246 The influence of supplemental alfalfa pellet levels on beef cattle grazing winter foothill rangelands

Abstract This study evaluated the influences of graded levels of supplemental alfalfa pellets on beef cattle performance during mid-late gestation of multiparous beef cows. Angus based bred cows (n = 120) were used in an 84-d winter grazing experiment that took place on native foothill rangelands. Cattle were stratified by age and body condition and, within stratum, randomly assigned to one of four treatments: 1) no supplement, 2) cows fed 0.76 kg×d-1 supplement, 3) cows fed 1.52 kgּ d-1 supplement, and 4) cows fed 2.27 kgּ d-1 supplement. Protein supplement fed was a 18% CP alfalfa pellet. Cows were gathered 3-times weekly and provided supplement on a replicated pen basis. Supplement was provided through d 84 and then cows were introduced to a common diet until d 203. Performance data was analyzed as a completely randomized design with linear and quadratic contrasts used for mean separation (reps = 5; n = 6). Body weights (BW) and body condition score (BCS) were recorded every 28-d period throughout the study and at 203 d post calving, calf BW were obtained at birth. A treatment × period interaction was detected for BW change (P 0.01), where increasing protein supplementation resulted in linear increase in BW gains (P 0.01) relative to the control treatment, with BW change ranging from -23.6 kg for control cattle to 14.64 kg in the cattle fed the high level of supplementation. BCS change also exhibited a linear response for all four BW periods (P 0.01) where cattle from the control treatment expressed a -0.49 loss of BCS over the duration of the study while high supplemented cattle-maintained condition only losing 0.02. No difference in calf BW was observed between the control and any supplemental treatments (P = 0.30) with an overall BW average of 38.37 kg. In conclusion, increasing levels of supplemental protein resulted in linear improvements of both BW and BCS of grazing beef cattle during the winter. These differences observed were then maintained throughout d 203 after all cattle were introduced to a common management regime. Birth weights of calves were not affected by the level of protein supplementation.