The relationship between anogenital distance and fertility, and genome-wide associations for anogenital distance in Irish Holstein-Friesian cows

Abstract

The evaluation of anogenital distance (AGD), the distance from the center of the anus to base of the clitoris, as a potential fertility trait for genetic selection in dairy cows has generated recent interest. The objectives of this cross-sectional observational study were to (1) characterize the distribution and variability of AGD, (2) determine factors associated with AGD, (3) estimate heritability for AGD, (4) identify single nucleotide polymorphisms (SNP) associated with phenotypic variation of AGD, and (5) validate the relationship between categories of AGD and fertility in Irish Holstein-Friesian cows. Anogenital distance was measured using digital calipers in 1,180 Holstein cows (mean ± standard deviation: 225 ± 79 d in milk) from 10 dairy herds located in Munster, Ireland. In addition, age (yr), weight (kg), height at hip (cm), and body condition score (BCS) at the time of AGD measurement were determined in a subset of 281 cows. Genotype information available from 908 cows was subsequently imputed to the Illumina Bovine High Density BeadChip (Illumina Inc., San Diego, CA) for genome-wide association analysis of phenotypic variation in AGD. Overall, AGD had a normal distribution and high variability (mean ± standard deviation; 119.2 ± 11.6 mm). Anogenital distance was weakly but positively associated with cow age, hip height, and body weight, and negatively associated with BCS; the phenotypic variation in AGD that was explainable by these variables was small (coefficient of determination; R 2 = 0.09, 0.06, 0.10, and 0.02, respectively). The estimated heritability for AGD was 0.37 (standard error of mean ± 0.08). Six SNP of suggestive significance were identified on Bos taurus autosomes 6, 15, 20, and 26; however, none of these SNP was related to previously identified candidate genes for fertility. Cows were categorized into quartiles (Q1; 86 to 111 mm; n = 311, Q2; 112 to 120 mm; n = 330; Q3; 121 to 127 mm; n = 265, and Q4; 128 to 160 mm; n = 274) based on AGD and the association with reproductive outcomes examined (21-d submission rate, pregnancy to first AI, pregnancy rate within 21, 42 and 84-d after the farm mating start date, and number of times bred). None of the reproductive variables differed significantly between AGD categories. In summary, despite identification of high variability and moderate heritability for AGD in Irish Holstein-Friesian cows, reproductive outcomes did not differ between categories of AGD. This latter result differs from our previous finding of an inverse relationship between AGD and pregnancy outcomes in first-and second-parity Canadian Holstein cows, emphasizing the need to test and validate this new phenotype in diverse cow populations.

Investigating anogenital distance and antral follicle count as novel markers of fertility within a herd of cows with positive or negative genetic merit for fertility traits

“…The AGD showed the most promise as an easy-to-measure marker of future reproductive success. Distribution of AGD was normal and variable, comparable with previous studies in Canadian Holstein and Irish Holstein-Friesian cows (Gobikrushanth et al, 2017(Gobikrushanth et al, , 2019. The final cut-off for AGD was based on recalving within 6 wk of the calving period in lactation 2 (DairyNZ, 2018).…”

“…It is easier and less invasive to measure than AFC. Anogenital distance was inversely associated with reproductive outcome in Canadian Holstein cows (Gobikrushanth et al, 2017); however, researchers could not determine any association between AGD and reproductive performance in Irish Holstein-Friesians cows (Gobikrushanth et al, 2019). They concluded that the lack of an association may be due to the increased emphasis on genetic improvement for fertility in Ireland in the last 10 yr.…”

“…They concluded that the lack of an association may be due to the increased emphasis on genetic improvement for fertility in Ireland in the last 10 yr. The heritability of AGD in cattle was reported to be 0.37 (Gobikrushanth et al, 2019), slightly greater than AFC.…”

“…In Nellore cattle, regions of interest included chromosomes 1 and 26, which accounted for 6.2 and 7.3% of the total additive genetic variance, respectively (Grigoletto et al, 2020). For AGD, strong genetic markers are yet to be reported in cows (Gobikrushanth et al, 2019).…”

Reproductive Performance of Water Buffalo Cows: A Review of Affecting Factors

“…Recently in two studies, a negative relationship between anogenital distance and pregnancy rate in dairy cows was observed [220,221]. This could be considered a new phenotype for genetic selection for higher fertility, and in dairy cows, the heritability of anogenital distance was 0.37±0.08 [222]. The selection of dairy cows for a higher body condition score improved health and fertility [223,224,225], and dairy cows with positive genetic merit to fertility had a higher dry matter intake and kept a higher body condition score [226].…”