Diurnal Shifts in Nutritive Value of Alfalfa Harvested as Hay and Evaluated by Animal Intake and Digestion

Forages accumulate nonstructural carbohydrates during the day, with animals showing preference and improved daily responses from afternoon compared with morning cut hays. This study evaluated alfalfa (Medicago sativa L.) hay harvested at 0700, 1000, 1300, 1600, and 1900 h to determine how nutritive value changes during the day and to assess the impact of these changes on animal preference using cattle (Bos taurus L.), sheep (Ovis aries L.), and goat (Capra hircus L.) responses. Total nonstructural carbohydrates were altered by time of cut (cubic contrast, P < 0.01) ranging 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). Fiber fractions also varied diurnally, with a quadratic decrease from 418 g kg−1 at 0700 h to 387 g kg−1 by 1900 h in neutral detergent fiber. A combined analysis of three animal trials showed a linear increase in dry matter intake (DMI) with later hay harvest, a cubic response for dry matter digestion (DMD), and a linear increase in digestible DMI. Mean DMI increased from 27.5 g kg−1 body weight at 0700 h to a maximum of 30.8 g kg−1 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 increased from 18.1 g kg−1 body weight at 0700 h to a maximum of 20.5 g kg−1 body weight at 1600 h. No additional advantages in animal responses were noted by cutting after 1600 h.