Weaning age influences the severity of gastrointestinal microbiome shifts in dairy calves
Twenty female Holstein dairy calves were randomly assigned at birth to be weaned at 6 (early) or 8 (late) weeks of age. Calves were offered 6 L from d 1 to 3, 7 L from d 4 to 6, and 8 L from d 7 until their respected time of step-down weaning. The early-weaning group was stepped down to 4 L/d on d 36 and weaned on d 43. The late-weaning group was stepped down to 4 L/d on d 50 and weaned on d 57 . Rumen and faecal samples were collected on d 35, 49 and 63 of life. Rumen fluid and faecal samples were used for DNA extraction .The V4 region of 16S rRNA gene was targeted for PCR amplification using modified F515/R806 primers.