Another disadvantage with the darkness system is that it denies the pigeons access to a full days exposure to the sun's rays. Sunlight is a great sexual stimulator. So birds that are denied the full days exposure to the sun, can have a reduced sexual drive. This will have a detrimental effect on the racing performance of some of the older youngbirds, in particular those youngbird cocks that are raced on a semi widowhood system, in which they are allowed to mix with the hens prior to sending. In addition to all this, when fliers change to the darkness system they frequently just darken their existing loft, with little or no modifications, except for a curtain or shutter.
Little regard is paid to the sudden change in airflow, in and out of the loft.
Lofts become stuffy, the oxygen levels inside can drop and exhaled carbon dioxide will increase. In addition, the humidity within the loft will go up, and stale air from the droppings will hang around. This damp still air is ideal for the growth of bacteria and fungi and as a consequence airborne pathogens will increase. This environment will compromise the health of the pigeons and they won't perform at their best. Another drawback to limiting the amount of natural sunlight in the loft, is that the it reduces the amount of ultraviolet rays and these are a great antibacterial.