Reproduction in Domestic Animals

Genetic Improvement of Dairy Cow Reproductive Performance 91period for heifers (h) and cows (c), interval from calvingto first AI (c), interval from first to last AI (h, c) andreproductive treatments (c). Since the mid 1990s geneticevaluation for fertility has gradually been introduced inseveral countries, e.g. the Netherlands (Hoekstra et al.1994), UK (Wall et al. 2003) and US (VanRaden et al.2004). An international genetic evaluation for fertilitytraits was introduced for Holstein populations inFebruary 2007 by Interbull and an evaluation of fertilityin the other main breeds of the Interbull membercountries is under development (Jorjani 2007) (for moreinformation see http://www.interbull.org).Genetic trend for fertilityLindhe´ and Philipsson (2001) found a clear unfavourablegenetic trend in female fertility for SwedishHolsteins and a slightly favourable genetic trend forthe Swedish Red breed. In the Norwegian Red breed notrend or a slightly favourable genetic trend for fertilitytraits was found (Chang et al. 2006). Traditional breedingstrategies have been very successful in selecting highyielding dairy cows (Fig. 1a,b). While functional traitssuch as reproductive performance have declined in manycountries, especially for Holsteins, the largelyunchanged genetic trend in female fertility and calvingtraits for Danish, Finnish and Swedish Red (Ayrshire(a) 115DFS/SWE scale DFS/SWE scale1059585(b) 115751985 1990 1995 2000Years1059585751985 1990 1995 2000YearsMIFAPRSCLOCECFDOCMFig. 1. (a) Genetic trends for functional traits and milk productiontraits for Red (Ayrshire type) breeds. DFS ⁄ SWE, Danish, Finnish andSwedish Red breeds on a Swedish scale for breeding values (Jorjani2007, personal communication); MI, milk yield; FA, fat yield; PR,protein yield; SC, somatic cell scores; LO, longevity; CE, direct calvingease; CF, calving to first insemination; DO, days open; CM, clinicalmastitis. (b) Genetic trends for functional traits and milk productiontraits for HolsteinsMIFAPRSCLOCECFDOCMtype) breeds (Fig. 1a,b) shows that it is possible to avoida deterioration in these traits if they are properlyconsidered in the breeding programme. While forDanish, Swedish and Finnish Holsteins the breedingprogramme could not fully compensate for the use offoreign bull father genetic material for which functionaltraits such as reproduction were not known.Calving performance traitsFor first-parity Holstein cows, calf mortality is a greatproblem (Berglund and Philipsson 1992) and nowadaysreports are many of their high stillbirth rates, 10–13% atfirst calving. Stillbirths are approximately twice as high forHolstein first-calvers as for Swedish Red (Fig. 2). Theincreasing trend for stillbirth in Holsteins has not beenaccompanied by an increase in calving difficulty and thedivergent phenotypic trends may be an illustration of avitality problem. For second-calvers hardly any differencesin calving difficulty and stillbirth exist between the breeds.In a post-mortem examination of 76 calves from firstcalvingHolsteins, one-third of the calves were bornwithout any visible defects or injuries (Berglund et al.2003) and only half of the calves were born with signs of adifficult calving, indicating a vitality problem. The geneticcorrelations for stillbirth at first and second calving were0.45–0.48 for Swedish Holsteins (Steinbock et al. 2003),but 0.83–0.85 for the Swedish Red breed (Steinbock et al.2006). Thus there seem to be a genetic difference invitality of calves between these breeds at first calving.There are probably multifactorial reasons behindincreasing stillbirth rates. Adamec et al. (2005) recentlyshowed a consistently unfavourable effect of inbreedingon calving difficulty and stillbirth in US Holsteins, withlargest effects for first parity births. McParland et al.(2007) found that inbreeding had a deleterious effectupon most of the traits studied such as dystocia, stillbirthand calving interval in Irish Holstein-Friesians. A maximizedgenetic gain should be balanced against a minimizedinbreeding. There are now programmes to be builtinto the genetic evaluation programmes that maximizegenetic gain while minimizing inbreeding.Because calving difficulty and stillbirth mainly is aproblem for first parity cows, this category should be themain source of information for genetic evaluation. Forcertain breeds such as the Swedish Red breed the reliabilityin breeding values for calving ability could be increasedby including higher calving numbers (Steinbock et al.2006). Genetic evaluations should consider both calvingdifficulty and stillbirth as calf and maternal traits.Calving performance has been recorded in Swedensince the 1960s. The number of countries recordingcalving traits is increasing (Mark et al. 2005), and aninternational genetic evaluation was introduced in 2005(Jacobsen and Fikse 2005). Many of the member countriesof Interbull genetically evaluate calving difficulty andmost of them now also evaluate bulls for stillbirth, e.g. aroutine evaluation for stillbirth in Holsteins was implementedin the US in 2006 (Cole et al. 2007). Difficultcalving and stillbirth reduce reproductive performance(Bicalho et al. 2007), and genes associated with difficultbirth also reduce reproductive success (Lo´ pez de Maturanaet al. 2007).Ó 2008 The Author. Journal compilation Ó 2008 Blackwell Verlag