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Genetic analysis of the reproductive performance of West African Dwarf goats in the humid tropics

I.K. Odubote

Department of Animal Science, Faculty of Agriculture
Obafemi Awolowo University, Ile-Ife, Nigeria

Abstract
Introduction
Materials and methods
Results and discussion
Conclusions
References

Abstract

A total of 587 kidding records of the West African Dwarf (WAD) goats over a period of 10 years (1982-91) were used for this study. The mean kidding interval and litter size at birth were 275.68±6.08 days and 1.79±0.05 kids, respectively. Effect of parity, season and year of birth were significant (P<0.05) for kidding interval. Parity also had significant effect (P<0.05) on litter size at birth. Heritability estimates of 0.35±0.05 and 0.32±0.07 were obtained from sire and sire-dam group, respectively, for litter size at birth. The heritability estimate for kidding interval was 0.03±0.01 for the sire-dam group. Repeatability estimates of 0.38±0.05 and 0.33±0.03 were obtained for litter size at birth from the dam and sire-dam groups, respectively, while 0.06±0.04 and 0.04±0.02 were obtained for kidding interval from dam and sire dam groups, respectively. Selection for multiple birth is likely to result in larger litter size and culling of does for long kidding interval should be based on more than two records.

Introduction

Genetic improvement of the small ruminants is imperative considering the improvement in productivity that has been achieved by changes in management practices. Van Vlaenderen (1989), Adu et al (1988) and Odubote (1992), among other workers, have reported on these improved performances. In order to optimise gains from environmental influences, genetic parameters and attributes of the animals for economic traits should be appraised regularly so as to enable breeders to determine the breeding tools of choice.

To date only limited published reports (Odubote 1992) have estimated genetic properties for metric traits in goat populations reared in tropical and subtropical environments. Specifically, heritability and repeatability estimates are lacking for the Nigerian breeds of goat except for the earlier reports of Odubote and Akinokun (1992) on the West African Dwarf (WAD) goat and Adu et al (1979) on the Red Sokoto goat. Due to the availability of more records, it became necessary to reappraise the genetic attributes of the WAD goat population.

Materials and methods

Records of 587 kiddings from WAD goat matings of 11 sires to 163 does between 1982 and 1991 were used for this study. The goats were kept at the Goat Unit of the Obafemi Awolowo University Teaching and Research Farm, Ile-Ife, in the humid tropics of Nigeria. The rainfall pattern is bimodal averaging 1205 mm per year.

The history and management of the flock have been reported by Odubote (1992). The goats were kept under zero grazing management and stall fed twice daily on a diet consisting of Panicum maximum, Leucaena leucocephala and Gliricidia sepium. Concentrates were also fed when available. The health care package included dipping, deworming and annual vaccination against peste des petite ruminants (PPR). Animals were treated for pneumonia and diarrhoea when infection occurred. Mating was controlled and inbreeding was avoided in the herd.

Statistical analysis

The data were analysed by the General Linear Model (SAS 1986) using mixed models to determine the effects of the nth doe of the mth parity mated to the 1th sire producing kth litter size in the jth season of the ith year on litter size at birth and kidding interval.

Significant differences between means were determined using Duncan's New Multiple Range Test (Steel and Torrie 1980). The data were adjusted for significant environmental effects before estimating the genetic variance components. The variance components were calculated using sire, dam and combined sire-dam groups according to the method of Becker (1968).

Formulae:

From sire group:

From dam group:

From sire-dam group:

Standard errors for the estimates were computed as described by Falconer (1981).

Results and discussion

The least squares means for kidding interval and litter size at birth are provided in Table 1. The partitioning of the variance components and estimates of heritability and repeatability are shown in Table 2.

Kidding interval

The kidding interval ranged from 187 to 478 days. Mean kidding interval was considerably high. This may be probably due to the transfer of does for other experimental purposes and the control of mating schedule. High kidding interval has been associated with controlled mating and confinement (Wilson et al 1989). The results suggest that kidding interval is highly influenced by management restrictions.

Some cases of repeat breeders and abortions were observed in the flock. There was a significant decrease in the kidding interval from the fifth parity. The trend of the effect of type of birth and year of birth on kidding interval is not clear. There was, however, a decrease in the kidding interval from 1985 onwards. This may be traced to changes in management practices such as culling of does for poor productivity.

The repeatability estimates of 0.06±0.04 and 0.04±0.02 obtained for kidding interval are low but not significantly different from those reported earlier by Odubote and Akinokun (1992). Also there was no difference in the estimates using the two approaches of computation. The estimate of heritability could not be done because of the negative sire component of variance.

Litter size at birth

Contrary to an earlier report on the same flock (Odubote et al 1993), quadruplets were observed in the present study. The birth ratio was 37:53:9:1 for singles, twins, triplets and quadruplets, respectively. Mean litter size compared favourably with the earlier reports for the WAD breed (Adu et al 1988; Odubote and Akinokun 1992).

Table 1. Least squares means for kidding interval and litter size at birth in West African Dwarf goats.


Variable

Kidding interval (days)

Litter size at birth (no.)

N

Mean

SE

N

Mean

SE

Overall mean

316

275.68

6.08

587

1.79

0.05

Season of birth


Dry

165

260.30a

5.74

371

1.84a

0.04

Rain

151

291.06b

8.13

216

1.73a

0.06

Year of birth


1982

12

276.31b

6.11

28

1.65ab

0.13

1983

23

364.45d

10.23

50

1.70ab

0.05

1984

21

317.26c

9.68

41

1.68ab

0.02

1985

47

264.14b

4.70

93

1.59a

0.06

1986

62

260.00b

5.45

112

1.54a

0.04

1987

44

238.94a

8.03

91

1.62a

0.07

1988

15

266.33b

7.04

32

1.67ab

0.03

1989

31

253.32b

4.93

39

1.89c

0.05

1990

32

273.13b

6.80

49

1.83c

0.03

1991

29

278.55b

5.46

52

1.84c

0.07

Parity


1

-

146

-

1.43a

0.02


2

116

282.14ab

6.48

148

1.59ab

0.04

3

69

304.36c

8.41

93

1.72ab

0.05

4

53

288.69c

8.32

77

1.74bc

0.03

5

30

261.04ab

5.06

45

1.85bc

0.07

6

21

259.78ab

6.81

35

1.90bc

0.06

7

15

249.68a

7.84

23

2.07de

0.09

8

8

248.01a

5.49

14

2.02cde

0.14

9

4

252.04a

4.82

6

1.98cd

0.13

Litter size at birth


1

119

261.32a

5.64




2

166

286.45ab

3.07




3

27

265.21a

8.45




4

4

304.16b

9.63




N refers to the number of observations.

Means within each class and in each column with different superscripts differ significantly (P<0.05).

SE = standard error of the mean.

Table 2. Partitioning of variance components and estimates of heritability (h2) and repeatability ® of litter size at birth and kidding intervals in WAD goats.


Traits

Variance components

Sire

Doe

Remainder

r ± SE

h2 ± SE

(a)

From sire group


Litter size at birth

0.06*

N/A

0.65

N/A

0.35±0.05


Kidding interval

-12.02

N/A

23.64

N/A

b

(b)

From dam group


Litter size at birth

N/A

0.43**

0.70

0.38±0.05

N/A


Kidding interval

N/A

7.93*

124.24

0.06±0.04

N/A

(c)

From sire and dam group


Litter size at birth

0.05*

0.20**

0.37

0.33±0.03

0.32±0.07


Kidding interval

0.61

3.03

85.62

0.04±0.02

0.03±0.01

N/A = not applicable;
b = negative variance component estimate set to zero.
* P<0.05;
** P<0.01.

Litter size at birth tended to improve over the years and with parity (P<0.05). This may be due to the efficiency of reproduction as the doe matures (Levasseur and Thibault 1980). Secondly, since 1987, the management system permitted the culling of does with small litters which may partially account for the significant increase in litter size.

The heritability estimates of 0.35±0.05 and 0.32±0.07 obtained for litter size at birth were higher than the earlier estimate of 0.28 (Odubote 1992) for the same flock. The estimates were also higher than estimates reported (Adu et al 1979), Ricordeau (1981) and Wilson (1989) for other breeds of goats. The extent to which observed differences in a trait are heritable is indicative of the magnitude of expected response to selection. Thus, selection would lead to higher litter size at birth. However, this calls for caution (for the WAD goat) as this may lead to a higher incidence of triplets and quadruplets. The benefit of the incidence of triplets and quadruplets should be evaluated in terms of survival of the kids, dystocia in the does, effect on kidding interval and body weight of the kid at birth. In the present study, no problems were observed to be associated with multiple birth in the flock.

The repeatability estimates obtained for litter size were 0.38±0.05 and 0.33±0.03. As a result of the moderate repeatability estimates a single record of a doe can be taken as a fair assessment of its potential. Systematic culling of unproductive animals may be the most important management practice to increase the litter size at birth. Also breeding males from parents with poor fertility should be avoided since effect of stud buck was observed to be significant (P<0.05). Estimates of genetic parameters for extensively managed goat population are still required.

Conclusions

Efforts should be made to reduce the kidding interval by changes in management restrictions especially re-breeding interval. Not much reliance can be placed on two subsequent kidding records for culling purposes. More records should thus be collected before deciding on culling levels for unproductive does.

References

Adu I.F., Buvanendran V. and Lakpini C.A.M. 1979. The reproductive performance of Red Sokoto goats in Nigeria. Journal of Agricultural Science (Cambridge) 93:563-566.

Adu I.F., Odeniyi A.O. and Taiwo B.B.A. 1988. Production characteristics of a herd of West African Dwarf goats at Ubiaja, Bendel State of Nigeria. In: Smith O.B. and Bosman H.G. (eds), Goat Production in the Humid Tropics. Proceedings of a workshop at the University of Ife, Ile-Ife, 20-24 July 1987. Pudoc Scientific Publishers, Wageningen, The Netherlands. pp. 140-144.

Becker W.A. 1968. Manual of Procedures in Quantitative Genetics. 2nd edition. Academic Enterprises, Pullman, Washington, USA. 62 pp.

Falconer D.S. 1981. Introduction to Quantitative Genetics. 2nd edition. Longman, London, UK. 340 pp.

Levasseur M. and Thibault C. 1980. Reproductive life cycles. In: Hafez E.S.E. (ed), Reproduction in Farm Animals. 4th edition. Lea and Febiger, Philadelphia, USA. pp. 130-149.

Odubote I.K. 1992. Genetic and Non-Genetic Sources of Variation in Litter Size, Kidding Interval and Body Weight at Various Ages in West African Dwarf Goats. PhD thesis, Obafemi Awolowo University, Ile-Ife, Nigeria. 161 pp.

Odubote I.K. and Akinokun J.O. 1992. Estimates of genetic parameters for economic traits in West African Dwarf Goat. Nigerian Journal of Animal Production 19:114-119.

Odubote I.K., Akinokun J.O. and Ademosun A.A. 1993. Production characteristics of West African Dwarf goats under improved management system. In: Ayeni A.O. and Bosman H.G. (eds), Systems of Goat Production. Proceedings of an International Workshop held at the Obafemi Awolowo University, Ile-Ife, 6-9 July 1992. Pudoc Scientific Publishers, Wageningen, The Netherlands. pp. 202-207.

SAS (Statistical Analysis System). 1986. SAS Users Guide: Statistics. SAS Inc., Cary, North Carolina, USA. 923 pp.

Steel R.G.D. and Torrie J.H. 1980. Principles and Procedures of Statistics. 2nd edition. McGraw Hill, London, UK. 633 pp.

Van Vlaenderen G. 1989. Togo: A study of village level sheep and goat development. In: Timon V.H. and Babar R.P. (eds), Sheep and Goat Meat Production in the Humid Tropics of West Africa. Animal Production and Health Paper 70. FAO (Food and Agriculture Organization of the United Nations), Rome, Italy. pp. 142-169.

Wilson R.T., Murayi T. and Rocha A. 1989. Indigenous African small ruminant strains with potentially high reproductive performance. Small Ruminant Research 2: 107-117.


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