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Investigation of direct and maternal genetic effects on birth and
weaning weight of Chios lambs
a ,
*
b b aCh. 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.R.E.F., 63 200 N. Moudania, Greece
Received 10 June 1999; received in revised form 15 December 1999; accepted 23 February 2000
Abstract
Direct additive and maternal genetic effects on birth and weaning weight of Chios lambs were investigated. The data originated from the Agricultural Research Station of Chalkidiki and comprised 7318 lambs, raised over the period from 1977 to 1992. Variance components were estimated using restricted maximum likelihood, fitting six different animal models, by
2
including or excluding maternal effects. The direct heritability (h ) for birth weight decreased from 0.38 to 0.13 whend
2
maternal genetic effects were included in the model, while h for weaning weight decreased from 0.29 to 0.15. The maternald
2
heritability (m ) for birth weight was 0.33 when only maternal genetic effects were included in the model and ranged from
2 2
0.13 to 0.19 when the permanent environment of the dam (c ) was added. The respective values of m for weaning weight ranged from 0.14 to 0.16 and 0.05 to 0.07. The permanent environmental effect of the dam was significant for both traits. Negative genetic covariance between direct and maternal genetic effects (sam) was observed, which was significant only for birth weight. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Chios sheep; Maternal effects; Variance components; Heritability; Lamb weights
1. Introduction Therefore, the dam contributes to the phenotypic
value of her offspring, not only by a sample half of In mammalian species maternal effects influence her genes but also through her genes responsible for growth traits, particularly pre-weaning. Maternal maternal traits. The confounding of this double effects imply an impact of the mother on her contribution of the dam and the possibility of a offspring other than that through the genes she negative correlation between direct and maternal transmits to it and arise from mother’s ability to effects have led to the investigation of the magnitude produce the milk needed for growth of the lambs and of these effects (Hanrahan, 1976; Willham, 1980). her general maternal behaviour (Bradford, 1972). When growth traits are included in the breeding goal, both direct and maternal genetic effects should be taken into account in order to achieve optimum
*Corresponding author. Tel.: 130-31-471-256; fax: 1
30-31-genetic progress. Hence, accurate estimates for the
998-719.
E-mail address: [email protected] (Ch. Ligda). maternal genetic effects and their correlations with
Table 1
2 2 2
Estimates of direct heritability (h ), maternal heritability (m ), permanent environment of the dam (c ) and direct-maternal geneticd
correlation (rdm) from literature for birth weight and weaning weight of lambs
A. Birth weight B. Weaning weight Literature source Breed
2 2 2 2 2 2
hd m c rdm hd m c rdm
0.39 0.22 0.37 20.56 0.16 0.14 0.27 20.57 Tosh and Kemp, 1994 Hampshire 0.12 0.31 0.27 20.35 0.21 0.19 0.18 20.42 Tosh and Kemp, 1994 Polled Dorset 0.07 0.13 0.32 20.13 0.05 0.06 0.21 20.39 Tosh and Kemp, 1994 Romanov
0.04 0.22 0.10 0.34 0.25 0.00 Maria et al., 1993 Romanov
0.22 0.09 0.12 0.33 0.17 Snyman et al., 1995 South African Afrino
0.07 0.30 0.11 0.13 0.13 0.47 Nasholm and Danell, 1994 Swedish Landrace
0.35 0.26 Gabriilidis et al., 1995 Chios
0.13 0.17 Mavrogenis and Constantinou, 1990 Chios
direct effects are required. Recent developments in birth and at weaning. Lambing season ranged from statistical methods of variance components estima- October to March. Weaning of the lambs occurred at tion have simplified the partitioning of variance into an average of 42 days after lambing. Variance direct and maternal effects and as linear models used components were estimated with restricted maximum in animal genetic evaluation become more detailed, likelihood techniques using a derivative-free algo-these effects can be included in animal model rithm and fitting six different animal models into analyses (Meyer, 1992). Recently published each trait. Maternal genetic effects or permanent heritability estimates for lambs’ birth and weaning environmental effects were taken into account by weights are summarized in Table 1. including the appropriate random effects in the
Gabriilidis et al. (1995) estimated the direct model. The following models were used: heritability for birth and weaning weights of Chios
Y5Xb1Z a1e (1)
a
lambs, using a sire model, without taking into account the maternal genetic and environmental
Y5Xb1Z a1Z c1e (2)
a c
effects as 0.3560.033 and 0.2660.029, respectively. The aim of this study was to investigate the
impor-Y5Xb1Z a1Z m1e Cov(a, m)50 (3) a m
tance of maternal effects on birth and weaning weight of Chios lambs, fitting different animal
Y5Xb1Z a1Z m1e Cov(a, m)5As (4)
a m am
models including both genetic maternal and environ-mental effects.
Data used in this study were obtained from the
Cov(a, m)5As (6)
am
Agricultural Research Station of Chalkidiki during
the period from 1977 until 1992. In total 4214 where Y is the vector of observations, b, a, m, c and lambings of Chios ewes were included in the analy- e are the vectors of fixed effects, direct additive
sis, with 7951 and 7549 lambs at birth and at genetic effects (animal), maternal genetic effects, weaning, respectively. After excluding from the file permanent environmental effect of dam and the the records with missing values in either of the two residual, respectively. X, Z , Za m and Z , are thec
2 2 Table 2
identity matrix, V(a)5s A, V(m)5s A, V(c)5
a m
2 2 Means, standard deviations and CV (%) for birth weight and
s I, V(e)5s I and Cov(a, m)5s A, wheres is
c e am am weaning weight of Chios lambs
the covariance between direct and maternal genetic
2 2 Birth weight Weaning weight
effects,s , the direct additive genetic variance, s ,
a m
2
the maternal genetic variance,sc, the variance of the N 7318 7318
2 Mean (kg) 3.8 14.1
permanent environmental effect of the dam and s , e
S.D. (kg) 0.83 2.9
the variance of the residuals.
CV (%) 21.8 20.6
Gabriilidis et al. (1995) found that the fixed effects, significantly influencing weight of the lambs,
were litter size, parity, sex of lamb and season of lambs represented 18%, 52% and 30% of the data, birth. Therefore, in the present study, the fixed part respectively. The descriptive statistics for birth and of the model included the effects of productive weaning weight are given in Table 2.
period by season of birth (15 years32 seasons, 30
levels), parity (1, 2, 3, $4), litter size (single, twin, 3.1. Birth weight triplets and more) and sex of lamb (two levels). The
lambing season was divided in two parts, the first Estimates of variance components are presented in from October until December and the second from Table 3. The inclusion of maternal genetic effects in January until March. models (3)–(6) resulted in a significant increase of Calculations were carried out using the DFREML the log likelihood, in comparison with models (1)
programme (Meyer, 1993). Depending on the model, and (2). In model (6) the permanent environment of
2
the log likelihood function was maximised with the dam (c ) and the covariance between direct and
2
respect to direct heritability (h ), maternal heritabili-d maternal genetic effects (cam) were significant and
2
ty (m ), permanent environmental variance of the therefore this model was considered the most
suit-2
dam as a proportion of the phenotypic variance (c ), able.
and the genetic covariance between direct and mater- In model (1), where maternal effects were ig-nal genetic effects as a proportion of the total nored, heritability was biased upwards, while the
variance (cam). inclusion of maternal genetic effects in models (3)
The genetic correlations between direct and mater- and (4) reduced the direct heritability by 65%. When
2
nal genetic effects and total heritability (h ) wereT the maternal effects, genetic and / or environmental, calculated from the (co)variance components at were included in the model, the direct additive convergence. Total heritability was calculated ac- variance ranged from 0.07 to 0.09. Depending on the cording to Willham (1972) as: model used, the maternal effect was partitioned into genetic and environmental components. In model
2 2 2 2
h 5(s 10.5s 11.5s ) /s .
T a m am p (6), in which both genetic and environmental
mater-nal effects were taken into account, 19.1% of the Log likelihood ratio tests were carried out to total variance was attributed to the maternal genetic determine the most appropriate model for each trait effects and 16.7% to the permanent environment of
2
(Meyer, 1992). Parameters were considered to be the dam. It is evident that the relative values of hd 2
different from zero, when the estimate divided by the and m were greatly influenced by the model used in standard error was greater than the corresponding the analysis. As the maternal genetic effect and the values of the standard normal distribution (Tosh and permanent environment of the dam were of about the
Kemp, 1994). same magnitude, the common environment of the
lambs born in the same litter should not be neglected from the model. When the permanent environment of
3. Results and discussion the dam was ignored, the total variance was
Table 3
Estimates of (co)variance components and genetic parameters of birth weight
Model 1 Model 2 Model 3 Model 4 Model 5 Model 6
2
sa 0.196 0.083 0.072 0.072 0.073 0.094
2
sm 0.179 0.179 0.068 0.098
sam 0.58 E217 20.042
2
sc 0.142 0.085 0.085
2
se 0.321 0.286 0.296 0.296 0.290 0.278
2
sp 0.516 0.511 0.548 0.547 0.516 0.512
2
hd 0.38*** 0.16*** 0.13*** 0.13*** 0.14*** 0.18***
a
(0.023) (0.024) (0.021) (0.019) (0.022) (0.028)
2
m 0.33*** 0.33*** 0.13*** 0.19***
(0.018) (20.0001) (0.027) (0.034)
cam 0.0000 20.083**
The standard errors of the heritabilities are in parentheses.
b 2 2 2 2
h calculated as (s 10.5s 11.5s ) /s .
T a m am p
c
Log L as deviation from model (6). ***P,0.001; **P,0.01.
effects was 20.04 and the genetic correlation be- 20.56, while Maria et al. (1993) reported higher tween them was estimated as 20.44. negative estimates which they attributed to the small
2
Estimates of the maternal heritability and c were number and the structure of the data. Cundiff (1972) in the range reported by several authors. Tosh and argued that the negative covariance between direct Kemp (1994) obtained estimates for maternal and maternal genetic effects, explained from an
2
heritability and c of 0.22 and 0.37 in Hampshire evolutionary point of view, prevents species from lambs, 0.31 and 0.27 in Polled Dorset and 0.13 and becoming increasingly larger. The findings of 0.32 in Romanov lambs, respectively. The estimates Nasholm and Danell (1994) were not in agreement reported from Maria et al. (1993) for Romanov with this assumption, but also several authors men-lambs using a similar model were 0.22 and 0.10 for tioned that a possible existence of a negative
en-2
maternal heritability and c , respectively. Snyman et vironmental covariance between dam and offspring al. (1995), who reported an estimate of 0.12 for the could result in a biased estimation of genetic correla-permanent environmental effect of the dam, ascribed tion between direct and maternal effects (Meyer, this high value to the permanent environmental effect 1992).
of the uterus and the effect of multiple births. They
also reported an estimate of 0.09 for the heritability 3.2. Weaning weight of maternal genetic effects, which was lower than
Table 4
Estimates of (co)variance components and genetic parameters of weaning weight
Model 1 Model 2 Model 3 Model 4 Model 5 Model 6
2
sa 1.626 0.967 0.864 0.975 0.876 0.976
2
sm 0.782 0.929 0.288 0.387
sam 20.206 20.158
2
sc 0.691 0.472 0.474
2
se 4.067 3.956 4.076 4.006 3.994 3.932
2
sp 5.629 5.614 5.721 5.704 5.630 5.611
2
hd 0.29*** 0.17*** 0.15*** 0.17*** 0.16*** 0.17***
a
(0.025) (0.024) (0.022) (0.044) (0.024) (0.011)
2
The standard errors of the heritabilities are in parentheses.
b 2 2 2 2
h calculated as (s 10.5s 11.5s ) /s .
T a m am p
c
Log L as deviation from model (6). ***P,0.001; **P,0.01.
genetic effects was not significant and hence, model contributed to a great extent to the total phenotypic (5) was considered as the most appropriate. Maternal variance, as the estimates for the three traits varied effects, genetic and environmental, followed the from 0.18 to 0.27. Maria et al. (1993) reported same trend as for birth weight, but they were smaller maternal heritability of 0.25 for Romanov lambs in in magnitude. Maternal heritability was lower than Spain but they did not detect any environmental direct heritability and ranged from 0.07 to 0.16 in variance due to the permanent effect of the dam. models (3)–(6). In model (5), in which both genetic
and environmental maternal effects were taken into
account, 5% of the total variance was attributed to 4. Conclusion maternal genetic effects and 8% to the permanent
variances due to direct and maternal effects for growth traits of
the permanent environment of the dam was about
Romanov sheep. J. Anim. Sci. 71, 845–849.
half and the maternal genetic effect about one third
Mavrogenis, A., Constantinou, A., 1990. Relationships between
of the additive genetic effect. pre-weaning growth, post-weaning growth and mature body
size in Chios sheep. Anim. Prod. 30, 271–276.
Meyer, K., 1992. Variance components due to direct and maternal effects for growth traits of Australian beef cattle. Livest. Prod.
Acknowledgements
Sci. 31, 179–204.
Meyer, K., 1993.DFREML— a set of programs to estimate variance
The authors thank Dr. K. Meyer for supplying the components by restricted maximum likelihood using a de-set of programs DFREML 2.1 for the estimation of rivative-free algorithm. In: User Notes. Version 2.0. University
variance components. of New England, Armidale, p. 101.
Nasholm, A., Danell, O., 1994. Maternal effects on lamb weights. In: Proceedings of the 5th World Congress on Genetics Applied to Livestock Production, University of Guelph, Canada, Vol.
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