96 Impacts of Postweaning Dry Matter Intake Classification on Beef Heifer Performance and Cyclicity

Abstract

Abstract The objective was to evaluate the relationship of postweaning dry matter intake (DMI) classifications on performance and cyclicity in fall-born beef heifers. Heifers were classified based on DMI as either low (LoDMI; < -0.5 SD from mean), average (AvgDMI; ± 0.5 SD from mean), or high (HiDMI; > +0.5 SD from mean). Hifers (n = 147), either Angus or Hereford sired by commercial dams, were utilized in the analysis. Heifers were early weaned at 82 ± 7 days of age. Following weaning, heifers were managed in partially covered, drylot pens and fed a high-energy grain diet. At postweaning intake evaluation initiation (day 1), heifers were 170 ± 22 kg and 156 ± 7 days of age. Heifer DMI was determined over 56 days using GrowSafe system, and weights were collected every 14 days. Following the postweaning intake evaluation, heifers rotationally grazed endophyte-infected tall fescue paddocks. During the 166-day grazing period, heifers were weighed and assigned a hair shedding score monthly. Heifers returned to drylot pens on day 223 for a prebreeding feed efficiency evaluation on a high-forage diet. Foot scores were assigned on day 1 and 237. Heat detection patches were used to determine percentage of heifers cycling before synchronization. Cyclicity data were analyzed using GLIMMIX and all other response variables were analyzed using the MIXED procedure of SAS 9.4. By design, postweaning DMI differed (P < 0.01) between treatments (5.5, 6.2, and 6.9 kg/d for LoDMI, AvgDMI, and HiDMI, respectively). Average daily gain (ADG) differed (P < 0.01) during the postweaning evaluation period, with LoDMI being least, AvgDMI intermediate, and HiDMI greatest. On days 1 and 56, body weights (BW) differed (P < 0.01); LoDMI were lightest, AvgDMI were intermediate, and HiDMI were heaviest. However, gain to feed during the postweaning evaluation period was not different (P = 0.33) by DMI classification. During the grazing period, BW differed (P < 0.01) on days 84 and 141; HiDMI were heavier than LoDMI and AvgDMI. On day 113, BW differed (P < 0.01); LoDMI were lightest, AvgDMI were intermediate, and HiDMI were heaviest. However, ADG and final grazing BW did not differ (P ≤ 0.12) during the grazing period by DMI classification. Hair shredding score was greater (P ≤ 0.04) for LoDMI than HiDMI on days 56, 84, and 113. Foot scores differed (P = 0.02) on day 1; LoDMI was less than AvgDMI and HiDMI. However, they only tended (P = 0.08) to be different on day 237. Percent cycling prior to synchronization did not differ (P = 0.25) by classification. In summary, LoDMI heifers performed poorer during postweaning evaluation than HiDMI heifers. However, grazing performance and cyclicity was similar among DMI classifications.