Utilização de blend de óleos essenciais na dieta líquida de bezerros

Abstract

The aim of this study was to evaluate if a commercial blend of essential oils supplemented in the liquid diet would affect 1) feed intake, performance, body development, blood cells and metabolites, insulin-like growth factor-1 (IGF-1), rumen fermentation, fecal scores, and respiratory scores; and 2) digestibility, internal organs weight and histology, gene expression, and a spleen cell proliferation of pre-weaned calves. All outcomes were evaluated during pre-weaning (4 – 60 d of age) for bull and heifer calves, and carry-over effects during post-weaning (61 – 90 d of age) for heifer calves. It was enrolled 45 newborn Holstein and Hostein × Gyr crossbred calves, with body weight (BW) at birth of 32.6 ± 4.9 kg. Experimental units were assigned to either a control (CON, n = 15 heifers, and n = 8 bull calves) or a blend of essential oil supplementation treatment (BEO, n = 14 heifers, and n = 8 bull calves). The BEO was supplemented in the milk replacer (MR) with 1 g/d/calf (Apex Calf, Adisseo, China). During the pre-weaning phase, all calves were fed daily 5 L of MR/d reconstituted to 15% with water and starter provision ad libitum. During the post-weaning, heifers received 3 kg of starter/d, and ad libitum corn silage. Feed intake, fecal and respiratory scores were evaluated daily. The BW was measured every three days, while body development was recorded weekly. Blood samples were collected on 0, 30, and 60 days 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:propionate proportion - C2:C3) were measured on days 14, 28, 42, 60, 74 and 90. Apparent total nutrient digestibility was determined from d 55 to 60 of age, and on d 60 ± 1 animals were euthanized for organ weight, histology, spleen cell proliferation, and intestinal gene expression analysis. Data were analyzed independently using linear mixed models using the REML method in nlme package in R for continuous outcomes, and a non-parametric test was used for ordered categorical outcomes. There were no differences on feed intake, performance, body development, and blood metabolites during both pre-weaning and post-weaning periods for bulls and heifer calves. However, heifer’s proportion of C2:C3 during pre- and post-weaning (P = 0.05) were affected, as well as basophil (P ≤ 0.001), and platelet (P = 0.04) counts during pre-weaning, and a cumulative effect for lymphocytes (P ≤ 0.001). Heifers’ fecal scores were significant (P = 0.04) during pre-weaning, with lower values for BEO. There were no differences for digestibility, intestinal gene expression, and spleen cell proliferation assay for the bull calves. The BEO bull calves presented a lower ruminal pH, bigger pancreas, heavier intestines, bigger ileum villi, and higher cecum butyrate levels (P < 0.05). The bulls from the CON group had a heavier respiratory tract and a higher eosinophil count (P< 0.05). These results demonstrate that supplementing essential oils to dairy calves could contribute to ruminal manipulation, gut development, and immune function.