Effect of cell walls, dry matter and protein supply on endogenous nitrogen flow in the small intestine of sheep

Effect of dietary dry matter intake on endogenous nitrogen flows in growing lambs

The effect of dietary dry matter intake (DMI) on endogenous nitrogen (N) flows at different part of the digestive tract of growing lambs was determined using a ¹⁵ N isotope dilution technique. Three Kazakh male lambs (30 ± 2.75 kg of body weights and 4 months old, average daily gain 200 g/day) were fitted with ruminal, duodenal and ileal cannulae and raised in metabolic cage individually. The experiment was conducted in a 3 × 3 Latin square design with three lambs, three DMI levels (1100, 920 and 736 g/day respectively) and three periods. Each period lasted 18 days, consisting of 10 days for adaptation, 8 days for the continuous infusion of l-[¹⁵ N]leucine, during which the intestinal flow of N and ¹⁵ N enrichment were determined. The total endogenous secretions in the forestomach (S_fs ) were decreased (p = 0.0512) with increased level of DMI. On the contrary, endogenous nitrogen (EN) secretions into the small intestine (S_i ) increased (p = 0.0249) significantly with the high level of DMI (HI) group compared with that of low level of DMI (LI). Total absorption from forestomach was reduced (p = 0.0121) with increased level of DMI, whereas total absorption from small intestine for HI group increased (p = 0.0116) significantly compared with that of LI treatment. The real digestibility of N in the rumen accompanied with the increase in feed intake is decreased (p = 0.081). In contrast, there were no effects of DMI level on the computed real digestibility of N across both small intestine and whole tract. The results of this study indicate that the total flows of EN at duodenum may be unaffected by the level of DMI; however, the EN flow at ileal level increased from 12% to 37% with the increase in DMI level, corresponding to 33% of total N flow at ileum.

Dietary starch source influences in growing goats: the intestinal losses of endogenous nitrogen and amino acids

Four goats (20 (SD2·5) kg) fitted with ruminal, duodenal and ileal cannulae were used in a 4 × 4 Latin square design to estimate the effects of a dietary starch source on the duodenal and ileal flows of endogenous N (EN) and endogenous amino acids (EAA) in growing goats. Goats were fed total mixed rations containing four starch sources (mainly from maize (MR), wheat (WR), paddy (PR) and sorghum (SR) treatments). There were no significant (P>0·05) effects of the dietary starch source on the intestinal flows of EN and EAA. The duodenal flows of EN were 2·40, 2·39, 2·18 and 1·56 g/d for the MR, WR, PR and SR treatments, respectively, as determined by the difference method, and the duodenal flows of EAA were 10·76, 11·29, 10·95 and 10·96 g/d by estimation with the amino acid profile method. The flows of EN and EAA at the ileum were 1·17, 1·12, 1·01, 0·70 and 4·87, 4·95, 4·94, 4·99 g/d, respectively, as estimated by the water-soluble method. The average intestinal reabsorption of EN and EAA was 57·5 %, and the endogenous Leu by the MR treatment was significantly (P < 0·05) lower than that of the other three treatments. The present results indicate that losses of endogenous protein in the intestine were not affected by the dietary starch source.

A Model of Net Amino Acid Absorption and Utilization by the Portal-Drained Viscera of the Lactating Dairy Cow

A more complete understanding of amino acid (AA) metabolism by the various tissues of the body is required to improve upon current systems for predicting the use of absorbed AA. The objective of this work was to construct and parameterize a model of net removal of AA by the portal-drained viscera (PDV). Six cows were prepared with arterial, portal, and hepatic catheters and infused abomasally with 0, 200, 400, or 600 g of casein daily. Casein infusion increased milk yield quadratically and tended to increase milk protein yield quadratically. Arterial concentrations of a number of essential AA increased linearly with respect to infusion amount. When infused casein was assumed to have a true digestion coefficient of 0.95, the minimum likely true digestion coefficient for noninfused duodenal protein was found to be 0.80. Net PDV use of AA appeared to be linearly related to total supply (arterial plus absorption), and extraction percentages ranged from 0.5 to 7.25% for essential AA. Prediction errors for portal vein AA concentrations ranged from 4 to 9% of the observed mean concentrations. Removal of AA by PDV represented approximately 33% of total postabsorptive catabolic use, including use during absorption but excluding use for milk protein synthesis, and was apparently adequate to support endogenous N losses in feces of 18.4 g/d. As 69% of this use was from arterial blood, increased PDV catabolism of AA in part represents increased absorption of AA in excess of amounts required by other body tissues. Based on the present model, increased anabolic use of AA in the mammary and other tissues would reduce the catabolic use of AA by the PDV.

Effects of altering energy and protein supply to dairy cows during the dry period. 1. Intake, body condition, and milk production

We used 48 Holstein-Friesian cows to investigate the effects of altering energy and protein supply to dry cows. Cows were fed one of three diets for 6 wk prior to parturition: (a) a 60:40 (DM basis) mixture of grass silage with barley straw ad libitum; (b) grass silage ad libitum; or (c) 0.5 kg/d of prairie meal with grass silage ad libitum. The standard lactation diet was a flat-rate allocation of concentrates and grass silage ad libitum. We evaluated dry-period diets using four dry fistulated cows; rumen pH remained high (mean = 6.6) and ammonia concentrations followed N intake. The inclusion of straw reduced apparent ruminal digestion of OM, N, and NDF as well as microbial protein yield, though microbial yield per unit of OM apparently digested in the rumen remained unchanged. Voluntary intake of forage was reduced by the inclusion of straw, while the inclusion of prairie meal had little effect. The decline in intake as calving approached was lower with the silage and straw mix diet. There were large differences in the BW change over the final 5 wk of the dry period, although the opposite effect was seen in early lactation, and differences in BW and body condition score were small by lactation wk 22. Despite the substantial differences in nutrient supply and effects on body reserves, there was little effect of dry-period diet on subsequent performance. Lower forage intakes and yields of protein and lactose were confined to the first month of lactation for cows previously offered straw.

Passage of ribonucleic acid along the intestine of sheep

Sheep (Flemish female x Texel male, 55 kg BW), fitted with a PVC cannula in the dorsal rumen and single T-shaped PVC cannulas in the proximal duodenum, distal duodenum, mid-jejunum and terminal ileum were fed hay or hay-concentrate diets at various levels of nitrogen and cell walls (NDF) (22 to 32 g N/d; 150 to 699 g NDF/d). Co-EDTA and Cr-NDF were used as markers to measure the flow rate of digesta. Ribonucleic acid (RNA) intestinal digesta and in rumen bacteria was determined with orcinol after extraction with sodium chloride, precipitation with tungstophosphoric acid and alkaline hydrolysis. The RNA:total N ratio in bacteria, harvested from the rumen, amounted to 0.70 (CV 4.4%). The apparent digestibility of RNA in different sections of the intestine was higher than of total N. About 6% of RNA entering the duodenum disappeared between the proximal and distal duodenum. At jejunum, the net disappearance of RNA amounted to 68% of the quantity which entered the proximal duodenum. A higher result of 71% was obtained at the ileum. Total net disappearance of RNA between the proximal duodenum and rectum averaged 75%. Sixteen percent of RNA leaving the ileum was apparently digested in the large intestine. The true digestibility of RNA between the proximal duodenum and the terminal ileum, as estimated by multiple regression analysis, amounted to 78%. Of the amount of RNA entering the ileum, 24% was of endogenous origin. At ileum, the RNA passage was positively related to the ileal flow of NDF (R2 = 0.67) and N (R2 = 0.94). The passage of RNA increased by 3 mg RNA per g ileal indigestible NDF. Ileal endogenous N consisting of approximately 2% of endogenous RNA-N. In conclusion, the digestion capacity in the first part of the small intestine is high. Rising flows of indigestible cell walls and nitrogen increase the loss of ileal RNA. Further, using RNA as a microbial marker to assess the amount of microbial protein entering the duodenum of ruminants, digesta samples should be collected immediately post pylorus at the proximal duodenum, in order to avoid underestimation of the microbial protein synthesis in the rumen.