The effect of the dietary protein restriction and re-feeding on the content of leptin, IGF-I and urea nitrogen in the blood plasma and growth performance in pigs

The aim of the present study was to examine the effect of the dietary protein restriction on the plasma concentrations of leptin, insulin-like growth factor (IGF-I), blood urea nitrogen (BUN) and growth performance in growing pigs. A total of 12 gilts were divided into experimental (ET) and control (CT) treatments. After the 14-day dietary restriction period during which the ET fed a low-protein diet (LPD, 5% of crude protein) and the CT fed a standard diet (SD, 16% of crude protein) the second 14-day re-feeding period followed, in which LPD was replaced by a SD that was fed by the both treatments. During the dietary protein restriction reduced (P < 0.05) N intake, average daily gain (ADG), concentration of BUN and tendency (P = 0.084) to the lower IGF-I in ET compared with CT were observed. Feed to gain ratio was greater (P < 0.05) in ET. During the subsequent re-feeding period, there was a tendency to the greater daily feed intake (P = 0.068) and N intake (P = 0.070), greater (P < 0.05) ADG, BUN and plasma leptin but no IGF-I in ET. These observations suggest that dietary protein restriction promotes body growth in pigs, which is associated with increase in blood leptin and BUN level in ET during the re-feeding, indicating that the increased ADG can be due to increased fat deposition but not of protein synthesis.