Cattle and pastoralism: Survival and production in arid lands

Human Ecology, VoL 14, No. 1, 1986

Cattle and Pastoralism: Survival and

Production in Arid Lands

D a v i d W e s t e r n 1 a n d Virg in ia F i n c h 2

Traditional subsistence pastoralists in East Africa tend to keep large herds, milk cattle in preference to eating them, and subject them to long foraging treks. Such practices are widely considered ill-suited to arid lands and are believed to arise because cattle are raised more for social prestige than food production. Whether this is true can only be judged by considering the responses of cattle to arid zones and, given the herder's goals and options, his management practices. In considering these factors, we show that indigenous East African cattle demonstrate energy-sparing capabilities during drought. Pastoralists can therefore herd cattle at great distances from water at little more cost than animals on the normal maintenance diet and watered more frequently. The physiological response o f cattle to drought, the ecological constraints imposed by livestock and wildlife competition, and the energetic efficiency o f mixed milk and meat pastoralism explain why herders traditionally select their characteristic management practices.

KEY WORDS: cattle; pastoralism; Maasai seasonality; drought; physiological response; herding strategies; carrying capacity.

I N T R O D U C T I O N

Although a third of the earth's land surface consists of arid and semi- arid rangelands which support over 30 million people engaged primarily in pastoralism (Sanford, 1976), most accounts of the rationale and efficiency of subsistence livestock management remain rudimentary and anecdotal. Most studies have been anthropological, yet the paucity of ecological data have

~Resource Ecologist, Wildlife Conservation International, New York Zoological Society, P.O. Box 62844, Nairobi.

2Wilwood, Ramornie Station Road, Via South Grafton, N.S.W. 2X61, Australia.

77 0300-7839/86/03004)077505.00/0 �9 1986 Plenum Publishing Corporation

78 Western and Finch

not deterred speculations about the adaptive or maladaptive nature of pastoralism (Brown, 1971; Ruthenburg, 1971).

Subsistence pastoralists are often criticized by ecologists (Glover and Gwynne, 1961; Dasmann, Milton, and Freeman, 1973; Picardi and Seifert, 1976) and agricultural scientists (Ruthenberg, 1971; Pratt and Gwynne, 1977) on three main counts: their mobility, their preoccupation with livestock numbers rather than quality, and their emphasis on milk rather than beef production. Infrequent livestock watering and long foraging treks are also seen as mismanagement. Some authors (Brown, 1971; Ruthenberg, 1971) think that the prestige of large herds, rather than optimal production, dic- tates pastoral practices. Other authors argue that pastoral husbandry is both necessary and productive in marginal rangelands (Western, 1973, 1982; Widenstrand, 1975; Nechayeva, 1976; Kates, Johnson, and Johnson, 1977).

These conflicting views are difficult to reconcile for a number of reasons. First, the merits of pastoralism and commercial ranching have not been ade- quately compared in similar areas over a sustained period of time, especially through drought cycles. Second, the pastoralist's management options and goals are either disregarded, or commonly treated as identical to commercial ranching in less extreme environments (Dyson-Hudson, 1972). Yet, realistically, we must address these points before deciding whether pastoral practices are inefficient and how they can be improved upon. Finally, remarkably little information exists on the physiological responses of livestock to arid rangeland conditions (Ledger and Sayers, 1977), especially to restricted water and forage intake.

Whether pastoralism is appropriate to the rangelands can only satisfac- torily be answered by considering the physiology of indigenous cattle and the ability of the herders to support themselves better under alternative husbandry practices and on other cattle breeds. Conceivably, many pastoral practices might arise from the physiological responses of livestock to extreme food and water deprivation. Indeed, Ledger and Sayers (1977) pointed out that the question raised by Trowbridge, Moulton, and Haigh (1915), " . . . does a beef animal accustom itself to a lower plane of nutrition so that the costs become less and less?" remains unanswered, even though extremely perti- nent to livestock productivity in the arid zones. The minimum nutrient requirements of livestock have been treated as fixed (ARC, 1965), despite a number of studies (Silver, Colovos, Holter, and Hayes, 1969; Black, Graham, and Faichney, 1976; Ledger and Sayers, 1977) suggesting otherwise in wild and domestic species. Indeed, numerous studies on arid adapted species suggest that body temperature and metabolic ability are specialized adaptations to conserve water (MacFarlane, 1964; Schmidt-Nielson, 1964). Recent studies show that livestock respond similarly to deprivation. Taylor (1970), for in- stance, showed that East African zebu conserve water by reducing their

Cattle and Pastoralism 79

metabolic rate during sustained dehydration, and Ledger and Sayers (1977) found that various breeds of cattle maintain stable weight on rations 37% below predicted maintenance needs.

If livestock can adjust physiologically to food and water deprivation, it begs the question of whether those responses are understood by pastoralists, and whether herding practices are adjusted accordingly. Here we explore how cattle respond to the pronounced seasonality and periodic droughts characteristic of the rangelands. We also consider the significance of such responses to pastoral herd management, and specifically whether it helps explain the pastoralist's tendency to keep large milk, rather than small beef herds. Finally, we present a model demonstrating the relative advantages of pastoralism and commercial beef production in various environments.

To explore these issues, we focus on the pastoral Maasai, the largest of the cattle-keeping tribes in East Africa. A general description of their society, economy, and ecology can be found in Jacobs (1965a). We have several reasons for concentrating on the pastoral Maasai. One of us has studied their ecology in the Amboseli ecosystem, southern Kenya, since 1967 (Western and Dunne, 1979; Western, 1982); the other simultaneously studied the environmental physiology of their cattle at a nearby location (Finch, 1976). The Maasi are also among the most dependent of any pastoralists on livestock (Jacobs, 1965b), having little reliance on other food sources until relatively recently. Their survival therefore depends more on their husbandry skills than pastoralists who rely substantially on agriculture, hunting, or fishing, and, consequently, Maasai herding strategies are likely to be more attuned to livestock adaptability.

Although some data are available on livestock drought responses, none of the experiments to date was designed specifically to simulate pastoral herding practices during droughts. Here, we first identify the environmental factors that distinguish the arid rangelands from the moister tropics and summarize how pastoral Maasai manage their herds. Next, we describe the results of experiments simulating those conditions. Finally, we consider the implications for herd management. Our analysis is confined to cattle, rather than other livestock, because they dominate the live weight of Maasai herds (Western, 1975).

THE ARID R A N G E L A N D S

Because we focus on cattel pastoralists in eastern Africa, we will brief- ly describe the environmental conditions of this region. Rainfall, which is generally less than 600 mm, is usually correlated with altitude (Brown and Cocheme, 1969). The more arid the region, the greater is rainfall variability


in space and time (Brown and Cocheme, 1969). Low precipitation and high variability is further exacerbated by high net radiation, high ambient temperatures, high wind speeds, and low cloud cover, all of which contribute to high evapotranspiration (Finch and Western, 1977). Below an annual precipitation of approximately 700 mm, primary production is linearly correlated with rainfall (Coe, Cummings, and Phillipson, 1976) and, therefore, shows the same degree of high spatial and temporal variability. The fast turn- over rate of vegetation production in arid regions and large proportion of annual plant species (Western, 1980, 1982) further accentuates fodder seasonality.

Conditions in the arid regions are thus especially rigorous for livestock due to seasonal food and water supplies and to extreme heat stress (Payne, 1965). Both the total pasture crop and its digestibility to herbivores declines sharply through the dry season (Sinclair, 1975). When the rains fail, there may be inadequate forage to maintain livestock and wildlife numbers. The precise timing and intensity of drought is unpredictable, even though, given good records, we can state the probable recurrence intervals for droughts of any magnitude (Barry, 1969). Given that drought intensity is proportional to time and that primary production is roughly proportional to rainfall (Coe et al., 1976), it follows that the longer the management horizon, the lower the carrying capacity.

Abbreviated, patchy, arid land rains typically produce rapid growth and highly digestible forage. However, nutrients are translocated to the roots after growth ceases (Sosebee and Wiebe, 1971). Consequently, the available digestible energy declines sharply after the rains, even though the standing crop may remain high (Pratt and Gwynne, 1977). Dry season water sources also dwindle, further restricting pasture availability (Western, 1975).

The problem confronting livestock management in the arid and semi- arid rangelands can therefore be summarized as prolonged periods of sparse, patchily distributed, poor forage, punctuated by ephemeral locally abundant, rich forage. Water is scarce when food and heat stress are greatest.

H E R D I N G P R A C T I C E S

The traditional Maasai confronting the vagaries of the rangelands routinely employ a number of herding practices that, they consider, improve the welfare and increase the productivity of their cattle (Western, 1973, 1982). We only emphasize here the common herding practices used during the dry season. The Maasai in Amboseli and elsewhere use two herding techniques during the dry season. Some herders, in order to reach distant, sparsely used pastures, elect to water their cattle on alternate days. These herders locate


their settlements between 8-12 km from water to balance food and water requirements of cattle which, on average, walk 16 km daily.

Other herders who graze cattle in the swamps locate their settlement within 3 km of water, water their herds daily and walk them 8 km on average. It would seem that the added stress of water deprivation and walking imposed by the 2-day, 16-km regime, would be considerably greater than the alternative strategy. Some herders forced their cattle to walk up to 22 km to graze and watered them only every third day during extreme droughts. We were interested in measuring how cattle responded physiologically to drought under these alternate management regimes.

CATTLE RESPONSES TO SIMULATED D R O U G H T MA N A G EMEN T

To find out whether any physiological drought adjustment do occur in cattle, a series of experiments were designed to simulate food and water deprivation (Finch and King, 1982). During the 1978 hot, dry season (Trial I), 12 small East African zebu steers were subjected to simulated drought conditions on the Athi Kapiti Plains. In a pre-period of 1.5 months, all steers walked 8 km/d , were watered daily, and were offered a maintenance ration. Following this, the steers were divided into two groups of six animals over the next 3.7 months; one group continued walking 8 km/d , and the other group increased the distance to 16 km/d . Food and water were lessened during these months. First, 65% of the maintenance ration was offered for 0.7 months, followed by a further reduction to 50~ of maintenance for the re- maining 3 months. All steers drank water every day for the first 2 months and then every second day for the last 1.7 months.

In a second experiment during the 1979 dry season (Trial II), 12 other steers were again subjected to a month's pre-period, during which the steers were offered a maintenance ration, were watered every day, but were walked 16 km/d. Following the pre-period, the steers were divided into two groups of six animals; one group was watered every day, the other group every second day. This watering regime continued for the 2 months' duration of Trial II. Food was reduced in the same pattern as Trial I, i.e., first, 65~ of maintenance was offered for 0.7 months, followed by a reduction to 50% of maintenance. The experimental schedules have been summarized in Table I. During the course of the experiments, metabolic rate, live weight, water intake, and digestibility coefficients were periodically measured. The methods are given elsewhere (Finch and King, 1982).

The weights of cattle declined during both Trials I and II, but no significant difference (p > 0.5) occurred in the weight loss of steers subjected to different treatment within a Trial (Table I). In Trial I, doubling the distance


walked each day did not result in differential weight loss. In Trial II, cattle watered every 2 days lost no more weight than those watered daily. In neither trial did steers watered on alternate days eat less than those watered daily, or increase their apparent digestibility of food. Weight losses resulted solely from the enforced reduction of food and not in response to either the watering or walking regimes.

The changes in fasting metabolic rate (FMR), calculated from measured resting metabolic rate and estimated heat increment of food, can be described by the curve:

FMR -- 83.9 - 9.03 logl0t (r = 0.949, p < 0.001, n = 17)

where t is time in days (Fig. 1). As all values for the different watering and walking regimes fall within the 95~ confidence limits of the curve, the different treatments of watering and walking did not significantly influence the rate of change in FMR. In fact, the decline in FMR followed the temporal pattern of response to a change in food intake described for cattle by Turner and Taylor (in press). The greatest decrease, amounting to 68~ of the ultimate decrease, occurred within the first 30 days. This reduction in FMR was an adjustment in minimal energy requirements due to lowered metabolic activi-

PRE-PERiOD PERIOD I PERIOD 2 PERIOD 3

. . . .

- 7O �9

EO

5O

B4~

0.5 1.0 1.5 Z.O 2.5 3.0 35

TIME (MONTHS)

Fig. 1. Change in fasting metabolic rate during Trial I and II. Each point represents the mean for six steers. The amount of food offered each day is shown at the top of the figure. Walking and watering regimes are denoted by: Trial: (e) = DW, 8 km/d; (~) = 16 km/d; (Q) = 2DW, 8 km/d; (•) = 2DW, 16 km/d. Trial II: (&) = DW, 16 km/d; (A) = 2DW, 16 km/d. All abbreviations are as shown in Table I.


ty within active tissue. The physiological mechanism by which FMR was reduced in response to food deficits is not known. However, the phenomenon is reported in a variety of species, including man (Grande, 1964), white-tailed deer (Silver et al., 1969), and sheep (Black et al., 1976).

One consequence of a lowered metabolic rate can be seen in the change which occurred in the energy cost of walking during the trial I (Fig. 2). The slopes of the two regressions relating energy cost to walking speeds during the pre-period and at the end of the experiment are not significantly different. Every increase in speed of walking required the same increase in energy, regardless of treatment. Thus, there was no change in efficiency of walking as a result of treatments. However, the total metabolic expenditure while walking at any speed was less by some 40% at the end of the experiment. This decrease was due to the reduction in intensity of FMR, and to the smaller heat increment of food.

28

24

20

\

16

~ t2

8 ~ ~ o ~o o o

0

i ~ i i i J I i

0 I 3 4 5 6 ? 8

SPEED (KPH, I

Fig. 2. Energy expenditure o f four steers walking at varying speeds measured in Trial I at the end of the pre-period and at the end o f the experiment. Each steer was measured 8-10 times and each point is a single measurement . Energetic equivalent of one liter 02 = 20.29 kJ. Slope for pre-period: (e) = 2.21 kJ /kg -km (p < 0.001). Slope for end of experiment: (0) = 2.11 kJ/kg-krn (p < 0.001).


It was surprising that steers walking 16 km daily did not lose more weight than those walking 8 km (Table I). An increase in efficiency of walking could not explain the maintenance of weight. However, as the experiment proceed- ed, the steers traveling the longer distance walked more slowly, so that their total metabolic expenditure while walking may have been less (Fig. 2).

Another consequence of reduced metabolic rate was the change in daily energy requirements of the steers (Table II). Incremental costs above resting metabolic rate of the activities of eating or drinking, ruminating, and walking have been estimated for the pre-period and the end of Trial I (period 3). Reduction in costs of eating, drinking, and ruminating were a function of reduced time spent engaged in these activities. On the other hand, the cost of walking doubled when the steers increased their daily travel from 8-16 km, but this resulted in only a small increase in the net energy required for activities. There was a substantial decrease in resting metabolic rate, deter- mined when the steers were standing or lying, which incorporated the reduction in FMR and the heat increment of food. Thus, when the energy of activities and resting metabolic rate were summed for the pre-period and the end of the experiment, the total daily metabolic expenditure per kilogram body weight decreased by 11.5%. The decrease is the energy sparing during the duration of the experiment. When the total daily energy requirements (J/kg. d • wt) for the pre-period (31.9 MJ/d) and end of experiment (24.3 M J/d) were calculated, the decrease in energy requirements was 27%. This represents both the energy spared due to a reduced metabolism, and a reduc-

Table I. Weight Changes (kg + SE) of Cattle in Trials I and II at the End of Each Period a

Number of Durat ion Period of t reatments cattle (months) Weight (kg)

Trial I

Pre-period M, DW, 8 k m / d 12 1.6 223 +_ 3.72 Period 1 0.65 M, DW, 8 k m / d 6 0.7 217 + 3.5

0.65 M, DW, 16 k m / d 6 212 _+ 2.9 Period 2 0.5 M, DW, 8 k m / d 6 1.3 213 __ 2.91

0.5 M, DW, 16 k m / d 6 208 _+ 2.95 Period 3 0.5 M, 2 DW, 8 k m / d 6 1.7 194 _+ 3.02

0.5 M, 2 DW, t6 k m / d 6 192 _+ 3.23

Pre-period M, DW, 16 k m / d 12 1.0 221 + 5.8 Period 1 0.65 M, DW, 16 k m / d 6 0.7 217 _+ 3.5

0.65 M, 2 DW, 16 k m / d 6 221 + 4.8 Period 2 0.5 M, DW, 16 k m / d 6 1.3 202 + 3.8

0.5 M, 2 DW, 16 k m / d 6 208 _+ 5.0

aAbbrcviations: M = maintenance ration, 0.65 M = 65% of maintenance, 0.5 M = 50% of maintenance, DW = daily water, 2 DW = water every other day, walking 8 k m / d a y or 16 k m / d .

Tab

le I

I. E

nerg

y R

equi

rem

ents

of

Cat

tle

in T

rial

I d

urin

g th

e P

re-P

erio

d an

d at

the

End

of

the

Exp

eri-

m

ent

(Per

iod

3) W

alki

ng 1

6 km

/d"

e~

o

Tre

atm

ents

Pre

-per

iod

b P

erio

d c

Ene

rgy

Ene

rgy

Item

s A

mou

nt

cost

(k

J/k

g'

d)

Am

ount

co

st (

kJ/k

g" d

)

Eat

ing/

drin

king

(2.

6 k

J/k

g'h

) 2.

5 h

6.4

1.2

h 3.

1 R

umin

atin

g (0

.5 k

J/k

g'h

) 7.

0 h

3.4

5.0

h 2.

6 W

alki

ng

5.3

km

/h

17.6

4

km

/h

35.2

S

ubto

tal

27.4

41

.1

Res

ting

met

abol

ic r

ate

115.

5 85

.4

Tot

al e

nerg

y co

st

142.

9 12

6.5

Fas

ting

met

abol

ic r

ate

84.6

65

.4

"Abb

revi

atio

ns a

re a

s in

Tab

le I

. bM

, D

W,

8 km

/d,

wei

ght

223

kg.

r M

, 2

DW

, 16

km

/d,

wei

ght

192

kg.

CIO


tion in energy required due to tissue loss. Weight loss, though a passive result of food restriction, can be regarded as another adaptation to poor nutrition. It seems reasonable to conclude that a reduction of energy requirements slows the loss of body tissue during deprivation, but the experiments slows the loss of body tissue during deprivation, but the experiments were not designed to test this possibility.

Concurrent with a decrease in FMR, the water requirements of cattle also declined (Finch and King, 1982). MacFarlane (1976) has pointed out the close relationship between water and energy metabolism; thus, as FMR/kg body weight declines, we can anticipate that water requirements will also decline. However, cattle walking 16 km daily in hot weather required 0.7 liters/100 kg more water than those traveling 8 km daily, an increase that was significant, but small. Taylor (1970) found that dehydration, indepen- dent of food intake, reduced standard metabolic rate in zebu cattle by 42%. We found no such effect in comparing FMR in cattle on a daily and 2-day water schedule (Trial II, Table I). Our results suggest that the various management practices of the Maasai involved in walking greater distances, and in watering less frequently in order to graze further from water, impose little measurable energetic costs on their zebu cattle. The principal mechanism involved in food and water economy can be explained by reduced maintenance requirements in response to food shortages. This favors prolonged productivity, slows weight loss, increases survival, and prolongs meat and milk production.

W E I G H T R E C O V E R Y

At the end of both trials, the steers were offered food ad libitum, and the time taken to recorver weight to the levels of the pre-period was record- ed. In both instances, cattle walked about 8 km and watered daily; the food made available to them was, however, varied. In Trial I, the steers were given dry hay similar to that of the experiment, but with a higher protein content and digestibility. In Trial II, the cattle grazed after rain on flowering grasses, which were presumably highly palatable.

Weight gains in Trial I (0.6 kg/d) were less rapid than in Trial II (0.8 kg/d), but in both instances, the gains were faster than weight loss, which did not differ in the two trials (0.3 kg/day). After Trial I, 1.8 months were required for complete weight recovery, and after Trial II, only 0.7 months. This difference reflects both the poorer nutritive value of the food and the greater weight loss which occurred during Trial I.

The enhanced food intake of cattle after a period of food deprivation (Allden, 1970) is the major component of compensatory growth (Graham and Searle, 1975). FMR also responds and increases, and rate of weight gain


and FMR are positively related (Frisch and Vercoe, 1977). Although not specifically measured during the recovery experiments, we believe the rapid weight gains (especially in Trial II) indicate a rapid response of metabolic rate. The reduction in FMR when nutritive conditions deteriorate, and the rapid weight increase when they improve, can be regarded as the drought- adapted attributes of the zebu cattle used in these experiments.

THE RATIONALE OF PASTORAL STRATEGIES

Can the physiological response of cattle to seasona variations in food and water availability and long treks help explain the large herds and milk practice of cattle pastoralists?

Competition for limited resources is a dominant feature of the East African pastoral lands. Three factors contribute to its intensity: the seasonality and vagaries of climate, lack of individual land ownership, and competition from wildlife (Western, 1982). Periodic forage deficits are inevitable where rainfall is highly seasonal, patchy, and unpredictable. Moreover, the longer the time-frame, the more severe the worst drought experience will be. A herder's sustainable stocking rates must therefore decrease in proportion to his management horizons. In other words, stocking rates cannot be regarded as absolute, but will vary with time-frame, with the level of acceptable drought mortality, and with the environmental impact a society is willing to tolerate. Thus, short-term food-maximizing goals favor high production at high risk and high environmental impact; long-term sustainable food goals favor low production at low risk and low environmental impact. Risks can be minimized and production maximized on heterogenous pastures by op- timizing migratory pathways between quality patches. Consequently, migrants experience less resource seasonality and are more productive than resident herbivores (Western, 1982).

Migration, however, has a cost. Mobility precludes individual land ownership and exacerbates competition because a migrant herder cannot conserve for poor seasons pastures he rarely uses otherwise. Further, even though kin and nonkin alliances make altruistic pasture management theoretically possible, the inability of traditional societies to exterminate wildlife negates their efforts to preserve drought reserves. Competition from unallied herders and wildlife therefore accentuates forage seasonality and drought shortages and favors short-term production goals. We must consider the advantages gained by cattle energy-sparing capabilities to appreciate the significance of the pastoralist's herd practices.

Calves born during the wet season have a higher survival than those born during the dry season when milk yields decline with forage conditions


(Dahl and Hjort, 1976). Cattle births are therefore scheduled in the rains (Dyson-Hudson, 1969), as in wild ungulate grazers (Leuthold, 1977).

Milk must be available in sufficient quantities to sustain calves to wean- ing age. The surplus is available for human consumption. Offtake that deprives calves, though benefiting the pastoralist in the short-term, will im- pair herd replacement and growth rate in the long-term. The herder must therefore balance his immediate and long-term needs when milking (Spencer, 1965). Moreover, because milk yields decline through the dry season for both the calf and human dependent, the herder must rely increasingly on alternative livestock products, or other food sources (Dyson-Hudson, 1969). Blood forms a small proportion of the energy that the pastoralist obtains from the herds, usually less than 2% (Dahl and Hjort, 1976). The only reliable food source during the dry season is meat from surplus cattle, either males or in- fertile females, or sheep and goat.

It is worth noting here that the need for alternative food sources is greatest among Sahelio-Sudanic pastoralists, whose cattle cannot lactate throughout the long dry season following the single annual rainfall. In contrast, the East African pastoralists can survive more exclusively on milk because the double rainfall allows year-round milking. The difference in rainfall regimes explains why the Sahelio-Sudanic pastoralists rely more than East African herders on agriculture, hunting, and fishing.

Large herds are a method of storing surplus "meat on the hoof" (Swift, 1973; Western, 1982); that is, surplus production from good seasons pro- vides the reserves for poor seasons. However, although the "meat on the hoof" hypothesis does offer a rational explanation for large herds, we consider that, based on the responses of zebu cattle to simulated arid conditions, there are more benefits and fewer costs associated with this strategy than have previous- ly been realized.

Confronted with the harsh seasonal and competitive conditions of arid lands, those cattle able to reduce their maintenance needs for forage and water will survive longer than those unable to do so. Thus, in the simulation experiments outlined earlier, cattle lacking any energy-sparing capabilities would have died far sooner than the experimental animals.

During good seasons, milk yields are sufficient to sustain human needs. During poor seasons, milk yields are inadequate and must be supplemented by meat consumption. However, it should be pointed out that the severity of a season is an outcome of pasture shortage, which reflects herbivore stocking levels just as much as it does antecedent rainfall. Livestock will even starve after good rains if the prevailing stocking levels are very high.

What then is the advantage of a large herd under such conditions? A large herd owner produces more milk during good years, and has greater meat reserves and skins for sale or barter during poor years than a small herd owner.


The large herd owner can also take greater risks and prudently begin to slaughter and consume animals in anticipation of their death from star- vation. In doing so he obtains more meat from animals still in moderate condition than if they died later of emaciation.

Food shortages are particularly acute after severe droughts when continued offtake reduces the rate of herd recovery. A larger herd can harvest more surplus forage and, consequently, has the capacity to supply to the herder more energy throughout the recovery period. Given the time lag in population responses (Dahl and Hjort, 1976) a beef herder would need to replenish his herd capital before resuming consumption of surplus animals. In contrast, the milk pastoralist can meet the immediate needs of his dependents by taking advantage of the rapid metabolic and milk response of cattle during realimentation.

Although East African zebu give less milk than Eurasian cattle, the supply is far less sensitive to food deficiency and recovers sooner following droughts (Lampkin and Lampkin, 1960). The birth seasonality ensures that a substantial proportion of animals begin lactating shortly after the onset of the rains. Despite the loss of more than 50% of the cattle population during a severe Amboseli drought (Western and Grimsdell, 1979), enough females survived pregnancy to give birth and produce milk shortly after the rains resumed.

The timing of energy supply is not the only advantage of a mixed milk and meat economy. The energy conversion efficiency of milk from pasture is 14%, compared with 3% for meat (Blaxter, 1962). An efficient herder can obtain over 2.5 times the energy from milk and meat than from meat offtake alone (Western, 1973, 1982). A similar differential is evident in the herd production figures given in Dahl and Hjort's (1976) extensive review of pastoral herd management. If family size (and social influence) is the ultimate objective of a pastoralist's herd management (Western, 1982), then, in a noncash economy, milk and meat offtake can support more dependents than beef offtake alone. Livestock numbers are an efficient means of obtaining wives through the birdeprice and ultimately in producing a large family.

The symbolic value of cattle is, in our view, a proximate rather than ultimate explanation. Indeed, even the Maasai, who have the highest per capita holdings of any pastoral society (Jacobs, 1965b), have too few cattle to survive the worst droughts (Western, 1973, 1982). This is contrary to the surplus predicted if cattle reflect symbolic wealth alone (Ruthenburg, 1971).

Viewed in evolutionary perspective, if cattle numbers and prestige were the sole objective, prestige herds would be rapidly displaced by herders who invested surplus stock in larger families and in forging social alliances. Enlarg- ed families and stock alliance (Spencer, 1965; Almagor, 1978) in turn permit a pastoralist to split his herd, usually according to feeding specialization dic- tated by species, age, sex, and lactation. Animals in smaller herds forage


more efficiently and survive food shortages better than animals in large herds (Jarman and Sinclair, 1979). In other words, a pastoralist's immediate survival and ultimate evolutionary success emerges from the tight link he makes between livestock production and social influence.

Brown (1971) contends that milk-dependent subsistence pastoralists are irrational and unproductive compared with beef producers. To the contrary, we consider that traditional milk pastoralism can be rationalized once the constraints of their environment and the adaptations of their livestock are appreciated. Sophisticated production and drought-survival tactics, not irrational management, explain the pastoralist's herd practices.

THE IMPLICATIONS OF DROUGHT RESPONSES IN ,LIVESTOCK

Several important deductions can be made about livestock management in the semi-arid rangeland based on the observed livestock responses to extreme conditions of food and water deprivation. First, pastoralists are suffi- ciently aware of energy-sparing abilities in cattle, and possibly other livestock, to adjust their herding techniques accordingly. The negligible cost incurred by less frequent watering and greater foraging treks helps the astute herder to increase herd production substantially. By watering cattle less frequently, the herder can drive animals to distant, little-used pastures; alternatively, the time saved in commuting gives animals more time to graze selectively when pasture quality is poor (Sinclair, 1975). Herds are also subdivided on the basis of an animal's individual foraging abilities. Calves and small stock are herded near the settlement on reserved pastures (Western and Dunne, 1979); adult stock, typically the milking females, are grazed further off, within daily travel of the family settlement. Surplus animals (nonlactating females and steers) are grazed on more distant pastures, often a day's walk or more away (Spencer, 1965; Western, 1980).

The separation of stock by sex, age, and lactational status minimizes competition within herds and frees physically capable adult animals to forage up to 25 km from water, a distance considerably greater than wild herbivores encumbered by young can manage (Western, 1975).

Second, it can be deduced that the carrying capacity of metabolically labile livestock in arid lands is greater than predicted by models assuming fixed metabolic rates (see Fig. 3). Carrying capacity in the semi-arid regions is thus relative, rather than absolute, varying with management horizons, acceptable degree of risk, and environmental impact.

Finally, a labile metabolic rate helps buffer animals against seasonally fluctuation food and water supplies. The greater the seasonality, the more advantageous the mechanism. Livestock maintained on high-production, low-


D 20-

(3

t~

~ C k ,~ I0-

~ B

5-

o ~ ,b ,~ 2'o 2's 3~ DISTANCE FROM WATER (Kin)

Fig. 3. The effect o f energy-sparing strategies and foraging distance from water on the population of cattle supported in an arid ecosystem. Population size increases in proportion to the square of distance from water. Normal maintenance diet assumes a stocking density of 10 ha per animal; energy-sparing strategy assumes maintenance requirements are reduced 30%. A is then the potential population capacity when cattle water daily and cover 8 km each day; B is when they water on alternate days and cover 16 km daily; C is the same regimen when cattle use energy-sparing mechanisms; and D is when they use energy-sparing mechanisms, are watered every third day, and cover up to 16 km daily-the most extreme herding strategy used by pastoral Maasai.

s easona l i ty pas tu res do no t benef i t by a lowered m e t a b o l i s m , since it wou ld penal ize g rowth ra te and r ep roduc t ive po ten t i a l . The o p t i m a l s t ra tegy will, we suggest , va ry with seasona l i ty (Fig. 4). The grea ter the seasonal i ty , bo th in te rms o f d u r a t i o n and ampl i tude , the greater the number o f cat t le a herder can ca r ry i f f o o d and wate r r equ i remen t s a re reduced . Converse ly , the more equ i t ab le the seasons , the grea te r will be the a d v a n t a g e o f a high me tabo l i c rate . O u r mode l predic ts t ha t t r ad i t i ona l pas to ra l m a n a g e m e n t s trategies a re mos t effect ive in a r id env i ronmen t s and noncash economies , and swings in f avo r o f conven t iona l commerc i a l r anch ing in less seasona l env i ronment s .


~ ~ K I

~ K2

DURATION

Fig. 4. Hypothetical model demonstrating how cattle-carrying capacity will vary along a gradient of pasture seasonality according to whether (K,) or not (K1) they adopt energy- sparing mechanisms. K2 assumes cattle possess no energy-sparing capability in which case carrying capacity declines directly with dry season food availability; KI shows the progressive advantage in seasonal environments of cattle able to apply energy-sparing mechanisms.

The relative price of beef and agricultural produce will determine the will- ingness of a traditional subsistence herder to sell cattle and purchase grain (Brown, 1971).

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Documents

Cattle and pastoralism: Survival and production in arid lands