Reproduction in Domestic Animals

Reprod Dom Anim 43 (Suppl. 2), 89–95 (2008); doi: 10.1111/j.1439-0531.2008.01147.xISSN 0936-6768Genetic Improvement of Dairy Cow Reproductive PerformanceB BerglundDepartment of Animal Breeding and Genetics, Swedish University of Agricultural Sciences and Centre for Reproductive Biology in Uppsala, Uppsala,SwedenContentsThe welfare of cow along with profitability in production areimportant issues in sustainable animal breeding programmes.Along with an intense ⁄ intensive selection for increased milkyield, reproductive performance has declined in many countries,in part due to an unfavourable genetic relationship. Thelargely unchanged genetic trend in female fertility and calvingtraits for Scandinavian Red breeds shows that it is possible toavoid deterioration in these traits if they are properly consideredin the breeding programme. Today’s breeding is internationalwith a global selection and extensive use of the best bulls.The Nordic countries have traditionally recorded and performedgenetic evaluation for a broad range of functional traitsincluding reproduction. In recent years many other countrieshave also implemented genetic evaluation for these traits. Thus,the relative emphasis of dairy cattle breeding objectives hasgradually shifted from production to functional traits such asreproduction. Improved ways of recording traits, e.g. physiologicalmeasures, early indicator traits, assisted reproductivetechniques and increased knowledge of genes and their regulationmay improve the genetic selection strategies and havelarge impact on present and future genetic evaluation programmes.Extensive data bases with phenotypic recordings oftraits for individuals and their pedigree are a prerequisite.Quantitative trait loci have been associated to the reproductivecomplex. Most important traits, including reproduction traitsare regulated by a multitude of genes and environmental factorsin a complex relationship, however. Genomic selection mighttherefore be important in future breeding programmes. Informationon single nucleotide polymorphism has already beenintroduced in the selection programmes of some countries.IntroductionThere are strong motives for including reproduction ingenetic selection programmes. A good reproductiveperformance is crucial for economic as well as ethicalreasons. Without reproduction there will be no animalproduction. The unfavourable genetic correlation withmilk production has led to a decline in reproduction indairy cattle, at least in part due to an insufficientconsideration of this trait when selecting for a highermilk production. There are several reports that theincreasing use of Holstein genetics has caused decliningfertility as well as calving performance during the latestdecades (e.g. Berglund and Philipsson 1992; Royal et al.2000; Lucy 2001; Hansen et al. 2004). This has causeddeterioration in fertility in countries that heavily used thisbreed even if they have had reproductive performanceboth in the breeding goal and in the selection criteria. Forinstance, in Swedish Holsteins (SH), daughter fertilityhas fallen by approximately 1.2 index units per year overthe last fifteen years until now (Lindhe´ B, 2007: SvenskAvel, Skara, Sweden, personal communication), whereasthe Swedish Red breed (SRB), with similar milk yieldlevels and genetic trend, has largely maintained fertility.A national breeding programme considering reproductiontraits for more than three decades may explain this.However for Holsteins the inclusion of fertility in theSwedish breeding goal has not been enough to withstandthe large imports of genetic material from countries thathave low, or no weighting on fertility in their breedingobjective.In 2006 the World Holstein Friesian Federationinitiated a survey of the status on fertility in the Holsteinpopulation around the world. The conclusion from thissurvey was that fertility is a problem and actions need tobe taken both internationally and within each country(Sørensen et al. 2007). Many countries have implementedgenetic evaluation for fertility traits in recentyears. More traits are gradually being evaluated andmore sophisticated evaluation methods are being implemented.Maybe the decline in fertility now has levelledout and reached a plateau, as was concluded from aninternational conference on fertility in dairy cows held inLiverpool, 2007 (Crowe 2007, personal communication).Still the low level of reproductive performance is aproblem. Reproduction problems are among the mostcommon reason for culling in dairy production. This isthe major cause for involuntary culling, e.g. in Swedishdairy cattle (Swedish Dairy Association 2007).Today’s breeding is international, intensive and usesmodern reproductive and molecular genetic techniques.The welfare of cows along with profitability in productionare important issues in sustainable animal breedingprogrammes. Nielsen et al. (2006) suggested that whendefining breeding goals for sustainable production,breeding organizations should predict the selectionresponse based on market economic value and addnon-market value for traits with unacceptable selectionresponses. New ways of measuring, recording andanalysing traits, new reproductive techniques andincreased knowledge of genes and their regulation mayimprove the genetic selection strategies and have a largeimpact on genetic evaluation programmes. This paperwill focus on the genetic improvement of the femalefertility and calving traits.Difficulties in Selection for ReproductionMany reproduction traits are difficult to handle inparameter estimation and genetic evaluation. In generalheritabilities are low, usually less than 5%, mainly due toa large influence of management and environmentaleffects. Most traits are not normally distributed and havecensored records, which complicates the analysis of thetraits. In addition to the other features of the reproductiveÓ 2008 The Author. Journal compilation Ó 2008 Blackwell Verlag