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Genetic parameters for lean meat yield, meat quality,
reproduction and feed efficiency traits for Australian pigs
3. Genetic parameters for reproduction traits and genetic
correlations with production, carcase and meat quality traits
a ,
*
b aS. Hermesch
, B.G. Luxford , H.-U. Graser
a
Animal Genetics and Breeding Unit, Joint Institute of NSW Agriculture and The University of New England,
University of New England, Armidale, NSW 2351, Australia
b
Bunge Meat Industries, Corowa, NSW 2646, Australia
Received 15 September 1998; received in revised form 12 November 1999; accepted 9 December 1999
Abstract
Genetic parameters were obtained using REML procedures applied to a multiple trait animal model for number born alive (NBA), litter birth weight (LBW), average piglet weight at birth (ABW) recorded in the first, second and third parity (NBA1,2,3, LBW1,2,3, ABW1,2,3) and 21-day litter weight (LW21 ) for 6050 Large White and Landrace sows. Heritability1 estimates ranged from 0.06 to 0.22 for these reproductive traits, with lowest estimates for NBA1,2,3 and LW21 .1
Reproductive performance in the first parity should be regarded as a different trait than reproductive performance in later parities (range of genetic correlations (rg): 0.52–0.78, 60.16–0.30). NBA was unfavourably related with LBW ,
1,2,3 1
ABW1,2,3and LW21 . In addition, NBA1 1,2,3was negatively correlated with growth rate traits, feed intake and weight of the back leg and ham (BLW, LMW) (rg range: 20.45 to 20.01,60.13–0.15). In contrast, genetic correlations were favourable
between LBW , ABW and growth rate, BLW and LMW (rg values: 0.08–0.55,60.12–0.25). NBA and ABW
1,2,3 1,2,3 1,2,3 1,2,3
were not genetically related with backfat measurements, while a low backfat was associated with a high LBW1,2,3 (rg:
20.54 to 20.08, 60.09–0.36). Genetic correlations between reproduction traits and meat quality traits were inconsistent
between traits and parities. A lower intramuscular fat content was associated with a higher LBW1,2,3 and ABW1,2,3 (rg:
20.37 to 20.12,60.12–0.18). In summary, genetic correlations between reproduction traits and performance traits were
only unfavourable between litter size and growth rate and feed intake. Genetic correlations between litter birth weight and average piglet weight at birth indicate that selection for leanness will also improve litter weight traits. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Pigs; Reproduction; Production; Carcase; Meat quality; Genetic parameters
1. Introduction
*Corresponding author. Tel.: 161-267-73-3787; fax: 1
61-Genetic improvement of sow productivity has 267-73-3266.
E-mail address: [email protected] (S. Hermesch). mainly been focussing on litter size (i.e., de Vries and
Kanis, 1994). However, an increase in litter size The proportion of crossbred litters for the first three appears to be associated with decrease in piglet birth parities were 60.3, 64.4 and 74.2% for Large White weight and survival (Haley et al., 1988). Rydhmer et sows and 52.0, 56.2 and 69.1% for Landrace sows. al. (1992) found that a low average piglet weight at Each litter originated from the first mating only and birth increases piglet mortality. Therefore, in order to the proportion of litters from artificial insemination increase the number of piglets weaned per sow was 18.3, 23.0 and 24.8% for the first to third parity. through genetic improvement further reproductive The farrowing age for the first litter was restricted to traits of the sow including litter birth weight, average 270–500 days. Age of litter when litter weight was piglet weight at birth and 21-day litter weight should recorded ranged from 10 to 28 days with a mean of be considered in breeding programs. In addition, 19 days.
these reproductive traits might have stronger genetic Reproductive traits were analysed as a different relationships with other production traits as currently trait in the first, second and third parity and included assumed. Knowledge about genetic parameters be- number of piglets born alive (NBA1,2,3), litter birth tween reproduction traits and other performance weight (LBW1,2,3), average piglet weight at birth traits is mostly limited to growth rate, feed intake (ABW1,2,3) and litter weight at 21-days in the first and backfat (Short et al., 1994; Rydhmer et al., 1995; parity (LW21 ). Records available for 21-day litter1 Tholen et al., 1996; Crump et al., 1997) with varying weight recorded in the second and third parity were estimates between studies and data sets. Breeding not sufficient to analyse them as separate traits. programs consider a number of production, carcase Furthermore, recording procedures for litter birth and meat quality traits, and their genetic relationship weight and consequently average piglet birth weight with reproductive traits is required in order to changed in the third quarter of 1993 when litter establish whether reproductive traits should also be weight was recorded 3 days after birth. In total, analysed in a multitrait analysis. The objective of 13 518 litters were available for analysis.
this study was to obtain genetic parameters for
reproductive traits of the sow and to obtain genetic 2.2. Production, carcase and meat quality data correlations between reproduction traits and
product-ion, carcase and meat quality traits. Analysis of production, carcase and meat quality data was based on performance records from 1799 Large White and 1522 Landrace boars. Performance
models included date of recording (all traits), breed and quadratic covariable), and time period from (not significant for ADG2, FDINT, FCR, pH24 and farrowing to weighing (linear covariable). The num-CMD) and parity (ADG1, ADG2, BLW, LMW). ber of piglets weighed represented the sow’s own Weight of the animal at test beginning was fitted for piglets as well as piglets that were cross-fostered feed intake and feed conversion ratio. Backfat mea- from other sows. Breed of service sire was not surements, muscle depth and intramuscular fat con- significant for any reproductive trait.
tent were corrected for weight of the animal at Only a small proportion (1–3%) of the total slaughter. Litter was fitted for growth rate and back variation was explained by the fixed effect model for leg weight traits as an additional random effect. A number of piglets born alive. In contrast, the fixed detailed description of the data structure and the effect model explained 53–63% of the total variation analysed traits was given in Hermesch et al. (2000a) for litter birth weight and 30–48% for average piglet along with derivation of the appropriate model and weight at birth. These high coefficients of determi-heritability estimate for each trait. Furthermore, nation were mainly due to farrowing season and genetic correlations between these traits were pre- were caused by a change in performance recording sented in Hermesch et al. (2000b). of litter birth weight. Since October 1993, litter birth weight has been recorded 3 days after farrowing and 2.3. Analysis therefore includes piglets that were cross-fostered. In addition, comparing least-squares means of farrow-The significance of fixed effects fitted in the model ing seasons showed that litter birth weight increased for each trait was analysed using PROC GLM (SAS, by 3 kg from March 1992, but no explanation could 1991). Significant fixed effects included in the be given for this increase which was probably caused models to analyse reproductive traits of the sow were by a change in recording procedure.
farrowing season which was defined in 3-month Variance components were obtained from an ani-periods within year, breed of the sow, farrowing unit mal model with restricted maximum likelihood pro-and whether the sow was artificially inseminated or cedures (DFREML, Meyer, 1997) which provides naturally mated (Table 1). Covariables fitted for approximations of standard errors for heritabilities reproductive traits included the age at farrowing and genetic correlations. Whenever the approxima-(linear covariable), number of piglets weighed approxima-(linear tion of standard errors for genetic correlations failed
Table 1
2 a
Fixed and random effects for reproductive traits of the sow and total variation explained by fixed effects (R )
Fixed effects Random effect
2
R FS breed AI FU FA n Period Animal
NBA1 0.02 * *** * * *** ✓
NBA2 0.03 *** * *** *** ✓
NBA3 0.01 *** *** ✓
LBW1 0.43 *** *** *** ✓
LBW2 0.51 *** *** * * ✓
LBW3 0.44 *** *** ** ✓
ABW1 0.30 *** *** ✓
ABW2 0.45 *** *** *** ✓
ABW3 0.48 *** *** ✓
LW211 0.26 *** *** *** *** ✓
a
NBA1,2,3, litter size in the first to third parity; LBW1,2,3, litter weight in the first to third parity; ABW1,2,3, average piglet weight in the first to third parity; LW21 , litter weight at 21-days in the first parity; FS, farrowing season; AI, artificial insemination; FU, farrowing unit;1
FA, age at farrowing (linear covariable); n, number of weighed piglets for LW21 (linear and quadratic covariable); Period, period of time1
to converge, standard errors for genetic correlations weights in the second and third parity with estimates were obtained using the formula of Robertson of 0.22 and 0.20. A lower genetic variance rather (1959). than an increase in environmental variance is the Significant random effects were tested with a log cause for this reduced heritability for litter birth likelihood ratio test. For reproductive traits of the weight in the first parity. Gilts were farrowing at 337 sow only maternal effects were analysed as an days on average and their uterine capacity is smaller additional random effect. Only 19% of all sows with in comparison to multiparous sows. This might have records had at least one full sister available in the been a restriction on expression of their genetic data set and the data structure did not allow to fit potential in litter birth weight. Heritabilities were litter effect as an additional random effect. General- 0.15, 0.16, 0.15 for average piglet birth weight in the ly, maternal effects were not significant for reproduc- first three parities.
tive traits of the sow and were therefore not fitted in Literature estimates of heritabilities for litter birth the model. weight and average piglet weight at birth varied between research data and field data. Heritabilities for litter birth weight were 0.13 and 0.21 in the study
3. Results and discussion of Crump et al. (1997), which was based on field data. In contrast, high estimates of heritabilities with 3.1. Heritability estimates for reproductive traits of a range of 0.42–0.65 were obtained by Irvin and the sow Swiger (1984) and by Ferguson et al. (1985) for litter birth weight and average piglet weight at birth, Heritabilities and variance components for re- using data from research herds. Rydhmer et al. production traits of the sow are presented in Table 2 (1992) pointed out that litter birth weight is in-along with the number of records and means for each fluenced by the milk intake of piglets after birth trait. Litter size was lowly heritable with estimates of which depends on the milk performance of the sow. 0.08, 0.09 and 0.08 for the first three parities pooled An early weighing of the litter after birth is therefore over both breeds. These estimates are in agreement important, and delays in recording litter birth weight with literature estimates (Southwood and Kennedy, in field data might be the reason for lower 1990; Alfonso et al., 1994; Irgang et al., 1994; heritabilities. The recording policy for litter birth
¨
Rydhmer et al., 1994; Rohe and Kennedy, 1995; weight changed in the third quarter of 1993 in this Ducos and Bidanel, 1996; Tholen et al., 1996). herd, when litter birth weight was recorded 3 days Litter birth weight in the first parity had a lower after farrowing and includes cross-fostered piglets. heritability (0.08) in comparison to litter birth This inconsistency in data recording and weighing after cross-fostering leads to an increase in environ-mental variation and therefore reduced heritability Table 2
2 (Tholen et al., 1996).
Number of records (n), means, heritabilities (h ) with standard
2
errors (S.E.) and phenotypic variances (s ) for reproduction traits Litter weight at 21-days recorded in the first parity
p a
of the sow (LW21 ) was lowly heritable (Table 2), which is in
1
2 2 2
Trait n Mean h S.E. of h s agreement with estimates presented by Kaplon et al.
p
(1991), Siewerdt et al. (1995) and Tholen et al.
NBA1 5986 9.61 0.08 0.02 5.90
(1996). Litter weight at 21-days was strongly
in-NBA2 4113 10.06 0.09 0.02 5.94
NBA3 2965 10.79 0.08 0.03 6.11 fluenced by number of piglets weighed and the age LBW (Kg)1 4306 12.55 0.08 0.02 7.26 of the litter at weighing. Tholen et al. (1996) LBW (Kg)2 2084 13.41 0.22 0.05 8.44 compared regression coefficients for number of LBW (Kg)3 1234 14.65 0.20 0.07 10.49
piglets after weighing. Linear and quadratic regres-ABW (g)1 4206 1342 0.15 0.03 124 129
sion coefficients varied considerably across parities ABW (g)2 2032 1390 0.16 0.04 98 286
ABW (g)3 1216 1419 0.15 0.06 79 504 and herds. This shows possible limitations in adjust-LW21 (Kg)1 1111 41.73 0.07 0.06 86.52 ing environmental variation caused by different
a
3.2. Estimation of genetic correlations first to third parity (rg5 20.15, 20.12, 20.20). However, litter birth weight in later parities was 3.2.1. Reproductive traits of the sow mainly positively correlated with number born alive Genetic and environmental correlations between (rg5 20.04 to 0.43). In this study litter birth weight reproduction traits of the sow are presented in Table was not corrected for number born alive. Using a 3. Estimates of genetic correlations between litter similar model, Bereskin (1984), Irvin and Swiger size in the first to third parity (NBA1,2,3) were (1984) and Siewerdt et al. (1995) found positive positive. Number born alive in the first parity was genetic correlations ranging from 0.42 to 0.92. The genetically a different trait than litter size in the negative genetic correlations found in this study second and third parity (genetic correlation (rg)5 between litter birth weight and number born alive 0.62 for NBA , rg50.61 for NBA ) supporting the could be caused by the recording procedure of litter
2 3
analysis of number born alive in the first parity as a birth weight. Piglet mortality is higher in larger separate trait to litter size in later parities. Although litters and in litters with a lower average birth weight Haley et al. (1988) suggested analysing litter size as (Fraser, 1990). Therefore, gilts with large litters are repeated records, results from more recent studies more likely to have a higher mortality rate,
especial-¨
(i.e., Alfonso et al., 1994; Rohe and Kennedy, 1995; ly within the first few days after farrowing. With the Tholen et al., 1996) confirm that number born alive delay of recording litter birth weight this will reduce in the first parity should be regarded as a different the total litter weight. In addition, the cross-fostering trait than litter size in later parities. The genetic practice of putting smaller piglets on to gilts and correlation between number born alive in the second taking their own bigger piglets away to older sows and third parity was high (0.95) and these traits can could also lead to this negative genetic correlation. It therefore be treated as repeated records in selection was not possible to incorporate these cross-fostering programs. Similar, genetic correlations between litter practices in the model.
birth weight and average piglet weight at birth in the Genetic correlations between litter size and aver-first parity and performance in these two traits in the age piglet weight at birth varied from 20.86 to second and third parity were significantly different 20.27 (Table 3). Rydhmer et al. (1992) also found from one ranging from 0.52 to 0.79. Litter birth an unfavourable relationship between number born weight and average piglet weight at birth in the first alive and average piglet weight at birth (rg5 litter should therefore be analysed as a separate trait 20.34), while Irvin and Swiger (1984) found no while performance in later parities should be re- relationship (rg50.05) between these two traits. garded as repeated records. Litter birth weight and average piglet weight at
Litter birth weight in the first parity had low birth were moderately correlated (rg50.29–0.87). negative genetic correlations with litter size in the Irvin and Swiger (1984) found a positive genetic
Table 3
Genetic correlations (above diagonal) with standard errors (in brackets) and environmental correlations (below diagonal) between reproduction traits
NBA1 NBA2 NBA3 LBW1 LBW2 LBW3 ABW1 ABW2 ABW3 LW211
a
NBA1 0.62(0.19) 0.61(0.30) 20.15(0.17) 0.13(0.22) 20.04(0.20) 20.74(0.10) 20.34(0.25) 20.27(0.32) 20.14(0.32)
a
NBA2 0.11 0.95(0.04) 20.12(0.17) 0.43(0.18) 0.28(0.29) 20.41(0.21) 20.69(0.16) 20.40(0.35) 20.15(0.30)
a
NBA3 0.09 0.12 20.20(0.30) 0.22(0.27) 0.25(0.29) 20.51(0.24) 20.86(0.36) 20.56(0.25) 20.75(0.17)
a
LBW1 0.42 0.06 0.10 0.78(0.16) 0.52(0.28) 0.78(0.13) 0.87(0.23) 0.55(0.36) 0.14(0.32)
a
LBW2 0.08 0.45 0.05 0.10 0.98(0.34) 0.47(0.17) 0.29(0.21) 0.41(0.32) 20.10(0.31)
a
LBW3 0.06 0.04 0.62 0.11 0.00 0.29(0.28) 0.48(0.29) 0.73(0.27) 0.43(0.31)
a
Table 4
a
Genetic correlations with standard errors (in brackets) between reproduction and production, carcase and meat quality traits
NBA1 NBA2 NBA3 LBW1 LBW2 LBW3 ABW1 ABW2 ABW3
ADG1, average daily gain from 3 to 18 weeks; ADG2, average daily gain during station testing from 18 to 22 weeks; FDINT, feed intake recorded during station testing from 18 to 22 weeks; FCR, feed conversion ratio defined as feed intake over growth rate (18–22 weeks); LFDP2, backfat depth at P2 measured with real time ultrasound; LFD3 / 4, backfat depth between the third and fourth last ribs measured with real time ultrasound; LMD3 / 4, muscle depth of m. longissimusdorsi between the third and fourth last ribs on the live animal; FDP2, backfat depth at P2 measured with Hennesy Chong grading machine; FD3 / 4, backfat depth between third and fourth last ribs measured with Hennesy Chong grading machine; BLW, weight of whole left back leg; LMW, weight of slash boned left back leg; pH45, pH measured 45 min after slaughter; pH24, pH measured 24 h after slaughter; CLD, L value of Minolta chromameter of m. longissimus dorsi; CMD, L value of Minolta chromameter of m. multifidus dorsi; DLP, drip loss percentage; IMF, intramuscular fat content.
b
Estimates of standard errors obtained from approximation of Robertson (1959). *Estimate did not converge.
differ in accordance with expectations. Therefore, Litter birth weight and average piglet weight at these analyses indicate that the negative genetic birth were both positively correlated with growth rate correlation between growth rate measured earlier in (rg50.08–0.45). Positive genetic correlations be-life (ADG1) and litter size in the first parity may tween growth rate and litter birth weight and average have been influenced by the direct effect of litter size piglet weight at birth have also been reported by on growth rate. However, genetic correlations be- Vangen (1980), Hutchens et al. (1981), Rydhmer et tween other trait combinations seem not to be al. (1992), Tholen et al. (1996) and Crump et al. influenced by the direct effect of litter size. (1997).
Considering that a high growth rate was associated Low negative genetic correlations were found with a high feed intake (Hermesch et al., 2000b), the between litter birth weight and feed intake. Litter lowly negative genetic correlations (rg5 20.19, birth weight and average piglet weight at birth were 20.24, 20.05) between litter size and feed intake both negatively correlated with feed conversion ratio.
litter birth weight and growth rate and lowly negative apparent between pH45 and litter birth weight (rg genetic correlations between litter birth weight and range, 20.40 to 20.22). A darker colour is related feed intake. Furthermore, this favourable genetic to a larger litter size (rg range, 20.53 to 20.11) relationship is supported by Kerr and Cameron and a higher litter birth weight (rg range, 20.28 to (1995) who found a reduced litter weight in the 0.00). Genetic correlations ranged from 20.08 to selection line selected for high lean feed conversion 0.34 for litter size in the first to third parity and drip ratio. loss percentage. Overall, genetic correlations be-tween reproduction traits and meat quality traits were inconsistent and mostly of low magnitude indicating 3.2.3. Reproduction and carcase traits
no clear genetic relationships between these trait Genetic correlations between number born alive
groups. Estimates of genetic correlations between and backfat measured with real time ultrasound
reproduction traits and meat quality traits were not ranged from 20.07 to 0.17 (Table 4). Estimates of
available in the literature. genetic correlations between litter size and carcase
Finally, intramuscular fat content had no genetic backfat measurements varied from 20.28 to 0.16.
relationship with litter size. However, a higher This indicates no genetic relationship between
lean-intramuscular fat content was associated with a lower ness and litter size which is also apparent in genetic
litter birth weight with genetic correlations ranging correlations of muscle depth with litter size.
Litera-from 20.37 to 20.26 and a lower average piglet ture estimates between litter size and leanness were
weight at birth. Genetic correlations were 20.15, generally close to zero (Johansson and Kennedy, 2
0.19 and 20.12 for the first three parities. In-1983; Short et al., 1994; Ducos and Bidanel, 1996;
tramuscular fat content was reduced for leaner pigs Tholen et al., 1996).
(Hermesch et al., 2000b). Leanness was not ge-Weight of the back leg and lean meat weight of
netically related to litter size (Table 4), while litter the back leg were closely related to average daily
birth weight and average piglet weight at birth were gain (Hermesch et al., 2000b). Negative genetic
favourably related to leanness. These genetic correla-correlations in the range of 20.45 to 20.08
tions between reproduction traits and intramuscular between these two weight measurements and litter
fat content are therefore in agreement with results size are therefore in agreement with genetic
correla-between leanness and reproduction traits. tions found between average daily gain traits and
litter size.
In contrast to litter size, litter weight at birth had a
4. Conclusions
favourable genetic relationship with backfat mea-surements and leanness. Genetic correlations for
Reproductive performance of the sow is lowly litter birth weight and backfat measurements ranged
heritable. Reproductive performance in the first from 20.54 to 20.08. These estimates are of
parity should be regarded as a different trait to higher magnitude than the genetic correlation of
reproductive performance in later parities in the 20.05 presented by Young et al. (1978) for backfat
populations investigated. Litter size was unfavourab-and litter birth weight. Genetic correlations between
ly correlated with litter birth weight in the first average piglet weight at birth and backfat
measure-parity, average piglet weight at birth and 21-day ments ranged from 20.33 to 0.13, which was not
litter weight and these traits should be analysed in a significantly different from zero in most cases.
Hutchens, L.K., Hintz, R.L., Johnson, R.K., 1981. Genetic and growth does also lead to an increase in litter birth
phenotypic relationships between pubertal and growth charac-weight and average piglet charac-weight at birth.
teristics of gilts. J. Anim. Sci. 53, 946–951.
Irgang, R., Favero, J.A., Kennedy, B.W., 1994. Genetic parameters for litter size of different parities in Duroc, Landrace and Large White sows. J. Anim. Sci. 72, 2237–2246.
Acknowledgements
Irvin, K.M., Swiger, L.A., 1984. Genetic and phenotypic parame-ters for sow productivity. J. Anim. Sci. 58, 1144–1150. This work was funded by the Pig Research and Johansson, K., Kennedy, B.W., 1983. Genetic and phenotypic Development Corporation under project UNE17P. relationships of performance test measurements with fertility in Swedish Landrace and Yorkshire sows. Acta Agric. Scand. 33, Staff of Bunge Meat Industries are gratefully
ack-195–199. nowledged for data collection. Constructive
com-Kaplon, M.J., Rothschild, M.F., Berger, P.J., Healey, M., 1991. ments from the anonymous referees are greatly Population parameter estimates for performance and reproduc-appreciated. tive traits in polish large white nucleus herds. J. Anim. Sci. 69,
91–98.
Kerr, J.C., Cameron, N.D., 1995. Reproductive performance of pigs selected for components of efficient lean growth. Anim.
References Sci. 60, 281–290.
Merks, J.W.M., Molendijk, R.J.F., 1995. Genetic Correlations Alfonso, L., Noquera, J.L., Babot, D., Estany, J., 1994. Selection Between Production Traits and First Parity Traits. In: 46th
for litter size in swine using a multivariate animal model. In: Annual Meeting of the EAAP, Prague, 4.11.
5th World Congr. Genet. Appl. Livest. Prod. Guelph, pp. Meyer, K., 1997. An ‘average information’ Restricted Maximum
347–350. Likelihood algorithm for estimating reduced rank genetic
Bereskin, B., 1984. A genetic analysis of sow productivity traits. covariance matrices or covariance functions for animal models J. Anim. Sci. 59, 1149–1163. with equal design matrices. Gen. Sel. Evol. 29, 97–116. Crump, R.E., Thompson, R., Haley, C.S., Mercer, J., 1997. Robertson, A., 1959. The sampling variance of the genetic
Individual animal model estimates of genetic correlations correlation coefficient. Biometrics 15, 459–485. ¨
between performance test and reproduction traits of Landrace Rohe, R., Kennedy, B.W., 1995. Estimation of genetic parameters pigs performance tested in a commercial nucleus herd. Anim. for litter size in Canadian Yorkshire and Landrace swine with Sci. 65, 291–298. each parity of farrowing treated as a different trait. J. Anim. de Vries, A.G., Kanis, E., 1994. Selection for efficiency of lean Sci. 73, 2959–2970.
tissue deposition in pigs. In: Principles of Pig Science. Nottin- Rydhmer, L., Johansson, K., Stern, S., Eliasson-Selling, L., 1992. gham University Press, Nottingham, pp. 23–42. A genetic study of pubertal age, litter traits, weight loss during Ducos, A., Bidanel, J.P., 1996. Genetic correlations between lactation and relations to growth and leanness in gilts. Acta
production and reproductive traits measured on the farm, in the Agric. Scand. Sect. A Anim. Sci. 42, 211–219.
Large White and French Landrace pig breeds. Anim. Breed. Rydhmer, L., Eliasson-Selling, L., Johannsson, K., Stern, S., Genet. 113, 493–504. Andersson, K., 1994. A genetic study of estrus symptoms at Dwyer, C.M., Stickland, N.C., Fletcher, J.M., 1994. The influence puberty and their relationship to growth and leanness in gilts. J.
of maternal nutrition on muscle fiber number development in Anim. Sci. 72, 1964–1970.
the porcine fetus and on subsequent postnatal growth. J. Anim. Rydhmer, L., Lundeheim, N., Johannsson, K., 1995. Genetic Sci. 72, 911–917. parameters for reproduction traits in sows and relations to Ferguson, P.W., Harvey, W.R., Irvin, K.M., 1985. Genetic, pheno- performance-test measurements. J. Anim. Breed. Genet. 112,
typic and environmental relationships between sow body 33–42.
weight and sow productivity traits. J. Anim. Sci. 60, 375–384. SAS / STATS, 1991. User’s Guide. Release 6.03 edition, SAS Fraser, D., 1990. Behavioural perspectives on piglet survival. J. Institute Inc.
Reprod. Fertil. 40, 335–370. Short, T.H., Wilson, E.R., McLaren, D.G., 1994. Relationships Haley, C.S., Avalos, E., Smith, C., 1988. Selection for litter size in between growth and litter traits in pig dam lines. In: 5th World
the pig. Anim. Breed. Abstr. 56, 317–332. Congr. Genet. Appl. Livest. Prod. Guelph, pp. 413–416. Hermesch, S., Luxford, B.G., Graser, H.-U., 2000a. Genetic Siewerdt, F., Cardellino, R.A., Costa da Rosa, V., 1995. Genetic
parameters for lean meat yield, meat quality, reproduction and parameters for litter traits in three pig breeds in southern feed efficiency traits for Australian pigs. 1. Description of traits Brazil. Braz. J. Genet. 18, 199–205.
and heritability estimates. Livest. Prod. Sci. 65, 239–248. Southwood, O.I., Kennedy, B.W., 1990. Estimation of direct and Hermesch, S., Luxford, B.G., Graser, H.-U., 2000b. Genetic maternal genetic variance for litter size in Canadian Yorkshire parameters for lean meat yield, meat quality, reproduction and and Landrace swine using an animal model. J. Anim. Sci. 68, feed efficiency traits for Australian pigs. 2. Genetic relation- 1884–1887.
Aus-tralian pig populations: II. Relationships between weaning to Young, L.D., Pumfrey, R.A., Cunningham, P.J., Zimmermann, conception interval, farrowing interval, stayability and other D.R., 1978. Heritabilities and genetic and phenotypic correla-common reproduction and production traits. Austr. J. Agric. tions for prebreeding traits, reproductive traits and principal Res. 47, 1275–1290. components. J. Anim. Sci. 46, 937–949.
