EM van Tonder

Regional Veterinary Laboratory






The most important factor for the average mutton producing farmer is the number of animals available for marketing every year. This is dependent upon the presence or absence of specific disease conditions, the nutritional status of the animals, the reproductive rate of the flock and the incidence of sporadic preventable losses, which are all determined by the level of management on the farm.

Animal losses caused by diseases and parasites cannot be eliminated completely, but an attempt should nevertheless be made to reduce them to a minimum. As not all prevailing diseases and parasitic infestations can be fully prevented or even controlled, the aim should be to limit losses only to those conditions against which no preventative measures presently exist.



The intensity of animal losses may vary considerably, depending upon a variety of epizootological factors, including the cause, the host animal, intermediate carriers, climatic conditions, etc. These losses can be classified as follows:


Direct losses

Direct losses do not only result from deaths of grown animals, but also from abortion and perinatal mortality. These losses, irrespective of their cause, are usually highest in young and more susceptible animals.

In a mutton production unit these losses result in an immediate reduction of the number of animals available for marketing, thus affecting the main source of income of such an enterprise.


Indirect Losses

Indirect losses constitute production and reproduction losses, which are normally inconspicuous and usually overlooked.

These losses can be subdivided into two categories. In the first instance there are those suffered as a result of lowered lambing percentages and secondly there are those incurred through a drop in weight or retarded weight gains.

The most important cause of a reduction in lambing percentage is the mating of animals outside the natural breeding season when sexual activity is at its lowest. This not only decreases the conception rate, but also the percentage of multiple births.

Low lambing percentages may also result from the use of either infertile rams or rams of low fertility. Such rams may occupy receptive ewes during a limited mating period and eliminate fertile competition; thus bringing about an overall poor reproductive performance in the flock.

Weight losses, on the other hand, can also occur in two ways. Firstly there are weight losses which are directly associated with diseases and parasitic infestations and result from decreased appetite and food intake. The economic consequence will be that animals are marketed with lower carcass weights, slaughter animals are fed to regain marketing weights or stunted animals are sold at a loss. Secondly, in young animals, weight losses or poor weight gains can be caused indirectly. This is usually the result of lowered milk production in ewes with suckling lambs. The decrease in milk yield is a sequel to either a systemic disease or local udder damage.



If a small stock unit is taken to represent 1 adult sheep, 1,5 weaned lambs or 2 unweaned lambs, an imaginary flock of 1 000 small stock units will consist of approximately 20 rams, 650 breeding ewes, 240 young replacement ewes and 340 unweaned or weaned lambs.

Under ideal conditions, it can be assumed that at least 95% of ewes would lamb every year with an average lambing percentage of 140%. This would amount to a lamb crop of approximately 860 lambs.

When all ram lambs and 25% of ewe lambs are marketed at about weaning age and 25% of the breeding ewes are replaced every year, approximately 500 lambs, 160 old ewes and 150 young ewes (culled at 15 months of age) should be available for marketing every year.

In order to calculate the expected gross income for such an imaginary mutton production unit, it is assumed that all surplus animals are sold for slaughter at the average dressed carcass weights, levels of grading and mean prices as are given in Table 1.



Based on these estimates, the gross income of the supposed mutton-producing farm will amount to R49 000 per year.

As the various cost items, such as transport and marketing costs, feeding expenses and interest rates, will vary from time to time and from area to area, all calculations are based on gross figures.



Direct losses

In estimating the possible annual losses that can be suffered on account of death, flock sheep were rated at replacement values, while losses in marketable sheep were taken at the average market prices.


Table 2 reflects potential financial losses in flock sheep at different mortality rates.



The financial losses in marketable sheep based on carcass values, at the same death rate as for flock sheep, are given in Table 3. In the case of marketable sheep the additional losses in offals and skins which should also be brought into account will vary from R169,20 to R394,80 per year, depending on the death rate.



Direct financial losses owing to abortion and perinatal mortality will affect the whole lamb crop, which was calculated at approximately 860 lambs. Since it was assumed that all ram lambs, taken to constitute 50% of the lamb crop, and 25% of the ewe lambs will be marketed at the appropriate age, losses in this group will be valued at market prices. The rest of the ewe lambs, retained for selecting replacements when old breeding ewes are culled, will be valued at a fixed price of RI5,00.

As lambs and young animals are usually more susceptible to disease, higher percentages of losses may be expected in these age groups. In Table 4 potential financial losses were therefore calculated at death rates of 3, 5 and 10ro respectively.



Losses in potential offals and skins in the marketable sheep will amount to RIIO,40 , R186,30 and R372,60 for the three different death rates respectively, which will then bring the total financial losses in the three categories to R1 078,14, R1 858,70 and R3 621,72 respectively.


Indirect losses

Decreased lambing percentages can bring about indirect financial losses in various ways. Financial losses may be effected by a reduction in the number of ewes that conceive, by the use of too few or infertile rams, mating outside the breeding season or breeding with animals in poor condition.

In the suggested unit a lambing percentage of 95% and percentage of lambs of 140% were assumed under ideal circumstances. In calculating the losses as a result of a decrease in conception rate (Table 5), the percentage of lambs produced by the number of ewes that lamb will be maintained at 140% thus 1,4 lambs per ewe.



If the losses in offals and skins as a result of a decrease in the number of marketable lambs are also taken into account, the total indirect financial losses in the three different categories will amount to R1078,14 , R1 858,70 and R3 621,72 respectively.

Although a reduction of 10% in conception rate might appear to be very drastic, the overall lambing percentage in this particular farming unit is still 85%, which, generally speaking, represents a good average lambing percentage.

Indirect losses may also occur as a result of a decrease in the percentage of lambs. The percentage of lambs in this imaginary unit was taken as 140%, which, from a practical point of view, also represents a very high average. A reduction in this percentage of 5, 10 and 20% can be regarded as conservative, as this will result in lambing percentages of 135, 130 and 120% respectively, which still represent very good averages. The financial losses that may be inflicted indirectly by decreases of this nature are reflected in Table 6.



When the losses in offals and skins as a result of a decrease in the number of marketable lambs are taken into account, the total indirect financial losses in the three categories of reduced lambing percentages will amount to R2 140,90, R4 327,82 and R8 581,54 respectively.

Weight loss is probably the most common and underrated cause of indirect financial losses, as it is a sequel to most diseases and parasite infestations. It is however very difficult to estimate its real impact in a mutton production unit. A few examples will nevertheless suffice to illustrate its importance.

In the first instance, weight losses might be experienced to such an extent that the animals, though still marketable, will fetch lower prices. This is particularly so in more mild disease conditions or parasitic infestations. If it is assumed that only 50% of the marketable animals are affected in this way and that an average loss of only 1 kg in carcass weight is experienced, without affecting the grading of the animals, the financial losses incurred will be as presented in Table 7.



From Table 7 it can be seen what the financial impact could amount to if more animals and their grading are affected and when greater weight losses are experienced.

In this example it was assumed that the animals were still marketable, but it is commonly experienced that, as a result of diseases and parasitic infestations, weight losses occur to the extent that animals have to be kept and fed for variable periods in order to regain their original weight. It is well. known that sick or infested animals can lose weight rapidly, even up to 15 kilograms in a few weeks. In the following example (Table 8) it will be assumed that only 10% of the marketable stock in the proposed production unit is affected in this way and that an average weight loss of 5 kg per affected animal occurred. Under intensive feeding conditions it normally takes 4,4 days for a sheep to regain 1 kg of body weight, which in this case will amount to 22 days. In order to allow the animal to recover fully from the effects of disease or parasitic infestation and to regain its optimum appetite, another 8 days can be added, which then brings the total period to 30 days. Feeding costs are taken at 35 cents per sheep per day.



In young suckling lambs, losses in weight or poor weight gains are commonly encountered and, depending on the cause, severity and duration thereof and the age of the lamb, may result in permanent damage and varying degrees of stunted growth. Apart from certain diseases and parasitic infestations, retarded growth can result from poor milk production in the ewe. Lambs affected in this way either have to be sacrificed at a complete loss or have to be disposed of at unprofitable prices.

If only 5% of young lambs in the proposed flock are disposed of at 50% of the value of a grade 1 lamb, the total financial loss could amount to R500,00.

Internal parasites constitute the most common problem in any mutton production unit and are probably responsible for a major share of the financial losses suffered annually. It was, for instance, found that mild infestations were responsible for an average decrease in body weight of 3,5 kg per sheep in 3 months and that heavier infestations could reduce food intake by as much as 50% within 6 weeks.

If assumed that internal parasites are responsible for a weight loss of only 0,5 kg per marketable sheep, the total financial losses for the proposed mutton production unit would be as given in Table 9.




In order to get a picture of all the losses and expenses that can be caused by diseases and parasites in a mutton production unit consisting of 1 000 small stock units, the lowest and highest estimates are given in Table 10.



From Table 10 it is clear that the total financial losses that can be expected as a result of diseases and parasites in a mutton production unit consisting of 1 000 small stock units could vary between RI0 000 and R26 000. Seen against a maximum gross income of roughly R49 000, such losses will seriously affect the profitability of such a unit.



It should be stressed that no health programme would under practical circumstances succeed in eliminating losses entirely, the reason being that in some instances, particularly in the more sporadic type of diseases, preventative measures are either non-existent or are not fully effective.

Some diseases might be so sporadic. or even absent from a particular farm or area. that preventative measures are not considered until they make their appearance, in which case losses will be suffered before preventative steps are taken.

However, a minimum routine health programme should be worked out in collaboration with the nearest veterinarian, taking into account conditions prevailing in the area and on the farm. The aim should be to prevent losses owing to diseases and parasites that can be effectively controlled.

It has been proved by study groups in the Karoo Region of the Cape Province, that the highest net income per small stock unit is directly correlated to the expenses involved in the control of diseases and parasites according to a routine programme.

In the routine health programme for which the minimum expenses involved are given in Table 10, provision has only been made for the control of internal and external parasites and a few commonly encountered diseases such as pulpy kidney, bluetongue and enzootic abortion, while a minimum amount was set aside for unpredictable expenses.

With regard to internal parasites a minimum number of 6 treatments for the flock sheep and 2 treatments for the marketable lambs, at an average cost of 14 cents for all sheep, was used as basis.

In some areas and on pastures more treatments might be necessary, which will obviously lead to greater expenses.

For the control of external parasites the calculations were based on one complete immersion dip and four belly baths for flock sheep and only one complete dip for marketable lambs. Again an average cost was taken for all sheep at 15 cents per full dip and 10 cents per belly bath.

The cost for vaccines were taken at current prices and the total expenses based on the number of animals on the farm as given in Table 11.



If the marketable lambs are excluded, the total expenses for the flock sheep would average at Rl,80 per animal, which can be regarded as somewhat high at the present moment. This could be owing to the high average dosing price for internal parasite remedies, particularly for the young lambs, and the consideration of belly baths which will only be applicable in limited areas.

However, taken on this basis, the annual costs of the proposed unit will amount to R2521,10. This annual expense will now have to be valued against the possible benefits that can be obtained.

If this proposed health programme could succeed in reducing the losses from the higher level (see Table 10) to the lower level, it would mean a reduction of almost Rl6 000 per annum.



It is acceded that this paper is based on many assumptions and possibly on a very theoretical basis, but it is believed that it will at least afford some idea of the importance of herd health in the economy of mutton production.

Although a venture of this nature cannot be generalised, it is hoped that it will at least present a formula on which the true situation for any given unit can be based.



Karoo Agric 3 (2), 18-24

Article source: Grootfontein Agricultural Development Institute -