A. Th. van't Klooster

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.

Effects of reducing dietary [(Na+ + K+) − (Cl− + SO4=] on the rate of calcium mobilisation by dairy cows at parturition

Abstract The effects of feeding diets with different milliequivalents (meq) of dietary [(Na+ + K+) − (Cl− SO4=)] to dairy cows during the last seven weeks of pregnancy on their acid-base status and calcium mobilisation rate around parturition were studied. Ten monozygotic twin pairs of pregnant cows (five pairs of parity 1 or 2, and five pairs of parity 3 or more) were allocated to two diets which were formulated to provide either - 4 meq (anion diet) or +572·5 meq (cation diet) of [(Na+ + K+) − (Cl− + SO4=)] kg−1 dietary dry matter ( dm ). The daily rations consisted of 4 kg grass hay and 7 kg concentrates. Changes in meq of dietary [(Na+ + K+) − (Cl− + SO4=)] were achieved by adding KCl, K2SO4 and (NH4)2SO4 (anion diet) or K2CO3 (cation diet) to basal concentrates. Plasma calcium concentration and blood acid-base parameters were not affected by dietary treatment. However, urinary calcium excretion was markedly higher and urinary pH and bicarbonate excretion significantly lower in cows fed the anion diet than in cows fed the cation diet. The responses to hypocalcaemia induced by an intravenous infusion of edta solution were similar in the cows fed either diet.

Microbial and nutritional aspects of feeding fermented feed (poultry by‐products) to pigs

Broiler by-products (heads, feet, and viscera) mixed with 4% dextrose were pasteurized for 4 min at 90 degrees C core temperature, cooled to 20 degrees C, and fermented with Lactobacillus plantarum as starter culture. These fermented poultry by-products were fed to 12 individually housed fattening pigs as part (17.6% of the dry matter) of their fattening ration, the remainder composed of compound pig feed. Control pigs received a compound pig feed only. Both groups of pigs were fed restrictively on the basis of body weight. The technical results of the pigs fed the experimental diet showed a significantly improved feed:gain ratio (2.46 vs 2.57), a significantly higher carcass weight (86.1 vs 81.8 kg), a lower meat percentage (50.9 vs 52.5%) and an increased backfat thickness (21.5 vs 18.7%). The bacterial flora in the intestinal tract of the pigs fed the experimental diet differed significantly from the control animals. Decreased colony counts of mesophilic aerobic bacteria, Enterobacteriaceae, enterococci and lactobacilli were found in the rectal content and the prevalence of salmonella was lower. It is suggested that the improved feed:gain ratio and the reduced bacterial activity of the measured groups of bacteria is a result of 1) the higher energy content of the diet, and(or) 2) an assumed enhanced digestibility of nutritional components in the diet, and(or) 3) the lower incidence of diarrhea in the pigs fed with fermented poultry by-products. This resulted in a lower contamination level of enteropathogenic bacteria like, salmonella and Escherichia coli, in the gastro-intestinal tract of the pigs fed fermented poultry by-products.

Nitrate poisoning in cattle.

Summary In a series of experiments the effect of administering KNO(2) was studied, during parturition, on the capability of oxygen transport of maternal blood and on oxygen transfer to foetal blood. The following blood parameters were analysed, MHb percentage, pO(2), O(2)-saturation, pH, pCO(2), and (NO(2)) in maternal arterial blood (carotid art.) and venous blood (jugular vein) and in foetal arterial blood (umbilical art.) and venous blood (umbilical vein). The relative O(2)-saturation was calculated from the estimated O(2)-saturation by multiplying with the factor Hb (mmol/1) minus MHb (mmol/1), divided by Hb (mmol/1). In addition, blood pressure in the carotid artery, heart rate, and respiration rate in the dam were continuously recorded for some hours. A dosage of 9 to 12 mg of NO(2)/kg body weight intravenously or of 30 mg of NO(2)/kg body weight orally to the dam caused much higher MHb percentages and NO(2) contents in the maternal blood than in the foetal blood. In maternal blood the ratio of NO(2) content td MHb percentage was proportional to that in foetal blood. In the arterial blood, MHb percentages were almost as high as in the venous blood. After administering of nitrite, relative O(2)-saturation dropped simultaneously with the increase in methaemoglobin. Nitrite treatment caused a drop in the maternal blood pressure; heart rate and respiration rate increased. O(2)-saturation in the blood in the umbilical vein was much lower in the animals with nitrite treatment than in those without. These experimental results show clearly that the oxygen capacity of the blood decreases after nitrite treatment. In pregnant cows the oxygen supply to the foetus will be adversely affected after nitrate intake, especially by the lower oxygen transfer via the placenta, though hardly at all by methaemoglobin formation in the foetal blood. When the oxygen transfer to the foetal blood decreases too sharply, intra-uterine death and ultimately abortion may result.

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.

Characterization of microbial proteolytic enzymes in the rumen

Up to 43% of the viable bacteria from the rumen of cows fed grass and concentrates grew on a medium containing casein as the main substrate. Proteolytic counts for a cow fed on straw and concentrates or for a hay-fed cow were lower than counts for cows fed grass and concentrates, both in absolute terms and in relation to the total anaerobic count.In crude enzyme preparations derived from the rumen protozoa, amino acid arylamidase (leucine aminopeptidase)-like activity was the main proteolytic activity observed. In enzyme preparations extracted from the rumen bacteria in the presence of Triton X-100, trypsin-like activity was predominant. Amino acid arylamidase-and metal-chelating proteinase-like activity together with lower activities of carboxypeptidase A and B and a very low chymotrypsin-like activity were found as well.Studies with enzyme inhibitors showed that the bacterial trypsin-like activity was largely of the cysteine-protease type in a hay-fed cow, but in addition comprised serine-protease activity in a cow fed grass and concentrates. Total proteolytic activity of the enzymes in the bacterial fraction and the spectrum of proteolytic enzymes were found to vary with the ration.

Effects of reducing dietary ([Na+ + K+]-[Cl- + SO4 =]) on bone in dairy cows at parturition.

The effects of feeding diets with different milliequivalents (mEq) of dietary ([Na+ + K+]-[Cl- + SO4 =]) to dairy cows during the last seven weeks of pregnancy on bone morphology at parturition were studied. Nine monozygotic twin pairs of pregnant cows (five pairs of parity 1 or 2 and four pairs of parity 3 or more) were allocated to two diets which were formulated to provide either -4 mEq (anion diet) or +572.5 mEq (cation diet) of ([Na+ + K+]-[Cl- + SO4 =]) kg-1 dietary dry matter. Bone biopsies were taken from the tuber coxae between three and eight hours after parturition. The plasma concentrations of calcium and inorganic phosphorus, the total plasma alkaline phosphatase activity and the urinary hydroxyproline:creatinine ratio were not significantly affected by diet during the experimental period. In low parity (2 or less) cows the percentage trabecular bone volume, the percentage osteoclast surface and the mean number of osteoclasts per microscopic field (identified by Goldner staining) were lower on the anion diet than on the cation diet (P < 0.02). In the high parity cows, the percentage osteoid volume (P < 0.05) and the ratio of percentage osteoid volume to percentage osteoid surface (P < 0.001) were greater in the cows fed the anion diet than in the cows fed the cation diet. The results show that reducing the mEq of dietary ([Na+ + K+]-[Cl- + SO4 =]) to -4 mEq kg-1 dietary dry matter affected some of the parameters of bone formation but did not enhance bone resorption.

Effects of a deficient magnesium supply during the dry period on bone turnover of dairy cows at parturition

The bone activity and bone mineral content in rib bones resected from 33 dairy cows between 3 and 8 h after parturition were measured, and the effects upon them of a deficient supply of dietary magnesium (Mg) during the last seven weeks of pregnancy were studied. The cows were fed a diet containing either 0.22% magnesium (low Mg) or 0.82% magnesium (high Mg) in the dry matter (DM), and the potassium content of both rations was increased to approximately 4.1% in the DM to reduce the absorption of magnesium. In the cows fed the low-Mg diet a fall in plasma Mg concentration was observed. In the low-Mg, low-parity cows the plasma Mg concentrations at parturition were higher than in the low-Mg, high-parity cows, i.e. 0.83 mmol/l and 0.54 mmol/l, respectively. After parturition four cows in the low-Mg, high-parity group showed clinical signs of hypocalcaemia but none of the other groups did so. The bone formation in low-parity cows was significantly (P less than 0.05) affected by Mg supply, with higher percentages of both trabecular surface covered by osteoid and osteoid volume in the low-Mg group. In the high-parity cows no significant differences in bone formation were found between the low- and high-Mg groups. An inadequate Mg supply resulted in a significantly (P less than 0.05) higher Ca content in the bone ash of low-parity cows and a significantly (P less than 0.05) higher bone ash percentage in the bone of high-parity cows.

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.

Effects of low and high calcium intake prepartum on calcium mobilization rate around parturition in dairy cows

Forty-one dairy cows were fed a low (LCa-13 g/d) and a high (HCa-83.5 g/d) calcium ration in the 8 weeks prior to parturition and the effect on the Ca mobilization rate around parturition was studied. Plasma Ca values were stable in the LCa group around parturition. In the older cows of the HCa group a very slight decrease in the mean plasma Ca was observed: 2.58 mmol/l at 12-36 h ante partum decreased to 2.38 mmol/l at parturition. Hypocalcaemia, which commonly occurs around parturition, did not occur in 40 of the cows. A subclinical hypocalcaemia (1.8 mmol/l) occurred in one cow (parity 10) from the HCa group. To assess the efficiency of Ca mobilization, a severe hypocalcaemia (1.0 mmol/l) with clinical signs was induced by means of Na2EDTA infusion (0.90 mmol/min), starting at 10 h post-partum. The older cows in the LCa group required more Na2EDTA than those in the HCa group. Higher urinary hydroxyproline excretion in the week before parturition in the LCa than in the HCa group suggested a higher bone turnover. Plasma PTH levels around parturition were not significantly different between the groups. The amount of colostrum milked out in the first 10 h post-partum did not influence Ca homeostasis around parturition. The results contradict those of many other experiments in which hypocalcaemia was observed in cows ingesting high levels of Ca. It is concluded that the restricted feed intake prepartum possibly had a favourable effect on Ca homeostasis.