Ma. Mcguire et al., NUTRITIONAL MODULATION OF THE SOMATOTROPIN INSULIN-LIKE GROWTH-FACTORSYSTEM - RESPONSE TO FEED DEPRIVATION IN LACTATING COWS, The Journal of nutrition, 125(3), 1995, pp. 493-502
Mid-lactation Holstein cows (n = 4) were used to evaluate the effects
of complete feed deprivation on circulating insulin-like growth factor
s (IGF) and their binding proteins (IGFBP). Comparisons were made betw
een cows in fed and unfed conditions and included response to a single
injection of bovine somatotropin (bST). Two days of feed deprivation
decreased milk yield 66%. Concentrations of bST nearly doubled during
feed deprivation, whereas glucose and insulin steadily decreased. Circ
ulating concentrations of IGF-I decreased nearly 50%, IGF-II decreased
28% and IGFBP-2 increased 49% during the 2 d of feed deprivation. In
contrast, IGFBP-3 was not affected. Eighteen to 24 h after the bST cha
llenge, circulating concentrations of IGF-I rose 100% during the fed p
eriod, but there was no response during the unfed period. Blood concen
trations of IGF-II decreased 17% after bST challenge in the fed period
but were unchanged in the unfed period. More moderate undernutrition
(80% of requirements) did not affect circulating IGFBP-2 but did alter
the response of IGFBP-2 to bST. A conceptual model was developed that
illustrates that nutritional regulation of the ST/IGF system represen
ts a key component signaling the appropriate use of nutrients. Overall
, results demonstrate that nutritional modulation of the ST/IGF system
plays a key role in animal performance and well-being over a wide ran
ge of physiological situations.