Over the course of the year the number of natural daylight hours changes from 9 to 16 hours in Michigan, with the shortest day in mid-December and the longest day in mid-June. Previous research has reported increased productivity from many livestock species in response to photoperiod manipulation. This includes greater egg production for chickens and greater milk production for dairy cows exposed to a greater photoperiod length. This article will review some studies investigating the effects of photoperiod on the performance of growing cattle and discuss the impact for beef producers.
According to a 1984 article “The influence of photoperiod on body weight gain, body composition, nutrient intake and hormone secretion” by the Journal of Animal Science, a large quantity of the research investigating the effects of photoperiod on cattle production compares short-daylength (SDL; 8 hours light:16 hours darkness) with long-daylength (LDL; 16 hours light:8 hours darkness). Therefore, this type of research is primarily conducted during the winter months that have SDL and artificial lighting is used to extend the photoperiod to emulate LDL. Much of the early research investigating the effects of photoperiod on cattle performance was conducted at Michigan State University (MSU) using Holstein heifer and bull calves. Initial studies reported a 16% greater body weight gain for Holstein heifer calves exposed to LDL compared with SDL. Interestingly, 24 hours of continuous light exposure resulted in a similar performance response between Holstein heifer calves receiving SDL, whereas heifer calves exposed to LDL had a 10-15% greater average daily gain (ADG) and 7% greater feed intake compared with SDL and 24 hours of continuous light. Improved growth in these experiments occurred after the initiation of 14 to 17 hours of light exposure or the initiation of 8 to 10 hours of darkness. Therefore, the regulation of growth in cattle appears to be regulated in a circadian rhythm requiring both periods of light and dark.
The use of continuous lighting has been practiced for many years, anticipating increased hours of light exposure would increase cattle performance by encouraging a greater number of bunk visits and greater feed intake. A study done by Tucker and others in the Journal of Dairy Science, no differences were observed for the eating behavior, including total eating time, number of meals, and average time spent eating for Holstein cows when exposed to either 24 hours of continuous light or LDL. Studies from Tucker and others reported more eating events during daylight hours for Holstein heifers exposed to LDL compared with SDL, but no differences in the amount of total feed consumed. When offered a similar amount of feed, high energy diets comprised of mostly high moisture corn resulted in a 18% greater ADG and lower energy diets containing mostly corn silage resulted in a 11% greater ADG for Holstein heifer calves exposed to LDL compared with SDL. A 1996 article “The influence of day length and temperature on food intake and growth rate of bulls given concentrate or grass silage ad libitum in two housing systems” by Animal Science, reported that for bulls in Sweden, ADG increased as daylength increased (December to May) and ADG decreased as daylength decreased (June to November). Similarly, energy intake slightly lagged ADG, such that energy intake was greatest in June and lowest in December for bulls offered a high concentrate diet. It appears that a greater voluntary feed intake may not be necessary for the improvement of growth rate due to LDL when compared with SDL, as the increase in feed intake typically lags the change in ADG.
In agreement, a 1992 article “Random variation in voluntary dry matter intake and the effect of day length on feed intake capacity in growing cattle” by Acta Agriculturae Scandinavica A-Animal Sciences, reported a relatively small increase (+0.32%) in dry matter intake per hour of increased day length for bulls consuming a low energy diet, which would correspond to a 2.24% difference in dry matter intake between December and June in Michigan. In contrast, a 1990 article “Dry matter intake by feedlot beef steers: Influence of initial weight, time on feed, and season of year received in yard” by the Journal of Animal Science, reported a 10% difference in dry matter intake between the highest and lowest months, with a greater feed intake occurring during the fall and spring and a lesser feed intake occurring during the winter and summer months by feedlot cattle consuming a high concentrate diet. While no reports were made because of daylength, the same researchers suggest heat stress decreased feed intake in heavier cattle, while cold stress tended to decrease the feed intake of lighter weight cattle in Oklahoma. The effect of confounding or uncontrolled variables, such as temperature, quite possibly influence or mask the effect of daylength on cattle growth and performance, which likely contributes to some of the conflicting results.