Diurnal Variations in Plasma Insulin and Growth Hormone Associated with Two Stages of Lactation in High Producing Dairy Cows*

Abstract

Plasma concentrations of GH, insulin, glucose, and FFA were measured in high yielding dairy cows at periods of peak milk production and later during periods of increased feed intake. During each period, five cows were prepared with indwelling jugular catheters, and blood was sampled at 10-min intervals for 24 h, followed by hourly sampling for an additional 24 h. During early lactation (30 days post partum), the plasma GH concentration was elevated (13.2 ng/ml) compared to that in later lactation (90 days post partum; 9.8 ng/ml). This increased GH status was due to a greater magnitude of individual secretory spikes (27.3 vs. 20.2 ng/ml) rather than a difference in the frequency of spikes or in baseline plasma levels of GH. As lactation progressed from 30-90 days post partum, milk yield decreased, feed intake increased, and overall plasma concentration of insulin increased (17.3 vs. 29.3 microU/ml), reflecting both an elevated magnitude of hormone secretory spikes (30.2 vs. 55.2 microU/ml) and an elevated baseline concentration (16.8 vs. 27.3 microU/ml). The short term repeatability of overall mean and total 24-h GH and insulin secretion in lactating cows was demonstrated as well as the uniqueness of individual cow GH secretory patterns. Significant differences were not found in either glucose or FFA concentrations between lactation periods. Increased GH and decreased insulin during early lactation are likely to promote the mobilization of adipose tissue stores needed to supplement dietary energy consumption.

Growth hormone: roles in female reproduction

“…Indeed, treatment of dairy cows with bGH increases milk yield by 10-40%, by affecting both mammogenesis and lactogenesis (Breier et al 1991). The importance of GH in ruminant lactation is further shown by the correlation between GH gene polymorphisms (Lucy et al 1993b, Lee et al 1996, Yao et al 1996, GHR gene polymorphisms (Falaki et al 1996), plasma GH levels (Powell & Keisler 1995) and heritable patterns of GH secretion (Vasilatos & Wangsness 1981, Klindt 1988, Beerepoot et al 1991 with milk production. GH treatment also increases milk yield in humans (Milsom et al 1992) and milk yield and glucose concentration in goats (Driancourt & Disenhaus 1997, Faulkner 1999.…”

A review of bovine growth hormone

“…Although the precise signal transduction mechanisms of the type I receptor are not known, it may possess tyrosine kinase activity (reviewed by Sara and Hall 1990 During natural lactation, increasing milk yield is associated with an elevated blood concentration of GH (Ingalls et al 1973; Hart et al 1979;Vasilatos and Wangsness 1981 ;Bines and Hart 1982;Sartin et al 1985) which declines during later lactation (Koprowski and Tucker 1973). High-yielding cows have also been shown to have higher serum GH concentrations than low-yielding cows during lactation (Hart et al 1978;Sartin et al 1988).…”

Modulation of Growth Hormone-Releasing Factor Stimulated Growth Hormone Secretion by Plasma Glucose and Free Fatty Acid Concentrations in Sheep

“…Interestingly, fasting in sheep was accompanied by elevated basal GH concentrations and an increased sensi tivity to growth hormone-releasing factor (GRF) injection [4], Lactation in dairy cows is another condition associated with altered metabolic status as well as changes in GH con centrations. Basal GH was elevated in early lactation in dairy cows [18]. Declining glucose concentrations following glucose infusion [II] and GRF injection [12] also had a greater effect on GH in early lactation, when energy intake Received: February 26, 1988 Accepted after revision: April 25, 1988 did not meet energy needs of the cow.…”