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Dairy cows may suffer events of hypocalcemia and hypomagnesemia, commonly known as milk fever and tetany. Milk fever is characterized by hypocalcemia at parturition as a consequence of a sudden increase in Ca demand and an unavoidable delay in Ca metabolism adaptation. Tetany is due to impaired Mg absorption from the rumen that cannot be compensated by absorptive or excretory adaptation, resulting in a net nutritional shortage of Mg and culminating in hypomagnesemia. Prevention strategies require triggering the activation of Ca gastrointestinal absorption and avoiding factors limiting ruminal Mg absorption., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Objective: To describe the country's progress in eliminating neonatal tetanus based on the information obtained from epidemiologic surveillance., Material and Methods: A retrospective descriptive study of the epidemiological surveillance of neonatal tetanus in Colombia in the period ranging from 1989 to 2005. Available information was consulted regarding confirmations of this event of interest for Public Health., Results: During the study period, a total of 830 cases of neonatal tetanus were reported. In 1989, the rate of neonatal tetanus in Colombia was 0.22 per 1000 live births. In 2005, this value was reduced to 0.01 cases per 1000 live births; a reduction of nearly 94 %., Conclusions: Given the information provided by epidemiological surveillance, Colombia has achieved the goal of maintaining a rate<1 case per 1000 live births. Nevertheless, even one case anywhere in the country should be considered a failure of the healthcare system.

In the present work a comparative quantitative evaluation of the differential effects of neuromuscular blockers on twitches and tetani was performed, encompassing: atracurium, cisatracurium, mivacurium, pancuronium, rocuronium and vecuronium. The sciatic nerve-extensor digitorum longus muscle of the rat was used, in vitro. Twitches were evoked at 0.1 Hz and tetani at 50 Hz. The differential effects of the studied compounds on twitches and tetani were statistically compared using simultaneous confidence intervals for the ratios between mean IC(50) for the block of twitches and mean IC(50) for the block of tetani. The results of ratios of mean IC(50) together with their corresponding 95% simultaneous confidence intervals were: vecuronium: 2.5 (1.8-3.5); mivacurium: 3.8 (3.0-4.9); pancuronium: 3.9 (2.0-7.6); rocuronium: 6.1 (3.8-9.9); atracurium: 9.0 (6.4-12.6); cisatracurium: 13.1 (6.0-28.4). Using the criteria that neuromuscular blockers displaying disjunct confidence intervals for the ratios of mean IC(50) differ statistically with regard to differential effects on twitches and tetani, significant differences in ratios of IC(50) were detected in the following cases: vecuronium vs. rocuronium, vs. atracurium and vs. cisatracurium and mivacurium vs: cisatracurium and vs. atracurium. The results show that the magnitude of the differential effects of neuromuscular blockers on twitches and tetani, as evaluated in the present work in the form of ratios of mean IC(50), does not depend on the chemical structure (comparing steroidal and isoquinolinic compounds), but seems to depend on differential pre- and post-synaptic effects of the compounds. It is also suggested that the greater the ability of a compound to block twitches and tetani in a differential manner, the safer is the compound from the clinical anesthesiology viewpoint.

Magnesium is an essential mineral with many physiologic and biochemical functions. Surprisingly, Mg homeostasis is not regulated by a hormonal feedback system, but simply depends on inflow (absorption) from the gastrointestinal tract and outflow (endogenous secretion, requirement for milk production, uptake by tissues). Any surplus (inflow greater than outflow) is excreted via urine. Conversely, if the outflow (mainly milk secretion and endogenous loss) exceeds inflow, hypomagnesemia occurs because of the lack of hormonal mechanisms of homeostasis. The major reason for insufficient inflow is a reduced absorption of Mg from the forestomachs. Recent studies from our laboratory and data from the literature permit the proposal of a putative transport model for the secondary active transport of Mg across the rumen epithelium. This model includes two uptake mechanisms across the luminal membrane (PD-dependent and PD-independent) and basolateral extrusion via a Na/Mg exchange. The well-known negative interaction between ruminal K concentration and Mg absorption can be explained on the basis of this model: an increase of ruminal K depolarizes the potential difference of the luminal membrane, PDa, and as the driving force for PD-dependent (or K-sensitive) Mg uptake. Because Na deficiency causes an increase of K concentration in saliva and ruminal fluid, Na deficiency should be considered a potentially important risk factor. The data obtained from in vitro and in vivo studies on the association of Mg transport, changes of ruminal K concentration, and PDa are extensive and confirm the model, if the ruminal Mg concentrations are below 2 to 3 mM. It is further proposed by the model that the PD-independent Mg uptake mechanism is primarily working at high ruminal Mg concentration (above 2 mM). Mg absorption becomes more and more independent of ruminal K with increasing Mg concentration, which can be considered as an explanation for the well-known prophylaxis of hypomagnesemia by increasing oral Mg intake. Fermentation products, NH4+ and SCFA, influence Mg absorption. The possible meaning regarding the pathogenesis of hypomagnesemia is not quite clear. A sudden increase of ruminal NH4+ should be avoided, because high NH4+ concentrations transiently reduce Mg absorption. The most prominent signs of hypomagnesemia are excitations and muscle cramps, which are closely correlated with the Mg concentration in the CSF. It is suggested that the clinical signs are caused by spontaneous activation of neurons in the CNS at low Mg concentrations, which leads to tetany. Prophylactic measures are discussed in context with the known effects on ruminal Mg absorption.

The acute crisis of tetany appears generally on spasmophilic backgrounds, triggered most often by stress and anxiety. Always benign, it can however be quite annoying because of its length. The authors study that crisis successively from an etiological, therapeutical and preventive point of view.

The effects of removing extracellular Ca++ ions or of adding the organic calcium channel antagonist, nitrendipine, were tested on twitches and tetani (100 Hz for 2 sec) in frog toe muscles. Under conditions that did not reduce or that potentiated twitches, both procedures reduced the size of the tetanic responses. This depression was seen as an inability to maintain the maximum tetanic tension for more than 0.5 sec. Intracellular microelectrode recordings showed that the muscle fibers were depolarized (mean about 23 mV) during the stimulus train and the fiber only slowly repolarized after the train. The latter effect is the "late negative afterpotential" and it is produced by the accumulation of K+ ions in the t-tubules during the action potential train. Neither the depolarization nor the late negative afterpotentials were decreased in amplitude by nitrendipine. These results indicate that the voltage-sensitive, slow Ca++ channels are opened by the accumulation of K+ ions in the t-tubules during the tetanus and that the Ca++ ions entering via these channels are required to maintain the full strength of the tetanic contraction. It is suggested that this is a function of these Ca++ channels concentrated in the t-tubules of skeletal muscle fibers.

Rates of increase in plasma Mg following rectal or oral administration of solutions containing 30 g MgCl2.6H2O were compared in 10 Holstein bull calves receiving wheat straw (.07% Mg) and concentrates (.04 or .24% Mg) fed separately for ad libitum consumption. Treatments were administered in a sequence, which involved each calf with all combinations of MgCl2.6H2O dosing routes and dietary Mg within a 6-wk period. Plasma Mg concentration averaged 1.95 mg/dl initially but fell below 1 mg/dl within 2 wk after supplemental Mg was omitted. Maximum increases in plasma Mg concentration following oral or rectal dosing were 16 or 47% when dietary Mg was adequate and 48 or 124% when Mg was deficient. Calves fed either diet responded maximally to rectal infusion within 10 min, but plasma Mg of deficient calves increased throughout 160 min after oral dosing. Plasma Mg of deficient calves responded quicker and reached higher concentrations after rectal infusion, but the response was sustained longer after oral administration.

Thirty pregnant beef cows were utilized to determine the effects of winter Mg supplementation regimen on blood minerals after cows were turned to a spring tetanigenic tall fescue pasture. The winter Mg treatments were (1) tall fescue hay with free access to a Mg-deficient salt-mineral mix, (2) 6.4 kg of corn silage dry matter plus 114 g MgO/d and (3) tall fescue hay with free access to a salt-mineral mix containing 40% MgO from January 1 to February 15. All cows were then placed on the same tetanigenic pasture from February 15 to April 17 with free access to a Mg-deficient salt-mineral supplement. Forage Mg remained below .2% during the experiment. Forage Ca, P and Al changed throughout the spring, attaining maximum values of .35%, .46% and 415 ppm, respectively. Forage N and K also increased throughout the spring, reaching values of 3.5 and 3.8%, respectively, at the April 3 sampling. The forage K:(Ca + Mg) ratio approached 2.2 by March 26, which coincided closely with the average tetany date (March 29). Serum Mg averaged 1.97, 3.58 and 2.06 mg/dl for treatments 1, 2 and 3, respectively, on February 15 before turning cows to pasture. There were no treatment differences for serum Ca, P and K during the experiment. Eight cows exhibited symptoms of grass tetany (collapse) on an average date of March 29. Winter Mg supplementation provided little long-term protection against hypomagnesemia after turning cows to tetanigenic pasture, indicating that cows must have a supplemental source of Mg during this critical period.

Two cow-calf grazing studies and 2 rate-of-disappearance trials in steers surgically prepared with rumen fistula were conducted to evaluate the efficacy of a large Mg alloy rumen bolus in preventing hypomagnesemic tetany (grass tetany). The mineral composition of the forage and results of study of 2 cows in the cow-calf studies indicated that an environment conducive to the occurrence of grass tetany existed. Grass tetany occurred in a cow that was given a Mg bolus and in a control cow. Administration of 1 or 2 mg boluses did not affect blood serum Mg, Ca, P, and K concentrations. Bolus treatment did not affect cow-calf performance or conception rate. The rate of weight loss of the boluses in the surgically prepared steers (rumen fistula) ranged from 0.71 to 1.43 g/day or 0.66 to 1.33 g of Mg/day. Steer differences affected the rates of disappearance patterns of the boluses. The rate of disappearance was relatively constant over a 175-day period and regurgitation or passage was not a problem. Although administration of the boluses could have prevented tetany in some animals (borderline), the rate of Mg release appears too slow to be highly effective in preventing grass tetany.

In a study of dairy and beef herds on 120 farms in south-western Victoria, losses attributed to grass tetany were shown to have been an important cause of economic loss during the cooler months of 1980. Thin dairy cows had a higher incidence of suspected grass tetany than dairy cows in moderate body condition, and both thin and fat beef cows had a higher incidence than beef cows in moderate body condition. A lower incidence was found among dairy cows when the available pasture or hay contained a high percentage of clover, when cows in moderate body condition had been grazed on pastures topdressed with low rates of potassium fertilisers, and when cows had been rotated onto fresh pasture at least daily rather than at 2 or 3 day intervals. The incidence among dairy cows was also associated with the length of available pasture, the correlation being positive for cows of moderate body condition, but negative for thin cows. Possible reasons for the associations are discussed. Only a small proportion of farmers adopted measures to prevent grass tetany, and those who did often applied them inefficiently. Practicable control measures are suggested on the basis of the survey results.

British breeds of cattle are not so effective as Zebu in extracting nutrients from low-quality roughages, and these breeds differ in their nutrient metabolism and animal physiology. Breeds of cattle may differ in their requirements for Mg. Brahman cows are less susceptible to death from disease and metabolic disorders than are British breeds of cattle, whereas cows with 50% or greater dairy breeding (Holstein and Jersey) are more susceptible than British or Brahman breeds when maintained in beef production herds. Brahman or Brahman crossbred cows are less susceptible than other breeds to metabolic disorders such as grass tetany. Magnesium absorption has been shown to be greater in Brahman than in Jersey, Holstein and Hereford cows. These differences in the efficiency of Mg absorption between different breeds of cows may be due to genetic variation in the absorptive mechanisms of Mg, in feeding behavior, in gastrointestinal tract motility, in gastrointestinal tract fill or to some combination.

To minimize the incidence of grass tetany, winter pastures should be established on soils containing Mg-rich minerals, drainage should be improved on five-textured soils, legumes should be included in the sward and soil pH should be at least 5.5. Liming acid soils with dolomitic lime increases forage Mg by supplying Mg and by raising soil pH. Calcitic lime applications also can increase Mg availability to plants on soils with adequate Mg. Low rates of application of soluble Mg salts (less than 100 kg/ha of Mg) effectively increase Mg uptake from noncalcareous soils with low cation exchange capacity. Potassium levels in soils and plants should be kept in the lower range of recommended values. Nitrogen application should be regulated to provide the desired level of forage production. Nitrogen fertilizers, especially the nitrate form, stimulate plant Mg uptake if Mg is available in the soil. The most practical and cost-efficient method of supplementing dietary Mg intake is to provide free-choice Mg. Supplements must be palatable and placed in locations frequently used by cow herds. Including a high-energy feed in the supplement may at times increase its preventive effectiveness by increasing Mg absorption and reducing lipolysis. Regardless of the supplement formulation, Mg intake should be monitored on a regular basis, and formulation or management changes should be initiated if Mg consumption is below required levels. In severe grass tetany outbreaks, foliar application of Mg or administration of Mg via the drinking water may be warranted.