Effects of time of second Improvest dose on growth and carcass yield of immunologically-castrated compared to physically-castrated barrows and gilts

Improvest® (Zoetis, also known as Improvac) is an anti-GnRF vaccine for the immunological castration of male pigs for the control of boar taint. However, there is limited information on the impact of timing of 2nd Improvest dose relative to the time of harvest on growth and carcass parameters. The objective of this study was to compare different times of the 2nd on the performance of immunological-castrates (IC) relative to physical-castrates (PC) and gilts (G).

The study was carried out as a RCBD with 12 treatments: Treatments 1 to 4, IC given 2nd Improvest dose at wk 14, 16, 18, and 20 of age, respectively; harvested at wk 24 of age; Treatments 5 and 6, IC given 2nd dose at wk 20 of age; harvested at either wk 26 or 28 of age; Treatments 7 to 9, PC harvested at either wk 24, 26, or 28 of age, respectively; and Treatments 10 to 12, G harvested at either wk 24, 26, or 28 of age, respectively. A total of 288 pigs were housed in groups of 3 (8 groups/treatment). Diets were formulated for requirements of intact males; pigs had ad libitum access to feed. Pigs were harvested at a commercial facility and hot carcass weight was measured.

Growth performance results are from 29.3±3.30 kg body weight to respective harvest time (134.3±10.4, 144.3±12.1, and 153.7±11.9 kg BW for wk 24, 26, and 28 of age, respectively). G had lower (P≤0.05) ADG and ADFI, and greater (P≤0.05) G:F than the other genders. ADG was greater (P≤0.05) for all IC than PC treatments (1023, 1015, 1003, 1048, 1039, 975, 971, 958, and 921 g for Treatments 1 to 9, respectively; SEM 15.4). ADFI was lower (P≤0.05) for Treatment 3 and 4 than the other IC and PC treatments (2.93, 2.97, 2.77, 2.77, 2.93, 2.93, 2.89, 2.98, and 2.96 kg for Treatments 1 to 9, respectively; SEM 0.054). G:F was greatest (P≤0.05) for Treatment 4 compared to the other IC and PC treatments (0.350, 0.343, 0.363, 0.378, 0.355, 0.333, 0.336, 0.323, 0.311 for Treatments 1 to 9, respectively; SEM 0.0051). Carcass yield was similar (P> 0.05) for PC and G. Increasing the time from 2nd dose to harvest in IC harvested at wk 24 of age tended (P=0.08) to increase carcass yields (73.7, 73.9, 73.0, and 73,1% for Treatments 1 to 4, respectively; SEM 0.32). Carcass yield was greater (P< 0.001) for IC given the 2nd dose at wk 20 and harvested at wk 28 compared to wk 24 with those harvested at wk 26 being intermediate (73.1, 74.1, and 74.8% for Treatments 4, 5, and 6, respectively; SEM 0.29).

These results suggest that the optimum economic approach to producing IC will depend on the balance between the reduction in growth performance and the improvements in carcass yield from increasing the time between the 2nd Improvest dose and harvest.

Disclosure of Interest: C. L. Puls Conflict with: supported by Zoetis, M. Ellis Conflict with: supported by Zoetis, M. A. Mellencamp Conflict with: employee, W. Beckman Conflict with: employee, A. L. Schroeder Conflict with: employee, F. K. McKeith Conflict with: supported by Zoetis, A. Aldaz Conflict with: employee.