A mechanistic model of small intestinal starch digestion and glucose uptake in the cow

The high contribution of postruminal starch digestion (up to 50%) to total-tract starch digestion on energy-dense, starch-rich diets demands that limitations to small intestinal starch digestion be identified. A mechanistic model of the small intestine was described and evaluated with regard to its ability to simulate observations from abomasal carbohydrate infusions in the dairy cow. The 7 state variables represent starch, oligosaccharide, glucose, and pancreatic amylase in the intestinal lumen, oligosaccharide and glucose in the unstirred water layer at the intestinal wall, and intracellular glucose of the enterocyte. Enzymatic hydrolysis of starch was modeled as a 2-stage process involving the activity of pancreatic amylase in the lumen and of oligosaccharidase at the brush border of the enterocyte confined within the unstirred water layer. The Na+-dependent glucose transport into the enterocyte was represented along with a facilitative glucose transporter 2 transport system on the basolateral membrane. The small intestine is subdivided into 3 main sections, representing the duodenum, jejunum, and ileum for parameterization. Further subsections are defined between which continual digesta flow is represented. The model predicted nonstructural carbohydrate disappearance in the small intestine for cattle unadapted to duodenal infusion with a coefficient of determination of 0.92 and a root mean square prediction error of 25.4%. Simulation of glucose disappearance for mature Holstein heifers adapted to various levels of duodenal glucose infusion yielded a coefficient of determination of 0.81 and a root mean square prediction error of 38.6%. Analysis of model behavior identified limitations to the efficiency of small intestinal starch digestion with high levels of duodenal starch flow. Limitations to individual processes, particularly starch digestion in the proximal section of the intestine, can create asynchrony between starch hydrolysis and glucose uptake capacity

Investigation of different levels of RDP in the rations of lactating cows and their effects on MUN, BUN and urinary N excretion

Twenty-one multiparous Holstein cows in the late stages of their lactation period were used in complete randomized<br />design to investigate the effect of rumen degradable protein on milk urea nitrogen (MUN) and some blood metabolites.<br />Experimental periods were 6 weeks in length, with days 1 to 14 used for adjustment and weeks 3 to week 6 used for<br />sampling (urine, blood, and milk). Three concentrations of a rumen-degradable protein (RDP) supplement according to<br />National Research Council recommendations (9.3, 11.4, and 14% of dry matter intake) were treatments. Dietary RDP<br />content altered both total urinary N and urinary N concentration, leading to increased urinary output. Estimations for<br />microbial protein yield were compared with the measured excretion of purine derivative as yeast RNA equivalent, in urine.<br />No significant effect of concentration of RDP supplement was detected on microbial N production. Plasma cholesterol concentration<br />decreased linearity by increasing RDP concentration in diets (P<.05). In this regard, milk urea nitrogen, as<br />well as triglyceride concentration in plasma, was not associated with dietary RDP concentration. To ensure a correct balance<br />between energy and protein available in the rumen and consequently higher N efficiency for late lactation cows, a<br />MUN content of 15.1mg/dl milk is the upper margin. Milk urea N is a simple and noninvasive measurement that can be<br />used to monitor N efficiency in dairy cows

Correlation between microbial enzyme activities in the rumen fluid of sheep under different treatments

Five total mixed rations prepared from finger millet (Eleusine Coracana) straw as a roughage (48%) and mixed concentrate (52%), supplemented with a 1% isoacid mixture (i-C$_4$, i-C$_5$, C$_5$ and phenylacetic acid in equal proportions) or oil (groundnut oil, 5% more than the control) or urea (5% more nitrogen than the control), and protein (groundnut cake, 5% more nitrogen than the control) were given in a Latin square experiment to sheep. Enzymatic activities were estimated for urease, cellulase, protease, amylase, and lipase in various fractions of rumen fluid on the one hand and rumen microbial biomass on the other hand. Rumen samples were taken 3-4 hours after feeding and mixed rumen bacteria were separated as a strained rumen fluid without protozoa (SRFWP), cell free rumen fluid (CFRF) and enzymes associated with the bacteria cell (EABC). Samples of SRFWP and EABC contained higher enzyme activities than CFRF. Depending on the type of enzymes in each fraction, some significant coefficient of determination ($r^2$) was seen. These values showed very close cooperative action between proteolytic and amylolytic enzymes under the experimental conditions, or perhaps the presence of some species of bacteria with both activities. Lipolytic bacteria are completely specialized for lipase production only ($P < 0.05$). The results showed oil, isoacid and crude protein enhanced microbial production ($P < 0.05$) and this can change the pattern of enzymes in the rumen of sheep

Supplementation of different selenium sources during early lactation of native goats and their effects on nutrient digestibility, nitrogen and energy status

The aim of this study was to compare the effects of two Se sources on the early lactation of native goats, on nutrient digestibility, as well as nitrogen and energy status of Iranian native goats. Twenty-one native goats aged, approximately 41 ± 9 months and having body weights of 46 ± 8 kg were selected for the experiment. The goats were randomly divided into three groups with an equal number of goats. One group was supplemented with Selemax 2000® as the organic selenium (OS), the second group received diluted sodium selenite as the inorganic selenium, while the third group received no supplementation and served as the control group (C). The results of this research showed that the selenium supplement did not have a significant effect on nutrient digestibility (apart from crude fat) (P > .05) but, the dry matter, organic matter and crude protein intake significantly increased. However, faecal N, urinary N, total N production and energy status were affected by the treatments (P < .05). It can be concluded that OS seems to be a better choice, considering the nitrogen and energy available for metabolism and its partition between milk production and deposit/mobilization within the body