Review of a histological intestinal approach to assessing the intestinal function in chickens and pigs

The general histological features of the small intestine are well known. However, histological intestinal alterations induced by ingested feeds have not been established. To demonstrate such a relationship; (i) the post-hatching development of intestinal villi in chickens was observed; (ii) histological intestinal differences were compared in White Leghorns and broilers; and (iii) histological intestinal alteration was investigated in fasting and refeeding treatments, using chickens and piglets. Histological intestinal recovery responses; (iv) to luminal nutrient absorption, intraluminal physical stimulation, or intravenous parenteral alimentation in fasted chickens, as well as; (v) to particle size and nutritional level of refed diets in fasted chickens and piglets were also compared. To induce compensatory enlargement of ileal villi; (vi) the jejunum was surgically resected. To reconfirm the histological intestinal alterations induced artificially; (vii) conventional feeding experiments were enforced in chickens and piglets. These fundamental investigations demonstrate that the high values of villus height, cell area and cell mitosis numbers as well as protuberated epithelial cells are hypertrophied by ingested feeds. Finally, as examples of practical use in the animal production field; (viii) useful feed resources to improve the growth performance by activating the intestinal function in chickens and piglets; and (ix) an effective forced molting method are introduced. Based on the histological intestinal alterations related with growth performance in chickens and piglets, this article reviews progress in the establishment of a histological intestinal index to assess the intestinal function.