Abstract
The present study investigated the impact of providing different supplemental essential amino acids (EAA) in a low crude protein (CP) diet on growth performance in weanling pigs. A total of 324 mixed-sex 24-d weaned piglets (initial BW 6.9 ± 0.34 kg) were used in a 27-d growth trial with six dietary treatments immediately post-weaning. The first two treatments were a control standard CP (19%) diet (positive control; PC) and a negative control (NC) diet with low CP (16%) and reduced Ile, Leu, and histidine levels. The rest of the treatments had low CP with varied EAA types and levels; T1 had similar Ile, Leu, and His levels as PC but with low CP (16%), while T2 had low CP and 10% higher His, Thr, Trp, and Met+Cys compared to PC. The T3 was a low CP diet with 10% supplemental Leu, Ile, and Val compared to PC, while T4 was a low CP diet with 10% supplementation with all the EAA except Lys compared to PC. The initial body weight (BW) was not statistically different (P > 0.05) among the treatments. Also, on d 6, no statistical differences in BW were observed among the treatments. The average BW recorded on d 13, 20, and 27 showed significant treatment differences where the PC had consistently higher BW than all the other treatments (P < 0.05). The average daily gain (ADG) of the PC was higher than the rest of the treatments. Between d 13 and 20, the average daily feed intake (ADFI) for PC was not different from NC and T1 (P > 0.05), but compared to T2, T3, and T4, the PC treatment showed a high ADFI (P < 0.05). Overall (d 0-27), the ADFI for PC was not different from T1 and was significantly higher than all other treatments. Overall, results showed that the gain to feed (G:F) ratio was higher (P < 0.05) for PC compared to other dietary treatments. In summary, although the treatments (T1-T4) consisted of varying levels of EAA above the recommended requirement levels for optimal performance, we did not see a significant impact on growth performance improvement, which may indicate that the targeted EAA (His, Val, Thr, lle, Leu, Trp, and Met) may not have been limiting in these diets. On the other hand, the phenylalanine (Phe) requirement may be limited in the current formulations, or perhaps the EAA: total N ratio in T1, T2, T3, and T4 may have been too high, resulting in the inefficiency of EAA utilization for growth.