DISEASES OF FARM STOCK

Taranaki Daily News, 24 August 1931, Page 15

DISEASES OF FARM STOCK

WAR AGAINST CONTAGION

EXTENSIVE RESEARCH REVIEWED.

JfO SOVEREIGN REMEDY ObUERED

There was no sovereign remedy to offer for the three chief diseases of dairy stock, contagious abortion, contagious mastitis and sterility, said Mr. Webster, departmental research officer, in an address at New Plymouth. The diseases were world-wide and extensive

research into their cause and preveni tion was progressing in every country in- which dairying was carried on to any extent. Despite all that work, however, the scientists were unanimous that, speaking generally, no remedy was yet discovered which would cure any one of the diseases. - There was an old adage that prevention was better than cure, and as the causes and effects of these diseases were being gradually laid bare by careful investigation, so, it was becoming

possible to lay down rules, the observance of which would steadily and progressively check them: prevent their spread. Contagious abortion an mastitis were two diseases alike in their cause and effect in whatever part of the world they might occur, but in many respects temporary- sterility was a peculiar problem of New Zealand since conditions were so o"c.ent here. In this Dominion the dairy industry was strictly seasonal, stock were not housed and they produced .their milk en a natural diet of pasture.'k; All-the-year-round dairying, housing for ex-, tended periods and heavy concentrated feeding on artificial by-products ouch as were practised in most-countries entailed their ow.’ peculiar problems in sterility investigations, so that results in other countries were in many respects not strictly comparable with those in New Zealand.

CAUSES OF DISEASE. Contagious abortion was due to a specific germ. The popular name for the disease was unfortunate. The act of abortion was only the most obvious symptom of the disease and occurred in perhaps 25 per cent, of affected cows. The farmer, however, was lulled into a false sense of security in thinking that only those cows which actually aborted were infected. What actually happened -was that the germ was- generally ■picked up from the pasture during grazing, but might occasionally be transmitted by the bull or through abrasions on the skin, and made its way to the pregnant womb and/or the udder. In the womb it set up a -slo~ chronic inflammation which gradually destroyed the points of attachment - between mother and calf, through which the nourishment of the calf wasdrawn. When sufficient of these attachments had been destroyed the calf could no longer maintain life, but died and an abortion resulted.

, The whole process was slow, however, and the time taken between contraction of infection and actual abortion varied from six weeks;.-to four months,, or was even longer. Thus many cows might contract the infection and yet carry a full-time calf, particularly if they were, already several months in calf, before becoming infected. Frequently such cows failed to clean, normally after calving, and their calves, though not premature, might be weakly. The discharges from an infected cow, even though she might calve and clean normally, were teeming with the germs of tho disease which were thus easily broadcast over the paddocks, where they yet may be picked up by other Susceptible cows while grazing.

MIGRATION OF ORGANISMS. ■ The womb was clear of. the germs •within a few weeks of calving, but that did not :mean that the cow was free from infection. The organisms migrated to the udder, where they sot up a very mild form of mastitis. When the cow bred again they returned to the womb and repeated the process. After the first attack, however, the womb acquired considerable resistance and not many ..cows would', actually abort their- >• secondtime, although’ they' were just as much l a source of danger to others at. a subsequent calving. Gen,-• erally,'aborting cows bred again .without much difficulty, but in a small proportion of cases secondary' germs invaded the unhealthy womb after calving and there ensued a 'more or less permanent form of sterility, difficult to treat satisfactorily. r s Fortunately it was. possible by a reliable laboratory test of a small sample of blood to detect infected cows at any time, whether they had aborted or not. The whole scheme for the control of the disease rested upon this blood test. Many thousands of tests in New Zealand had shown that 20 to 25 per cent, of cows had reacted. In Taranaki the records of 24,000 cows showed that about 5 per cent, of them actually aborted. Recently a much wider survey covering every part of New Zealand gave just under 4 per cent, abortions in nearly 130,000 cows. It was obvious, therefore, that actual abortions accounted for only a small fraction of the infected cows'. Production records had shown that the average cows reacting to the blood test showed a 12 to 15 per cent, decrease in production compared with negative or non-infect-td cows.

INFECTION OF HUMANS. Recently an added importance had been given to the disease by . the discovery that man not infrequently became infected with the germ, through drinking milk or handling infected animals. The disease was termed “undulant fever” in the human being. It •was more prevalent amongst men than women, and its most characteristic feature was recurrent attacks of fever

lasting for a week or. more and repeat- „ ed at intervals for a period of months or even a year in some cases. It had . also been found to affect other animals, particularly pigs and poultry and sometimes horses. In the United States

most human eases had been traced to

infection from pigs. In New Zealand quite a number of cases of undulant fever had come to notice within -the past year or two Presumably they had been contracted from cattle, since pigs had not yet been found affected. Nevertheless. a keen look-out was being kept for it in view of the experience i in.: the .United : States and if. any : .farmer . laid any premature, births Wmong; his breeding sows . Jio : , should! report the. matter and allow-Mr. Web-.

ster to take blood samples. However, apart from that aspect the loss to the dairy farmer from abortion disease might be summarised under four heads; (1) Actual abortions; loss, of calves and in the case of early abortions, loss of season’s milk production. (2) Unthrifty calves from, infected cows which did not abort. (3) Decreased milk yield of all infected cows whether aborting or not. (4) A certain percentage of more or less permanent sterility as a sequel.

No method of a curative treatment had hitherto given any success with the disease. Vaccination had been tried very extensively. Several thousand cattle had been treated by that method in New Zealand under carefully controlled conditions, with entirely negative results. When it had been introduced great hopes were entertained for that method and it was extensively advocated in England by the Ministry of Agriculture, which supplied the vaccine. The results were so discouraging, however, that the Ministry in England was endeavouring to discourage that method of treatment as far as possible.

CONTROL OF THE DISEASE. Control of the disease, was based on the knowledge of the method of spread and the blood test. The latter enabled them 'to detect all infected animals in a herd and the ideal method of eliminating the.disease was to dispose of the reacting cows and replace them subject to the blood test, -quarantining all replacements for a period as a precaution. That scheme was by far the most satisfactory when infected cows were few in number, but when they represented

a. third or more of the herd as was frequently the case, it presented serious financial difficulties and the alternative was what was termed the “segregation system.” That scheme was used extensively and with encouraging results in the United States and was : working; satisfactorily in a number, of herds in New Zealand. 'Since- the disease was spread mainly by way of the digestive system through grazing infected pas-

ture that plan involved the division of the herd into clean and infected groups with a separate grazing rotation arranged fdr each. Great care had to be taken that the possibility of any grazing common to both groups was entirely eliminated. Additional precautions were necessary at milking time. Whenever possible the two groups should be milked in separate sheds. When that was impossible the infected group must invariably be~milked last .no the machines and utensils carefully cleansed after each milking. The disease was not congenital or hereditary ~nd heifers, provided they were removed from' any source of in-., fection prior to reaching breeding age, automatically augmented tho clean group, while the reactors were culled as the heifers replace them. Thus within three years at most and frequently by the end of the second season it was ■possible to dispose of the whole of the reactors and build up a clean herd at no cost beyond the extra trouble involved in running a double herd for a period of- two or three seasons. By that means large areas in the United States had been entirely freed from the disease. Fortunately the abortion disease bacillus quickly died out on contaminated pastures under the combined influence of sunlight and fresh aii- and after an isolation period of a few months (for example, while a paddock was shut for hay) it was safe to use it again for clean stock.

HELP OF THE DEPARTMENT. The' department did all the blood testing necessary and supplied all other necessary advice to any farmers willing'to adopt the scheme. The. scheme admittedly involved .considerable trou-, ble for a period, but when it could be adopted with any prospect of success the results undoubtedly justified the extra labour involved. At the same time when it was considered that it could not be put into force .’through labour difficulties or insufficient * subdivision of paddocks, then Mr. Webster strongly advised that the herd be main-' tained by home reared heifers. The heifers would be liable to infection .certainly, but a certain herd tolerance.developed to that particular infection. On the other hand when heifers or. cows were brought in from outside sources, a fresh strain of the germ was often introduced and resulted, in an increased virulence and a., greater , percentage of infectioh, with its attendant 7 consequences. That fact had been brought ; out by statistics... .It was found'., that the percentage of actual abortions was, on' an average, significantly higher in herd maintained by outside purchases as compared with those self maintained. . Contagious mastitis, like contagious abortion, was very insidious in its outset and infinitely more widely distributed than the average dairy farmer realised. - Mr. Webster impressed upon farmers that every case of mastitis should be considered contagious unlees there was definite evidence in the form of an external bruise or wound on the udder that it "was accidental. Mastitis was lying latent or dormant in the udders of a very high percentage of cows, requiring only favourable circumstances to develop into an acute, easily recognisable case. The so-called chills that one so frequently heard mentioned were only those latent cases which had flared up owing to a sudden change in the weather having temporarily lowered the natural powers of resistance which had previously held, it . in check.. The great majority of cases of mastitis were due to a germ called a streptococcus. In those cases in which there was fever and swelling in the udder and which usually ended in abscess formation the cause was some other germ, but such cases were comparatively few.

MASTITIS SYMPTOMS. Streptococcic mastitis of the type the farmer could recognise varied from the form in which the only evidence was a tiny elot or two in the fore milk, with little or no swelling of the quarter, through all stages to that

in which the quarter was hard and firm and the secretion much diminished in quantity and yellow brown in colour and containing many clots. Apart from those recognisable cases, however, a laboratory examination of milk sam-

pies from a herd revealed other cows

obviously affected with the disease yet showing no clinical evidence whatever. Yet since the disease was contagious, such were obviously potential sources of infection to an even greater extent than clinical cases, since they were unrecognised and no precautions were adopted. Within the past few months that disease had assumed .an even greater, significance since eqmb, ...experiments had strongly suggested ilidt ithp • -. aihouiit of mastitis in a., herd jpjg'ht .. ......’.I .b-wT fOO-fl ;

have a decided bearing on the quality of the cheese manufactured from the milk.

" As a result of work during the past two or three seasons a very great deal more was known about that disease. There was no cure for mastitis and there was little doubt but that once a cow was infected she was infected for life. The cures attributed to so many different remedies were only apparent. The more acute symptoms subsided, but a laboratory examination of the milk from such a quarter would infallibly show that the infection existed in latent form and it was certain that at some time it would again develop and might again subside, but the quarter became gradually weaker and eventually was more or less completely lost. Vaccination had been extensively practised but had proved entirely valueless in controlling this disease. In view of the divided lay opinions on that subject it was interesting to note that Dr. Minnctt, the foremost authority on that subject in England, expressed an identical opinion at the international veterinary congress last year.

ATTACK OF THE GERM.

The internal structure of the udder somewhat resembled that of a sponge. The milk was actually secreted *by the cells lining the smallest terminal pores and gradually collected in the large cavities which communicated with one another and finally wit'll the teat duct. The mastitis germ attacked the secreting cells in the deepest, most inaccessible parts ori the udder and gradually destroyed them. At the same time the animal’s system mobilised its defences in the. shape of the leucocytes—the white corpuscles of the blood. Those congregated at the invaded part and caused dwelling and inflammation. These leucocytes or pus cells, as they were often called, passed out into the milk spaces of the udder and attacked and destroyed the mastitis germs and were secreted with the milk. It was ■ largely their presence -that enabled them in the laboratory to decide at a glance whether ■or not mastitis was present in a milk sample. The streptococci themselves could often be detects cd only with great care or after culturing the milk, but a microscopic examination at once revealed the presence of the pus cells, which did not occur in milk from a normal quarter. Often in a yellow clotted secretion the pus cells were present in very large numbers and the germs were difficult to detect because the altered character of the milk indicated a specially strong effort to resist the infection and the germs were probably overpowered for the moment. Soon the secretion from the quarter became more or less normal in appearance again. The pus cells had relaxed their vigilance. If a sample of that apparently normal milk was examined, pus cells .would be found present in considerable numbers still, but in addition the streptococci were often seen in great numbers. Sooner or later the latter, gained the upper hand again and stimulated t'he system to, a fresh effort. ’

SPREAD OF DISEASE. There was no doubt about the contagion of mastitis. The disearsc was in all probability spread during milking both by hand and machine and appeared to gain entrance mainly through cracks and sores on the-teats. Another probable way of entry was by the teat canal itself. In the ordinary way the external opening of the teat duct was tightly closed by a small muscle which surrounded it, but after milking—particularly if the vacuum pressure had been too .high or the machine left on longer than was necessary—-that muscle became paralysed for a time and the entrance of the duct was left wide open, inviting entrance of any .germs which might gain access to it. In the case of abortion certain tolerance was acquired and after t'he first acute manifestation, the effects tended to become less obvious; on the other hand no such tolerance or acquired immunity appeared to occur with mastitis, the effects of which tended to her come progressively worse with each acute manifestation. Control of the disease was being based on. those adopted.for abortion—the segregation; of the clean from the affected cows and the gradual elimination of the latter as circumstances per-, mitted. The . application of that, system .-was not; attended by nearly the same difficulties.. They had no evidence whatever that mastitis wais spreadby grazing contaminated pasture.C'on-

jscquently all that .was necessary was to segregate the two groups at milking time. The .clean cows had to be milked first and the infected cows last each time and particular care taken to cleanse machines and utensils after each milking. It was useless, however, to attempt segregation' on a naked eye examination of the milk or a manual examination of, the quarters. He had already made it clear that such a method failed to detect many affected cows. A laboratory examination of the milk from every cow in the herd required to be made three or four times during the reason. That scheme had been used during the past season to some extent in - the Waikato with very promising results. It appeared to be definitely checking the spread off the disease in those herds and the affected cows were being culled as opportunity permitted. Another valuable precaution was to disinfect the teats after milking. The more potent coal tar antiseptics < ould.be used for that purpose since any odour would •disappear long before the next milking.- A pint enamel mug filled with the antiseptic solution served the purpose admirably. It was the work of a moment to dip each of the four teats in the pannikin last thing before the cow was released from the bail. A closer watch on the machines was also most desirable—some cows milked out much more quickly than others and the practice of removing the machines and

hanging them up if the strippers were not ready should be universally adopted, rather than the usual method of leaving the machines on the cow until the stripper was ready to complete the milking or another cow had come into the opposite bail. In connection with the examination of milk samples, any farmer bringing them ' into the laboratory would be shown for himself what his milk looked like under the microscope. As regarded treatment, no improvement was known on the well established method of thorough and repeated massage and stripping. That -must be undertaken as soon as a quarter was noted to be abnormal. That treatment, coupled with a pound dose of salts, if conscientiously carried out would in the majority of eases produce a normal appearing milk within a short time.

Abortion and mactitls were. contagious di&e'ases due to a, specific germ in each instance, and. though, he. had. referred. tq sterility l( in,jargon eral way

an a disease, yet strictly speaking it was a group of diseases due to a number of causes and. in many instances •was not in an accurate sense a disease at all but rather a physiological lowering of the breeding efficiency. They had made infinitely more progress in unravelling that problem than in the preceding two, and there was no doubt that the adoption o e more careful farming methods would go a long way towards checking the economic loss resulting from temporary sterility, the failure of cows to breed at the proper time and their return to the bull a number of times before holding. The normal period for a cow to return was three weeks; a few came back at shorter intervals, but many after longer periods, and the average for all returns was about. 25 days. Every-time a cow returned meant, a loss of 25 days from her milking period in the ensuing season. If in a herd of 50 cows there were only 10 returns it was a very good record. , Nevertheless it represented the loss, of 2ll' milking days in the following year, or almost the whole season’s production for one cow. In comparing the breeding efficiency of different herds they calculated what was termed the breeding efficiency index. That was a figure obtained by dividing the total numbei of services recorded by the number of cows in the herd. In the case mentioned the index would be 1.2 (00 services) divided by 50 (cows). That was a good standard. Yet on many farms the breeding index was much higer, a figure of 1.0 being common and in some herds it was as i high as 2.0. TARANAKI STATISTICS.

Statistics had been- collected from 550 herds in Taranaki numbering 24,000 cows. Those herds, maintained by home beared heifers and in which - the bull was kept separate and the cows handserved, had an average of 74 per cent, of the cows calved by August .31. At the other extreme, herds in which the bull was run with the cows and the herd kept up by means of sale-yard purchases had an aver ,ge of only 02 per cent, of cows calving by August 31. It was obvious that to calve by August 31 the majority of cows must have held to the first service, although a lew of the earlier ones might have returned once. However', it was obvious from these figures that the breeding efficiency of the herd could be considerably improved by better farming practice. Running the bull with the herd was an objectional custom from many points of view and he had already referred to the advantage of home-reared heifers when dealing with abortion. A great deal was heard about the mineral requirements of stock and it was becoming generally realised that adequate mineral supplies were essential for both production and reproduction. Pasture samples had been analysed for mineral contents from a large number of representative farms, 50 in all, throughout North Taranaki, from Opunake to Uruti and southwards as far as Stratford. All those farmers were rearing their own heifers ' and hand-serving their cows. The breeding indices varied from 1.1 to-2.1.

On the average the farms with a high phosphoric acid content in the pasture had a high breeding efficiency and as the phosphoric fell so did the breeding efficiency . become poorer. Statistically they would account for something like 50 per cent, of the variation in the breeding, efficiency ■in that of the mineral content of the pastures. Phosphorus was the most important mineral. However, the ratio of lime to phosphorus was just as closely connected with breeding efficiency. A narrow ration was correlated with good breeding results and a wide ratio • with poor results. There was no indication of any -shortage of lime in any of the North• Taranaki pastures analysed;- indeed, the average lime content was the highest of any he had seen reported in any part of the world. On the other hand, there was a suggestion that the lime content of some of them was rather too high to give the best results. In any case nothing could be done to counteract this, but in the case of phosphorus, which was definitely deficient on many of the. pastures, the deficiency could be made«good. It was a significant fact that all those farms had been regularly top-dressed with phosphatic manures. Topdressing would eventually bring the phosphoric acid content of the pastures up. to standard, but would I ■be; an expensive, process- bit many 'of the poorer farms. 'Additional . phos-' phate's could satisfactorily be supplied by licks and other means, and there ap-. peared no doubt that., the' widespread use of licks would result' in an‘improvement in the general breeding efficiency.

PRODUCTION AND STERILITY.

There wae a widespread idea that

the high producers were generally the cows that" gave most breeding trouble. As the majority of the farms mentioned were under test they ’were able to go into that side of the question also. In the better farms with high mineral content there was no connection be-

tween production and sterility, but on the poorer farms there was a definite though not very marked- tendency for the high producing individuals to give

most trouble in breeding. The-' butterfat records afforded much valuable information. The herd production varied from an average of 1.43 lb. of butterfat per' day down to 0.85 per day. Here again they could account for roughly 50 per cent, of the variation

lirectly in the mineral content of the

pasture. High phosphoric acid and high production were correlated, and wliei'c the phosphorus was low the production was also low. The lime/phosp'horus ratio was of lesser importance in that direction than the total phosphorus content, and there appeared to be no connection between the lime content, and production.

There was a very close connection between the phosphoric acid content of pasture and its stage of growth; young growing, pasture contained the highest amount,* but the latter' fell rapidly as the pasture ripened. It was significant that the association between the phosphoric acid content of the pasture and the butterfat production were distinctly closer in the autumn than in the spring. That, fact' indicated the importance of good pasture management so as to keep a young green growth throughout the season as far as possible.

There appeared to be strong grounds for assuming that the widespread provision . of supplementary ■ phosphates would result in not only a higher breeding efficiency but also increased butterfat production. In deciding whether supplementary phosphates were required, they should let the stock be the judge. Two farmers from whom pasture samples had ; been - taken: i both asked Mr. Webster’s bpinion-of a certain lick. The Cost was in' the.(neighbourhood of 50s per cwt. -Both men considered the • lick

was no good, but for different reasons. The first eaid his cows would not look at it, whilst the second said hie cowe ate the whole lot in five days and he could not afford such luxuries for them. Yet the explanation was simple. In the first case the pasture analysis showed a very high mineral content while in the second the phosphorus was very low.

The cheapest lick to provide additional phosphorus was composed of two parts steamed bone flour and one part coarse salt. This was best mixed with sufficient molasses: thinned with water to give the whole/ the consistency of brown sugar. If stock took this lick it was a sure indication that they required extra phosphates. Additional supplies of that mineral might be obtained by- adding superphosphate to the hay and ensilage stacks in the same way as salt—l to 2cwt. per stack; a little sprinkled over from time to time during building. A few pounds of superphosphate could be placed in the drinking troughs at intervals of a week or so.

Another side of the sterility problem to which great attention had been given was the question of how far t'he bul. was responsible for breeding trouble. As a result of their work he had no hesitation in saying that the bull played a much bigger part than ever he had been given credit, for in the past. The view had hitherto been held that a bull was cither all right or all wrong, and that provided he d 1 his work normally, and succeeded in getting some of the 'cows in calf that obviously he was not to blame and that the trouble lay with the cows. They had found that was far from being the case and that individual bulls varied in their fertility. Whilst some bulls were a cause of loss purely through their uncertain fertility, others were a source of grave danger since they might be infected with disease germs which they would transmit to the cows.

By a laboratory_jexamination of semen samples they were now able to diagnose with some degree of assurance the breeding prospects of any bull. If a higher proportion of the-cows in any herd returned to the bull than had been the rule in previous seasons the' bull should be at once suspected. It was obvious that the bull was a very important factor in sterility; just how important he was not prepared to say at present, but to settle that point they must have many more bulls examined, which could not be done without the co-operation of the farmer. It was therefore up to the farmer to help and he hoped that during the coming spring they would not forget that point, but would get in touch with him, because they badly needed normal bulls for comparative purposes as well as suspects.

NO SATISFACTORY TREATMENT.

When an outbreak of sterility occurred

they did not as yet know any satisfactory means of.. treatment. A method which was tried on a small scale last season gave some promise and would be given a much extended test as opportunity offered. Fortunately the infection tended to clear up spontaneously

in the course of nine to ten weeks and the cows then bred successfully as a rule. How far the infected bull recovered they were not yet certain. He did recover to a greater or lesser degree in 1 some instances, and occasionally threw off the actual infection, but was

■eft permanently damaged to some ex-

tent and was not so sure a breedtr. However, as the majority of such bulls were quickly consigned to the slaught-er-house it was difficult to get subsequent histories of large numbers. The risk of the epidemic form of sterility was greatly increased by introducing saleyard purchases into the herd. Statistics had shown that the majority of herds in which it broke out were maintained by outside purchases—another strong argument in favour of rearing heifers. Mention must be made of the small proportion of more permanent forms of sterility which were most frequently a sequel of contagious abortion. Such cases were usually isolated —one or two in a herd —and showed chronic inflammation of the womb and oviducts and degenerative changes in the ovaries themselves. Each case, required treatment on its. merits. The treatment could only be applied by a qualified ,man and required considerable time and ■ patience. The prospects were not good in many cases, though a fair percentage of cures could sometimes be effected. Statistical data had' shown that about'4—s per cent.,'of cows were carried ' through empty, arid it was common knowledge that many, of those bred at the first attempt ' the. following season. Probably the majority of those failed to breed owing to some slight mineral deficiency. They were not infrequently high producing, individuals. If they were eliminated a. very small percentage 'of permanent sterility due t-o diseaee of the reproductive organs was left.

Mr. Hill Motion said, he differed from the conclusions arrived at, by the speaker on a number of important,points and the chairman suggested an opportunity should be given Mr. Hill. Motion at a later date to address a meeting and place his views on the .question before farmers.