed cows (P < 0.01). The coefficient of variation for day-to-day and pen-to-pen variation for cows consuming free choice mineral was 81 and 36%, respectively. There was no variation in supplemental mineral intake for +M Cube and +M+I Cube fed cows due to complete consumption of all forage cubes offered. Dietary treatment did not influence mean serum Cu and Zn concentration or plasma ceruloplasmin oxidase (Cp) activity of cows (P > 0.05). However, liver Cu concentration (mg kg^-1) of +M+I Cube fed cows tended to be higher than for the other treatment groups (P = 0.06). Calf ADG at 6 wk of age was not affected by dietary treatment of dams (P > 0.05). Copper and Zn status of calves at 6 wk of age was not different among dam dietary treatments. However, plasma Cp activity declined more rapidly in +M+I Cube calves compared with +M Cube calves (P < 0.05), which may be attributed to the presence of monensin in the +M+I Cube diet of late gestation cows. Fortified cubes may be used as an effective means of eliminating the variability in mineral intake associated with free choice consumption with no detrimental effect on mineral status of cows and their suckling calves. Key words: Forage cubes, trace minerals, monensin, pregnant cows, calves