E. Strandberg

Genotype by Environment Interaction in Nordic Dairy Cattle Studied Using Reaction Norms

Genotype by environment interaction for production and fertility was studied by use of a reaction norm model. Milk recording data, comprising 927 929 records, were analysed to predict reaction norms for young bulls of the Nordic Red dairy breeds. Random regressions were estimated for each bull, regressing phenotypic values of daughters on herd environment. The phenotypic measures were 305 days kg protein production and days open in first lactation. The herd environment was defined as the herd-year average of protein production and days open, respectively. Heritability of protein production and days open and genetic correlation between the two traits were estimated as functions of the herd environment. The results showed that the genetic parameters change over environments, which are measured on a continuous scale across countries. Grouping of observations is avoided and thereby the problem of genetic connectedness between groups or countries may be avoided. Although significant genetic variation for the slope of the reaction norm was found, there was little reranking of sires, except between extreme environments. More appropriate models and methods need to be developed for further studies of genetic variation in reaction norms.

Genetic and Environmental Correlations Among Female Fertility Traits and Milk Production in Different Parities of Swedish Red and White Dairy Cattle

The main objective of this study was to estimate genetic correlations between fertility and production traits in first, second and third lactations as well as between fertility traits measured in the same way at different ages. The fertility traits studied were: number of inseminations per service period, number of treatments for reproductive disturbances, interval between first and last inseminations, interval between calving and first insemination, and interval between calving and last insemination. Early milk production was measured as the average of the energy-corrected milk yield at the second and third monthly testdays in a lactation. The number of records was approximately 450 000, 350 000, 180 000 and 75 000 in the heifer period, first, second, and third lactations, respectively. A linear, trivariate model that included the effects of herd-year, year, month, age and sire of the cow was applied. To reduce the effect of ongoing selection, 305-days kg protein production in first lactation was included as a variate in all of the analyses. Correlations between the herd-year effects indicated that factors of herd-year level conducive to increased production had a tendency to increase the number of inseminations as well as the number of reproductive treatments, although there was an earlier start and termination of the insemination period. Genetic correlations between fertility traits and production were in the range of 0.2-0.4, all of them unfavourable and higher at later parities. The genetic correlations between fertility traits in the heifer period and the same traits in first lactation were 0.7. Genetic correlations between the first and second lactation varied between 0.7 and 0.9, and between the second and third lactation they were all 0.9 or higher. In conclusion, fertility and production traits need to be selected for simultaneously if fertility is going to be maintained along further genetic improvement on production, and such selection should include fertility results from lactating cows.

The genetic contribution to canine personality.

The domestic dog may be exceptionally well suited for behavioral genetic studies owing to its population history and the striking behavior differences among breeds. To explore to what extent and how behavioral traits are transmitted between generations, heritabilities and genetic correlations for behavioral traits were estimated in a cohort containing over 10 000 behaviorally tested German shepherd and Rottweiler dogs. In both breeds, the pattern of co‐inheritance was found to be similar for the 16 examined behavioral traits. Furthermore, over 50% of the additive genetic variation of the behavioral traits could be explained by one underlying principal component, indicating a shared genetic component behind most of the examined behavioral traits. Only aggression appears to be inherited independently of the other traits. The results support a genetic basis for a broad personality trait previously named shyness–boldness dimension, and heritability was estimated to be 0.25 in the two breeds. Therefore, breeds of dogs appear to constitute a valuable resource for behavioral genetic research on the normal behavioral differences in broad personality traits.

Relationship between somatic cell count and milk yield in different stages of lactation

The association between somatic cell count (SCC) and daily milk yield in different stages of lactation was investigated in cows free of clinical mastitis (CM). Data were recorded between 1989 and 2004 in a research herd, and consisted of weekly test-day (TD) records from 1,155 lactations of Swedish Holstein and Swedish Red cows. The main data set (data set A) containing 36,117 records excluded TD affected by CM. In this data set, the geometric mean SCC was 55,000 and 95,000 cells/mL in primiparous and multiparous cows, respectively. A subset of data set A (data set B), containing 27,753 records excluding all TD sampled in lactations affected by CM, was created to investigate the effect of subclinical mastitis (SCM) in lactations free of CM. Daily milk yields were analyzed using a mixed linear model with lactation stage; linear, quadratic and cubic regressions of log(2)-transformed and centered SCC nested within lactation stage; weeks in lactation; TD season; parity; breed; pregnancy status; year-season of calving; calving, reproductive, metabolic and claw disorders; and housing system as fixed effects. A random regression was included to further improve the modeling of the lactation curve. Primiparous and multiparous cows were analyzed separately. The magnitude of daily milk loss associated with increased SCC depended on stage of lactation and parity, and was most extensive in late lactation irrespective of parity. In data set A, daily milk loss at an SCC of 500,000 cells/mL ranged from 0.7 to 2.0 kg (3 to 9%) in primiparous cows, depending on stage of lactation. In multiparous cows, corresponding loss was 1.1 to 3.7 kg (4 to 18%). Regression coefficients of primiparous cows estimated from data set B were consistent with those obtained from data set A, whereas data set B generated more negative regression coefficients of multiparous cows suggesting a higher milk loss associated with increased SCC in lactations in which the cow did not develop CM. The 305-d milk loss in the average lactation affected with SCM was 155 kg of milk (2%) in primiparous cows and 445 kg of milk (5%) in multiparous cows. It was concluded that multiparous cows in late lactation can be expected to be responsible for the majority of the herd-level production loss caused by SCM, and that preventive measures need to focus on reducing the incidence of SCM in such cows.

Estimates of longevity and causes of culling and death in Swedish warmblood and coldblood horses.

Data on several different horse populations were analysed and compared regarding length of life and diseases or injuries leading to death or culling. In order to include information for horses still alive, a failure time (survival) analysis was used. The first material included 1847 warmblood horses born between 1968 and 1982, that had participated in the Swedish Riding Horse Quality Test (RHQT) as 4-year-olds. The next two materials included 344 warmblood and 204 coldblood horses owned by the Swedish Cavalry Horse Foundation (CHF), born between 1970 and 1975. The last population consisted of 481 warmblood brood-mares born between 1965 and 1967. According to this study it was important to estimate the median length of life separately for each sex. For warmblood brood-mares and mares that had participated in the RHQT, comparable figures of 18.6 and 18.3 years were found. Close agreement was also found between geldings of the CHF and males that had participated in the RHQT; the estimates were 14.7 and 13.9 years, respectively. There was a positive trend in the median length of life over time for horses that had participated in the RHQT, and the median length-of-life curve increased more steeply for mares than for males. This study showed a longer median length of life for coldblood geldings, 17.6 years, than for the mares, 16.4 years. The most common causes of death of warmblood horses were diseases of the musculoskeletal system (56-57%), respiratory diseases (8-9%), diseases of the digestive system (5-6%) and accidents (3-9%). The primary causes of death of coldblood horses were temperamental disorders (23%), diseases of the musculoskeletal system (14%) and hoof diseases (8%).

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.

Genetic correlations between field test results of Swedish Warmblood Riding Horses as 4-year-olds and lifetime performance results in dressage and show jumping

Abstract The main objective of this study was to estimate genetic correlations between traits of young sport horses (4 years old) evaluated in the Swedish Riding Horse Quality Test (RHQT) and later competition results in dressage and show jumping. The data comprised 3708 Warmblood horses born between 1968 and 1982 that had participated in the RHQT as 4-year-olds and 25 605 horses born between 1953 and 1995 with competition records. According to the criteria between 1206 and 1879 horses were common to this two files and were available for the estimations of the genetic correlations. Competition performance traits were cumulative points and cumulative placings received during a horse’s lifetime, and a log 10 transformation was used to achieve a more normal distribution of the data. Genetic correlations between gait traits scored in the RHQT and competition results in dressage were favourable, in the range 0.63–0.75, and between jumping traits scored in the RHQT and results in show jumping 0.83–0.93. Estimated heritabilities for gait and jumping traits scored in the RHQT were in the range 0.09–0.27 and 0.10–0.18, respectively. Estimated heritabilities for the cumulative points and cumulative placings in dressage and show jumping were 0.17/0.16 and 0.23/0.27, respectively. Thus, the results from the RHQT have proved to be useful for early genetic evaluation and selection of both mares and stallions for sport performance traits.

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.

Factors affecting length of productive life in Swedish commercial sows1

The objective of this study was to investigate factors that might influence the length of productive life in Swedish crossbred (Landrace x Yorkshire) sows. The data set consisted of 20,310 sows farrowing between 2001 and 2004 in 21 commercial piglet-producing herds. Productive life (PL) was defined as the number of days between first farrowing and removal or termination of data collection. In addition to the overall risk analysis of PL, another 4 longevity traits were analyzed (competing risk analyses): reproductive disorder-determined length of PL (RPL), udder problem-determined length of PL (UPL), lameness-determined length of PL (LPL), and mortality-determined length of PL (MPL). Analyses were performed by using survival analysis, applying a Weibull model with 6 time-dependent and 1 time-independent variable (age at first farrowing). The factor with the largest contribution to the likelihood function for PL was days after farrowing, followed by parity, the herd x year combination, the total number of piglets born, days between weaning and next farrowing, farrowing month, and age at first farrowing. For all 4 competing risk traits, the factors contributing most to the likelihood function were days after farrowing, the herd x year combination, and parity, with a varied order between traits. The hazard for removal was greatest 30 to 40 d after farrowing (after weaning) for PL, UPL, and LPL (P < 0.001). However, for MPL the hazard was greatest just after farrowing (0 to 10 d), and for RPL the hazard peaked at 70 to 100 d after farrowing. The hazard for removal was, compared with parity 1, less in parities 2 to 7 and greater from parity 8 for PL (P < 0.001). The hazard was greatest in parity 1 (P < 0.01) for RPL, UPL, and LPL, whereas for MPL the hazard increased with greater parity number and was markedly greater from parity 9 (P < 0.001). Sows with litters of 9 piglets or less had a greater hazard for removal than sows with litters of 12 to 13 piglets (P < 0.001). Intervals between 120 and 122 d from weaning to the next farrowing showed the lowest hazard for removal (P < 0.001). The influence of farrowing month displayed no clear pattern for PL. Sows of 14 mo or older at their first farrowing had a 20% greater hazard for removal than younger sows (P < 0.001). The hazard for removal was greater for smaller litters in all parities but was more accentuated in greater parities. Overall, days after farrowing was the main risk factor for sow removal. Removal hazard was greatest shortly after weaning, and this peak increased with greater parity number.

Genetic analysis of functional, fertility-, mastitis-, and production-determined length of productive life in Swedish dairy cattle

Abstract Our objective was to estimate genetic parameters for different definitions of longevity: (1) length of productive life (PL), all cows culled before the end of data collection were considered as uncensored; (2) fertility-determined PL (FPL); (3) mastitis-determined PL (MPL); and (4) production-determined PL (PPL): only cows that were culled due to fertility problems, mastitis-related problems, or production, respectively, were uncensored. Survival analysis was used and the hazard was modelled as: a random time-dependent (TD) effect of herd–year–season, fixed TD effects of parity by year–season, parity by stage of lactation, parity by the cows peak yield deviation from herd–year–mates (not for PPL), parity by age at first calving, and random effects of the cows sire and maternal grandsire. Apart from in first lactation, there was a high risk of culling during the first 10 days of lactation for PL and MPL. Thereafter the culling risk decreased abruptly, and then increased steadily by stage of lactation. For FPL, the culling risk was very low up to 180 days of lactation. The risk of being culled due to mastitis was increased between 180 and 270 days of lactation. The risk of being culled due to low production was low during the first lactation and in later lactations the highest risk was between 180 and 270 days of lactation. For PL, FPL, and MPL, there was a general increase in culling risk with increasing parity, and cows in the lowest peak yield classes ran a far higher risk of being culled. Heritability estimates were 6.3, 10.0, 17.9, and 24.9% for PL, FPL, MPL, and PPL, respectively. Approximate genetic correlations between fertility, mastitis, and milk production traits and FPL, MPL and PPL, respectively, were higher than corresponding correlations with PL. The expected selection response in fertility and mastitis from indirect selection for FPL and MPL was lower than from direct selection, but higher than if PL was used as selection index trait.