Late gestational nutrient restriction in primiparous beef females: Performance and metabolic status of lactating dams and pre-weaning calves

Authors: REDIFER, COLBY - University Of Missouri; WICHMAN, LINDSEY - University Of Missouri; DAVIES-JENKINS, SHELBY - 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: 1/18/2024
Publication Date: 1/19/2024
Citation: Redifer, C.A., Wichman, L.G., Davies-Jenkins, S.L., Rathert-Williams, A.R., Freetly, H.C., Meyer, A.M. 2024. Late gestational nutrient restriction in primiparous beef females: Performance and metabolic status of lactating dams and pre-weaning calves. Journal of Animal Science. 102. Article skae015. https://doi.org/10.1093/jas/skae015.
DOI: https://doi.org/10.1093/jas/skae015

Interpretive Summary: Nutrient requirements increase substantially during late gestation in the beef female; however, challenges of poor forage nutrient availability mean undernutrition can occur. For heifers, the added nutrient requirements needed to continue growing during their first pregnancy and lactation pose an even greater challenge. Even when beef females are fed adequately during lactation, lingering effects of late gestational nutrient restriction on the dam and calf may exist. We demonstrated that first-parity beef females who were nutrient restricted during late gestation and then fed to estimated nutrient requirements during lactation recovered quickly metabolically and experienced compensatory growth, but still had less body condition at weaning than controls. Late gestational nutrient restriction did not affect calf size at birth. Nutrient restriction resulted in calf body weight and size measures diverging early in life and ultimately a 12.8% decrease in weaning weight, which was likely due to decreased milk production (in companion paper). Despite this, metabolic status of calves born to nutrient restricted dams was not greatly altered. In summary, first-parity beef females that were nutrient restricted during late gestation prioritized partitioning nutrients to maternal growth over milk production during lactation, but cows were thinner at weaning and pre-weaning calf growth was slowed.

Technical Abstract: Fall-calving primiparous beef females [body weight (BW): 451 ± 28 (SD) kg; body condition score (BCS): 5.4 ± 0.7] were individually-fed 100% (control; CON; n = 13) or 70% (nutrient restricted; NR; n = 13) of estimated metabolizable energy and metabolizable protein requirements from day 160 of gestation to calving. Post-calving, all dams were individually-fed tall fescue hay supplemented to meet estimated nutrient requirements for maintenance, growth, and lactation in Calan gates until day 149 of lactation, which limited calves to milk only. From day 150 of lactation until weaning at day 243, dams and calves were group-fed in drylots. Dam BW and metabolic status were determined every 21 d, and BCS and backfat (BF) were determined every 42 d of lactation until weaning. Pre-weaning calf BW, size, and metabolic status were determined every 21 d. Data were analyzed with nutritional plane, calving date, and calf sex (when P < 0.25) as fixed effects. Circulating metabolites included day and nutritional plane × day as repeated measures. We previously reported that post-calving, NR dams were 64 kg and 2.0 BCS less than CON, but calf BW and size at birth were not affected. During the first 147 d of lactation, NR dams gained more (P < 0.01) BW than CON and increased (P < 0.01) BCS, while CON decreased (P /= 0.73). At weaning, NR dams weighed 17 kg less (P = 0.15), were 0.67 BCS lower (P < 0.01), and tended to have less (P = 0.06) BF. Calves born to NR dams weighed less (P = 0.02) than CON by day 42 of age and were 13% smaller (P < 0.01) at weaning. Calf girth measures diverged (P /= 0.16). In summary, first-parity beef females that were nutrient restricted during late gestation experienced compensatory growth and gained body condition during lactation but were still thinner at weaning. Nutrient restriction reduced pre-weaning calf growth, likely due to decreased milk production.