Photoperiod: a topic on which to shed light!

Photoperiodism refers to the set of responses that organisms exhibit to varying periods of light and darkness. This phenomenon has enormous biological importance because it influences the morphology, physiology, ethology and ecology of living things.

The photoperiod is the duration to ‘exposure of light in 24 hours.

To understand how photoperiod can affect with dairy cattle production, we need to project its application in the right context.

To date, the work involved in managing a dairy farm, seems to increasingly require attention to the technological tools that are now indispensable to the business: it is now well known that the farmer’s expert eye alone is no longer sufficient to govern the farm.
The difference of a business with a positive balance sheet or a lot of wasted effort comes from the correct interpretation of the information gathered by the technology supporting the farm.
Interviewing technical experts in the field, in light of the above information, it seems that there is still room to improve the productivity of our cattle.
Beyond genetics, which works on the productivity of the individual, we need to intervene on the quality of herd management so as to ensure continuity in production.

From the elaborations of official data collected on the entire herd of Italian dairy cows, a recurring problem seems to emerge in the autumn months; and in particular in October that, with the same average days in lactation and generally with the same environmental temperatures as in April, differently there is a drastic drop in production, estimated at 2.4 kg less milk!

This downturn has been termed “Low Milk Production Syndrome in the Fall.” Although the causes are diverse in nature and to be sought through a complex holistic approach, three factors are outlined that are certainly relevant:

• the continuation of the negative effects of summer heat stress
• an alteration of the estrous period resulting in a concentration of births in the fall and summer
• the change of season with consequent reduction of daylight hours.

The resolution of the problem, as mentioned above, is not to be found in one direction, but with a true 360-degree approach; however, manipulation of the photoperiod could be one way to mitigate its effects.

There is a proven correlation between trends in annual milk production and the period of solar declination, better known as the summer solstice and winter solstice, which represent the longest and shortest days of the year, respectively.

This relationship is further confirmed by looking at data from herds located in the ‘southern hemisphere, where the same trend in production is shown, but reversed, just as it happens to the seasons.

Similarly, calving predisposition also seems to align with the period of shorter days, manifesting a further link between 24-hour light exposure and cow behavior.

It is scientifically proven that the light stimulus through the optic nerve reaches the hypothalamus influencing the “secretion” of GnRH, which in turn modulates the pituitary production of hormones, including melatonin. Melatonin in brief is the pituitary hormone responsible for the body’s circadian (24-hour) rhythm; it is produced during darkness and serves the “rearrangement” of metabolism and hormones.

Through manipulation of the photoperiod, thus the duration to ‘exposure to light of lactating cows, it is reliable to obtain benefits on production, milk, fertility, growth, and efficiency of the immune system.

Management of the photoperiod is possible by installing an intelligent lighting system that can ensure a certain and constant light intensity for 16 to 18 hours a day, 365 days a year (referred to as the “long day”).

The use of “long day,” is functional for lactating cows and results can be observed after 3 to 4 weeks of exposure, with care taken to ensure at least 6 hours a day of low light to give them adequate rest.

Conversely, dry cows find benefit in ‘implementing the “short day” by limiting the hours per day of light to 8, manifesting results during the next lactation, but difficult to implement due to the impossibility of permanent confinement.

The result to be achieved is to increase lactation, due to the increased ability of the cow to feed over time, but above all by obtaining a better management of fertility distributed over the ‘whole year, thus avoiding the confinement of cows put in dry during the stressful summer periods, and the consequent loss of production in subsequent lactations.

In conclusion, photoperiod management is a tool that current technology can make available to the farmer, and if properly employed, it can improve farm conditions and make production more efficient.

m.a.