Effect of variety and maturity stage on chemical composition, carbohydrate and protein subfractions, in vitro rumen degradability and energy values of timothy and alfalfa

The objective of this study was to investigate the effects of forage variety and stage of maturity on chemical composition, protein and carbohydrate subfractions, in vitro rumen degradability and energy content under the climatic conditions of western Canada. Two varieties of alfalfa (Medicago sativa L. cvs. Pioneer and Beaver) and timothy (Phleum pratense L. cvs. Climax and Joliette), grown at three locations in Saskatchewan (Canada), were cut at three stages [1 = 1 wk before commercial cut (early bud for alfalfa; joint for timothy); 2 = at commercial cut (late bud for alfalfa; pre-bloom head for timothy); and 3 = one week after commercial cut (early bloom for alfalfa; full head for timothy)]. The results showed that: (1) the varieties had minimal effects on nutritional value; however, (2) stage of cutting had a large impact on chemical composition, protein and carbohydrate fractions, in vitro rumen degradability and energy value. As plant maturity advanced from stage I to 3, the following changes were noticed: (a) CP was decreased [alfalfa: 20.2 to 17.6; timothy: I I.I to 7.9% dry matter (DM)]; fibre was affected very little in alfalfa but increased in timothy [acid detergent fibre (ADF): 38.0 to 40.7; neutral detergent fibre (NDF): 68.7 to 72.8% DM]; lignin and neutral detergent insoluble protein (NDIP) were not affected in either forage; acid detergent insoluble protein (ADIP) was increased in alfalfa (3.5 to 17.1% CP), but no effect was seen in timothy; (b) the rapidly degradable protein fraction (PA) was reduced in alfalfa (51.2 to 34.8% CP) but increased in timothy (9.2 to 27.5% CP); the rapidly degradable fraction (PBI) increased in alfalfa (0.0 to 25.2% CP), but decreased in timothy (31.6 to 16.7%); the intermediate degradable fraction (PB2) decreased in both forages (alfalfa: 14.1 to 5.2; timothy: 37.8 to 29.4% CP); the slowly degradable fraction (PB3) declined in alfalfa (33.1 to 17.7% CP), but was not affected in timothy (averaging 21.3% CP); the unavailable fraction (PC) associated with the cell wall increased in alfalfa (3.5 to 17.1% CP), but did not change in timothy (averaging 5.2% CP); (c) in vitro rumen degradabilities of DM (IVDMD) and NDF (IVNDFD) increased at stage 2 and then declined at stage 3. The highest IVDMD and IVNDFD after a 48-h incubation were at cutting stage 2 (50.5 and 37.3%; 42.8 and 37.3% for alfalfa and timothy, respectively); (d) the energy content behaved in a quadratic fashion; it increased initially and then decreased with the highest energy contents at stage 2 for both forages (TDN , DE, DE, MEp, NEp: 63.8% DM, 2.92, 2.68, 2.26, 1.40 Meal kg^-1 DM for alfalfa; 45.3% DM, 2.03, 1.86, 1.43, 0.82 Mcal kg- DM for timothy, respectively). In general, the best cutting was found at stage 2, which was latebud for alfalfa varieties and pre-bloom head for timothy.