Genetics of new phenotypes of pregnancy loss in dairy cattle

Abstract

This thesis examined use of novel phenotypes of pregnancy loss to improve genetic progress in female fertility in dairy cattle. Genomic information was used to identify candidate genes associated with pregnancy loss traits, and to estimate the extent and effect of genetic defects on pregnancy outcome. Automatically recorded progesterone (P4) data from 14 Herd NavigatorTM herds and pregnancy-associated glycoprotein (PAG) levels recorded in 1119 herds affiliated to the Swedish milk recording scheme were used to evaluate embryo, fetal and total pregnancy loss. The extent of pregnancy loss was considerable according to both diagnosis methods, ranging from 30 to 60%. In most cases, Swedish Red cows showed better pregnancy maintenance than Swedish Holstein. The P4 and PAG concentrations in milk were significantly lower in initially pregnant cows after losing their pregnancy compared with full-term pregnant cows, which indicates the importance of continuously high P4 and PAG levels during gestation to support embryo and fetus development. Similarly to calving and insemination-based fertility traits, heritability estimates of pregnancy loss traits were low (0.00-0.07). A single-step genome-wide association study identified 19 candidate genes associated with pregnancy loss traits, several of which are known to influence embryonic and fetal development. Mating two carriers of genetic defects adversely affected fertility and caused 14-15% higher mortality compared with non-carrier matings. Considering pregnancy loss in future routine genetic and genomic evaluations of fertility in dairy cattle could genetically improve cow fertility by reducing pregnancy losses in milk production, while also preventing economic losses arising from extended service period and calving interval, and involuntary culling due to infertility.