**Background:** Livestock production in the Amazon is associated with deforestation, and strategies to intensify production while reducing environmental impact are needed. Palm kernel cake (PKC), a by-product of palm oil extraction, has crude protein (~17%) and metabolizable energy (~7.6 MJ/kg DM) and is increasingly available in the region. However, PKC has high acid-detergent fiber and lignin content, which may limit intake, degradability, and performance. This study tested the hypothesis that an optimal PKC supplementation level exists that maximizes productive performance in grazing buffaloes.
**Methods:** The experiment was conducted at Embrapa Eastern Amazon in Belém, Pará, Brazil (Afi climate, annual rainfall 3001 mm). Two seasonal periods were evaluated: wettest season (WS, January–June) and less rainy season (LR, July–December). For intake and performance, 52 crossbred buffaloes were used: 24 in LR (age 34±4 months, initial weight 503±48 kg) and 24 in WS (age 40±4 months, initial weight 605±56 kg). Animals were randomly assigned to four treatments: PKC0 (control, 0% PKC), PKC0.2 (0.25% BW), PKC0.5 (0.5% BW), and PKC1 (1% BW), with six replicates per treatment. All animals received 0.15% BW of wheat bran for adaptation. Animals grazed Marandu grass (Urochloa brizantha) paddocks (1.2 ha each, total 9.6 ha) under intermittent stocking (4 days occupation, 28 days rest) with ad libitum water and mineral mixture. Supplement was offered once daily at 08:00 h in individual stalls. Forage intake was estimated using titanium dioxide (10 g/animal/day) as an external marker and indigestible NDF as an internal marker. Performance was assessed by weighing every 28 days after 16 h fasting. For degradability, 4 rumen-cannulated buffaloes (34±4 months, 503±48 kg) were used in a 4×4 Latin square design. The in situ bag technique was employed with incubation times of 0, 6, 12, 24, 48, 72, and 96 h. Degradation parameters were estimated using the Ørskov and McDonald model. Statistical analysis used PROC GLIMMIX in SAS 9.1 with significance at p<0.05.
**Key Results:** Supplement intake increased linearly with PKC inclusion, reaching 5.57 kg/day (WS) and 5.31 kg/day (LR) at the 1% BW level. Forage consumption decreased with PKC supplementation and was lower in LR. Total DM intake was influenced only by season (higher in WS). Ether extract (EE) intake increased by 136.7% and non-fibrous carbohydrate (NFC) intake decreased by 33.5% at the highest PKC level. NFC consumption reduced linearly by 25% in WS and 42.2% in LR between PKC0 and PKC1. For degradability, PKC inclusion did not affect Marandu grass DM degradability but influenced NDF and CP degradation. PKC DM colonization time was greater in PKC1, and the highest effective degradability rates were from PKC0. Wheat bran DM and CP degradation were affected by PKC inclusion, with colonization time increasing by 101 min (DM) and 140 min (CP) between PKC0 and PKC1. Performance was not significantly different across treatments: average daily gain ranged from 0.478–0.544 kg/day (LR) and 0.211–0.339 kg/day (WS); total weight gain ranged from 86–98 kg (LR) and 26–62 kg (WS).
**Clinical Implications:** PKC supplementation up to 1% of body weight can be recommended for grazing buffaloes in the eastern Amazon without compromising productive performance, despite reducing forage intake and altering some degradability parameters. This strategy may reduce the need for additional pasture area, contributing to more sustainable livestock production in the Amazon region. The reduction in forage consumption with maintained performance suggests improved feed efficiency. Further research is needed to optimize PKC use in different production systems and to evaluate long-term effects on animal health and product quality.