Ruman degradation is crucial in the supply of dietary nutrients to meet the nutrient demands of the anaerobic microbes and body tissues of ruminant animals. Therefore, it is essential to study the dynamics of rumen degradation of various feeds before their potential use to formulate nutritious diets for ruminant animals. Amongst many methods that have been used in the past, the in sacco method has been the most effective method to study rumen degradation. However, this method is undesirable due to its implications for animal welfare and costs. While many in vitro methods have been tested as possible alternatives to the in sacco method to study rumen degradation of feeds, they were unable to remove the need to use fistulated animals to obtain rumen fluid. Although solubility, enzyme-and faeces-based in vitro methods do not require rumen fluid, they still need data from either the in sacco method or the rumen fluid-based in vitro methods for comparison and validation. Therefore, there is a need to develop in vitro methods that do not require the need to surgically modify ruminants to obtain rumen fluid to study rumen degradation. We review the potentials and problems associated with the existing methods to study rumen degradation and their implications for the animal industry in different situations.Rumen degradation: Animal feed: In vivo method: In sacco method: In vitro method

ABSTRACT:The present factorial experiment tested the thawed rumen fluid from frozen rumen contents against fresh rumen fluid from the same slaughtered cattle to estimate in vitro degradation of rapeseed meal (RSM) and grass nuts (GN) as two contrasting feeds at various times. Fresh rumen fluid showed higher (P < 0.05) in vitro dry matter (DMD) and crude protein (CPD) degradation than the thawed rumen fluid at most incubation times. Significant differences (P < 0.05) were found between fresh and differently prepared thawed rumen fluids for mean degradation constants (a, b, c) and effective degradability (P 0.02 ) of feeds. While the thawed rumen fluids had lower (P < 0.01) degradation than the fresh rumen fluid, their degradation values correlated very well (R 2 ≥ 0.95) with those for the fresh rumen fluid. It appeared that the thawed rumen fluid can be used to predict in vitro degradation of the selected feeds when frequent access to slaughtered or fistulated animals is restricted. Nevertheless it would be vital to improve the activity of thawed rumen fluid prior to testing its suitability for numerous feeds before recommending its routine use to estimate degradation of ruminant feeds.

Despite its beneficial role in almost all feed evaluation systems, the in sacco method is inconsistent and labour intensive in estimating the degradation of ruminant feeds. This study compared a rumen fluid-based in vitro method with the in sacco method to estimate degradation of 12 feeds comprising six concentrates and six grasses representing three fields during two seasons of winter and spring. Three feed groups (n = 4) were formed by using two grasses (one per season) and two concentrates. These feeds were incubated alongside blanks, in duplicate, for various hours either in sacco in three fistulated sheep or in vitro by using rumen fluid from the same sheep over three periods using two separate 3 × 3 Latin square designs. The in sacco and in vitro data were statistically compared for the effects of sheep, feed group and period on degradation at each incubation time within each method. The degradation data were fitted exponentially to derive water soluble (a), insoluble (b) and degradation rate (c) constants to estimate effective degradability at rumen outflow rate of 0.02 (P0.02) for each feed in each method. These values were statistically compared for variations within and between feed types for each method. The sheep, group and period did not differ significantly (P > 0.05) for feed degradation at most incubation times within any of these two methods. The in vitro method was able to mimic the in sacco degradation of feeds, although the absolute in vitro values were always lower than the in sacco values. The higher in sacco degradation for almost all feeds were partly attributed to the much greater losses of these feeds during their washing with water at 0 h. The in vitro method did identify significant differences (P < 0.05) in dry matter or crude protein degradations between and within different concentrates and grasses in parallel to the in sacco method. The ranking of feeds was comparable for these methods. The in vitro method can be used in parallel to the in sacco method to estimate degradation of various feeds. However, there is a need for coordinated studies to improve the prediction ability of the in vitro method for its adoption to routinely estimate the degradation of ruminant feeds.

Thawed rumen contents have been used to obtain strained rumen fluid (SRF) to estimate in vitro dry matter degradation (DMD) of feeds (Mohamed et al., 2002). However, thawed SRF (TSRF) gave lower DMD than fresh SRF (FSRF) which was partly attributed to reduced microbial activity in TRSF following storage at -20°C. This study examined the addition of glycerol (G) as cryopreservative and washing from particle associated microbes to SRF before its storage for later use as TSRF to estimate in vitro degradation of rapeseed meal (Rsd) and grass nut (Gnt).