Late gestational nutrient restriction decreases placental size and calf birth weight without altering uterine blood flow in primiparous beef females

Authors: Redifer, Colby; RATHERT-WILLIAMS, ABIGAIL - University Of Missouri; MEYER, ALLISON - University Of Missouri

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2025
Publication Date: 5/13/2025
Citation: Redifer, C.A., Rathert-Williams, A.R., Meyer, A.M. 2025. Late gestational nutrient restriction decreases placental size and calf birth weight without altering uterine blood flow in primiparous beef females. Journal of Animal Science. 103. Article skaf163. https://doi.org/10.1093/jas/skaf163.
DOI: https://doi.org/10.1093/jas/skaf163

Interpretive Summary: Even in well-managed herds, it is possible for beef females to be nutrient restricted during late gestation due to challenges of poor forage quality or availability and environmental stress. For heifers, the added nutrient requirements to continue growing pose an even greater challenge during their first pregnancy. In previous late gestational undernutrition studies, calf birth weight was decreased approximately half of the time and was not affected the other half of the time, but the placental adaptations that occurred to cause this were rarely determined. Our data show that heifers who were nutrient restricted during late gestation lost maternal body weight and mobilized adipose and muscle tissue stores but maintained appropriate skeletal growth compared with adequately-fed females. Less nutrients were available in maternal circulation and heart rate was decreased in nutrient restricted females, but total uterine artery blood flow was not affected. Nutrient restricted females also had smaller placentas but only minimal changes in cotyledonary nutrient transporter expression. The insult to nutrient availability in maternal circulation and placental size were enough to comprise uteroplacental nutrient transport capacity, and calves born to nutrient restricted females were smaller than calves born to controls.

Technical Abstract: To investigate impacts of late gestational nutrient restriction in first-parity beef females on prenatal nutrient availability to calves, fall-calving heifers [body weight (BW): 472 ± 33 (SD) kg; body condition score (BCS): 5.4 ± 0.5] were individually-fed 100% (control; CON; n = 13) or 70% (nutrient restricted; NR; n = 13) of metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from day 160 of gestation to calving. Maternal measures were determined every 21 d (BW and metabolites) or 42 d (BCS, backfat, and longissimus muscle area) during gestation and post-calving. Doppler ultrasonography of both uterine arteries was conducted every 21 d until day 244 of gestation. At birth, calf BW and size were measured, and expelled placentas were dissected and dried. Targeted messenger ribonucleic acid (mRNA) expression was determined for cotyledons. Data were analyzed with nutritional plane, treatment initiation date, heifer’s sire, and calf sex (when P < 0.25) as fixed effects. Metabolites and uterine blood flow included day and nutritional plane × day as repeated measures. Circulating glucose was less (P = 0.05) for NR dams than CON. Circulating urea N and triglycerides were less (P /= 0.15) ipsilateral, contralateral, or total uterine artery blood flow. Number of cotyledons was greater (P = 0.03), average cotyledon weight was less (P = 0.04), and total placental weight tended to be less (P = 0.10) for NR than CON. Cotyledonary relative mRNA expression of GLUT1 was greater (P = 0.04) and SNAT2 tended to be greater (P = 0.07) for NR, but other nutrient transporters, angiogenic factors, and PAG2 were not affected (P >/= 0.13). Calves born to NR dams weighed 14.4% (P = 0.03) less at birth and had smaller (P