Livestock Research for Rural Development 18 (11) 2006 Guidelines to authors LRRD News

Citation of this paper

Effect of stocking rate on growth of lambs grazed on dry season tropical mixed pasture in Ethiopia

Tesfaye Lemma and Diriba Geleti*

Adami Tulu Agricultural Research Centre, PO Box 35, Ziway, Ethiopia
*Bako Agricultural Research Centre, P O Box 3, Bako, Ethiopia
tlemmag@yahoo.co.in

 

Abstract

The study was conducted to assess effects of stocking rate (SR) [20 animals/0.66 ha (HSR), 20 animals/0.97 ha (MSR) and 20 animals/1.98 ha (LSR)] on growth of lambs grazed on dry season rhodes grass (Chloris gayana)-siratro (Macroptilium atropurpureum) pasture in 2 successive years. A total of 60 Horro lambs were observed for 3 months in each of the years.

Total DM yield of pasture was significantly (P<0.01) higher for Year 1 (3.95 vs 3.34 t/ha). The pastures were heavily grass-dominant with the legume representing less than 10% of available dry matter overall. In both years, legume percentage in the pasture declined with time. Available dry matter yields declined during the study in both years but increased at the final sampling, following significant falls of rain. Weight gains of lambs were small (overall mean of 1.15kg/head) and tended to be indirectly related to stocking rate but differences were not significant (P>0.05). Year of stocking rate significantly (P<0.05) affected growth of the lambs.

In the years experienced, there was no benefit in lamb performance in reducing the stocking rate and strategic supplementation with concentrate would be required to obtain satisfactory growth rates of lambs.

Key words: Dry season, growth, lambs, mixed pasture, stocking rate


Introduction

In Ethiopia, sheep represent an important component of the farming system (Tembely 1997). Western Ethiopia (Wollega, Elebabur and part of western Shoa) accounts for about 17% of sheep production of the country (Gemeda et al 2002). However, sheep feeding follows traditional methods, which is based on grazing of native pasture (20 animals/ha) all year round. In the area, the quality and quantity of pasture varies from season to season. During the dry season (November-May), pasture condition is poor and quality of the native pastures deteriorates, which is reflected in the body condition of animals (Tesfaye et al 1999). One possible system for finishing of lambs on pasture is to keep them on native pastures from June to October, when satisfactory growth rates can be obtained (Galal et al 1991). They could then be transferred to a sown mixed rhodes grass (Chloris gayana)-siratro (Macroptilium atropurpureum) pasture, which has been allowed to stand over during the wet season (June - September). This study was conducted to determine the performance of lambs on this mixed pasture and to examine the effect of variation in stocking rate during the dry season on performance of the lambs.


Materials and methods

Location

The study area (90 07' N, 37o 05' E; elevation 1650m asl) has a mean annual rainfall of about 1270 mm, of which 80% falls from May-September. Mean annual temperature is 21O C. Soil type of the study area belongs to the Nitosol series, is reddish-brown in colour, and has a clay to sandy clay-loam texture with pH ranging from 5.3-6.

Pasture

A rhodes grass-siratro pasture (3.6 ha) was established at Bako one year before the study and divided into 3 paddocks (0.66ha, 0.97ha and 1.98ha). Prior to commencement of the study, the pasture was rotationally grazed and fertilised with di-ammonium phosphate (50 kg/ha) and urea (50 kg/ha). In the second year, only urea (50 kg/ha) was applied.

Dry matter (DM) yield, and percentage of leaf, stem, grass, legume, dead and green matter were measured at the start of grazing and then every 2 weeks after the grazing study commenced.

Animals

In each year, a total of 60 Horro lambs purchased from the local market were randomly assigned to 3 groups of 20 head, which were then randomly allocated to the 3 paddocks/stocking rates (SR). This gave SRs of 20 animals/0.66 ha (high SR), 20 animals/0.97 ha (medium SR) and 20 animals/1.98 ha (low SR). All necessary health care treatments were applied to the animals during the study period. Twelve-hour fasted body weight was taken fortnightly over the period of study.

Data analyses
Pasture parameters

Parameters measured to evaluate pasture condition (total DM yield, percentage of leaf, stem, grass, legume, dead and green matter) were subjected to analysis of variance using the MSTATIC computer software. Data for the 2 years were analysed separately. The model components included time of sampling, starting from the period before the start of grazing and every 2 weeks after the study started. Significant differences were separated using the LSD procedure and s.e. of means was computed based on error variance and number of observations per mean for the values compared.

Animal parameters

Initial weights (Iwt), final weights (Fwt), total gains (TG) and daily gains (DG) of animals were subjected to analysis of variance (ANOVA) using general linear models of Statistical Analysis System (SAS), Version 8.2.


Results and discussion

Pasture condition

Total DM yield and percentage of grass, legume and plant fractions (leaf and stem, green and dead matter) averaged over the 5 samplings for each of the 2 years are given in Table 1.


Table 1.  Total DM yield (t/ha) and percent composition of the different components and plant fractions for the rhodes grass-siratro mixture across the different stocking rates

Year

Traits

Stocking rate

s.e.

High

Medium

Low

1

Total DM1

4.43a2

3.75b

3.67b

0.14

 

% grass

92.45

92.75

96.02

1.78

 

% legume

7.56

7.25

3.98

1.78

 

% leaf

57.19

56.79

58.09

1.68

 

% stem

42.81

43.21

41.91

1.68

 

% green

64.15

65.78

62.53

5.09

 

% dead

35.78

33.62

37.47

5.09

2

Total DM

2.45

3.47

4.09

0.44

 

% grass

94.46

91.47

94.91

0.45

 

% legume

7.17

8.53

5.08

0.05

 

% leaf

46.54

33.29

50.83

0.39

 

% stem

53.46

49.42

49.14

0.21

 

% green

35.94b

42.45ab

46.24a

0.17

 

% dead

64.06

57.55

53.76

0.35

1Each value in the table is an average of 5 samples collected across the study period in each year

2 Values within rows followed by different letters differ significantly (P<0.01)


Total DM yield was significantly (P<0.01) affected by SR for Year 1, being higher for HSR (4.43 t/ha) than for MSR and LSR (3.75 and 3.67 t/ha, respectively). There were virtually no differences between SRs in terms of pasture components (P>0.05). In both years, pasture DM was predominantly grass for all SRs (91.5-96%), while the legume component was low in both Year 1 (4-7.5%) and Year 2 (5-8.5%). Percentage leaf and % green were higher in Year 1 than in Year 2. In Year 2, % green was affected by SR (P<0.05), increasing from 35.9% for the HSR to 46.2% for the LSR.

Dynamics of total DM yield and other yield components during the grazing study are given in Table 2.


Table 2.   Change in total forage DM yield (t/ha) and other pasture components across the study period

Year

 

Measurement period2

P level

s.e.

Traits1

1

2

3

4

5

1

Total DM

5.06a3

3.57b

2.97b

3.16b

4.98ab

**

0.18

 

% grass

89.27

92.6

93.9

95.92

97.00

 

2.29

 

% legume

16.36a

11.56b

3.87b

4.28b

0.20b

**

0.06

 

% leaf

59.00ab

63.50a

56.89ab

54.63b

52.77b

*

2.16

 

% stem

41.00ab

36.50b

43.11ab

45.37a

47.23a

*

2.16

 

% green

67.66

70.97

65.21

52.25

64.67

 

6.58

 

% dead

32.23

28.03

34.79

47.75

35.33

 

6.58

2

Total DM

4.42ab

2.14bc

2.51bc

1.24c

6.39a

**

0.57

 

% grass

83.64ab

91.58b

96.13b

95.63b

99.78a

**

0.58

 

% legume

10.73

7.40

6.10

4.07

3.00

 

2.29

 

% leaf

55.20

47.73

48.15

44.46

38.54

 

0.51

 

% stem

44.79b

52.27b

51.85b

55.54b

61.46a

**

0.27

 

% green

55.04a

39.47b

36.58b

36.62b

45.08a

**

0.22

 

% dead

44.96ab

60.53b

63.42b

63.78b

54.92a

**

0.46

1Each value in the table is averaged over 3 stocking rates.

21 = before starting grazing; 2-5 = 2, 4, 6 and 8 weeks after grazing started.

3 Values within rows followed by different letters are significantly different


During Year 1, total DM yield, percentage leaf and stem were significantly influenced by time of measurement across the study period. For both years, trends were irregular and this could be attributed to fluctuations in weather parameters during the study period particularly moisture availability. Total DM yield was high for the sample taken just before the start of grazing in Year 1 (5.06 t/ha). In both years, the pastures remained heavily grass-dominant, while the legume component declined with time. During the second year, all morphological traits were influenced by time of sampling except percentage leaf and percentage legume. However, for most of the traits studied, there were no consistent trends across the study period.

Stocking rate and lamb growth

The least squares mean values for Iwt, Fwt, TG and DG are given in Table 3.


Table 3.   LSM s.e. of growth parameters (kg) of lambs as affected by different stocking rates and years

Traits

Stocking rates1

Years

H

M

L

1

2

IWt

19.0 0.16

19.0 0.16

19.1 0.16

19.0 0.15

19.0 0.15

Fwt

19.7 0.30

19.9 0.30

20.8 0.30

20.3 0.28a2

20.0 0.29b

TG

0.7 0.31

0.9 0.31

1.7 0.31

1.3 0.28a

1.0 0.29b

DG

0.010.003

0.01 .003

0.02 0.003

0.03 0.00a

0.01 0.00b

1H = 20 sheep/0.66 ha; M = 20 sheep/0.97 ha; L = 20 sheep/1.98ha.

2For between-year comparison, values within rows followed by different letters are different (P<0.05)


Growth rates of lambs in both years were low, although they were higher (P<0.05) in Year 1. This is indicative of the poor quality of the pasture grazed by the animals, particularly the grass component, during the study period. Personal observation during the study period indicated that the grass was over-mature and during the early phases of grazing animals selected the legume component of the pasture due to the lower palatability of the grass. The superior performance in Year 1 could in part be due to better availability of legume in the pasture in the first year. There was no effect of stocking rate on growth rates of lambs in either year. Similar findings were obtained from another site by Galal et al (1991), which indicated that, without supplementation of grain and oil seed cake, varying SR during the dry season did not improve body condition of sheep. Dry season grazing could not improve cattle body weight performance (Tesfaye et al 1999) at the same site. Legume proportion in the pasture was low and the dead biomass was high. These also contributed to low performance of the animals.


Conclusion
s


References

Galal E S E, Taylor M S, Tadesse T and Yohanes G 1991 Dry season grazing of lambs on cultivated pasture and their subsequent finishing performance. Ethiopian Journal of Agriculture Science 3 (1), 24-29.

Gemeda D, Birhanu S, Diriba G and Yosef K 2002 Recommended research results for improving crop, livestock and resources productivity in Western Oromia. Users manual, OARI, Bako Research Center, Oromia, Ethiopia, p. 12.

Tembely S 1997 Small ruminants production in Ethiopia; prospect of improving productivity. In Proceedings of fifth National Conference of Ethiopian Society of Animal Production held on 15-17 May 1997. Addis Ababa, Ethiopia, p.35.

Tesfaye L, Geberegziabher G, Gizaw K and Mulugeta K 1999 Body weight changes of male cattle grazed on natural pasture. In Proceedings of 7th National Conference of Ethiopian Society of Animal Production held on 15-17 May 1999. Addis Ababa, Ethiopia, p. 217-221.


Received 25 July 2006; Accepted 13 September 2006; Published 1 November 2006

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