Nutrient Balance and Stage of Lactation Affect Responses of Insulin, Insulin-Like Growth Factors I and II, and Insulin-Like Growth Factor-Binding Protein 2 to Somatotropin Administration in Dairy Cows

Abstract

Six Holstein cows were used in a complete block design to examine effects of period of lactation and somatotropin (bST) administration on concentrations of insulin, insulin-like growth factors (IGF-I, IGF-II), and IGF-binding protein 2 (IGFBP-2). During late lactation, the dry period and the subsequent early lactation, cows received injections of NaHCO3 buffer for 5 d and bST for 7 d. Cows were in positive energy and protein balances during late lactation and the dry period and in slight negative balances during early lactation. Basal insulin concentrations were highest in late lactation (170 pmol/L), whereas bST concentrations were higher in early lactation (0.6 micrograms/L). Insulin was increased by bST in the dry period (255 pmol/L) and late lactation (149 pmol/L) but not in early lactation (14 pmol/L), probably because of greater availability of glucose during positive nutrient balance. Basal IGF-I was lowest in early lactation (63.6 micrograms/L) but was increased by bST during all periods. The IGF-I response to bST administration was lower during early lactation (74.1 micrograms/L) compared with late lactation (123.6 micrograms/L) and dry period (146.0 micrograms/L). The IGF-II concentrations were not affected by period of lactation of bST administration but IGF-II tended to be higher during bST administration when cows were dry. Concentration of IGFBP-2 was higher during early lactation when cows were in negative nutrient balance (479.5 micrograms/L) than during the dry period (289.2 micrograms/L) and was decreased with bST. These data support a role of insulin and IGF in regulation of milk production. Availability of nutrients may be involved in regulating these hormones, particularly during bST treatment.

Effect of feed restriction on serum somatotropin, insulin-like growth factor-I-(IGF-I) and IGF binding proteins in cyclic heifers actively immunized against growth hormone releasing factor

“…(4,7,28,38,39). Our observation that low ering serum ST increased IGFBP-2 and decreased IGFBP-3 is consistent with observations that exogenous ST increased IGFBP-3 (28) and decreased IGFBP-2 in dairy cows (28,39). These data provide evidence that feed restriction in ruminants elevates ST through a mechanism involving an increase in frequency of ST release.…”

“…In contrast to reports in humans (4,9) and pigs (7), we failed to observe an effect of acute feed restriction on IGFBP in ruminants. Other reports have failed to show a clear effect of feed restriction on IGFBP in ruminants (5); however, Vincini (39) reported that IGFBP-2 was higher during early lactation when cows were in negative energy balance. Gallaher (10) found that fasting castrate sheep decreased IGFBP-3 and increased IGFBP-2; however, fast ing in pregnant ewes was associated with a slight decrease in IGFBP-3, but no change in IGFBP-2.…”

Post-ruminal or intravenous infusions of carbohydrates or amino acids to dairy cows 2. Late lactation

“…This is related to the parallel increase in milk yield and milk protein yield (Lemosquet et al, 2004). Low circulating concentrations of IGF-1 in early lactation have been associated with negative energy balance (Spicer et al, 1990;Vicini et al, 1991) and with negative protein balance when energy balance is not already limiting (Ronge et al, 1988).…”

Effect of exogenous insulin and fasting on growth hormone receptor and IGF-I expression in the pre-ovulatory follicle of ewes

“…In this situation, IGF-I expression is no longer capable of increase in response to the secretion of GH by the pituitary (Vicini et al, 1991). This happens -E-mail: augusto.schneider@live.com because insulin concentration is reduced, and so is GHR expression in the liver (Butler et al, 2003).…”