PSI-19 - Neonatal lamb growth and thermoregulation after nutrient specific restriction in gestation

Abstract: Depending on seasonal availability and quality of range forage, extensively managed ewes can experience nutrient restriction 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 practical nutrient restriction experienced over the course of a production cycle impacts lamb success. Therefore, the objective of this study was to investigate first week fetal growth and development, and thermoregulation biomarkers in neonatal lambs from ewes fed a diet that simulates winter forage. Time-mated and confirmed pregnant Rambouillet x Merino ewes were blocked by body weight and allocated to one of two dietary treatments. Treatments consisted of: 1) Control diet (CONT) formulated to meet or exceed the National Research Council (NRC) nutrient requirements for gestating ewes fed throughout gestation; 2) Nutrient restricted diet (NR) formulated to meet 70% of total digestible nutrient (TDN) and 50% of protein requirements from 30-125 d of gestation (dGA) and then re-alimented with the CONT diet for the remainder of gestation. Ewes were individually fed from 25 dGA to 137 dGA, then group fed through lambing. From 30 dGA to lambing, weekly body weights, bimonthly body condition scores (BCS), and monthly blood glucose concentrations were recorded for all ewes. A treatment by time interaction was observed where NR ewes weighed less (P < 0.05) starting at week 8 of the treatment period through lambing. There were effects of treatment and time on BCS, as ewes receiving the NR diet had lesser (P < 0.05) BCS compared to CONT ewes regardless of time in gestation. There were no observed differences in blood glucose concentrations between groups. At lambing, rectal temperature, birth weight and morphometrics (crown-rump length, abdominal circumference, head circumference, and cannon bone length) were collected on all lambs. Collection of rectal temperature and bodyweight continued daily for the first week of life. There were no differences in birthweight or birth morphometrics; however, growth by body weight in the first week of life was greater (P < 0.05) in NR (n=10) compared to CONT lambs (n=12), with an effect of progeny number. Additionally, treatment by day interactions were observed with NR lambs having lower (P < 0.05) body temperatures on days one, four, and five compared to CONT lambs. These data suggest that sustained nutrient challenge during gestation, even when re-alimented in late gestation, may produce lambs that are at increased risk of hypothermia. While maternal nutrient supplementation in late gestation is a common practice, it is crucial for producers to consider nutritional supplementation strategies throughout gestation to limit the number of lambs that require increased intervention after birth.