RESULTS

Chemical composition of experimental feeds

The feed ingredients and chemical compositions of the concentrate mixture, rice straw, and LGP used in the experiment are presented in Table 1. As expected for standard basal diets, the concentrate and rice straw contained 14.7% and 2.2% CP, respectively. Notably, the formulated LGP exhibited a favorable nutritional profile, containing 24.6% CP, 32.5% neutral detergent fiber, and 25.2% ADF. In addition, LGP served as a substantial source of bioactive compounds, providing 6.8% CT and 2.4% flavonoids. L. leucocephala is a widely distributed leguminous species in tropical regions with a high protein content and is commonly used as a feed resource for ruminants.

Feed intake and nutrient digestibility

The effects of dietary treatments on feed intake and nutrient digestibility are presented in Table 2. Supplementation with LGP had no effect on rice straw intake, concentrate intake, or total feed intake among treatment groups (p > 0.05). However, increasing LGP levels (p < 0.05) increased the digestibility of DM and neutral detergent fiber. In contrast, the digestibility of OM, CP, and ADF was not affected by LGP supplementation (p > 0.05).

When expressed as a percentage of BW, total daily DM intake ranged from approximately 2.5% to 2.7% across treatments, which is within the normal range for beef cattle. Feed intake is influenced by the chemical composition and physical characteristics of the diet, which in turn affect animal productivity. The absence of significant differences in feed intake among treatments indicates that LGP supplementation did not adversely affect feed consumption.

Items | 0 | 50 | 100 | 150 | SEM | Linear | Quadratic | Cubic
Rice straw intake, kg DM/day | 3.6 | 3.5 | 3.8 | 3.8 | 0.18 | 0.43 | 0.52 | 0.90
Concentrate intake, kg DM/day | 2.1 | 2.1 | 2.2 | 2.3 | 0.06 | 0.42 | 0.18 | 0.78
 |  |  |  |  |  |  |  | 
LGP, kg DM/day | 0 | 0.05 | 0.10 | 0.15 | – | – | – | –

Total feed intake, kg DM/day | 5.7 | 5.7 | 6.1 | 6.2 | 0.18 | 0.30 | 0.84 | 0.83
Apparent digestibility (%) |  |  |  |  |  |  |  | 
DM | 55.4ᵃ | 57.4ᵇ | 58.9ᵇ | 60.0ᶜ | 3.46 | 0.02 | 0.80 | 0.95
Organic matter | 61.6 | 64.3 | 65.0 | 68.3 | 3.52 | 0.23 | 0.92 | 0.77
Crude protein | 52.2 | 54.0 | 57.1 | 58.5 | 2.95 | 0.07 | 0.81 | 0.91
Neutral detergent fiber | 60.1ᵃ | 62.5ᵇ | 64.0ᶜ | 67.6ᵈ | 2.01 | 0.03 | 0.80 | 0.74
Acid detergent fiber | 45.2 | 46.7 | 48.2 | 48.8 | 1.11 | 0.14 | 0.73 | 0.84

Rumen fermentation characteristics, blood metabolites, and microbial populations

The effects of dietary treatments on rumen fermentation characteristics, blood metabolites, and microbial populations are presented in Table 3. Supplementation with LGP had no effect on ruminal temperature, pH, or blood urea nitrogen (BUN) concentration (p > 0.05). Rumen fermentation, microbial growth, and microbial activity were maintained within the optimal pH range of 6.7-6.8. Increasing the level of LGP supplementation did not significantly affect NH3-N concentrations, which remained within the normal range of 13.7-18.5 mg/dL. BUN concentrations were closely associated with ruminal NH3-N concentrations, although no significant differences in BUN concentrations were observed among treatments.

Increasing LGP supplementation levels resulted in higher propionic acid concentrations and lower estimated CH4 production (p < 0.05), particularly at 150 g/head/day. However, total VFA concentration, acetic acid concentration, butyric acid concentration, and the acetic acid-to-propionic acid ratio did not differ significantly among treatment groups (p > 0.05).

Furthermore, increasing levels of LGP supplementation increased bacterial populations (p < 0.05) and decreased protozoal populations (p < 0.05), as shown in Table 3.

Items | 0 | 50 | 100 | 150 | SEM | Linear | Quadratic | Cubic
Ruminal pH | 6.7 | 6.7 | 6.7 | 6.8 | 0.12 | 0.28 | 0.30 | 0.05
Ruminal temperature (°C) | 37.5 | 38.1 | 38.0 | 38.3 | 0.25 | 0.07 | 0.16 | 0.54
NH3-N concentration (mg/dL) | 13.7 | 16.1 | 17.2 | 18.5 | 0.96 | 0.93 | 0.39 | 0.58
Blood urea nitrogen (mg/dL) | 10.3 | 10.4 | 11.3 | 12.0 | 0.59 | 0.89 | 0.75 | 0.96
Total VFA (mmol/L) | 111.0 | 109.1 | 108.3 | 106.9 | 3.28 | 0.40 | 0.93 | 0.91
VFA (mol/100 mol) |  |  |  |  |  |  |  | 
Acetic acid (C2) | 68.8 | 67.3 | 66.5 | 63.6 | 2.05 | 0.12 | 0.74 | 0.76
Propionic acid (C3) | 21.2ᵃ | 24.5ᵇ | 25.3ᵇ | 28.8ᶜ | 1.93 | 0.04 | 0.93 | 0.57
Butyric acid (C4) | 10.0 | 8.3 | 8.2 | 7.5 | 1.60 | 0.34 | 0.75 | 0.75
Acetic acid/propionic acid ratio | 3.3 | 2.8 | 2.8 | 2.3 | 1.22 | 0.07 | 0.91 | 0.36
Methane production¹ (mol/100 mol VFA) | 29.1ᵃ | 26.9ᵇ | 26.3ᵇ | 23.7ᶜ | 1.38 | 0.02 | 0.91 | 0.57
Rumen microbial population (cells/mL) |  |  |  |  |  |  |  | 
Bacteria (×10⁹) | 6.3ᵃ | 7.2ᵇ | 8.3ᶜ | 8.7ᶜ | 0.36 | 0.01 | 0.63 | 0.83
Protozoa (×10⁶) | 8.4ᵃ | 6.9ᵇ | 5.6ᶜ | 4.8ᵈ | 0.45 | 0.03 | 0.83 | 0.96

Microbial protein synthesis

The effects of dietary treatments on microbial protein synthesis are presented in Table 4. Supplementation with LGP had no significant effect on absorbed or excreted urinary purine derivatives (p > 0.05). However, microbial protein synthesis and efficiency of microbial nitrogen synthesis increased significantly (p < 0.05) when cattle received 150 g/head/day of LGP.

Items | 0 | 50 | 100 | 150 | SEM | Linear | Quadratic | Cubic
Urinary purine derivatives (mmol/day) |  |  |  |  |  |  |  | 
Allantoin excretion | 31.5 | 34.0 | 36.5 | 37.3 | 4.46 | 0.76 | 0.14 | 0.45
Allantoin absorption | 90.9 | 92.6 | 97.2 | 98.7 | 4.40 | 0.12 | 0.23 | 0.26
Microbial protein supply (g N/day) | 60.3ᵃ | 64.3ᵇ | 67.9ᶜ | 68.1ᶜ | 4.45 | 0.04 | 0.16 | 0.22
Efficiency of microbial nitrogen synthesis (g/kg organic matter digested in the rumen)¹ | 28.5ᵃ | 31.4ᵇ | 32.9ᵇ | 35.5ᶜ | 0.61 | 0.02 | 0.28 | 0.47