Oregano Essential Oil as a Natural Plant Additive Affects Growth Performance and Serum Antibody Levels by Regulating the Rumen Microbiota of Calves.

This experiment aimed to investigate whether supplementation of calves with different doses of oregano essential oil (OEO) could promote the development of the gastrointestinal tract and enhance the immune ability of calves by regulating the rumen microbiota. Twenty-four 70-day-old healthy and disease-free Holstein male calves were randomly divided into four groups, with the control group fed a basal diet, and the treatment group provided 4 g, 6 g, and 8 g of oregano essential oil per day in addition to the basal diet. After the 14-day pre-test, a 56-day formal test was conducted. At days 0 and 56 of the standard test period, calves were weighed, the average daily weight gain of calves during the test period was calculated, and serum samples were collected to measure the concentration of immunoglobulins (IgA, IgG, and IgM) in the serum; at day 56 of the formal test period, rumen fluid was collected from the calves, and 16SrRNA was sequenced to analyze changes in the rumen microbiota of the calves. The changes in the rumen microbiota of calves were analyzed by 16SrRNA sequencing. The results of the study showed that (1) OEO supplementation in calves significantly increased end weight and average daily gain (p < 0.05); (2) OEO supplementation in calves significantly increased serum concentrations of immunoglobulins IgA and IgM (p < 0.05); (3) OEO supplementation in calves significantly increased the abundance and diversity of rumen microbial organisms (p < 0.05); (4) OEO supplementation in calves significantly regulates the relative abundance of some species, and biomarkers with significant differences were screened by LEfSe analysis: g_Turicibacter, g_Romboutsia, f_Peptostreptococcaceae, f_Clostridiaceae, g_Clostridium_sensu_stricto_1, o_Clostridiales, g_unclassified_f_Synergistaceae, c_Coriobacteriia, o_Coriobacteriales, f_Atopobiaceae, g_Olsenella, p_Actinobacteriota, g_Defluviitaleaceae_UCG-011, f_Defluviitaleaceae, o_Corynebacteriales, g_Corynebacterium, f_Corynebacteriaceae, g_Shuttleworthia, f_Hungateiclostridiaceae, o_norank_c_Clostridia, g_Saccharofermentans, g_Streptococcus, f_Streptococcaceae, g_unclassified_o_Oscillospirales, and f_unclassified_o_Oscillospirales (p < 0.05, LDA ≥ 3); and (5) OEO supplementation in calves significantly enriched the metabolism of cofactors and vitamins pathway (p < 0.05). (6) Using Superman's correlation analysis, we screened unclassified_c_Clostridia, Shuttleworthia, and Christensenellaceae_R-7_group, three beneficial strains for calves. (7) Daily supplementation with 8g of OEO significantly affected rumen microbiota regulation in calves.

Calf starter containing a blend of essential oils and prebiotics affects the growth performance of Holstein calves.

Essential oils extracted from specific plants can exhibit antimicrobial properties that make them potential antibiotic alternatives. The objective was to evaluate an essential oil and prebiotic combination (EOC) on the growth, development, and health status of growing neonatal calves. Forty Holstein newborn calves were blocked by birth date and alternately assigned to 1 of 2 treatments. Treatments were a pelleted calf starter (CS) without (control) or with EOC at 44.1 ppm. Calves were fed the experimental CS for ad libitum consumption from 3 d of age through the end of the 70-d experiment. Calves were fed 2 L of whole milk twice daily to 10 d of age, then 3 L twice daily through d 35, and then fed 3 L once daily with abrupt weaning occurring after 42 d of age. The average daily gain (0.78 and 0.87 kg/d for control and EOC, respectively) was greater for calves fed EOC compared with calves fed the control. Calves fed EOC demonstrated greater dry matter intake (1.63 and 1.74 kg/d) compared with calves fed the control. Feed conversion ratio (0.62 and 0.65 kg of gain/kg of dry matter intake) was greater for calves fed EOC compared with calves fed the control. At 70 d of age, calves fed EOC demonstrated increased body frame measurements (hip height, body length, heart girth, abdominal girth, and pastern) compared with calves fed the control. The incidence of scours score 4 (mild diarrhea) was 3.5 incidences lower for calves fed EOC compared with calves fed the control, whereas the incidence of scours score 5 (severe diarrhea) for calves fed EOC was 0.5 incidences lower than calves fed the control. Blood concentrations of IgG and IgM on d 14, IgA on d 28, and total serum protein on d 42 were all greater for calves fed EOC compared with calves fed the control. The blood volatile fatty acid concentrations were greater for calves fed EOC compared with calves fed the control, which indicated enhanced ruminal development. Total-tract digestibility of dry matter, crude protein, acid detergent fiber, neutral detergent fiber, starch, and many minerals were increased for calves fed EOC compared with calves fed the control. The inclusion of an EOC blend into a CS demonstrates promising benefits for enhancing calf growth, ruminal development, gut health, nutrient digestibility, and immunity. The use of an EOC blend can be a plausible alternative to feeding subtherapeutic antibiotics for improving calf performance, health, and immunity.