• Insulin restores GH responsiveness during lactation-induced negative energy balance in dairy cattle: effects on expression of IGF-I and GH receptor 1A

      Butler, Stephen T.; Marr, A.L.; Pelton, Susanne H.; Radcliff, R.P.; Lucy, Matt C.; Butler, W.R.; US Department of Agriculture; Teagasc Walsh Fellowship Programme; NE-161 (Bioscientifica, 2003-02-01)
      Early lactation in dairy cattle is a period of severe negative energy balance (NEB) characterized by reduced blood glucose and insulin concentrations and elevated blood growth hormone (GH) concentrations. The liver is refractory to GH during NEB and this uncoupling of the GH-insulin-like growth factor (IGF) axis results in diminished plasma concentrations of IGF-I. Our objectives were to examine the effects of insulin administration during the immediate postpartum period on plasma IGF-I and GH concentrations and to examine the hepatic expression of total GH receptor (all GH receptor transcripts), GH receptor 1A (GHR 1A) and IGF-I. In addition, we examined adipose tissue for total GH receptor and IGF-I mRNA levels to establish the effects of chronic hyperinsulinemia on an insulin-responsive peripheral tissue. Holstein cows (n = 14) were subjected to either a hyperinsulinemic-euglycemic clamp (insulin; INS) or saline infusion (control; CTL) for 96 hours starting on day 10 postpartum. Insulin was infused intravenously (1µg • kg BW-1 • h-1), blood samples were collected hourly, and euglycemia was maintained by infusion of glucose. Insulin concentrations during the infusions were increased 8-fold in INS cows compared with CTL cows (2.33 ± 0.14 vs. 0.27 ± 0.14 ng/ml; P < 0.001) while blood glucose concentrations were not different between treatments (45.3 ± 2.2 vs. 42.5 ± 2.2 mg/dl; P > 0.1). Plasma IGF-I increased continuously during the insulin infusion, and reached the highest concentrations at the end of the clamp, being almost four-fold higher in INS compared with CTL cows (117 ± 4 vs. 30 ± 4 ng/ml; P < 0.001). Hepatic expression of GHR 1A and IGF-I mRNA was low in CTL cows, but was increased 3.6-fold (P < 0.05) and 6.3-fold (P < 0.001) respectively in INS cows. By contrast, in adipose tissue the changes in gene expression in response to insulin were reversed with decreases in both total GHR and IGF-I mRNA. The expression of GHR 1A and IGF-I mRNA in liver tissue were correlated in INS (r = 0.86; P < 0.05), but not CTL cows (r = 0.43; P > 0.1). Insulin appears to be a key metabolic signal in coupling the GH-IGF axis, thus orchestrating a marked elevation in circulating IGF-I concentrations.
    • Residual feed intake phenotype and gender affect the expression of key genes of the lipogenesis pathway in subcutaneous adipose tissue of beef cattle

      McKenna, Clare; Porter, Richard K; Keogh, Kate; Waters, Sinead M.; McGee, Mark; Kenny, David A.; Teagasc Walsh Fellowship Programme (Biomed Central, 2018-09-20)
      Background Feed accounts for up to 75% of costs in beef production systems, thus any improvement in feed efficiency (FE) will benefit the profitability of this enterprise. Residual feed intake (RFI) is a measure of FE that is independent of level of production. Adipose tissue (AT) is a major endocrine organ and the primary metabolic energy reservoir. It modulates a variety of processes related to FE such as lipid metabolism and glucose homeostasis and thus measures of inter-animal variation in adiposity are frequently included in the calculation of the RFI index. The aim of this study was to determine the effect of phenotypic RFI status and gender on the expression of key candidate genes related to processes involved in energy metabolism within AT. Dry matter intake (DMI) and average daily gain (ADG) were measured over a period of 70 d for 52 purebred Simmental heifers (n = 24) and bulls (n = 28) with an initial BW±SD of 372±39.6 kg and 387±50.6 kg, respectively. Residual feed intake was calculated and animals were ranked within gender by RFI into high (inefficient; n = 9 heifers and n = 8 bulls) and low (efficient; n = 9 heifers and n = 8 bulls) groups. Results Average daily gain ±SD and daily DMI ±SD for heifers and bulls were 1.2±0.4 kg and 9.1±0.5 kg, and 1.8±0.3 kg and 9.5±1 kg respectively. High RFI heifers and bulls consumed 10% and 15% more (P < 0.05) than their low RFI counterparts, respectively. Heifers had a higher expression of all genes measured than bulls (P < 0.05). A gender × RFI interaction was detected for HMGCS2(P < 0.05) in which high RFI bulls tended to have lower expression of HMGCS2 than low RFI bulls (P < 0.1), whereas high RFI heifers had higher expression than low RFI heifers (P < 0.05) and high RFI bulls (P < 0.05). SLC2A4 expression was consistently higher in subcutaneous AT of low RFI animals across gender. Conclusion The findings of this study indicate that low RFI cattle exhibit upregulation of the molecular mechanisms governing glucose metabolism in adipose tissue, in particular, glucose clearance. The decreased expression of SLC2A4 in the inefficient cattle may result in less efficient glucose metabolism in these animals. We conclude that SLC2A4 may be a potential biomarker for RFI in cattle.