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Estimation of genetic parameters for production traits of Chios

sheep using a multitrait animal model

a ,

_*

b b a

Ch. Ligda

, G. Gabriilidis , Th. Papadopoulos , A. Georgoudis

a

Department of Animal Production, Faculty of Agriculture, Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece

b

Agricultural Research Station of Chalkidiki, N.AG.RE.F., 63 200 N. Moudania, Greece Received 10 June 1999; received in revised form 10 January 2000; accepted 23 February 2000

Abstract

Genetic parameters for commercial milk yield, litter size at birth and mean litter weight at weaning of Chios sheep were estimated. The data originated from the Agricultural Research Station of Chalkidiki and included 5343 lactations of 2315 ewes with lambings from 1977 until 1996. Variance components were estimated using restricted maximum likelihood, fitting a multitrait animal model. The random effects included in the model were the additive genetic effect of the animal, the effect of the permanent environment of the animal and the residuals. Heritability estimates were 0.236_{0.015, 0.16}6_{0.011 and}

0.166_{0.010, for commercial milk yield, litter size at birth and mean litter weight at weaning, respectively. In the same}

sequence the repeatabilities of the traits were 0.38, 0.18 and 0.16. Genetic correlations were 0.036_{0.040 between milk yield}

and litter size, 2_0.776_{0.036 between litter size at birth and mean litter weight at weaning and} 2_0.066_{0.037 between milk}

Keywords: Chios sheep; Multitrait animal model; Genetic parameters; Milk yield; Litter size; Weaning weight

1. Introduction extension of the breed was pursued in collaboration

with the Section of the Ministry of Agriculture The Chios sheep breed is widely known for its responsible for the livestock genetic improvement, high milk production and prolificacy. Since 1977, a by the distribution of superior genetic material for nucleus flock of the breed was established in the the upgrading of several flocks in the country Agricultural Research Station of Chalkidiki (Gabriilidis et al., 1988). Although today, the origi-(A.R.S.C.), within the framework of a nationwide nal nucleus of the breed in the island of Chios has programme for protecting, studying and improving decreased to 500 animals (Ministry of Agriculture, important indigenous sheep breeds (Hatziminaoglou 1999, personal communication), the breed has been et al., 1996). Along with the above programme, the spread all over the Greek mainland. The breed is mainly raised in Chalkidiki and in Central Macedonia, in the region near Thessaloniki. The *Corresponding author. Tel.: 130-31-471-256; fax: 1

30-31-purebred population under milk control is 4500 998-719.

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crossbred animals is |100,000 heads. The economic lactation records of 2315 ewes. In the final pedigree

importance of the Chios sheep breed has led several data file a total of 3057 animals were included, of researchers to investigate the characteristics of the which 596 were sires, 2315 were ewes with records breed. Early publications on the Chios breed and 146 were dams without records.

concerned the population in the homonymous island Estimates of (co)variances were obtained by re-(Zervas, 1965) and the genetic parameters of the stricted maximum likelihood with a multitrait in-productive and rein-productive traits of the breed dividual animal model, using the V.C.E.4.2 software (Mavrogenis, 1982, 1985, 1988; Zervas et al., 1988; (Groeneveld and Kovac, 1994). Standard errors of Georgoudis et al., 1990; Gabriilidis et al., 1995). heritabilities, permanent environment effects and Although a number of publications considered the genetic correlations were also estimated.

genetic parameters of the productive and reproduc- The model was: tive traits of the breed and the selection scheme

Y 5_Year 1_Month 1_Lact 1_a 1_perm

ijklmn i j k l m

applied in Cyprus (Mavrogenis and Constantinou,

1_e 1991; Mavrogenis, 1995, 1997), the breeding objec- ijklmn tive of the breed and the development of appropriate

where Y is the observations’ vector for the three selection schemes, under Greek conditions, have not ijklmn

traits (commercial milk yield, litter size and mean been studied extensively yet.

litter weight at weaning), Year is the fixed effect of In the present study, data on commercial milk i

the productive period (i5_{1, . . . , 20), Month is the} yield, litter size at birth and average litter weight at j

fixed effect of the lambing month ( j5_{1, . . . , 6) and} weaning of Chios ewes were analyzed, since the

Lact is the fixed effect of the parity (k5_{1, . . . , 4).} main revenues of the farmers are from the milk k

The random effects included in the model were, the production and the lambs weaned per ewe. The

additive genetic effect of the animal (a , l5_{1, . . . ,} purpose of this paper is the estimation of the genetic l

3057), the permanent environmental effect (perm , parameters and especially the genetic correlations m

m5_{1, . . . , 2315) and the residual (e} _). between the above traits using a multitrait animal ijklmn model, taking into account all known relationships

between animals.

3. Results and discussion

2. Materials and methods The descriptive statistics for the three traits

ana-lyzed are given in Table 1 and the means and The data used in this study were collected from standard deviations by productive year are presented 1976 to 1996 at the Agricultural Research Station of in Table 2. During the period from 1977 till 1996, an Chalkidiki (A.R.S.C), in the framework of the re- average annual increase of 2.4 kg for milk yield, cording scheme for production and reproduction 0.01 lambs and 0.04 kg for the mean litter weight traits. Commercial milk yield was calculated using was observed. The estimates of the variance com-the Fleischmann method, from test day records taken

at 28-days interval, starting in the first week after

Table 1

weaning. Litter size was defined as the number of _{Descriptive statistics for commercial milk yield, litter size and} lambs born alive per ewe lambing. Lambings mean litter weight at weaning

occurred from October till March. The suckling _Commercial _Litter _{Mean litter} period of the lambs was 42 days, followed by a milk yield size at weight milking period of circa 190 days. Records of ani- (kg) birth at weaning

(kg / ewe) mals, with less than 50 kg of commercial milk

and / or were milked less than 70 days, were excluded Observations 5343 5343 5343

Mean 198.8 1.9 14.5

from the analysis. Moreover, only the records with

S.D. 85.2 0.78 2.7

observations in all three traits investigated were used

C.V. (%) 43 41 19

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Table 2

Means and standard deviations of the traits analyzed by productive year

Productive Numbers Commercial Litter Mean litter weight

year milk yield (kg) size at weaning (kg)

Mean S.D. Mean S.D. Mean S.D.

1977 55 187.8 81.98 1.8 0.79 13.9 3.05

1978 163 146.9 59.99 1.6 0.73 14.8 2.50

1979 245 132.2 50.12 1.8 0.83 14.0 2.79

1980 298 207.4 85.78 1.9 0.78 14.1 2.78

1981 283 164.0 72.18 1.9 0.80 14.2 2.72

1982 272 212.5 90.21 2.0 0.79 14.1 3.08

1983 257 230.6 85.51 1.9 0.75 14.3 2.74

1984 317 193.7 77.97 2.0 0.78 14.0 2.69

1985 307 215.0 85.62 2.0 0.84 14.3 2.57

1986 238 207.4 89.30 2.0 0.80 15.0 2.49

1987 289 194.3 84.03 1.9 0.82 14.3 2.94

1988 340 179.5 76.97 1.9 0.73 14.8 2.54

1989 323 185.4 84.40 1.9 0.71 15.1 2.36

1990 287 215.0 89.63 1.9 0.72 15.4 2.49

1991 266 221.5 80.32 2.0 0.77 14.8 2.44

1992 265 214.7 84.88 2.0 0.81 14.4 2.53

1993 230 222.6 90.98 1.9 0.76 14.8 2.90

1994 325 219.8 89.90 1.9 0.82 15.3 2.61

1995 269 202.8 82.71 2.0 0.83 14.5 2.46

1996 314 195.9 74.42 2.0 0.81 14.2 2.81

Table 3 _{ponents are presented in Tables 3 and 4. The}

Estimates of variance components, heritabilities, permanent

en-heritability estimates were 0.236_{0.02, 0.16}6_0.01

vironment effect and repeatabilities for the three traits

and 0.166_{0.01 for commercial milk yield, litter size}

Commercial Litter size Mean litter weight

and average litter weight at weaning, respectively milk yield (kg) at birth at weaning (kg)

(Table 3). These results are close to the results of a

2

s _1370.4 _0.09 _1.14

a previous investigation with a subset of the Station’s

2

s _900.7 _0.017 _0.04

c

data with a single trait animal model. However, in

2

s _3805.6 _0.48 _5.79

e

2 the previous study the total number of lambs born

s _6076.7 _0.587 _6.97

p

2

was considered (Georgoudis et al., 1990). The

hd 0.225 0.153 0.163

2

c 0.148 0.028 0.0057 _{estimates for milk yield of Chios sheep raised in} r 0.373 0.181 0.169 _{Cyprus, are higher ranging from 0.29 to 0.39}

(Mav-Table 4

Estimates of covariance components and phenotypic, genetic and permanent environment correlations for the three traits

Commercial milk Commercial milk yield Litter size at birth

yield and litter and mean litter and mean litter

size at birth weight at weaning weight at weaning

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rogenis, 1982, 1988; Mavrogenis and Constantinou, production compared with ewes with only one lamb, 1991). Heritabilities for milk yield in other dairy no significant difference was observed between the sheep breeds, obtained also by REML, are within the two groups regarding the commercial milk yield. The same range as those obtained in the present study. authors explained these results, by the diminishing of Kominakis et al. (1998) using transformed or un- the suckling stimulus effect of twin lambs after transformed data of milk yield in Boutsiko dairy weaning.

sheep reported heritability that varied from 0.18 to The high negative genetic correlation between 0.30. Serrano et al. (1994) estimated heritabilities of litter size and mean litter weight at weaning (2_0.77), 0.29 and 0.33 for normalised and total milk yield, reflects the fact that lambs born in large litters are respectively, in the Manchega sheep breed. The weaned at lower weights. Contrary to these results, a heritability of milk yield in Churra sheep is 0.25 (de high positive genetic correlation (0.48) between litter la Fuente et al., 1995). size and weaning weight of the lambs was reported Heritability of litter size (0.16) was higher than by Analla et al. (1997), analyzing data of the the values reported for other sheep breeds. For the Segurena sheep with a model that included the litter Boutsiko mountain breed, the values for litter size size as a fixed effect. However, they pointed out that varied from 0.06 to 0.07, depending on the model the net phenotypic values for weights of lambs from and the use of transformed or untransformed data multiple births would be smaller than those of lambs (Kominakis et al., 1998). Analla et al. (1997) born as single, due to the systematic effect of type of reported for the Segurena sheep a heritability of 0.08, birth. The estimated genetic correlation between milk while Puntila and Nylander (1998), analyzing data yield and average litter weight at weaning was from a Finnsheep nucleus, reported estimates of 0.08 2_{0.06 indicating the absence of a genetic} relation-and 0.03 for litter size at birth relation-and at weaning, ship between the two traits.

respectively. Similar values are reported by Davis et The repeatabilities of milk yield, litter size and al. (1998) analyzing data of New Zealand sheep. average litter weight at weaning were 0.38, 0.18 and Bradford (1985) pointed out that heritability of litter 0.17, respectively, and were at the same levels with size is quite low and summarizing over 30 estimates values reported in the literature. Repeatability of for different breeds and methods of estimation milk yield varied from 0.31 to 0.40 (Moioli and reported a range from 2_{0.15 to 0.35 and a mean of} _{Pilla, 1994; Serrano et al., 1994; de la Fuente et al.,} 0.10. 1995), while repeatability of litter size and average The heritability for the average litter weight at litter weight varied from 0.07 to 0.20 (Analla et al., weaning (0.16), although higher, in general is com- 1997; Davis et al., 1998; Kominakis et al., 1998; parable with values found in the literature. From data Puntila and Nylander, 1998). The low values of the on total litter weight at weaning of the Chios sheep permanent environmental variance in litter size at in Cyprus, Mavrogenis (1985, 1988) estimated birth and mean litter weight (0.028 and 0.0057, heritability of 0.11 and 0.13. Puntila and Nylander respectively) indicate, that these traits are influenced (1998), in a Finnsheep nucleus, estimated heritability to a small extent by non-additive genetic effects and for the total and average litter weight at weaning of the permanent environment.

0.11 and 0.10, respectively.

The genetic correlation between milk yield and

litter size was estimated at 0.03. This value is in 4. Conclusion

agreement with the results reported by Barillet et al.

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Hatziminaoglou, I., Georgoudis, A., Zervas, N., Boyazoglu, J., weaning should be included in the breeding goal to

1996. Prolific breeds of Greece. In: Fahmy, M.H. (Ed.), Prolific avoid decrease in the total lamb weight, due to its

Sheep, CAB International, UK, pp. 73–92.

high negative correlation with litter size. Neverthe- _{Kominakis, A., Rogdakis, E., Koutsotolis, K., 1998. Genetic} less the decrease of weaning weight due to the parameters for milk yield and litter size in Boutsiko dairy increase of litter size is counterbalanced by the sheep. Can. J. Anim. Sci. 78, 525–532.

Mavrogenis, A.P., 1982. Environmental and genetic factors in-increase of the total lambs sold per ewe. In the index

fluencing milk production and lamb output of Chios sheep. planning to be applied, the three traits included will

Livest. Prod. Sci. 8, 519–527.

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Mavrogenis, A.P., 1988. Genetic improvement of sheep in Cyprus by selection and / or crossbreeding. In: Thompson, E.F., Thompson, F.S. (Eds.), Increasing Small Ruminant

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