Turn your heifers into lean, mean growing machines by exposing them to long-day lighting.

According to research conducted at the University of Illinois, heifers exposed to a longer day length — 16 hours of light — reached puberty 24 days earlier than heifers exposed to only eight hours of light per day. Doing so also did not harm skeletal growth or mammary development — two risk factors associated with growing heifers for a faster rate of gain.

During the study, the researchers also increased the level of rumen-undegradable protein (RUP) in the diet of heifers exposed to long-day and short-day lighting. They fed RUP because it is a good source of metabolizable protein, which promotes lean, yet rapid growth. In contrast, feeding heifers more dietary energy to promote rapid gains can make them too fat. They hoped the combination of lighting and RUP would overcome the negative consequences associated with growing heifers faster.

The researchers measured bodyweight, withers height, hip height and heart girth every two weeks during the experiment. Heifers participated in the study from about three months of age until puberty.

Although there was no effect of diet on age at puberty, heifers exposed to the long-day lighting and RUP combination were taller at the hips and withers than heifers exposed to short-day lighting without RUP.

The results, published in the December 2005 Journal of Dairy Science, also show that heifers exposed to long-day lighting gained about 2.7 pounds per day, versus about 2.5 pounds per day for the short-day heifers. 

In conclusion, the researchers say that combining photoperiod with elevated dietary RUP is “a feasible management tool” for accelerating growth and puberty, without hurting body size at breeding.

December 2005 Journal of Dairy Science