L. Rydhmer

Genetics of sow reproduction, including puberty, oestrus, pregnancy, farrowing and lactation

Abstract The possibility to improve different sow reproduction traits, such as age at puberty, oestrous symptoms, ability to become pregnant, litter size, piglet survival and weight, milk production, maternal behaviour and ability to show oestrus after weaning, are discussed in this review. Relations between different reproduction traits as well as between reproduction and production traits are also described. The current genetic progress in litter size at birth increases the need for a broader breeding program which includes piglet survival and growth.

Genetic Parameters for the Piglet Mortality Traits Crushing, Stillbirth and Total Mortality, and their Relation to Birth Weight

The aim of this study was to estimate genetic and phenotypic parameters for the three mortality traits crushing, stillbirth and total mortality in piglets, and their respective correlations with birth weight. Records were available from 11 016 Yorkshire piglets from 1046 first parity litters in a Swedish experimental herd. Each mortality trait was analysed jointly with birth weight, using bivariate models. Both mixed linear models and threshold models were used. The threshold models took environmental and maternal genetic effects into account, whereas the linear models also included a direct genetic effect of the piglet on its birth weight. The estimated heritabilities were low for all mortality traits (0.01-0.15), with the lowest estimate for crushing and the highest for stillbirth. The estimated environmental correlations between the different mortality traits and birth weight were negative. The estimated genetic correlations between crushing and birth weight (both direct and maternal effect) were also negative in both models, indicating that sows with low-weight piglets are more likely to crush piglets. However, the genetic correlations between stillbirth and birth weight (both direct and maternal effect) were positive. These results suggest that stillbirth and crushing are traits with different genetic backgrounds, and that genetically increasing the birth weight of the piglets may result in more stillborn piglets.

Relation between early fear- and anxiety-related behaviour and maternal ability in sows

Abstract Fear induced by exposure to humans, and anxiety induced by novel environmental changes may both function as stressors and have negative effects on reproduction in pigs. An earlier experiment indicated that reactions to humans and novelty had some repeatability between the ages of 8 and 24 weeks, thus reflecting personality traits. The present experiment therefore tested for predicted negative relationships between behaviour related to fear and anxiety measured at 8 weeks of age and later reproduction in 30 sows. Factor analysis of behaviour in a voluntary human approach test performed in the home cage and a novel object test performed in a novel arena indicated that behavioural measures related to investigation of these stimuli loaded on separate factors and may therefore reflect independent underlying dimensions. One factor related to investigation of the human was interpreted as reflecting the level of fear of humans, while another was correlated to investigation of the novel object and interpreted as indicating novelty-induced anxiety. Factor scores were generated for ‘fear’ and ‘anxiety’ and used in regression analysis as predictors of maternal behaviour and reproductive parameters. Higher levels of fear of humans were associated with longer durations of farrowing, larger variation in inter-birth intervals, and a higher number of piglets dying without milk in their stomachs. The duration of farrowing was positively correlated to the number of live born piglets dying within 3 weeks of age. Higher fear also tended to associate with a higher number of stillborn and a higher number of live born piglets dying within 3 weeks of age. High anxiety only tended to be associated with a higher number of stillborn. These results are interpreted as supporting the hypothesis that there are negative associations between fear of humans and maternal ability in sows.

Genetic validation of postmixing skin injuries in pigs as an indicator of aggressiveness and the relationship with injuries under more stable social conditions

The objective of the study was to estimate genetic correlations between skin lesions and aggressive behavior postmixing and under more stable social conditions as a potential means of selecting against pig aggressiveness. Postmixing aggression in commercial pig production is common, compromises welfare and profitability, and cannot be significantly reduced by low-cost changes to the environment. A genetic component to individual aggressiveness has been described in pigs and other species. Selective breeding against aggressiveness ought to be possible if an easily measured indicator trait can be shown to be genetically associated with aggressive behavior. Aggressive behavior was recorded continuously for 24 h after mixing, and a count of skin lesions (lesion count, LC) was recorded at 24 h and 3 wk postmixing on 1,663 pigs. Two behavioral traits were found to have a moderate to high heritability similar to that of growth traits; duration of involvement in reciprocal fighting (0.43 +/- 0.04) and delivery of nonreciprocal aggression (NRA; 0.31 +/- 0.04), whereas receipt of NRA had a lower heritability (0.08 +/- 0.03). Genetic correlations (r(g)) suggested that lesions to the anterior region of the body 24 h after mixing were associated with reciprocal fighting (r(g) = 0.67 +/- 0.04), receipt of NRA (r(g) = 0.70 +/- 0.11), and to a lesser extent, delivery of NRA (r(g) = 0.31 +/- 0.06). Lesions to the center and rear were primarily genetically associated with receipt of NRA (r(g) = 0.80 +/- 0.05, 0.79 +/- 0.05). Genetic correlations indicated that pigs that engaged in reciprocal fighting delivered NRA to other animals (r(g) = 0.84 +/- 0.04) but were less likely to receive NRA themselves (r(g) = -0.41 +/- 0.14). A genetic merit index using lesions to the anterior region as one trait and those to the center or rear or both as a second trait should allow selection against animals involved in reciprocal fighting and the delivery of NRA. Positive correlations between LC 24 h and 3 wk after mixing were found, especially for lesions to the center and rear of the body, indicating that postmixing lesions are predictive of those received under more stable group conditions. As well as reducing immediate aggression at mixing, selection on postmixing LC is expected to have a long-term impact on injuries from aggression, even after dominance relationships are established.

Relationship between litter size and perinatal and pre-weaning survival in pigs

The objective of this study was to analyse the relationship between direct and maternal genetic effects on litter size and piglet survival. The analyses were performed on records from 26 564 Landrace litters and 15 103 Yorkshire litters from first parity dams in Finnish herds. The trivariate model fitted total number of piglets born, proportion alive at birth and proportion survived from birth until 3 weeks as traits of the litter. The model included direct genetic and maternal genetic effects for all traits. In Landrace pigs, maternal heritabilities were estimated to be 0·11 for total number born , 0·06 for proportion alive at birth, and 0·08 for proportion survived from birth until 3 weeks. The corresponding estimates for the Yorkshire breed were 0·14, 0·06 and 0·01. All heritability estimates of direct effects were below 0·05. In the Landrace breed, there was a negative correlation of ‐0·39 between maternal genetic effects on total number born and maternal genetic effects on proportion survived from birth until 3 weeks and a negative correlation of ‐0·41 between direct and maternal genetic effects on proportion survived from birth until 3 weeks. These correlations were not significant in the Yorkshire breed. The results show that selection for number born in total alone will lead to a deterioration in the maternal ability of sows. Selection for pre-weaning survival could be achieved by selecting on direct and maternal components jointly.

Nursing behaviour of sows during 5 weeks lactation and effects on piglet growth

Abstract The main goal of this study was to investigate the effect of sow nursing behaviour on piglet weight gain and within-litter variation (WLV) in piglet weight gain under as naturalistic conditions as possible. In order to achieve this, patterns of sow nursing behaviour and piglet weight gain were recorded during 5 weeks lactation. In addition, to be able to assess importance of sow behaviour on piglet growth more definitely, individual within-lactation repeatability of sow behaviour was also evaluated. Average piglet daily weight gain (ADG) and within-litter variation in weight gain during lactation were recorded by weighing the piglets of 21 individually penned, unrestrained Yorkshire sows on days 1, 4, 8, 15, 22 postpartum (PP) and at weaning (day 35±2). Nursing behaviour and sternal recumbency from five 24h periods (days 3, 6, 13, 20 and 30 postpartum) were described as frequency of successful nursings (SFREQ), frequency of unsuccessful nursings (USFREQ), total duration of all nursings (TOTDUR), percentage of nursings terminated by the sow (%SOW), average duration of sow-terminated nursings (SOWDUR) and percentage of observations when the sow was lying sternally (%STERN). With proceeding lactation, the only significant change in SFREQ was an increase on day 6. USFREQ increased to day 13, and then decreased towards the end of lactation. TOTDUR began decreasing after day 13, while SOWDUR decreased already after day 3. %SOW and %STERN both increased with proceeding lactation. All behavioural measures showed within-sow repeatability (first-order autoregression coefficient (AR(1))=0.39–0.73). Average piglet weight gain (ADG) was influenced positively by SFREQ ( P =0.02), while none of the other behavioural variables affected ADG. The effect of SFREQ on ADG was similar throughout lactation, the model estimated a 5.12g increase in ADG with one more successful nursing per 24h. Within-litter variation was not influenced by any of the selected variables. The results indicate that (i) nursing behaviour changes during lactation, according to a pattern suggesting an ongoing weaning process; (ii) sow behaviour is repeatable within-sow and within-lactation; (iii) a high frequency of successful nursings affects piglet growth positively also in sows that are not experimentally manipulated, and throughout the full course of lactation.

Aggressive and sexual behaviour of growing and finishing pigs reared in groups, without castration

Abstract Aggressive and sexual behaviour in entire males and females were studied on 408 pigs. The sum of aggressive interactions in the pen during routine feeding (ALP) was lowest in single-sex pens with females. ALP was higher at 132 than at 155 days. High ALP correlated with high average growth rate. Aggressive interactions in a competition test (IA) increased after slaughter of the three fastest-growing pigs in a pen (at 155 days), although the slaughtered pigs had initiated the most IA earlier (at 132 days). Entire male pigs displayed more sexual behaviour (mounting) than females. In 15% of entire males and 6% of females there were health problems specifically involving lameness or injured legs or feet. Five entire males and one female were euthanized in response to lameness or leg fracture. The rearing of entire male pigs may cause welfare problems, given their higher levels of aggression and sexual behaviour.

Genetic analysis of on-farm tests of maternal behaviour in sows

Abstract In this field-study, four behaviour traits were genetically evaluated as possible selection traits for improving piglet survival: the sow’s reaction to a piglet scream, the sow’s reaction to her piglets being handled, avoidance of and aggression towards the stockperson. The scream test was recorded on the first day after farrowing, and the other tests around day 4. Variance components were estimated using a linear-threshold model and Gibbs sampling. Recordings were done in 10 herds and the analyses of the tests included 741–1335 records on Swedish Yorkshire sows. The estimated heritability for the scream test was 0.06, the handling test had a heritability of 0.01, and fear and aggression both had a heritability of 0.08. No phenotypic relation between either of the behaviour tests and piglet mortality was found; however, there were moderate genetic correlations between response in the scream test and mortality of piglets born alive (−0.24) and between avoidance and mortality (0.37). This indicates that selection for a strong response in the scream test, or selection against sows that avoid humans would result in a correlated genetic improvement in piglet survival. Avoidance may reflect underlying fear, and selection for lower levels of fear in sows would improve both sow and piglet welfare.

Immunocastration reduces aggressive and sexual behaviour in male pigs

The aim of this study was to evaluate the effectiveness of a gonadotropin-releasing hormone (GnRH) vaccine, Improvac™ (Pfizer Ltd), in suppressing aggressive and sexual behaviour of male pigs. One hundred and thirty-six pigs were assigned to three treatments: entire male pigs (n = 64), immunocastration against GnRH (n = 48) and surgical castration (n = 24). Surgical castration was performed before the age of 1 week. Vaccination comprised two injections: the first injection was given 8 to 11 weeks before slaughter and the second injection 4 weeks before slaughter. After the second injection, immunocastrated pigs showed less non-violent social and aggressive behaviours than entire male pigs of the same age. Mounting was reduced to the same low level as observed in surgically castrated pigs, and more immunocastrated pigs were without skin lesions compared with entire male pigs. Pigs that received the second injection only 1 week before the observation day did not differ significantly in behaviour from those that received the injection 3 weeks before the observation day. Thus, the behaviour seems to change soon after the second injection and these changes remain until slaughter.

Survival of Swedish Landrace and Yorkshire sows in relation to osteochondrosis: a genetic study.

A genetic study was carried out to: (1) conduct a genetic analysis of longevity of Swedish Yorkshire sows, (2) study the environmental and genetic factors that influence the presence and severity of osteochondrosis, and (3) investigate the relationship between breeding values for osteochondrosis and longevity of sows. The data for the longevity analyses were extracted from the Swedish litter-recording scheme data bank (Quality Genetics, former Scan Avel HB). After editing original data, records of 9814 Yorkshire sows with 7553 (77%) uncensored and 2261 (23%) censored born 1986 through 1997 were used in the analyses. Litter size at first and last farrowing, age at first farrowing, backfat thickness, daily gain and weight at completion of performance test (~170 days) were included as fixed effects in all analyses. The combination of herd-year effect was treated as fixed or random, time-independent or time-dependent in different analyses. Sire effect was considered as the source of genetic variation and thus a sire model was used. The analyses of osteochondrosis were based on information on 14 388 Landrace and 14 458 Yorkshire pigs from the Swedish pig progeny-testing scheme, recorded from 1987 through 1997. The birth herd and the combination of sex, testing station, year and month for start of test were included as fixed effects in the statistical model. Variance and covariance components for osteochondrosis recorded at elbow and knee joints were estimated in a bivariate animal model by the restricted maximum likelihood method within each breed. In the survival analyses (Yorkshire sows), the fixed effects of herd-year (when it was treated as fixed effect), litter size at first and at last farrowing, age at first farrowing, backfat and gain at completion of performance test were highly significant ( P P P