PSIX-6 - Gastrointestinal microbiome of calves fed solid diets containing different levels and sources of NDF

Different levels and sources of NDF can modify the gastrointestinal microbiome. This study evaluated 18 Holstein calves housed in not-bedded suspended individual cages and fed one of three treatments: 22NDF - conventional starter containing 22% NDF (n = 7); 31NDF - starter with 31% NDF, replacing part of the corn by soybean hull (n = 6); and 22NDF+H - conventional starter with 22% NDF plus coast-cross hay ad libitum (n = 5). All animals received 4 L of milk replacer daily (24% CP; 18.5% fat; diluted to 12.5% solids), divided into two meals, being weaned at 8^th week of age. After weaning, animals were housed in tropical shelters, fed with the respective solid diet and coast-cross hay ad libitum for all treatments. To evaluate the microbiome, ruminal fluid samples were collected using a modified Geishauser oral probe at weeks 2, 4, 6, 8 and 10, two hours after the morning feeding, and fecal samples were collected at birth (0) and at weeks 1, 2, 4, 8 and 10. The microbial community was determined by sequencing V3 and V4 region amplicons of the 16S rRNA gene that was amplified by PCR and sequenced by the Illumina MiSeq platform. Ruminal microbiome had no differences in diversity for the effects of weeks, treatments or interaction of both factors (Table 1). In feces, the diversity indices and evenness were higher for 22NDF+H when compared to 22NDF, with no difference for 31NDF. All indices were significantly affected by calves age. At birth, calves had the greatest diversity and richness. Week 1 and 2 had less evenness and diversity. Bacteroidota, Firmicutes_A and Firmicutes_C were the most abundant phylum in rumen and feces. The supply of hay was only effective in modifying the fecal microbiome of dairy calves, suggesting a resilience in the ruminal microbiome.