Characteristics of tall versus short-type varieties of forage sorghum grown under two irrigation levels, for summer and subsequent fall harvests, and digestibility by sheep of their silages

Abstract Changes in the response of short (Tal) and tall (FS-5) types of forage sorghum varieties to irrigation level during summer and subsequent fall growth were measured with respect to crop yield, assimilate partitioning, chemical composition and digestibility. The digestibility by sheep of silages made from Tal or FS-5 plants grown for summer and fall harvests was also investigated. During summer cycle, FS-5 plants attained maximal height of 3.2 m and stem diameter of 2–2.1 cm, whereas the upper height of Tal plants was lower (1.7–1.8 m, P P in vitro DM digestibility (0.59–0.61) for both growth cycles. During ensilage most of the soluble carbohydrates and in the case of Tal also part of the solubilized hemicelluloses were converted mainly into lactate, acetate and ethanol, resulting in similar and low pH values (3.7–4.0). High DM recovery during ensilage was found in all the genotypes. Voluntary intake by sheep of DM and NDF from diets based on the fall silages was higher than that of the summer silages however, there was no difference in forage intake between the two genotypes. In vivo DM digestibility by sheep was similar (0.61–0.64) in the two genotypes irrespective of the growth season, and reflected their similarity in NDF (0.51–0.55) and cellulose (0.61–0.64) digestibility. The main difference between genotypes was observed in CP intake and digestibility that were higher ( P