Oregano extract fed to pre-weaned dairy calves. Part 2: Effect on ruminal and intestinal morphology of pre-weaned calves

Abstract

The aim of this study was to evaluate the effects of oregano extract (Origanum vulgare) supplementation on the histological and morphological variables of the gastrointestinal tract (GIT) of suckling dairy calves. Ten Holsteins calves from commercial dairy farms were fed 6 L/day of milk replacer, calf starter ad libitum from the first day of the trial, as well were fed hay ad libitum from the third week of the start of the study period. Calves had free access to drinking water during the trial. Calves were distributed in two treatments: (1) basal diet without additive (CON); (2) the same diet, but containing 60 mg/kg body weight/day of oregano extract (OR). Weaning occurred on the 53rd day of the trial (56th day of life). On the 54th day of the trial, all calves were euthanized and the full and empty tracts were weighed and tissue samples from the rumen, jejunum, cecum and colon were also taken for histological analysis. The variables observed were: full and empty weight of the gastrointestinal tract; papillae height, tunica of the submucosa, number of papillae, number of branches, branch height and number of papillae/branch in the rumen; number of glands, villi length, mucosal thickness, submucosal thickness, muscle thickness in the jejunum, cecum and colon. Oregano extract increased the empty weight of the abomasum without changing the weight of the other segments. In the rumen, OR-supplemented calves showed lower number of branches, branch height and number of papillae/branches. Calves in CON tended to have thicker muscle layer at the jejunum than calves in OR. Nutrient fractions intake were positively correlated with empty weights of rumen, reticulum, omasum, abomasum and large intestine, but they did not correlate with full and empty weights of small intestine. The intake of the solid diet was not related with GIT organs’ weight. Rumen papillae length, jejunum mucosal and submucosal layer thickness values were positively related with nutrients intake, while rumen submucosal layer thickness were negatively related with nutrients intake. Most histological variables evaluated were not affected by OR supplementation. Essential oils are promising replacements for antibiotics. However, the dose, administration routes and supply time deserve further studies, allowing for better performance and health of the animal to be achieved.