E. Teller

Insitu Degradability of Organic-matter, Crude Protein and Cell-wall of Various Tree Forages

Leaves of Leucaena leucocephala, Sesbania sesban and Calliandra callothyrsus were harvested in Rwanda from young shoots at 8 weeks after the first cutting. They were dried, ground and incubated at the same time in polyester bags in three non-lactating Holstein-Friesian cows each fitted with a ruminal cannula. The bags were removed at 0, 2, 4, 8, 24, 48, 72 and 144 h after the start of incubations. The different parameters characterizing extent and rate of ruminal degradation of organic matter (OM), neutral-detergent fibre (NDF), and crude protein (CP) were calculated. In vitro digestibility of residual protein after 24 h and 48 h incubation was also determined. Sesbania sesban had lowest cell wall contents and gave highest ruminal degradability for OM, NDF and CP. Leucaena leucocephala was degraded to a lesser extent, but its undegraded protein had a somewhat higher in vitro digestibility. In contrast, protein of Calliandra callothyrsus was poorly degraded and digested. The proportion and composition of cell wall could not explain these differences in digestion characteristics and other measurements, such as tannins, were incriminated. Increased ruminal incubation time augmented the extent of ruminal degradation and reduced in vitro digestibility of undegraded protein but did not affect the undigestible protein fraction.

Chewing behaviour and voluntary grass silage intake by cattle

Six Friesian heifers (Experiment 1) and four lactating dairy cows (83% Holstein; Experiment 2) were fed ad libitum with direct-cut or wilted grass silage. All animals were fitted with ruminal and duodenal cannulae. Extent and rate of ruminal forage digestibility were measured and chewing behaviour of the animals was recorded. Mean faecal particle size was also determined. Neither the concentration of fermentation products in the silages, i.e. their palatability, nor the rate and extent of ruminal digestion or the extent of particle-size reduction in the digestive tract could explain the increased dry-matter intake of wilted versus direct-cut silage (17.7% in heifers and 28.4% in lactating cows). The time spent eating per kilogram dry-matter intake was substantially reduced after wilting of the grass prior to ensiling (28% in heifers and 37% in lactating cows), but the time spent ruminating was not significantly different between the two types of silages. It was inferred that ruminating is firmly involved in augmenting functional density of feed particles in the reticulorumen by expelling pockets of air or fermentation gases. This permits sedimentation of the particles and their passage through the reticulo-omasal orifice. As daily chewing capacity of the animals is limited to around 950 min, the farmer can help more efficient eaters by facilitating dry-matter ingestion (wilting, chopping, etc.) and in this way, liberating more time and more jaw movements for ruminating. More direct evidence is needed to ascertain the exact mechanism and the importance of favouring ruminating at the expense of eating activity in relation to rumen fill.

Effect of ammonia or urea treatment of straw on chewing behaviour and ruminal digestion processes in non-lactating dairy cows

Three non-lactating Holstein-Friesian cows (575 kg average body weight) fitted with ruminal and duodenal cannulas were used to examine fermentation products and extent of digestion in the rumen in relation to chewing behaviour. They were fed isonitrogenous diets composed of chopped straw (70%) and concentrate (30%). The straw was either untreated (US) and supplemented with urea or treated with ammonia (ATS) or urea (UTS). Apparent organic matter (OM) digestibility in the rumen did not differ among the three diets whereas true OM digestibility tended to be slightly greater with the treated straws. Total nitrogen reaching the intestine also was greater with treated-straw diets, resulting from an increase of bacterial protein synthesis. Bacterial nitrogen flow was 104 g day(-1) with ATS and UTS, but only 81 g day(-1) with US. The cows devoted more time and jaw movements to eating untreated straw than to eating treated straws. The figures for duration (min) and number of jaw movements devoted to eating, expressed per kg of dry matter intake, were 52.4 and 2610 for ATS, and 60.4 and 3150 for UTS, compared with 74.5 and 3400 for US. Consequently, the cows spent more time ruminating each kilogram of US compared with ATS and UTS. Frequency of jaw movements was also increased markedly after treatment of the straw. The results are interpreted to suggest that ammonia or urea treatment of wheat straw increased bacterial protein synthesis in the rumen in addition to the expected increase of cell wall digestion, leading to a substantially increased nitrogen value for the forage.

Prediction of the voluntary intake of low quality roughages by sheep from chemical composition and ruminal degradation characteristics

Six cereal straws and two traditional hays were used to study the relationship between voluntary dry matter (DM) intake and chemical composition and ruminal degradation characteristics. The voluntary DM intake was measured during 60 days using Barbarin adult ewes given food individually in four groups of six animals. The forages were offered to the ewes twice daily and were supplemented with 10 g DM of soya-bean meal per kg M(0.75) per day and 30 g per ewe per day of a commercial mixture of minerals and vitamins. The chemical composition and the leaf/stem (LIS) ratio of forages were determined. Their ruminal degradation characteristics were measured by using the nylon bag technique according to the exponenfini model Dg = a + b (1 - e(-ct)). Crude protein contents of straws ranged from 22 to 35 g/kg DM and that of hays from 35 to 57 g/kg DM. The corresponding values of L/S ratio varied from 0 . 68 to 0 . 88. The voltintauy DM intake was highly variable and the hays were ingested at greater amounts than the straws, although their degradable (b) and their rate of digestion (c) were not significantly different (P > 0 . 05). Significant relationships were established between voluntary DM intake and the neutral-detergent fibre (R(2) = -0 . 72; P < 0 . 001), acid-detergent fibre (R(2) = -0 . 75; P < 0 . 001) and a values (R(2) = 0 . 83; P < 0 . 001). The precision of the prediction was significantly improved using ruminal degradation characteristics (S-yx = 4 . 42)compared with the chemical composition (S-yx = 5 . 60).