Effects of immunocastration and time after second Improvest dose on adipose tissue fatty acid profile of finishing barrows.

The effects of immunocastration and time after second Improvest dose on proximate composition and fatty acid profile of adipose tissue from jowl and belly of finishing barrows were determined. Physically castrated (PC) and immunologically castrated (IC) barrows were assigned to treatments at birth. Within 5 d of age, PC barrows were physically castrated and IC barrows were administered Improvest (gonadotropin-releasing factor analog; Zoetis, Kalamazoo, MI) at 16 and 20 wk of age. Diets were formulated with corn and soybean meal and did not contain ethanol coproducts. Subsequently, PC (n = 23) and IC (n = 24) barrows were slaughtered biweekly from 22 to 28 wk of age, 2 to 8 wk following second Improvest dose. Adipose tissue samples were collected from the jowl and belly. Main effects of castration method and time after second Improvest dose and their interaction were analyzed with the MIXED procedure of SAS. Overall, IC barrows were heavier at slaughter (136.1 vs. 100.6 kg; P < 0.01), had similar HCW (P = 0.13), and were leaner (50.9 vs. 48.9%; P < 0.01) than PC barrows. In jowl adipose tissue, IC barrows had less lipid content (64.7 vs. 80.2%; P < 0.01) than PC barrows at 2 wk. However, there were no differences (P ≥ 0.75) in lipid content between IC and PC barrows from 4 to 8 wk. Total MUFA content was reduced (42.5 vs. 44.8%; P = 0.04) and PUFA content was greater (16.9 vs. 14.8%; P < 0.01) in IC compared to PC barrows. Increasing time after second dose reduced (P = 0.04) PUFA content from 17.5% at 2 wk to 15.4% at 8 wk. In IC barrows, iodine value (IV) was increased by 6.9 and 3.3 g/100 g compared with PC barrows at 2 and 4 wk, but IV was not different between castration methods (P ≥ 0.95) at both 6 and 8 wk. Meanwhile, in belly adipose tissue, IC barrows had less lipid content than PC barrows (75.3 vs. 82.7%; P < 0.01). Lipid content was unchanged over time (P = 0.34) in either PC or IC barrows. Total SFA and MUFA content of the belly were similar for both IC and PC barrows. Belly adipose tissue from IC barrows had greater concentrations of PUFA than PC barrows (16.2 vs. 14.7%; P < 0.01). In IC barrows, IV was increased by 5.3 g/100 g compared with PC barrows at 2 wk, but IV was not different between castration methods (P ≥ 0.91) from 4 to 8 wk. Results indicate that as time after second Improvest dose progressed, IV of jowl and belly was reduced. This was accompanied by an increase in lipid deposition in jowl, while lipid content remained constant in belly.