S. R. McLennan

Intake, retention time in the rumen and microbial protein production of Bos indicus steers consuming grasses varying in crude protein content

Feed intake, rumen function, microbial protein (MCP) production and the efficiency of MCP production were determined in steers fed four different forage hays varying markedly in crude protein content. Low quality tropical forage (speargrass and Mitchell grass) hays had lower crude protein content, higher neutral detergent fibre content and lower digestibility than a medium quality tropical forage (pangola grass) hay and a temperate forage (ryegrass) hay. Steers fed speargrass and Mitchell grass hays had lower MCP production (80 and 170 g MCP/day, respectively) and efficiency of MCP production (78 and 79 g MCP/kg digestible organic matter (DOM), respectively) than steers fed pangola grass (328gMCP/day;102gMCP/kgDOM)andryegrass(627gMCP/day;135gMCP/kgDOM)hays,whichwasdirectlyrelated to the supply of DOM and rumen degradable protein. Intake was greatest for ryegrass hay, followed by pangola grass, Mitchellgrassandspeargrasshays(17.6,15.6,10.1and5.5gDM/kgW.day,respectively). TheretentiontimeofDMinthe rumen was 72.1, 47.7, 28.6 and 19.1 h for speargrass, Mitchell grass, pangola grass and ryegrass hays, respectively, with a similar trend apparent for the retention time of neutral detergent fibre, lignin, chromium-EDTA and ytterbium labelled digesta. The difference in the protein : energy ratio of absorbed substrates (measured as efficiency of MCP production) did not appear to account for all the differences in intake, nor did a purely physical mechanism.

Spirulina (Spirulina platensis) algae supplementation increases microbial protein production and feed intake and decreases retention time of digesta in the rumen of cattle

Cattle consuming pastures low in protein have low liveweight gain due to low rumen degradable protein (RDP) supply and thus low microbial crude protein (MCP) production and efficiency of MCP production [EMCP, g MCP/kg digestible organic matter (DOM)]. Nitrogen supplements can increase MCP production and EMCP of cattle grazing low protein pastures. The objective of this study was to compare the effects of supplementation with a non-protein-N source (NPN), in this case urea and ammonium sulfate (US), with a single-cell algal protein source (Spirulina platensis), on intake, microbial protein supply and digestibility in cattle. Nine cannulated Bos indicus steers [initial liveweight 250.1 ± 10.86 (s.d.) kg] were fed Mitchell grass hay (Astrebla spp; 6.1 g N, 746 g NDF/kg DM) ad libitum and were supplied with increasing amounts of US (0, 6, 13, 19 and 33 g US DM/kg hay DM) or Spirulina 0, 0.5, 1.4, 2.5 and 6.1 g Spirulina DM/kg W.day in an incomplete Latin square design. The response of MCP production and EMCP to increasing amounts of the two supplements was different, with a greater response to Spirulina evident. The MCP production was predicted to peak at 140 and 568 g MCP/day (0.64 and 2.02 g MCP/kg W.day) for the US and Spirulina supplements, respectively. The highest measured EMCP were 92 and 166 g MCP/kg DOM for the US and Spirulina treatments at 170 and 290 g RDP/kg DOM, respectively, or a Spirulina intake of 5.7 g DM/kg W.day. Increasing RDP intake from US and Spirulina resulted in an increase in Mitchell grass hay intake and rumen NH3-N concentration and reduced the retention time of liquid and particulate markers and digesta DM, NDF and lignin in the rumen with greater changes due to Spirulina. Total DM intake peaked at a Spirulina supplement level of 4.6 g Spirulina DM/kg W.day with a 2.3-fold higher DOM intake than Control steers. Rumen NH3-N concentrations reached 128 and 264 mg NH3-N/L for the US and Spirulina treatments with a significant increase in the concentration of branched-chain fatty acids for the Spirulina treatment. The minimum retention time of liquid (Cr-EDTA; 23 and 13 h) and particulate (Yb; 34 and 22 h) markers in the rumen were significantly lower for Spirulina compared with US and lower than unsupplemented animals at 24 and 34 h for Cr-EDTA and Yb, respectively. Spirulina could be provided safely at much higher N intakes than NPN supplements. The results suggest that, at an equivalent RDP supply, Spirulina provided greater increases than US in MCP production, EMCP and feed intake of Bos indicus cattle consuming low protein forage and could also be fed safely at higher levels of N intake.

Effect of the concentration of Spirulina (Spirulina platensis) algae in the drinking water on water intake by cattle and the proportion of algae bypassing the rumen

Spirulina, a freshwater microalgae, has previously been shown to increase the efficiency of microbial protein production in cattle fed hay with a low crude protein content. The present study was carried out to determine the effect of increasing the concentration of Spirulina in the drinking water on the intake of water and the amount of water containing Spirulina bypassing the rumen of cattle. Five rumen-cannulated steers were given a fixed amount of pangola grass hay (14 g DM/kg W.day–1) and water containing 0, 1, 2, 2.7 and 3.5% (w/w) Spirulina in an incomplete Latin square design. Water intake by the control steers (0% Spirulina) was 29.7 and 49.3 g/kg W for the first drinking event after it was made available and over 24 h, respectively. For steers receiving the algae, intake of water plus Spirulina increased linearly (P < 0.01) from 42.7 to 60.2 g/kg W during the first drinking event, as the concentration of Spirulina in the drinking water increased, but over 24 h was not affected by Spirulina concentration and averaged 74.4 g/kg W. The bypass of water through the rumen, as determined using chromium-EDTA as a marker, averaged 20.5 ± 1.2% and was not affected by the concentration of Spirulina in the drinking water. Increasing inclusion of Spirulina was associated with a decrease in rumen pH, an increase in urea concentration in blood serum, and an increase in ammonia-N concentration, propionate and branched-chain fatty acids, and a decrease in butyrate proportions in rumen fluid. Spirulina inclusion in the drinking water increased water intake and may provide a potential safe and inexpensive alternative to urea for extensively grazed ruminants.

A comparison of the excretion rate of endogenous purine derivatives in the urine of Bos indicus and Bos taurus steers

Estimates of microbial crude protein (MCP) production by ruminants, using a method based on the excretion of purine derivatives in urine, require an estimate of the excretion of endogenous purine derivatives (PD) by the animal. Current methods allocate a single value to all cattle. An experiment was carried out to compare the endogenous PD excretion in Bos taurus and high-content B. indicus ( hereafter, B. indicus) cattle. Five Holstein - Friesian ( B. taurus) and 5 Brahman (> 75% B. indicus) steers ( mean liveweight 326 +/- 3.0 kg) were used in a fasting study. Steers were fed a low-quality buffel grass (Cenchrus ciliaris; 59.4 g crude protein/kg dry matter) hay at estimated maintenance requirements for 19 days, after which hay intake was incrementally reduced for 2 days and the steers were fasted for 7 days. The excretion of PD in urine was measured daily for the last 6 days of the fasting period and the mean represented the daily endogenous PD excretion. Excretion of endogenous PD in the urine of B. indicus steers was less than half that of the B. taurus steers ( 190 mu mol/kg W-0.75. day v. 414 mu mol/kg W-0.75. day; combined s.e. 37.2 mu mol/kg W-0.75. day; P< 0.001). It was concluded that the use of a single value for endogenous PD excretion is inappropriate for use in MCP estimations and that subspecies-specific values would improve precision.

Ruminal protein degradability of a range of tropical pastures

The rumen degradability parameters of the diet selected by two to four oesophageal-fistulated Brahman steers grazing a range of tropical pastures were determined by incubation of extrusa in nylon bags suspended in the rumen of rumen-fistulated (RF) Brahman steers. The effective protein degradability (Edg) was determined by measuring the rate of disappearance of neutral detergent insoluble nitrogen (NDIN) less acid detergent insoluble nitrogen (ADIN) in the incubated extrusa. Six to eight RF steers also grazed each of the pastures along with the oesophageal-fistulated steers, to allow determination of key rumen parameters and rumen particulate matter fractional outflow rates (FOR). The seven pastures studied included: native tropical grass (C4) pasture (major species Heteropogon contortus and Bothriochloa bladhii), studied in the early wet (NPEW), the wet/dry transition (NPT) and the dry (NPD) seasons; introduced tropical grass (C4) pasture (Bothriochloa insculpta), studied in the mid wet season (BB); the introduced tropical legumes (C3), Lablab purpureus (LL) and Clitoria ternatea (BP); and the temperate grass (C3) pasture, ryegrass (Lolium multiflorum, RG). Using the measured particle FOR values in calculations, the Edg estimates were very high for both C4 and C3 species: 0.82–0.91 and 0.95–0.98 g/g crude protein (CP), respectively. Substitution of an assumed FOR (kp = 0.02/h) for the measured values for each pasture type did not markedly affect estimates of Edg. However, C4 tropical grasses had much lower effective rumen degradable protein (ERDP) fractions (23–66 g/kg DM) than the C3 pasture species RG and LL (356 and 243 g/kg DM, respectively). This was associated with a lower potential degradability and degradation rate of organic matter (OM) in sacco, lower in vitro organic matter digestibility (IVOMD) and CP concentrations in the extrusa, and lower ammonia-N and branched-chain fatty acid concentrations in rumen fluid for the tropical grasses. As tropical grass pastures senesced, there was a decline in Edg, the ERDP and rumen undegradable protein (UDP) fractions, the potential degradability and degradation rate of OM and the IVOMD. These results provide useful data for estimating protein supply to cattle grazing tropical pastures.

Effect of sorghum ergot (Claviceps africana) on the performance of steers (Bos taurus) in a feedlot

The effect of ergot (Claviceps africana) in naturally infected sorghum was assessed in feedlot rations. Thirty-two Hereford steers (Bos taurus) in individual pens with access to shade were adapted to feedlot conditions and then offered one of four rations containing 0, 4.4, 8.8 or 17.6 mg/kg of ergot alkaloids (84% dihydroergosine, 10% dihydroelymoclavine and 6% festuclavine), equivalent to ~0, 10, 20 or 40 g/kg ergot (sclerotia/sphacelia) in the rations. These rations were withdrawn at noon on the second day because of severe hyperthermia and almost complete feed refusal in ergot-fed steers. After recovery on ergot-free rations for 5 days, treatment groups were incrementally introduced, over a further 3–12 days, to rations containing 0, 1.1, 2.2 or 4.4 mg/kg of alkaloids (~0, 2.5, 5 or 10 g/kg ergot, respectively). Relative exposure to ergot was maintained, so that the zero- (control), low-, medium- and high-ergot groups remained so. Steers were individually fed ad libitum, and water was freely available. Steers in all ergot-fed groups had significantly elevated rectal temperatures at 0800–1000 hours, even when the temperature–humidity index was only moderate (~70), and displayed other signs of hyperthermia (increased respiration rate, mouth breathing, excessive salivation and urination), as the temperature–humidity index increased to 73–79 during the day. Plasma prolactin was significantly reduced in ergot-fed groups. Voluntary feed intakes (liveweight basis) of the ergot-fed groups were significantly reduced, averaging 94, 86 and 86%, respectively, of the feed intakes of the control group. Hair coats were rough. While the control steers grew from a mean initial liveweight of 275 kg to a suitable slaughter weight of 455 kg in 17 weeks (growth rate 1.45 kg/day), ergot-fed groups gained only 0.77–1.10 kg/day and took at least 5 weeks longer to reach the slaughter weight, despite removal of ergot at the same time as control steers were sent to slaughter. Sorghum ergot, even at low concentrations (1.1 mg alkaloids/kg feed) is severely detrimental to the performance of steers in the feedlot.

Supplementation of cattle fed tropical grasses with microalgae increases microbial protein production and average daily gain

A series of 3 experiments were conducted to evaluate the use of microalgae as supplements for ruminants consuming low-CP tropical grasses. In Exp. 1, the chemical composition and in vitro protein degradability of 9 algae species and 4 protein supplements were determined. In Exp. 2, rumen function and microbial protein (MCP) production were determined in steers fed speargrass hay alone or supplemented with , , , or cottonseed meal (CSM). In Exp. 3, DMI and ADG were determined in steers fed speargrass hay alone or supplemented with increasing amounts of NPN (urea combined with ammonia sulfate), CSM, or . In Exp. 1, the CP content of and (675 and 580 g/kg DM) was highest among the algae species and higher than the other protein supplements evaluated, and sp. had the highest crude lipid (CL) content (198 g/kg DM). In Exp. 2, supplementation increased speargrass hay intake, the efficiency of MCP production, the fractional outflow rate of digesta from the rumen, the concentration of NHN, and the molar proportion of branched-chain fatty acids in the rumen fluid of steers above all other treatments. acceptance by steers was low and this resulted in no significant difference to unsupplemented steers for all parameters measured for this algae supplement. In Exp. 3, ADG linearly increased with increasing supplementary N intake from both and NPN, with no difference between the 2 supplements. In contrast, ADG quadratically increased with increasing supplementary N intake from CSM. It was concluded that and may potentially be used as protein sources for cattle grazing low-CP pastures.

Effect of varying the proportion of molasses in the diet on intake, digestion and microbial protein production by steers

The present experiment was conducted to determine the efficiency of microbial protein production in the rumen and intake by cattle fed high-molasses diets. Intake and microbial crude protein (MCP) production were measured along with the concentration of rumen ammonia-nitrogen (N) and volatile fatty acids (VFA), pH and the rate of digestion of roughage in the rumen. Eight Brahman crossbred steers weighing 211 ± 19.3 (± s.d.) kg were used in a double 4 × 4 Latin square design. Steers were allocated to one of four total mixed rations: control (pangola hay only), 25M (25% molasses/urea mix + 75% hay), 50M (50% molasses/urea + 50% hay), and 75M (75% molasses/urea + 25% hay). The production and efficiency of production of MCP (EMCP) of the diet increased quadratically as the level of molasses in the diet increased. The EMCP from the molasses/urea mix was estimated as 166 g MCP/kg digestible organic matter (DOM), a relatively high value. Intake of dry matter (DM) and DOM increased quadratically, reaching a peak when molasses was ~50% (as fed) of the ration. Digestibility of DM increased quadratically and that of neutral detergent fibre decreased linearly with increasing level of molasses in the diet. Molasses inclusion in the diet had no effect on rumen pH, ammonia and VFA concentration in the rumen fluid, plasma urea-N, urine pH or ruminal fractional outflow rate of ytterbium-labelled particles and Cr-EDTA. It was concluded that a diet with a high level of molasses (>50%) and supplemented with adequate N had high EMCP, and that low MCP production was not a factor limiting intake or performance of cattle consuming high-molasses diets.

Responses to various protein and energy supplements by steers fed low-quality tropical hay. 1. Comparison of response surfaces for young steers

Response curves were established for different supplements, offered at intakes ranging from 0 to 20 g/kg liveweight (W).day to young Bos indicus crossbred steers fed low-quality Rhodes grass (Chloris gayana) hay ad libitum in two pen experiments. Supplements included protein meals of varying rumen-degradability (cottonseed meal (CSM) or fishmeal), as well as ‘energy sources’ comprising grains of high and low ruminal starch degradability (barley and sorghum) and a highly fermentable sugar source (molasses), with all diets adjusted for rumen-degradable nitrogen and mineral content. Unsupplemented steers gained 0.08 and 0.15 kg/day, in Experiments 1 and 2, respectively. Growth of steers increased linearly with intake of ‘energy source’ supplements in increasing order of molasses, sorghum and barley (all differences P < 0.05). Steer growth rate also increased linearly with fishmeal, albeit over a narrow intake range (0–4.1 g/kg W.day), whereas the response with CSM was asymptotic, showing a steep response at low intake before levelling at ~1.2 kg/day. All supplement types were associated with a linear reduction in hay intake by the steers (energy substitution) where the reduction was greater (P < 0.05) for barley and molasses (not different) than for sorghum (P < 0.05), and for fishmeal compared with CSM (P < 0.05). In concurrent metabolism studies with the same rations, organic matter digestibility of the total ration (561–578 g/kg DM, unsupplemented) was increased linearly by barley and molasses (both P < 0.05) but was unaffected by CSM and sorghum supplements. The efficiency of microbial protein synthesis in steers increased linearly, from 91 g microbial crude protein/kg digestible organic matter (unsupplemented), in both molasses and CSM-supplemented steers, with the trend for a higher response to molasses (P = 0.05), and appeared most closely related to digestible organic matter intake. The response curves from these studies provide the practical framework upon which to formulate rations for cattle grazing low-quality forages.

Liveweight gain and feed intake of weaned Bali cattle fed grass and tree legumes in West Nusa Tenggara, Indonesia

Two experiments were conducted with weaned entire male Bali cattle (Bos javanicus) between 6 and 12 months of age. A randomised block design was used in both experiments, which consisted of four treatments (diets), with five replicates (animals) per treatment. In both experiments, the average daily liveweight gain (LWG), feed and water intake and diet digestibility were determined over 8 or 10 weeks, with chest girth and wither height measured at the commencement and end of the experiments. In Experiment 1, the treatments were fresh native grass, native grass supplemented with fresh sesbania, fresh sesbania and fresh sesbania supplemented with rice bran. In Experiment 2, the treatments were sole diets of leucaena hay, sesbania hay, moringa hay or gliricidia hay supplemented with sesbania hay. In Experiment 1, animals fed sesbania supplemented with rice bran had higher DM intake than did animals fed the other three diets. DM digestibility (DMD) was significantly lower for weaners fed the native grass diet than for those fed the other diets. Animals fed sesbania or sesbania supplemented with rice bran had a higher LWG (0.34 and 0.43 kg/day, respectively) and estimated metabolisable energy (ME) intake (0.71 and 0.80 MJ of ME/kg W0.75.day, respectively) than did animals fed native grass alone (0.03 kg/day; 0.58 MJ of ME/kg W0.75.day) or native grass supplemented with sesbania (0.07 kg/day; 0.64 MJ of ME/kg W0.75.day). In Experiment 2, animals fed gliricidia hay had the lowest DM intake. DM intake of animals fed moringa hay was higher than that of animals fed gliricidia hay, but lower than the intake of animals fed sesbania hay or leucaena hay. DMD of the sesbania and leucaena hay diets was lower than that of the gliricidia and moringa hay diets. Animals fed leucaena and sesbania hays had a higher LWG (0.47 and 0.43 kg/day, respectively) and estimated ME intake (0.75 and 0.78 MJ of ME/kg W0.75.day, respectively) than did animals fed moringa hay (0.22 kg/day; 0.66 MJ ME/kg W0.75.day) or gliricidia hay supplemented with sesbania hay (0.0 kg/day; 0.48 MJ ME/kg W0.75.day). In conclusion, tree legumes can safely be fed to growing Bali cattle as the sole component of the diet and some of them will increase LWGs above that of native grasses, which are typically fed to Bali cattle in villages.