Effects of type of glucogenic feed additive on reproductive performance of young postpartum range cows

Objective: This study evaluated the effects of the in- clusion of either monensin (Rumensin 90, Elanco Animal Health) or propionate salt (NutroCal 100, Kemin Industries) in protein supplements on BW change, BCS, energy metabolism, reproduction, milk production, and calf weaning BW in young 2- and 3-yr-old postpartum range cows.Materials and Methods: In a 3-yr study at the Gud- mundsen Sandhills Laboratory near Whitman, Nebraska, March-calving, young range cows (n = 189) were individu- ally supplemented 908 g/d with a 30% CP supplement with the addition of either (1) 160 mg<middle dot>cow(-1)<middle dot>d(-1) monensin (MON) or (2) 40 g<middle dot>cow(-1)<middle dot>d(-1) propionate salt (CAP). Sup- plementation started approximately 10 d after parturition and continued for an average of 70 d postpartum. Cow BW and BCS data were collected weekly. Weekly blood samples were taken beginning 45 d postpartum. A com- pletely randomized design was used and data were ana- lyzed using MIXED procedure (SAS Institute Inc., Cary, NC). All binomial data were analyzed using PROC GLIM- MIX. Cow served as experimental unit, with supplemental treatment, year, and cow age set as fixed effects.Results and Discussion: Cow BW (P >= 0.19) and BCS (P >= 0.11) were not affected by postpartum supple- mentation during the study. However, BW change from calving to breeding was influenced (P = 0.04; -7 vs. -2 kg for CAP and MON; respectively) by supplementation, with cows receiving CAP losing greater BW. Calf BW at birth, weaning, or 205 d were not affected (P >= 0.68) by the postpartum supplementation strategy. Cows fed CAP had lower (P = 0.01; Table 4) circulating blood serum BHB concentrations than their counterparts. Cows receiving CAP supplementation had an increase (P = 0.04; 89% vs. 80% for CAP and MON; respectively) in overall pregnancy rate.Implications and Applications: This study implies that feeding young postpartum cows additional glucogenic precursors in the form of propionate salts increased re- productive efficiency without affecting BW or BCS. This increase in reproductive performance may have been en- hanced by improved dietary energy utilization as seen by decreased blood serum BHB concentration. In addition, economic efficiency was increased due to the increased reproductive performance and timing of when cows were bred.