Hepatic mRNA expression of acid labile subunit and deiodinase 1 differs between cows selected for high versus low concentrations of insulin-like growth factor 1 in late pregnancy

Abstract

The somatotropic axis is a key metabolic pathway during transition from late pregnancy to early lactation in dairy cows. The first objective of this study was to determine the feasibility of selecting cows with persistent differences in total insulin-like growth factor 1 (IGF-1) concentration by taking only a single antepartum blood sample. The second objective was to elucidate the underlying causes of differences in peripheral IGF-1 concentrations throughout late pregnancy and whether hormonal axes also differed in dairy cows with low versus high IGF-1. Twenty clinically healthy Holstein Friesian cows were chosen based on their plasma IGF-1 concentration at 244 to 254 d after artificial insemination (AI) and other selection criteria (health status, body condition score, number of lactations). These cows were selected from a large-scale farm, transported to the clinic, and monitored daily from 261 to 275 d after AI. The concentrations of IGF-1, growth hormone, IGF binding proteins 2, 3, and 4, insulin, cortisol, thyroid hormones, progesterone, and estradiol were measured. Ultimately, 7 IGF-1-low and 7 IGF-1-high cows were statistically analyzed. Additionally, a liver biopsy was taken on d 270 ± 1 after AI for analysis of gene expression of somatotropic family members, liver deiodinase 1, and suppressor of cytokine signaling-2. It was possible to select cows with different IGF-1 concentrations based upon only 1 blood sample collected in late pregnancy. Concentrations of IGF-1 in IGF-1-low versus IGF-1-high animals (n=7 each) remained significantly different between groups from the day of selection of the animals until d 275 after AI. Second, the differences in total plasma IGF-1 concentration between experimental groups may be attributed to differences in hepatic production of acid labile subunit. The ability of IGFBP-3 to bind IGF-1 declined before calving in all cows. Furthermore, in addition to decreased mRNA expression of growth hormone receptor 1A and IGF-1 relative to calving, serum binding capacities for IGF-1 also decreased. Insulin-like growth factor binding protein 4 mRNA expression was higher in cows with low IGF-1 concentrations; this binding protein inhibits IGF-1 action at the tissue level and therefore may reduce IGF-1 bioavailability. Finally, other endocrine end points (e.g., insulin and thyroid hormones) differed between the 2 groups.

Antepartal insulin-like growth factor concentrations indicating differences in the metabolic adaptive capacity of dairy cows

“…In a previous study, cows from one large-scale dairy farm were fed comparable diets and had significantly different antepartal IGF-I concentrations [24]. These results support the idea that additional factors may block IGF-I production by inhibiting the GHR signal transduction.…”

“…At the dairy farm, the cows were housed throughout the year in a free-stall barn with rubber mats. The animals were fed a total mixed ration twice a day as previously described by Piechotta et al [24] automatically by a band-conveyor system and provided with a mineral supply (Deutsche Vilomix Tierernährung, Germany) along with free access to water.…”

“…The plasma IGF-I concentrations were measured immediately using a previously described method [24] and cows were selected following a previously established protocol [24]. Due to logistical reasons, two cows were selected during each farm visit as previously described [24].…”

“…During the peripartal period, liver GHR expression decreases in dairy cows along with hepatic IGF-I production while GH concentrations increase due to reduced negative feedback signaling [20,24]. It is well known that the production of GHR transcript, GHR1A, decreases as parturition approaches [20] along with the binding of GH to hepatic GHR [27].…”

“…It was previously demonstrated that cows which were fed "limited" regarding their energy requirements showed higher estradiol concentrations and parallel also have elevated hepatic SOCS2 expression [34]. Furthermore, cows selected for low IGF-I concentrations during late pregnancy were shown to have comparable GHR1A expression levels and produced higher amounts of SOCS2 mRNA [24]. Based on these data, the goals of the present study were to monitor cows selected based on antepartal IGF-I concentrations until spontaneous calving, and evaluate the interrelationships between endocrine endpoints using a structural equation model.…”