Performance recording is a necessary pre-requisite to effective decision making on breeding policy. But the choice of recording systems and type of records will differ with the other uses to which they are put, e.g. the monitoring of populations or herd level management. Nonetheless, they should all take into account the aggregate effects of the various traits of productive significance and should provide a characterization of the environment under which the production is recorded.
In many countries, a fair amount of information from institutional and commercial herds is already available which should be analysed before introducing new schemes for recording.
Recording for the purpose of national decision making should take into consideration the ecological zones in which livestock are kept, the farming system, whether nomadic, settled, smallholder or intensive, the role of crops in the farming system, the breed or breeds used and the problems of disease, adaptation and survival in each breed/production system combination.
The initial step usually involves surveillance studies designed to obtain baseline data on productivity parameters and on the constraints to increased productivity. In their simplest form, they consist of interviews of chosen farmers conducted by selected personnel to obtain approximate parameters of birth, growth, production, mortality, etc. (Ellis, 1980). A representative sample of farms and animals in each combination of ecological zone, production system and breed should be chosen and, if any development project is being implemented, the response of traditional farmers to the developmental process should also be recorded. The total number of animals in the survey could be a few thousand.
The next step involves the regular monitoring of the performance of particular populations over a given period of time. The herds chosen should be representative of the different production systems and the monitoring should relate to herd structure, fertility, mortality and disposal, health and productivity. The parameters should, where possible, be related to feed inputs. An important aspect of the monitoring process should be the study of livestock development programmes. Such programmes are essentially large-scale experiments which cannot be reproduced within more conventional research programmes and can therefore provide invaluable information on the response to environments. Where such development programmes do not operate, it may be necessary to introduce improvements in some herds as part of the monitoring programme in order to provide this information.
Performance recording of individual animals is usually associated with selection for genetic improvement. However, such recording may be even more important for management decisions. In the initial stages of introduction of a recording scheme, emphasis should be on immediate benefits that could be derived from management changes, e.g. more surviving progeny or an increase in saleable produce.
Cooperation between the farmer and the field recorder is a basic requirement for the successful operation of any recording scheme. This cooperation can only come through an understanding of the use of records. The recording scheme should therefore be capable of performing an educational role, not merely a service one.
The transfer of recording systems used in temperate countries to the tropics has in most cases proved impracticable. No standard system of recording can be devised that is suitable for all farming conditions. The level of recording that is possible depends on the kind of management adopted and the stage of development of the livestock industry. With large flocks reared extensively under nomadic conditions, the identification of animals with good fertility and longevity may be all that is possible. Recording is thus an evolutionary process and advances can be made only when there is progress in levels of husbandry.
At every stage, it is important that no more than the essential records are maintained. This is necessary not only because of inadequacies in the educational level of livestock farmers in the tropics but also due to the lack of qualified recorders to operate more sophisticated systems. A further reason is the inverse relationship between the rate of genetic progress and the number of traits for which selection is practised. Optimum deployment of recording systems therefore requires that it be limited to traits which can be measured easily and with a high degree of accuracy and which have an economic value.
In most tropical countries, large herds are kept in governmental and research institutes to serve as sources of superior male breeding stock. The recording done in these herds may involve extensive written records. In privately owned herds, the type of information that can be extracted depends on the farming system. For example, although it is futile to attempt recording milk yield or growth rate in nomadic herds, they can nevertheless provide valuable information on longevity and reproductive performance under conditions of nutritional stress and disease challenge. Simple procedures (e.g. ear notching) can be adopted to place animals in different performance categories. This would aid in the selection of progeny that can then be subjected to further tests in testing stations or institutional herds. The chief advantage of nomadic herds is their large size which could allow a high selection intensity. In contrast, sedentary herds, despite their accessibility to recorders and the facility they provide for recording more traits, have the disadvantages associated with small size.
Any performance recording system in the tropics must satisfy a number of criteria if it is to be effective.
The system must be simple, i.e. involve little paper work for the farmer. It should not require major alterations in his farming routine.
The traits should be economically important and the resulting products should be either marketable or consumed by the producer. Their number should be kept as low as possible. Information extracted should also aid in management.
The system should be efficient in terms of time and cost.
The records should make it possible to identify the best and poorest animals at the farm level and genetic differences between populations at the national level.
The usual practice in milk recording is for milk and butterfat to be estimated from a limited number of measurements made at intervals throughout the lactation. The longer the interval between these measurements, the greater the error of the estimates is likely to be. When the interval is shortened, the expense of recording is increased, so that in practice a compromise is made between the needs of accuracy and economy.
Generally, milk recording in the developed countries has involved the weighing and sampling of the milk produced by individual cows on farms that are visited by official recorders at intervals of 3–4 weeks throughout the year. Morning and evening milk yields are recorded and composite samples of the two are taken for fat (and protein) determination. With the increasing cost of recording, there is a trend now towards the farmer doing his own recording (Lindhé, 1980).
Monthly records may not be sufficiently elastic to meet the requirements of herd owners whose primary interest is in using the records for feeding and management. They are therefore encouraged to make entries of production at more frequent intervals - weekly or even daily.
Institutional herds in the tropics can adopt the same procedures of milk recording used in developed countries. Similar practices can also be used in large private herds. However, a large proportion of dairy cattle in the tropics are owned by small farmers and it is here that the problem of milk recording lies.
The major constraints are the small average herd size, poor communication and lack of incentives for recording. Other possible reasons are inadequate appreciation of the value of progeny tested sires, low educational level of farmers and lack of qualified recorders. Where AI services are relatively undeveloped, the value of a recording service may be questioned. However, even in such situations, recording can assist in the culling of unproductive females in addition to aiding in herd management.
When introducing a milk recording scheme, certain incentives may have to be provided to encourage farmers to cooperate, e.g. free veterinary care, advice on management and feeding, low cost AI. It may even be necessary to pay a fee to farmers who cooperate in recording daughters of bulls used in progeny testing.
The main costs of milk recording are the recorder's salary and expenses. These tend to be high in the tropics because of the small size of herds, their scattered distribution and the need to include a large number of herds and cows to facilitate progeny testing.
Different methods can be adopted to overcome the financial stress of recording. There could be a reduction in the number of visits paid to each farmer, so that the recorder may cover more herds and cows. Recorders may also be employed on a part-time basis and could undertake other work as well. Thus, AI personnel can be trained in recording work and may serve as part-time recorders. This has particular application in the tropics.
In countries with organized AI services and where AI personnel make daily rounds, it may be possible to arrange their routine so that they call on one or more farmers daily for milk recording. The technician need not do the milk recording himself but could provide the farmer with a recording device and on the following day collect it from him together with the milk records. It would of course be necessary for the technician to be present when the recording is done for the first time to demonstrate the procedure.
In situations such as the above, where it is not possible to have the services of official recorders except perhaps in a supervisory capacity, an owner sampling system can be introduced. Here, the farmer does the routine weighing himself, but periodic visits are made by the official recorder. The measuring equipment used by the farmer could be very simple. It may be plastic buckets or bottles premarked into ½ kg sections by the use of exact measuring equipment.
In many tropical countries where milk is consumed primarily for its protein and not for fat, testing for butterfat content may not be necessary. However, bulk milk samples may be tested for fat content to assess the overall herd situation in instances where the price of milk is determined by its fat content. If it is necessary to know the fat composition of milk from individual cows, monthly testing of samples taken during the course of the lactation is adequate.
Protein content is usually determined from fewer samples - four samples taken during a lactation being adequate (Lindhé, 1980). Semi-automatic machines for quick determination of protein content are now available which make it possible to analyse a large number of samples at a central laboratory. A preservative such as potassium dichromate should be added to the samples before despatch to the laboratory.
Samples for milk composition testing should preferably be taken by official recorders to ensure proper sampling procedures. Usually a composite sample proportional to the yield at the two milkings is taken for testing purposes.
Testing for milk composition requires more organization and a dependable communication system. Be that as it may, the importance of milk yield as a selection criterion far outweighs that of milk composition. Hence, non-availability of facilities to test for milk composition should not stand in the way of implementing a milk recording programme.
Bimonthly recording: In this system, the recorder visits the farm every alternate month and records the yield obtained during a 24-hour period. The percentage of large errors of individual cow records in bimonthly recording is higher than with monthly testing but its level of accuracy is adequate for progeny testing purposes.
A.M.-P.M. sampling: In this method, the morning milk is weighed one month, and the evening milk the next month. It is more accurate than bimonthly testing but less accurate than monthly testing. Its chief advantage is that it is cheaper than monthly testing but maintains the same frequency of visits to the farmers.
Sampling at particular stages of lactation: The total yield estimated from monthly records is moderately correlated with the yield obtained on a single day during the third to the sixth month of lactation (Lindström, 1976). This has led to the suggestion that a reasonably accurate progeny test of bull could be obtained from such records if large progeny groups are available. For example, a progeny test based on a single day's record of 100–150 daughters would be as accurate as a progeny test based on about 35 daughters with complete records. However, this system would be difficult to implement in herds calving year round since the cows will be in different stages of lactation when the recorder visits the farm. But if the farmers provide the data or if AI personnel are involved in the recording, it should prove workable.
The methods used in estimating total lactation yields depend on the recording system. The centering method of calculating yields is preferable to other methods in monthly recording. In this procedure, the test day yield is multiplied by the number of days in the period of which it is the centre, and these products are summed to give an estimated lactation yield. At the beginning and end of lactation, the test day will not necessarily be the centre day of the test period; the first test period runs from four days after calving to the beginning of the following period, and the last period runs from the end of the preceding period to the end of the lactation.
In general, fortnightly recordings are required for individual cow selection. Monthly recording gives reliable information for sire proving, but bimonthly or A.M.-P.M. methods may be used if a slight loss of accuracy is acceptable. If used as an aid in management, particularly in deciding on feeding levels, recording weekly or at more frequent intervals may be required.
Many zebu cows do not let their milk down unless the calf is allowed to suck. This problem is partially overcome by allowing the calf to suck for a very short period to induce milk let-down followed by hand milking. This process of stimulation of the dam by the calf and milking may be repeated if necessary until all the milk has been drawn. In using this method, the calf should be separated from the dam for the period intervening between P.M. and A.M. milking; otherwise the first record taken in the morning will be erroneous.
Apart from yield and composition, other traits are also important in the tropics. In most zebu breeds, milk yields and lactation length are strongly correlated (Mahadevan, 1966). Lactation length can thus be used as an indirect selection trait in situations where yield is not measured, e.g. in nomadic herds. Age at first calving and calving intervals can be readily measured and are important indicators of adaptability to stress conditions.
In most farm situations in the tropics, the individual cow record (Figure 2.1) is the only one that needs to be kept by the herd owner. Lactation summaries, calving and breeding records and calf identification would be the responsibility of the official recorder.
Figure 2.1 Dairy record sheets
A. — Permanent Information (one sheet per cow)
| Cow's ear (tattoo) No................ | Cow's breed.......................... |
| Cow's birth date....................... | Sire of cow........................... |
| Dam of cow......................... |
| Lact. No. | Service dates | Bulls used | Calving date | Calf | Lactation length (days) | 305-day production (kg) | Total production (kg) | % fat or protein | Day's dry | |||
| Day | Month | Year | Sex | Ear No. | ||||||||
| 1 | ............ ............ | ............ ............ | ||||||||||
| 2 | ............ ............ | ............ ............ | ||||||||||
B. — Test day production
| Test day | Cow No. | Milk yield kg (AM or PM) | % protein (% fat) | Remarks on calving, services, drying off, illnesses |
A summary based on the data collected on the test day should be sent to the farmer shortly after the test to enable him to take the necessary management decisions. These should include (i) the test-day lactation report showing each animal's milk production and total production to the last test day and (ii) a herd summary giving information on animals for breeding, pregnancy checking, drying and culling during the next 30 days. The latter report should also give the means of milk yield, composition and calving intervals of animals that completed lactation during the last 12 months.
Performance recording in beef cattle even in countries with advanced beef industries has not attained the same degree of uniformity and refinement as that of the dairy industry. This is due to the diversity of environments and management systems under which beef cattle are raised and the different production systems used for beef production. The management systems under which beef animals are maintained in the tropics are even more variable. With the exception of the small proportion of cattle kept in commercial ranches, the majority of cattle are raised under extensive systems and are not accessible for recording. Records taken in the latter animals may have to be limited to traits that can be obtained by questioning the owners, e.g. reproductive traits, mortality.
Official recording schemes for collection of beef cattle records are in operation in many developed countries. Examples are the Meat and Livestock Commission (MLC) in the United Kingdom, Performance Registry International in USA, Record of Performance (ROP) in Canada and Beefplan in New Zealand. These organizations obtain records of pedigree, growth rate of calves and calving difficulties from private farmer herds. In addition, carcass data are recorded on animals slaughtered. The home recording scheme as operated by the MLC involves weighing calves in private herds four times a year by MLC staff till the animals are 20 months old. The farmer pays a fee for this service, the amount paid depending on the size of the herd and whether the MLC weighbridge or the farmer's scale is used. It also operates a Central Performance Testing scheme where bulls from different herds are recorded together at a central station under standard management. Measurements recorded are weight changes, feed intakes to calculate feed conversion efficiency, withers height as a measure of stature and backfat thickness using a “scanogram” as a crude measure of carcass merit. Bulls are also scored for type at the end of the test.
Since recording for beef requires more effort on the part of the producer than milk recording, it is necessary to ensure that he sees tangible benefits in return. The traits that should be recorded are as follows:
Reproductive performance: Fertility in beef cattle is usually measured in terms of calving rate, i.e. the number of calves born in relation to the number of mature females exposed to bulls. This estimate is generally adequate for survey studies and is easily obtainable where calving dates are collected over a period of time. It may not be adequate for management purpose since it does not reveal the extent of fertility disorders until actual calving occur. Where calving rate is to be deduced from an examination made on one visit, it can only estimated indirectly. Such estimates have been made in tropical beef cattle, e.g. in Colombia and Botswana, but they involve pregnancy testing and estimation of age of foetuses. For selection purpose, individual cow data are required for which the parameter usually used is the calving interval. Where records on calving dates are not obtainable, the only record that may be useful is the previous parous state of the cow, i.e. whether or not she had a calf during the year.
Mothering ability: The ability of the dam to wean a heavy calf is important in beef cattle, particularly in cow-calf operations. It involves measurement of two traits - viability of the calf and weaning weight. Viability is simply a record of whether a calf died before weaning age and the cause of death. Ideally, weaning weight should be taken at a constant age between 180 and 240 days. However, for ease of management, calves are generally weaned in groups, each group consisting of animals born during a particular fortnight or month. In such situations, date of weaning should also be recorded to adjust weaning weight for age at weaning.
Post-weaning weight: A sufficiently long time should elapse after weaning before post-weaning weight is taken to allow for adjustments caused by compensatory growth mechanisms and to permit animals to exhibit their own genetic potential. Weights are usually taken at some given end-point such as 12, 18 or 24 months of age depending on the management system. Where animals are recorded in test stations, the measurements obtained are weight changes from the beginning to end of test. There are also situations where calves are raised on range and finished in feedlot, e.g. feedlot operations in Kenya. In such circumstances, though weight changes in the two systems may be recorded for management decisions, the average daily gain at the end of the finishing period, which includes the components of weight gains on rangeland and during finishing, is adequate for selection purposes.
Other weights: Birth weight is of economic importance in breeds prone to dystocia. In other breeds, it provides an accurate measure of liveweight gain from birth to weaning. Dam weight at parturition is of use in adjusting weaning weight while weight change of the dam from parturition to weaning is an indication of the ability of the cow to maintain weight during lactation. The recording of these weights is difficult under field conditions and may therefore be omitted except in institutional herds.
Tick resistance: The susceptibility of animals to tick infections is highly heritable. It is therefore an advantage to measure tick resistance in areas where ticks are endemic. The important points to be observed in measuring tick resistance are as follows: (a) Assessments of tick burden should be done when infestation is likely to be high, which is during the wet season; a population mean of at least 25 ticks per side of animal is considered desirable to reveal the genetic variation between animals. (b) Animals to be compared should have been together for at least 6 months. The assessment is usually made on the basis of two counts of the number of replete female ticks (4.5–8.0 mm in size for Boophilus microplus) after exposure to either natural or artificial infestation (Seifert, 1971). This method is suitable for one-host ticks (Boophilus spp) and may not be applicable to other types.
Longevity: Longevity in terms of length of productive life in a herd is important in the tropics since animals reach puberty later in life and therefore the longer they remain productive, the lower is the cost of raising a heifer per year of productive life. Animals with a long productive life should be identified so that their close relatives could be selected. Simple procedures such as ear notching could be used even in herds that are not recorded for production traits.
Coat type: Coat type is a good indication of tropical adaptation in temperate breeds or in zebu x temperate crosses. Coat-type classification is made on the basis of a subjective score in which the primary criterion is the length of hair or depth of coat, with “handle” (a subjective assessment of diameter of hair) a modifying factor. Usually, the coat on the midside is scored by moving the palm of the hand over the side. Scores range from 1 to 7, 1 representing an extremely short type as found in zebus and 7 a very wooly coat (Turner and Schleger, 1960).
Colour and conformation: Colour is of little economic significance but gross deviations from the established norm warrant recording for possible culling since such animals may not be saleable as breeding stock. Visual assessment of conformation is a poor estimator of carcass quality in terms of muscle to bone ratio. It is merely indicative of condition which is a measure of fat cover. Therefore use of condition scores to reject animals selected on other economic criteria should be avoided.
Carcass quality: Accurate estimation of carcass quality involves slaughter of animals. Practical and efficient methods for estimating carcass value in the live animal are still in the development phase. Hence this trait may be ignored in recording.
Field recording for beef production in the tropics requires more organization and elaborate arrangements since weighbridges are usually not available in private herds. The method of recording given below in respect of weights and classification is being used successfully in Kenya (ILCA, 1977) and Botswana (Buck, 1981) in large herds. It is not of value in sedentary herds with a small number of cattle or in nomadic herds which may not be available for recording when required.
Identification: The procedure adopted should give each animal a unique identification. Tamperproof metal ear tags are the best as they can be applied at birth and loss rates are low. For rapid identification in the field and also to serve as a back-up in case of loss, the tag number should also be branded on the upper thigh by hot iron at weaning.
Classification of animals: When a herd is recorded for the first time, the animals are classified into one of two groups - breeding cows and other stock. The former includes females of breeding age and weight while the latter includes steers and bulls. Pedigree relationships should also be established at the first recording. Thus before an animal leaves the crush, its relationship with any other animal in the herd is determined. If it is a cow, information on whether she has a calf is obtained and similarly, if it is a calf, its dam number is obtained.
Records: For breeding cows, records taken are: breed, date of birth (actual or determined approximately from dentition), sire and dam if known, previous parous state and weight. Similarly, for other stock, records of breed, date of birth, sex (male, female or castrate), sire and dam number, dam's age and its previous parous state and weight are taken.
Weight: Weights are obtained monthly using either permanent or mobile weighbridges of (a) calves weaned during the month and (b) animals in the age range of 18–24 months. The ranch is informed in advance of the date of weighing so that animals to be weighed can be assembled the previous evening and kept off feed and water.
In addition to the above records which are taken by the central recording office, the ranch keeps separate books for birth records, weight records and treatment records. Sample sheets of the birth and treatment record book are shown in Figures 2.2 and 2.3. The latter record covers all information on breeding (services, etc.), health, management (weaning, castration), feeding (supplementary feeding) and stock changes (purchases, sales, etc.). The weight-record book is simply a record of the date of weighing and weights of the two group of animals - weaned stock and those 18–24 months of age.
Figure 2.2 Birth records sheet
| Date of birth | Calf No. | Sex | Dam No. | Birth weight | Sire No. | Herd | Remarks |
Figure 2.3 Treatment records sheet
| Date | Animal number | Treatment |
| 27/5/77 | 274 277 282 294 | Heifers to bull 204 |
| 28/5/77 | 397 | Died after being slashed by lion |
| 28/5/77 | Cow herd 1 | Moved to grazing area P4 |
| 30/5/77 | 201 | Steer sold to butcher 750/= |
| 1/6/77 | 502 to 600 | Weaned from cow herd 2 |
Systems of sheep and goat breeding in developed countries have not shown as much change as those for dairy cattle, partly because important characteristics such as fleece or body weight can be seen or measured in both sexes and also because these animals are associated with less' favourable environments. One exception is the introduction of cooperative breeding schemes for sheep in New Zealand and Australia in recent years; these involve selection on measured performance.
Sheep and goats can produce meat, fibre and milk. However, some breeds (e.g. Merino sheep and Angora goats) are kept primarily for their fleece, others for milk (e.g. the sheep breeds producing Roquefort cheese in France, or European goat breeds such as the Saanen), others again mainly for meat. Traits of importance for each product will be discussed in relation to sheep; recording methods for goats are similar.
Reproduction: Reproductive rate is important in all systems of sheep production. An increased rate lowers overhead maintenance costs for ewes, allows an increased selection differential for productive traits and gives more surplus animals for sale. The measurement of economic significance is the number of lambs weaned per ewe joined per year which takes into account both lambing rate and lamb survival rate.
In addition to litter size at birth, the New Zealand “Sheeplan” (national recording system) records weight of lamb weaned per ewe, which places emphasis on number of lambs weaned rather than number born, and so includes survival rate.
Mortality: Mortality at all ages, but particularly from birth to weaning, is a serious problem in the sheep industry and should be recorded. Survival rates of lambs to weaning are usually lower for multiple-born than single-born lambs, but in developed countries are seldom less than half (Lax and Turner, 1965), so that multiple births still give more lambs at weaning. Adult mortality can also be as high as lamb mortality in the tropics and should therefore be recorded.
Birth weight: The only reason for recording birth weight would be to make it possible to calculate growth rate to weaning, but this is seldom worthwhile. It is usually sufficient to record weaning weight at a known age.
Milk yield: Milk yield accounts for most of the variation in early growth of lambs. Where lamb growth is to be used as a measure of maternal milk yield, growth over the first 4–5 weeks is a good indicator as the correlation between milk yield and lamb growth at this stage is high. In dairy breeds of sheep and goats, direct estimation of milk yield as in dairy cattle is often not possible as the dam generally suckles the young and milking and suckling are concurrent. She-goats in particular are temperamental and may refuse to let down milk if separated from their kids.
Growth rate: The end product of meat breeds of sheep raised in advanced sheep-raising countries is the weaned lamb. Weaning weight is thus an important trait for performance recording, though Young et al. (1965) showed that weight at 15–16 months of age in Merinos had a higher heritability and a high genetic correlation with weaning weight. In the tropics, animals are rarely slaughtered at weaning, so body weights at later ages with their high heritability are more important than weaning weight.
Wool: Wool is an important aspect of sheep production in some areas of the tropics and with this product end use must be carefully considered. The main division is into apparel and carpet wools, the most important traits for both being:
Quantity measured by wool weight per head: The required weight is the clean weight, but greasy weight is simpler to measure and has a high heritability (Turner, 1972) and a high genetic correlation with clean weight.
Quality, the important traits being average fibre diameter (finer for apparel, coarser for carpet wool), staple length (a minimum desirable length for both), percent medullated fibres (low or zero for apparel, present to a certain extent for carpet wool), kemp (preferably completely absent for both) and fibre strength (no tender spots along the staple): Besides these main points, consideration should also be given to market requirements. Thus, hand processing, e.g. cottage industries, cannot deal with fine wools, particularly in the scouring and spinning stages. This is important for apparel wools, but not for carpet wools. In wool meant for world markets or for machine processing in the country of origin, the standards are usually laid down by the users.
Where records are used as an adjunct to the management of commercial flocks, individual identification is not necessary, as flock records are adequate. The minimum records necessary for this purpose are costs of supplementary feed and labour and sale value of animals, milk and wool. When information on the performance of the flock is required, periodic surveys may be made to gather data on the number of lambs weaned per ewe and mortality rates of lambs and older animals.
The procedures adopted in recording schemes for genetic improvement very with the objectives and capabilities of each flock. A flexible system of recording can be used, starting with minimal records that could be made elaborate with progress in record keeping. The type of records are set out below:
Identification: Some effective but less accurate selection procedures are possible even without individual identification. Where it is necessary to carry out more accurate selection procedures, permanent identification is achieved by the use of metal or plastic tags, tattooing on the ear or tail and horn branding.
Pedigree records: Dam identification is adequate for simple selection procedures. It should be done within a few hours after lambing by pairing ewes and lambs. Where identity of the sire is required, it is necessary to resort to hand mating or to run each ram with a group of females in fenced paddocks.
Lambing and weaning record of ewe: The lambing record of the ewe should indicate whether she was barren or produced single or multiple-born lambs and the number of lambs she raised to weaning age. The date of lambing, and the sex and identification of each lamb should be stated. In the flocks that lamb seasonally, lambing records should be preferably be taken daily. However, in many tropical countries, the rams run with the females throughout the year, so that there is no definite lambing season. Recording of births may then be done fortnightly or monthly. In flocks that are not individually identified, ewes which fail to lamb during each 12-month period may be given ear notches to aid culling of barren ewes.
Weaning weight: Since lambs are usually weaned in groups, all animals in a group are weighed on the day of weaning. Even where weaning is staggered, weighings could be done on predetermined dates and data adjusted for age differences.
Post-weaning weight: This is usually taken at any age between 12 and 18 months of age. Where type of birth and age of dam are not recorded, the weight should be taken at an age close to 18 months when the effects due to these factors are minimal.
Wool:
Quantity: For sheep shorn once a year, records of wool weights at 13–18 months of age, following a previous shearing at weaning, are a good indication of lifetime production. Sheep in many tropical countries, however, may be shorn twice or even three times a year. The sum of the weights at the second and third shearings should be recorded for sheep that are shorn twice a year, and at the second, third and fourth if shorn three times. Accurate records of the time between shearings should also be kept. Greasy weight is adequate in most cases but, for Merino types, it may be desirable to measure percent clean yield.
Quality: Fineness in apparel wools has traditionally been estimated through the number of crimps per inch of staple. However, this is an inaccurate guide (Turner and Young, 1969) and it has therefore been replaced in Australia by measurements taken on a sample from the midside. The measurements include fibre diameter, percent clean yield and amount and type of vegetable matter.
Milk yield: Indirect methods are used in estimating milk yield to overcome the difficulties caused by suckling. One method involves separation of the young from its dam for a 24-hour period on recording days which are usually one month apart. Another method is based on the liveweight increase of the lamb from birth to 2 months of age. This is multiplied by a conversion factor to estimate the amount of milk sucked which is then added to the amount milked out.
Disease: Records of ill-health and their causes are also sometimes recorded.
