Abstract
Indigestible gut permeability markers are used to assess gut integrity and can be administered to calves via a milk meal (MM) or orally pulsed (OP). This study investigated how marker administration route (ADM_R) affects the estimation of gut permeability in relation to milk replacer (MR) fat inclusion. Thirty-two newborn Holstein calves were blocked based on their arrival sequence at the facility. Within each block of 4 calves, calves were randomly assigned to one of 2 treatments (n = 16/treatment): a MR high in lactose (HL) and a MR high in fat (HF). During the first 5 d, calves were fed 6.0 L/d followed by 7.0 L/d offered in 2 meals per day at 15% solids. To evaluate gut permeability, indigestible markers (lactulose, d-mannitol, and chromium [Cr]-EDTA) were administered in 2 periods, on Tuesday and Thursday in the third week after arrival. Within each block, calves with different MR treatments were randomly assigned to a different marker ADM_R order: MM in the first period and OP in the second (n = 16) or the opposite order (n = 16). Thus, one block of 4 calves included all combinations of MR and ADM_R. Following marker administration, urine was collected over 2 sampling periods: the first from 0 to 6 h and the second from 6 to 24 h. Measurements included weekly BW and daily MR intake and fecal scoring. Intake, growth, and fecal consistency were not affected by dietary treatments or by ADM_R. The urinary recovery of lactulose was greater in calves fed HF during the 6- to 24-h and the overall 24-h collection period. Consistently, d-mannitol recovery tended to be greater in calves fed HF during the 24-h collection. With OP administration, the urinary recovery of all markers was greater between 0 and 6 h, whereas in the 6- to 24-h period, the recovery of lactose and d-mannitol were lower. Over 24 h of collection, Cr-EDTA recovery was greater with OP. No interaction between ADM_R and MR composition was detected. This suggests that both ADM_R were equivalent in assessing the effects of dietary interventions on gut permeability. However, different ADM_R likely affected the trajectory and time spent by the markers in each segment of the gut.