| Resum: |
The main goals of this study were to determine whether boars and gilts respond differently to the standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and model the response to optimize growth performance. A total of 780 finishing pigs, 390 boars and 390 gilts [Pietrain NN × (Landrace × Large White)], with an initial individual body weight of 70. 4 ± 9. 2 for boars and 68. 7 ± 8. 0 kg for gilts, were used in a 41-d dose-response experiment. Pens (13 pigs per pen) were randomly allocated to a dietary treatment (2. 64, 3. 05, 3. 46, 3. 86, 4. 27 g SID Lys/Mcal NE) by block and sex, with six replicates per treatment and sex. Two isoenergetic diets (2,460 kcal NE/kg), representing the extreme SID Lys:NE, were formulated and then mixed. Pigs were individually weighed at days 0, 22, and 41, when the experiment finished. The differential effect of SID Lys:NE on growth performance and carcass composition between sexes was analyzed with orthogonal polynomial contrasts to compare the linear and quadratic trends in each sex. In addition, broken-line linear (BLL) models to optimize average daily gain (ADG), including average daily feed intake (ADFI) as a covariate, were fitted when possible. As expected, boars had a greater ADG and feed efficiency (G:F; P < 0. 001) than gilts, but there was no evidence of differences in ADFI (P = 0. 470). Increasing SID Lys:NE had a greater linear impact on boars ADG (P = 0. 087), G:F (P = 0. 003), and carcass leanness (P = 0. 032). In contrast, gilts showed a greater linear increase in SID Lys intake per kg gain (P < 0. 001) and feed cost per kg gain (P = 0. 005). The best fitting BLL models showed that boars maximized ADG at 3. 63 g SID Lys/Mcal NE [95% confidence interval (CI): (3. 32 to 3. 94)], although another model with a similar fit, compared with the Bayesian information criterion, reported the optimum at 4. 01 g SID Lys/Mcal NE [95% CI: (3. 60, 4. 42)]. The optimum to maximize ADG for gilts was estimated at 3. 10 g SID Lys/Mcal NE [95% CI: (2. 74, 3. 47)]. Thus, the present study confirmed that boars and gilts have a different linear response to SID Lys:NE, explained by the greater protein deposition potential of boars. Likewise, BLL models indicated that boars require a higher SID Lys:NE to maximize ADG from 70 to 89 kg. These results suggest that split feeding of finishing boars and gilts could be beneficial in terms of both performance and cost return. |
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(Vall Companys Group)
