Effects of feed additives in the diet of male dairy beef calves on physiological status and rumen microbial fermentation pre- and postweaning

Abstract

In Spain, a large number of unweaned calves from northern Europe's dairy industry are transported for intensive beef production, which could pose health risks around weaning due to the separation from their mothers. This study evaluated the impact of including different feed additives in starter concentrate on blood parameters and rumen functional development in 112 calves at the growing farm. We hypothesized that feed additives could enhance rumen function and mitigate health risks associated with transportation and intensive management. The treatments tested, against a control diet (CTL), included: blend of essential oils from plant extracts (EO), yeast-based products (SYN) and a mix of yeast probiotics, oregano-based essential oil and sodium butyrate (MIX). Each treatment was administered during the preweaning stage, with all calves transitioning to the MIX diet postweaning. In the experiment, blood and rumen samples were collected before weaning (8 weeks old) and two months after weaning (18 weeks old) for rumen fermentation and microbial population analyses. Calves were weighed upon arrival (3 weeks), at weaning (10 weeks) and two months postweaning (18 weeks) to assess performance. Results from the experiment showed that rumen fermentation profiles remained stable with regard to volatile fatty acids (VFA) concentrations and pH, indicating effective solid feed consumption and microbial activity before weaning. Postweaning, all feed additives treatments improved rumen fermentation by increasing total VFA and lowering pH, though body weight gains remained unaffected. Concentrations of bacteria and archaea increased compared to preweaning levels, protozoa were absent, and anaerobic fungi did not become established until 2 months postweaning. In conclusion, feed additives provided preweaning improved rumen development, although they did not increase productivity. The treatment should be applied preweaning, highlighting the importance of this particular window of time.