The effect of different levels of licorice root powder in the starter diet on performance, skeletal growth indicators and blood cells of Holstein suckling calves

Background and objectives: Using of antibiotics as promoters of growth has widely been prohibited in animal nutrition, because antibiotic resistance has become a major clinical and public health problem. This issue has caused researchers to look for a suitable alternative to antibiotics in animal nutrition, among which probiotics and plant additives can be mentioned. Licorice with the scientific name Glycyrrhiza glabra and the English name licorice, is a perennial plant from the legume family. Licorice root has various compounds, one of which is glycyrrhizin, which is about 50 times sweeter than sugar. In several studies, licorice plant has been used as a supplement in combination with other plants and secondary plant compounds as a feed additive in suckling calves and sheep. However, the use of licorice alone in animal diets has rarely been investigated, therefore, the aim of this study was to investigate the effect of using different levels of licorice root powder (LRP) on the performance, weaning age and weight, blood cells and skeletal growth indicators of Holstein suckling calves.
Materials and methods: In this experiment, 30 Holstein calves (15 males and 15 females) from three days to two weeks after weaning with an average weight of 40±1.9 kg were used with 3 treatments and 10 replications as a factorial trial in a completely randomized design. Starter diets containing 0, 2.5 and 5% LRP (replaced with wheat bran). Calves had free access to diet and fresh water all times. The weaning criteria was to consume 1 kg of starter per day for 3 consecutive days, and then the calves were gradually weaned during 4 days. The measured traits were dry matter intake (DMI), daily weight gain (DWG), feed conversion ratio, weaning age, feces consistency, skeletal growth indicators and blood cells. Daily DMI was measured with a digital scale. Feces consistency was checked by visual evaluation method. From birth to the end of the experiment the calves were weighed every week with a digital scale. Calves were examined every week in terms of skeletal growth parameters. Blood samples were taken from the calves on three times (three and six weeks old and two weeks after weaning).
Results: The DMI in calves fed diets containing LRP was significantly higher than the control group (P<0.05). The DMI in the entire period of experiment was 738.7 g/d with 5% LRP and 538 g/d with control diet. The DWG in before and after weaning was affected by the treatments, and the calves fed with starter diets containing LRP had a higher DWG than the control group (P<0.05). Compared to the control group, the calves fed experimental diets with LRP had a lower weaning age (P<0.05). The weaning age in calves fed with LRP was about 10 days lower than the control group. The effect of experimental diets on the feces consistency and skeletal growth parameters of calves was not significant. Blood cells, including the number of RBC, platelets, WBC, and the percentage of lymphocytes, granulocytes, and monocytes, and blood hemoglobin concentration are not affected by feeding with starter diets.

Conclusion: The results showed that the addition of LRP in the starter diet of Holstein dairy calves increases DMI and weaning weight, improves performance and decreases weaning age, and therefore it can be used 5% LRP to improve the nutritional system in calves.