Impact of Increasing Level of Milk Production on Cow and Calf Behavior and Performance in the Nebraska Sandhills

Selection for increased milk production across the United States has resulted in variable cow and calf production responses. Better understanding of calf nursing and grazing behaviors may provide opportunities to help estimate how milk and grazed forage intake influence variability in calf performance. In a 2-yr study, cow-calf pairs (n = 65) were equipped with neck collars containing global positioning system (GPS) units to validate the efficacy of high-frequency GPS data to accurately identify calf nursing events and grazing behavior. Data were collected during 3-wk tracking periods during early lactation (calf age 65.4 ± 10.0 d; EARLY) and late lactation (calf age 162 ± 22.3 d; LATE). Calf behavior was visually observed for a total of 350 hrs and was used in a training dataset for a random forest (RF) classification model. Out of bag (OOB) estimates of individual behaviors indicated relatively low misclassification error rates, less than 4%, suggesting that high frequency GPS tracking can be used to effectively classify calf nursing and grazing behaviors. Behavior prediction results in this study match ranges reported in previous literature, supporting the efficacy of this technique to assess behavior in beef calves. In a 2-yr study, crossbred cow-calf pairs (n = 118) from March- and May-calving herds were used to determine the impact of increasing total milk production on cow body weight (BW), body condition score (BCS), reproductive performance, calf BW, and calf average daily gain (ADG). On approximately 30, 60, 90, 120, and 210 d postpartum, individual cow 24-h milk yield was estimated with weigh-suckle-weigh techniques. Milk area under the curve (AUC) values were calculated and data were analyzed using linear regression analysis. Cow BW, BW change, and reproductive performance were not (P \u3e 0.12) associated with milk AUC, except for a tendency (P = 0.09) for lower BW at breeding. At weaning, cow BCS was negatively associated (P = 0.09) with increasing milk AUC but was not associated at any other physiological stage. A significant positive association with calf average daily gain (ADG) was observed from birth to age 120 d and a tendency (P = 0.09) for a positive association was observed from age 120 d to weaning. Steer ADG in the finishing phase was not (P = 0.63) associated with dam milk production. In this environment, increasing milk production had a positive increase in calf growth during the pre-weaning phase without any negative impacts on overall cow-calf production. Advisors: J. Travis Mulliniks and Mitchell B. Stephenso