251 Effect of diets containing soybean co-products formulated for developing heifers on reproductive efficiency

Abstract The objectives of this study were to determine the effects of including soybean oil in supplemental diets for developing heifers on reproductive tract scores, time of puberty and cyclicity, and successful artificial insemination. Angus crossbred heifers [n = 80; body weight (BW) = 248 ± 21 kg) were sorted randomly into one of eight pastures (n = 10 heifers/pasture) and pastures were assigned randomly to one of two treatment groups (n = 4 pastures/treatment), being: 1) control group fed an isonitrogenous and isocaloric grain supplement with no soy product (CON); and 2) treated group fed grain supplemented with soybean oil at 2% of estimated total diet dry matter intake (SBO). Heifers grazed 2.4 ha mixed grass pastures and when forage was limited heifers were offered bermudagrass hay for ad libitum intake. Supplements were offered beginning approximately 30 d after weaning and continued through the breeding season. Body weights, hair coat scores, and body condition scores (BCS) were recorded monthly. When heifers weighed > 295 kg, rectal palpation was performed and an ultrasound used to determine ovary size, dominant follicle size (> 10 mm), and follicular structures on the ovary (presence or absence of corpus luteum), and the tone and diameter of the uterine horns were determined (reproductive tract score; RTS). At 7-d intervals beginning on d 56, blood samples were collected via jugular venipuncture. Samples were used to measure serum progesterone concentrations to determine the percentage of heifers pubertal and cyclic. Heifers were classified as pubertal when serum progesterone concentrations were greater than 1 ng/mL. Heifers that maintained progesterone concentrations greater than 1 ng/mL for two consecutive samples were classified as cyclic. Cyclic heifers were not sampled further. Heifers were bred by artificial insemination (AI) at approximately 14 mo of age. Statistical analyses were performed using the MIXED and GLIMMIX procedures of SAS 9.4 (Cary, NC) to assess treatment effects. Treatment had no effect on hair coat shedding scores (P = 0.87), BCS (P = 0.13), and RTS (P = 0.27). Pubertal (P = 0.39) and cyclicity (P = 0.34) status were not affected by treatment. The percentage of females pubertal and cyclic by d 147 were numerically greater for the CON treatment (89.3% vs. 90.1%) than on the SBO treatment (80.5% and 75.2%). Heifers supplemented with SBO had numerically greater AI conception compared with CON supplemented heifers (52.6% vs. 42.5 %, respectively), but were not statistically different (P = 0.38). Further research is being performed to gather additional data for AI and overall pregnancy rates, effects of soybean co-product inclusion in supplements on uterine blood flow and corpus luteum perfusion, and resulting calf performance to AI-bred females.