Reproduction in Domestic Animals

90 B Berglundtraits calving performance traits are influenced by aneffect of the mother and a direct effect of the young(Steinbock et al. 2003; Hansen et al. 2004) and it may bedifficult to correctly estimate these (co)variances. To getselection response in reproduction traits a well developedrecording scheme is needed and a breeding structureallowing large daughter group sizes.Several sub-traitsReproduction, especially female fertility, is a complextrait composed of several sub-traits. Thus it is importantto include all important aspects of fertility to achieve agood and expected selection response. A challenge indoing this is the data collection and the quality of data.Traditionally, most fertility traits are based on calvingand insemination data and each trait has its strengthsand weaknesses. For female fertility there are measuresreflecting the ability to resume oestrous cycles aftercalving and the ability to conceive, or measurescombining these abilities like calving to last insemination(CLI), often also called days open (DO). Informationabout treatments and culling for reproductivedisorders are recorded and used mainly in the Nordiccountries. In Sweden scores for heat symptoms arerecorded as well. Heat detection plays a considerablerole for the economy. A visible manifestation of oestrusand a high oestrus detection rate is important especiallywhen using AI and in countries where hormones foroestrus synchronization are not generally used. Dobsonet al. (2007) reported from the UK that the number ofoestrous animals standing-to-be-mounted has declinedfrom 80% to 50% over the past 30–50 years.Antagonistic genetic correlations to other traitsThe antagonistic relationship between fertility and milkproduction is well-known and was shown already byJanson and Andre´ asson (1981). These correlations wereconfirmed in studies by Roxstro¨ m et al. (2001b), whereunfavourable genetic correlation for, e.g. number ofinseminations per service period, interval from calvingto first AI and treatments for reproductive disorders tomilk production was shown. The correlations rangedfrom 0.2 to 0.4, increasing with lactation number,possibly as a consequence of a higher energy demandwith increasing production level and steeper lactationcurves. Due to the antagonistic genetic correlation tomilk production, undesirable trends are expected forthe reproductive traits if they are not included in thebreeding goal. Even if included in the breeding objectivethere is a risk for deterioration of this trait due to thelow heritability if too small a breeding goal weight ordaughter groups are used. Ethic values (cow welfare,consumer preference, etc.) should be put into thebreeding goal weight and those are not easily accessible.Moreover, there are unfavourable correlations amongthe reproduction traits that are important to consider.Negative energy balance and reproductionA top producing cow might not cope with the energyrequirements for both milk production and maintainedreproduction and health even though the cows have acapacity to mobilize from their energy reserves. In ourstudies of Swedish Red (SRB) and Swedish Holsteins(SH) we have seen that SH has a thinner layer ofsubcutaneous fat than SRB which may be important inthis aspect (Hjertén 2006). A negative energy balance isassociated with inferior embryo quality. A review paperon metabolic changes and embryo quality was given byChagas et al. (2007). Hayhurst et al. (2007a) found asignificant genetic variation in embryo quality andestimated a heritability of 0.13 for this trait, implyinga possibility of genetically selecting cattle with inherentquality to produce high quality embryos.Body condition score (BCS) is an internationallyaccepted, rapid, inexpensive and non-invasive method ofestimating body energy reserves in dairy cattle (Berryet al. 2007). Even though mainly used for managementpurposes, BCS may also add to the information ingenetic evaluations, especially when data on more directtraits are lacking. BCS is moderately heritable (0.09–0.45) and favourably correlated to fertility and survival.BCS is used as a predictor trait for genetic merit forfertility in some countries, e.g. the Netherlands (De Jong2005) and in Irish and UK cattle (Berry et al. 2007).Current Status in Breeding ProgrammesThe general breeding goal for the reproduction of cows israther similar in different countries and may be formulatedas follows: cows that return to normal cyclicity earlyafter calving show strong and regular heats, and whichconceive when inseminated at a correct time. Furthermore,the cow should carry her pregnancy to term, have agood calving ability and give birth to viable calves.Female fertilityEarly studies by Janson (1980) showed that even thoughheritability for fertility traits was low, the additivegenetic variation was shown to be substantial. Furthermore,the importance of including both interval andpregnancy measures at different ages in the geneticevaluation for fertility was underlined. These resultswere later confirmed in large field studies by Roxstro¨ met al. (2001a,b). The Nordic countries have traditionallyrecorded and performed genetic evaluation for a broadrange of functional traits including reproduction, but inrecent years many other countries have also implementedgenetic evaluation for these traits. Thus, therelative emphasis of dairy cattle breeding objectives hasgradually shifted from production to functional traitssuch as reproduction during the past couple of decades(Miglior et al. 2005).Breeding values for daughter fertility were introducedin Sweden as early as 1972, and have since been used inselection. In the Nordic countries, the integration of cowdata bases (pedigree, milk recording, AI and diseasedata) has facilitated selection for reproductive traits.Three of the Nordic (Denmark, Finland and Sweden)breeding organizations have had a joint genetic evaluationand breeding programme since 2005 (for moreinformation see http://www.nordicebv.info). The Nordicfertility index includes the traits number of AI per serviceÓ 2008 The Author. Journal compilation Ó 2008 Blackwell Verlag