83 - Impacts of Heifer Post-weaning Intake Classification on Performance Measurements of Lactating and Non-lactating Two-, Five- and Eight-year-old Angus Beef Females

Abstract: Data used in these studies were part of another project described by Parsons et al. (2021). These studies evaluated heifer post-weaning intake classification on performance measurements of two-, five- and eight-year-old lactating or non-lactating Angus females. We analyzed intake and production data of 57 pregnant, non-lactating (Study 1) and 54 lactating, non-pregnant (Study 2) females. Heifer post-weaning intake was calculated over 80 test days following weaning using GrowSafe units. Heifers were categorized based on intake as low (< -0.05 SD from the mean), average (± 0.05 SD from the mean), or high ( > 0.50 SD from the mean) within year. Non-lactating females showed an age effect (P ≤ 0.05) for cow body weight (BW), dry matter intake (DMI) rate (grams/minute), and time spent at the feeder (minutes/day). Intake rate was greater in five- and eight-year-old cows compared with two-year-old cows, and eight-year-old cows spent more time at the feeder than two- and five-year-old cows. Cow BW for non-lactating cows was significant for age (P < 0.001), intake classification (P = 0.03) and showed a tendency for age*intake interaction (P = 0.10), with older cows weighing more than younger cows. Milk production expressed as kilograms and grams per kilogram of BW of the cow had an age*intake (P < 0.001) effect. Two-year-olds with low and average intake classifications had greater milk production (P < 0.001) and milk produced as grams per kilogram of BW (P < 0.001) than two-year-old cows with high intake classifications. Additionally, five-year-old cows with average and high intake classifications had greater milk production (P < 0.001) and grams of milk produced per kilogram of BW (P < 0.001) compared with five-year-old cows classified as low intake. In summary, heifer post-weaning intake classification had minor impacts on performance measurements in three age classes of beef females at two different production levels.