Relationship between phytomass productivity, animal forage preference and environmental factors on semi-arid grazed and ungrazed key range plants in Tanzania

M.M.S. Lugenja

Tanzania Livestock Research Organization
Livestock Research Centre, P.O. Box 5016, Tanga, Tanzania

R.N. Mero

Tanzania Livestock Research Organization
Livestock Research Centre, P.O. Box S. Kongwa, Tanzania

A.R. Kajuni

P.O. Box 446, Tukuyu, Tanzania

Introduction
Materials and methods
Results
Discussion
Conclusion
Acknowledgements
References

Abstract

The relationship between phytomass productivity, animal forage preference and environmental factors on semi-arid grazed and ungrazed range plants in Tanzania was investigated from 1979 to 1982, on three range sites at: Pasture Research Centre, Kongwa; Livestock Multiplication Unit, Mabuki, and Livestock Research Centre, West Kilimanjaro. Phytomass production was obtained from nine random quadrats harvested at middle and end of rains. Height-weight relationship from grazed and ungrazed plants coupled with timed observation on grazing animals, and CP content was used to determine animal preference. Phytomass productivity from grazed paddocks ranged from 2.20 to 4.74 tonnes DM ha^-1 as compared to 2.04 to 3.95 tonnes on ungrazed ones. The combined yield of grasses and browse plants increased phytomass productivity to about 15 tonnes per hectare. There was significant difference (P>0.05) in the utilisation of the key range plants at Kongwa, West Kilimanjaro and Mabuki. Cattle preferred grazing on perennial grasses while goats preferred trees and shrubs. Regression of animal forage preference on phytomass productivity, crude protein and environmental factors, and phytomass productivity on environmental factors for Kongwa and West Kilimanjaro were nonsignificant (P>0.05). To maximise range resources for sustained animal productivity mixed stocking is suggested.

Introduction

Tanzania has an area under rangeland estimated to be about 60 m ha which supports about 20 million stock units (Anon, 1983). This level of animal production has, however, been below the national nutritional demand (Akilimali, 1983; Chagula, 1983).

Several factors are responsible for the low animal production levels, but the most important of all is shortage of adequate quantity and quality feed in the dry season. This is manifested in overgrazing which is a common feature in all livestock farming systems.

High levels of animal production can, however, be attained from these rangelands provided good range management principles are applied. Practices such as grazing at optimum stocking rate, use of proper grazing management systems and the use of the right kind of animals restore balance between forage supply and animal nutritional requirements.

Grazing animals are known to prefer certain grasses and legumes at some stages of growth, and such behaviour was observed in palatability studies (Johnstone-Wallace and Kennedy, 1944). As a result of selective grazing chemical and botanical composition, herbage consumed by grazing animals differs from the average of the composition of the sward in the field (Johnstone-Wallace and Kennedy, 1944). The amount of green herbage on offer influenced the grazing animal's intake (Johnstone-Wallace and Kennedy, 1944). Similar findings were reported by Chacon and Stobbs (1976), and that intake and total yield of herbage on offer was high and positively correlated.

Cattle also prefer certain plant species at certain stages of growth and various parts of an individual plant (Hafez and Bouissou, 1975). It was further reported that the taste of ingested materials probably provided ultimate basis upon which the animals formed a decision as to whether the material was highly preferred, merely tolerated or completely rejected. On the other hand, the grazing habits of goats was described by Knight (1964), who showed that grass formed the major food preference for East African goats. However, these findings were not in agreement with those obtained by Staples et al., (1942), Jordan (1957), Wilson (1957), Edward (1948), and Lugenja and Kajuni (1979), who concluded that goat diet comprised mainly trees and shrubs.

Although Hancock (1954) found no relationship between temperature and grazing behaviours, Stricklin et al. (1976) reported that occurrence of thunderstorms forced animals to stop grazing. Similar observations were reported by Arave and Albright (1981). However, Smith (1959) did not observe any increase in the proportion of the night grazing of individual cattle under high daylight temperature.

In this study attempts have been made to establish the relationship between phytomass productivity (PP), animal forage preference (AFP) and environmental factors (EF) on semi-arid grazed and ungrazed plants in Tanzania.

Materials and methods

A total of 15.4 ha in 14 paddocks, each 105 m x 105 m at Kongwa Pasture Research Centre (PRC), the West Kilimanjaro Livestock Research Centre (LRC) and the Mabuki Livestock Multiplication Unit (LMU) were used for the study. The mean annual rainfall and temperatures were: 250 to 500 mm and 27° to 33°C (PRC, Kongwa), 300 to 400 mm and 20° to 30°C (LRC, West Kilimanjaro) and 700 to 800 mm and 29° to 32°C (LMU, Mabuki). The soils are derived from granite and gneisses at PRC, Kongwa (Owen, 1964); neugene alkaline volcanic materials at LRC, West Kilimanjaro (Anderson and Naveh, 1965) and alluvial lacustrine origin at LMU, Mabuki (Hathout, 1983). In general, all locations are dominated by Commiphora and Acacia trees, associated with Aristida, Pennisetum and Cynodon grass species.

Primary productivity (PP) of grasses in tonnes dry matter (DM) was obtained at the middle and end of rains from 1 m² quadrats, randomly located in the paddocks. However, PP of trees and shrubs was estimated from twigs of current year's growth of key browse plant within 1.67 metres height. All twigs in predetermined direction were harvested. The bulked-up samples were analysed for crude protein, (CP) calcium (Ca) and phosphorus (P). The grass data were pooled for one season and analysed as split plot by way of ANOVA (Steel and Torrie, 1980). Duncan's multiple range test (DMRT) was used to separate means, and chi-square of independence test was used for chemical analyses data (Sokal and Rohlf, 1969). Tree and shrub yield data were inadequate for statistical analyses.

AFP was determined by recording the time spent by animals on each plant species. Five to ten cows (zebu cattle) and 30-40 goats (blended castrates and females) were used at Kongwa and West Kilimanjaro locations. The species were observed on different dates between 0800-1200 hours at each location and site during the middle and end of rains. Cattle alone were used at LMU, Mabuki. The animals were observed for an hour at all locations, and different species of animals were observed on different days. The percent time spent by cattle and goats grazing on different plant species were summarised under four major plant classifications, namely: annual grasses (Urochloa trichopus, Aristida adscensionis, Chloris pyonothrix, Chloris virgata, Setaria verticillata, Dactyloctenium aegyptium, Digitaria velutina, Brachiaria deflect); perennial grasses (Bothriochloa insculpta, Chloris gayana, Cenchrus ciliaris, Cynodon dactylon, Pennisetum spp., Sporobolus spp., Hyparrhenia spp., Themeda triandra); herbaceous plants (Astripomoea hyosciamoides, Monechma blepharis spp., Dalbegia spp., Rynchosia sennaarensis, Sida spp., Tephrosia spp.); and trees and shrubs (Acacia mizera, A. tortilis, Blepharispermum zangubaricum, Bauhinia spp., Cadaba spp., Combretum spp., Euphorbia cuneata, Indigafera spp.).

Forage utilisation of key range plants (grasses) at Kongwa and West Kilimanjaro was determined from locally compiled height-weight tables as described by Lammasson and Jamson (1942).

Phosphorus, calcium and crude protein were determined using the Molybdenum blue Fiske and Subbarow method, the Oxalate method and the Kjeldahl method respectively. This was in turn used to assess AFP.

Environmental factors (percent relative humidity = % RH, maximum temperatures = Tmax., evaporation = E and rainfall = R) were collected twice daily at 09.00 and 15.00. Percent relative humidity was calculated from standard meteorological tables (Goodchild, 1983).

Regression of AFP (pooled for cattle and goats, grazing animal diet) on PP, AFP on CP, EF on AFP and PP on EF, for Kongwa and West Kilimanjaro locations, were used to establish the relationship between different factors (Sokal and Rohlf, 1969). Data from LMU, Mabuki were too scanty to be included in the regression analyses.

Results

Phytomass Productivity (PP)

Ungrazed paddocks at Kongwa produced 14% more phytomass in tonnes DM ha^-1 (P<0.05) than that which was produced on grazed ones (Table 1a). On the other hand, grazed paddocks at West Kilimanjaro and Mabuki produced 12% more phytomass in tonnes DM ha^-1 (P>0.05) than that which was produced on unglazed paddocks, respectively (Tables 1b and 1c). Sites 2 and 3 at Kongwa produced significantly more phytomass in tonnes DM ha^-1 (p<0.05) than that produced on site 1. There was no significant difference (P>0.05) in the phytomass in tonnes DM ha^-1 produced on the three sites at West Kilimanjaro. However, site 3 produced 60% and 99% more phytomass in tonnes DM ha^-1 than that which was produced on sites 1 and 2, respectively (Table 1b).

Table 1a. Mean phytomass productivity in tonnes DM ha^-1 at Kongwa.

Paddocks	Sites			Mean
	1	2	3
Grazed	2.61	3.57	2.97	3.05a*
Ungrazed	2.74	3.95	3 75		± 0.10
Mean	2.68a	3.76b	3.36b	3.48b
			SE ± 0.57

SE = Standard error
* Means with different superscripts differ significantly at 5% by DMRT.

Table 1b. Mean phytomass productivity in tones DM ha^-1 at west Kilimanjaro.

Paddocks	Sites			Mean
	1	2	3
Grazed	2.75	0.89	4.74	2.79a
Ungrazed	1.91	2.89	2.72	2.49a ± 1.20
Mean		SE ± 1.01

SE = Standard error.
* Means with different superscripts differ significantly at 5% by DMRT.

Tree and shrub data from Kongwa location (Table 1d), indicated that high (15.04 tonnes) DM ha^-1 was produced from site 1. Site 3 was the least productive, with only 0.76 tonnes. Acacia mizera produced the highest mean DM (8.52 tonnes) at site 2. The least productive shrub was Cadaba kirkii, with mean DM yield of 0.24 tonnes.

Table 1c. Mean phytomass productivity in tonnes DM ha^-1 at Mabuki.

Paddocks	Sites
	1	2	3
Grazed	2.59	-	-
Ungrazed	2.04	-	-
Mean	2.32 NS
	SE ± 0.30

SD = Standard deviation.
Means with different superscripts differ significantly at 5% by DMRT.

Table 1d. Mean phytomass productivity of trees and shrubs in tonnes DM ha^-1 at Kongwa.

Species	Sites
	1	2	3
Euphorbia cuneata	1.58	1.70	-
Vittex spp.	1.63	-	-
Grewia spp.	0.60	-	-
Dirichletia pubescens	2.51	-	-
Blepharispermum zangubaricum	8.40	-	-
Acacia tortilis	-	2.56	-
Acacia mizera	-	8. 52	-
Cadaba kirkii	0.32	0.24	0.76

Animal Forage Preference (AFB)

Cattle at Kongwa spent 26% more time grazing on perennial grass species than on annual grasses during mid-grains (Table 2a). Least time (14%) was spent on herbaceous plants, and trees and shrubs. A similar trend was observed at the end of the rains (Table 2b). Cattle at West Kilimanjaro spent 66% more time grazing on perennial grasses than they did on annual grasses and herbaceous species (Tables 2c and 2d). However, observations made at Mabuki (Table 2e) indicated that cattle spent 16% more time grazing on perennial grasses than they did on herbaceous plants and annual grasses.

Table 2a. Animal preference (as percent time spent on annual and perennial grasses, and herbaceous plants and trees and shrubs) at Kongwa in January to March 1980, 1981 and 1982.

Plant classification	Sites
	1		2		3
	Cattle	Goats	Cattle	Goats	Cattle	Goats
Annual grasses	49	18	21	2	46	2
Perennial grasses	23	21	75	18	46	6
Herbaceous plants	4	21	0	28	4	18
Trees and shrubs	10	30	0	40	0	70

Table 2b. Animal preference (as percent time spent on annual and perennial grasses and herbaceous plants and trees and shrubs) at Kongwa in June to July 1980, 1981 and 1982.

Plant classification	Sites
	1		2		3
	Cattle	Goats	Cattle	Goats	Cattle	Goats
Annual grasses	31	8	33	0	29	9
Perennial grasses	36	15	55	29	46	30
Herbaceous plants	17	34	6	23	7	8
Trees and shrubs	5	15	5	48	14	57

Although cattle spent 17% more time grazing on perennial grasses in 1981 than they did in 1982 (Table 2e), there was no significant difference (P>0.05) in the way cattle grazed in 1981 and 1982. On the other hand, goats spent 50% of the time browsing on trees and shrubs at Kongwa during mid-rains, and 50% of the time at West Kilimanjaro at the end of the dry season. Least time was spent on grasses as shown in Tables 2a and 2b. Similar trends were observed at the end of the rains (Table 2b).

Table 2c. Animal preference (as percent time spent on annual and perennial grasses, and Herbaceous plants and trees and shrubs) at West Kilimanjaro in January to March 1980 and 1981.

Plant classification	Sites
	1		2		3
	Cattle	Goats	Cattle	Goats	Cattle	Goats
Annual grasses	1	1	35	4	8	0
Perennial grasses	99	88	60	26	86	42
Herbaceous plants	0	1	3	0	0	2
Trees and shrubs	0	3	0	40	1	39

Table 2d. Animal preferences (as percent time spent on annual and perennial grasses, Herbaceous plants and trees and shrubs) at West Kilimanjaro in October 1982.

Plant classification	Sites
	1		2		3
	Cattle	Goats	Cattle	Goats	Cattle	Goats
Annual grasses	21	4	40	4	17	8
Perennial grasses	71	18	55	18	70	18
Herbaceous plants	0	0	0	0	0	0
Trees and shrubs	1	53	5	51	12	44

Table 2e. Cattle preference (as percent time spent on annual and perennial grasses, Herbaceous plants, and trees and shrubs) at Mabuki in July to September.

Plant classification	Year		Mean
	1981	1982
Annual grasses	4	14	9
Perennial grasses	57	40	49
Herbaceous plants	35	11	23

Species utilisation: At the West Kilimanjaro location, plant species were 2.27 and 5.67 more utilised than Kongwa and Mabuki locations, respectively (Table 3). However, there was no significant difference (P>0.05) in the way species in the three locations were utilised. Urochloa trichopus had the highest (38.3%) utilisation of all the key species at the three locations. Pennisetum spp. and Chloris virgata followed closely. Bothriochloa insculpta was the least (28.05%) utilised species.

Table 3. Mean percent utilisation of key range plants (grasses) for the years 1980-1982.

Species	Locations
	Kongwa	West Kilimanjaro	Mabuki
Aristida adscensions	28.55	31.40	-
Bothriochloa insculpta	28.05	35.50	-
Cenchrus ciliaris	32.91	30.20	-
Cynodon dactylon	30.63	28.20	-
Chloris virgata	36.25	-	-
Urochloa trichopus	-	38.40	25.75
Pennisetum spp.	-	37.60	30.00

Chemical composition: Analysis of herbage materials, (Table 4a) shows that site 3 at Kongwa had the highest (14.72%) mean percent CP compared to that which was obtained at site 1 (10.75%) and site 2 (9.2%).

Table 4a. Chemical composition (percent, on DM basis) of forage plants in grazed paddocks at Kongwa.

Sites	1981			1982			Mean
	CP	Ca	P	CP	Ca	P	CP	Ca	P
1	9.28	0.49	0.10	12.22	0.78	0.15	10.75	0.64	0.13
2	13.40	1.42	0.13	5.13	0.34	0.08	9.27	0.88	0.11
3	16.65	1.27	0.20	12.78	0.55	0.12	14.72	0.91	0.16

The highest (11.65%) mean percent CP, at West Kilimanjaro (Table 4b) was obtained from site 1. This was closely followed by site 2 (9.97%) and site 3 (9.38%). There was no pattern in the way Ca and P occurred in the three sites at the three locations. Chi-square of independence indicated that year of grazing had no influence (P>0.05) on the chemical composition. However, sites influenced chemical composition at the two locations (P<0.05).

Table 4b. Chemical composition percent of DM of pasture plants on grazed paddock at West Kilimanjaro.

Sites	1981			1982			Mean
	CP	Ca	P	CP	Ca	P	CP	Ca	P
1	17.10	0.62	0.23	6.70	0.54	0.07	11.56	0.56	0.13
2	13.39	0.88	0.17	6.35	0.30	0.06	9.97	0.59	0.12
3	9.38	1.25	0.26	-	-	-	9.38	1.25	0.26

Environmental Factors

Kongwa location experienced high (30.87°C) but less variable (CV = 3.98%) mean temperatures when compared to that at West Kilimanjaro (26.21°C) and Mabuki (30.15°C). However, it was 23.23% and 27.09% more humid at west Kilimanjaro than it wars at Kongwa and Mabuki locations respectively. The amount of moisture lost through evaporation ranged from 3.0 to 25.0 mls. West Kilimanjaro received 67% and 16% more precipitation, than that received at Kongwa and Mabuki respectively (Table 5).

Table 5. A summary of environmental factors.

		Relative humidity	Maximum temperature	Evaporation	Rainfall	Wind velocity
		(%)	(°C)	(mls)	(mm)
Kongwa:	Range	36.00 to 66.00	28.50 to 32.60	3.00 to 6.00	8.60 to 138.80	-
	Mean	32.40	30.90	5.00	67.70	-
	CV	6.03	3.98	23.07	11.01	-
W/Kilimanjaro:	Range	68.00 to 88.00	22.30 to 36.10	4.00 to 24.70	4.70 to 239.00	5.70 to 44.40
	Mean	75.70	26.20	9.90	113.20	98.40
	CV	3.38	7.97	25.81	7.82	11.42
Mabuki:	Range	28.40 to 76.40	29.30 to 31.90	-	7.50 to 196.20	-
	Mean	48.50	30.15	-	78.80	-
	CV	7.87	4.11	-	9.63	-

Regression Analyses

Relationship between AFP and PP, CP, EF and PP and EF are summarised in Table 6.

The results show that T max, R and E were major factors in determining AFP at Kongwa (P>0.05). Phytomass productivity (PP), CP and percent RH were not the major factors determining AFP at that location. On the other hand, PP, CP, T max and R were major determinant factors of AFP (P>0.05), while percent RH and E were less important factors at West Kilimanjaro location.

Table 6. Relationship between AFP and PP, AFP and CP, AFP and EF and PP and EF at Kongwa and West Kilimanjaro locations.

Dependent	Independent	Regression equation	Coefficient of determination (r²)	Level of significant
AFP	PP	AFP = 21.97+0.55 PP	0.07	NS
AFP	CP	AFP = 21.32+0.20 CP	0.24	NS
AFP	%RH	AFP = 25.18-0.02 %RH	0.03	NS
AFP	Tmax.	AFP = 87.20+3.56 Tmax.	0.79	NS
AFP	R	AFP = 44.55-0.30 R	0.94	NS
AFP	E	AFP = 9.90+3.80 E	0.56	NS
PP	RH	PP = 7.66-0.07 %RH	0.98	NS
PP	Tmax.	PP = 33.09+1.35 Tmax.	0.48	NS
PP	R	PP = 8.31-0.08 R	0.26	NS
PP	E	PP = 6.65-1.00 E	0.18	NS
West Kilimanjaro
AFP	PP	AFP = 21.70+0.90 PP	0.77	NS
AFP	CP	AFP = 15.90+0.58 CP	0.77	NS
AFP	%RH	AFP = 15.91+0.08 %RH	0.14	NS
AFP	Tmax.	AFP = 30.72-0.31 Tmax.	0.52	NS
AFP	R	AFP = 20.93+0.02 R	0.98	NS
AFP	E	AFP = 25.47-0.40 E	0.16	NS
PP	RH	PP = 35.26-0.44 %RH	0.67	NS
PP	Tmax.	PP = 12.44+1.35 Tmax.	0.26	NS
PP	R	PP = 1.94+0.01 R	0. 08	NS
PP	E	PP = 14.68+1.99 E	0.66	NS

NS = non significant at P<0.05.

Discussion

Phytomass Productivity (PP)

At Kongwa unglazed paddocks produced 14% more mean PP in tonnes DM ha^-1 than grazed paddocks, in contrast to Mabuki and West Kilimanjaro locations (Tables la, b, and c). The relatively low mean PP produced on grazed paddocks at the two locations were probably due to less grazing effect. The high phytomass produced on ungrazed paddocks at Kongwa is comparable to that obtained by Pearson (1965) who reported that grazed areas produced about 1.78 tonnes DM^-1 ha annual top growth when compared to protected areas (1.99 tonnes DM ha^-1). The low mean PP obtained on ungrazed paddocks at Mabuki and West Kilimanjaro locations might be due to low moisture infiltration rates resulting from soil surface crusting. The high mean PP produced by A. mizera (8. 52 tonnes) and B. zangubaricum (8.40 tonnes) shown in Table 1d is probably due to the growth habit of the shrubs. A. mizera tends to branch about a metre from the surface of the soil and these branches usually terminate into productive branchlets within browsing height. B. zangubaricum tends to sprout profusely at the base, forming large clumps, with abundant forage within browsing height. On the other hand E. cuneata, Vittex spp., Grewia spp., D. pubescent, and C. kirkii are either single-stemmed, or branch high up, thereby contributing less to grazing.

Animal Forage Preference (AFP)

The high preference for annual and perennial grasses by cattle, and herbaceous plants and trees and shrubs by goats, observed at Kongwa, West Kilimanjaro and Mabuki (Table 2) confirm those of Staples et al. (1942), Edward (1948), Jordan (1957), Wilson (1957), and Lugenja and Kajuni (1979). In New South Wales, goats were observed to eat Acacia aneura and Cabtis spp., while cattle had a high preference for Calotis spp. and Chenopodium anidiphylum (Squires, 1982). The highest preference for perennial grasses exhibited by cattle (99%) on site 1 at West Kilimanjaro (Table 2c) was probably due to high percent CP content in the grazing (Table 4), which was mainly made up of Cynodon and Bothriochloa spp. This trend was, however, not observed on other sites and locations. In a study of cattle browsing behaviour in semi-arid area of Tanganyika, Payne (1963) observed that nutritive value and succulence determined the species that were browsed. The highest preference for perennial grasses exhibited by goats (88%) (Table 2c) was possibly due to the absence of trees and shrubs with forage within browsing height.

Utilisation

The highest mean percent utilisation (33.55%) observed at West Kilimanjaro is probably due to common use in practice at the location. The non-significant differences in the utilisation of key range plants at the three locations suggest that the experimental animals had probably low grazing action.

Environmental Factors (EF)

The high mean maximum temperature (30.9°C) observed at Kongwa location, relative to those at West Kilimanjaro and Mabuki (Table 5), suggest that the location experienced more adverse conditions for plant growth than either West Kilimanjaro or Mabuki. The high coefficient of variation (25.81%) observed at West Kilimanjaro suggest that the location was probably influenced by the mountain's effect. On the other hand, the high percent relative humidity observed at West Kilimanjaro was probably due to high precipitation coupled by low temperatures (Table 5). The high wind velocities (98.4 km/hour) were probably responsible for the high moisture (99.0 mls) lost through evaporation whereas, the high amount of precipitation received probably suggests that the experimental period fell in more than average rainfall years.

Regression Analyses

The variation in AFP associated with differences in PP and CP at West Kilimanjaro (r² = 0.77) is probably due to decrease in leaf availability as grazing progressed in the season. Between January and March pastures at West Kilimanjaro and Kongwa are usually mature and dry and although the animals graze selectively, the choice at West Kilimanjaro is limited by the abundancy of less palatable species of Pennisetum. These observations are similar to those by Chacon and Stobbs (1976) working with cattle in Australia. The authors showed that the number of bites and intake declined when leaf decreased. They attributed these observations to lack of desire by ruminants to harvest feed, to nitrogen or mineral deficiencies, or to bulk in the rumen thus preventing the development of an eating drive.

The variation in AFP associated with differences in T max (r² = 0.79) and rainfall R (r² = 0.94) for Kongwa and T max (r² = 0.52) and rainfall (r² = 0.98) for West Kilimanjaro, is probably due to favourable influence of high ambient temperatures and rainfall they have on PP (Table 6). However, these factors tend to decrease CP and subsequently digestibility (Deinum and van Soest, 1968). The low AFP might also be due to rumen pH depression associated with high ambient temperature and humidity (Mishra et al., 1970).

The high, but non-significant effect of T max on AFP (Tables 5 and 6) is probably due to inherent differences in the herds used in the study at Kongwa and West Kilimanjaro locations. The herd at Kongwa seems to have been more adapted to temperature conditions than that at West Kilimanjaro. There was no pattern in the way R and E affected AFP and PP at the two locations. However, percent relative humidity seem to have been negatively correlated with PP at these locations. The high but nonsignificant negative relationship between AFP and R at Kongwa probably suggests the detrimental effect of non-effective precipitation on grazing animals under semi-arid conditions. Non-effective precipitation encourages termite activity, resulting in low standing matter (Lugenja and Kajuni, 1979).

The high but non-significant positive relationship between AFP and E at Kongwa and West Kilimanjaro is probably due to conducive environmental conditions experienced as a result of evaporation. The two locations are characterised by high wind velocities which probably bring about cooling effect to grazing animals. On the other hand, the non-significant positive relationship between PP and E at the two locations, is in agreement with the established fact that DM production depends on the amount of moisture lost through evaporation and transpiration processes (Lane, 1976).

Conclusion

The results show that the mean PP in tonnes DM ha^-1 of the range increased from 4 to 15 tonnes DM ha^-1, when grasses and browse plant productivity is taken into consideration. The results also show that cattle grazed mainly on grasses while goats grazed mainly on herbaceous plants, trees and shrubs in this trial at Kongwa and West Kilimanjaro. The results further show that cattle and goats grazed grasses and browse plants to some degree, suggesting that there is a dietary overlap between the two animal species. These observations imply that for better and uniform range utilisation, cattle and goats should be mixed during grazing periods. In future intensive studies on stocking rate will be carried out for the different ecological zones in order to achieve optimum multiple range use, and identification of the major browse plants and establishing their roles in ruminant nutrition will be done.

Acknowledgements

The authors wish to thank Messrs Raphael Kamate and Mwinyishe Abdallah for collecting the data and Mr. S. Kaganda and Miss Rose Kutona for compiling the data. The International Foundation for Science (IFS) is acknowledged for the provision of funds to carry out this experiment. Finally our thanks are due to Dr. A.M. Macha, Director General, TALIRO, for permission to attend the PANESA Workshop and present the paper.

References

Akilimali, B.M. 1983. The present and potential role of beef production in meeting nutritional requirements of the nation. Proc. 10th Scientific Conference of Tanzania Society of Animal Production, Morogoro, Tanzania. pp. 44-65.

Anderson, G.D. and Naveh, Z. 1965. The influence of climate and soil on the productivity of certain promising grasses and legumes in Northern Tanzania. Afr. Soils 10:241-251.

Anon. 1983. Livestock Policy. Ministry of Livestock Development, Dar es Salaam. Government Printers, Tanzania.

Arave, C.W. and Albright, J.L. 1981. Cattle behaviour. J. Dairy Sci. 64:1318-1327.

Chacon, E. and Stobbs, T.H. 1976. Influence of progressive defoliation of a grass sward on the eating behaviour of cattle. Aust. J. Agric. Res. 27:709-727.

Chagula, A.M. 1983. The present and potential role of beef production in the traditional sector in meeting nutritional requirements of the nation. Proc. 10th Scientific Conference of Tanzania Society of Animal Production, Morogoro, Tanzania. pp. 72-74.

Deinum, B., van Es, A.J.H. and van Soest, P.J. 1968. Climate, nitrogen and grass. II. The influence of light intensity, temperature and nitrogen on in vitro digestibility of grass and the prediction of these effects from some chemical procedures. Neth. J. Agric. Sci. 16:217-223.

Edward, L.C. 1948. Some notes on the food of goats in a semiarid area. E. Afric. Agric. J. 13: 221-223.

Goodchild, A.V. 1983. A new approximation for saturation vapour pressure in humidity calculation. Proceedings of the sixth meeting of the National Agrometeorological Committee, Dar es Salaam, 23-24 November, 1983. Tanzania.

Hafez, E.S.E. and Bouissou, M.F. 1975. Behaviour of cattle. In: E.S.E. Hafez. (ed.), The behaviour of domestic animals. The Williams and Wilkins Co., Baltimore. pp. 203-211.

Hancock, J. 1954. Studies of grazing behaviour in relation to grassland management. 1. Variation in grazing habits of dairy cattle. J. Agric. Sci. 44:240-432.

Hathout, S.A. 1983. Soil Atlas of Tanzania. Dar es Salaam. Tanzania Publishing House, Map 7.

Johnstone-Wallace, D.B. and Kennedy, K. 1944. Grazing management practices and their relationship to the behaviour and grazing habits of cattle. J. Agric. Sci. 34:190-196.

Jordan, S.M. 1957. Reclamation and pasture management in the semiarid areas of Kitui District, Kenya. E. Afr. Agr. For. J. 23:84-88.

Knight, J. 1964. Some observations on the feeding habits of goats in the Baringo District of Kenya. E. Afr. Agric. For. J. 30:182-188.

Lammasson, T. and Jamson, C. 1942. Determining utilization of range grasses from height-weight tables. Mimeo, Department of Agriculture, U.S.A.

Lane, I.R. 1976. A consideration of factors determining potential stocking rate in Tanzania. Proceedings of the 3rd Annual Scientific Conference of the Tanzania Society of Animal Production 17-19 May, 1976, Morogoro, Tanzania.

Lugenja, M.M.S. and Kajuni, A.R. 1979. Range management in central Tanzania: Results of grazing management systems at Pasture Research Station, Kongwa. Proceedings of the Tanzania Society of Animal Production, Morogoro 6, 24-51.

Mishra, M., Martz, F.A., Stanley, R.W., H.D. Campbell, J.R. and Hilderbrand, E. 1970. Effect of diet and ambient temperature-humidity on ruminal pH, oxidation reduction potential, ammonia and lactic acid in lactating cows. J. Anim. Sci. 31(2):1023-1028.

Owen, M.A. 1964. A study of grassland problems on the upland soils of the Kongwa Plain, central Tanzania, with investigations into some pasture establishment techniques. M.Sc. thesis, University of Wales, U.K.

Payne, W.J.A. 1963. A brief study of cattle browsing behaviour in semi-arid area of Tanganyika. E. Afr. Agric. For. J. 29:131-133.

Pearson, L.C. 1965. Primary production in grazed and ungrazed desert communities of eastern Idaho. Ecol. 46:278-285.

Smith, C.A. 1959. Studies on the Northern Rhodesia Hyparrhenia Veld. I. The grazing behaviour of indigenous cattle grazed at light and heavy stocking rates. J. Agr. Sci. 52: 369-375.

Sokal, R. and Rohlf, F. 1969. Introduction to biostatistics. W.H. Freeman and Company, San Francisco. Chap. 12 and 13.

Squires, V.R. 1982. Dietary overlap between sheep, cattle and goats when grazing in common. J. Range Manage. 35:116-119.

Staples, R.R., Hornby, H.E. and Hornby, Robina, M. 1942. A study of the comparative effects of goats and cattle on a mixed grass-bush pasture. E. Afr. Agric. J. 8:62-70.

Steel, R.G.D. and Torrie, J.H. 1980. Principles and procedures of statistics - A biometrical approach. 2nd edition. McGraw-Hill Book Company, New York, USA.

Stricklin, W.R., Wilson, L.I. and Graves, H.B. 1976. Feeding behaviour of Angus and Charolais. Angus cows during summer and winter. J. Anim. Sci. 43:721-731.

Wilson, P.N. 1957. Studies of the browsing and reproductive behaviour of the East African dwarf goat. E. Afr. Agric. J. 23:138-147.