5 eggs you should never incubate

• extremely large or small eggs, which have a low hatching rate;

• unnaturally-shaped eggs, which have a low hatching rate;

• weak-shelled eggs, which are more prone to breakage, bacteria, and mould;

• eggs with a poor-quality interior, eg meat spot, blood spot, uneven colour of yolk – 'candle' eggs (shine a bright light through them in a darkened room) to check for flaws;

• dirty eggs, which are likely to be contaminated. Use only clean eggs for hatching or ones where you can use a dry paper towel to remove superficial dirt or manure. An egg's shell is porous, and bacteria can be forced through the pores by rubbing or washing.