Abstract
The aim was to evaluate the effect of different feed additives on intake, performance, and fecal consistency index (FCI) of dairy calves from 6–60 d of age and its residual effect 15 d after weaning. Fifty Holstein calves (38 ± 1.0 kg BW) were fed 5 L/d of milk plus starter feed until weaning, and corn silage and concentrate after weaning. The treatments were: control (CON), monensin (MON; 30 mg/kg of starter), probiotic E. faecium (PROB; 70 mg/kg of starter), essential oils (EO; 300 mg/kg of starter), or PROB + EO (EOPROB). Fecal score and dry matter intake (DMI) were measured daily, and animals were weighed every 15 d. A DNA extraction from feces was performed to identify the presence of microorganisms (E. coli, Hafnia, Shiguella, Lactobacillus spp, Enterococcus spp, and Enterococcus faecium NCIMB 10415) by PCR. Two 72-h digestibility trials were performed at days 20–28 and 50–56, by total fecal collection. The DMI before weaning was greater for EO (903.0 g/d) compared with MON (794.3 g/d) and EOPROB (783.1 g/d). The FCI decreased during pre-weaning for EO and MON. Average daily gain (ADG) and feed efficiency (FE) did not differ among treatments before weaning. After weaning, DMI and FCI did not differ among treatments. The EO had greater ADG (917.5 g/d) compared with CON (615.8 g/d) and PROB (592.6 g/d). The FE improved with EO (0.72 g/g) over CON (0.36 g/g), MON (0.49 g/g), and PROB (0.36 g/g). The PCR results showed absence of E. faecium NCIMB 10415 in animals fed PROB and CON. Animals fed PROB had greater intake of CP and NDF than animals fed EOPROB. The EO can be added to the dairy calf ration to improve fecal score and increase DMI. The pre-weaning FCI decrease with MON and increase with PROB.
Highlights
Animals fed probiotic E. faecium (PROB) had greater (P < 0.05) intake of dry matter (DM) and crude protein (CP) when compared with EOPROB and greater (P < 0.05) neutral detergent fiber (NDF) intake when compared with CON and EOPROB (Table 2)
Before weaning, the average dry matter intake (DMI) over the course of the experiment was greater (P = 0.046) for essential oils (EO) (903.0 g/d) compared with MON (749.3 g/d) and EOPROB (783.1 g/d; Table 3), while no difference was found between the PROB and CON treatments (843.9 and 845.0 g/d, respectively)
At day 35, all animals were dehorned, a very stressful procedure, but we found that this procedure was less likely to affect the health of animals fed EO and MON, compared with PROB-fed calves
Summary
Monensin is an ionophore antibiotic that exhibits anticoccidial and antibacterial properties. It is commoly used, commercially, as a coccidiostat for poultry and as a growth promoter for ruminants [4]. The use of ionophores in livestock production has been banned in several countries due to development of monensin resistance by some bacteria [5]. Some products such as probiotics and essential oils have been used as alternatives to antibiotics, aiming minimize environmental risks and ensure food safety [3,6]
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