Value of the Dutch Holstein Friesian germplasm collection to increase genetic variability and improve genetic merit

National gene bank collections for Holstein Friesian (HF) dairy cattle were set up in the 1990s. In this study, we assessed the value of bulls from the Dutch HF germplasm collection, also known as cryobank bulls, to increase genetic variability and improve genetic merit in the current bull population (bulls born in 2010–2015). Genetic variability was defined as 1 minus the mean genomic similarity (SIMSNP) or as 1 minus the mean pedigree-based kinship (fPED). Genetic merit was defined as the mean estimated breeding value for the total merit index or for 1 of 3 subindices (yield, fertility, and udder health). Using optimal contribution selection, we minimized relatedness (maximized variability) or maximized genetic merit at restricted levels of relatedness. We compared breeding schemes with only bulls from 2010 to 2015 with schemes in which cryobank bulls were also included. When we minimized relatedness, inclusion of genotyped cryobank bulls decreased mean SIMSNP by 0.7% and inclusion of both genotyped and nongenotyped cryobank bulls decreased mean fPED by 2.6% (in absolute terms). When we maximized merit at restricted levels of relatedness, inclusion of cryobank bulls provided additional merit at any level of mean SIMSNP or mean fPED except for the total merit index at high levels of mean SIMSNP. Additional merit from cryobank bulls depended on (1) the relative emphasis on genetic variability and (2) the selection criterion. Additional merit was higher when more emphasis was put on genetic variability. For fertility, for example, it was 1.74 SD at a mean SIMSNP restriction of 64.5% and 0.37 SD at a mean SIMSNP restriction of 67.5%. Additional merit was low to nonexistent for the total merit index and higher for the subindices, especially for fertility. At a mean SIMSNP of 64.5%, for example, it was 0.60 SD for the total merit index and 1.74 SD for fertility. In conclusion, Dutch HF cryobank bulls can be used to increase genetic variability and improve genetic merit in the current population, although their value is very limited when selecting for the current total merit index. Anticipating changes in the breeding goal in the future, the germplasm collection is a valuable resource for commercial breeding populations.</p

Limits to genetic rescue by outcross in pedigree dogs

Outcrossing should reduce inbreeding levels and associated negative effects in highly inbred populations. In this study, we investigated the effectiveness of different outcrossing schemes using computer simulations. The inbreeding rate estimated for a 25-year period of 2.1% per generation in a highly inbred dog breed reduced to 1.8% when a single litter was produced by an outcross without backcrosses. To reduce the inbreeding rate below 1%, more than eight of the 14 litters born yearly in the recipient breed had to be outcrossed. However, outcrossing in pedigree dogs is usually followed by backcrossing and generally involves one or a few litters. Backcrossing reduced the effect of outcrossing considerably. When two litters were produced by an outcross followed by one generation of backcross, the inbreeding rate was 2.0% per generation. Continuously outcrossing was more effective than a single or a few outcrosses. When each newborn litter during 25 years had a 5% chance of being produced by an outcross, the inbreeding rate reduced to −0.2%. To investigate the possibility that new alleles were introduced from the donor population into the recipient population, the fate of different type of alleles (varying from completely lethal to beneficial) before and after an outcross was investigated by first simulating 80 years of natural selection prior to the outcross and then different types of outcross. Because natural selection reduced the frequency of lethal alleles before outcrossing, the introduction of a lethal allele that was segregating in the donor breed but not in the recipient breed occurred rarely. Introduction of slightly detrimental alleles or neutral alleles occurred more frequently. In conclusion, outcrossing only had a limited short-term effect unless repeated continuously. Nevertheless, it may help to buy time in which the population structure can be changed so that the effective population size increases.</p

Analysis of social behaviors in large groups: simulation and genetic evaluation

Harmful social interactions, such as injurious feather pecking in poultry and tail biting in swine, reduce both animal welfare and efficiency. While these traits are heritable, application of breeding is still limited due to the lack of proper genetic models and precise phenotyping methods for large groups. In the near future, large scale longitudinal data on social interactions will become available thanks to developments in computer vision and artificial intelligence. Here we present models to simulate and analyze such data, which are an extension of the classic social genetic model. Latent traits were defined to represent the tendency of individuals to be engaged in behavioral interactions, distinguishing performer and recipient effects. Binary interaction records were simulated and subsequently analyzed using generalized linear mixed models. Results show that high accuracies of estimated breeding values can be obtained (0.4-0.7), despite the low observed-scale heritability of the binomial trait (0.05-0.2). We conclude that our model can be promising for breeding value estimation for social traits in large groups

Inbreeding depression in livestock: comparing trait groups and inbreeding measures

Inbreeding depression has been documented for many livestock populations. We compared inbreeding depression estimates (1) between trait groups, and (2) between different pedigree-based and genomic inbreeding measures. Inbreeding was found to affect all sorts of traits to a similar extent, independent of heritability and of whether a trait is a primary fitness trait or not. Inbreeding depression estimates were moderately to highly correlated between different pedigree-based and genomic inbreeding measures, but those based on genomic measures tended to have lower P-values, suggesting more power to detect inbreeding depression with genomic measures (assuming there is a true inbreeding depression effect). Among different genomic measures (based on genomic relationship matrix, regions of homozygosity, or percentage of homozygous markers), there were no consistent differences in P-values

Genomic selection and inbreeding and kinship in Dutch-Flemish Holstein Friesian cattle

Since 2009, genomic selection (GS) has been widely applied in Holstein Friesian (HF) breeding programs. In this study, we evaluated how the introduction of GS in the Dutch-Flemish HF breeding program has affected inbreeding and kinship trends, using both pedigree-based and genomic measures. Rates of inbreeding and kinship for artificial insemination (AI) bulls increased with the introduction of GS, from 0.1-0.7% in 2003-2009 to 1.6-2.5% in 2009-2015. Rates of inbreeding and kinship for cows also increased with GS, although they were lower than for AI-bulls (i.e. 0.79-1.14% in 2009-2017). Levels of identical by state (IBS), which include relatedness due to both recent and distant common ancestors, increased faster than levels of identical by descent (IBD), which include only recent inbreeding and kinship. Accumulation of inbreeding varied substantially across the genome over time, with specific regions showing a striking increase in inbreeding since the introduction of GS. These findings emphasize the need for efficient genomic management of inbreeding in GS-schemes

Genomic selection and inbreeding and kinship in Dutch-Flemish Holstein Friesian cattle

Since 2009, genomic selection (GS) has been widely applied in Holstein Friesian (HF) breeding programs. In this study, we evaluated how the introduction of GS in the Dutch-Flemish HF breeding program has affected inbreeding and kinship trends, using both pedigree-based and genomic measures. Rates of inbreeding and kinship for artificial insemination (AI) bulls increased with the introduction of GS, from 0.1-0.7% in 2003-2009 to 1.6-2.5% in 2009-2015. Rates of inbreeding and kinship for cows also increased with GS, although they were lower than for AI-bulls (i.e. 0.79-1.14% in 2009-2017). Levels of identical by state (IBS), which include relatedness due to both recent and distant common ancestors, increased faster than levels of identical by descent (IBD), which include only recent inbreeding and kinship. Accumulation of inbreeding varied substantially across the genome over time, with specific regions showing a striking increase in inbreeding since the introduction of GS. These findings emphasize the need for efficient genomic management of inbreeding in GS-schemes