Linus Pauling Institute

Two experiments investigated the effects of supplementing Ca salts of soybean oil (CSSO) during early gestation on reproductive function and pregnancy rates to artificial insemination (AI) in Bos taurus beef cows. In Exp. 1, 771 suckled, lactating, multiparous Angus cows were divided into 22 groups of approximately 35 cows/group, and timed-inseminated on d 0. After AI, groups were assigned randomly to receive (as-fed basis) 100 g of ground corn + 100 g of soybean meal per cow/d, in addition to: 1) 100 g/cow daily of CSSO (n = 11), or 2) 87 g of prilled saturated fat + 13 g of limestone per cow/d (CON; n = 11). Groups were maintained in individual tall fescue-dominated pastures, and offered treatments from d 0 to 21. Pregnancy status was determined between d 45 and 55 via transrectal ultrasonography. Cows receiving CSSO had greater (P = 0.01) pregnancy rates to timed AI compared with CON (60.2 vs. 51.7%; SEM = 4.2). In Exp. 2, 90 suckled, lactating, multiparous Angus × Hereford cows housed in 18 drylot pens (5 cows/pen) were assigned to the same timed AI program and treatments from Exp. 1 (9 pens/treatment), and received 20 kg/d (dry matter basis) of grass-alfalfa hay. Transrectal ultrasonography was performed to verify ovulation and corpus luteum (CL) volume before AI (d 0), on d 7 and 15. After ultrasonography on d 15, cows diagnosed without a CL on d 0, but with a CL greater than 0.38 cm3 in volume on d 7 and 15 (2 or 3 cows per pen; CSSO, n = 20; CON, n = 24), were assigned to conceptus collection via transcervical flushing and endometrial biopsy in the uterine horn ipsilateral to the CL. Blood samples were collected for fatty acids (FA) analysis on d 0, 7, and 15. Blood was collected from cows not assigned to conceptus collection for whole blood RNA extraction on d 20, and for pregnancy diagnosis on d 30 by measuring concentrations of pregnancy-associated glycoproteins. Cows receiving CSSO had greater (P ≤ 0.04) mean plasma concentrations of linoleic acid and ω-6 FA compared with CON on d 7 and 15. Moreover, CSSO supplementation increased (P = 0.05) mRNA expression of interferon-tau by the conceptus, and blood mRNA expression of interferon-stimulated gene 15 and 20,50-oligoadenylate synthetase on d 20 in gestating cows. Hence, post-AI CSSO supplementation to B. taurus beef cows improved pregnancy rates to timed AI, which can be associated with increased mRNA expression of interferon-tau by the conceptus when CSSO is supplemented during early gestation.