61 The Effects of Frame Score, Breed, and Day Relative to Estrus on Dry Matter Intake and Feeding Behaviors of Crossbred Beef Heifers

Abstract

Abstract The objective was to determine if changes in DMI, time spent eating (TIME), and number of meals per day (MEALS) within interactions of frame score group (FSG) or primary ancestral breed type (PAB) with day relative to estrus (DRE) exist. We hypothesized that different FSG or PAB responses would vary between d -3 to d +3 surrounding estrus (d 0). Over four years, 295 crossbred heifers (347.03 ± 47.39 kg) were monitored. Using calculated frame score, heifers were classified as FSG small (< 4.00), moderately small (4.00 to 5.50), moderately large (5.50 to 6.50), and large (> 6.50). Admixture analysis classified heifers into five PAB (greatest proportion; Angus and Red Angus, American Aberdeen, Shorthorn, Simmental, and crossbred). Estrus was detected using visual checks [patches or chin ball markers, bull present (BP), year 1, n = 87] or heat detection devices (BP or absent, year 2 to 4, n = 208). The last 45 d of the feeding trial had BP. Conception date was estimated using ultrasound fetal size captured at pregnancy checks. Heifers were fed a forage-based diet using the Insentec feeding system. Software errors were removed; then estrus and feeding data were paired based on calendar date. A 7-d range was kept for each heifer using estrus categories (EC) of: 1) last without a BP (n = 195), 2) first with a BP (n = 285), and 3) at estimated conception date (n = 247). The statistical model included fixed effects of year, PAB, FSG, DRE, interactions of FSG x DRE (n = 28) and PAB x DRE (n = 42), and fixed covariate of calendar date. Repeated measures were modeled with unstructured covariance structure and heifer as experimental unit. Square root transformation for TIME and MEALS was used due to normality concerns. Across EC, no interactions for DMI were found (P ≥ 0.5529). For TIME, differences existed within FSG x DRE (P = 0.0375; EC-3) suggesting large heifers responded differently than others. All EC showed DMI (P ≤ 0.0083) and TIME (P ≤ 0.0373) declined on d 0, with less reduction observed when BP (DMI, TIME: 1) -17.09%, -21.56%; 2) -9.01%, -15.02%; 3) -9.21%, -13.45%). A recovery surge occurred on d +1 (> 15%). For MEALS, PAB x DRE (P ≤ 0.0495; EC-1,2) and FSG x DRE (P ≤ 0.0494; EC-2,3) were different. A similar trend as DMI and TIME in response to estrus was observed in small heifers but no other FSG. Size did influence MEALS (P ≤ 0.0024), where smaller heifers ate more MEALS than larger heifers. Results indicate differences in TIME and MEALS likely exist between small and large heifers in response to estrus, but all respond similarly in DMI.