Effects of feeding colostrum volume at 6%, 8%, 10%, or 12% of birth body weight on efficiency of IgG absorption, gastric emptying, and postfeeding behavior in Holstein calves.

Our objective was to evaluate how feeding colostrum at different volumes at the first feeding affects IgG absorption, gastric emptying, and calf behavior. Female Holstein calves (n = 88) were enrolled in a randomized block design to receive a single colostrum volume corresponding to 6%, 8%, 10%, or 12% of birth body weight (BBW). A subset of animals in 8 blocks (n = 32 calves) also received a gastric emptying marker acetaminophen (Ac) at a dose of 150 mg/kg metabolic body weight (BBW^0.75). Colostrum was administered within 2 h of birth via esophageal tube feeder. Blood samples were collected before (0 h) and 24 h after feeding. For the calves receiving Ac, plasma samples were also collected at 2, 4, 6, 8, 10, and 48 h after feeding. Colostrum and 24-h serum IgG concentrations were measured using radial immunodiffusion. Apparent efficiency of absorption (AEA) was calculated from 24-h serum IgG concentrations. Plasma Ac concentration was determined using an enzymatic colorimetric assay, and the proportion of Ac remaining in the stomach (Ac_s) at 8 h was modeled. Audio and video recordings of calf behavior during the first 2 h after feeding were analyzed with a custom ethogram. Data analysis was performed using mixed models or Fisher's exact tests as appropriate. Results are reported as LSM with 95% CI unless otherwise specified. The mean (range) BBW of calves was 40 (31.8-49.1) kg. Pooled colostrum had a median (range) Brix value of 24.2% (21.2%-29.6%) and IgG concentrations of 86.7 g/L (73.2-121.1 g/L). Calves in the 6%, 8%, 10%, and 12% groups were fed median (range) colostrum volumes (L) of 2.3 (2.0-2.8), 3.1 (2.5-3.9), 4.0 (3.5-4.5), and 4.8 (4.2-5.6), respectively. The 24-h serum IgG concentrations (g/L) were lowest in the 6% group (28.8 [25.8-31.8]), increased to 37.4 (34.4-40.4) in the 8% group, and were highest in the 10% and 12% groups (41.1 [38.1-44.1] and 43.4 [40.4-46.4], respectively). Group differences were observed for AEA (%), which gradually declined with an increasing feeding rate and was highest in the 6% and 8% groups (47.8 [44.9-50.7] and 46.2 [43.3-49.0], respectively), declined to 41.0 (38.1-43.9) in the 10% group, and was lowest at 36.3 (33.5-39.2) in the 12% group. At 8 h, Ac_s (%) was 50.4 (43.8-57.0), 55.3 (49.2-61.5), 57.9 (51.8-64.0), and 65.5 (59.2-71.8) of the original dose in the 6%, 8%, 10%, and 12% groups, respectively. Group differences in behavior were identified for kicking, a colic-like behavior, which was observed only in the 10% (n = 21 kicks total) and 12% (n = 40 kicks total) groups. Feeding a single colostrum meal equivalent to 8% or 10% of BBW within 2 h after birth offers a compromise in terms of IgG absorption, gastric emptying, and calf behavior. A larger volume (12% BBW) resulted in marginal improvement in serum IgG concentration, reduced AEA and gastric emptying, and was associated with increased colic-like behaviors.