Effects of maternal nutrient restriction and rumen-protected arginine supplementation of ewes on carotid artery hemodynamics during gestation and lamb birth weights

Abstract Text: The objective of this study was to use changes in carotid arterial blood flow as indices for changes in systemic blood flow during gestation based on plane of nutrition, arginine supplementation, and day of gestation. Our hypothesis was that maternal nutrient restriction would increase pulsatility index (PI) and resistance index (RI) in gestating ewes, and reduce lamb birth weights.  We also hypothesized that rumen-protected arginine supplementation would recover PI, RI, and lamb birth weights. To test this hypothesis, multiparous, Rambouillet ewes (n = 32; 67.7 ± 6.2 kg initial BW) were allocated to 3 treatments in a completely randomized design at 54 ± 3.9 d of gestation. Dietary treatments were allocated as a complete pelleted diet with either 100% of requirements (control, CON), 60% of control (restricted, RES), or RES plus a rumen-protected arginine supplement dosed at 180 mg/kg BW once daily and delivered in a 50 g fine ground corn carrier (RES-ARG). Ewes were penned individually in a temperature- and light-controlled facility. At parturition, lambs were removed from the ewes, weighed, and reared independently. We used Doppler ultrasonography to examine carotid blood flow in ewes from each treatment at d 50, 90, and 130 of pregnancy. The measurements acquired at d 50 were designated our baseline measurements, as this was before any arginine supplementation. Data were analyzed using the mixed procedure of SAS including repeated measures. No day of pregnancy × treatment interactions were observed (P ≥ 0.17). Pulsatility index was increased in RES and RES-ARG ewes (P ≤ 0.03), suggesting that restricted ewes experienced greater vascular resistance and lower tissue perfusion of blood compared to CON. We did not observe any treatment or day of gestation differences in RI (P ≥ 0.38). In ewes from all treatments, PI was increased at d 90 and 130 as compared with d 50 (P ≤ 0.001). Peak systolic velocity and end diastolic velocity were greater at d 130 than at d 50 and 90 (P ≤ 0.04). Birth weight was greater in lambs from CON ewes than lambs from RES ewes (P = 0.04), with lambs from RES-ARG ewes intermediate in weight (5.23, 4.45, and 4.60 ± 0.257 kg, respectively). These results support our hypothesis that maternal nutrient restriction increases PI and decreases lamb birth weight, whereas rumen-protected arginine supplementation did not recover PI or RI and only partially recovered lamb birth weights.

Keywords: arginine, carotid blood flow, ewes