Nutrient Utilization in Entire Male Pigs Immunized to Control Boar Taint

Due to decreased production costs and improved lean gain, raising entire male pigs (EM) is preferred. However, the presence of boar taint compounds in meat from EM raises consumer acceptability issues. Additionally, the conventional use of surgical castration to circumvent boar taint is under continuing scrutiny from animal welfare groups and consumers. Immunization against gonadotropin-releasing factor (GnRF) with IMPROVEST inhibits the action of the hypothalamic-pituitary-gonadal axis, reduces the production of boar taint and affects subsequent growth and feed intake in immunized male pigs (IM). The objective of this experiment was to evaluate dynamics and hormonal control of whole body nitrogen (N-) retention and boar taint factors.

Using a series of N-balances the dynamics of N-retention were determined in IM and compared to EM, conventional, early castrates (EC) and male pigs castrated between 25 and 40 kg (late castrates; LC; 9 pigs per Treatment). Furthermore, serial blood and fat sampling were conducted to measure the boar taint compounds androstenone and skatole, and to identify potential hormones regulating changes in body protein deposition. Immunized males received the initial dose of IMPROVEST at 30 kg and the booster dose at 70 kg. All male pigs were fed common corn-soybean meal based diets that were highly fortified to allow for high levels of body protein deposition. Repeated analysis was conducted using the mixed procedure of SAS (V 9.2 SAS Inst. Inc., Cary, NC). The model included the fixed effects of Treatment and time and the random effects of block and litter within block. Contrasts were constructed to compare Treatments within each sampling period: EC vs. LC; EM vs. EC and LC; EM vs. IM; IM vs. EC and LC. These contrasts were orthogonal across time but not Treatment.

Immunization against GnRF was effective at removing androstenone from both plasma and fat tissue by d 18 after administering the booster dose. Feed intake increased in IM in the first week after administering the booster dose and remained higher than EM but similar to EC and LC until slaughter. Across periods, N-retention for EC and LC were similar (32.7 vs. 33.6±2.9 g/d, P>0.10), and lower than EM (39.2±2.9 g/d, P<0.001). The N-retention in EM and IM was similar until d 7 (37.8 vs. 38.5±2.5 g/d, P>0.10), tended to be higher for EM than IM between d 9 and 16 (38.4 vs. 34.9±2.2 g/d, P=0.07) and was higher for EM than IM after d 20 (40.9 vs. 34.9±2.9 g/d, P<0.05). Between d 9 and 36 N-retention in IM was similar to EC and LC (P>0.10). The dynamics of plasma urea nitrogen, as a measure of amino acid catabolism, confirmed the relative differences in N-retention across treatments. Plasma levels of estrone sulphate (E1S) were similar in EM and IM up to d 5 (9.02 vs. 10.47±3.4 pg/ml, P>0.10). From d 8 to d 37 E1S levels were higher in EM than IM (12.78 vs. 0.30±2.0 pg/ml, P<.0001) and after d 5 E1S level did not differ between IM and EC and LC (0.21 vs. 0.20±0.20 pg/ml, P>0.10).

Entire male pigs immunized against GnRF maintain EM-like N-retention until approximately one week after administering the booster dose. Plasma levels of E1S support feed intake and N-retention observations.

These results suggest that diets high in essential nutrients for body protein deposition should be offered to IM until approximately one week after administering the booster dose of IMPROVEST. Thereafter, feeding diets appropriate for EC would also be suitable for IM as N-retention decreases and feed intake becomes similar to EC.

Keywords. Entire male pigs, IMPROVEST, nitrogen retention.