Supplementation of <i>Saccharomyces cerevisiae</i> fermentation product to beef cows grazing fescue-based pastures and its impact on reproductive performance

The study aimed to evaluate the effects of Saccharomyces cerevisiae fermentation product (SCFP) supplementation during the breeding season on reproductive performance of beef cows grazing fescue-dominated pastures (Festuca arundinacea). A total of 883 multiparous suckled beef cows across eight locations were stratified by age and days postpartum (DPP) and randomly assigned to one of two treatments: 1) CON-mineral supplementation at 90 g/hd/d (n = 439 cows; 13 experimental units), or 2) SCFP-mineral with 9 g SCFP (NaturSafe, Diamond V, Cedar Rapids, IA; n = 444 cows; 13 experimental units). Supplementation began 21 d pre-breeding and continued through the breeding season (approx. 171 d). Cows grazed tall-fescue pastures and followed a fixed-time artificial insemination (TAI) protocol (7-d CO-Synch + CIDR) with natural service and clean-up bulls for a 70-d breeding season. Pregnancy diagnoses were performed by ultrasonography at 55 d post-TAI and 40 d after the breeding season. Cow body weight (BW) and body condition score (BCS) were recorded at TAI (day 0) and weaning (day 150). Mineral disappearance was measured weekly. Data were analyzed using GLIMMIX for binomial data and MIXED for continuous data. Cow age and DPP did not differ (<i>P</i> > 0.10) between treatments (6.0 ± 1.0 yr and 79.7 ± 2.6 d, respectively). Mineral disappearance was similar (<i>P</i> = 0.97) between treatments (99.2 and 99.8 ± 8.76 g/hd/d for CON and SCFP, respectively). No differences were observed (<i>P</i> > 0.10) in BW and BCS between treatments on days 0 and 150. SCFP supplementation did not affect estrus expression (63.2% vs 63.7% ± 2.6% for CON and SCFP, respectively; <i>P</i> = 0.91), but TAI pregnancy rates were higher (<i>P</i> = 0.025) in SCFP (65.9% ± 2.5%) compared to CON (57.9% ± 2.5%). Final pregnancy rates tended to be higher (<i>P</i> = 0.057) for SCFP (92.9% ± 1.4%) vs CON (89.0% ± 1.4%), with no effect on calf performance (<i>P</i> > 0.10). In conclusion, SCFP supplementation during the breeding season did not influence BW or BCS but improved TAI pregnancy rates in beef cows grazing endophyte-infected tall fescue.