The effect of feeding regimen on apparent and true ileal nitrogen digestibility for rats fed diets containing different sources of protein

Abstract

A standard protocol is required for carrying out routine ileal nitrogen (N) digestibility rat bioassays. The aim of this study was to determine the effects of feeding regimen on ileal N digestibility in rats fed diets containing different protein sources and chromic oxide as an indigestible marker. The experimental design was seven diets (protein-free (PF), enzyme-hydrolysed casein (EHC), lactalbumin (LAC), wheat gluten (GLU), ®sh ®llets (FIS), soy protein isolate (SOY), zein) by three feeding regimens (frequent, meal, ad libitum) with 10 rats per diet. In frequent feeding, food was provided for eight 10 min periods between 09:00 and 16:00; in meal feeding, food was provided for one 3 h period at 09:00; in ad libitum feeding, food was available at all times. Rats were fed for 8 days, killed and digesta were collected from the terminal 20 cm of the ileum. The diets and freeze-dried digesta were then analysed for N and chromium (Cr). There were statistically signi®cant effects of feeding regimen on ileal digesta weight, ileal N/Cr ratio and apparent (AND) and true (PF TND, EHC TND) N digestibility. Mean N digestibilities, averaged over four dietary treatments (LAC, GLU, FIS, SOY), for the frequent, meal and ad libitum feeding regimens respectively were: AND, 88.8, 90.4, 85.8; PF TND, 94.9, 96.4, 97.0; EHC TND, 92.7, 94.0, 95.6. Although the N digestibilities were higher for rats on meal feeding compared with frequent feeding, the only statistically signi®cant differences were for the lactalbumin treatment, and these were small in absolute terms. This study demonstrated that meal feeding was suitable and frequent feeding was unnecessary for most protein sources tested, and that ad libitum feeding was not ideal because of the smaller and more variable quantities of digesta collected and the more variable ileal N/Cr ratios. INTRODUCTIONThe determination of protein and amino acid digestibility is an integral component of protein quality evaluation procedures. In the past, determination of protein digestibility in monogastric animals has generally been accomplished using nutrient balance techniques to measure the amount of faecal nitrogen (N) that is excreted in relation to dietary N intake. Inaccuracy with this approach has been recognised 1±5 and this arises from microbial metabolism of undigested dietary protein and endogenously secreted, N-containing compounds entering the large bowel from the small intestine. As a consequence, protein digestibility is now frequently given as apparent and true ileal digestibility based on the measurement of N ow at the terminal ileum.

The effect of food dry matter intake on the flow of amino acids at the terminal ileum for rats fed an enzyme‐hydrolysed casein‐based diet

“…ANOVA of the isoleucine and cystine data from the four highest levels of intake showed that there was no effect of food intake over the range of 0.7 (8.0 g) to unrestricted. In a related study13 the food intakes for rats fed a variety of protein diets (lactalbumin, wheat gluten, fish fillets, soy protein isolate, zein) were in the range of 8.7–13.3 g, which indicates that, within the practical range of food intakes observed in the present feeding trial, there is no practical significance to the statistically significant slopes for the isoleucine and cystine data. Food intakes found in other studies using similar‐sized rats fed meat and bone meal diets were also found to be at the top end of and beyond the range used in the present study 25.…”

“…Earlier work had shown that a meal feeding regimen was suitable for obtaining representative samples and the measurement of endogenous amino acid flows 6. 13 The procedure adopted for this study, which was based on a meal feeding regimen, was successful in obtaining a range of food dry matter intakes. At all levels of intake below 1.0 (unrestricted intake within the 3 h feeding period) the mean proportions of food dry matter eaten, compared with the amounts offered, exceeded 98%.…”

Effects of circadian iron administration on iron bioavailability and biological rhythm in pigs

“…Transcriptions of genes related to iron absorption including divalent metal transport 1 (DMT1) and duodenal cytochrome B ferric reductase (CYBRD1) in intestinal epithelial cells were also under circadian clock regulation 15 . Several studies have found that a circadian feeding schedule could affect the circadian rhythm and improve nutrient metabolism 16‐18 . However, the contribution of circadian iron administration to circadian rhythm and iron metabolism has not been fully understood.…”