Livestock productivity and management

Introduction
Evolution of survey methodology
The ground survey
A comparison of some results from initial and continued surveys
Additional notes on weight and milk recordings
References
Productivité et gestion du bétail

R. Trevor Wilson¹ and P. Semenye²
¹Team Leader' Arid Zones (West Africa) Programme, ILCA Mali
²Animal Scientist, Arid Zones (Eastern and Southern Africa) Programme, ILCA Kenya.

Introduction

Effective and realistic planning for total development in Third World areas requires not only that baseline data be obtained relating to the existing situation but also that future trends are predicted with a reasonable degree of accuracy. While it is possible for economists to derive output figures using a variety of methods for "with project" situations it is usually the "without project" and the "base" situation which are suspect, as often the base utilised is little better than an educated guess.

Of all the elements utilised for the formulation of an integrated development plan it has normally been the livestock sub-sector which has been the weakest link. Perhaps there have been good - even almost valid - reasons for this. The traditional reluctance of pastoralists and livestock owners in general to enumerate, or to have enumerated, their animals and the mobile nature of the assets in question have ma-de accurate or even reasonably approximate estimations of total numbers almost impossible to obtain. Indirect methods of estimation such as those based on returns for tax, marketed output, sales of hides and skins are also notoriously inefficient. Aerial surveys have to some extent alleviated this problem but is not only at the population or regional level that errors are apparent: parameters at the level of the herd and of individual animals have also been generally unknown. In the latter case estimates of production - birth and death rates, growth, offtake - have been based on factors derived from usually non-comparable situations in more developed economies or data from experimental or livestock breeding units where management for "improvement" of local breeds (usually by crossing with exotic, i.e. highly specialised and non-adapted stock) takes place.

In recent years methods have been developed for the more realistic estimation of livestock parameters in traditional systems. These relate to estimates of total livestock in a given area as well as to the determination of individual and herd production characteristics. By combining the two sets of data, precise figures for the total livestock output of an area can be derived, with known confidence limits. Once this point has been reached it is feasible to manipulate the data for predictive purposes, taking into account natural factors such as rainfall variability and effects of disease and anthropogenic factors such as responses to market stimuli and improved veterinary control.

Evolution of survey methodology

Low-level aerial surveys are particularly suitable for the enumeration of total animal numbers related to both time and space. Sequential surveys at fixed or varying intervals can be used to establish short-term changes in livestock numbers, trends in total effective size of the herd and seasonal or longer-term movement patterns.

The method is particularly suitable for the determination of total animal numbers and, provided a series of flights over time is flown, can also be used to establish the gross dynamics of an animal population. It is not possible to obtain precise data on recruitment (birth) and mortality rates from aerial surveys, nor is it possible to establish population structure or sex ratios with any accuracy although in early surveys attempts at this were made using size criteria based on photographic samples. Thus for establishment of population dynamics and demography, as well as for individual growth rates, production parameters for meat and milk production and levels of offtake, some sort of ground survey is necessary.

Until the early 1970s livestock production data for traditional societies were almost invariably based on the work of anthropologists and sociologists whose main interests were outside the field of livestock production. Otherwise data have been compiled, often by economists who themselves have usually had little experience of livestock production, from questionnaire surveys. In general it can be considered that both socio-anthropological and formal questionnaire methods provide too little and too inaccurate data of the kind required to established livestock population and production parameters. There are exceptions, however, some of these types being adequate for certain data: the good ones generally result from the quality and knowledge of the observer rather than from the raw information given. In addition (but perhaps to a decreasing extent as social and educational horizons expand) formal questionnaires may induce a response block in the more conservative pastoral societies. There is no substitute for physical inspection - and physical contact with - as large a number of animals as possible. Once the livestock owner realizes that the researcher has a real interest in (and an ability with !) the animals, then considerable information, as opposed to the "data" of an elicited response caused by a questionnaire, is usually forthcoming.

Thus, some years ago, attempts were made to establish a "zootechnical" method of survey which would provide data of the kind and of the accuracy required for detailed development planning. The method, which is described fully in the next section, was primarily designed for use with cattle, sheep and goats. It has also been used in camel and donkey studies. Integrated development plans for several semi-arid areas in northeast Africa have been formulated using livestock data from these studies. These include plans for Darfur in western Sudan in which livestock data were obtained from transhumant Baqqara Arabs and indigenous sedentary cultivators; and for Tigre in northern Ethiopia with data from short-cycle transhumant Afar in the Rift Valley and sedentary Tigrean cultivators on the Ethiopian Plateau. In West Africa a study of agropastoral systems forming part of the ILCA semi-arid and arid programme used data obtained from transhumant Fulani and sedentary Bambara cultivators in central Mali. Further studies forming part of the ILCA subhumid and humid programme and of their monitoring programme are under way in Nigeria and Kenya respectively.

The ground survey

Three levels or depths of intensity of survey can be recognized:

1. pre-survey
2. initial survey
3. continued survey

The ultimate level of survey will depend on the kind of information required and the use to which the data will be put. It should be noted, however, that it is a prerequisite of the method that the earlier stages must be carried out. It may be possible to telescope a continued survey either with one or with both earlier survey stages but usually some initial work will need to be done.

Pre-survey

A knowledge of the natural environment, the social groups and the general pattern of livestock distribution and ownership is fundamental to any further survey. Initial stratification can be carried out using LANDSAT imagery and (if an integrated aerial/ground survey is envisaged) aerial reconnaissance. Some time, however, must be spent on the ground in all parts of the survey area, preferably as part of multi-disciplinary team. This should comprise at least the animal scientist, a range ecologist and a social anthropologist or socio-economist. Unless one of these is thoroughly familiar with the area in question and/or the local language a guide/interpreter will be required and in any case may be desirable or necessary for political reasons.

During this phase it should be possible to select representative areas and representative villages or other units for the initial survey stage. An outline of the subsequent stages should also be given to the probable participating units.

If an aerial census to determine total numbers is not to form part of the subsequent stages of survey then available statistical data should be collected at this point. In any case such data may well be useful for comparative purposes and also may help to establish household and individual ownership patterns. Market and slaughterhouse figures also need to be collected.

At this point, however, we think it would be useful to illustrate some of the problems which are inherent in the published data relating to these aspects. The FAO Production Yearbooks are the most commonly quoted source for livestock numbers. These rely to a considerable extent on national authorities for their data, although they often make adjustments. They give little idea, unfortunately, of the distribution of animals within countries and among people in these countries. Some preliminary work may well be required to determine the importance of livestock in the area being studied - not simply in terms of numbers but in the contribution of livestock to the overall economy. ILCA is using a classification of "pastoral" for people obtaining more than 50 % of their gross income from livestock and "agropastoral" for those obtaining between 10 % and 50 % from animals. Another problem is the continuing lack of importance attached to small ruminants by national authorities and development agencies. Yet in the seven countries which occupy the semi-arid belt of northern tropical Africa from the Atlantic to the Red Sea, sheep and goats together account for 15.5 % of the standing domestic ruminant biomass. This is shown in Table 1 which also includes figures for Kenya. In some statistics small ruminants are virtually ignored altogether and we can quote here the Office du Niger in Mali which, as Table 2 which is taken from the census records shows, indicated only 12.0 % of families owning goats. The real situation (Table 3) is very different and this table also shows another aspect, not evident in Table 1 except for Niger and Kenya: in the semi-arid zones, particularly in the agropastoral areas, goats are generally of much more importance than sheep numerically and, on account of their potential birth rate, are probably creating an ever widening gap. Ownership patterns and flock sizes are one aspect that would be useful for us to look into during the field studies.

Table 1. The importance of sheep and goats in selected African countries

	Biomass of sheep & goats as % of total	Numbers of sheep & goats ('000 head)	Ratio: No. of sheep to one goat	Number of sheep & goats per inhabitant
Senegal	12.2	2 805	1.95	0.73
Mauritania	28.2	8 200	1.56	6.41
Mali	22.8	11 478	1.04	2.13
Niger	21.7	9 360	0.40	2.10
Tchad	10.2	4 508	1.00	1.27
Sudan	13.7	27 644	1.31	2.13
Ethiopia	14.4	40 270	1.35	1.65
Kenya	8.8	8 395	0.90	0.73
TOTAL	14.7	112 805	1.16	1.67

Table 2. Livestock holding according to official statistics in a sample of villages in both millet and rice subsystems in the central Mali agropastoral system

Table 3. Ownership patterns of sheep and goats in an agropastoral area in central Mali

	Irrigated rice subsystem		Rainfed millet subsystem
	Goats	Sheep	Goats	Sheep
Number of owners	27		16
Number owning sheep or goats	26	15	16	9
Number owning goats but no sheep	12		7
Number owning sheep but no goats	1		0
Mean flock size¹	9.0	6.4	38.2	7.1
Mean flock size²	9.3	11.5	38.2	12.6
Range in flock size	0-23	0-64	2-91	0-58

¹Of all owners, i.e. irrespective of whether the holding of one species is nil.
²Of only those flocks in which animals are held, i.e. nil holding excluded.

Initial survey

This stage is designed primarily to provide data on population structure and individual animal growth rates. From these parameters it is possible to postulate instantaneous individual and flock output without any additional knowledge of birth rate, death rate or actual levels of offtake. Indeed some of these parameters may be deduced from the population structure at least as accurately as they can be extrapolated from questionnaires.

Large numbers of each animal species are required to establish realistic population means with a sufficient level of reliability. In real terms this will probably involve not less than 1,000 head of each species (in Darfur data were collected in this phase for 5,600 cattle, 1,900 goats and 1,200 sheep and in central Mali almost 10,000 smallstock were involved). Population classes based on dentition - 4 pairs incisors worn, 4,3,2,1 pairs incisors and milk teeth - while subject to some reservations, are likely to provide data on demography just as valuable as can be obtained using the more or less subjective ages in years given by most owners. For the class of milk teeth some reasonably accurate age indications of younger animals can be expected and can, with experience, be utilised in conjunction with tooth growth and wear to establish sub-groups within this class.

Fig. 1 shows the kind of population data which can be obtained using a questionnaire technique (this one was done in Tchad) compared with that obtainable from a "handling and mouthing" exercise (this was done in Mali) and relates to sheep. Fig. 2 shows data for cattle at two extremes of the range of systems likely to be encountered in the traditional sector, both these being obtained by the latter method. We think it probable that for Mali we have sufficient population data of this kind but it may be worthwhile doing some demographic work in other countries. What might be useful in Mali in the rice subsystem of the agropastoral sector would be to compare the percentage of work oxen in large herds with those in smaller ones.

Sample selection within the broader ecological/social strata established during the pre-survey poses some problems. A frame suitable for randomisation of the sample is unlikely to exist given the differences which will probably be found in ownership patterns and flock sizes. Some subjectivity might need to be accepted, after the primary stratification governing locality and group size has been adequately taken into consideration. A representative sample should be the aim.

At this stage considerable additional information on the animals may be obtained at little extra cost. In all cases this might include details of external morphology: such physical data may have little direct relevance to the primary objectives of the study but nevertheless may well provide useful comparisons, particularly as existing descriptions of African livestock, and especially of small-stock, are generally inadequate and often of considerable antiquity. In some cases, and certainly where a continued survey is not envisaged, it is worthwhile attempting to obtain individual reproductive histories of breeding females: if such data can be obtained then it is possible to calculate such parameters as birth rate, frequencies of multiple births and parturition histories.

Fig 1. Population demography of Sahelian smallstock

Fig 2. Sex and age composition of the three principal domestic species presented for slaughter at
Niono

Tables 4 and 5 illustrate the kind of information which can be compiled with a lot of perseverance and not a little luck. Where a continued survey is expected these latter parameters are probably of too tenuous a nature to be worth the investment in time required at this stage.

Table 4. Data on kidding for 42 flocks of sedentary goats in the Niono area (calculated from initial survey)

Parameter		4 pairs incisors	3 pairs incisors	2 pairs incisors	1 pair incisors	Milk teeth	All goats
Number in sample		180	77	61	111	15	444
Type of birth
	Triplet	8					8
	Twin	203	11	4	1		219
	Single	457	139	81	77	5	759
Total births		668	150	85	78	5	986
Total kids born		887	161	89	79	5	1221
Average litter size		1.33	1.07	1.05	1.01	1.00	1.24
Parturitions
	Mean	3.71	1.95	1.39	0.70	0.33	2.22
	Mode	3	2	1	1	0	1
	Range	0 - 10	0 - 5	0 - 3	0 - 1	0 - 1	0 - 10

Table 5. Number of partaritions per breeding cow for sedentary cattle in the Mopti area from initial type survey)

Age (years)	Number of calves								Total		Number of cow reproductive years
	0	1	2	3	4	5	6	7+	Cows	Calves
0-1	197								197
1-2	180								180
2-3	205	1							206	1
3-4	145	27	1						173	29	86.5
4-5	28	95	14						137	123	205.5
5-6	12	56	43	2	2				115	156	287.5
6-7	6	23	51	19	1				100	186	350.0
7-8	2	3	18	20	31				74	223	333.0
8-9		1	7	8	6	4			26	83	143.0
9-10	1		2	7	18	7	3		38	150	247.0
10+	1			1	3			1	6	23	45.0
TOTAL	777	206	136	57	61	11	3	1	1252	974	1697.5

In addition to normal help from the livestock owners a team composed of the animal scientist and a recorder is the minimum required. Providing there is a degree of confidence between these two, that both are aware of the descriptive "shorthand" being used and both understand the principal language of communication within the studied community, good results can be expected. Up to 300 head of smallstock or 80-100 cattle can be processed in a five-hour session.

A complete "initial survey" of this type might be expected to take about six to eight man-months occupying a time span of four to six months including full data analysis and report completion.

Continued survey

The continued survey is designed to provide full and reliable data over the whole range of production parameters. These include birth, death and offtake rate (the latter by components such as sales, gifts, ritual and emergency slaughter), individual weight gains by season and year, meat and milk production and flock dynamics. Individual identification of animals is necessary. The most convenient method from the point of vi- of the survey is by coloured and numbered plastic ear tags. The application of these can be expected to create some consternation and initial resistance in most societies, but this has so far not proved too difficult to overcome. It does again, however, condition sample selection and the aim should be a representation of the generality of the areas. A minimum of ten units for each species should be aimed at with not less than 300 animals of each species being recorded initially. Very small units and atypically large ones should be avoided. If the latter are selected they may lead to inaccurate estimate of offtake, particularly if they are operated on a commercial rather than a subsistence basis and if the study is aimed at establishing production and identifying constraints in the traditional sector.

At this first visit when each animal is identified, as much information as possible on its physical characteristics and its relationships to other animals in the unit should be obtained. All this information should be transferred subsequently to the back of an individual record card.

Recently we have analysed here in Addis Ababa, with the aid of the ILCA computer, some three and a half years' data for Mali and about two and half years' data for Kenya. Data from the highlands programme and from the programme in Nigeria have also been, or are in the process of being, analysed. So we now have considerable expertise in field data collection and analysis of results including programmes for analysis and modelling.

Physical and family relationship data enable positive identification to be made should ear tags become accidentally lost; family data are also useful in establishing the most prolific and productive blood lines.

Subsequent visits need to be made at fairly short intervals (two weeks or less) in the early stages of this phase. All events in the flock in the intervening interval should be recorded and subsequently entered on the individual card. Newborn animals need to be identified, cross-referenced to their dams and weighed: relevant details should be entered on the dam's card and on a new card for the young.

A canvas sling suspended from a spring balance of the dial type is suitable for weighing smallstock but some kind of crush and weighbridge will be needed for cattle. A crush is also required for adult horses but a suitable sling and a 200 kg dial can be used for donkeys and foals. Came] weighing poses problems and undoubtedly requires some ingenuity (in the Darfur studies "live" weights were established post-mortem in concurrent slaughterhouse studies). We were able to arrive at a formula for estimating the weight of camels and there is another one available. These are given in Fig 3.

Fig 3. Estimation of camel weight from linear measurements.

	p = 53 TAH
where	P = Weight in kilograms
	T = Girth behind the breast pad
	A = Abdominal girth over the hump	in metres
	H = Shoulder height

	Y = 5.071 X - 457
where	Y = Weight in kilograms
	X = Girth in front of breast pad in centimetres (best taken with camel in squatting position?

The main problems in the early period of this stage are associated with getting the livestock owner to appreciate the need for full reports of all events. Outgoings in which the tag is returned to the recorder are less of a problem than incomings. The principal deficits in the latter respect are failure to report deaths of newborn animals in which both birth and death have occurred between visits; failure to report stillbirths or abortions; and failure to report deaths of one or more siblings of multiple births. It is not necessary to check every animal physically at each visit but whole unit checks need to be carried out at regular intervals to identify any discrepancies.

Once some confidence in the ability of both the researcher and the owner to record and report all events has been achieved, the frequency of visits can be reduced to something between four and six weeks. Longer intervals may be acceptable where there is some literacy in the group being studied and where a group member undertakes to record data.

In order to achieve worthwhile and reliable results which can be used for productive purposes or as aids to biotechnical innovation this type of study should take a minimum of three years. Such a period would minimize seasonal effects in the results other than in exceptional cases. Normally, some useful indications of production parameters would be forthcoming after the first 12 to 18 months.

A programme involving the three main species of domestic livestock in 30 units totalling 1000 head in the region could be expected to occupy a technician more or less full time, with supervisory scientific and analytical work including report writing, in the region of three man-months per year.

A comparison of some results from initial and continued surveys

In both Kenya and Mali in 1978 we carried out initial surveys of the type decribed here with the intention in both countries of going on to continued surveys. How much and what kind of information have we obtained from the latter and how does it differ from that obtained in the former?

For population structure the initial survey obviously is the definitive one as we generally use much larger numbers of animals. We have already had some examples of this in Figs 1 and 2 and we have tried to indicate how population structure is affected by management objectives.

We have also said that for establishing weight or growth curves the initial survey can be satisfactory. This is true, however, only for certain limited objectives, for example to find a generalised growth curve and mature average weights. Fig. 4 shows direct comparisons for Mali for initial and continued surveys for sheep and goats from birth to 18 months. There is quite a lot of correspondence but also some divergences. The main problems are at the older end of this age range where, either the ages in the initial survey were underestimated, or they were weighed at a time of the year which was particularly favourable to them. What Fig. 4 cannot show, and what can only be obtained from a continued survey, is a breakdown of weights by type of birth and parity. With a continued survey we can also have weight curves by season of birth among other things. Initial surveys do not give seasonal weight variations either: an example of these for cattle, using the same age classes by dentition that we might use in an initial survey, is given in Fig 5. This shows the magnitude of seasonal weight changes indicating the main stress points, and where, for example, supplementary feeding needs to be considered and to what classes of stock it should be given. Continued surveys can also give a much better idea of the variations in weight for age as shown in Fig 6.

Fig 4. A comparison of growth curves for the same population when estimated from a single survey and calculated from long-term data.

Turning to reproductive traits, we saw in Table 4, taken from an initial survey, the kind of data it is possible to extract. Comparing tables 4 and 6 it can be seen that one reproductive trait is fairly close for the goat in both surveys - the average litter size. We also came very close, at 1.06, for sheep in the initial survey although, as we have implied earlier, we think we were lucky. What the initial survey will not tell us is the age at first parturition (although we can get some idea of this from dentition/parturition data), the parturition interval or the distribution or parturition intervals in relation to parity. The continued survey will show us this, as can be seen from Figs 7 and 8; Fig. 7 also shows the increase in litter size with parity, something which can be deduced but with less accuracy from an initial survey as table 4 illustrates.

One of the principal drawbacks of an initial survey is the lack of any firm data on deaths and offtake. Again it is possible to compile some figures from population structure and individual breeding female histories - total animals born, now in flock, died, sold etc., but these are subject to considerable errors of recall. A continued survey enables us to establish precise figures for these parameters.

Fig 5. Seasonal weight changes in cattle

Fig 6. Computer scattergram of individual weights and calculated growth curve for a sheep population

Table 6. Some reproductive parameters for sedentary sheep and goats in the Niono area

Parameter			Sheep	Goats
A. Age at first parturition
	Age (days)		470.5	484.4
	Standard deviation		90.5	105.5
	Range		341-673	275-739
	Number in sample		52	54
B. Interval between successive births
	Interval (days)		253.9	271.3
	Standard deviation		69.1	79.5
	Range		150-491	156-638
	Number in sample		225	280
C. Multiple births: litter size
	I. Number (%) of parturitions		557 (100.0)	668 (100.0)
		Single	528 ( 94.8)	521 (78.0)
		Twin	28 (5.0)	144 (21.6)
		Triplet	1 (0.2)	3 (0.4)
	II. Number (%) of young		587 (100.0)	818 (100.0)
		Single	528 (89.9)	512 (63.7)
		Twin	56 (9.5)	288 (35.2)
		Triplet.	3 (0.5)	9 ( 0.1)
	III. Average litter size (II/I)		1.054	1.225
D. Number of young per annum (CII x 365)/B			1.52	1.62

Note: Calculated from data obtained over 3 years of ILCA continued surveys.

Fig 7 . Components of small ruminant annual reproduction rate - Parturition interval

Fig 7 . Components of small ruminant annual reproduction rate - Litter sixe

Fig 8. Distribution of parturition intervals and ages at first parturition for sheep and goats

The great advantage of the continued survey is its preciseness and the opportunity it provides to calculate and utilise statistically significant values. The combination of various parameters such as the birth rate (a function of parturition interval and litter size), death rates, weights of females and young at weaning enable us to calculate certain production indices. These are extremely useful for determining the effect of management, biological and economic factors on production. Table 7 shows the differences which can arise between, for example, species and also between sexes, parities, seasons, flocks and so on. These factors then indicate, by their magnitude, their relevance and their importance in any proposals for improving livestock production. Fig 9 illustrates a possible improvement pathway for small ruminants. It has the initial advantage of costing very little in financial terms and should provide real benefits in a comparatively short space of time.

Table 7. Ratios of comparative advantages for sources of variation in indices I, II and III in the agropastoral system

Source		Index I		Index II		Index III
		Goats	Sheep	Goats	Sheep	Goats	Sheep
Sex:
	males to females	1.08	1.05	1.04	1.03	1.03	1.05
Parity: all parities to first		1.54	1.29	1.42	1.25	1.40	1.23
Birth type:
	twin to singles	1.37	1.23	1.48	1.45	1.55	1.43
Season:
	best to worst	1.17	1.11	1.26	1.16	1.23	1.14
System:
	rice to millet	1.82	1.45	1.53	1.31	1.58	1.33
Flocks:
	millet best to worst	2.17		2.62		2.43
	rice best to worst	9.34		5.30		5.58

Fig 9. Interventions pathways for small ruminants in the agropastoral system

Additional notes on weight and milk recordings

Livestock weighing

Weighing just after daylight on each weighing day is comparatively easy on the animals and holds variation to a minimum. Weighing of cattle later than the time they are usually released from their night enclosure causes a lot of commotion, and should be avoided. Also to be avoided is weighing when animals are coming back for the night after grazing the whole day or soon after drinking water. However, there are situations, as in Kenya, where calves are weighed in the evenings in an effort to spread livestock activities throughout the day. Calves in this case are weighed late in the evenings, because they are left by their dams early in the morning after suckling and they do not feed until the dams come back for the night. Whatever time of weighing is picked, the key thing is consistency.

Frequency of weighing

Accurate weights should be obtained at all times. To ensure this the scales being used should be calibrated frequently and test weights should be used before any weighing and strategically thereafter.

For calves four weighings are necessary up to the age of two years. The weights are at the ages of 1, 3, 7 and 18 months. "Birth weight" should be taken within 24 hours of actual birth whenever possible. On the other hand it weight at actual birth of the breed in question is not known at all, it is then worthwhile to measure it.

We have weighed 53 calves in Kenya once every month up to the age of four months. The correlation of 30 days with that of 60 days is 95 %, for 60 and 90 days is 95 % and for 90 and 120 days is 94 %. Because of this high correlation it is obvious that one can cut down the number of weighings to two without losing accuracy.

For weighing calves up to the age of 120 days a weighbridge is not necessary. Up to this age liveweights are easily taken by a scale of 100 kg hanging from a tripod. Above this age weighbridge is necessary. An ideal weighbridge is one with a yoke as it facilitates tagging and mouthing and it restrains an animal for other measurements. A weighing scale mounted on the back of a four-wheel drive pick-up is better than one on a trailer. The former can be moved faster and more easily from one site to another, covering distances of over 100 km per day.

Two weighings are recommended within the first four months as this is a critical period of the life of a calf. It is also the period when calf growth is nearly entirely dependent on milk. It therefore gives the best measure of milking ability. Weighing at the age of seven months is taken as the weaning weight, for measuring the mothering ability. It is not possible to weigh all calves at the exact age of seven months and adjustment is necessary for calves falling between six and eight months, to correct them to 210 days.

The final calf weight at 18 months after standardisation for age differences is a better measure of genetic differences in growth rate than earlier weights discussed above.

Monitoring of seasonal weight changes

If a measure of the productivity value of the range is desired as dictated by seasons, mature steers or wethers are the choice. Steers and wethers are preferred because changes in their liveweights are not affected by physiological status of pregnancy or milk production. In some situations one may require to study seasonal effects on liveweight as affected by specific animal product, e.g. milk production, in which case the appropriate animal type is used.

Milk yield measurement

Zebu cows are known for refusing to let down their milk without the stimulus of a calf sucking. So when computing lactation yield of zebu cows milk taken by calves must be taken into consideration.

Several methods of measuring total milk yield have been tried: weighing before and after suckling, oxytocin injection, bucket feeding, partial suckling and liveweight growth rate milk equivalent.

Weighing of calves, lambs or kids before and after suckling is a very sound method except that it requires a very sensitive scale able to pick differences in the range of 50 g to 3.5 kg. Such scales exist but are not suitable for weighing livestock which never remain still during weighing. The weight difference obtained in some cases is negative due to the fact that before weighing after suckling the young animal may have urinated or defecated. This method requires a lot of labour, so that not many animals can be recorded and a very small sample may to be taken, leading to unsatisfactory statistical analyses.

Injection of oxytocin to stimulate milk let-down is possible only on a research station. In some countries, e.g. Kenya, oxytocin can be administered only by a qualified veterinarian. How many calves and sampling times is it possible to study under free range conditions ? Bucket feeding and partial suckling methods are related. In order to bucket-feed partial suckling is necessary first to stimulate milk let-down and calves have to be taught how to drink from a bucket. Complete milking-out under-estimates total yield from milking plus suckling by as much as 18 % (Amble et al, 1965).

Calculation of the amount of milk equivalent to observed growth rate is good only for the first three or four month of the life of a calf, that is before it starts grazing. Necessary formulae for converting liveweight and growth rate to milk equivalent are available (Konandreas and Anderson, 1982; MAFF, 1975). The remainder of the lactation yield is best estimated by computing the net energy available for milk production, combined with milk offtake measurements. With this method yield evaluation of many cows is possible and in Kenya the method is used with over 600 cows. A cows are known to attain their peak production within the first four months of lactation this method is therefore adequate in estimating maximum milk yield potential.

Number of milk measurements and yield rating

Milk offtake is normally recorded twice a day. Pastoralists normally milk twice and, among the Maasai, approximately 80 % milk twice and 20 % once a day.

With the Kenyan pastoral tribe of Maasai a paired 't' test was conducted between a.m. and p.m. yields on 2,939 milking days. The difference between the two means (30 ml) was significant
(P 0.05) but not large enough to matter. It is therefore suggested to do only one milk offtake measurement per day. This will cut down the cost of evaluating zebu cows' potential for milk and beef production, leading to increased number of such evaluations for improvement purposes.

The minimum number of measurements is four per month, preferably two in the morning and two in the evening. These should also be made on days of average activities, rather than when cows are on heat or following vaccinations or dipping.

Pastoral tribes rate their cows for their yield potential by simple classifications into good, average and poor on milk offtake. This classification is specially applicable to cows with a previous lactation. Cows on their first lactation are rated provisionally on their current yields. On analysis of 2,301 records, actual production was found to conform with the yield rating of the owners; good cows gave 1.28, average 0.96 and poor 0.86 liters per day. The differences were highly significant (P 0.005). If breed improvement is envisaged it would be easy to use pastoral peoples' rating to identify the good producers, the best of which could be used as dams of young bulls for progeny testing.

As an added variable to milk offtake it is recommended to note the number of teats being milked on each measurement occasion, and also the method of calf restraint.

References

Amble, V.N. et al. 1965. Estimation of the amount of milk sucked by calves. Indian J. Vet. Sci. 35: 56-67.

Konandreas, P.A. and Anderson, F.M. 1982. Cattle herd dynamics: an integer and stochastic model for evaluating production alternatives. ILCA Research Report 2, Addis Ababa.

MAFF (Ministry of Agriculture, Fisheries and Food, United Kingdom) 1975. Energy allowances and feeding systems for ruminants. Technical Bulletin No. 33, London.

Productivité et gestion du bétail

Résumé

Cet exposé décrit l'évolution de la méthodologique d'enquête, y compris celle utilisée pour les enquêtes à basse altitude, les enquêtes par questionnaires et les méthodes "zootechniques" d'enquête. Il examine ensuite les enquêtes au sol à trois niveaux: la pré-enquête, l'enquête initiale et l'enquête continue.

La pré-enquête fournit des données sur l'environnement naturel, sur les groupes sociaux et sur la structure générale de la distribution et de la propriété du bétail. Au cours de cette phase, il devrait être possible de sélectionner des zones, villages ou autres unités territoriales représentatifs pour la phase "enquête initiale".

La phase enquête initiale est conçue tout d'abord pour fournir des données sur la structure de la population animale et sur les taux de croissance individuelle. A partir de ces paramètres, il est possible de calculer la production instantanée des individus et du troupeau même si l'on ne dispose pas de données supplémentaires sur les taux des naissances et de mortalité ou sur les niveaux réels de l'écoulement. Une enquête initiale complète peut prendre environ six à huit mois/homme (et s'échelonner) sur une période allant de quatre à six mois, y compris l'analyse complète des données et l'élaboration du rapport.

L'enquête continue est conçue pour fournir des données complètes et fiables sur l'ensemble des paramètres de production. Celles-ci incluent les taux de naissance; de mortalité et d'écoulement (ce dernier étant composé d'éléments tels que vente, don, abattage rituel et in extremis), les gains pondéreux individuels par saison et année, la production carnée et laitière et la dynamique des troupeaux.

L'identification individuelle des animaux est nécessaire. Ce type d'étude devrait durer un minimum de 3 ans pour produire des résultats valables et fiables. Une telle période permettrait de réduire au minimum les effets saisonniers sur les performances, sauf dans les cas exceptionnels. Normalement, certaines données utiles sur les paramètres de production apparaissent après les 12 à 18 premiers mois.

Il est ensuite procédé à la comparaison des résultats obtenus dans le cadre d'enquêtes initiales et continues au Kenya et au Mali; des informations supplémentaires sur les poids et la production de lait sont données. Il est recommandé d'effectuer le pesage juste après la tombée du jour. Les animaux en souffrent relativement moins et cela réduit au minimum les variations. On devrait pouvoir connaître les poids précis à tout moment et les balances devraient être fréquemment calibrées.

Les avantages relatifs de plusieurs méthodes de mesure de la production laitière sont examinés. Ceux-ci incluent le pesage avant et après l'allaitement, les injections d'oxytocine, l'engraissement à façon, l'allaitement partiel et l'équivalent en lait du taux de croissance pondéral. Le prélèvement de lait est normalement enregistré deux fois par jour.