BackgroundLongevity expressed as the number of days between birth and death is a trait of great importance for both human and animal populations. In our analysis we use dairy cattle to demonstrate how the association of Single Nucleotide Polymorphisms (SNPs) located within selected genes with longevity can be modeled. Such an approach can be extended to any genotyped population with time to endpoint information available. Our study is focused on selected genes in order to answer the question whether genes, known to be involved into the physiological determination of milk production, also influence individual's survival.ResultsGenerally, the highest risk differences among animals with different genotypes are observed for polymorphisms located within the leptin gene. The polymorphism with a highest effect on functional longevity is LEP-R25C, for which the relative risk of culling for cows with genotype CC is 3.14 times higher than for the heterozygous animals. Apart from LEP-R25C, also FF homozygotes at the LEP-Y7F substitution attribute 3.64 times higher risk of culling than the YY homozygotes and VV homozygotes at LEP-A80V have 1.83 times higher risk of culling than AA homozygotes. Differences in risks between genotypes of polymorphisms within the other genes (the butyrophilin subfamily 1 member A1 gene, BTN1A1; the acyl-CoA:diacylglycerol acyltransferase 1 gene, DGAT1; the leptin receptor gene, LEPR; the ATP-binding cassette sub-family G member 2, ABCG2) are much smaller.ConclusionsOur results indicate association between LEP and longevity and are very well supported by results of other studies related to dairy cattle. In view of the growing importance of functional traits in dairy cattle, LEP polymorphisms should be considered as markers supporting selection decisions. Furthermore, since the relationship between both LEP polymorphism and its protein product with longevity in humans is well documented, with our result we were able to demonstrate that livestock with its detailed records of family structure, genetic, and environmental factors as well as extensive trait recording can be a good model organism for research aspects related to humans.

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Morek-Kopeć M., Zarnecki A. (2017): Genetic evaluation for functional longevity in Polish Simmental cattle. Czech J. Anim. Sci., 62, 276-286.The Weibull proportional hazards model was applied for genetic evaluation of functional longevity in Polish Simmentals. Data consisted of production and disposal records for 12 527 Simmental cows, daughters of 294 sires, calving for the first time from 1995 to 2014 in 286 herds. Length of productive life of cows was calculated as number of days from the first calving to culling or censoring. Average length of productive life of 4462 cows with complete (uncensored) survival records was 1198 days (39.3 months); mean censoring time for the remaining 8065 cows was 1093 days (35.8 months). Functional longevity was defined as length of productive life corrected for production. The model included time-independent fixed effect of age at first calving, time-dependent fixed effects of year-season, parity-stage of lactation, annual change in herd size, relative fat yield and protein yield, and random herd-year-season and sire effects. Likelihood ratio tests showed a highly significant impact of all fixed effects on longevity, except for relative fat yield. Estimated sire variance was 0.069, resulting in the equivalent (accounting for censoring level) heritability of 0.09. Standardized relative breeding values (RBV) ranged from 71 to 139 (mean 101.4, SD 9.12). Average reliability of RBVs was 0.47. Moderate heritability supports the possibility of effective selection for functional longevity, which will be included in the total selection index for Polish Simmentals.

Longevity is one of the functional traits that considerably affect dairy herd profitability. A Weibull proportional hazards model was used to evaluate the impact of difficult calvings and calf stillbirths on cow functional longevity, defined as length of productive life corrected for milk production. The data for analysis comprised calving ease and calf mortality scores of 2,163,426 calvings, 34.4% of which came from primiparous cows. The percentage of male calves was 53.4%. Calving ease was scored as “without assistance” (34.44%), “with assistance” (62.03%), “difficult—hard pull” (3.39%), and “very difficult, including caesarean section” (0.14%). Calf mortality scores were “live born” (94.21%) and “stillborn or died within 24 h” (5.79%). The Weibull proportional hazards model included classes of calving ease or calf mortality scores × parity (1, ≥2) × sex of calf as time-dependent fixed effect. The model also included time-dependent fixed effects of year × season, parity × stage of lactation, annual change in herd size, fat yield and protein yield, time-independent fixed effect of age at first calving, and time dependent random herd × year × season. In first-parity cows, very difficult birth of a bull or heifer increased the relative risk of culling, respectively, 2.18 or 1.26 times as compared with calving without assistance. In later parities, the relative risk of culling related to very difficult calving was 2.0 times (for male calves) and 1.33 times (for female calves) higher than the relative risk of culling associated with calving without assistance. Calf mortality showed a negative impact on longevity in both heifers and cows. First-parity stillbirth increased the relative risk of culling depending on sex of calf by 18% in females and by 15% in males; in later parities the increase of the relative risk of culling was lower (by 7% for females, 9% for males). Difficult calvings and their consequences, especially in primiparous cows, may negatively influence dairy herd profitability by reducing the length of cows’ productive life.

Type classification records of 87,352 Black-and-White cows collected between 1995 and 2000 were analysed. The linear evaluation system included 15 traits scored from 1 to 9, height measured at rump, and the final score made of four breakdown traits. Linearly scored traits varied much more than the remaining traits, ranging from 15.7% for body depth to 22.7% for central ligament. The mean scores for teat length and fore teat placement were much lower than the scores for muscularity, dairy character and chest width. The phenotypic correlations between traits were, in general, smaller than the genetic correlations. Highest heritability was obtained for height measure at rump (0.463). Heritabilities of breakdown traits were high to moderate. The highest was heritability of size (0.416). Heritability of final score reached almost 0.30, slightly lower (0.291) was heritability of conformation and dairy character, and the lowest was heritability of udder and legs. Heritabilities of linear scores of 9 traits ranged between 0.204 and 0.301, of the four traits between 0.1 to 0.2, and in foot angle was only 0.074. The final score was genetically correlated with its component traits, especially with conformation and dairy character (0.850). Dairy character was correlated with body depth and chest width. Some of the udder traits were genetically correlated, especially udder height with udder width and central ligament with rear udder height and udder depth. The estimated parameters indicate that some conformation traits possibly can be improved.