Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Photoperiod management of dairy cows is an effective method to improve production efficiency. Long days (16L: 8D) increase milk production in lactating cows, whereas short day (8L: 16D) exposure during the dry period improves production in the subsequent lactation. Long days also increase growth and hasten puberty in prepubertal calves. In addition to these effects on growth, reproduction, and lactation, emerging data suggest that immune function is influenced by photoperiod. Specifically, short day exposure increases lymphocyte proliferation in calves, and this effect is reversible with a transition to long days. This immune response is associated with photoperiod driven shifts in secretion of and sensitivity to the hormone prolactin, which has previously been implicated as an immune system modifier. These data support the concept that an animals environment can affect not only performance, but also health and well-being.