Unthriftiness of Lambs in South Canterbury

New Zealand Journal of Agriculture, Volume 99, Issue 4, 15 October 1959, Page 335

Unthriftiness of Lambs in South Canterbury

FINDINGS and recommendations from investigations into 70 outbreaks l" of unthriftiness of lambs in South Canterbury over the past two summers were presented in a paper by M. C. Armstrong, Veterinarian, Department of Agriculture, Timaru, io the Lincoln Farmers Conference this year. An adaptation of the paper follows and summarised recommendations appear in the panel below.

OUTBREAKS of serious ill thrift of lambs in South Canterbury were not widespread during the summer and autumn of 1959. Drought conditions prevailed over most of the district from early spring until the middle of March. There were, however, numerous sporadic occurrences of unthriftiness and deaths of lambs and these presented opportunities for investigations and trials, the results of which are contained in this '

article. It is emphasised that more information is required on the possible detrimental effects of high levels of nitrate-nitrite on appetite and digestion, the role of cobalt on heavier soils, the importance of selenium, and the pathogenic significance of Nematodirus species of intestinal parasites in lambs from October onward.

In this article the terms ill thrift and unthriftiness are synonymous, because in practice both are applied to define lambs failing to thrive in varying circumstances and apparently by different complexities of causes.

The intensity of unthriftiness varies greatly from farm to farm within seasons and between seasons. ■ In different lamb flocks it varies greatly from a contrasting tail-end problem to a general effect on all lambs. We have investigated all of these, particularly several severe outbreaks in 1958 in which all lambs were affected and in which death rates were as high as 50 per cent. Unthriftiness occurred with scouring and without scouring, with appetite and without appetite, and with varying levels of blood volume.

Unthriftiness usually occurs in spring and summer and there is a general tendency for affected lambs to improve in autumn. Outbreaks have

been investigated on all classes of soils from heavy downland clay loams to light stony silt and sandy loams.

Occurrence on Light Soils

The most severe losses occurred over large areas of improved stony soils in the summer of 1957-58. They were limited geographically to stony silt and sandy loams of the following description: Ashwick, Lismore, Steward, Eyre, Paparua stony silt loams, and Pukeuri shallow silt loam. This light land ill thrift coincided with a spring and summer of unusually abundant growth of foliage. It was apparent in early November in lambs six to eight weeks of age and became most severe after weaning time. Trouble was experienced on pasture, lucerne, and rape.

Occurrence on Heavy Soils

On heavy soils the ill thrift tends to appear in a varying proportion of tail-end lambs before weaning and

often at a time when the tops are being drafted as fats. This occurs in seasons of plenty as well as in seasons of scarcity. Some severe outbreaks in November with high incidence and big losses have occurred on heavy land where stock density was high. Outbreaks tend to be more severe under set stocking systems and in the absence of pasture spelling and control by cattle.

Nature of Investigations

During the investigations of 70 outbreaks over the past two summers we have recorded information on management and lamb health. Affected lambs were examined clinically and some typical ones killed for post-mortems. Freshly killed lambs were preferred for true parasite assessments and blood pictures. As a

general rule gut specimens were submitted to the Wallaceville Diagnostic Station for counts of parasites, bacterial examinations, and liver estimates of cobalt and copper.

Numerous cobalt supplement trials were conducted on all classes of land with particular attention to the areas of severely affected light land in 1958. In three of these trials the benefit of an iron, copper, and cobalt mixture was compared with that from cobalt alone. Since early February this year the Department of Agriculture has conducted 44 cobalt trials mainly on heavier fertile soils, on which a percentage of unthrifty lambs was more apparent than on the light land soils, where cobalt had been extensively applied.

In addition seven selenium trials have been conducted —three on cobaltised light land, two on heavy land, and two on non-cobaltised light land. The last four trials were tests of selenium with and without cobalt.

Findings

I. Copper

Normal levels of liver copper existed on all but two farms where odd livers had moderately low copper estimates.

On one of these farms a copper supplement was of no benefit when used in a trial with and without cobalt.

2. Iron

In three trials with severe ill-thrifty lambs on light land soils in 1958 iron was used in combination with copper and cobalt and no benefit was obtained beyond that derived from cobalt alone.

3. Cobalt

The existence of a seasonal deficiency of cobalt over extensive areas of improved light land during the 1957-58 summer was indicated by low deficiency levels in livers and by the results of cobalt trials with unthrifty lambs on various pastures and on rape (Armstrong,. 1958) . This was reported in the “Journal” for September 1958.' Where

cobalt deficiency existed appetites were depressed and blood volumes low. This occurrence of incipient cobalt deficiency was undoubtedly induced by the rapid abundant growth of foliage on leached soils adequately topdressed with lime and phosphate. No molybdenum had been used on these soils, but some had been heavily treated with lime at 6 tons per acre within six . years. . No correlation could ,be established, however, between the severity of ill thrift and the quantity of lime used per acre during the previous six years. More information is required to show what detrimental effects various levels of soil pH may have on cobalt availability in Canterbury soils. It was shown in two trials that the presence of a moderate cobalt deficiency ' could be alleviated by short pasture or sparse grazings where soil contamination of food occurred. Because soil contains about 30 times as much cobalt as pasture, it is considered that the ingestion of soil with short or heavily grazed pasture provides sufficient cobalt for lambs under moderate deficiency conditions (Andrews and others, 1958). New Zealand observations are that seasons favouring lush growth of pastures tend to cause the development of cobalt deficiency disease and the cobalt content of pastures tends to decrease in spring and summer and increase in late autumn and winter. The effect is probably a double one owing to longer, cleaner pasture with less soil contamination and to a lower cobalt uptake in rapidly growing plants.

In the 44 cobalt trials started in South Canterbury since early February 1959, mostly on heavier soils, no responses have been obtained. Pasture conditions for the first few weeks were short and dry and when growth did occur in March and April it was not rapid, long, and lush.

Though extensive seasonal cobalt deficiency was found on light land areas in 1958, there is no information that the heavier soils are similarly affected in South Canterbury and the role of cobalt on heavy land during seasons of lush growth has to be examined in the future.

4. Selenium

In our seven selenium trials this year we have recorded small favourable responses in all of them on various soils. Improved weight gains averaging between 2 and 5 lb per head were obtained in 60 to 70 days during autumn (14 February to 8 May 1959) on ordinary pasture, irrigated pasture, and a mixture of turnips and grass.

It is pertinent to record that there was no history of white muscle disease on any of these farms. These results, with those recorded by McLean and others (1959) and the unpublished information from the Department of Agriculture, . suggest that a selenium deficiency may retard the optimum thrift of lambs during spring, summer, and autumn in Canterbury. 5. Nitrogen Unthrifty lambs killed on two farms in April 1959 showed chocolate coloured arterial blood. With these rare exceptions there have been no clinical or post-mortem signs of nitrate-nitrite poisoning associated with outbreaks of ill thrift. Information is required nevertheless on the significance of sub-lethal amounts of nitrate-nitrite in the ill-thrift complex. 6. Internal Parasitism In South Canterbury our investigations have shown pathogenic counts of parasites in all severe outbreaks of unthriftiness, and the milder outbreaks of tail-end unthriftiness have been associated with either pathogenic or near pathogenic counts in all but a few. The widespread occurrence of unthriftiness on the light land areas in 1957-58 was a “clean tailed”, nonscouring disease in which consistent high counts of Ostertagia species of small stomach worms were present. Copper sulphate-nicotine sulphate and ordinary dose rates of phenothiazine were not found to be effective. Good growth responses of • lambs, however, followed the removal of Ostertagia

species by increased dose rates of fineparticle phenothiazine equivalent to 1-g fl. oz. of a phenothiazine containing at least 60 per cent of particles under 5 microns in size. This gave field confirmation to the experimental work of Thomas and Elliot at Wallaceville (1957). Investigations in the spring, summer, and autumn of 1958-59 in 32 outbreaks have shown the presence of significant counts of Nematodirus species of intestinal worms in 30 (94 per cent) out breaks; Ostertagia species were present in significant numbers in 22 outbreaks or 70 per cent; and Trichostrongylus species were significant in 12 or 37 per cent. Trichostrongylus species were accompanied by Nematodirus and Ostertagia as mixed infestations. Dirty tails and scouring occurred where Nematodirus or Trichostrongylus were significant. In several outbreaks on heavy land severe early ill thrift and losses of lambs in November-December were associated . with high counts of Nematodirus species. Many affected lambs had a secondary bacterial infection and the combined effects were severe and usually fatal. In the United Kingdom acute Nematodirus disease causes serious losses and unthriftiness in young lambs from six weeks of age onward (Scarnell and Rawes, 1959). The drug of choice to use at present is bephenium embonate (“Frantin”) which is efficient for both treatment and prevention. The pathogenic significance of Nematodirus infections in New Zealand is not

11 Book Review I || i-LniiLiLuju jujiU

“The Scientific Principles of Crop Protection”: Hubert Martin

’T'HIS book will be found useful for reference by students, research workers, and others who want to know something of all phases of crop protection. As is evident from the topics discussed, there are many facets to this subject. They include fungicides and insecticides, biological control, the nature of plant resistance, weedkillers, fumigants, seed and soil treatments, nutritional and climatic factors, repellants, and traps. The emphasis throughout is on principles. The book is very readable, full of information, and copiously annotated

with references to published research. Of particular value are the references given .immediately after each topic discussed. This is the fourth edition, the previous one having been printed in 1940. The author, who is the Director of the Science Service Laboratory, Department of Agriculture, Ontario, Canada, has accounted for many advances in the use of chemicals developed since the Second World War. —K.C. Edward Arnold Ltd., London. 655.

known and trials with bephenium embonate are necessary.

Internal parasitism was most severe under conditions of high stock density and where . there was inadequate spelling of pastures from sheep. There were many good recoveries from unthriftiness by worm control alone, especially on heavy soils. Furthermore, in both our cobalt and selenium trials the maximum and most regular weight gains were obtained in the presence of worm control. The great advantage in weight gains by controlling parasites in addition to the use of cobalt and selenium has emphasised the harmful nature of the parasites encountered in these outbreaks. References E. D. Andrews and others, “New Zealand Journal of Agricultural Research”, vol. 1, p. 125, 1958. M. C. Armstrong, “New Zealand Journal of Agriculture”, vol. 97, p. 241, 1958. J. W. McLean and others, “New Zealand -Veterinary Journal”, vol. 7, p. 47, 1959. J. . Scarnell and D. A. Rawes, “Veterinary Record”, vol. 71, p. 163, .1959. P. L. Thomas and D. C. Elliot, “New Zealand Veterinary Journal”, vol. 5, p. 66, 1957.

Swedish Landrace Pigs for Breeding Scheme at Ruakura

PUREBRED Swedish Landrace pigs imported from Australia by a New Zealand breeder are to be lent to the Ruakura Animal Research Station, where under the direction of D. M. Smith, Senior Principal Scientific Officer, their potentialities will be investigated and their possible use in the hybrid breeding programme explored.

THE first of the stock, an in-pig gilt, arrived at Ruakura on 21 August after a month’s quarantine in this country. She farrowed a litter of 10 piglets in mid September. Acquisition of Landrace stock opens the possibility of using, the three-breed rotational cross system of breeding (Berkshire-Large White-Landrace) and thus keeping hybrid vigour up to a maximum. This system has been very successfully exploited in America and was studied there by Mr Smith several years ago. The sow and her progeny will be tried out at Ruakura under standard conditions to compare growth rate, feed conversion efficiency, and carcass quality with the same qualities in New Zealand pigs, on which a great deal of data has been assembled at Ruakura. Two Swedish Landrace boars are already in the country and two more are coming. An importing breeder has promised to make a total of six sows and two boars available to Ruakura. The Pig Producers Council, which has supported and encouraged the hybrid breeding work already done at Ruakura, is showing keen interest in the possibilities presented

by the acquisition of this new breed for use in the scheme. The Swedish Landrace is performing very well in England. Some stock have gone to Northern Ireland, whence importation to New Zealand is permissible because of the absence of rhinitis there. Mr Smith is enthusiastic about the future possibilities of pig improvement in New Zealand offered by use of Swedish Landrace boars across crossbred sows.

Mob Stocking of Ewes at Weaning

RUNNING the ewes in large mobs after weaning is a management practice now widely adopted, but weaning, is not done early enough on many farms to get the best results from mob stocking. Research has shown that once lambs are three and a half to four months old they will do as well away from their mothers provided plenty of clean, fresh grass is available for them. This can be arranged by increasing the stocking rate for better control of the pastures during the spring flush on part of the farm and saving for the weaned lambs the paddocks from which the sheep have been removed; the top growth in these paddocks is controlled by the cattle. By early weaning the mob of ewes can be used more or less as a mowing machine at a time when they can do some real good in cleaning up roughage from paddocks in turn, in cleaning up rough gullies and shady faces,

and in the control of bracken fern, weeds, and small second growth. They can be crushed on to areas that want severe treatment or used on the poorer pastures while the best of the feed is saved for fattening stock. It is surprising how white clover will flower and set seed after a mob of ewes has been crushed on to a paddock in . November or early December. Paddocks that have been so treated and then spelled for eight to 10 weeks provide excellent feed for lambs in late February and March and the clover will thicken up through the reseeding. Having the ewes in a mob before shearing is of course a great convenience.

—E. C. AYSON,

Farm Advisory Officer, Department of Agriculture, Wairoa . .

Recommendations

THE use of additional cobalt is .indicated on' light stony soils where unthriftiness in lambs has been troublesome. Warm, wet seasons with fast, lush growth of pastures favour incipient cobalt deficiencies, and cobalt trials on other soils are worth repeating during seasons of unusually rapid pasture growth associated with unthrifty lambs.

The control of internal parasites on pastures in South Canterbury cannot be assured at present by providing known nutritional factors. Satisfactory control should be maintained by spelling pastures, cleaning up with cattle, and by the preventive use of fine-particle phenothiazine. Care should be taken not to give phenothiazine to partially dehydrated lambs under dry conditions off dry feed.

Where Nematodirus infestation is suspected before* weaning, trials with bephenium embonate ("Frantin") are suggested.

No recommendations can be given at present tor the use of selenium and field trials with this will be continued in the future.