Reconstitution of Grain Sorghum for Ruminants

The mechanisms by which reconstitution increases rumen degradation of grain sorghum and relevant studies that have measured effects of reconstitution on growth performance by finishing cattle were reviewed. The growth performance data summarized indicate that reconstitution of sorghum improved feed efficiency by 15% when compared to dry-rolled sorghum with a 7.6% increase in rate of gain. Individual trial responses to reconstitution have varied greatly both for feed efficiency and rate of gain. The extent to which differences in reconstitution techniques have contributed to this inconsistency is not clear, but laboratory trials indicate that the impact could be large. Laboratory data indicate that an aerobic germination period of 1 to 5 d with grain whole prior to anaerobic storage is a critical step in the reconstitution process. This germination period allows initiation of endogenous starch hydrolysis through gibberellin-like hormones that migrate to the aleurone layer and cause protease and amylase enzymes to be released. Endogenous starch hydrolysis ceases under anaerobic conditions, but grain nitrogen becomes increasingly soluble as the duration of both germination and ensiling increase; this increases microbial access to starch granules. Access of starch granules for microbial attack is not readily reflected by enzymatic starch availability measurements. INTRODUCTION Cereal grains fed to growing and finishing cattle typically are processed to increase ruminal digestion by increasing the rate of digestion (Kd) in the rumen relative to the rate of passage (Kp) from the rumen. The Kd of cereal grains can be increased by several mechanisms including particle size reduction (e.g., grinding, rolling), solublization of the protein matrix surrounding starch granules of the endosperm (e.g., fermentation during storage), and gelatinization of endosperm starch in concert with physical disruption of the protein matrix surrounding starch granules (e.g., steam flaking, popping, extruding, micronizing). For fermentation, grain can be harvested before it dries in the field (high moisture harvest) or water can be added to dry grain (reconstitution) with this material being allowed to ferment. The harvest window during which grain moisture remains within the range ideal for production of high moisture corn lasts 7 to 14 days; for sorghum grain this period lasts only 2 to 5 days due to direct exposure of the grain in the sorghum head to the environment. Because of this short harvest window, reconstitution has been the preferred method to achieve fermentation with sorghum grain. Traditionally, reconstitution has been defined as the process of rehydrating dry grain (1215% moisture) to approximately 30% moisture, storing the whole wet grain under oxygen-limiting conditions for approximately 3 weeks for fermentation, and rolling or grinding the fermented grain prior to feeding. Storage time will dictate the extent to which fermentation progresses. The objectives of this paper are to review the mechanisms by which reconstitution increases the Kd of grain sorghum, and to review relevant studies that have measured the effects of reconstitution on growth performance by finishing cattle. Growth Performance Studies: Prior to 1976 Hinders (1976) reviewed much of the performance data with reconstituted grain sorghum conducted prior to 1976. He differentiated between grain that was reconstituted whole and stored in an oxygen-limited environment versus grain that was rolled or ground prior to storage. Particle size reduction before reconstitution allows the product to be stored in bunker silos. Relative rates of gain and relative feed efficiency for reconstituted grain sorghum relative to dry rolled grain sorghum from the individual studies reported by Hinders (1976) are shown in Figures 1a and 1b; data summarized across studies are in Figure 1c. In most studies, feed efficiency and rate of gain were improved when sorghum was reconstituted in the whole form but the magnitude of improvement varied considerably across trials. Three studies conducted during or prior to 1976 that were not included in this review were those of Schake et al. (1972), Riley et al. (1975), and Bolsen and Riley (1976).