Factors affecting intestinal starch digestion in ruminants: A review

Carbohydrates are the main source of energy in ruminants. Their site, extent and kinetics of digestion highly impact the amount and profile of nutrients delivered to peripheral tissues, and the responses of the animal, i.e. ingestion, efficiency of production, N and methane excretion, quality of products and welfare. Development of multi-objective feed evaluation systems thus requires a more integrated quantitative knowledge on carbohydrate digestion and yield of terminal products, as well as on their metabolism by splanchnic tissues. The objective of this paper is to review (i) quantitative knowledge on fibre, starch and sugar digestion, volatile fatty acids (VFA) and glucose production and splanchnic metabolism and (ii) modelling approaches which aim at representing and/or predicting nutrient fluxes in the digestive tract, portal and hepatic drainage. It shows that the representation of carbohydrate digestion and VFA yield is relatively homogeneous among models. Although published quantitative comparisons of these models are scarce, they stress that prediction of fibre digestion and VFA yield and composition is still not good enough for use in feed formulation, whereas prediction of microbial N yield and ruminal starch digestion seems to be more satisfactory. Uncertainties on VFA stoichiometric coefficients and absorption rates may partly explain the poor predictions of VFA. Hardly any mechanistic models have been developed on portal-drained viscera (PDV) metabolism whereas a few exist for liver metabolism. A qualitative comparison of these models is presented. Most are focused on dairy cows and their level of aggregation in the representation of nutrient fluxes and metabolism highly differs depending on their objectives. Quantitative comparison of these models is still lacking. However, recent advances have been achieved with the empirical prediction of VFA and glucose production and fluxes through PDV and liver based on the current INRA feed evaluation system. These advances are presented. They illustrate that empirical prediction of ruminal VFA and intestinal glucose production can be evaluated by comparison with measured net portal net fluxes. We also illustrate the potential synergy between empirical and mechanistic modelling. It is concluded that concomitant empirical and mechanistic approach may likely help to progress towards development of multi-objective feed evaluation systems based on nutrient fluxes.

Section: Starch Intestinal Digestion and Glucose Absorptionmentioning

confidence: 99%

Carbohydrate quantitative digestion and absorption in ruminants: from feed starch and fibre to nutrients available for tissues

Nozière

Ortigues-Marty

Loncke

et al. 2010

“…In contrast to barley, more starch from corn escapes from rumen fermentation, resulting in a higher intestinal starch flow (Offner et al, 2003). A limited amylolytic activity in the small intestine of dairy cows (Matthe et al, 2001), combined with a limited microbial fermentation of starch in the large intestine (Harmon et al, 2004), may attribute to the increased fecal excretion of corn starch. This assumption is supported by in situ data, whereby cows fed diets containing corn grain had higher fecal potential degradability in situ compared with barley grain alone (Table 4), indicating the presence of higher amounts of potentially degradable substrate, most probably undigested starch, in the feces of cows fed diets consisting of corn and barley grain than in those fed barley grain alone.…”

mentioning

confidence: 99%

Grain source and marginal changes in forage particle size modulate digestive processes and nutrient intake of dairy cows

Nasrollahi

Khorvash

Ghorbani

et al. 2012

This study investigated the effects of, and interactions between, dietary grain source and marginal changes in alfalfa hay (AH) particle size (PS) on digestive processes of dairy cows. A total of eight Holstein dairy cows (175 days in milk) were allocated in a replicated 4 3 4 Latin square design with four 21-day periods. The experiment was a 2 3 2 factorial arrangement with two levels of theoretical PS of AH (fine 5 15 mm or long 5 30 mm) each combined with two different sources of cereal grains (barley grain alone or barley plus corn grain in a 50 : 50 ratio). Results showed that cows consuming diets supplemented with corn had greater dry matter and nutrient intakes (P , 0.01), independent of forage PS. In addition, the apparent digestibility of fiber fractions was greater for diets supplemented with corn (P 5 0.01). The feeding of barley grain-based diets was associated with greater apparent digestibility of non-fiber carbohydrates, and this variable was even greater when long AH was fed (P 5 0.04). Moreover, the feeding of long AH resulted in longer time spent eating (P 5 0.03) and higher pH (P , 0.01), as well as a tendency for higher acetate-to-propionate ratio in the rumen fluid (P 5 0.06) at 3 h post feeding. In conclusion, the results indicated that the marginal increase of PS of AH may prolong eating time and improve rumen fermentation, particularly in diets based on barley grain. Partial substitution of barley grain by corn can improve feed intake and fiber digestibility in mid-lactation dairy cows.Keywords: physically effective NDF, hay particle size, barley, corn ImplicationsThis study tested the hypothesis that grain fermentability and particle size (PS) of alfalfa hay have the potential to modify rumen conditions, digestion and performance of mid-lactation dairy cows. Indeed, the results showed an improved rumen environment and nutrient digestibility in cows fed a diet containing corn grain and long forage PS, respectively.

“…-E-mail: Martin.Weisbjerg@agrsci.dk not appear to be a quantitative limitation to intestinal starch digestion (Harmon et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

Assessment of the mobile bag method for estimation of in vivo starch digestibility

Ghoorchi

Lund

Larsen

et al. 2013

The objective was to assess the ability of the in situ mobile nylon bag method for predicting small intestinal and total tract starch digestibility. Starch disappearance was measured for 18 samples of different cereals and legumes subjected to different physical and chemical processing methods and compared with coherent in vivo digestibility. Starch disappearance was measured both with and without initial ruminal pre-incubation during 4 h. Bags were retrieved from either the ileal cannula or faeces. Two dry Danish Holstein cows fitted with rumen cannulas were used for rumen pre-incubations and two lactating Danish Holstein cows fitted with duodenal and ileal cannulas were used for intestinal incubations. Rumen pre-incubation had no significant effect on disappearance from bags recovered in faeces. The disappearance of legume starch was lower, both in the rumen and small intestine, compared with starch from barley, wheat, oats, ear maize and maize. Transit times of the mobile bags from duodenum to ileum were not significantly different between feeds. A weak positive correlation was found between in vivo small intestinal and total tract digestibility of starch and disappearance obtained using the mobile bag technique across a broad range of starch sources. Omitting two less conventional starch sources (NaOH wheat and xylose-treated barley) resulted in a high (0.87) correlation between total tract in vivo digestibility and mobile bag disappearance. The use of the mobile bag method for estimation of in vivo starch digestibility will therefore depend on the starch type.