The formulas to calculate manure production for pigs are:

1. For 3-8 months:

\[ W_m = 2.20 \cdot N_a \cdot N_d \]

2. For 18-36 kg:

\[ W_m = 2.55 \cdot N_a \cdot N_d \]

3. For 36-55 kg:

\[ W_m = 5.22 \cdot N_a \cdot N_d \]

4. For 55-73 kg:

\[ W_m = 6.67 \cdot N_a \cdot N_d \]

5. For 73-91 kg:

\[ W_m = 8.00 \cdot N_a \cdot N_d \]

Where:

• \(W_m\) is the weight of manure produced in kilograms (kg).
• \(N_a\) is the number of animals.
• \(N_d\) is the number of days.