This study was conducted to generate information on the dynamics in nutritional qualities of natural pasture hay as affected by harvesting stage, storage method and storage duration at Holetta representing cool tropical environment in the central highlands of Ethiopia. The study was designed with a factorial combinations of four harvesting stages/times (mid-October, late-October, mid-November, late-November), two storage methods (open-air, shelter shade) and five storage durations (zero, two, four, six and eight months). Crude protein (CP), in vitro OM digestibility (IVOMD), metabolizable energy (ME), neutral detergent fiber (NDF), acid detergent fiber (ADF) and lignin contents in the hay were significantly (P < 0.05) affected by harvesting stages, storage methods and storage durations. The mean CP content was reduced by 30.2%, while both IVOMD and ME contents were reduced by 17.8% each with the delay in harvesting time from mid-October (full heading stage of the pasture) to late-November (one and half months past the full heading stage). On the other hand, the mean of NDF, ADF and lignin contents were increased by 13.8, 21.6 and 36.0%, respectively with the delay in harvesting time within the specified periods. Harvesting during late-October resulted in higher yields of DM (6.83 t/ha), CP (0.48 t/ha) and digestible OM yield (3.77 t/ha) than the other harvests suggesting that late-October is the ideal harvesting time for producing large quantity of better quality hay from natural pasture in the area. The nutritional qualities of the hay also showed considerable dynamism during the eight months storage period both under shade and in open air storage methods. However, the regression analysis indicated that daily rates of changes in nutritional qualities (the rates of decline in CP content and IVOMD, and the rates of increase in the fiber fractions) during storage were higher when the hay was stored in open air than under shade. The result generally showed that in terms of contents of the important nutritional parameters (CP, IVOMD, ME, NDF, ADF and lignin), hay-based feeding could be detrimental to the nutrition of dairy cattle with the delay in harvesting beyond the late-October. Substantial reductions in nutritional qualities were also observed during storage with higher rates of nutrient losses when the hay was stored in open-air than under shade. Therefore, current findings should be supported by further animal performance studies in order to establish proper supplementation schemes considering harvesting stage, storage method and storage duration in hay-based feeding system of dairy cattle in the highlands of Ethiopia.
Key words: Native pasture hay, harvesting stage, hay storage, nutritional qualities, cool highlands.
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