A supplementation study was conducted to evaluate level of propionate salt (Ca-propionate) on young cow performance over two years. One hundred-twenty cows were allocated to one of three treatments at calving. Propionate salt was incorporated in a protein supplement at a rate of 0, 80 or 160 g/d. Cows were individually supplemented twice weekly at 2 lbs/d. In year 1, cows had access to pasture and hay. In year 2, cows had access to a native range pasture. Blood was collected weekly and analyzed for progesterone (P4) to determine postpartum interval (≥1 ng P4/ml). Weights and body condition scores (BCS) were assigned at calving, end of supplementation, start of breeding season, and weaning. Cow weight and BCS changed over time through the study (P < 0.01 but was not affected (P > 0.10) by treatment. Calf weight was not different (P > 0.10) between treatments. Calf weight increased through the study (P < 0.01). Pregnancy rates did not differ between treatments (P > 0.10 but were affected by cow age (P<0.01, 77% and 100% for 2- and 3-year-olds, respectively). In year 1, the percentage of cows initiating estrous cycles before the breeding season was greater (P<0.05) for cows receiving 160 g (47.6%) compared to 0 g (15.6%) of propionate salt and tended to be greater than cows receiving 80 g (P<0.10, 20.0%). Based on ultrasonography, 3-year-old cows conceived earlier (P<0.01, 184 d) than 2-year cows (207 d). In year 2, postpartum anestrous interval (P = 0.70), percentage of cows initiating estrous cycles before the breeding season (P = 0.54), conception rate to AI (P = 0.68), and season-long pregnancy rates (P = 0.87) were not different among treatments. In summary, propionate salt can influence reproductive performance, however, response is not consistent.
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