No abstract

To determine the effects of incremental quebracho tannin extract (QTE) infusions on rumen fermentation and yield and composition of microbial mass, a study was conducted that consisted of 1 control period (Control I) without QTE dosing; 4 periods when all animals received 1, 2, 4, or 6% QTE of the diet (DM basis); and a second control period (Control II). Each period consisted of 9 d of adaptation, 6 d of urine collection, and 1 d of rumen sampling. Three rumen-fistulated heifers (495 kg BW [SE 14]) were offered 2.6 kg/d grass hay, 2.6 kg/d concentrates, and 60 g/d mineral-vitamin premix (as fed) in 2 equal meals. Half the daily QTE dosage was intraruminally administered at every meal. Urine and rumen fluids were analyzed for purine derivatives and short-chain fatty acids, respectively. Nitrogen and purine base (PB) concentrations were determined in liquid-associated microbes in rumen fluid (LAMF), liquid-associated microbes in the solid phase (LAMS), and particle-associated microbes (PAM). Increasing QTE dosages linearly increased propionate and butyrate proportions in rumen fluid ( = 0.37, = 0.004 and = 0.51, < 0.001, respectively). Instead, proportions of acetate ( = 0.75, < 0.001), isobutyrate ( = 0.66, < 0.001), and isovalerate ( = 0.49, < 0.001) and urinary purine derivatives excretions ( = 0.66, < 0.001) linearly decreased with increasing QTE infusions. Inconsistent differences were observed for LAMF, but concentrations of PB in LAMS ( ≤ 0.018) and of N in PAM ( < 0.001) were greater at 6% QTE than at Control I, II, and 1% QTE. Hence, low to moderate QTE dosages hamper rumen fermentation and microbial biomass yields. Alongside the nutritional consequences for the host, the methodological implications of these effects should be considered in studies evaluating the targeted use of tannins in ruminant feeding.

No abstract

This study investigated the response of urinary purine derivatives (PD) excretion to increasing levels of intraruminal glucose infusion to evaluate how well this indicator reflects induced changes in microbial crude protein flow. Four rumen-cannulated heifers (482 ± 25 kg body weight) were fed at maintenance energy level with a basal diet (on fresh matter basis) of 4 kg/d hay, 1.5 kg/d concentrate and 60 g/d minerals in two equal meals. The trial comprised a control period (Control I) without glucose infusion followed by four consecutive periods in which all animals received 125 g, 250 g, 500 g or 1000 g/d of glucose, respectively. For this, daily dosages of glucose and urea (90 g/d during all periods) were divided into three portions that were dissolved in water and directly administered into the rumen during morning and afternoon feedings and once during noon. After the highest glucose dosage, a second control period was carried out (Control II). Urinary PD excretion increased with glucose infusion of 125 g/d (71.4 mmol/d) and 1000 g/d (74.2 mmol/d) over the level at Control I (53.9 mmol/d (standard error of the mean (SEM) 3.4; p = 0.012). After withdrawing glucose infusion, PD excretion (79.0 mmol/d) did not return to Control I level (p = 0.001). In contrast, faecal nitrogen (N) excretions linearly increased with incremental glucose infusion (p < 0.001) from 33.9 g/d at Control I to 39.7 g/d (SEM 0.5) at 1000 g/d of glucose and were similar in Control I and II (p = 0.086). The contradicting responses in the excretions of faecal N and urinary PD to increasing glucose infusions highlight the limited accuracy of the PD excretion as a non-invasive indicator when incremental dosages of rapidly fermentable carbohydrates are supplied.

No abstract