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Impacts of dietary protein level and feed restriction during prepuberty on mammogenesis in gilts^1,2

C. Farmer^*,3, D. Petitclerc^*, M. T. Sorensen, M. Vignola and J. Y. Dourmad

^* Agriculture and Agri-Food Canada, Dairy and Swine R & D Centre, Lennoxville, Québec J1M 1Z3, Canada; and Danish Institute of Agricultural Sciences, Foulum Research Centre, Tjele, DK-8830 Denmark; and Shur-Gain, Brossard, J4W 3E7 Canada; and and INRA, Unité Mixte de Recherches sur le Veau et le Porc, 35590 Saint Gilles, France

³ Correspondence: phone: 819-565-9174, ext. 222; fax: 819-564-5507; e-mail: farmerc{at}agr.gc.ca.

The possible roles of dietary protein level and feed restriction in regulating mammary development of prepubertal gilts were investigated. Crossbred 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.

Key Words: Mammary Development • Mammary Glands • Pigs • Prepubertal Females • Protein Intake • Restricted Feeding

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