The use of standing dead biomass, during the winter that was produced by warm-season grasses in the previous growing season by pregnant beef cows may be an alternative to grazing systems in the semi-arid Pampean Region of Argentina. This study, conducted over 2 years, 1990 and 1991, compared the winter forage quality produced during the previous growing season for 4 warm-season grasses; switchgrass (Panicurn virgutum L. cv. Pathfinder), kleingrass (Panicurn colorutum L.), tetrachne (Tetruchne dregei New) and weeping lovegrass (Erugrostis curvula (Schrad), Nees cv. Tanganyka). Five harvests of the summer growth started after the first frost, and were spaced evenly throughout the winter period. Changes in the standing crop of dry matter were measured and subsamples of forage were divided into leaf and stem fractions. Forage quality analyses included: crude protein (CP), in vitro dry matter digestibility @VDMD), effective rumen degradability (ED), neutral (NDF) and acid (ADF) detergent fiber and lignin. Tetruclzne dregei produced forage with a higher leafxtem ratio and of generally higher quality, than the other species, although the differences were not always significant. Its CP content was marginally below the maintenance requirements of cows. Dry matter yield of tetrachne was lower than that of weeping lovegrass, but differences were only significant in 1990. Kleingrass generally was high in quality and dry matter yield, although it was the lowest in percentage of leaves of the 4 species evaluated. Switchgrass was the least productive; the nutritive value of its forage was low, comparable or lower than that of weeping lovegrass. The first harvest date was higher in nutritive value. Although the nutritive value of leaves and stems were not compared statistically, the leaves tended to be higher than the stems. Tetruchne dregei, the best of the species evaluated in this study, is a very promising warm-season grass, which could provide nutritious forage for winter grazing systems in the semiarid Pampean Region of Argentina.

The effects of nitrogen (N) fertilization of a rye pasture (Secale cereale L.) on the chemical composition of forage and its utilization in vivo and in situ were investigated in winter (W) and early spring (S). Half of the paddock to be assayed was spread with 93 kg urea-N ha )1 (treatment F), and the other half was not fertilized (treatment NF). Each experiment lasted for 17 days; apparent dry matter digestibility in vivo, voluntary dry matter intake (DMI) and digestible DMI were measured on nine rams per treatment. Two rumen cannulated animals per treatment were under the same feeding regime, and used to collect samples of rumen contents. The concentrations of ammonia (NH 3 ) and short-chain fatty acids and pH were measured in these samples. The offered forage was also incubated in the rumen of three Holstein-Friesian steers to estimate its degradation parameters in situ. Fertilization with N increased total N and decreased dry matter (DM) and non-structural carbohydrate concentrations in both periods. DMI was reduced by fertilization. The rumen concentrations of NH 3 were higher in F than in NF in both periods. In both periods, the effective DM degradability of forage was higher in F than in NF. N fertilization affects chemical composition, voluntary intake and rumen digestion of forage from rye pasture.

Although the conventional in situ ruminal degradability method is a relevant tool to describe the nutritional value of ruminant feeds, its need for rumen-fistulated animals may impose a restriction on its use when considering animal welfare issues and cost. The aim of the present work was to develop a ruminal degradability technique which avoids using surgically prepared animals. The concept was to orally dose a series of porous bags containing the test feeds at different times before slaughter, when the bags would be removed from the rumen for degradation measurement. Bags, smaller than those used in the conventional nylon bag technique, were made from woven nylon fabric, following two shape designs (rectangular flat shape, tetrahedral shape) and were fitted with one of three types of device for preventing their regurgitation. These bags were used in two experiments with individually housed non-pregnant, non-lactating sheep, as host animals for the in situ ruminal incubation of forage substrates. The bags were closed at the top edge by machine stitching and wrapped in tissue paper before oral dosing. Standard times for ruminal incubation of substrates in all of the tests were 4, 8, 16, 24, 48, 72 and 96 h before slaughter. The purpose of the first experiment was to compare the effectiveness of the three anti-regurgitation device designs, constructed from nylon cable ties ('Z-shaped', ARD1; 'double Z-shaped', ARD2; 'umbrella-shaped', ARD3), and to observe whether viable degradation curves could be generated using grass hay as the substrate. In the second experiment, three other substrates (perennial ryegrass, red clover and barley straw) were compared using flat and tetrahedral bags fitted with type ARD1 anti-regurgitation devices. Non-linear mixed-effect regression models were used to fit asymptotic exponential curves of the percentage dry matter loss of the four substrates against time of incubation in the reticulorumen, and the effect of type of anti-regurgitation device and the shape of nylon bag. All three devices were highly successful at preventing regurgitation with 93% to 100% of dosed bags being recovered in the reticulorumen at slaughter. Ruminal degradation data obtained for tested forages were in accordance with those expected from the conventional degradability technique using fistulated animals, with no significant differences in the asymptotic values of degradation curves between bag shape or anti-regurgitation device. The results of this research demonstrate the potential for using a small bag technique with intact sheep to characterise the in situ ruminal degradability of roughages.

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The quantitative relationship between the urinary excretion of benzoic acid @A) and the uptake of 3-phenylpropionic (PPA) and cyclohexanecarboxylic (CHCA) acids was assessed. PPA and CHCA are produced in the rumen by microbial fermentation of lignocellulosic feeds and metabolized, after absorption, to BA which Is excreted in the urine mainly as its glycine conjugate hippuric acid (HA). Ruminants excrete large quantities of benzoic acid (BA) derivatives in their urine due to the ingestion of lignocelluosic feedstuffs. The BA derivatives are the excretory products of hydroxycinnamic acids such as p-coumaric, caffeic and ferulic acids (Martin, 1983) and of hydroxycyclohexanecarboxylic acids such as quinic and shikimic acids (Martin, 1982~). These compounds are involved in the biosynthesis of lignin and are ubiquitous in vascular plants. Since these compounds are of no nutritional value they are often called xenobiotics, that is, foreign to the normal energy-yielding metabolism of the animal (Caldwell, 1989). By reduction and hydrolysis during microbial fermentation in the rumen, the hydroxycinnamic and hydroxycyclohexanecarboxylic acids are converted to phenylpropionic (PPA) and cyclohexanecarboxylic (CHCA) acids respectively. The PPA and CHCA are then absorbed from the rumen and posterior digestive tract compartments, and converted to BA mainly in the liver by oxidative reactions. BA can be excreted in the urine either as the free acid or as its conjugates with glycine or glucuronic acid (Martin, 1978). Fig. 1 shows the metabolic pathways for the formation of BA from PPA and CHCA. Hippuric acid (HA), the glycine conjugate of BA, is quantitatively the most important BA derivative. For