Lambs from ewes fed a poor-quality diet with realimentation exhibit increased incidence of hypothermia and divergent pre-weaning growth.

Depending on seasonal availability and quality of range forage, extensively managed ewes can experience nutritional challenge during any point of gestation. Neonatal lamb performance after severe experimental nutrient restriction during gestation has been well studied; however, there is a gap in understanding of how nutrient restriction experienced over the course of a production cycle impacts lamb success. Therefore, the objective of this study was to investigate early life performance of lambs from ewes fed a diet simulating winter forage in the Intermountain West. Timed-mated Rambouillet × Merino ewes were allocated to one of two dietary treatments, consisting of a diet formulated to meet nutritional requirements for the entirety of gestation based on National Research Council (NRC) recommendations (balanced diet) or a poor-quality diet fed from 30 to 125 d of gestation (dGA) and then realimented with the nutritionally balanced diet for the remainder of gestation. From 30 dGA to lambing, BW were obtained every 7 d and body condition scores (BCS) every 14 d. At the end of gestation ewes were group housed in a fully enclosed barn for lambing, to produce lambs born to balanced diet ewes (CONT; n = 33) and lambs born to poor-quality diet ewes (NC; n = 33). For the first week of life, rectal temperature and blood samples were collected daily from all lambs. Bodyweight and morphometrics (crown-rump length, CRL; abdominal circumference, AC; crown circumference, CC; and cannon bone length, CBL) were collected at birth, and then weekly thereafter. Treatment by time interactions were observed where poor-quality diet ewes weighed less (P < 0.05) from weeks 6 to 17 and had lower (P < 0.05). BCS from weeks 6 to 16 of the treatment period There were no differences in birthweight or birth morphometrics between treatments. There was an increased (P < 0.05) incidence of hypothermic events (rectal temperatures < 38 °C) in NC lambs in the first week of life, despite having normal blood glucose concentrations. Beginning at 4 wk of life through weaning (70 d), NC lambs weighed less (P < 0.05) compared to CONT. Nutrient challenged lambs also exhibited asymmetric growth, indicated by increased (P < 0.05) CRL/BW, CC/BL, CRL/BW, and AC/BW ratios compared to CONT. These data suggest that sustained moderate nutritional challenge during gestation, even when supplemented in late gestation, negatively impacts offspring pre-weaning performance.