PSIV-A-4 - Effect of late gestational nutrient restriction on locomotor activity of beef heifers

Abstract: The objective of this study was to determine the effects of nutrient restriction on locomotor behavior during late gestation. Fall-calving crossbred beef heifers were moved to 3.7 × 15.8 m partially-covered pens and individually-fed 100% (control; n = 13) or 70% (nutrient restricted; n = 13) of NASEM metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Diets were based on chopped sorghum sudan hay fed in Calan gates and supplemented to meet targeted nutritional planes. IceQube accelerometers (iceRobotics, Edinburgh, UK) were placed on the left hind fetlock between d 158 and 168 of gestation to determine standing time, lying time, step count, number of lying bouts, and motion index. Daily behavior data were averaged for 5 distinct periods (period 1: IceQube placement to d 180 of gestation; period 2: d 181 to 201 of gestation; period 3: d 202 to 222 of gestation; period 4: d 223 to 243 of gestation; and period 5: 244 to 264 of gestation). Days in which animals were moved from their pens were excluded from the data set, resulting in an average of 17.2 ± 2.35 d per period. Data were analyzed with fixed effects of nutritional plane, period, and their interaction in the model. Maternal sire and day of treatment initiation were included as covariates. The number of lying bouts was affected (P = 0.02) by the nutritional plane × period interaction. Within period, there was no effect (P ≥ 0.20) of nutritional plane on lying bouts. Lying bouts in control heifers decreased (P = 0.008) from period 1 to 2, whereas lying bouts in nutrient restricted heifers decreased (P = 0.002) from period 1 to 2 before increasing (P = 0.02) again from period 2 to 3. Motion index and step count were affected (P ≤ 0.05) by nutritional plane, where both were greater in control heifers. Motion index and step count were affected (P < 0.001) by period, while standing time and lying time tended to be affected (P ≤ 0.09) by period. Motion index and step count decreased (P < 0.001) between periods 1 and 2 and periods 3 and 4 but increased (P ≤ 0.004) between periods 2 and 3 and periods 4 and 5. Standing time decreased (P = 0.02), while lying time increased (P = 0.02), between periods 3 and 4. These data suggest that nutrient restricted heifers may have reduced locomotor behavior in late gestation compared with control heifers. Throughout all periods of gestation, control heifers took more daily steps and had a greater motion index, suggesting that nutrient availability in late gestation may directly impact locomotor behavior of beef heifers.