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Estimate of genetic and phenotypic parameters for the Dorper, Red Maasai and their crosses

P.M. Kiriro

Egerton College, Njoro, P. O. Box 536, Njoro, Kenya


Abstract
Introduction
Materials and method
Results and discussion
Conclusions
References


Abstract

Data accumulated over 10 years (1971-1981) by the Ministry of Livestock Development and FAO/UNDP (Food and Agriculture Organization of the United Nations/United Nations Development Programme) were analysed to estimate the growth performance of Dorper and Red Maasai sheep and their crosses. The heritability, heterosis, phenotypic and genotypic correlations were determined for birth weight, average daily gain and weaning weight.

The animals' genotype, year, season and type of birth, sex of lamb and its rearing affected (P<0.01) all the growth parameters. Direct and maternal heterosis made sizeable contributions to birth weight (4.50 and 4.89%), weaning weight (10.95 and 6.50%) and average daily gain (9.36 and 8.93%). The heritability estimates were 0.14 ± 0.8, 0.08 ± 0.05 and 0.10 ± 0.06 for birth weight, weaning weight and average daily gain, respectively. These low estimates indicate that selection will not be an appropriate option for improving weaning weights and average daily gains. The genetic and phenotypic correlation estimates of the growth characteristics of Dorper lambs suggest that birth weight and average daily gain could be increased by selecting for heavier lambs at weaning.

Estimation des paramètres génétiques et phénotypiques chez les moutons Dorper, Red Maasaï et les produits de leur croisement

Résumé

Les données accumulées pendant dix ans (1971-1981) par le Ministère du développement de l'élevage et la FAO/PNUD (Organisation des Nations Unies pour l'alimentation et l'agriculture/Programme des Nations Unies pour le développement) au Kenya ont été analysées afin d'estimer les performances de croissance des moutons Dorper et Red Maasaï et des produits de leur croisement. L'héritabilité, l'hétérosis et les corrélations phénotypiques et génotypiques pour le poids à la naissance, le gain moyen quotidien et le poids au sevrage ont été déterminés.

Le génotype des animaux, l'année, la saison et le mode de naissance, le sexe des agneaux et le mode d'élevage influaient (P<0,01) sur tous les paramètres de croissance. L'hétérosis direct et l'hétérosis maternel intervenaient pour une part importante dans le poids à la naissance (4,50 et 4,89%), le poids au sevrage (10,95 et 6,50~o) et le gain moyen quotidien (9,36 et 8,93%). La valeur estimée de l'héritabilité était de 0,14 ± 0,8, 0,08 ± 0,05 et 0,10 ± 0,06 respectivement pour le poids à la naissance, le poids au sevrage et le gain moyen quotidien. Ces faibles valeurs montrent que la sélection n'est pas le moyen à retenir pour améliorer les poids au sevrage et les gains moyens quotidiens. D'après les valeurs calculées des corrélations génétiques et phénotypiques des paramètres de croissance des agneaux Dorper, on pourrait obtenir un accroissement des poids à la naissance et des gains moyens quotidiens en sélectionnant sur le poids des agneaux au sevrage.

Introduction

Maasai sheep are part of a wide variety of indigenous fat-tailed hair sheep scattered over many parts of Kenya, Uganda and Tanzania. They have a medium red-brown body. Maasai sheep and particularly Red Maasai sheep are found in large numbers in the Rift Valley Province of Kenya. Red Maasai sheep attracted the attention of livestock scientists because of their large population, wide distribution, uniformity of body colour and hardiness. It was also observed that with slightly better nutrition, disease control and selection, it was possible for the Red Maasai sheep to increase in body size, grow faster and produce more milk.

The Dorper sheep were first introduced into Kenya in 1952 at the then Katumani research station of the Ministry of Agriculture. As a breed they were developed in South Africa between 1945 and l950, mainly at Grootfontein, from Dorset Horn and Blackhead Persian sheep. They have a medium-white body with a black head, neck and legs. The Breed Society was formed in South Africa in 1950. By 1970, Dorper sheep had spread to Eastern, Rift Valley and Coast Provinces of Kenya. In the 1970s more Dorpers were imported from Southern Africa for research and multiplication.

When the Kenyan Government decided to initiate a sheep and goat development project in collaboration with FAO/UNDP in 1970, the Red Maasai was identified as the most important indigenous breed of sheep. Since then, short-term investigative research aimed at characterising the Red Maasai has been conducted. Studies have been carried out to determine the relationships between body weight and body measurements (FAO, 1975). Studies to compare Red Maasai and the Blackhead Persian have also been conducted in Tanzania. There were considerable differences in body weights and average daily gains at different stages of growth and between sexes.

Red Maasai were bred pure to ascertain their production potential. They were also crossbred with Dorper and Hampshire rams to incorporate the superior production traits of the two exotic breeds into the Red Maasai sheep. The Dorper sheep was also used to improve other indigenous fat-tailed sheep in many parts of arid Kenya. The Dorper was considered suitable to Kenyan conditions because it was developed from a desert fat-rumped sheep (Blackhead Persian) very similar to the Somali or the Blackhead sheep of Northern Kenya. According to Erasmus (1968), the Dorper has an ideal body conformation that adapts it to dry conditions. It is also hardy, has a high quality carcass, high lambing percentages, good mothering qualities and is extremely suitable for upgrading haired breeds of sheep.

The Dorper is probably the breed in Kenya that has been studied the longest in research stations. In 1975, the Sheep and Goat Development Project published 15 years of production data on Dorper sheep. The data showed that the Dorper has a birth rate of about 84%, a 24% twinning rate, a birth weight of about 3.5 kg, average daily gain of about 117 g and lamb mortality of 15%.

So far, however, no work has been done to establish the level of some economically important genetic parameters, e.g. heritability estimates of birth weight, average daily gain and weaning weight. The amount of hybrid vigour resulting from crossbreeding Dorper with Red Maasai sheep has also not been established. A breeding project was initiated at the Ol'Magogo division of the National Animal Husbandry Research Station, Naivasha and managed by the Sheep and Goat Development Project/FAO in 1970. It was expected to generate data to help investigate the importance of Dorper and the Red Maasai and their crosses. The sheep data from Ol'Magogo were analysed to fulfill these objectives:

· to estimate breed means for birth weight, average daily gain and weaning weight of Dorper, Red Maasai and their crosses;

· to estimate heritability of birth weight, growth rate and weaning weight;

· to estimate genetic and phenotypic correlations between birth weight, average daily gain and weaning weight; and

· to estimate heterosis of birth weight, average daily gain and weaning weight.

Materials and method

History

The studies that generated this data were carried out at Naivasha National Animal Husbandry research station by officials of the Ministry of Livestock Development and FAO/UNDP between 1971 and 1981. The study was conducted at the Ol'Magogo division of the station. The foundation flock was established from Dorper and Red Maasai sheep already in the country. Dorper sheep were from Mariakani, Katumani and Kiboko research stations. The Red Maasais were purchased from Nanyuki, Gilgil and Baringo (Figure 1).

Activities on foundation flock

The following activities were carried out:

· pure breeding of Dorper and Red Maasai to expand the flocks;

· short-term breed characterisation studies;

· studies on the effects of frequent mating (joining every eight months) on productivity;

· disease tolerance; and

· crossbreeding Dorper and Red Maasai to measure the improvement in productivity and develop a new breed.

Data collected and records

The breeding policy and the entire management strategies were designed to collect the maximum amount of data on the dam, sire and lambs. The data collected in this study covered the pre-mating and mating periods, lambing, lamb rearing, weaning, postweaning and treatment records. This study reports the results of data analysed up to weaning.

Statistical analysis

Data on growth characters were analysed by ANOVA using SAS (1982). The statistical model was: Yijklmn = U + Bi + (YW); + Rk + S1 + Em + eijklm where U is overall mean, B is breed of lamb, (YW) year of birth-season effect, R is type of birth, S is sex of lamb effect, E is age of lamb effect and e is the random error. The effects of crossbreeding on growth characters were analysed using a model similar to that used by Robinson et al (1981) which was executed using SAS (1982). Analyses for the genetic parameters, i.e. heritabilities and correlations for growth characters were conducted using the Least Square Maximum Likelihood program (LSML76) of Harvey (1982). Heritabilities and correlations analyses were restricted to the Dorper breed because of higher numbers of observations of sires, and to lambs whose sires were known. The genetic and phenotypic correlations were calculated by paternal half-sib procedure (Falconer, 1981).

Figure 1. Geographical location of Naivasha.

Results and discussion

Genetic and environmental effects on growth characters

Breed of lamb affected (P<0.001) birth weight (BW), weaning weight (WOO) and average daily gain (ADO) of all the breed groups (Table 1). The magnitude of difference in growth characters was closely associated with divergence in genotype (Figures 2 and 3). Lambs which were heavy at birth performed better than light lambs.

Table 1. Least squares means and standard errors for birth weight (BW), weaning weight (WOO) and average daily gain (ADO) for each breed and sex of lamb.

Category

Body characters (kg, SE)

BW

WW

ADG

Breed of lamb1


Dorper (D)

3.64 (0.04)a

19.50 (0.23)a

159.35 (2.27)b


Red Maasai (R)

2.90 (0.05)c

15.56 (0.28)c

127.06 (2.78)d


D x R

3.33 (0.06)

17.51 (0.32)b

138.61 (3.23)c


D x DR

3.64 (0.05)a

19.63 (0.26)a

161.59 (2.60)b


D x DDR

3.49 (0.13)b

20.82 (0.70)a

169.91 (7.06)a


D x DDDR

3.60 (0.13)a

19.44 (0.71)a

161.69 (7.19)b


DDR x DDR

3.58 (0.05)a

19.80 (030)a

162.88 (2.99)b

Sex


Male

3.53 (0.05)

19.44 (0.27)

158.80 (2.70)


Female

3.38 (0.05)

18.34 (0.27)

150.10 (2.71)

¹Letters on left of x represent sire breed.
SE = standard error.
abcd = Means within a column carrying different superscripts are significantly different (P<0.001).

Figure 2. Growth trends of Dorper (D), Red Maasai (R) and their crosses.

Figure 3. Effects of percentage of Dorper in the cross on BW, WW and ADG. Percentages of Dorper in the cross are represented by: 0 = Red Maasai (R); 100 = Dorper (D); 50 = DxR; 75 = DxDR; 87.50 = DxDDR; and 93.75 = DxDDDR.

Year of birth-season affected (P<0.001) birth weight, weaning weights and average daily gain. The effect was closely related to rainfall. Type of birth, rearing and sex of lamb affected (P<0.001) all growth characters.

Heterosis

Average direct heterosis shows that crossbred lambs were heavier by 0.15 kg (4.5%) for birth weight, 1.92 kg (10.95%) for weaning weight and 13.8 g (9.36%) for average daily gain. The study shows that heterosis for average daily gain was almost similar to that obtained for weaning weights. Similar observations were made by Sidwell and Miller (1971a, 1971b), Holtman and Bernard (1969) and Singh et al (1981).

Maternal heterosis estimates of 0.16 kg (4.89%), 1.14 kg (6.50%) and 12.8 g (8.93%) were obtained for birth weight, weaning weight and average daily gain, respectively. The results show that maternal heterosis contributed significantly to birth weights, weaning weights and average daily gains of crossbred lambs. Similar observations were reported by Farid et al (1977), Holtman and Bernard (1969) and Willham (1970).

All lambs from known sires were used in the heritability estimates.

Heritability estimates

Heritability estimates (h²) were obtained from 1202 observations (Table 2). The heritability estimates were low, indicating that it would be difficult to improve weaning weights and average daily gains through selection. Similar observations were reported by Johor and Norton (1977), Suvindra and Tomar (1982) and Shelton and Menzies (1968). The uniformity of the growth traits of the flock might have led to low heritability estimates for weaning weights and average daily gains.

Correlation estimates

Genetic and phenotypic correlations of growth characters for Dorper lambs are shown in Table 3.

Positive genetic correlations were obtained between birth weight and weaning weight and between weaning weight and average daily gain.

Phenotypic correlation between birth weight and weaning weight and weaning weight and average daily gain were positive.

Conclusions

The results obtained imply that little change in either birth weight or average daily gain would be expected by selecting for these traits. They are genetically and phenotypically only very slightly negatively correlated. However, significant improvements to birth weights and average daily gains could be obtained by selecting for heavier weaning weights.

Table 2. Estimate of heritabilities (h²) and standard errors of growth characters of Dorper lambs.

 

Number of sires

Number of observations (lambs)

h²(SE)

Character

Birth weight

44

1202

0.138(0.060)

Weaning weight

44

1202

0.08 (0.051)

Average daily gain

44

1202

0.107 (0.055)

All lambs from known sires were used in the heritability estimates.

Table 3. Genetic and phenotypic correlations of growth characters for Dorper lambs.

Growth character

Birth weight

Weaning weight

Average daily gain

Birth weight


0.546

-0.038

Weaning weight

0.199


0.838

Average daily gain

-0.022

0.942


Genetic correlations above diagonal, phenotypic below.
Correlations were estimated from 1202 observations.

References

Erasmus L S. 1968. The small stock industry in South Africa. Agricultural Research Institute of the Karoo Region, Middleburg, C.P. The Non-wooled Mutton Breeds. Government Printer, South Africa, Pretoria. pp. 55-63.

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

FAO (Food and Agriculture Organization of the United Nations/Sheep and Goat Development Project). 1975. 15 Years 'production data on Dorper sheep at Katumani Research Station, Machakos. Technical note 12. Katumani Research Station, Machakos, Kenya.

Farid A, Makarechian M and Sefidbakht N. 1977. Crossbreeding of Iranian fat-tailed sheep: Lamb performance of Karakul, Mehraban and Naeni breeds. Journal of Animal Science 44:542.

Holtman W B and Bernard C. 1969. Effects of general combination ability and maternal ability of Oxford, Suffolk and North Country Cheviot breeds of sheep. Journal of Animal Science 28:155.

Johor K S and Norton N W. 1977. Genetic study on birth and weaning weight of Suffolk and Torghee sheep. Indian Veterinary Journal 54:902.

Robinson O W. McDaniel B T and Rincon B T. 1981. Estimation of direct and maternal additive and heterotic effects from crossbreeding experiments in animals. Journal of Animal Science 52:45.

SAS (Statistical Analysis System). 1982. SAS user's guide: Statistics. SAS Inc., Cary, North Carolina. USA, 404 pp.

Shelton M and Menzies J W. 1968. Genetic parameters of some performance characteristics of range fine wool sheep. Journal of Animal Science 27:1219.

Sidwell G M and Miller L R. 1971a. Production in some pure breeds of sheep and their crosses. I. Reproductive efficiency in ewes. Journal of Animal Science 32: 1084-1089.

Sidwell G M and Miller L R. 1971b. Production in some pure breeds of sheep and their crosses. II. Birth weights and weaning weights of lambs. Journal of Animal Science 32: 1090-1094.

Singh B P. Arora C L, Bohra S D J. Bapna D L and Nivsarkas A E. 1981. Notes on the variation in the pre-and postweaning body weights of Malpura and Sonad, and their crosses with Suffolk and Dorset. Indian Journal of Animal Sciences 26:261.

Suvindra K and Tomar N S. 1982. Genetic studies on Corriedale sheep in India. Indian Veterinary Journal 59:948.

Willham R L. 1970. Genetic consequences of crossbreeding. Journal of Animal Science 30:690-693.


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