Until recently it had been fairly widely accepted that it is not easy to induce, experimentally, a hypocalcaemia in sheep. The late Sir Arnold Theiler, Dr. H. H. Green who was closely associated with him for a number of years at Onderstepoort, and others, have referred to the difficulty of making sheep hypocalcaemic. Our work does not support this.
If conditions are suitable, hypocalcaemia is not confined to in-lamb ewes, or to ewes with lambs at foot, but may occur in any class of sheep and at any time of the year.
A hypocalcaemla may be encountered or may be induced in rams, in pregnant and in non-pregnant ewes, in weaners or in lambs which are still running with their mothers. It may occur under apparently good or bad feed conditions and in good or in poor-conditioned ewes.
Animals which have become hypocalcaemic will not necessarily show the clinical symptoms commonly associated with the disease. This latter point is an important one and possibly one which is insufficiently appreciated by those interested in the problem. The following examples will illustrate this point.
Several years ago the writer was called out to treat two ewes which were suffering from hypocalcaemia. One animal was at the comatose stage, the other could still walk but was showing staggery symptoms. Both responded successfully to intravenous injections of calcium gluconate. Their serum calcium, prior to treatment, was 2.66 and 3.73 mg. per 100 cc. respectively. On exercising the remainder of the flock two more were soon detected as showing very early clinical symptoms. Both were hypocalcaemic with serum calcium values of 3.85 and 4.78 mg. respectively. The enforced exercise was necessary to detect the condition. Such animals probably should be regarded as "potential" cases of clinical hypocalcaemla. Later work has supported this finding.
Thus it is possible to have these "potential" cases of clinical hypocalcaemla present in a flock of ewes. Under suitable conditions, if lambing has not yet taken place, they may lamb normally and one may never realise that these border line cases had been present in the flock. However, where clinical cases of the disease do occur the above example illustrates the desirability of gentle exercise of the remainder of the flock in order to detect, and treat if necessary, these early cases which might otherwise go undetected.
The following are some of the factors which may reduce the level of serum or blood calcium:—
Dietary influences may so influence the level of the blood calcium in sheep that they will develop clinical symptoms of hypocalcaemia. A ration may be so deficient in calcium or may be so unbalanced in respect to the amount of calcium and phosphorus supplied that ewes on such feed may become severely hypocalcaemic and may show the usual symptoms commonly associated with this disease.
Where heavy hand-feeding with rations rich in cereal products is practiced a rapid reduction in serum calcium may take place For instance, in experiments which have been carried out at the McMaster Laboratory in Sydney, ewes with lambs at foot which have been fed on a ration of wheat and chaff, oats, bran and linseed meal have, in less than three weeks, suffered a drop in their serum calcium from normal values of 8 to 10 mg. down to levels ranging from 5 to 6 mg. per 100 cc. serum. The fall in the serum calcium of some of the lambs has been just as rapid and as severe.
In other experiments groups of Merino weaners, approximately 5 to 6 months old when placed on rations containing equal mixtures of wheaten chaff and a cereal grain have, irrespective of whether the grain be maize, oats or wheat, become severely hypocalcaemic within four to five months. Clinical cases of hypocalcaemia have developed subsequently and serum calcium values as low as 2.73 mg. per 100 cc. have been recorded.
Similar effects have been noted where ewes, unused to such feed, have been given access to pasture or wheat stubble grazing which is badly contaminated with sorrell (Rumex acetosella). The hypocalcaemic condition in this instance is due to the high oxalate content of the sorrel. Similar outbreaks of acute clinical hypocalcaemia in South Australia, where hungry sheep have been transferred to areas containing soursob (Oxalis censua) have been brought to our notice by veterinary officers of that State.
Here, in New South Wales, many plant species, rich in oxalates, occur when conditions are suitable for their growth. There is little doubt that heavy mortality among sheep, particularly among travelling and hungry stock, occurs after the consumption of such plant material. Included among these are such well known plant species as pig weed (Portulacca oleracca and P. australia) parakeelya (Calandrania spp), roly poly (Salsoli kali), New Zealand spinach (Tetragonia expansa), and other species which have been shown to contain very large quantities of soluble oxalates. Where stock are accustomed to grazing such material along with other plant species trouble is rarely encountered.
Outbreaks of clinical hypocalcaernia frequently occur among stock which suffer a food check during crunching, trucking, or other operations. This suggests either that mobs so affected contain a percentage of sheep with a sub-normal blood calcium level and that the operations referred to lead to the development of clinical symptoms, or that starvation forces the blood calcium down to a pathological level.
While our work has demonstrated that some of the ewes in a flock may have a subnormal blood calcium, we have found that starvation rapidly causes a serious drop in the serum calcium level. For example, in one experiment carried out recently twelve ewes were selected as being mildly hypocalcaemic prior to fasting. Their serum calcium averaged 7.88 mg., ranging from 7.30 to 8.33 mg. After 24 hours fasting seven had fallen below 7.0 mg., the lowest reaching 5.97 mg. Five of these had dropped to levels ranging from 4.40 to 5.30 mg. after a further 48 hours fast. Among ten other ewes which had a pre-fasting serum calcium level of 9.15 mg. (range 8.62 to 9,76 mg.) a similar drop was recorded. At the end of the three-day fast their average serum calcium was 6.90 mg. (range 5.56 to 8.27 mg.). Other experiments with dry and in-lamb ewes have confirmed these results. More recently we have obtained similar results with 2-tooth and 4-tooth stud Merino rams.
Where the fasting period is extended to periods varying from one to two weeks the serum calcium level recovers to values which are as high as, or often higher than, the prefasting level.
Reference has already been made to the value of exercise in detecting ewes in a flock which are already hypocalcaemic. In addition, our experiments have shown that exercise may cause a further drop in serum calcium. For example, in one experiment carried out at the McMaster Laboratory, the serum calcium of a group of ewes which were driven 2½ miles in one and three-quarter hours dropped from, on an average 7.61 to 6.48 mg. During the same period the serum calcium or a similar group of unexercised ewes rose from 8.90 to 9.32 mg.
The above three factors—nutritional, fasting and exercise—are probably among the more important of those responsible for the development of a hypocalcaemic condition in sheep. The in-lamb or lactating ewe, because of the greater demand for an adequate supply of mineral may be expected to show the greatest effect if circumstances are unfavourable.
In addition to these causes heavy parasitic infestation, particularly with Trichostrongylus species, may result in the development of a severely hypocalcaemic condition.
Poor condition may often, but by no means always, be found associated with a hypocalcaemic condition. For example, where groups of poor—and of good—conditioned sheep have been selected from the one mob of sheep the serum calcium of the poor group has frequently been significantly lower than that of the good group.
Dosing with carbon tetrachloride may also cause a large drop in the serum calcium level. This may occur within several hours after dosing. It has been established that carbon tetrachloride may effect temporarily the appetite of sheep, but the drop in the serum calcium occurs relatively soon after drenching before the fasting effect could be expected to play any significant part in the change.
No attempt will be made here to discus in any detail the treatment of clinical hyopcalcaemia. Among those whose work brings them into contact with outbreaks in the field the success attending calcium gluconate therapy is well known. However, the following points may be worth recording here.
The most satisfactory methods of treatment of this complaint include:—
(1). The injection, either intravenously or subcutaneously, of suitable calcium salts. Several years ago calcium chloride solution was used for this purpose and is still used by some workers. For intravenous therapy its use is satisfactory but if used subcutaneously may later cause serious sloughing at the seat of injection.
Calcium gluconate, or calcium borogluconate, is the most widely used calcium salt at the present time. Calcium gluconate itself, has a low solubility but if boric acid is added in the following proportions:—
|Calcium gluconate||20 parts by weight.|
|Boric acid||5 parts by weight.|
|Water||100 parts by weight.|
and the mixture heated, no difficulty will be exeprienced in obtaining a concentrated solution which will keep indefinitely. A mould may develop in this solution after standing for some time but this may be prevented by adding a few drops of thymol solution to it when first made up.
Dose rates vary among different workers. Some use as little as 20 cc. of the solution for each affected animal. Theoretically this should be ample and the majority of cases respond satisfactorily to this quantity. However, when ample supplies are available for treatment, the writer prefers to use up to 100 cc. of the 20 per cent. calcium borogluconate solution, either intravenously or subcutaneously. Either a 4 oz, nickel plated metal syringe or a gravity feed arrangement is best used for the injection.
(2). Mammary gland inflation, treatment comparable to that for milk fever in dairy cows, has been used successfully but is of doubtful value unless active milk secretion is occurring.
(3). Oral dosing with molasses may also be used provided the condition of the animal and facilities available ensure that the drench goes into the stomach and not into the lungs. Most grades of molasses contain a relatively high percentage of water-soluble calcium which is rapidly absorbed into the blood stream and will result in a temporary increase in the blood calcium level, and its use, therefore, is a rational method for the treatment of clinical hypocalcaemla.
In conclusion, It is worth stressing that when treating affected animals suffering from hypocalcaemia, uncomplicated by other disease conditions, no case should be regarded as too advanced for treatment.