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This article was published in 1960
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.

Neo-Natal Mortalities — Sheep

A. N. A. HARRIS, B.V.Sc., H.D.A., District Veterinary Officer, Armidale

Introduction

In introducing this subject, it is of interest to examine the overall lambing percentages in New South Wales.

Figures from the New South Wales Statistical Register show that for the period 1903-1956, the average lambing percentage in New South Wales has been approximately 65 per cent.; with less abrupt fluctuations in the last 30 years.

The influence of the British Breeds and their crosses probably has become more marked in recent years; for between 1925 and 1953 there was a ten-fold increase in the number of British Breeds in New South Wales. (350,000 in 1925 to 3½ million in 1953; while crossbreds rose from 2 million to 6 million in this period). Their influence is particularly obvious in the Riverina and on the Southern Slopes.

Lambing percentages will be quoted when investigating Neo-Natal mortalities, and it is as well to examine the expected reproductive efficiency of Merino ewes in a flock.

It probably is reasonable under average husbandry conditions to expect only about a 75 per cent. marking. Strain differences and selection for twinning will, of course, affect this figure. Over a mating period of 5-6 weeks, covering two heat periods, the conception rate per service can be expected to be approximately 75 per cent., which over a period of two services can result at the most in only about a 95 per cent. conception. This will leave about 5 per cent. dry ewes. Then there is the effect of maiden ewes on lambing percentages. Owners seldom keep ewes after the 6th lamb, so that the average number of maidens in a flock is 15-20 per cent. Of this number, it is quite usual to expect one in six to fail to rear a lamb due to bad mothering.

Finally, post-war surveys have shown that it is quite normal under average conditions of management to expect a 15-20 per cent. loss in lambs prior to weaning; and 80 per cent. of these losses can be expected within the first few days of birth.

Although some of the losses of young lambs are unaccountable with our present knowledge, the principal factors involved are:—

1. LOSSES DUE TO INFECTIOUS DISEASE

Ovine Brucellosis: This is a venereal disease affecting both males and females. It is featured by epididymitis, abortion and neo-natal deaths. In flock matings no serious depreciation in lambing percentages has been attributed to this disease; providing 2½-3 per cent. of rams are used. It can be serious in studs.

Toxoplasmosis: This is a disease causing encephalitis, and in New Zealand has been considered responsible for abortions.

Enzootic Abortion: Recorded in Scotland as causing abortions and birth of premature, still born or weakly lambs. Weakly lambs born at or just before term are often "pot bellied"; with or without some subcutaneous oedema. A clinical feature of the disease is the birth of a normal lamb at full-term; immediately preceded or followed by a recently dead or degenerated twin. Affected ewes show vaginal discharge and are unthrifty in condition. Retention of the placenta is common (Stamp et al. 1950; Littlejohn, 1950).

This disease of the foetal membrane of the lamb is caused by infection with an agent resembling the Rickettsiae and the Psittacosis-lymphogranuloma group of infective agents. Smears of amniotic fluid and cotyledons may be of value for diagnosis.

Salmonella Abortions: Outbreaks caused by S. abortus ovis have been reported overseas (Lovell, 1931).

Drenching Effects - Phenothiazine: Stillbirths 1-9 days after drenching have been observed in trials at Hawkesbury Agricultural College (Hungerford, 1944).

2. DEATHS DURING PARTURITION

Deaths from uterine inertia and dystocia are reported often, and are associated in some instances with over-fatness. C.S.I.R.O. experiments at "Chiswick" showed Merino ewes lambed in fat to very fat condition (mean live weight: 119 lbs.) had lambs of heavier birth weight than ewes in forward store to fat condition (mean live weight: 106 lbs). The incidence of dystocia and lamb deaths were slightly but not significantly higher in the first group. It was thought that ewes would have to be grossly over-fat to experience trouble from dystocia (Barrett, 1958).

The genestein content in herbage may play a part. Instance the problem of Red Clover infertility at Glen Innes and the number of manifestations of the condition of sub. clover infertility as seen in Western Australia. Initially only a high incidence of dystocia with uterine inertia was experienced. Quite possibly the high content of genestein may not persist long enough in some feed to produce the more permanent stage of cystic uteri and reduced conception. A flush spring growth of feed in certain areas could conceivably have a high content of genestein; and hence indicate a need for later lambing (Barrett. 1958).

The C.S.I.R.O. tried in experiments at "Chiswick" to reproduce the Western Australian condition by injecting the ewes with Stilboestrol when 98-114 days pregnant. 7-10 days after injection there was evidence of swelling of the vulva and milk-like secretions. One ewe aborted. Others had serious lambing difficulties; with uterine inertia and dead lambs.

A further illustration of this point was the effect of hormone implantation in 4-5 months-old lambs at Tamworth. One week after treatment with 15 mgm. "Gromax" hormone pellets, approximately 60 per cent. of the ewe lambs showed udder development and inflamed vulvas. Approximately four weeks later, changes in the urogenital tract were particularly obvious - swollen vulvas, eversion of the uterus, swollen bulbo-urethral glands and prepuce. The implanted lambs were grazing on lucerne known to have an appreciable oestrogen content. It is logical therefore, to suspect that the type of feed and seasonal variations in the genestein content of the feed may produce ill-effects.

As regards starvation, it has been considered that ewes would have to be extremely emaciated to affect their ability in delivering lambs. Under-nutrition has more effect on the foetus and milk supply (Alexander).

Difficult lambing when mating Merinos with some British breeds has, of course, to be considered.

Lamb loss investigations at Rutherglen Research Station showed an association of heavier birth weight of lambs with difficult parturition. The observations were with Crossbred and Comeback flocks (McHugh and Edwards, 1958).

3. DEATHS WITHIN 24 HOURS OF BIRTH

The percentage of losses from accidents, mal-presentations, monstrosities and other anatomical abnormalities is generally very low.

4. DEATHS WITHIN 2-3 DAYS OF BIRTH

This includes lambs that have breathed but have not successfully suckled the ewes. 80 per cent. of the "normal" loss of lambs falls within this group. There is no evidence that infectious diseases are responsible for any significant proportion of lamb deaths, and average lambing husbandry practices under field conditions has little effect on reducing the total loss. In the majority of flocks, lambs die simply from mechanical or constitutional causes. It appears to be mainly a physiological problem and attention is being concentrated now on the physiology of the pregnant ewe and young lamb, and the ewe / lamb relationship during the first few critical hours following the birth of the lamb. Results of recent work by the C.S.I.R.O. on the physiological causes of death of lambs soon after birth are of interest.

IMPORTANCE OF PRE-NATAL NUTRITION

Birth Weight: The birth weight of lambs from poorly fed ewes was lower than from well fed ewes, although the lighter lambs were still quite vigorous. However, the heavier lambs withstood fasting for half as long again as those lighter lambs from the poorly fed ewes.

Gestation Period: Under-nutrition of the pregnant ewe shortened the gestation period and hence lambs were less well developed at birth.

Effect on Temperature: Lambs from poorly fed ewes had a consistently lower body temperature: 2 degrees F. or lower. Such lambs were slower in adjusting their body temperatures after birth. Any factor, such as rain, which tended to prevent adjustment resulted in continuing lower body temperatures. There was evidence also of lethargy and disinclination of the lambs to move and seek the ewes teats. More than half of their energy is obtained from fat, and lambs from poorly fed ewes contained a lower proportion of fat (Alexander 1958).

Weak lambs which had not suckled and had a low level of sugar in the blood, often responded to sugar injections. Lambs which had suckled and had normal amounts of sugar in their blood, would, if moribund from exposure, often respond simply to warmth.

Cold, wet windy conditions played an important part. Newborn lambs could have as much as 12 ozs. of fluid on their coats. Some is removed by the mother but evaporation results in large heat loss, particularly in windy weather. Adequate shelter, therefore, is essential and obviously lambs from poorly fed ewes suffer more from the effect of evaporation. The nature of the birth coat was important. There was less heat loss from lambs with wet long birth coats, and these lambs had a better chance of survival in cold, windy weather (Alexander. 1958).

Milk Production: Both the nature of the colostrum and the volume of milk during the first few hours after birth was affected by nutrition during the last few weeks of pregnancy. Typical colostrum did not appear in the udder of many poorly fed ewes until some hours later. This delay in coming into milk has been observed in the field. Ewes with plenty of milk, but which may have been dry at birth, have been found with dead lambs (Barrett. 1958). The rate of milk supply also was higher in well-fed ewes (Alexander. 1956).

With investigations carried out in the Goulburn District in 1958, the discovery of the low Vitamin A concentration in the body of affected lambs is rather extraordinary, and may be simply a reflection of their failure to obtain colostrum (Skillman. 1958).

OTHER HUSBANDRY ASPECTS AFFECTING SURVIVAL OF THE LAMB

Mothering: The requirements for good mothering have been found to be a reasonable level of nutrition, good milk supply, rapid and uncomplicated birth and lack of interference. The age effect on maternal instinct is also important.

In studies at "Chiswick" on losses due mainly to bad mothering, it was found that on the average maiden ewes failed to rear 20 per cent. of their lambs, second lambers 13-15 per cent. And 4-6 year-old ewes 5-10 per cent. On the average there are 15-20 per cent. maidens in the flock, so that one in six ewes fail to rear a lamb. At "Chiswick", 350 ewes containing 100 maidens lost 13 per cent.; even under good husbandry conditions.

Preferential treatment of maiden ewes as regards allocation of paddocks and facilities is therefore generally desirable. Unnecessary disturbance, handling or worry from dogs should be avoided.

There is also the effect of breed and strain influence on maternal instincts. This instinct is lowest in the fine wool Merinos, but well developed in the South Australian strain of Merino; similar to the Romney Marsh.

Ill-health is, of course, often responsible for ewes forsaking their lambs (Ophthalmia, Footrot, Blowfly infestation, Crow Pick,etc.).

Accessibility of the Udder: Lambing off-shears probably results in a saving of 2-3 per cent. of lambs according to C.S.I.R.O. findings at "Chiswick" (Barrett. 1958). This, or pre-lambing crutching of ewes, is probably very useful where wool is heavily burr infested.

Observations on the Southern Tablelands have illustrated the advantage of lambing off-shears. A ewe without its fleece will almost invariably seek shelter at lambing, and the overall effect on the lamb survival is quite significant.

Abnormalities of the Udder: Culling of ewes with unsound udders is advisable, although the effect on lambing percentages is probably not very great. The left teats commonly are damaged at shearing. Barrett doubts the significance of wax plugs in teats; if a lamb is vigorous, it should be able to obtain its requirements of milk.

Mastitis may be a problem in some flocks.

Type of Birth: Invariably losses among twins are much higher than those among singles. Fostering twins on ewes that have lost lambs may be useful if facilities and labour are available.

Time of Lambing: It is obvious that young lambs will not survive well during excessively hot or cold conditions. Results achieved at Shannon Vale have illustrated the value of the late spring lambing to improve lamb survival on the Northern Tablelands. Food supplies are reasonably assured, lambing off-shears is possible and there is less risk of inclement weather conditions.

This, of course, will not apply in the more western districts, where extremely hot conditions prevail and there is the risk of grass-seed infestation,etc.

3. DEATHS DUE TO INFECTIONS, DEFICIENCIES,etc.

In some focks infectious conditions may be important; as also certain deficiencies. Mycotic Dermatitis can often cause serious losses in newly born lambs; as also can contagious Ecthyma, Enterotoxaemia, Umbilical Infections, Arthritis, Grass seed,etc. Iodine deficiency has resulted in a high loss due to stillbirths in Tasmania; Endemic Goitre has been suspected on the Southern Tablelands of N.S.W. A high lambing loss in the Ouse District of Tasmania in 1956 seems to have been associated with the consumption by ewes, during the latter stage of pregnancy, of one of the Erodiums. There is some suggestion that some of the Cruciferous weeds lead to the appearance of goitrogens in the milk.

6. PREDATORS

Natural enemies such as foxes, crows and pigs contribute to high losses in some individual flocks. On some properties it is difficult to assess the extent of lamb losses due to predators, and often losses are attributed to other causes. This applies particularly to the North Western Districts of New South Wales.

STUDY OF LOW LAMB MARKING PERCENTAGES

Often when investigating low lamb marking percentages, there is no factual information on the relative importance of ewes failing to lamb, nor of loss of lambs between birth and marking. To ascertain where the major loss in reproductive efficiency is occurring, observations on a pilot flock are often helpful.

Effective reproduction is obviously dependent on factors influencing fertility of the ewes and rams, as well as on factors concerned with the survival and growth of lambs.

1. Factors affecting Male Reproduction.

(a) High atmospheric temperatures.

(b) High body temperature — fly strike and other infections, severe exercise in hot weather.

(d) Deficient nutrition — Vitamin A requirements.

(e) Epididymitis and other testicular abnormalities.

2. Factors affecting Female Reproduction and Lamb Survival.

(a) Breeding at peak of productive efficiency (Watson).

(b) Nutrition of ewe — promoting late pregnancy and early lactation.

(d) Disease — parasitic infestations, mastitis, defective udders.

(e) Prelambing crutching or shearing.

(f) Weather.

(g) Predators.

Having studied these salient points, an observation on a sample of ewes at lambing will help considerably in determining where the major loss in reproductive efficiency is occurring.

In selecting a sample group the same proportion of ewes of various ages should be included and the ewes should be selected at random;e.g. if 50 maiden ewes are to be selected from a group of 250, then every 5th ewe should be taken and not the first through the gate or drafting race.

The sample group should be selected one or two weeks before the anticipated date of lambing.

About 7-10 days before lambing the ewes should be examined individually, and those definitely in lamb transferred to a paddock reserved for them. The supposedly dry ewes should be examined again about 3 weeks later and any further animals considered to be definitely in lamb transferred to the lambing paddock. A record should be kept of the "in lamb" and "dry ewes".

During lambing a daily record should be kept of:—

1. No. of lambs found dead.

2. Age, and if possible, the weight of the dead lambs.

3. Whether the lambs have been attacked by predators.

At the end of lambing or lamb marking, a record should be obtained of:—

1. No. of surviving lambs.

2. No. of ewes suckling lambs.

3. No. of ewes which have lost their lambs.

From these observations will be determined:—

1. The percentage of ewes that reared lambs.

2. The percentage that lambed but lost their lambs before marking.

3. The percentage that did not lamb.

4. The performance of various age groups.

5. Whether losses between birth and marking were "normal".

References

Alexander, G. et. al. (1956)—Rural Research, C.S.I.R.O., 18 : 14
Alexander, G. (1958)—Proceedings of the An. Gen. Con. Meet of the Aust. & N.A. Assoc. for the Adv. of Sc., Adelaide. '58
Alexander, G. (1958)—Proceedings of Conf. of the Aust. Soc. of An. Pro.
Berrett, J.F. (1958)—Pers. Com.
Hungerford, T. (1944)—N.S.W Agric. Gaz., 55 : 92
Littlejohn, A. I. (1950)—Vet. Rec., 62 : 571
Lovell, (1931)—J. Path. & Bact., 34 : 13
McHugh, J. F. and Edwards, M. S. H. (1968)—Vic. J. Agric., 50 : 425
Skillman, G. J. (1957, 1958)—Pers. Com.
Stamp et al. (1950)—Vet. Rec., 62 : 251
Watson—cited by Cole, V. G. (1958)—"The Veterinary Inspector"