However, according to a couple of articles I recently came across, there was a more important reason: to reduce the risk of lamb mortality from blood poisoning and tetanus.
The central location helped avoid previously used yards that may have been contaminated.
This was especially those used for foot rot treatment, thereby lowering the chance of infection from dirty ground.
Sheep raising
New Zealand Herald, September 2, 1932
Losses in docking
Risks sometimes overlooked
By H.B.T
There is no doubt that a good deal of avoidable loss occurs at docking time, and as no avenue of increasing the income from sheep can be neglected at present, common mistakes might profitably be brought before the notice of farmers who will shortly be undertaking this annual job.
In the first place, many farmers, in an attempt to minimise the work, leave docking and earmarking until all the ewes have finished lambing, and the youngest lambs are a week or perhaps a fortnight old.
This certainly entails only one muster and eliminates drafting the ewes out of the flock as they lamb, but many of the lambs are, under this system, six weeks, or two months old before they are docked.
Such lambs suffer a bigger check at docking than those operated upon when only a week or two old.
They lose a comparatively greater quantity of blood, their wounds take longer to heal, and they are more likely to become mismothered than are very young lambs, which are more carefully attended by their mothers after the operation.
There is also more trouble and risk of dislocated joints in catching and holding the older lambs at this time.
Everything points, therefore, to the advantage of docking in each paddock at least twice, where this is practicable.
A Common Fault
A common fault at docking time is to commence operations immediately the ewes and lambs are yarded.
Lambs become very excited and do a lot of unnecessary running about on their first mustering and yarding.
Their blood becomes heated, and if docked in this condition, they lose an unnecessarily large amount of blood.
In this weakened condition, mismothering is more prevalent.
It pays to start the docking muster early in the morning, before the sheep have left their night camps.
This saves a lot of time and running about getting them together.
They should be brought in as quickly as possible, led by a quiet dog, and with the noisy huntaway kept well in hand.
The less dogs are allowed to work on ewes with lambs, the better.
When the ewes and lambs are about to be yarded, use docking sheets to prevent breaks, and take plenty of time over the business.
The early start will make it possible to let the sheep settle down for an hour or two.
Thus one will avoid docking which the lambs are heated, and it also gives the lambs time to mother up, which is important later on in the proceedings, as the drafts of ewes will then go out very shortly after their youngsters have been operated upon, and will have no difficulty in finding and suckling them quickly.
Change of venue
It is not always possible, though desirable, to erect docking yards on fresh ground every season, but docking yards should not be used during the year for other sheep work, such as foot-rotting, or for work the refuse from which would breed germs, otherwise, two evils are likely to affect the lambs.
The first of these is blood poisoning, which takes a toll of more lambs than is usually realised.
Tetanus is equally likely to result from newly-docked lambs lying on infected ground.
The chief evil resulting from docking in dirty yards is, however, undoubtedly lymphadenitis.
This is really a mild form of blood poisoning.
The germs, or poison, enter the wounds and start to make their way through the blood stream back toward the heart.
There are, however, glands placed at various points of the body, notably where the limbs join the carcase, which arrest, and if possible absorb these germs and poisons, destroying them before they can pollute the whole blood system.
These glands become swollen with lymph and other matter during the process of their beneficial work, and if the lamb is killed while they are in this state the carcase is usually rejected on account of “lymphadenitis.”
A visit to the freezing works when lambs are being inspected for this trouble will convince any fanner of the seriousness of this so-called disease, from the point of view of the lamb-fattener.
This is an excerpt – read the full article here.
Temporary Yards
Daily Telegraph (Napier), July 21, 1933
Docking Practices in Hawke’s Bay
Letter from Ex-Otago farmer
Movable yards strongly commended
Support for the views expressed on this page on Monday last, in favour of the use of temporary yards for docking purposes in Hawke’s Bay, is contained in a letter which I have received from an ex-Otago sheepman, now resident in Napier, who states that he received a surprise when he learned that apparently there were farmers in Hawke’s Bay, who utilised permanent yards for docking.
“When I was farming in South Otago, it was an almost unheard of practice there to use anything but temporary yards and a clean paddock for docking,” he writes.
“Whenever possible, the paddock was shut up for a week or ten days previously and in any case, cattle and horses were rigidly excluded.
“Needless to say, lamb mortality was negligible—in fact the loss of a lamb was something to wonder at and inquire into.
“As recommended by you, all cuttings were cleaned up and burnt, and the use of temporary netting fences was quite common. The yards were dismantled and re-erected on a new site for each draft of lambs, not only for each season. Operations were always ceased early to allow mothering to occur and the sheep to settle before dark.”
“As an actual fact, lamb mortality from blood-poisoning at docking time is comparatively rare in Hawke’s Bay, although cases have occurred in which mortality from such a case has been quite heavy, and where such cases have occurred, permanent yards have always been utilised for the purpose of docking.
“Another danger that exists in the use of permanent yards for this purpose is, of course, that of the spread of caseous lymphadenitis, a trouble which is present in Hawke’s Bay and which annually causes a small percentage of rejections amongst fat sheep and lambs at the Hawke’s Bay Freezing Works.
The only manner in which lambs can become affected with this trouble is at docking time and it would therefore pay sheepmen to watch their methods and with the use temporary yards and disinfected implements see to it that no danger of infection exists from this source.
As pointed out in the previous article, many of the most prominent and successful farmers in Hawke’s Bay have been docking from temporary yards for many seasons and have thus avoided any fear of mortality.
– Source: Papers Past