Feeding a calf starter containing monensin alone or in combination with an oregano, prebiotics, and cobalt blend to Holstein calves.

Gut health is critically important for growing neonatal calves and nutritional technologies are needed to prevent disease and stress challenges. Previous work feeding Monensin (MON) in combination with an oregano, prebiotic, and Co-lactate (EOC) blend had demonstrated improved calf gut health and growth performance. The objective was to evaluate MON and EOC alone or in combination on calf growth performance. Eighty (80) new born Holstein (37) female and (43) male calves were randomly assigned to one of four treatments arranged in a 2 x 2 factorial (MON and EOC). Treatments were: 1) Control without MON or EOC added to the calf starter (CS); 2) MON: 50.8 mg/kg CS (Elanco, Greenfield, IN); 3) EOC: 44.1 mg/kg CS (Rum-A-Fresh, Ralco Inc. Marshall, MN); 4 ) MON+EOC: MON and EOC added to CS. Calves were fed colostrum followed by whole milk through weaning at 42 d, while CS was fed ad libitum through the 70 d experimental period. The MON by EOC interaction was found to be nonsignificant (P > 0.41) for growth performance. Calves fed without or with MON demonstrated similar (P > 0.70) body weight (BW; 68.7 and 68.9 kg without and with MON, respectively), while calves fed EOC demonstrated greater (P 0.47) in ADG (0.88 and 0.91 kg/d) compared with calves fed without MON, however feeding calves a CS with EOC increased (P < 0.01) ADG (0.84 and 0.95 kg/d) 13% through the 70 d experimental period compared with calves not fed EOC. Frame measurements indicated that the greater ADG was due to increased (P < 0.10) frame growth for calves fed EO compared with calves fed without EO. A Monensin by EOC interaction (P < 0.01) for serum propionate concentration demonstrated calves fed MON+EOC and EOC were greater (P < 0.05) compared with calves fed Control, while calves fed MON were intermediate and different (P < 0.05 ). Feeding calves, a CS with EOC increased (P < 0.04) IgA, IgG, and IgM concentrations compared with calves fed without EOC. A MON by EOC interaction was detected (P < 0.01) for total tract starch digestibility for calves fed EOC or MON+EOC demonstrating greater (P < 0.05) starch digestibilities than Control fed calves. These data demonstrate that EOC and MON fed in combination was not beneficial for enhancing growth performance, but that calf growth performance can be improved with EOC compared to MON.