Partial corn replacement by soybean hull, or hay supplementation: Effects of increased NDF in diet on performance, metabolism and behavior of pre-weaned calves

The solid diet is a determining factor for ruminal development in calves. However, it is still unclear what is the optimal content and the best way to include fiber in the diet of pre-weaned calves. Thirty-five Holstein calves were used in a randomized block design, considering the sex, weight and birth date of the calves as blocking factor. Animals were housed in individual suspended cages without bedding and assigned to one of three treatments: (1) 22NDF: conventional ground starter concentrate with 220 g neutral detergent fiber (NDF)/kg dry matter (DM); (2) 31NDF: ground starter with 310 g NDF/kg DM, with partial replacement of corn by soybean hull; and (3) 22NDFhay: conventional starter with 220 g NDF/kg DM plus coast-cross hay fed separately ad libitum. The calves received 4 L of milk replacer with 12.5% solids, divided into two meals daily. Feed intake was measured daily. Weight gain and metabolic indicators of intermediate metabolism were evaluated weekly. Ruminal fluid was collected on week 4, 6 and 8 of age. The experiment lasted for 56 days. The increase of the NDF content in the concentrate starter up to 310 g/kg DM with replacement of corn by soybean hull or hay supplementation did not change the starter intake and performance of calves at weaning. The 31NDF diet resulted in higher concentration of short chain fatty acid (SCFA) at week 4, but 22NDF diet increased total SCFA concentration at week 8. Hay supplementation increased rumination time, and decreased non-nutritive oral behaviors during last week preweaning. Dietary NDF levels used in the ground starter concentrate may be higher than current recommendations without reducing intake and performance, as long as the NDF source has low ADF and lignin.