Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 2007
Publication Date: August 31, 2007
Citation: Burns, J.C., Fisher, D.S. 2007. Diurnal shifts in nutritive value of alfalfa harvested as hay and evaluated by animal intake and digestion.. Crop Science. 47:2190-2197. Interpretive Summary: Physiological studies have shown that plants accumulate soluble carbohydrates during the day light hours with declines occur during the night. A management strategy has been evaluated that harvested hay in the late PM (7:00) of a bright day resulting in greater nutritive value, compare with an AM harvest, without additional economic cost. Further, ruminants were able to detect the difference with greater animal response noted for the PM cut hay. In the humid Eastern US, however, the numbers of consecutive, bright days that are favorable for hay making are frequently limited. It would be advantageous to know if the maximum nutritive value of forage was reached earlier in the day to allow partial drying before dark. This study reports the diurnal shift in total nonstructural carbohydrates and fiber when alfalfa was cut at 7:00 AM, 10:00 AM, 1:00 PM, 4:00 PM, and 7:00 PM. In general carbohydrates increased linearly and fiber fractions decreased during the day. Overall, ruminants detected the diurnal shifts in the forage with either greater dry matter intake or digestible dry matter intake. Specifically, both sheep and cattle detected the diurnal shift in the hays, whereas goats showed the same trends but they were not significant. Further, there was no advantage in animals responses after the 4:00 PM cutting. This indicates that maximum animal response can be obtained early enough to permit partial drying of the forage before dark.
Technical Abstract: Forages accumulate nonstructural carbohydrates during the day with animals showing preference and improved daily responses from PM compared with AM cut hays. This study evaluated alfalfa hay harvested at 0700, 1000, 1300, 1600 and 1900 h to determine diurnal changes in nutritive value and assess the magnitude of the change using cattle, sheep and goat responses. Concentrations of TNC were altered by time of cut following a cubic trend (P<0.01) declining from 85 g kg-1 at 0700 h to 83 g kg-1 at 1000 h then increasing to 97 g kg-1 by 1600 h with little change at 1900 h (96 g kg-1). Associated was a quadratic decrease from 418 g kg-1 at 0700 h to 387 g kg-1 by 1900 h in neutral detergent fiber (NDF) and a quadratic increase from 204 g kg-1 at 0700 h to199 g kg-1 by 1300 h to 206 g kg-1 by 1900 h in crude protein (CP). Combining the three animal trials using ‘meta’ analysis showed an overall linear diurnal increase in dry matter intake (DMI), a cubic response for dry matter digestion (DMD) and a linear diurnal increase in digestible DMI. Mean DMI increased from 2.75 kg 100-1 kg body weight at 0700 h to a maximum of 3.08 kg 100-1 kg body weight at 1600 h, whereas DMD decreased from 658 g kg-1 at 0700 to 647 g kg-1 at 1300 h and peaked at 664 g kg-1 at 1600 h. Digestible DMI reflected DMI increasing from 1.81 kg 100-1 kg body weigh at 0700 h to a maximum of 2.05 kg 100-1 kg body weight at 1600 h. These overall diurnal animal responses reflect the individual specie trials but diurnal trends for goats were not significant. No advantages in animal responses were noted by cutting after 1600 h.