عنوان مقاله [English]
Introduction The present study was conducted to investigate the efficacy of inclusion peppermint, thyme, cinnamon essential oils and also probiotic supplement (Protexin, Probiotics International Ltd., south Petherton, UK) when added to whole milk on performance, some blood parameters, skeletal growth, and nutrient digestibility of Holstein dairy calves.
Material and Methods A total of 25 Holstein dairy calves (10 females and 15 males; 1–10 days) with 42 ± 8 kg of average birth weight were used in a completely randomized design in which calves were randomly assigned to one of five different dietary treatments including 1) control diet without inclusion of any milk essential oil supplementation, 2, 3 and 4) control diet + 40 ml (20 ml in the morning and 20 ml in evening meals) per day of peppermint, thyme, cinnamon essential oils, respectively and 5) control diet + 0.5 g per day probiotic Protexin. 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 with 10% of their birth weight until 80 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. Edible samples from calves were kept in the freezer (-20 °C) for approximate analysis experiments. Performance was analyzed in repeated measures of the mixed model (PROC MIXED) including initial BW as a covariate (covariate structure: compound symmetry) with treatment, week and their interaction as ﬁxed components and animal as random effect. Structural growth data were evaluated by GLM. Gender was considered a block but was not signiﬁcant and drop from the model. A mixed-effects regression analysis, which included calf and period as random effects and treatment and time relative to weaning (before or after) as ﬁxed effects, was then performed. Analytical model was Yij = µ + Ti + Aij + β (BWij - x) + eij, where Yij was each observation, μ was the overall mean, Ti was the fixed effect of treatment i, Aij was the random effect of calve j in treatment i, β (BWij - x) was using initial BW as a covariate and eij was residual error. Treatments means were statistically compared by the test of Duncan.
Results and Discussion The results showed that starter intake was not affected by the experimental treatments (p> 0.05). However, calves consuming cinnamon essential oil and probiotic Protexin had higher daily weight gain than other essential oils and control group (p <0.05). Calves fed milk without any additives had the lowest feed efficiency but it was highest for calves fed whole milk based on cinnamon essential oil or Protexin (p<0.05). Rumen parameters and ammonia nitrogen concentration were not affected by essential oils and probiotic intake (p> 0.05). Ruminal pH value was lower in calves were fed milk supplemented with different essential oils and Protexin than those fed control treatment (p<0.05). This decrease in pH by inclusion of essential oil and Protexin was probably due to increased ruminal propionate to acetate ratio. Addition of peppermint, thyme, cinnamon essential oils and probiotic Protexin to milk of Holstein calves had no detectable effect on the mean concentration of glucose, cholesterol, total protein, albumin, urea, aspartate-aminotransferase and alanine-aminotransferase (p> 0.05). The concentration of triglyceride in calves fed cinnamon essential oil was higher than that of other essential oils as well as probiotic Protexin (p <0.05). Inactivation of blood urea nitrogen concentration by the addition of essential oils was associated with a significant lack of ruminal ammonia nitrogen concentration. Increased ammonia nitrogen levels, more than the microbial requirement, lead to absorption through the rumen wall and hepatic vein, and most of it is converted into urea in the liver and ultimately increases in blood urea concentrations, which in this study did not affect the essential oils. Different effects of Protexin on ruminal ammonia nitrogen concentration resulted in no significant blood urea nitrogen concentration.
Hip width, heart girth, body barrel and wither height were not affected by the addition of essential oils, as well as probiotic supplementation (p> 0.05). However, body length and hip heights were higher in the calves fed cinnamon essential oil than the control group. The apparent digestibility of dry matter and organic matter in calves consumed cinnamon essential oil tended to increase than the control group (p=0.06 and p=0.07, respectively). The digestibility of crude protein and neutral detergent fiber was not affected by the type of essential oil and Protexin supplementation in Holstein dairy calves.
Conclusion Overall, essential oils especially cinnamon and probiotic Protexin may improve growth and performance by increasing daily gain and feed efficiency of Holstein dairy calves.
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