Impacts of dietary protein level and feed restriction during prepuberty on mammogenesis in gilts

The possible roles of dietary protein level and feed restriction in regulating mammary development of prepubertal gilts were investigated. Cross-bred gilts were fed a commercial diet until 90 d of age and then divided into four nutritional regimens based on two pelleted diets (as-fed basis): a high-protein diet (HP = 13.8 MJ of ME, 1.0% total lysine, 18.7% CP) and a low-protein diet (LP = 13.8 MJ of ME, 0.7% total lysine, 14.4% CP). Nutritional regimens were as follows: 1) HP ad libitum until slaughter (n = 22, T1); 2) HP ad libitum until 150 d of age followed by LP until slaughter (n = 20, T2); 3) LP ad libitum until slaughter (n = 21, T3); and 4) HP with a 20% feed restriction until slaughter (n = 19, T4). Gilts were weighed, their backfat thickness was measured, and jugular blood samples were obtained on d 90, 150, and at slaughter to determine concentrations of prolactin, IGF-I, leptin, and glucose. Gilts were slaughtered 8+/-1 d after their first or second estrus (202.7+/-14.5 d of age). Mammary glands were excised, parenchymal and extraparenchymal tissues were dissected, and composition of parenchymal tissue (protein, fat, DM, DNA, protein/DNA) was determined. The T4 gilts weighed less (P < 0.01) and had less backfat (P < 0.01) than did gilts on other treatments on d 150 and at slaughter. Treatments had no significant effects on prolactin, IGF-I, or glucose concentrations, but there was a treatment x day interaction (P < 0.01) for leptin, with concentrations being lower at slaughter in restricted-fed (T4) vs. LP (T3) gilts (P < 0.05). There was less extraparenchymal mammary tissue (P < 0.01) in T4 gilts than in gilts from the other groups and a tendency (P = 0.13) for the amount of parenchymal tissue to be lower in T4 gilts. In conclusion, a lower lysine intake during prepuberty did not hinder mammary development of gilts, but a 20% feed restriction decreased mass of parenchymal and extraparenchymal tissues. The effect of feed restriction on extraparenchymal tissue is most likely associated with the lower fat deposition.