Gastrointestinal morphology of preweaned dairy calves fed whole milk powder or a high-fat milk replacer.

The objective of this study was to evaluate effects of feeding a milk replacer (MR) of similar macronutrient composition to bovine whole milk and whole milk powder on growth, health and gastrointestinal (GIT) morphology. Male Holstein calves (n = 18, 1–3 d of age) were individually housed and blocked by day of arrival and age. Calves were not offered any solids to control nutrient intake and were fed 3L (135g/L) 3 times daily of either: 1) whole milk powder (WM, 26.0% fat, 24.5% protein, 38.0% lactose, n = 9); or 2) high fat MR (HF, 25% fat, 22.5% protein, 38.1% lactose, n = 9). BW (BW) was measured weekly and feed intake was recorded daily. Calves were euthanized at d 28 to obtain organ weights and intestinal samples to assess GIT morphology via histological analysis. Data were analyzed in SAS software using repeated measures GLIMMIX for weekly measures and Proc MIXED was used for dissection data. Weekly intake of MR (WM = 8.5L vs, HF = 8.6L; SE = 0.16L; P = 0.3) and BW at the time of dissection (WM = 56kg vs HF = 55kg; SE = 1.8; P = 0.8) did not differ between treatments throughout the experiment. Similarly, feed efficiency and metabolizable energy (ME) intake by week did not differ between treatment groups. In foregut digestive compartments, rumen (498g vs. 365g; SE = 39.6; P = 0.02), reticulum (100g vs. 73g; SE = 7.9g; P = 0.04), and omasum (215g vs. 148g; SE = 17.6g; P = 0.02), weights were found to be greater in WM than HF, respectively. Weights of the duodenum and ileum were similar between treatment groups but jejunum weight was greater in WM compared with HF (1462g vs. 1172g; SE = 63.7g; P = < 0.0001). Surface area of the duodenum and ileum did not vary between treatment groups; however, surface area of distal jejunum trended to be greater in WM than HF (1.1 vs. 0.99; SE = 0.08; P = 0.1). In visceral organs, no differences were found, albeit spleen weight was higher in HF than WM (270g vs. 2737g; SE = 10.2g; P = 0.01). Overall, the results suggest that the composition, other than macronutrient composition, of the liquid diet may influence GIT morphology during the preweaning period without affecting growth or feed efficiency.