Late gestational nutrient restriction in primiparous beef females: Nutrient partitioning among the dam, fetus, and colostrum during gestation

Authors: REDIFER, COLBY - University Of Missouri; WICHMAN, LINDSEY - University Of Missouri; RATHERT-WILLIAMS, ABIGAIL - University Of Missouri; Freetly, Harvey; MEYER, ALLISON - University Of Missouri

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2023
Publication Date: 6/14/2023
Citation: Redifer, C.A., Wichman, L.G., Rathert-Williams, A.R., Freetly, H.C., Meyer, A.M. 2023. Late gestational nutrient restriction in primiparous beef females: Nutrient partitioning among the dam, fetus, and colostrum during gestation. Journal of Animal Science. 101. Article skad195. https://doi.org/10.1093/jas/skad195.
DOI: https://doi.org/10.1093/jas/skad195

Interpretive Summary: Nutrient requirements increase substantially during late gestation in the beef female. Even in well-managed herds, it is possible for females to be nutrient restricted during this time due to challenges of low forage quality or availability and environmental stress. For heifers, the added nutrient requirements needed to continue growing pose an even greater challenge during their first pregnancy. However, little is known about how late gestational undernutrition impacts nutrient partitioning between maternal growth, the developing offspring, and colostrum production in beef heifers. Our data show that late gestational nutrient restriction in heifers halted the expected maternal growth and instead maternal tissue stores were catabolized. Less nutrients were available in the maternal circulation, yet calf weight and size at birth were not affected. Late gestational nutrient restriction resulted in less colostrum produced by the dam and less lactose available to the offspring, but the protein, fat, and immunoglobulins available in colostrum was not altered. In summary, beef heifers experiencing late gestational nutrient restriction prioritized partitioning nutrients to fetal growth and colostrum production over maternal growth and maintenance of body condition.

Technical Abstract: Fall-calving primiparous crossbred beef females [body weight (BW): 451 ± 28 (SD) kg; body condition score (BCS): 5.4 ± 0.7] were allocated by fetal sex and expected calving date to receive either 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. Heifers were individually-fed chopped poor quality hay and supplemented to meet targeted nutritional planes based on estimated hay intakes. Dam BW, BCS, backfat, and metabolic status were determined pre-treatment, every 21 d (BW and metabolic status) or 42 d (BCS and backfat) during gestation, and post-calving. At birth, calf BW and size were measured, and total colostrum from the most full rear quarter was collected pre-suckling. Data were analyzed with nutritional plane, treatment initiation date, and calf sex (when P < 0.25) as fixed effects. Gestational metabolites included day and nutritional plane × day as repeated measures. During late gestation, CON dams gained (P < 0.01) maternal (non-gravid) BW and maintained (P >/= 0.17) BCS and backfat, while NR dams lost (P < 0.01) maternal BW, BCS, and backfat. Circulating glucose, urea N, and triglycerides were less (P /= 0.27) gestation length, calf birth weight, or calf size at birth. Colostrum yield was 40% less (P = 0.04) in NR dams than CON. Protein and immunoglobulin concentrations were greater (P /= 0.55). In summary, beef heifers experiencing late gestational nutrient restriction prioritized partitioning nutrients to fetal growth and colostrum production over maternal growth. During undernutrition, fetal and colostral nutrient demands were largely compensated for by catabolism of maternal tissue stores.