Effects of a blend of essential oils in milk replacer on performance, rumen fermentation, blood parameters and health scores of dairy heifers
Authors: Campolina Joana P. , Coelho Sandra G. , Belli Anna Luiza , Machado Fernanda S. , Pereira Luiz G. R. , Tomich Thierry R. , Carvalho Wanessa A. , Silva Rodrigo O. S. , Voorsluys Alessandra L. , Jacob David V. , Campos Mariana M. 
Published: March 2020

The objective of this study was to evaluate how the inclusion of a blend of essential oils in milk replacer (MR) affects different outcomes of dairy heifers. The outcomes evaluated: feed intake, performance, body development, blood cells and metabolites, insulin-like growth factor-1 (IGF-1), rumen fermentation, fecal scores and respiratory scores. All outcomes were evaluated during pre-weaning (4 – 60 d of age), and carryover effects on post-weaning (61 – 90 d of age) periods. The experimental units utilized were 29 newborn Holstein × Gyr crossbred dairy heifers, with genetic composition of 5/8 or more Holstein and 3/8 or less Gyr and body weight (BW) at birth of 32.2 ± 5.2 kg. Experimental units were randomly assigned to either a control group (CON, n = 15) or a treatment group, consisting of supplementation of a blend of essential oils (BEO, n = 14) with1 g/d/calf (Apex Calf, Adisseo, China). During the pre-weaning phase, all heifers were fed 5 L of MR/d reconstituted at 15% (dry matter basis), divided into two equal meals. Water and starter were providedad libitum. During the post-weaning, animals received a maximum 3 kg of starter/d, andad libitumcorn silage, divided into two meals. The outcomes feed intake, fecal and respiratory scores were evaluated daily. BW was measured every three days, while body development was recorded weekly. Blood samples were collected on 0, 30 and 60 d of age for total blood cell count, weekly to determinate ß-hydroxybutyrate, urea and glucose, and biweekly for IGF-1. Ruminal parameters (pH, volatile fatty acids, ammonia-N and acetate:proprionate proportion - C2:C3) were measured each 14 days. A randomized complete block design with an interaction between treatment and week was the experimental method of choice to test the hypothesis of effect of BEO on all outcomes. An ANOVA procedure was used for continuous outcomes and a non-parametric test was used for the ordered categorical outcomes both adopting a C.I. = 95%. Results indicated that there was not enough evidence to accept the alternative hypothesis of effect of BEO in MR on: feed intake, performance, body development and blood metabolites during both pre-weaning and post-weaning periods. However, results indicated that the inclusion of BEO in MR significantly affects the proportion of C2:C3 during pre and post-weaning (P ≤ 0.05). Similarly, the effect is significant for basophil (P ≤ 0.001) and platelet (P ≤ 0.05) counts in pre-weaning. The interaction between week and treatment was also significant for lymphocytes (P ≤ 0.001), revealing a long-term treatment immunological effect. Lastly, the effect on fecal scores was also significant (P ≤ 0.05) during pre-weaning, with lower values for BEO. BEO contributed for ruminal manipulation on pre-weaning and carry over effect on post-weaning; immunity improvement and a decrease morbidity of neonatal diarrhea in pre-weaning phase.