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.

Pituitary growth hormone (GH) release and hepatic insulin-like growth factor-I (IGF-I) production increase after an injection of 17β-estradiol (E2) in ovariectomized dairy cattle. However, whether endogenous sexual steroid hormones also influence the hepatic GH receptor (GHR) signaling pathway during a physiological estrus cycle remains unclear. The aim of this study was to analyze the hepatic GHR signaling pathway during the luteal phase and after a period of increased E2 concentrations (after ovulation) as well as in 7 heifers before ovulation. Ovarian ultrasounds were performed daily during repeated physiological cycles (n = 56) of 30 Holstein Friesian heifers to determine ovulation [before ovulation (n = 7, bOv) and after ovulation 24-60 h after the appearance of estrus signs (n = 49, aOv)] and luteal phase (CLP; d 12 ± 1 after ovulation). Blood samples and liver biopsies were obtained, and blood concentrations of E2, P4, insulin-like growth factor (IGF)-I, IGF-II, and GH were measured. In the liver biopsies, we determined mRNA expression of the estrogen receptor α (ERα), GHR, Janus kinase 2 (JAK2), signal transducer and activator of transcription 5B (STAT5B), suppressor of cytokine signaling (SOCS)2 and 3, IGF-I, and IGF-II by quantitative reverse transcription-PCR. The concentration of E2 was higher bOv than aOv and CLP, as expected. The concentrations of IGF-I and GH were higher bOv and aOv compared with CLP. In contrast, concentrations of IGF-II were lower aOv compared with bOv and CLP. The mRNA expression of GHR was higher in liver biopsies obtained bOv compared with aOv and CLP. Notably, the expression of SOCS2 was higher bOv than aOv and in the CLP. Increased hepatic expression of SOCS2 during estrus was detectable when IGF-I concentrations were high; this result might indicate that SOCS2 expression attenuates the GHR signal transduction pathway during the phase of increased pituitary GH release. In conclusion, hepatic GHR and SOCS2 mRNA expression appeared to be promptly and sensitively regulated by increased E2 levels before ovulation of dairy heifers.

Cortisol is known to reflect the level of the stress response. However, measuring the cortisol concentration only once fails to provide sufficient information about the duration of the stress exposure. Moreover, handling is an acute stressor and increases cortisol secretion especially in wildlife species. Yet, in phocids reliable indicators are missing that reflect potential chronic effects of stress. The adrenal-derived steroid hormone dehydroepiandrosterone (DHEA) has been described as biomarker for the assessment of the stress status but has not been applied to marine mammal stress research. Therefore, DHEA, the sulfated precursor DHEAS and the cortisol/DHEA ratio were determined in serum of different seals. One group consisted of harbor ( Phoca vitulina) and gray seals ( Halichoerus grypus) that were habituated to human handling. The other two groups included healthy and free-ranging seals suffering from a disease. Blood samples were taken from 11 habituated (six males, five females), 17 wild_healthy (13 males, four females), and nine wild_diseased seals (four males, five females). No differences in serum cortisol levels could be detected between wild_healthy and wild_diseased seals. On the contrary, wild_diseased seals showed the lowest DHEA concentration compared to the other two groups. Wild_diseased seals also revealed the highest cortisol/DHEA ratio compared to the habituated_zoo (2,074.7 ± 351.4 vs. 121.5 ± 26.8, P < 0.001) and wild_healthy seals (827.9 ± 214.3, P < 0.01). DHEA and the cortisol/DHEA ratio may reflect differences in the functionality of the hypothalamic-pituitary-adrenal axis and therefore represent valuable tools for the assessment of stress-related effects in seals.

Cows with different Insulin-like Growth Factor-I (IGF-I) concentrations showed comparable expression levels of hepatic growth hormone receptor (GHR). Suppressor of cytokine signaling 2 (SOCS2), could be responsible for additional inhibition of the GHR signal cascade. The aims were to monitor cows with high or low antepartal IGF-I concentrations (IGF-Ihigh or IGF-Ilow), evaluate the interrelationships of endocrine endpoints, and measure hepatic SOCS2 expression. Dairy cows (n = 20) were selected (240 to 254 days after artificial insemination (AI)). Blood samples were drawn daily (day -17 until calving) and IGF-I, GH, insulin, thyroid hormones, estradiol, and progesterone concentrations were measured. Liver biopsies were taken (day 264 ± 1 after AI and postpartum) to measure mRNA expression (IGF-I, IGFBP-2, IGFBP-3, IGFBP-4, acid labile subunit (ALS), SOCS2, deiodinase1, GHR1A). IGF-I concentrations in the two groups were different (p < 0.0001). However, GH concentrations and GHR1A mRNA expression were comparable (p > 0.05). Thyroxine levels and ALS expression were higher in the IGF-Ihigh cows compared to IGF-Ilow cows. Estradiol concentration tended to be greater in the IGF-Ilow group (p = 0.06). It was hypothesized that low IGF-I levels are associated with enhanced SOCS2 expression although this could not be decisively confirmed by the present study.

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