When slaughtering an animal we are advise to always hang the carcass prior to butchery. Here is a great explanation on the science of what happens when meat is hung form Michael Hanley.
 
“…. from what i understand you need to wait out the rigor mortise process and allow the PH to drop. The time changes based on the animal (size and breed). Rigor can set in anywhere from 30 minutes to 3 hours after killing with a pig. Lactic acid is produced during this process which lowers the PH making the meat safer and tenderizing. Stress at the time of kill can also affect the PH and prevent it ever reaching Rigor resolution PH levels and producing tough meat..”
 
Taken from another site:
“… There are three stages to rigor mortise:
Pre-rigor: The muscle fibers begin to shorten due to the depletion of adenosine triphosphate (ATP), causing the muscles to become less extendable while hanging under load. With less oxygen available, the myosin and actin proteins form actomyosin after death occurs. The actomyosin produces a cross bridge between the actin and myosin filaments. In the living animal, these cross bridges are broken during the relaxation phase of a normal contraction cycle (e.g., movement such as walking). However, after death (post mortem), cross bridges are formed permanently as the muscles shorten.
Rigor maximum: The muscle fibres reach maximum shortening, resulting in stiff muscles. The cross bridges are now firmly in place.
Rigor resolution: The now stiff muscle fibres begin to extend again and stretch out to almost their original length. As this extension occurs, the cross bridges create a tearing effect. This phase results in tenderization during dry aging (hanging) or wet aging (storing in vacuum packaging) of carcass meat and is most noticeable in prime meat cuts from the short loin, sirloin, and 7-bone rib (prime rib) of beef. Another chemical process develops during this phase in which the still-living cells begin to produce lactic acid. Lactic acid is normally removed by the circulatory system of living animals; however, in rigor resolution it remains in the muscles, causing the pH to drop until the core temperature of the carcass reaches 4°C ….”