The effect of pregnancy on nitrogen retention, maternal insulin sensitivity, and mRNA abundance of genes involved in energy and amino acid metabolism in gilts

Emily G Miller, Lee-Anne Huber, John P Cant, Crystal L Levesque, Cornelis F M de Lange

Twenty one of each pregnant (P) and non-serviced, non-pregnant (NP) sister-pairs of gilts were selected to investigate the effect of pregnancy on protein deposition (Pd; whole body and maternal), insulin sensitivity, and mRNA abundance of genes involved in energy and AA metabolism. Between breeding (study d 0) and d 111, P and NP gilts received 2.16 kg of the experimental diet (3.34 Mcal ME/kg, 17.6 % crude protein, 0.78 % standardized ileal digestible lysine) that was formulated to meet the estimated ME requirements of pregnant gilts (and meet or exceed AA requirements). Nitrogen balances were conducted on d 63 and 102 ± 0.2 of the study during 4-d periods. Blood samples were collected on d 43, 56, 71, 85, 98, and 108 ± 0.3 of the study to determine plasma concentrations of fasted IGF-1, estradiol (E2), and estrone sulfate (E1S). Frequently sampled intravenous glucose tolerance tests (FSIGTT) were conducted on d 75 ± 0.7 in 6 P and 5 NP gilts and on d 107 ± 0.4 in 17 P and 17 NP gilts and the MINMOD approach was applied to evaluate whole body insulin sensitivity and pancreatic responsiveness. Longissimus muscle (LM) and s.c. adipose tissue (AD) samples were excised from 12 P and 12 NP gilts at d 111 ± 0.4 of the study after euthanasia to determine mRNA abundance of key genes. Whole body Pd was greater (P < 0.001) at d 102 and maternal Pd was lower (P < 0.002) at d 63 and 102 for P compared to NP gilts. Plasma concentrations of E1S and E2 increased (P < 0.05) with study day for P gilts and remained constant for NP gilts, which coincided with reduced plasma concentrations of IGF-1 and increased estrogen receptor alpha (ESR1) mRNA abundance in LM of P gilts. Glucose effectiveness was not different between P and NP gilts, but whole body insulin sensitivity was lower (P = 0.004) in P compared to NP gilts on d 75 and 107, which corresponded with reduced mRNA abundances of SLC2A4, HK2, SREBF1 and FASN, and increased abundances of PDK4 and PPARGC1A in LM and AD. When fed identically, P gilts had greater whole body Pd at d 102, which reflects Pd in the pregnancy-associated tissues (at the expense of maternal Pd), likely driven by estrogen-stimulated insulin resistance in peripheral tissue and subsequent modulation of gene expression relating to glucose metabolism.