J.Th. Schonewille

Stimulatory effect of an anion(chloride)-rich ration on apparent calcium absorption in dairy cows

Abstract The question addressed was whether an anion(chloride)-rich ration raises apparent calcium absorption in dairy cows. In a 24 × 24-day cross-over study with six non-pregnant, non-lactating, multiparous cows, the dietary cation-anion balance [mEq (Na + + K + ) − (Cl − + S 2− )] of the anion-rich and control ration were −170 and +276 mEq/kg dry matter. The two rations essentially differed with regard to their chloride contents. The anion-rich ration significantly reduced the blood base excess, caused a drop in urinary pH from 8.68 to 7.97, and significantly raised the urinary excretion of calcium from 0.8 to 11.6% of intake and the percentage apparent absorption of calcium from 3.4 to 9.5%. The raised absorption of calcium after feeding the anion-rich ration accounted for approximately 60% of the elevated urinary excretions of this mineral. The urinary output of hydroxyproline and the activity in plasma of alkaline phosphatase were unchanged by the anion-rich ration, suggesting that the extra urinary calcium did not originate from an increased bone resorption.

The effect of six different C18 fatty acids on body fat and energy metabolism in mice

We studied the effects of five high-fat semi-purified diets varying at a 4% (w/w) level in either stearic, oleic, linoleic, alpha-linolenic, or gamma-linolenic acid on body fat and energy metabolism in BALB/c mice. A diet containing caprylic, capric, lauric, and myristic acid was used as a reference diet and a diet with 4% conjugated linoleic acid (CLA) was used as a positive control as it is known to effectively lower body fat in mice. The diets were fed for 35 d. Body fat was significantly lower in the CLA group than in the other groups but was not significantly different among the non-CLA groups. Among the non-CLA groups, the linoleic acid group tended to have the highest and the alpha-linolenic acid group the lowest proportion of body fat. In energy-balance studies, the percentage of energy intake that was stored in the body was significantly lower in the CLA group compared with the other dietary groups. The percentage of energy intake eliminated in excreta was highest in the stearic acid group followed by the gamma-linolenic acid group. These results were reflected in apparent fat digestibility, which was lowest in the stearic acid group. The percentage of energy intake expended as heat was highest in the CLA-fed mice. The results of the present study suggest that body fat and energy accretion in mice fed diets containing different C18 fatty acids is by far the lowest with CLA and that linoleic acid produced the highest fat intake and energy accretion.

Intrinsic potassium in grass silage and magnesium absorption in dry cows

Abstract High dietary concentrations of K are known to inhibit Mg absorption in ruminants, but the influence of variation in concentrations higher than 30 g/kg dry matter was unknown, whereas such high concentrations are encountered in grass silages from various countries. Thus, the question addressed was whether K intrinsically prsent in grass silages, within the range of 30–45 g/kg dry matter, would be inversely related with apparent Mg absorption (percentage of intake) in dry cows. In a Latin-Square design, six non-pregnant and non-lactating cows were fed on six different grass silages that were supplemented with a low K, high Mg concentrate so that the amount of K in the whole ration ranged between 29 and 44 and that of Mg between 5.7 and 7.5 g/kg dry matter. Mg absorption was found not to be related with the level of K in the ration. Multiple regression analysis showed that only the dietary level of Mg contributed significantly to the explained variance in Mg absorption. For the observed lack of effect of dietary K on the low Mg absorption (approximately 12%), three explanations can be offered. First, the high levels of Mg in the whole ration (four times requirement) counteracted the inhibitory action of K on Mg absorption. Secondly, the high range of K levels in the rations may have caused maximum inhibition of Mg absorption so that no differences between rations emerged. Thirdly, the typical anion moiety of K salts occurring in grass silages might not allow for the inhibitory effect of K on Mg absorption to become expressed. In any event, this study indicates that high Mg dry cow ratios with K contents higher than 30 g/kg dry matter do not need to be further proportionally supplemented with extra Mg so as to prevent hypomagnesemia.

Impact of dietary soybean oil versus medium-chain triglycerides on plasma fatty acids in goats

The influence on lipid metabolism of dietary soybean oil with 52.6% linoleic acid (C18:2 n-6), was studied in 2-year-old, male-castrated Dutch white goats. A medium-chain triglycerides-product (MCT) containing 48.9% caprylic (C8:0) and 41.0% capric acid (C10:0) was used as control oil. Six goats were fed the diets containing either soybean oil or MCT according to a 21× 21 days cross-over design. The rations contained about 15% crude fat in the dietary dry matter. The soybean oil diet significantly ( P 0.05). This study provides evidence that dietary linoleic acid can escape from biohydrogenation in the rumen of goats and shows that the type of dietary fat has a marked impact on lipid metabolism in goats.

Magnesium in dairy cow nutrition: an overview

BackgroundMagnesium (Mg) is an essential nutrient in animals and thus an adequate supply of dietary magnesium is important to safeguard animal health. It is generally accepted that the efficiency of Mg absorption is the critical determinant in Mg supply of ruminants. Insufficient absorption of Mg in ruminants leads to Mg deficiency which manifests in clinical signs such as tetany (grass tetany) or paresis (milkfever).ScopeThis overview aims to provide insight in the most relevant dietary factors that influence Mg absorption in ruminants and the state of the art knowledge on the mechanism of Mg absorption.ConclusionsIn practice, the use of manure to fertilize the soil is associated with an increased risk on grass tetany because it increases the K content of grass. A high K intake is the most important dietary factor that inhibits Mg absorption which entails the risk on Mg deficiency. The inhibitory effect of K on the effciency of Mg absorption can be counteracted by supplemental Mg. Magnesium oxide is commonly used to prevent Mg defiency but solubility of MgO varies greatly in practice. Thus, it is recommended to use only tested MgO sources. In the light of prevention of milkfever, supplementation in the form of Mg-chloride might be of interest as well. Due to its chloride ion, Mg chloride has a beneficial effect on the dietary cation-anion difference (DCAD).

The relationships between potassium intakes, transmural potential difference of the rumen epithelium and magnesium absorption in wethers

In vitro studies with isolated sheep rumen epithelium have shown that an increase in the lumen K concentration induces an increase in the transmural potential difference across the rumen epithelium (serosal side: positive), which is associated with a decrease in Mg transport. However, at lumen K concentrations >80 mmol/l, Mg transport across the epithelium became independent of the lumen K concentration. The present study was carried out to determine whether this observation also occurs in vivo. Four ruminally fistulated wethers were fed four rations supplemented with KHCO3 (15.7, 37.6, 59.4 or 77.4 g K/kg DM) in a 4 x 4 Latin square design. Increased K intakes significantly increased the rumen K concentration. For all data combined, Mg absorption expressed as % intake was negatively correlated with the rumen K concentration. However, apparent Mg absorption either expressed in absolute terms (g/d) or as % intake was not significantly affected when the dietary K concentration was increased from 59.4 to 77.4 g/kg DM. Rumen K concentration was inversely correlated with the transmural potential difference (blood side: positive) (Pearsons r -0.709; R(2)adj 0.468, P=0.002, n 16). It is concluded that in wethers apparent Mg absorption becomes independent of the dietary K concentration when the K concentration is >60 g/kg DM or equivalent to a postprandial rumen K concentration of about 125 mmol/l.

Neither native nor popped cornmeal in the ration of dry cows affects magnesium absorption

Abstract The hypothesis tested was that addition of starch to the ration of cows would stimulate magnesium (Mg) absorption because of a lowering of ruminal pH, which renders Mg more soluble and thus more available for transport across the epithelium of the rumen, which is the major site of Mg absorption in ruminants. The trial had a 5×5 Latin-square design in which five non-pregnant, non-lactating multiparous cows were fed rations containing either a mix of cellulose and maizeglutenfeed or native or popped cornmeal each at two levels (equivalent to 11 or 20% starch in the dry matter). The dietary periods lasted 28 days. The amount and type of dietary starch did not significantly affect total gastro-intestinal tract Mg absorption, post-prandial ruminal pH, rumen fluid concentrations of Mg, K and total volatile fatty acids; for all five treatments combined, the measured values were 5.6±0.45% of intake, 6.5±0.04, 0.7±0.12 mmol/l, 41.0±0.63 mmol/l, and 105±2.3 mmol/l (means±S.E., n=5), respectively. For all cows and treatments combined, there was a significant, negative relationship between ruminal pH and Mg concentration in rumen fluid. The ruminal Mg concentrations were low when compared with earlier work. On the basis of published in-vitro studies showing that concentrations of soluble Mg fall to more or less constant, low values when pH values are above 6, it is suggested that the high baseline values of ruminal pH in this study, had prevented a statistically significant effect of starch intake, if any, on Mg absorption.

The effect of undernutrition on haematological and serum biochemical variables in wild boar (Sus scrofa)

The effect of induced long term undernutrition on the blood composition of wild boar was studied. During the first weeks, the activity of plasma alkaline phosphatase decreased, while creatinine concentrations increased, and the ratio urea/creatinine decreased, suggesting a renal mechanism as well as recycling of nitrogenous waste products to conserve nitrogen. During the last weeks, haemoglobin and packed cell volume decreased, suggesting protein or mineral deficiencies, and the ratio urea/creatinine increased, indicating substantial endogenous protein catabolism.

Time courses of plasma magnesium concentrations and urinary magnesium excretion in cows subjected to acute changes in potassium intake.

Abstract Hypomagnesaemic tetany in cows develops occasionally after an acute increase in K intake such as can occur when cows are transferred to spring grass. There is evidence that under these conditions plasma Mg concentrations are only transiently decreased. In this study the questions addressed were whether the plasma Mg concentration, indeed adapts to a high K intake as only dietary variable, and whether urinary Mg excretion is associated with this adaptation. Dry cows were fed rations containing either 26 or 50 g K/kg dm, the extra K being in the form of KHCO3. When the cows were acutely transferred from the low to the high K ration, plasma Mg concentrations fell slightly, but significantly from 0.86 to 0.76 mmo1/1 within five days, but rose again to 0.80 mmo1/1 after another 23 days, this rise being also statistically significant. None of the animals developed tetany. The decrease in plasma Mg concentration in individual animals after five days on the high‐K ration ranged from 6 to 21 %. The time course of urinary Mg excretion resembled that of plasma Mg concentration; minimum Mg excretion was seen after four to six days on the high‐K ration with a subsequent increase thereafter. To explain the transient lowering of plasma Mg concentration, it is suggested that the K‐induced decrease in Mg status caused a delayed increase in the carrier‐mediated component of Mg absorption, which in turn caused an increase in urinary Mg excretion. When the cows were acutely switched from the high to the low K ration, plasma Mg concentration and urinary Mg excretion rose, but no transient changes were seen.

High iron intake depresses hepatic copper content in goats.

Earlier studies with ruminants point to a depressant effect of dietary iron on the copper status. To verify this we determined hepatic copper concentrations in dry, non-pregnant goats subjected to a 56 x 56-days cross-over trial with adequate copper rations containing either 269 or 2380 mg iron/kg dry matter. High iron intake reduced the group mean plasma copper (by 18%) and caeruloplasmin activity (by 13%) and produced a significant decrease (27%) in hepatic copper concentrations. Hepatic iron concentrations were raised (by 56%) after feeding the high iron ration. It is concluded that high dietary levels of iron, within the range of their fluctuation in silage and forage, can impair the copper status of ruminants, especially when concurrent intakes of copper are low.