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This article was published in 1950
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Infant Lamb Mortalities

A FURTHER NOTE

G. CHARLES, B.V.Sc., Inspector of Stock, Forbes.

In a previous article on the above subject (1), a theory was postulated that the lambs were dying from starvation arising from their inability to reach the udders as a result of heavy wool growth along the lower edges of the flanks of the ewes.

In order to test this theory it was proposed to remove all the lower flank wool from the ewes at the time of pre-lambing crutching; leaving some untreated as controls. However, as a result of other economic factors, the owners of one property decided to shear their Romney Marsh flock ewes in late April, and this was done, but no unshorn controls were left. Consequently, the only comparison is with the unshorn sheep of the same age group in the previous year, for which similar records are available.

During both the 1948 and 1949 lambings, records were kept of lambs dropped, lambs dying within 72 hours of birth and lambs marked. A comparison is possible between these two sets of records. The weather during the 1948 lambing was the usual July-August weather expected on ihe Tablelands at an altitude of approximately 1,200 feet; being cold and frosty with wind and rain. The owner stated that the 1949 lambing season was harder than that of 1948.

In 1948, lambing records were kept of 1,026 Romney Marsh ewes aged 2 and 3 years, and it was found that the total lamb drop was 920 lambs, or 89.69%, Of these 920 lambs, a total of 220, or 23.91% of the drop, died before marking; the bulk of the deaths occurring within the first 72 hours after lambing. In 1949 the corresponding figures were 1,385 shorn ewes, of the same age groups as the previous year, mated; 1,122 lambs dropped, equivalent to 81%, and of these only 67 died before marking, representing 5.97% of the drop.

Taking into consideration the reported severer weather during the 1949 lambing, these figures would appear to indicate that ewes carrying 3 months' wool were more capable of successfully rearing their lambs than ewes carrying 9 months wool, most probably because the lambs could suckle more easily, and so were better nourished and thus could withstand the effects of the cold winter weather.

A point of interest apart from the main question is that feed conditions following shearing and up to October were only fair and the ewes lost condition noticeably. Mr. A.K. Cantrill (Sheep and Wool Instructor) is of the opinion that shearing was carried out too late in the autumn to enable a sufficient growth of wool to protect the ewes during the hard winter when there was insufficient feed to maintain both body temperature and condition. Shearing one month earlier probably would overcome this trouble without losing the benefit accruing to the lambs from the short wool.

On the second property, where losses were heavy in 1948, removal of the lower flank wool was effected at the pre-lambing crutching. Here again conditions were not as desired, since the owner's son-in-law, who managed the place and was willing to leave a percentage untreated as controls, was outvoted in family council and so all sheep were treated. The family attitude was that, in view of the losses in previous years, any action which might result in an increased marking should be followed to the fullest extent. This attitude could be appreciated when it was realised that 363 of the 1,797 lambs dropped in the preceding 3 years had died before marking, an overall loss of 20.19%. Once again comparison became possible only with the previous year's figures from untreated sheep.

The lambing season in that part of the Carcoar district where this holding is located, always is hard and accompanied quite frequently by snowfalls and periods of bleak, misty weather. In addition this property is very exposed, being cleared of almost all timber and being situated over 3,000 feet above sea level. Pastures consist of rye grass and sub. clover and are generally frost-burnt during the winter and carry very little nutriment.

In 1948, 690 ewes were mated and 594 lambs were dropped; this being 86.1%. Of these 594 lambs, 158, or 26.61% of the total drop, died before marking; and here again the greatest number died within the first 72 hours. In 1949, 711 ewes were mated and 685 lambs were dropped. equivalent to 96.34%. In this year only 83 lambs died before marking, representing 12.12% of the total drop. This is still too great a loss, but an improvement on the previous year's results. Once again the bulk of the losses occurred within three days of being dropped. A comparison of the results of the two lambings shows an appreciable drop in the deaths in 1949, and it is considered that this result, coupled with the results on the other property, gives some grounds for believing that the removal of wool as outlined above is of some value in preventing at least a percentage of infant lamb deaths. However, it is realised that the results are not conclusive and that further observations are required before the matter can be confirmed.

Analysis of the causes of the deaths on the second property gives rise to another line of thought as to a possible cause of some of these infant lamb mortalities, at least in some areas of the State. Of the 83 deaths, 30 were attributed to the bad weather and 18 to other known causes such as foxes, crow-pick, etc. The remaining 35 deaths all appeared to be associated with some upset of reproduction, in that 16 were born dead, 8 were full term but weak or premature and died, 5 were retained dead, 3 were malpresentation and 3 were born in unruptured foetal membranes. Possibly, also, some of the 30 deaths attributed to weather could be included in this group. At the moment there is insufficient evidence to implicate sub. clover as a definite cause of these 35 deaths as this plant is not the sole pasture available to the sheep. Another possibility which presents itself is Vitamin A deficiency. It is recognised that the vitamin value of all forage plants decreases after the bloom stage (2), and in a normal year on this property there is practically nothing but frost-bitten and dry feed available from the middle of April until lambing time in July and August, so that the intake of carotene must be extremely low during the major part of pregnancy, and it is possible that the Vitamin A content of the liver becomes sufficiently depleted to cause reproductive troubles, since the Vitamin A requirements for successful reproduction are somewhat higher than the minimum requirements for maintenance of mature animals (3) The symptoms of Vitamin A deficiency 49 have been enumerated and include, inter alia, abortion or premature labour, and the birth of weak or dead young (4).

The work of the past two years may be summarised thus:

(1) Excessive mortalities of infant lambs have been investigated.

(2) No pathogenic infection was found.

(3) There is evidence which tends to support the theory that the removal of wool along the lower edges of the flanks of pregnant ewes, thus giving better access to the udders, will reduce the mortality to an appreciable extent, but further observations are required to confirm this.

(4) Vitamin A deficiency is suggested as another possible cause of infant lamb mortalities in the higher altitudes of the Central Tablelands, where lambing occurs in July and August.

Once again the co-operation of Messrs. Rowlands and Witheford in making their sheep available and keeping the necessary records is gratefully acknowledged. Thanks are also due to Mr. J.N. Henry (D.V.O. West) for permission to quote from official papers.

References:

  1. Charles. G. : Yearbook of the Institute of Inspectors of Stock. 1949.
  2. Maynard, L.A. : Animal Nutrition. 1st Edition. McGraw-Hill Book Co. Inc. 1937. p 189.
  3. U.S. Dept. of Agriculture: Food and Life. Yearbook of Agriculture 1939. p. 486.
  4. Maynard, L.A. : Animal Nutrition 1st Edition. McGraw-Hi11 Book Co. Inc. 1937. p. 384.

 


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