Mammary development in prepubertal gilts fed restrictively or ad libitum in two sub-periods between weaning and puberty

Two experiments were conducted to assess whether feeding level in the period from weaning to puberty can affect the amount of mammary tissue at puberty. Four female pigs from eight (exp. 1) to ten (exp. 2) litters were allocated to four treatment groups within litter. From day 28 to 90 of age (period 1) and from day 90 to slaughter, at approximately 5 1/2 months of age (period 2), the gilts were given either ad libitum or restrictive access to feed in a 2 × 2 factorial arrangement. Neither the amount of dissected mammary tissue nor the amounts of DNA or RNA were affected by feeding regime in period 1. However, ad libitum feeding in period 2 gave rise to more dissected mammary tissue (52%, P < 0.0001), RNA (37%, P = 0.006) and DNA (28%, P = 0.005) compared to restricted feeding. Cyclicity gave rise to increases in mammary DNA (P = 0.05) and RNA (P = 0.02). There were no clear correlations between mammary measures and plasma IGF-I or IGF-binding proteins. It is concluded that a high feeding level from three months of age to puberty has a stimulatory effect on mammary development in prepubertal gilts.