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Effects of time from second Improvest dose to end of growth period on growth performance of immunologically-castrated barrows in comparison to physically-castrated barrows and gilts
This study evaluated the effect of time from second Improvest dose to end of growth period on the growth performance and carcass characteristics of immunologically-castrated barrows (IC) in comparison to physically-castrated barrows (PC) and gilts (G). The study was carried out as a RCBD with 12 treatments: Treatment 1) to 4) IC given second Improvest dose at wk 14, 16, 18, and 20 of age, respectively; end of growth period=wk 24 of age, Treatment 5) and 6) IC given second dose at wk 20 of age; end of growth period=26 and 28 wk of age, Treatment 7) to 9) PC; end of growth period=wk 24, 26, and 28 of age, respectively, and Treatment 10) to 12) G; end of growth period=wk 24, 26, and 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. Results for growth performance are from start (29.3 ± 3.30 kg BW) to respective end of test (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. Overall ADG was greater (P ≤ 0.05) for all IC treatments than PC treatments (1023, 1015, 1003, 1048, 1039, 975, 971, 958, and 921 g for Treatments 1 to 9, respectively; SEM 15.4). Overall 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). Overall 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). These results suggest that for IC the greatest growth performance was achieved by Treatment 4 (i.e., giving the second Improvest dose at wk 20, and ending the growth period after 4 wk). Also, extending the time between second Improvest dose and end of the growth period, either by giving the second dose earlier in the growth period or harvesting pigs later, reduced the growth performance advantages of IC compared to PC.
Keywords: immunological castration, Improvest, pigs