Effects of estradiol implantation on growth, carcass traits and circulating concentrations of insulin-like growth factors (IGFs) and IGF-binding protein-3 in finishing barrows

Eighty crossbred barrows aged 120 to 141 days and weighing 71.2±0.8 kg were randomly divided into eight pens, after which each of 40 animals in four pens was implanted with 24 mg of estradiol-17β (E2; Compudose®). The animals were allowed an unrestricted access to water and a finisher diet containing 16% crude protein and 3.4 Mcal DE/kg and slaughtered at 107.4±0.8 kg. Blood samples were obtained by jugular venipuncture at day 0 before the implantation and at days 21 and 42. Serum concentration of E2 increased between days 0 and 21 after the implantation and declined to a level above that of day 0 (P<0.01) by day 42. E2 implantation caused a decrease (P<0.01) in feed intake and backfat thickness and a tendency (P=0.08) of decreased average daily gain. However, feed conversion efficiency (FCE; live weight gain/feed intake) did not change due to the implantation (P=0.20). The E2 implantation did not affect physicochemical characteristics of longissimus muscle including percentages of protein (P=0.17) and fat (P=0.43), 24-h pH (P=0.39), drip loss (P=0.99), L* (lightness; P=0.78) and a* (redness; P=0.49) values. Serum concentration of insulin-like growth factor (IGF)-I decreased between days 0 and 21 (P<0.01) and also between days 21 and 42 (P<0.05) in unimplanted pigs, but not in implanted pigs (P>0.05), which resulted in a greater (P<0.05) mean IGF-I concentration in the implanted vs. unimplanted group. By contrast, serum concentrations of IGF-II and IGF-binding protein-3 did not differ between the two groups (P>0.05). In summary, results suggest that E2 suppresses voluntary feed intake and backfat deposition without significantly affecting growth efficiency and muscle characteristics in barrows and that effects of E2 may be partly mediated by IGF-I.