Late gestation supplementation with or without calcium propionate and rumen-protected methionine using nulliparous beef cows grazing dormant range forages

Authors: Waterman, Richard; Geary, Thomas; Reil, Mary; VAN EMON, MEGAN - Montana State University; Vermeire, Lance

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2026
Publication Date: 1/30/2026
Citation: Waterman, R.C., Geary, T.W., Reil, M.S., Van Emon, M.L., Vermeire, L.T. 2026. Late gestation supplementation with or without calcium propionate and rumen-protected methionine using nulliparous beef cows grazing dormant range forages. Animal Feed Science and Technology. 335. Article 116672. https://doi.org/10.1016/j.anifeedsci.2026.116672.
DOI: https://doi.org/10.1016/j.anifeedsci.2026.116672

Interpretive Summary: Supplementation during late gestation for nulliparous cows grazing senescent forages in a rangeland environment is essential to maintain body weight and prevent occurrence of negative energy balance if optimal production is desired. Current research to fully establish the role of rumen protected amino acids and metabolic enhancers such as calcium propionate will aid in this effort. The current study evaluates how rumen protected methionine with or without calcium propionate influence late gestation when grazing senescent forages. The exponential growth of the fetus during late gestation and conservation of maternal body weight must be met to optimize range cow beef production. Supplementation regimes in the current study did not influence cow body weight, calf birth weight and marginal changes were observed in metabolites and amino acid concentrations throughout a 101 or 127 d supplementation period over two consecutive years, respectively. Supplementation with calcium propionate alone did increase peak milk production by 3.8 kg, but this increase was not realized in calf BW gains. This study also evaluated two levels of stocking rate that targeted 40% (moderate) or 60% heavy) utilization over the two years. Cow BW was improved by 7 kg in the moderate stocking rate compared to cows in the heavy stocking rate pastures. In conclusion, cow in the northern Great Plains of the United States of America require supplementation of N when grazing senescent forages. Future research requires identification of supplemental nutrients that promote body weight gain, nutrients for fetal growth, and establish a positive energy balance following parturition to support milk production and reproductive efficiency to retain young cows in the production system.

Technical Abstract: Beef production in the northern Great Plains and similar semi-arid environments depends on raising young beef females that can adapt to intra and interannual changes in forages and nutritional quality that accompanies these changes. The objective of the study was to determine the effect of both rumen protected methionine and calcium propionate supplements fed to nulliparous beef cows on body weight, calf performance, and milk production. Four isocaloric and isonitrogenous supplements were formulated and fed at a rate of 908 g•cow-1•d-1 for 101d (Yr 1) and 127d (Yr 2). Supplements contained 183g CP and approx. 560g TDN: 1) control (Con); 2) rumen protected methionine (Met; inclusion of 20g Mepron85®, Evonik-Degussa Corp., Kennesaw, GA, USA 30144); 3) calcium propionate (Prop; inclusion of 50 g NutroCal®, Kemin Industries, Inc., Des Moines, IA); 4) or rumen protected methionine and calcium propionate (Met+Prop; inclusion of 20g Mepron85®, and 50 g NutroCal®). Cows from each supplement treatment were randomly assigned to pastures targeting one of two stocking rates to achieve either 40% (moderate) or 60% (heavy) utilization for two consecutive years. Nulliparous cows’ body weight at the termination of the supplementation period were similar (P = 0.99) for supplemental treatment, however cows in the moderate stocking rate pastures tended to be heavier (P = 0.06). A supplement x year interaction was measured for calf birth weight (P = 0.04) with no influence derived from pasture stocking rates on calf birth weight (P = 0.36). Calves born from cows that received the Met supplement were heavier in Yr 2 whereas calves in the Met+Prop treatment were heaviest in Yr 1 with all other treatment x year combinations being similar. A supplement x year effect was observed for peak milk production and energy corrected milk (ECM, P = 0.01 and P = 0.03, respectively). Peak milk yield was 3.8 kg•d-1 lower for Con when compared to the Prop cows and ECM was 3.9 kg•d-1 lower for Con when also compared to the Prop cows in Yr 2 of the study, whereas all other treatment combinations within and across the two years were similar. These data indicate that rumen protected methionine and calcium propionate can augment dietary efficiencies and magnitude of responses are dependent on environment.