Chalermpon Yuangklang

Increasing magnesium intakes in relation to magnesium absorption in dry cows

Earlier studies with temporarily isolated rumen of heifers show saturation kinetics of Mg efflux across the rumen wall. Therefore, we hypothesized that high Mg intakes would not further increase the rate of Mg absorption in cows. To test our hypothesis, six ruminally fistulated non-pregnant dry cows were given diets with different Mg concentrations in a 6 x 6 Latin square design. Desired concentrations of Mg were attained by adding MgO to the basal diet and the Mg concentrations in the total rations were 3.8, 6.4, 9.1, 11.8, 14.1 and 173 g Mg/kg dry matter, which provided Mg intakes of 27.1, 44.6, 64.6, 83.5, 100.4 and 124.3 g/d, respectively. Increasing Mg intakes were associated with increased (P<0.001) faecal Mg excretion. However, apparent Mg absorption expressed as g/d was not significantly different for Mg intakes from 100.4 to 124.3 g/d while Mg absorption expressed as a proportion of intake was not significantly different for Mg intakes ranging from 64.6 to 124.3 g/d. Mg concentrations in rumen fluid after feeding increased (P<0.001) with increasing Mg intakes. Apparent absorption of Mg appeared to become saturated at a ruminal Mg concentration of 17.5 mM (Mg intake of 83.5 g/d). Group-mean post-feeding concentrations of Mg and Na in rumen fluid were significantly correlated (Pearsons r=-0.96; P=0.003, n=6). This study showed that under conditions of practical dairy cow feeding, Mg absorption was maximal at Mg intakes > or = 84 g/d.

The Effects of Additives in Napier Grass Silages on Chemical Composition, Feed Intake, Nutrient Digestibility and Rumen Fermentation

The effect of silage additives on ensiling characteristics and nutritive value of Napier grass (Pennisetum purpureum) silages was studied. Napier grass silages were made with no additive, fermented juice of epiphytic lactic acid bacteria (FJLB), molasses or cassava meal. The ensiling characteristics were determined by ensiling Napier grass silages in airtight plastic pouches for 2, 4, 7, 14, 21 and 45 d. The effect of Napier grass silages treated with these additives on voluntary feed intake, digestibility, rumen fermentation and microbial rumen fermentation was determined in 4 fistulated cows using 4×4 Latin square design. The pH value of the treated silages rapidly decreased, and reached to the lowest value within 7 d of the start of fermentation, as compared to the control. Lactic acid content of silages treated with FJLB was stable at 14 d of fermentation and constant until 45 d of ensiling. At 45 d of ensiling, neutral detergent fiber (NDF) and acid detergent fiber (ADF) of silage treated with cassava meal were significantly lower (p<0.05) than the others. In the feeding trial, the intake of silage increased (p<0.05) in the cow fed with the treated silage. Among the treatments, dry matter intake was the lowest in the silage treated with cassava meal. The organic matter, crude protein and NDF digestibility of the silage treated with molasses was higher than the silage without additive and the silage treated with FJLB. The rumen parameters: ruminal pH, ammonia-nitrogen (NH3-N), volatile fatty acid (VFA), blood urea nitrogen (BUN) and bacterial populations were not significantly different among the treatments. In conclusion, these studies confirmed that the applying of molasses improved fermentative quality, feed intake and digestibility of Napier grass.

High intake of magnesium in relation to the ruminal transmural potential difference and magnesium absorption in wethers.

High potassium (K) intakes are known to decrease magnesium (Mg) absorption in ruminants by increasing the transmural potential difference (PDt, serosal side = positive). High Mg intakes are known to increase the amount of Mg absorbed, which may be explained by increasing the ruminal Mg concentration, but an effect on the PDt cannot be excluded. The objective of this study was to determine whether or not Mg intake affects the PDt. In a 3 x 3 Latin square design, six ruminally fistulated wethers were fed a low-Mg, low-K ration (3.88 g Mg/kg dry matter (DM); 30.7 g K/kg DM), a high-Mg, low K-ration (16.79 g Mg/kg DM; 30.7 g K/kg DM), and a low-Mg ration high-K (3.88 g Mg/kg DM or 62.1 g K/kg DM). When compared with the low-Mg, low-K ration, the high-Mg, low-K ration raised the absolute apparent Mg absorption (g/day) by 421% and the low-Mg, high-K ration decreased it by 20%. The intake of extra K produced a significant increase in the PDt. The intake of extra Mg did not change the PDt across the rumen wall but produced a significant increase of the ruminal Mg concentrations. On the basis of the individual values for three rations, the mean post feeding ruminal Mg concentrations were found to be unrelated to the PDt (Pearsons r = -0.329, p = 0.183, n = 18). Thus, it is concluded that the observed increase in Mg absorption after a high Mg intake can be explained by an increase in the ruminal Mg concentration rather than by a change in PDt.