The effect of maternal supply of rumen-protected protein during the dry period on the microbial composition of dairy cows' colostrum and calves' feces.

Colostrum production starts approximately 6 weeks before calving and ends abruptly after giving birth. For multiparous cows, this means that colostrum production occurs during the dry period. The dry period diet is characterized by a low energy and protein level. However, at the end of gestation, nutrient demand for the growing prenatal calf is at its maximum. Colostrum is essential for survival of the newborn calf. Interestingly, colostrum harbors a rich microbial community. The latter is believed to contribute in the colonization of the neonatal gut. However, the relation between the bacteria present in colostrum and in the feces of the calf is poorly understood. In the present study, we first aimed to determine the microbial composition of colostrum from mothers fed different crude protein (CP) levels during the dry period and next to investigate associations between the microbial composition of colostrum and that of calves feces.Multiparous dairy cows (n=71) were randomly assigned to one of two different dry period diets, a diet with a low CP level and with a high CP level by addition of rumen undegradable protein. Colostrum was collected within one hour after calving and IgG concentration was estimated with the brix refractometer. Forty-nine calves were enrolled in the trial with a 2x2 factorial design, with pre- and postnatal treatment as the two independent variables. Calves received 3x2L of colostrum within 2, 6 and 24h after birth, respectively. Meconium and feces were collected solely from female (n = 18) calves per rectum by digital palpation, immediately after birth and before colostrum administration and at day 3 of age, respectively. Microbial DNA was extracted from meconium (n=9) and feces (n=15) with the PowerFecal Pro DNA kit (Qiagen, Germany) and from colostrum (n=49) with the PowerFood microbial kit (Qiagen, Germany). Amplicon sequencing of the bacterial V3-V4 region of the 16S rRNA gene was performed using the Illumina MiSeq V3-technology (Macrogen, South-Korea).