Performance of crossbred dairy Friesian calves fed two levels of Saccharomyces cerevisiae: intake, digestion, ruminal fermentation, blood parameters and faecal pathogenic bacteria

Sampling and analysis of rumen fluid As described in Kholif et al. (2015), on the last day of the experiment (i.e. day 90), ruminal contents were sampled at 0, 3 and 6 h post-morning feeding to determine the pH and concentration of fermentation end-products. About 100 ml of rumen content was collected once at each sampling time from the ventral sac by using a stomach tube, and then the sample taken from each calf was strained through four layers of cheesecloth. The pH of ruminal fluid was measured immediately after collection using a pH meter (Orion™ Star A211 pH Benchtop Meter, Thermo Scientific, Beverly, MA, USA).One of the major challenges facing the animal production industry in developing countries is to improve efficiency of production and to maintain feed utilization. Many attempts have been made by researchers to overcome these challenges, such as including the incorporation of antimicrobials and other natural products into animal feeds (Ahmed et al. 2015; Rojo et al. 2015; Morsy et al. 2016). Feed additives of microbial origin, ionophores and antibiotics have become a common practice in ruminant nutrition; however, most studies have been conducted with lactating cows or in vitro, with few studies on pre-weaned calves