Follicular B‐Mode Echotexture Parameters at <scp>P</scp>4 Insert Removal and Their Association With Pregnancy Outcomes in Beef Cows Undergoing Timed <scp>AI</scp> Protocol

This study aimed to determine the relationship between echogenicity and heterogeneity of ovarian structures and cyclicity status, estrus expression and pregnancy per artificial insemination (P/AI) in multiparous beef cows during timed-artificial insemination (TAI). An ultrasound ovarian examination was carried out in 406 crossbred suckled cows at progesterone (P4) insert removal on D8 of a TAI protocol and at pregnancy diagnosis 30 days after TAI. Follicular (antrum, wall and perifollicular stroma) and luteal morphometry, and echotexture and heterogeneity parameters were analysed on D8 and D30 after TAI, respectively. Follicles that did not reach divergence (< 8.5 mm) at P4 removal had higher antral echotexture and heterogeneity values (p < 0.0001) than those that surpassed divergence (> 8.5 mm). Lower follicular antrum echotexture levels at P4 removal positively correlated with subsequent estrus expression and pregnancy outcomes (p < 0.05), and negatively with follicle size (p < 0.0001). Luteal echotexture varied according to the originating follicle size (p < 0.05), with no differences between pregnant and non-pregnant cows 30 days after TAI. Cows had higher odds of estrus expression (Se, 70.61%; Sp, 61.05%; AUC 0.80; p < 0.0001) and attaining P/AI (Se, 64.52%; Sp, 61.05%; AUC 0.73; p < 0.0001) with lower follicular antrum echotexture (overall cut-off ≤ 14.25). The results show that echotexture values in antral follicles on D8 are strongly associated with pregnancy outcomes and may be useful for predicting success in TAI protocols.