Introduction[1]: The present study was conducted to investigate the efficacy of adding Oregano L.onites and Althaea offieinalis essential oil into milk on performance, some blood parameters, skeletal growth, and metabolic responses of Holstein dairy calves. Higher milk consumption improves growth performance due to the increase in nutrients available to calves. In this experiment, it is assumed that high consumption of milk with better availability of nutrients and plant essential oils by eliminating pathogens and stabilizing the natural flora of the gastrointestinal tract improves calf function, reduces diarrhea and adequate growth during weaning.
Materials and Methods: A total of 60 Holstein dairy calves (30 females and 30 males; 7 days) with 42 ± 8 kg of average birth weight were used in a Factorial design (2 × 3) in which calves were randomly assigned to one of six different dietary treatments including 1) 6 L/d milk control without inclusion of any essential oil supplementation, 2) 6 L/d milk with Oregano L.onites essential oil, 3) 6 L/d milk with Althaea offieinalis essential oil, 4) 9 L/d milk control without inclusion of any essential oil supplementation, 5) 9 L/d milk with Oregano L.onites essential oil and 6) 9 L/d milk with Althaea offieinalis essential oil. Calves were individually housed and bedded with straw that was replaced every day. Feed and water were available ad libitum throughout the experiment. Calves were fed colostrum for 3 days and then fed high levels milk with 10% and 20% of their birth weight until 70 days of age. The rations were iso-energetic. Ruminal fluid samples were collected by esophagus tube after morning feeding at the end of study. Starter intake was recorded individually and daily. The amount of feed consumed daily was calculated throughout the experiment from the difference between the feed poured and the remaining feed. The experimental data were analyzed under the SAS 9.1 statistical program with general linear models (GLM). Comparisons of mean was done using Duncan test at a significance level of 5%.
Results and Discussion: In this study results showed that starter intake was affected by the experimental treatments (p > 0.05). Diet containing Oregano L.onites essential oil reduced feed intake in the period 56 to 70 and in the whole period with using 6 liters of milk (p < 0.05). Dry matter intake (feed dry matter with milk dry matter) in the period of 7 to 56, 56 to 70 days and in the whole period between the group receiving 6 liters and 9 liters of milk was not shown significant difference. Calves consuming 9 L/d milk in control group without inclusion of any essential oil supplementation had higher daily weight gain than other treatments (p < 0.05). The results indicated that calves fed milk without any additives had a higher feed efficiency (p < 0.05). Consuming 9 L/d milk in control group without inclusion of any essential oil supplementation had higher skeletal growth than other treatments (p < 0.05). Hip width, heart girth, body barrel and wither height were affected by the addition of essential oils supplementation (p> 0.05). Rumen parameters were not affected by essential oils (p > 0.05). Ruminal pH value was affected by the experimental treatments and in group of 6 L/d milk with Oregano L.onites essential oil had higher than other treatments (p < 0.05). Addition of Oregano L.onites essential oils to milk of Holstein calves had no detectable effect on the mean concentration of glucose, albumin, urea, aspartate-aminotransferase and alanine-aminotransferase (p > 0.05). The results showed that Feed behavior was affected by the experimental treatments (p > 0.05). Calves consuming Oregano L.onites essential oil supplementation had lowest ruminant and feed consume than other treatments (p > 0.05).
Conclusion: The results of this study showed that the addition of plant essential oils, especially oregano essential oil in high amounts of milk of Holstein calves did not lead to increased feed intake, weight gain and increased skeletal growth compared to the control group. However, the effect of oregano essential oil on feed efficiency was significant. Therefore, increasing the quantitative and qualitative growth of calves per unit time and expressing their genetic predisposition by using plant essential oils as done in this study did not lead to better performance of Holstein calves. In contrast, increasing the amount of milk consumed in infant Holstein calves improved growth performance, although the feed efficiency of the 9-liter milk group was lower than the 6-liter milk group.