Livestock Production Science 63 2000 255–264 www.elsevier.com locate livprodsci
Genetic study of longevity in Swedish Landrace sows
M.H. Yazdi , L. Rydhmer, E. Ringmar-Cederberg, N. Lundeheim, K. Johansson
¨ Department of Animal Breeding and Genetics
, Swedish University of Agricultural Sciences, Funbo-Lovsta, S-755 97 Uppsala, Sweden Received 27 August 1998; received in revised form 8 June 1999; accepted 17 June 1999
Abstract
Genetic parameters for length of productive life of Swedish Landrace sows were estimated using a proportional hazards model based on the Weibull distribution. Data were obtained from 7967 sows with at least one farrowing recorded, using the
Swedish litter-recording scheme, from 1986 through 1998 from nucleus and multiplier herds. Effects of litter size at first and last farrowing, age at first farrowing, daily gain from birth to performance test | 170 days of age, weight, and side-fat
thickness at performance test were included in the model as fixed and time-independent explanatory variables. The effect of herd 3 year of birth combinations was treated differently in several analyses random versus fixed and time-independent
versus time-dependent. The random effect of sires, incorporating full pedigree information, was taken into account in all analyses as the source of genetic variation sire model. The length of productive lifetime longevity of sows was the
dependent variable and was defined as the number of days from first farrowing until culling. The suitability of the Weibull model was assessed by evaluating the log-cumulative hazard versus the log of longevity in days, which indicated that the
Weibull model could be fitted to the data satisfactorily. All explanatory factors except daily gain and side-fat had a significant effect on longevity of sows in all analyses. The effect of herd 3 year had the largest influence among the factors
included. Among the various analyses, estimates of heritability for longevity ranged from 0.109 to 0.268 on the original scale. The estimates were similar within each group of models, averaging 0.13 for the time-independent and 0.25 for the
time-dependent herd 3 year effect in the model. Correlations between sires’ breeding value estimates were 0.98 between time-independent models and ranged from 0.96 to 0.98 among time-dependent models. It was concluded that there is genetic
variation that can be utilised for increasing longevity by selection.
2000 Elsevier Science B.V. All rights reserved.
Keywords : Heritability; Life length; Survival analysis; Swine; Weibull distribution
1. Introduction through the voluntary culling of sows with inferior
fertility or a low capacity to produce piglets. Sow Longevity of sows summarises the effects of
longevity is important to farmers owing to the high functional traits functional longevity, defined as the
costs of replacement. Results of several studies have ability to delay involuntary culling Ducrocq and
shown that long lifetime production and low culling ¨
Solkner, 1998a, and of reproductive performance rates in swine herds have substantial economic
benefits e.g. te Brake, 1986; Jalvingh et al., 1992. Thus, length of productive life from first farrowing
Corresponding author. Present address: Institute of Ecology
until culling is a trait that has received increasing
and Resource Management, University of Edinburgh, West Mains Road, Edinburgh EH9 3JG, Scotland, UK.
attention in swine breeding. This subject has also
0301-6226 00 – see front matter
2000 Elsevier Science B.V. All rights reserved. P I I : S 0 3 0 1 - 6 2 2 6 9 9 0 0 1 3 3 - 5
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.H. Yazdi et al. Livestock Production Science 63 2000 255 –264
been given more attention in other farm animals, i.e. from 1986 through 1997, with at least one farrowing
dairy cattle e.g. Dekkers et al., 1994; Strandberg and were available in the data bank. The individual
¨ Solkner, 1996.
record of each animal included herd the herd that The effects of environmental factors, such as herd
the animal was born in, date of birth, date of first management and housing systems, on longevity of
farrowing f date, date of culling c date, age at ]
] sows in Sweden have been investigated by several
first farrowing age, litter size born alive at first authors Eliasson-Selling and Lundeheim, 1996;
farrowing f ls, litter size at last farrowing l ls, ]
] Olsson, 1996; Ringmar-Cederberg and Jonsson,
weight of gilt weight at field performance test 1996; Ringmar-Cederberg et al., 1997. Although
| 170 days of age, daily gain gain from birth until there is indirect selection due to leg weakness, low
field performance test, and side-fat thickness fat at fertility, etc. for longevity in all pig breeding
field performance test. To base conclusions on more programmes, to our knowledge, sow longevity is not
precise estimates of the herd 3 year year of birth included systematically in any such programmes.
factor, only sows from nucleus and multiplier herds One method for analysing longevity data is surviv-
with more than 50 sows that were born, raised and al analysis which allows inclusion of both censored
farrowing in the same herd were kept in the data set. and uncensored records of animals Cox, 1972. This
In total, sows from 24 herds were included. Animals approach relies on the concept of hazard, instanta-
with extreme values for age at first farrowing 250 neous or age-specific failure rate Lawless, 1982;
and 480 days and records of sires with less than 2 Lee, 1992 or, in the animal breeding context, the
daughters were excluded. After editing, the data set animal’s risk of being culled at time t, conditional
included records of 7967 sows with 5484 69 upon survival to time t Ducrocq, 1987; Ducrocq et
uncensored and 2483 31 censored incomplete al., 1988a. Proportional hazards models have been
records, longevity of animal is equal or longer than extended to incorporate time-dependent covariates
known period records. The l ls was expressed as a ]
Kalbfleisch and Prentice, 1980. Further, the inclu- deviation from the average of litter size for all sows
sion of random effects in the proportional hazards in that particular parity. A constant value of 12 was
models Smith and Quaas, 1984 and, particularly, added to each sow’s deviation in order to avoid
the extension of mixed survival models to include negative values. Classes of f ls with 0, 1 and 2 litters
] relationships between sires Ducrocq and Casella,
were grouped together owing to the very low fre- 1996 and development of computer programs Duc-
quencies of these classes. Also, classes of 16 and ¨
rocq and Solkner, 1994, 1998b, have made it higher were added to class 15. The same procedure
possible to estimate the genetic potential of sows for was used for l ls for observations in classes outside
] a longer productive life.
the range 3 to 19. The end of the recording period In this study we analysed longevity data of
was defined as the latest date of farrowing in each Landrace sows from Swedish nucleus and multiplier
herd for most herds, it was in February 1998. herds with the aim of revealing the most important
Censoring code and longevity were defined as in factors influencing longevity. Since the genetic
Table 1. make-up of sows in the herd is thought to have an
There were 250 herd 3 year hy combinations, important influence on culling rates, the ultimate
and the size of these classes varied from 1 to 151 goal was to estimate the genetic parameters for
average 32 sows. The distribution of sows across hy longevity.
was unbalanced: 22 of hy classes had no censored records, 50 had 3 censored, and 9 had no
uncensored animals. The data set comprised a total
2. Material and methods of 792 sires with an average of 8 daughters each
