Nutrient partitioning in pregnant and lactating beef females

Abstract

We investigated the impacts of late gestational nutrient restriction in first-parity beef females on prenatal and postnatal nutrient availability to the offspring. During late gestation, nutrient restricted dams lost maternal body weight and body condition and had less circulating metabolites than adequately-fed dams. Despite contralateral placental growth being less in nutrient restricted dams, total uterine blood flow and total placental mass were maintained, and cotyledonary expression of nutrient transporters and an angiogenic factor were upregulated, which collectively allowed for calf size at birth to be spared. Nutrient restricted dams produced less colostrum, yet it was generally more concentrated so that total colostral nutrients and immunoglobulins, except lactose, were similar. When fed to meet nutrient requirements during lactation, previously nutrient restricted dams recovered quickly metabolically and experienced compensatory growth, but still had less body condition at weaning than adequately-fed dams. Nutrient restricted dams had decreased mammary blood flow, lower milk yield, reduced milk protein concentration, and less total milk nutrients available for their calves. Calves born to nutrient restricted dams diverged in body weight by day 42 of age and weighed less at weaning, but metabolic status pre-weaning was not greatly altered. In summary, first-parity beef females experiencing late gestational nutrient restriction prioritized partitioning nutrients to fetal growth and colostrum production over maternal growth. After parturition, previously nutrient restricted dams fed adequately during lactation partitioned nutrients to maternal growth and basal energy reserves over milk production.