COBALT DEFICIENCY IN SHEEP

New Zealand Journal of Agriculture, Volume 63, Issue 4, 15 October 1941, Page 287

COBALT DEFICIENCY IN SHEEP

iiiHHiiiii By titmtiitttti

J. F. FILMER,

Acting Director, Animal Research Division, Wellington.

Is Monthly Drenching Effective ?

r T' , OPDRESSING with cobaltised Topdressing with cobaitised 1 superphosphate is now widely recognised as a convenient and effective method of preventing “bush sickness.” Where autumn topdressing of pasture is practised, the application of soz. of cobalt sulphate (this amount is present in lcwt. of cobaltised superphosphate of the 61b. cobalt sulphate to the ton grade) per acre with the annual topdressing proves 100 per cent, effective, and no other method of control need be sought. There are, however, some ' areas where, for various reasons, regular topdressing is not practised. Here, cobalt must be supplied in some other way, and the most usual method is to allow free access to cobaitised licks. This is quite satisfactory if the sheep eat adequate quantities of the lick. A suitable lick may be made by mixing loz. of cobalt sulphate with 4cwt. of salt and lewt. of linseed meal. On “bush sick” country 100 sheep would require to eat about 71b. of such a lick each week to obtain sufficient cobalt to keep them healthy. Unfortunately it is often difficult to get sheep to eat a lick, and even where the majority take it readily, a significant percentage either neglect it altogether or else eat very small quantities, and these naturally become “bush sick.” ,

Drenching Trials

Because of this difficulty with licks, drenches have often been considered as a means of supplying cobalt. It has been quite definitely established that drenching regularly with cobalt at short intervals will both prevent and cure “bush sickness,” but this is not convenient with large numbers of sheep, and farmers have often inquired whether cobalt would be effective if given at monthly intervals. To settle this question, Dr. C. S. M. Hopkirk conducted some drenching trials on a

“bush sick” farm at Arohena between November, 1936, and April, 1937 (“New Zealand Journal Agriculture,” 54, 6, 344). Ewes with lambs at foot were divided into four groups. One of these received no treatment, while the others were drenched with cobalt sulphate solution. The doses were so arranged that in all of the treated groups each ewe' received 6 milligrams (mgs) and each lamb 3 mgs. of cobalt per month. (One ounce of cobalt sulphate contains about 5,600 milligrams of cobalt.) The total monthly amounts were, divided into drenches, which were given at the following intervals: —

"Group 1: Ewes twice weekly; lambs once weekly. Group 2: Ewes and lambs once weekly. ’ Group 3: Ewes and lambs once monthly. ' The results indicated that although the ewes and lambs which '■ were drenched monthly remained alive the lambs grew at only half the rate of those drenched every week. Some ewes and lambs which became “bush sick.” in the control group were also treated with the monthly drenches, but the results were not very satisfactory.

It will have been noted, that ,in this experiment the ewes and lambs drenched once a month received the same amount of cobalt per month as those drenched once or twice weekly. Dr. Hopkirk, in describing the experiment, mentioned that some farmers had been giving very much larger doses at long intervals. In April, 1939, attention was again drawn to this practice when one farmer reported very good results from monthly drenches in which ewes received 140 mgs. and lambs 70 mgs. cobalt each. It was therefore decided to try the effect of this treatment at the Mamaku State Farm, where experiments on the control of “bush sickness” were being conducted. Further Trial There were available 26 Romney lambs which had been born between August 14 and October 25, 1938, and had grazed in a “bush sick” paddock since birth without receiving any treatment. Starting on June 7, 1939, six of these lambs, which were all losing weight, received a drench containing

of cobalt twice weekly, and the other three groups of four ewes each received 10, 50, and 140 mgs. of cobalt respectively once a month. The experiment was started on October 26, 1939, and ended on February 13, 1941. The lambs born in 1939 and 1940 received the. same treatment as the ewes, and drenching began when they were about

one month old. The results are shown in Graphs 2 and 3. Average Weights It will be seen in Graph 2 that the untreated ewes maintained a fairly constant weight until the 1940 lambing, after which they lost weight rapidly. By the end of the experiment only

140 mgs. of cobalt once a month. The results are shown in Graph 1. The treated lambs responded immediately, and with one exception made remarkably fine gains. From June 7, 1939, to February 28, 1940, a period of 266 days, they made an average gain of 621 b. If one lamb which lost weight (probably from some cause other than “bush sickness”) be excluded, the average gain was 711 b. and the average weight' on February 28, when the sheep were 16 months old, was 1351 b. During the same period nine of t the 20 untreated lambs died, and with one exception the others all lost weight. These results suggested tjiat monthly drenches were quite effective in curing “bush sickness” if very large doses were given. Unfortunately, however, none of these lambs had been treated by the standard methods of grazing on cobalt-top-dressed paddocks, giving cobalt licks, or normal doses of cobalt- in drenches at short intervals. It . was thus not possible to say how this method of treatment compared with those more generally practised. A further experiment was therefore conducted. Shortly after lambing was completed in 1939, 34 Romney ewes which had been running in a “bush sick” ’ paddock since July, 1938, were divided into five groups. Seventeen were kept as untreated controls, five received 1 mg.

three out of 17 remained' alive, and their average . weight was . then only 1061 b. Of the treated ewes, those receiving 1 mg. of cobalt twice weekly did much the best, while the monthly drenched groups were arranged in order of the size of dose. One ewe in the group receiving 10 mgs. of cobalt per month died of “bush sickness.” The only other death was a ewe in the group drenched twice weekly which died at lambing. The average weights at the start and the end of the experiment, are shown in the following table. The rather wide divergence in initial weights is due to the fact that the groups were picked on the basis of lamb weights. •

Graph 3 shows the growth of the 1939 and the 1940 lambs from the above ewes. In addition, data for lambs from a paddock topdressed with cobaltised superphosphate have been graphed for both years, and for 1940 a group

of lambs, receiving cobalt lick has also been included. In 1939 all of the controls died from “bush sickness” during January, February, or March. No deaths from “bush sickness” occurred in any of the treated groups, but the lambs in the groups drenched once a month did not do nearly so well as those drenched twice weekly or those grazing on pasture topdressed with . cobaltised superphosphate. The average liveweight on October 24, 1940, of the lambs drenched twice weekly, those grazing on pasture topdressed with cobaltised superphosphate, and those receiving 140 mgms. of cobalt once a month were 1361 b., 1291 b., and 911 b. respectively. In 1940, similar (results were obtained. When the experiment terminated on February 13, 1941, the average weights were as follows: Drenched twice weekly, 881 b.; grazing cobalttopdr essed paddock, 931 b.; cobalt lick, 691 b.; 140 mgms. of cobalt once monthly, 671 b. The low average weight of the lambs on cobalt lick was due to the fact that several of these lambs were obviously not taking the lick. The heaviest lamb in this group was‘92lb., but there were three lambs under. 501 b., the lightest being only. 311 b.

Summary (1) Drenching at monthly intervals with very large doses of cobalt will keep ewes and lambs alive on “bush sick” country and will even cure “bush sickness.” (2) Lambs treated in this way do not grow nearly as rapidly as those drenched once or twice weekly or those grazing on pasture topdressed with cobaltised superphosphate. (3) Monthly drenching with very large doses of cobalt gave results similar to those obtained from giving free access to cobalt lick. It was, however, more expensive, as the drenched lambs received about, fifty times as much cobalt as the lambs on lick. (4) In view of the above results, monthly drenching should not be practised where topdressing is possible or where sheep will take licks. (5) If, for special reasons, it is necessary to resort to monthly drenching, the drench should be made by dissolving 11b. of cobalt sulphate in one gallon of water. The monthly dose for both ewes and lambs is half a fluid ounce. It is absolutely necessary to drench the ewes as well as the lambs.

„ , , 1 Ave. weights Treatment. I | Ave. weights 126/10/391 13/2/41 1 Untreated controls .. < .. 1 147 147 106 106 1 mgm. cobalt twice weekly | 115 115 167 167 10 mgms. cobalt once monthly 129 129 127 127 50 mgms. cobalt once monthly 149 149 148 148 140 mgms. cobalt once monthly 128 128 143 143