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Compensatory growth in Horro lambs of Ethiopia

Solomon Abegaz, Demmissie Tiyo and Lemma Gizachew

Bako Agricultural Research Center
Institute of Agricultural Research
P. O. Box 2003, Addis Ababa, Ethiopia

Abstract
Introduction
Materials and methods
Results
Discussion
Conclusion
References

Abstract

Compensatory growth response to liberal concentrate supplement of Horro lambs previously kept on poor natural pasture in the dry season was studied. Partial feed conversion efficiency (FCE) and variation in carcass characteristics were also studied. The total experimental period consisted of three phases of 63 (Phase 1), 49 (Phase 2), and 74 (Phase 3) days. There were four groups (1 to 4) of 10 lambs each. Group 4 was the unsupplemented control while the other three groups received high levels of supplement in the third phase after each of them were kept unsupplemented either in both of phases 1 and 2 (Group 3) or in Phase 1 alone (Group 2) or in neither of the two phases (Group 1). In Phase 1, Group 1 lambs gained 1.5 kg live weight while lambs in the other groups lost 2.0 kg. In phases 2 and 3, lambs in groups 2 and 3, respectively, showed compensatory growth. Liveweight differences between groups 1, 2 and 3 observed in previous phases became non-significant in the last phase. Partial FCE was higher in lambs which showed compensatory growth than in continuously growing lambs, particularly when liveweight differences between them became non-significant. All carcass measurement showed highly significant (P<0.01) correlation with live weight (coefficients ranging from 0.66 to 0.99). The study showed that under conditions where dry season supplementary feeding is impractical, Horro lambs can be maintained on grazing alone and subsequently fed supplements. This enables the lambs to benefit from compensatory growth and better partial FCE compared to lambs that are allowed to grow continuously under supplementation.

Introduction

Animals subjected to a period of undernutrition often exhibit very high growth during subsequent realimentation (McManus et al 1972; Thornton et al 1979). This phenomenon, known as compensatory growth, has very important implications in countries that depend largely on grazing to support animal production (Drew and Reid 1975).

In the Ethiopian highlands, sheep are raised on natural pasture and crop residues. There is annual fluctuation in the quality and quantity of these feed resources. Galal et al (1981) suggested lambing during the month of May (start of the main rainy season) as one possible lamb production system. This would allow lambs to be grown and weaned, and kept until the age of five months on good pasture. But after this age they face the poor pasture conditions of the dry season.

The current experiment was designed to study compensatory growth in weaned lambs which were maintained unsupplemented on poor natural pasture during the dry season for various periods, and then fed liberal concentrate supplement to finish them.

Materials and methods

Location

The study was carried out at the Bako Agricultural Research Center (09°6'N, 37°09'E, and 1650 m asl) of the Institute of Agricultural Research, Ethiopia. The Center receives a mean annual rainfall of about 1170 mm, out of which 80% falls in the months of May to September, and has mean maximum and minimum temperatures of 28°C and 13°C, respectively.

Animals and experimental treatment

Lambs used in this study belong to the Horro breed of sheep (Galal 1983). Forty weaned lambs of both sexes with mean live weight and age of 17.8 kg (SD=3.16) and 132 days (SD=11.6), respectively, were randomly assigned to 4 treatment groups (1 to 4). The whole experimental period (2 December 1988 to 6 June 1989) was divided into three phases of 63 (Phase 1),49 (Phase 2), and 74 days (Phase 3). Lambs in Group 1 were supplemented throughout the experimental period, those in Group 2 were supplemented in phases 2 and 3, and those in Group 3 were supplemented in Phase 3 only. Lambs in Group 4 received no supplement throughout the experiment.

Feed and management

The amount of concentrate supplement fed in the first two phases was 150 g/head per day while in the third phase it was 333 g/head per day. The supplement was estimated to contain 21.5% crude protein (CP) and 3.05 Mcal metabolisable energy (ME) per kilogram of dry matter (DM).

All lambs were kept as one flock each day of the experiment and grazed from 0830 to 1700 hours on poor natural pasture, which had an estimated yield of 4.8 t/ha with a DM content of 60% at the beginning of the experiment. Each evening the animals were separated into their respective treatment groups.

Carcass measurement

Sixteen male lambs (3, 5, 4, and 4 from groups 1, 2, 3 and 4, respectively) were selected at the end of the experiment for the measurement of carcass and non-carcass parts, weights, and the determination of dressing percentage. Shrunk live weight of the lambs was taken just before slaughter after they were deprived of water and feed for about 36 hours.

Statistical analysis

Analytical procedure for a completely randomised design was used to analyse between treatment differences in live weight and weight gain. Means were separated using the least significant differences (LSD) procedure (Gomez and Gomez 1984). Relationship between weight measurements of the various carcass parts and live weight was determined by regression procedures.

Partial feed conversion efficiency (FCE) of supplemented lambs was calculated from the total amount of supplement offered and liveweight gain obtained above those of unsupplemented lambs.

Results

Five lambs (two from Group 1 and one from each of the remaining groups) died from unknown causes before the end of the experiment and were excluded from the analysis.

Table 1. Liveweight changes and daily weight gains during each phase and the whole experimental period (mean±SE).



Treatment group

Overall

1

2

3

4

Number of lambs

35

8

9

9

9

Initial weight, kg

17.8±0.53

17.9±1.51a

17.9±0.96a

17.9±1.04a

17.4±0.95a

WEP1, kg

16.6±0.52

19.4±1.12a

15.50.96b

16.20.83b

15.5±0.80b

WEP2, kg

18.5±0.56

21.7±1.11a

19.4±0.99ab

17.0±0.78bc

16.4±0.58c

WEP3, kg

26.9±0.76

30.4±1.10a

28.5±1.11a

27.8±0.78a

21.3±0.81b

GP1, kg

- 1.2±0.31

1.5±0.43a

- 2.4±0.45b

- 1.7±0.48b

- 1.9±0.36b

GP2, kg

1.9±0.23

2.3±0.19b

3.9±0.28a

0.8±0.20c

0.9±0.21c

GP3, kg

8.4±0.45

8.7±0.46b

9.1±0.67b

10.80.67a

4.9±0.25c

Total gain, kg

9.1±0.61

12.5±0.59a

10.6±0.60b

9.8±0.50b

3.9±0.26c

First SS days of P3,kg

7.1±0.41

7.1±0.52b

7.7±0.72b

94±0.55a

4.3±0.30c

Last 19 days of P3, kg

1.3±0.13

1.6±0.18a

1.4±0.26a

1.4±0.27a

0.6±30.23b

WEP1, 2, 3 = weight at the end of phases 1, 2, 3.
GP1, 2, 3 = weight gain in phases 1, 2, 3.
Row means with different superscripts are significantly different (p<0.05).

Table 1 shows that in Phase 1 lambs in Group 1 gained an average of 1.5 kg live weight while lambs in groups 2, 3 and 4 lost an average of 2.0 kg. Upon supplementation in Phase 2, lambs in Group 2 gained significantly (P<0.05) more weight (3.9 kg) than lambs in group 1 (2.3 kg) which received supplementation from the start (group 1,2.3 kg) or unsupplemented lambs in groups 3 (0.8 kg) and 4 (0.9 kg). Group 3 lambs gained significantly (P<0.05) more weight (10.8 kg) than all the lambs in remaining groups (8.7, 9.1, and 4.9 kg for groups 1, 2 and 4, respectively) in the third phase. After the start of supplementary feeding live weight of previously unsupplemented lambs approached live weight attained by lambs receiving concentrate supplement from the start (Figure 1). However, the difference in gain between groups 1, 2 and 3 was found to be non-significant after the first 55 days of Phase 3.

Table 2 shows the response in gain due to supplementation and partial FCE of lambs given supplementary feed. For the whole experimental period, lambs in Group 3 had a better partial FCE (4.18) than lambs in groups 1 (4.82) and 2 (4.78). The observed superiority in conversion efficiency, however, declined as liveweight differences reached nonsignificant levels (last 19 days of Phase 3).

Table 3 shows mean weight and carcass characteristics of the treatment groups. All weights have shown a tendency to increase with increase in live weight. Pooled regression of shrunk live and carcass weights, dressing percentage and weight of other parts on live weight was found to be highly significant (P<0.01) with correlation coefficients ranging from O.66 to 0.99. Fat deposition as measured by omental and kidney fat (weighed together), and tail weight were also highly correlated with live weight (T=0.8 and r=0.7, respectively).

Table 2. Gain response to supplementation, quantity of supplementary feed offered and partial feed conversion efficiency.



Treatment group

1

2

3

Mean gain over unsupplemented


Phase 1a

3.50

-

-


Phase 2b

1.45

3.05

-


Phase 3c

3.80

4.20

5.90


Total

8.60

6.70

5.90


First 55 days of Phase 3

2.80

3.40

5.10


Last 19 days of Phase 3

1.00

0.80

0.90

Total supplementary feed given


Phase 1

9.45

-

-


Phase 2

7.35

7.35

-


Phase 3

24.67

24.6

24.67


Total

41.47

32.02

24.67


First 55 days of Phase 3

18.33

18.33

18.33


Last 19 days of Phase 3

6.33

6.33

6.33

Partial FCE


Phase 1

2.70

-

-


Phase 2

5.07

2.41

-


Phase 3

6.49

5.87

4.18


Total

4.82

4.78

4.18


First 55 days of Phase 3 FCE

6.55

5.39

3.59


Last 19 days of Phase 3

6.33

7.92

7.03

a = gain over mean gain of groups 2, 3 and 4.
b = gain over mean of groups 3 and 4.
c = gain over mean gain of group 4.

Figure 1. Growth curves of lambs in the different groups and rainfall in the respective period.

Discussion

Lambs given no supplementary feed and grazed on natural pasture in the dry season lost weight while the supplemented lambs gained weight. This shows that under Bako conditions, natural pasture alone cannot maintain weight or support growth of lambs in the dry season. Galal et al (1981) made a similar observation for the same sheep breed kept on cultivated pasture in the dry season when the stocking rate was high.

Upon supplementation, previously unsupplemented lambs which had lost weight gained more than the continuously supplemented lambs. Similar compensatory responses have been reported for Yankasa sheep (Lakpini et al 1982) and for Black Head Persian and Massai lambs (Massae and Mtenga 1992). On the contrary, Galal et al (1981) found no difference in growth rate of previously unsupplemented Horro lambs and continuously supplemented lambs during a final phase of ad libitum indoor feeding of a ration composed of 75% concentrate and 25% hay. However, in the study of Galal et al (1981), the ration type and the feeding regime could have resulted in differential adaptation and intake level between the two groups.

Upon supplementary feeding, the partial FCE of previously unsupplemented lambs was higher than the partial FCE of lambs supplemented continuously. Ørskov et al (1976) had reported similar improvements in FCE in sheep. Massae and Mtenga (1992) had also found a non-significant but superior trend in FCE of realimented lambs compared to those fed high level supplement continuously. Graham and Searle (1975), however, found no difference between FCE of realimented and continuously fed sheep. Difference in composition of gain between realimented and continuously fed animals has been reported (McMannus et al 1972; Drew and Read 1975) and as composition may vary with age and weight, differences in these factors may explain the discrepancy in the literature.

All carcass measurement and dressing percentage values have shown a tendency to increase with weight and correlation coefficients pooled over all the treatments were very high. The strong correlation between the various carcass measurement values and live weight suggests that within the growth stage of lambs in this study, similar live weights achieved either by compensatory or continuous growth can yield a carcass with similar composition and proportion of parts. Previously, Galal et al (1981) reported significant differences between realimented and continuously fed lambs in carcass weight and dressing percentage and fat deposition measurements, but liveweight differences were also significant.

Table 3. Carcass measurement values and dressing percentage and correlations with live weight.


Measurement


Overall

Treatment group

1

2

3

4

r2

Live weight, kg

27.7

31.7

28.1

29.5

22.4


Slaughter weight, kg

25.8

29.8

26.5

27.2

20.8

0.99**

Carcass weight, kg

11.9

14.3

12.2

2.6

9.2

0.98**

Dressing out, %

42.8

44.9

43.1

42.7

40.9

0.66**

Tail weight, kg

0.7

0.8

0.8

0.7

0.5

0.70**

Skin weight, kg

2.6

3.2

2.8

2.7

2.0

0.94**

Viscera full, kg

5.6

5.8

5.9

6.1

4.7

0.78**

Legs, kg

0.57

0.62

0.58

0.61

0.47

0.86**

Internal organs1, kg

1.24

1.32

1.25

1.32

1.10

0.92**

Omental and kidney fat, kg

0.06

0.08

0.07

0.06

0.04

0.80**

Head, kg

1.90

2.20

1.80

2.00

1.60

0.81**

1 = liver, lung and trachea, heart, kidney (fat-free), and spleen weighed together.
2 = correlation of carcass measurements with live weight.
** = Significant at P<0.01 level.

Conclusion

Horro lambs grazing on poor natural pasture during the dry season and given no supplementary feed were found to lose weight. Upon subsequent supplementary feeding the lambs showed compensatory growth and caught up with live weights of continuously supplemented lambs. There was no serious effect of compensatory growth on carcass characteristics, while it improved partial FCE. The results of this study suggest that in the dry season unsupplemented lambs grazing on natural pasture can tolerate weight losses of at least 10% with no long lasting effect, and upon subsequent supplementation they can experience compensatory gain with high FCE.

References

Drew K.R. and Reid J.T. 1975. Compensatory growth in immature sheep. 1. The effects of weight loss and realimentation on the whole body composition. Journal of Agricultural Science (Cambridge) 85:193-204.

Galal E.S.E. 1983. Sheep Germplasm in Ethiopia. Animal Genetic Information 1/83. FAO (Food and Agriculture Organization of the United Nations), Rome. Italy. pp. 4-12.

Galal E.S.E., Taylor M.S., Tadesse T.T. and Yohanes G. 1981. Dry season grazing of lambs on cultivated pasture and their subsequent finishing performance. Ethiopian Journal of Agricultural Sciences 3:15-30.

Gomez A.K. and Gomez A.A. 1984. Statistical Procedures for Agricultural Research. 2nd edition. John Wiley and Sons, New York, USA. 680 pp.

Graham N.M.C. and Searle T.W. 1975. Studies of weaner sheep during and after a period of weight stasis. 1. Energy and nitrogen utilization. Australian Journal of Agricultural Research 26:343-353.

Lakpini C.A.M., Adu I.F., Buvanedram V. and Umunna N.N. 1982. Compensatory growth in Yankasa lambs. 1. Feed intake, liveweight gain, and efficiency of feed conversion. Journal of Animal Production Research 2:69-80.

Massae E.E. and Mtenga L.A. 1992. Effects of plane of nutrition on growth performance and carcass composition on lambs in Tanzania. In: Rey B., Lebbie S.H.B. and Reynolds L. (eds), Small Ruminant Research and Development in Africa. Proceedings of the First Biennial Conference of the African Small Ruminant Research Network, ILRAD, Nairobi, Kenya, 10-14 December 1990. ILCA (International Livestock Centre for Africa), Nairobi, Kenya. pp. 401-415.

McMannus A.R., Reid J.T. and Donaldson L.E. 1972. Studies of compensatory growth in sheep. Journal of Agricultural Science (Cambridge) 79:1-12.

Ørskov E.R., McDonald I., Grubs D.A. and Pennie K. 1976. The nutrition of the early weaned lambs. IV. Effects on growth rate, food utilization and body composition of changes from a low to a high protein diet. Journal of Agricultural Science (Cambridge) 86:411-423.

Thornton R.F., Hood R.L., Jones P.N. and Re V.M. 1979. Compensatory growth in sheep. Australian Journal of Agricultural Research 30:135-151.


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