The combined effects of lucerne (Medicago sativa L.) extract supplementation and ammonia treatment of rice straw (Oryza sativa, variety Thaibonnet) on the ruminal digestion of cell wall components were investigated in six continuous culture systems using a randomised complete block design. Data were fitted to second-order polynomial models. Untreated rice straw had higher contents of ash-free cell wall residues (CWR; 763 v. 687 g/kg dry matter (DM)) and non-cellulosic sugars (191 v. 166 g/kg DM) than treated rice straw. Ammoniation preferentially removed xylose, which resulted in a lower xylose-to-arabinose ratio (5.1 v. 5.8). In absence of lucerne supplementation and ammoniation, degradability coefficients were 0.54, 0.46, 0.58, 0.54, 0.42 and 0.60 for cellulose–glucose, xylose, arabinose, galactose, mannose and uronic acids, respectively. Both factors had significant effects on the microbial degradation of structural polysaccharides. With lucerne extract at an optimal level, ammonia treatment increased ash-free cell wall degradation by more than 10%. The degradability coefficients were increased by ammoniation without any significant interaction with lucerne extract, except for glucose, whose degradability was mostly influenced by lucerne extract in a curvilinear way. The comparison of regression coefficients in cell wall and CWR models suggested that ammoniation improved the degradabilities of xylose, galactose and mannose by partly solubilising the corresponding hemicelluloses and by improving the susceptibility of the remaining fraction to microbial attack, whereas it increased the degradability of arabinose only by favouring microbial attack.

Three goats provided with oesophageal and ruminal cannulae were used to determine variations in dry matter (DM) and neutral-detergent fibre (NDF) degradability of the forage consumed when grazing thorn scrubland in the semi-arid region of north Mexico, during two consecutive dry and wet periods. Ingesta samples were incubated intraruminally, the data were fitted to the exponential equation P = a + b (l - e-ct) and statistically analysed using a randomized-block design. Organic matter and crude protein (CP) contents were higher (P < 0.05) in the wet seasons. Values of NDF were similar in dry and wet season of both years whereas higher numerical values of acid-detergent fibre (ADF), lignin and cellulose were registered in the dry seasons. DM and NDF degradabilities after 24 and 48 h of ruminal incubation were higher (P < 0.05) in the wet seasons. Higher values (P < 0.05) in DM and NDF bag losses at zero time (A fraction) were registered in the two wet seasons. The insoluble but fermentable DM and NDF (B fractions) were higher (P < 0.05) in the 1999 wet season and variable in the rest of the studied period. Numerically higher values of DM and NDF c fraction were found in wet periods, whereas DM and NDF potential degradabilities were higher (P < 0.05) in the wet season in 1999 and similar across seasons in 2000. Lowest (P < 0.05) contents of CP in grazed forage, DM and NDF degradabilities after 48 h of ruminal incubation, and A, and B, and c fractions were observed in the dry seasons. Thus, these results may be related to both the lower feeding value of forage consumed by the animals and lower performance of livestock during this period. Then, the DM and NDF degradability after 48 h, together with the insoluble but fermentable matter and the c fraction permit the nutritive value of the forage consumed by grazing goats to be accurately described.

A 5 ✕ 5 Latin square was conducted with ruminally and duodenally cannulated Dohne Merino wethers consuming wheat straw to determine the effect of different rumen degradable protein (RDP) levels on forage intake, fermentation characteristics, nutrient flow and digestion. The wethers had ad libitum access to water and wheat straw (32 g crude protein (CP) per kg dry matter (DM); 742 g neutral-detergent fibre (NDF) per kg DM) that was offered twice daily, immediately after intraruminal infusion of the supplements at 07:00 and 19:00 h. The supplemental RDP (calcium caseinate; 900 g CP per kg DM) levels were: 0, 40, 80, 120 and 160 g/day. Each period consisted of 14 days of adaptation and 6 days of sampling. Forage and total organic matter (OM) intakes increased in a linear manner (P < 0•01) with increasing supplemental RDP levels. Digestible organic matter intake (DOMI) displayed a quadratic increase with elevated amounts of RDP (P < 0•01). The effects of treatments on rumen and total tract digestion, as well as fluid dilution rate were minimal. Microbial nitrogen (MN) flow to the duodenum and microbial efficiency increased quadratically (P < 0•04) with increased RDP supplementation. Rumen ammonia nitrogen (NH3-N) concentrations increased linearly (P < 0•01) and total volatile fatty acids (VFA) tended to increase linearly (P = 0•07). In conclusion, RDP supplementation to Dohne Merino wethers consuming wheat straw generally enhanced rumen fermentation and forage intake. A total RDP intake (sources: calcium caseinate and wheat straw) of 3•30 g/kg M0•75 or 0•12 of DOM maximized DOMI.

Eight Hereford ✕ Friesian steers were used to investigate the effect of feeding Lolium perenne (L) forage containing elevated levels of water-soluble carbohydrate (WSC) on rumen metabolism and nitrogen (N) absorption from the small intestine. The steers were offered ad libitum access to one of two varieties with matched heading dates (Ba11353, high WSC, HS; AberElan, intermediate WSC, control) cut at different times of the day to accentuate WSC differentials, zero-grazed for 21 days. This was followed by a 14-day period where the animals were on grass silage to provide a covariate intake. Although the total N concentration was similar for the two grasses, all other measured values were significantly different. The dry matter (DM) concentration of HS was greater than that of the control (202 v. 167 g DM per kg; P 0·01). WSC and in-vitro dry matter digestibility (IVDMD) were 243 and 161 g/kg DM, and 0·61 and 0·56 for HS and control, respectively. In contrast, acid- and neutral-detergent fibre were 251 and 296 g/kg DM and 480 and 563 g/kg DM for HS compared with control, respectively. DM intake was increased (9·3 v. 6·7 kg/day; P 0·001) for HS animals and this contributed significantly towards higher flows of non-ammonia N to the duodenum as well as increased absorption of amino acids from the small intestine. This DM intake response was partly due to the elevation in DM concentration of HS. However fresh weight intake was increased proportionately by ca. 0·15 (P 0·05) in animals on HS compared with control. Rumen ammonia levels were lower (14·0 and 26·4 mg N per l; P 0·001) and concentrations of rumen propionate higher (P 0·01) and acetate lower (P 0·01; increasing the glucogenic: lipogenic volatile fatty acid ratio) in animals on HS compared with control. However, the efficiency of microbial protein synthesis (15·9 and 17·8 g microbial nitrogen per kg organic matter apparently digested) and flow of N to the duodenum per unit N intake (0·84 and 0·93) for HS and control, respectively, were similar across both diets.

Two trials were conducted to study the effect of the stage of maturity of fresh herbage on its digestibility by two breeds of sheep (Churra v. Merino). The sward consisted of a mixture of grasses and clover, and was harvested either in late May (early cut, EC) or in late July (late cut, LC). In each trial, 12 mature sheep of each breed were used. Each animal received a different amount of fresh herbage, so that levels of food intake ranged between 8·1 and 24·7 g dry matter (DM) per kg body weight per day. EC herbage showed higher crude protein content (116 v. 67 g/kg DM), lower neutral-detergent fibre concentration (494 v. 664 g/kg DM) and higher DM digestibility (0·687 (s.e. 0·005) v. 0·463 (s.e. 0·007)) than the LC herbage. DM digestibility coefficients observed in Churra (0·694 (s.e. 0·028) for EC and 0·476 (s.e.0·028) for LC herbage) tended to be greater than those observed in Merino sheep (0·680 (s.e. 0·021) for EC and 0·452 (s.e. 0·040) for LC herbage). With the EC herbage DM digestibility tended to decrease as the level of intake increased. Samples of dried herbage were incubated in the rumen of Churra and Merino sheep to determine the DM degradability by the in situ technique. Fractional degradation rates (c values) were significantly faster in the rumen of Churra than in Merino (0·046 (s.e. 0·003) v. 0·031 (s.e. 0·002)), with large differences between breeds in the DM disappearance rates at intermediate incubation times, and no significant differences between Churra and Merino sheep in the mean a + b values. Microbial N supply, calculated from the urinary excretion of purine derivatives, was significantly affected by the herbage maturity stage and by the level of DM intake, but not by the breed of sheep. It is suggested that differences between breeds of sheep in food digestibility may be related to their ability to digest fibrous diets.

To examine the effects of manipulating the amount and ruminal degradability of starch on food intake, milk production and digestion in the rumen of lactating dairy cows, cracked wheat (CW) and sodium hydroxide-treated wheat (SW) were compared when offered with either immature (IM) or mature (MM) maize silage given in a 3: 1 dry matter (DM) ratio with grass silage. The total mixed ration (TMR) contained (kg/t DM basis) forage 600, wheat (CW or SW) 170, rapeseed meal 100, soya-bean meal 100, molasses/urea supplement 30 and minerals and vitamins were added at 20 kg/t diet DM. In experiments 1 and 2 respectively, 16 multiparous Holstein-Friesian cows and four similar cows with duodenal and ruminal cannulas were offered four diets (IMCW, IMSW, MMCW, MMSW) in 4 ✕ 4 Latin-square designs. In experiment 3, the in sacco degradability of CW and SW was measured in the rumen of three lactating fistulated cows. In experiment 1 total DM intake was 0·7 kg/day higher and milk yield was 0·5 kg/day higher with MM than IM silage but the increases were not significant and type of wheat had no effect. Milk fat content was reduced by MM silage (P < 0·05) but was unaffected by type of wheat. For milk protein content SW caused a non-significant increase with IM but a decrease (P < 0·05) with MM silage (interaction P < 0·05). There were no significant effects on yield of fat or protein. Neutral-detergent fibre digestibility in the rumen was unaffected by the treatments. Starch intake increased (P < 0·05) with MM silage when compared with IM silage and was accompanied by an increase (P < 0·01) in starch flow to the duodenum and in the amount (P < 0·001) digested in the rumen, although there was no significant change in rumen digestibility. Replacing CW with SW increased starch flow to the duodenum (P < 0·05) and reduced rumen digestibility (P < 0·05). Although the amount of total nitrogen (TN) digested in the rumen and rumen digestibility decreased (P < 0·01) with crop maturity, the flow of TN and non-ammonia nitrogen to the duodenum was unaffected. Total tract digestibility of DM was unaffected by treatments. Although the amount of starch digested in the total tract increased for MM compared with IM silage, reflecting the higher starch intake, total tract starch digestibility was unaffected by treatment and averaged 0·972. There were no main treatment effects on daily mean pH, concentration of ammonia or concentration or molar proportions of volatile fatty acids in the rumen. With SW, effective degradability (outflow rate of 0·08 per h) for both DM and starch was reduced when compared with CW. In conclusion the studies confirm that SW is more slowly fermented than CW and can increase the supply of starch to the duodenum. However the concept that increasing starch supply to the duodenum by a combination of MM silage and SW is likely to be beneficial to milk protein yield or concentration is not established under the present dietary regimen.

The objective of this study was to determine the effects on animal performance and rumen digestion characteristics of supplementing cattle grazing autumn grass offered at two levels of allowance, with concentrates formulated from different carbohydrate sources. Seventy-two steers (494 (s.e. 38·4) kg) were assigned to one of six treatments which were arranged in a two grass allowances (5·5 or 11 kg grass dry matter (DM) per head per day) by three concentrate types (starch, starch + fibre or fibre-based diets) factorial design. The experiment commenced on 22 August and had a mean duration of 84 days. Concentrates were formulated to have similar metabolizable energy and crude protein and animals were offered 5 kg per head daily. Grass allowances were offered daily and concentrates were offered individually. Six rumen fistulated steers were used concurrently in a Latin square design to determine the effect of the diets on rumen digestion characteristics. Grass and concentrates degradabilities were measured using the nylon bag technique. The concentrate DM was degraded at 0·189, 0·102 and 0·094 per h for the starch, starch + fibre and fibre-based diets, respectively. Concentrate carbohydrate source and grass allowance did not affect (P > 0·05) degradation rate of grass DM or nitrogen in the rumen, rumen fluid pH, rumen fluid concentration of volatile fatty acids, total lactic acid or ammonia concentration or plasma concentration of glucose, urea or beta-hydroxybutyrate. Animals offered the low grass allowance had larger (P < 0·05) diurnal variation in the rumen fluid acetate: propionate ratio than those offered the high grass allowance. Increasing grass allowance increased (P < 0·01) carcass gain whereas concentrate type had no effect. There was no interaction between concentrate carbohydrate source and grass allowance on any of the production variables measured. It is concluded that the rumen environment in cattle grazing autumn grass buffered the effects of concentrate carbohydrate degradability such that similar productivity was achieved with each concentrate.

In a 12-week trial, 12 Alpine and 12 Saanen dairy goats in mid lactation were housed in individual stalls for behavioural, digestive and metabolic studies. Eight of them were fitted with ruminal cannulae. They were offered ad libitum four complete diets CR, CS, FR and FS (450 g dry matter (DM) per kg) in a 4 ✕ 4 Latin-square design. Forage: concentrate ratio was either low (C = 30: 70) or high (F = 55: 45) and starch source either rapidly (R, barley) or slowly (S, maize) degraded in the rumen.

Diet preferences were tested. DM intake, chewing activities and performance were determined. Ruminal pH and ammonia-nitrogen (NH3-N) concentrations were measured. Goats were also challenged intravenously with glucose (0·2 g/kg live weight) to assess glucose homeostasis.

CR was the most preferred diet. The level of intake differed according to the type of starch (2·2 kg DM per day of CR and FR and 2·0 kg DM per day of CS and FS). FS lowered ruminal pH significantly less than the other diets after the meal. Ruminal NH3-N concentrations were lower in goats given CR and CS than FR and FS. Goats’ resistance to a glucose challenge was not different among diets. Milk yield was 2·00, 1·85, 2·01, 1·85 kg/day on CR, CS, FR and FS respectively. Milk fat content decreased significantly with diets rich in concentrate (24 v. 26 g/kg milk) but milk protein content varied only a little.

In conclusion it appears that (1) higher forage: concentrate ratios were less preferred and decreased ruminal acidity but increased daily chewing, ruminal NH3-N and milk fat content; and (2) rapidly degraded starch increased intake, ruminal acidity and milk yield.

Effects of incorporation of urea and saccharose in diets, on intake and digestion by sheep of a 35-day-old pangola (Digitaria decumbens) hay, have been studied according to a 4 × 4 Latin-square design. Sixteen rams were given four diets: hay (C); hay plus urea (U, 23 g/kg hay); hay plus saccharose (S, 60 g/kg hay), hay plus urea and saccharose (SU). Acid-detergent fibre and crude protein (CP) content of the roughage were 395 and 78 g/kg dry matter (DM) respectively. Intake of hay (g DM per kg live weight0.75), supplemented with urea and sugar (42⋅9), was lower (F < 0.05) than with other diets (47.2, s.e. 1.6). The organic matter (OM) total tract and ruminal digestibility of the diet C, S, U and SU were 0.622, 0.590, 0.615 and 0.587 (s.e. 0.007); 0.361, 0.380, 0.378 and 0.345 (s.e. 0.015) respectively. Effective degradation and nylon bag kinetics of DM degradation were higher with U and SU compared with S or C. Few differences were observed between diets for ruminal concentration of volatile fatty acids. The ruminal ammonia concentrations were higher (P < 0.05) for the diets with urea than without urea (78 v. 215 mg/l). The efficiencies of the microbial synthesis (g nitrogen per kg OM fermented in the rumen) were, 23.6, 22.4, 24.9 and 29.3 (s.e. 1.7) for the diets C, U, S and SU respectively.

Even though additional urea increased nitrogen availability for ruminal bacteria, urea supplementation did not affect significantly intake or digestion of the pangola hay of medium CP content used in this experiment.

To measure the effect of partially replacing grass silage with urea-treated whole-crop wheat (WCW) four multiparous Holstein/Friesian lactating cows fitted with cannulas in the rumen and proximal duodenum were offered four diets in a Latin-square experiment. Grass silage (GS) was produced from the primary growth of a perennial ryegrass sward. Spring wheat (cv. Axona) was harvested at 603 g dry matter (DM) per kg and preserved with 20 (WCW-20) or 40 (WCW-40) kg urea per t DM. The diets were 6 kg DM of a dairy concentrate daily with one of four forages offered ad libitum The forage treatments were GS alone, a 2: 1 DM ratio of GS with WCW-40 (2: 1 40), or a 1: 2 DM ratio of GS with WCW-20 (1: 2 20) or WCW-40 (1: 2 40). Each period lasted 4 weeks with rumen and duodenal samples being taken on 2 days in the last week. Concentrations of milk fat and protein were increased by WCW inclusion. The digestibility in the rumen of DM, organic matter (OM) neutral-detergent fibre (NDF), acid-detergent fibre and starch fell with increasing WCW-40 inclusion in the diet. Flow of starch and non-ammonia nitrogen to the duodenum increased with WCW inclusion. It was estimated that the amounts of OM, starch, NDF and nitrogen digested post ruminally increased with WCW. With WCW there were increases in the rumen in the ratio of acetic acid plus n-butyric acid to propionic acid and in ammonia concentrations. The level of urea inclusion had no significant effects on rumen digestion. It is concluded that the large reduction in the contribution of the rumen to total OM digestion when WCW partially replaces grass silage may have implications for calculations of metabolizable protein supplies to animals given such diets. Possible means to improve food utilization include processing of the wheat grains and inclusion of readily fermentable carbohydrates in the diet to facilitate the utilization of the rumen ammonia.

The effects of diets formulated to have two rates of organic matter (OM) release and to be either synchronous or asynchronous with respect to their hourly release of nitrogen (N) and OM in the rumen on the growth, intake and metabolism of ewe lambs was studied. In experiment 1, the in situ degradation characteristics of N and OM for 16 food ingredients was determined. The foods varied considerably in their chemical composition and degradability coefficients of N and OM. Based on this information, four diets were formulated to differ in their rate of N and OM release in the rumen but to have a similar content of metabolizable energy (10·4 MJ/kg dry matter (DM)), crude protein (140 g/kg DM), daily ratio of N: OM released (34 g N per kg OM) and digestible undegradable protein (32 g/kg DM) but to be synchronous or asynchronous with respect to hourly N: OM ratio. The four diets were slow energy, synchronous (SS), slow energy asynchronous (SA), fast energy, synchronous (FS) and fast energy asynchronous (FA).

In experiment 2 the four diets were offered ad libitum to 24 ewe lambs of an initial live weight of 25 kg in a 2 × 2 factorial design. Lambs were slaughtered at 40 kg live weight. Animals offered diets FS and FA had a higher growth rate than those offered diets SA and SS (266 v. 225 g/day respectively; P < 0·05). There was a significant interaction between rate ofOM and N release on DM intake (DMI) with lambs offered diet FS consuming less than those offered FA (1·47 v. 1·67 kg DM per day; P < 0·05). Rate of energy release and synchrony had an effect on food conversion efficiency (FCE; kg gain per kg DMI) with lambs offered diets FS and FA having a greater FCE than those offered SS and SA (0·170 v. 0·146 respectively; P < 0·001) and those offered diets SS and FS had a greater FCE than those offered diets SA and FA (0·164 v. 0·152 respectively; P < 0·05). Diet had little effect on carcass composition. The proportion of propionate in rumen fluid was greater in lambs offered diets FS and FA than in those offered diets SS and SA (222 v. 168 mmol/mol respectively; P < 0·01). Plasma urea concentrations exhibited a cyclical trend throughout the day with highest concentrations occurring 2 h after fresh food was offered. Lambs offered diet FS had lower plasma urea concentrations at 6, 10 and 14 h after feeding. Plasma concentrations of ß-hydroxybutyrate were lower throughout the day in lambs offered diet FS. The current findings are consistent with the view that a rapid release of OM and synchronizing hourly N: OM release in the rumen can improve the efficiency of growth through improvements in protein and/or energy metabolism.

Comparative studies were performed on the in-situ rumen degradation rate (kd) and the in-situ rumen undegradable residue (U) of dry matter (DM) and crude protein (CP) in sheep and dairy cows. The effect of different treatmentsfor sheep were investigated together with the validity of using cow-based reference protein values of foods for sheep. The effect of different breeds (Texel ewes and crossbred ewes), dietary roughage: concentrate ratio and shearing (mild cold exposure) were investigated for sheep.

The in-situ rumen incubations were performed in accordance with standard operational procedures which were comparable for both species. The foods under consideration were hay and concentrates. Cows displayed lower (DM 0·53 , CP 0·86) Kds than sheep for concentrates.

For hay a clear trend between cows and sheep was not observed but cows displayed 0·40 lower Kds than Texel ewes and 0·30 higher Kds than crossbred ewes. For concentrates U levels did not differ between species but for hay cows had 0·45 higher U values than Texel ewes. Texel ewes showed 0·45 higher Kd and 0·35 lower U for DM and CP than crossbred ewes. Dietary roughage: concentrate ratio in sheep diets did not influence the Kds and Us of the foods under consideration. Shearing of crossbred ewes increased Kd of CP by 0·25 and reduced U for DM and CP by 0·20 and 0.24 .

In conclusion different in situ rumen degradation rates were found between dairy cows and sheep. This probably makes using reference protein values of foods invalid for sheep since they are based on data for cows. Differences (Kd andU) were also found between sheep breeds and between unshorn and shorn crossbred ewes (mild cold exposure). No effect on rumen degradation kinetics could be attributed to dietary roughage: concentrate ratio.

The disappearance of neutral-detergent fibre (NDF) from six fibrous foods (lucerne hay, NaOH-treated barley straw, olive leaves, paprika meal, soya-bean hulls and sunflower hulls) when incubated in the rumen of sheep in nylon bags was investigated. Source of fibre, time of incubation and its interaction had a significant (P < 0·01) effect on NDF degradation. Stepwise regression analysis showed that the best single predictor for NDF degradation rate was the hemicellulose fraction of NDF (HEMndf). The variables selected to predict potential degradability and degradability of NDF at 72 h were the proportions of acid-detergent lignin in NDF (ADLndf, first step) and of acid-detergent cutin in ADL (ADCadl, second step). For NDF degradability at 12 h, the variables selected were the proportions of HEMndf, ADLndf and ADCadl, in the first, second and third step, respectively. The results showed that ADC is an important component to understand NDF degradability at both 12 and 72 h.

The effect of underfeeding and ref eeding on digestion was studied in Bos taurus and Bos indicus cows. Eight nonlactating cows, four B. taurus and four B. indicus (live weight 156 kg and 207 kg respectively) were first given a forage-based diet at a level above energy maintenance requirements for 4 weeks (3·65 and 4·66 kg dry matter (DM) per day respectively for B. taurus and B. indicus). They were then restricted at a low level of intake for 2 months (1·83 and 2·33 kg DM per day respectively for B. taurus and B. indicus) and finally refed at the first level for 2 months. Digestion measurements were made before the underfeeding period, at 3 and 8 weeks of underfeeding and at 3 and 8 weeks ofref eeding. Organic matter apparent digestibility decreased with underfeeding and increased with refeeding (0·637, 0·591, 0·652, 0·692 and 0·669 in B. taurus and 0·674, 0·560, 0·580, 0·698 and 0·692 in B. indicus, respectively 1 week before, 3 and 8 weeks after underfeeding, and 3 and 8 weeks after refeeding). This lower apparent digestibility at low level of intake was not expected either by ruminal particle retention time, which increased when intake decreased, or by measurements ofmicrobial activity: DM degradability measured in situ and ruminal particle size did not vary with level of intake. An effect of the length of underfeeding and refeeding was seen: the apparent digestibility tended to increase after several weeks of undernutrition and was higher after refeeding than before underfeeding. No difference was observed between the two genotypes.

A study was carried out to compare the fermentation parameters and kinetics of digestion of a range of different foods in the rumen of two breeds of sheep (Churra and Merino). Ten mature sheep (five Churra and five Merino), each fitted with a rumen cannula, were used in this study. In situ rumen degradability of both dry matter (DM) and cell wall was greater in Churra than in Merino sheep, the breed differences being significant for most of the foods used in the study (P < 0·05). These differences were greater when the foods had a higher cell wall concentration and this could be related to differences in the ruminal environment. However, when the foods were incubated with rumen fluid their in vitro organic matter (OM) degradability was similar in both breeds. Rumen pH was higher (P < 0·05) and ammonia concentrations were lower (P < 0·05) in Churra than in Merino sheep. Rumen volatile fatty acid concentrations tended to be higher in Merino than in Churra sheep, though differences were only significant just before feeding (P < 0·05). The ratio acetate: propionate was higher in the Churra than Merino breed before and 12 h after feeding (P < 0·05). Protozoa numbers in rumen liquid were similar for both genotypes. The greater degradation of forages in the rumen of Churra sheep is discussed in relation to the possible higher activity of fibre-degrading micro-organisms and the greater buffering capacity of the rumen contents against fermentation acids, which could result in more favourable conditions for the microbial degradation of foods in the rumen.

The effects of spineless cactus (Opuntia ficus indica var. inermis) supply on digestion of wheat straw was studied n rumen cannulated sheep. In addition to urea (10 g) and mineral and vitamin mixture (30 g), the animals — received wheat straw alone or supplemented with graded levels of spineless cactus (150, 300, 450 or 600 g dry natter (DM) per head per day). The diets were studied in five successive 25-day periods from February to June 992 in Tunisia. "Water consumption, food intake, digestibility, diurnal variations of ruminal fermentation (pH, mmonia nitrogen, volatile fatty acids, protozoal concentrations in rumen fluid) and cellulolytic activity in the umen were measured.

Spineless cactus had high contents of ash (260 g/kg DM) and water (926 g/kg fresh weight) and low neutral-detergent fibre content (185 g NDF per kg DM). Crude protein (CP) content of spineless cactus was 2-5 times reater than that of wheat straw (58 v. 23 g/kg DM, respectively). Drinking water consumption was substantially educed (P < 0·001) as the level of spineless cactus increased. When spineless cactus supply exceeded 300 g DM peray, sheep consumed practically no drinking water. The voluntary intake of straw increased significantly with vineless cactus level. Total diet apparent digesibilities of DM, organic matter and CP tended to increase with mneless cactus supply. Such increase was significant only with the 450 and 600 g levels of cactus. NDF and acidetergent-fibre apparent digestibilities were not affected by spineless cactus supply. Addition of spineless cactus up i 300 g DM significantly increased ruminal ammonia nitrogen (P< 0·001) but there was no additional effect with irther supplementation. When sheep were supplemented with spineless cactus, total rumen volatile fatty acid icreased and acetate: propionate ratio decreased significantly. Moreover, spineless cactus supply increased total wtozoa number and reduced significantly rumen cellulolytic activity measured as DM and NDF disappearance of heat straw from incubated nylon bags.

Using a first-order model to describe ruminal in situ digestion implies that the rate of digestion is affected only by the quantity of potentially digestible substrate remaining. Other factors, like the microbial efficacy for digesting substrate, are assumed to be constant. However, microbes are not only the cause but also the result of digestion, being one of the digestion end-products. Two sigmoidal models (a logistic and a Gompertz-like model) were derived from a general digestion function in which the rate of digestion equals the product of the quantity of potentially digestible substrate remaining and a non-constant fractional rate of digestion (microbial efficacy function). The models were compared with a first-order model with a discrete lag time. The logistic model specifically accounted for the conversion of substrate mass to microbial mass, but did not describe microbial migration between the substrate and the ruminal fluid. In contrast, the Gompertz-like model assumed that the change in microbial efficacy was only time-dependent. There was little difference between models in estimates of scale parameters, but the asymptotic microbial efficacy was consistently higher for the logistic model than for the other models. Estimates of discrete lag time in the first-order model were biased towards obtaining values identical to the independent variable. Scale estimators appeared to be more robust than kinetic estimators. Lack-of-fit was present for most model-data set combinations. The similar patterns of residuals between models suggested that a four-parameter model may be insufficient to describe the data. It was concluded that if a four-parameter model is to be used, the model with a discrete lag time would be the least biologically appropriate.

The study determined the effects of partial removal of alkaloids (detoxification) in crushed lupin seed (CLS) on voluntary food intake, and yield and composition of milk from dairy cattle. Twenty multiparous Friesian dairy cows (first 90 days of lactation) were assigned, according to a randomized complete-block design, to five diets. The diets were formulated to be isonitrogenous (25·6 g N per kg of diet dry matter (DM)) and contained napier grass, lucerne hay, maize bran and urea. The control diet (CON) contained sunflower meal; two diets contained intact CLS at 150 (LUI-15) or 300 g (LUl-30) per kg diet DM. The other two diets contained detoxified CLS at 150 (LUD-15) or 300 g (LUD-30) per kg diet DM. Lupin seeds were detoxified by treatment with boiling water, followed by steeping in cold water. The diets were analysed by gas chromatography for the alkaloids, lupanine and 13-hydroxylupanine. The total alkaloid content of LUI-15 and LUl-30 was 3·8 and 8·0 g/kg diet DM, respectively; by contrast that of LUD-15 and LUD-30 was 2·1 and 5·2 g/kg diet DM respectively. Increasing the level of intact CLS in the diet led to a decrease in voluntary food intake. Cows given LUl-30 had a lower milk yield (11·1 kg/day) than those given LUI-15 (13·8 kg/day; P < 0·01) but there was no difference in either milk protein yield or content. Detoxification of lupin removed proportionately about 0·40 of the total alkaloids from intact CLS and increased food intake, and the yield of milk and milk protein (P < 0·05) but reduced milk fat content. Detoxification of CLS also reduced the rumen degradability of lupin protein (P< 0·05). It is concluded that the reduction in organic matter intake and milk yield of cows given diets containing intact CLS was due to the presence of lupanine and 13-hydroxylupanine. To maximize its usage in diets for dairy cattle, lupin should be detoxified; it can then be included at levels up to 300 g/kg diet DM.

An experiment using twenty-five bulls aged between 1 and 1·5 years and weighing 117 to 209 kg was carried out to estimate voluntary dry-matter intake (DMI), digestible dry-matter intake (DDMI), dry-matter apparent digestibility (DMD) and growth rate when the bulls were given 18 foods available from smallholder dairy farms on the slopes of Mount Kilimanjaro, Tanzania. The animals were randomly allocated to five groups of five animals each. Foods were then randomly allocated to the five groups for four periods of 60 days each during which DMI was measured. A digestion trial was made at the completion of each measurement. Outflow rates of solids from the rumen were determined by giving the animals 200 g Cr-mordanted fibre of each food and grab faecal samples were obtained. Dry matter (DM) degradation characteristics of the foods were determined in sacco in the rumen of three Boran steers fed on guatemala grass and the water soluble fraction (A) was measured. DMI varied from 2·2 kg for banana pseudostem to 4·77 kg/day for urea-treated maize stover. DMD ranged from 549 for untreated maize stover to 767 g/kg DM for banana pseudostem and growth rate ranged from 72 for banana leaves to 275 glday for urea-treated maize stover. Potential degradability (defined by A + B) (where B is the insoluble fraction degradable with time) for the DM ranged from 617 g for banana leaves to 874 g/kg DM for banana pseudostem and the degradation rate (c) ranged from 0·0168 for banana leaves to 0·0440 per h for green maize stover. The separate use of degradation characteristics A, B and c in multiple regression to predict DMI, DDMI, and growth rates gave better results than when A + B or (A + B) + c were used. Multiple correlation coefficients between degradation characteristics and DMI, DDMI and group rate were r– 0·90, 0·93 and 0·93 respectively. The results indicate that DMI, DDMI and growth rates by cattle fed on crop residues and forages could be predicted well using the rumen degradation characteristics of the foods.

Hydration of feeds and bacterial attachment to feed particles are thought to play major roles in rumen digestion of fibrous feedstuffs. The objective of the present study was to integrate these phenomena in a mechanistic model that could be used for data analysis. The proposed model was based on the conversion of biomass, where digestion end-products can be used for the synthesis of bacterial mass. Digestion of the potentially digestible fraction and subsequent accumulation of bacterial mass was based on a sequential, three-compartment model. These compartments represented substrate undergoing hydration, digestion, and bacterial mass accumulation. A fraction of the substrate was used for synthesis of bacterial mass. It was assumed that these bacteria associate either temporarily or permanently with the remaining substrate. Dacron bags containing either dry or fully-hydrated lucerne (Medicago sativa), maize (Zea mays) cobs, orchard grass (Dactylis glomeratd), and wheat straw were incubated in the rumen of a steer that was infused continuously with (15NH4)2SO4. The 15N-enrichments of isolated particle-associated bacteria and residue remaining in the bags were used to estimate bacterial attachment. Substrate remaining and microbial mass accumulation were analysed simultaneously. Hydration did not appear to limit digestion. Fractional rate of digestion and appearance of attached bacterial mass was fastest for lucerne. For lucerne, 5 % of the digestion end-products were used for synthesis of bacteria that associated with the substrate, whereas for maize cobs, orchard grass, and wheat straw this was 16, 14, and 19% respectively. Less than 2% of digestion end-products were used for synthesis of bacteria that permanently remained associated with the substrate. Permanent association can occur only with the indigestible fraction, and probably represents bacterial debris. Lysis and/or detachment of bacterial cells was highest for lucerne, and was indicative of the rapid dynamics of lucerne digestion.