Association of phenotypic and genetic traits with fertility in dairy cattle
Authors:   , Machado Andréia Ferreira 
Published: August 2024

In this thesis, the three chapters explore the association of phenotypic traits with fertility in dairy cattle. The objective of the first chapter was to characterize anogenital distance (AGD) as a proxy for Anti-Mullerian hormone (AMH) and in vitro embryo production (IVEP) in Bos indicus Gyr cattle. A single AGD measurement was collected from 552 donors from six herds in Brazil. Each donor had a raw average calculated for the number of recovered oocytes, viable oocytes, and produced embryos. It was observed that AGD had a normal distribution and was highly variable among the Gyr population. A phenotypic association of a greater number of produced embryos as AGD decreased was identified, while a positive and low genetic correlation was observed between AGD and viable oocytes and AGD and embryo rate. In summary, for the Gyr breed, AGD was phenotypically inversely associated with a quantity- related parameter, such as the total number of produced embryos. In contrast, AGD showed a low genetic correlation with qualitative-related outcomes such as viable oocytes and embryo rate. For the second chapter, the objective was to characterize phenotypic traits such as body condition score (BCS), weight, Anti-Mullerian hormone, antral follicle count (AFC), and anogenital distance in nulliparous Holstein heifers and their association with fertility. All measures were collected on 698 Holstein heifers from a single heifer yard in the State of Kansas (USA). Data from weight and fertility outcomes were retrieved from the on-farm herd management system on weekly backups. A tendency of association between AMH and AGD and a correlation between AFC and AGD was identified. Greater pregnancy at first AI and all services were observed for nulliparous heifers on the High BCS, as for Moderate AMH groups. To conclude, for the nulliparous Holstein heifers an association between the phenotypes AMH, AFC, and AGD was identified, whereas just BCS and AMH were associated with fertility. For the third chapter, the objective was to estimate the genetic and phenotypic association of oocytes and embryo production with linear type traits in Gyr dairy cattle. A repeatability model was applied to 14,251 ovum pick-up events from 1,916 Gyr donors, while 604 donors from the same group had their body measurements taken, donors were from six different herds in Brazil. Moderate heritability was observed for IVEP (0.20 to 0.38) and type traits (0.22 to 0.40). A high genetic correlation (0.83 to 0.99) was observed between the IVEP traits, and low to high correlations (-0.07 to 0.90) were demonstrated for the type traits. Low phenotypic correlations(0.01 to 0.13) between IVPE and type traits were observed, in contrast to a moderate genetic correlation indicated between IVEP and type traits, especially for ilium width (0.29 to 0.41), rump area (0.31 to 0.38), and hip height (0.23 to 0.33). Therefore, our study indicates the possibility of indirectly affecting IVEP selection based on type traits. Keywords: Reproduction. Gyr cattle. Holstein cattle. Genetics