Wageningen Livestock Research, Wageningen University & Research, Wageningen, the Netherlands.
Wageningen University & Research, Animal Nutrition Group, Wageningen, the Netherlands.
PLoS One. 2022 Sep 1;17(9):e0273852. doi: 10.1371/journal.pone.0273852. eCollection 2022.
High calcium (Ca) intake and fine limestone reduces precaecal phosphorus (P) absorption independently of P solubility in broilers. This study aimed to determine whether dietary total Ca: total P ratio (Ca:P) and limestone particle size (LPS) affect gene expression of P transporters in the small intestine. A total of 384 one-day-old Ross 308 male broiler chickens received diets low (0.50), medium (1.00) or high (1.75) in Ca:P containing either fine (160 μm) or coarse (1062 μm) limestone, in a 3×2 factorial arrangement. Expression of Ca- and P-related genes were determined using real-time quantitative PCR (RT-qPCR) in duodenum and jejunum. Increasing dietary Ca:P decreased duodenal calcium-sensing receptor (CaSR), calbindin-D28k (CaBP-D28k), plasma membrane Ca-ATPase 1 (PMCA1) and sodium-coupled P cotransporter type IIb (NaPi-IIb), but not transient receptor potential canonical 1 (TRPC1) mRNA. This effect was greater with fine limestone when Ca:P increased from low to medium, but greater with coarse limestone when increased from medium to high. A similar inhibitory effect was observed for jejunal CaBP-D28k expression where increasing dietary Ca:P and fine limestone decreased CaSR mRNA, while dietary Ca:P decreased TRPC1 mRNA only for coarse limestone. It also decreased jejunal NaPi-IIb mRNA irrespective of LPS. Dietary treatments did not affect jejunal PMCA1 mRNA expression or that of inorganic phosphate transporter 1 and 2 and xenotropic and polytropic retrovirus receptor 1 in both intestinal segments. Dietary Ca increase reduced mucosal claudin-2 mRNA in both segments, and jejunal zonula occludens-1 (ZO-1) mRNA only for coarse limestone. In conclusion, increasing dietary Ca:P reduced expression of duodenal P transporters (NaPi-IIb) in a LPS dependent manner, hence Ca induced reduction in intestinal P absorption is mediated by decreasing P transporters expression. Dietary Ca reduces Ca digestibility by downregulating mRNA expression of both Ca permeable claudin-2 and Ca transporters (CaBP-D28k, PMCA1).
高钙（Ca）摄入和细石灰石可独立于家禽盲肠中磷（P）的溶解度降低预肠 P 吸收。本研究旨在确定日粮总 Ca：总 P 比（Ca：P）和石灰石粒度（LPS）是否影响小肠中 P 转运体的基因表达。总共 384 只 1 日龄的 Ross 308 雄性肉鸡接受了低（0.50）、中（1.00）或高（1.75）Ca：P 日粮，其中含有细（160μm）或粗（1062μm）石灰石，采用 3×2 析因设计。使用实时定量 PCR（RT-qPCR）在十二指肠和空肠中测定 Ca 和 P 相关基因的表达。日粮 Ca：P 降低了十二指肠钙敏感受体（CaSR）、钙结合蛋白-D28k（CaBP-D28k）、质膜 Ca-ATP 酶 1（PMCA1）和钠偶联 P 协同转运蛋白 IIb（NaPi-IIb），但不影响瞬时受体电位经典通道 1（TRPC1）mRNA。当 Ca：P 从低到中增加时，细石灰石的效果更大，但当 Ca：P 从中等到高增加时，粗石灰石的效果更大。空肠 CaBP-D28k 表达也观察到类似的抑制作用，其中增加日粮 Ca：P 和细石灰石降低了 CaSR mRNA，而日粮 Ca：P 仅降低了粗石灰石的 TRPC1 mRNA。它还降低了空肠 NaPi-IIb mRNA，而与 LPS 无关。日粮处理不影响空肠 PMCA1 mRNA 表达或无机磷酸盐转运体 1 和 2 和异嗜性和多嗜性逆转录病毒受体 1 在两个肠段中的表达。日粮 Ca 增加降低了两个肠段的黏膜紧密连接蛋白-2（claudin-2）mRNA，而仅粗石灰石降低了空肠 zonula occludens-1（ZO-1）mRNA。总之，增加日粮 Ca：P 以 LPS 依赖的方式降低了十二指肠 P 转运体（NaPi-IIb）的表达，因此，Ca 诱导的肠道 P 吸收减少是通过降低 P 转运体的表达来介导的。日粮 Ca 通过下调钙通透紧密连接蛋白-2 和钙转运体（CaBP-D28k、PMCA1）的 mRNA 表达来降低 Ca 的消化率。
