Dietary protein and(or) energy restriction in mares: plasma growth hormone, IGF-I, prolactin, cortisol, and thyroid hormone responses to feeding, glucose, and epinephrine1

Abstract

Sixteen light horse mares were fed diets of bermudagrass hay and a corn/cottonseed hull-based supplement formulated to contain either 100% (control) or 50% (restricted) of the protein and(or) energy requirements for maintenance in a 2 x 2 factorial arrangement of treatments. Plasma IGF-I, prolactin, cortisol, triiodothyronine, and thyroxine were monitored for 33 d. On the 27th d, frequent blood samples were drawn throughout the day for the measurement of growth hormone (GH), and on the 29th d, an epinephrine challenge and an i.v. glucose tolerance test (IVGTT) were performed in the morning and afternoon, respectively. Restriction of protein and(or) energy reduced (P < .001) plasma IGF-I concentrations within 24 h, and the effect persisted through the 24th d. Energy restriction decreased (P = .01) plasma cortisol concentrations, whereas thyroid hormones were not influenced (P > .1) by restriction of protein and(or) energy. Plasma prolactin concentrations were low throughout the experiment and after the IVGTT, but they increased (P = .003) after feeding. Protein restriction increased (P = .09) the occurrence of GH episodes during the 14-h feeding period on d 27; the greatest effect occurred in the mares restricted in both nutrients. In contrast, energy restriction reduced (P = .05) the GH response to epinephrine injection. We conclude that 1) protein deficiency in mares increases GH secretion, whereas energy restriction alone does not, 2) a deficiency in energy and(or) protein reduces IGF-I secretion, and 3) prolactin concentrations increase after feeding, even at a time of year when secretion rates are naturally low.

Total and free iodothyronines profile in the donkey (Equus asinus) over a 12-month period

“…The results did not exclude the fact that some stress conditions such as stabling or Symbols indicate significant ( ▲ P < 0.05; ▲▲ P < 0.01) differences in average hormone compared to previous month management (Hoffman et al 1995;Malinowski et al 1996;Christensen et al 1997;Moons et al 2005) and diet (Messer et al 1995;Sticker et al 1995;Powell et al 2000) may determine higher T 4 , fT 3 and fT 4 concentrations in both barren and pregnant donkeys than data reported in horses. Stress conditions may be induced by blood drawing which was always performed in donkeys that were out to pasture.…”

A study of serum insulin-like growth factor type 1 (IGF-1) concentrations in resting untrained Andalusian horses: influence of age and gender

“…In our research, we recorded blood sampling times, and the multivariate analysis did not reveal significant differences in association with the time of blood extraction. Circulating concentrations of IGF-1, as well as GH, are clearly dependent on nutritional status in different species, including the horse (Philips, 1986;Thissen et al, 1994;Sticker et al, 1995;Christensen et al, 1997;Ropp et al, 2003). Restricted nutrition and dietary protein supply seem to be an important limiting factor for maximal stimulation of circulating IGF-1 concentrations (Sticker et al, 1995;Christensen et al, 1997;Ropp et al, 2003).…”

“…Circulating concentrations of IGF-1, as well as GH, are clearly dependent on nutritional status in different species, including the horse (Philips, 1986;Thissen et al, 1994;Sticker et al, 1995;Christensen et al, 1997;Ropp et al, 2003). Restricted nutrition and dietary protein supply seem to be an important limiting factor for maximal stimulation of circulating IGF-1 concentrations (Sticker et al, 1995;Christensen et al, 1997;Ropp et al, 2003). In fact, it has been demonstrated that food deprivation leads to reduced blood concentrations of IGF-1, which are reversed following refeeding in humans (Clemmons et al, 1981), mice (McKnight and Goddard, 1989), rats (Maes et al, 1983), pigs (Dauncey et al, 1990) and horses (Sticker et al, 1995;Christensen et al, 1997).…”

“…Restricted nutrition and dietary protein supply seem to be an important limiting factor for maximal stimulation of circulating IGF-1 concentrations (Sticker et al, 1995;Christensen et al, 1997;Ropp et al, 2003). In fact, it has been demonstrated that food deprivation leads to reduced blood concentrations of IGF-1, which are reversed following refeeding in humans (Clemmons et al, 1981), mice (McKnight and Goddard, 1989), rats (Maes et al, 1983), pigs (Dauncey et al, 1990) and horses (Sticker et al, 1995;Christensen et al, 1997). According to the data provided by Christensen et al (1997), a significant reduction in IGF-1 concentrations is apparent after 48 h of feed deprivation.…”

“…Serum IGF-1 concentrations in horses depend on many factors, such as breed (Tremblay et al, 1993;Ozawa et al, 1995), age (Malinowski et al, 1996;Champion et al, 2002;Fortier et al, 2005;Noble et al, 2007;Munoz et al, 2010a), sex (Ozawa et al, 1995), nutritional status, particularly dietary protein supply and feed deprivation and refeeding (Sticker et al, 1995;Christensen et al, 1997;Ropp et al, 2003), exercise, training and fitness level (Jackson et al, 2003;Noble et al, 2007).…”