Gastrointestinal structure and function of preweaning dairy calves fed a whole milk powder or a milk replacer high in fat

The composition of milk replacer (MR) for calves greatly differs from that of bovine whole milk (WM), which may affect gastrointestinal development of young calves. In this light, the objectives of the current study were to compare gastrointestinal tract structure and function in response to feeding liquid diets having a same macronutrient profile (e.g. fat, lactose, protein) in calves in the first month of life. Eighteen male Holstein calves (46.6 ± 5.12 kg; 1.8 ± 0.55 d of age at arrival; mean ± SD) were housed individually. Upon arrival, calves were blocked based on age and arrival day and within a block were randomly assigned to either a whole milk powder (WP; 26% fat, DM basis, n = 9) or a MR high in fat (MR, 25% fat, n = 9) fed three times 3.0 L daily at 135 g/L through teat buckets. On d 21, gut permeability was assessed with indigestible permeability markers (Cr-EDTA, lactulose, and D-mannitol). On d 29 after arrival, calves were euthanized: the weight of the total forestomach without contents was greater in WP-fed calves. Furthermore, duodenum and ileum weights were similar between treatment groups, but distal jejunum and total small intestine weights were greater in WP-fed calves. The surface area of the duodenum and ileum did not differ between treatment groups; however, the surface area of the proximal jejunum was greater in calves fed WP. Urinary lactulose and Cr-EDTA recoveries were greater in calves fed WP in the first 6 h post marker administration. Tight junction protein gene expression in the proximal jejunum or ileum did not differ between treatments. The free fatty acid and phospholipid fatty acid profiles in the proximal jejunum and ileum differed between treatments and generally reflected the fatty acid profile of each liquid diet. Feeding WP or MR altered gut permeability and fatty acid composition of the GIT and further investigation are needed to understand the biological relevance of the observed differences.

犊牛代乳粉（milk replacer, MR）的组成与牛乳全脂乳（bovine whole milk, WM）差异显著，这可能会影响幼犊的胃肠道发育。鉴于此，本研究旨在比较出生后首个月内的犊牛，在饲喂宏量营养素组成（如脂肪、乳糖、蛋白质）一致的液态日粮时，其胃肠道结构与功能的差异。本试验共选用18头雄性荷斯坦犊牛（初始体重46.6±5.12 kg，到场日龄1.8±0.55 d，数据以平均值±标准差表示），采用单栏饲养。到场后，根据犊牛日龄与到场日期进行区组划分，每个区组内的犊牛被随机分配至全脂乳粉组（whole milk powder, WP；干物质基础脂肪含量26%，n=9）或高脂代乳粉组（MR，干物质基础脂肪含量25%，n=9），通过奶桶饲喂，每日3次，每次3.0 L，日粮浓度为135 g/L。试验第21天，采用不可消化通透性标志物（铬-乙二胺四乙酸（Cr-EDTA）、乳果糖（lactulose）与D-甘露醇（D-mannitol））评估犊牛的肠道通透性。到场后第29天，对所有犊牛实施安乐死：全脂乳粉组犊牛的无内容物总前胃重量显著高于代乳粉组。此外，两组犊牛的十二指肠与回肠重量无显著差异，但空肠远端与总小肠重量在全脂乳粉组犊牛中更高。两组犊牛的十二指肠与回肠表面积无显著差异；然而，全脂乳粉组犊牛的近端空肠表面积更大。标志物灌服后最初6 h内，全脂乳粉组犊牛的尿乳果糖与Cr-EDTA回收率更高。近端空肠或回肠的紧密连接蛋白基因表达在两组间无显著差异。近端空肠与回肠的游离脂肪酸及磷脂脂肪酸组成在两组间存在差异，且整体匹配各自液态日粮的脂肪酸组成。饲喂全脂乳粉或代乳粉会改变犊牛的肠道通透性与胃肠道脂肪酸组成，后续还需进一步研究以明确上述观测差异的生物学意义。