CHEMICAL COMPOSITION AND IN VITRO DIGESTIBILITY OF FORAGE AS AFFECTED BY SEASON IN NORTHERN ONTARIO

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Abstract
Seasonal changes in the proximate constituents and in vitro digestibility of timothy and alfalfa were recorded at Kapuskasing during the 1963 growing season. A 20-week experiment extending from May 21 to October 8 was divided in four growing periods corresponding to various temperature regimes. There was a highly significant negative correlation between the percentage of crude fiber and that of crude protein and a significant positive correlation between protein content and in vitro digestibility. In the fall, digestibility and crude protein level showed the highest values while a corresponding significant drop was found in the crude fiber content. The percentage of crude protein and the digestibility of both dry and organic matter of alfalfa declined and the percentage of crude fiber increased with advance in maturity during all growth periods. The same trend was observed for timothy except in the fall, when digestibility and crude fiber showed no consistent fluctuations with advancing maturity. Changes in the crude fiber, fat, and ash and digestibility of timothy were smaller than in alfalfa, particularly in the second half of the season. Best yields of digestible dry matter in the first growth cycle were obtained by cutting on July 9, while best regrowth yields were reported in late summer–early fall.Temperature and precipitation in the week preceding each cut had no consistent influence on the chemical composition and digestibility.