Botanical traits, protein and carbohydrate fractions, ruminal degradability and energy contents of alfalfa hay harvested at three stages of maturity and in the afternoon and morning

Little information is available about nutrient profiles and availability of alfalfa harvested at different stages of maturity and harvested at different times during the day in relation to diet formulation for dairy cows. The objective of this study was to investigate the effect of stage of maturity and cutting time of alfalfa hay on botanical traits, nutrient profiles and in situ degradability of protein and carbohydrates and calculated energy content. Alfalfa was cut at early bud (June 15/16), late bud (June 26/27) and early flower stage (July 18/19) both in the afternoon (06:00 pm) and the next morning (06:00 am). With advancing maturity of alfalfa, leaf content, leaf:stem ratio, calculated energy values, crude protein (CP), in situ digestibilityʹs (especially at 12 and 36 h of incubation) and nitrogen (N) to energy [organic matter (OM), carbohydrates (CHO)] ratios decreased (P<0.05). While, neutral detergent fiber, acid detergent fiber, fiber associated CP (NDICP) and total CHO increased (P<0.05) with advancing maturity of alfalfa. Protein and CHO fractions (defined according to Cornell net carbohydrate and protein system) associated with different degradation characteristics stayed consisted with advancing maturity, except for intermediate degradable protein (PB2), which decreased at the early flower stage compared with early and late bud stages (P=0.03). Alfalfa harvested in the afternoon tended to have a higher leaf portion and leaf:stem ratio (P=0.06) and contained 13 g/kg CHO more soluble carbohydrates (TESC, i.e. CA; P<0.01), 27 g/kg CP more PB2 (P=0.02), and 0.33, 0.33, 0.27 MJ/kg DM more (P<0.05) net energy for maintenance, gain and lactation production, respectively, and had an improved rapidly degradable N to CHO ratio (PA:CA; 66 vs. 76 g/kg; P=0.02) compared with alfalfa harvested in the morning. Cutting time had no impact on in situ degradability of alfalfa hay. In conclusion, nutrient availability of alfalfa hay, grown under semi arid climate condition, was not only influenced by stage of maturity but also by cutting time. In general, alfalfa harvested at early and late bud but in the afternoon had the highest nutrient levels for dairy production.