R. A. Hunter

Methane production and energy partition of cattle in the tropics

The aim of this experiment was to determine CH4 production and energy partition for a range of diets fed to Bos indicus cattle. Six Brahman cattle were fed on three different diets in a replicated Latin square experiment over three periods. The diets were (1) long-chopped Angleton grass (Dicanthium aristatum) hay ad libitum (DM digestibility (DMD) 41 (SE 2)%; 4 g N/kg), (2) long-chopped Rhodes grass (Chloris gayana) hay ad libitum (DMD 60 (SE 1)%; 14 g N/kg) or (3) 2 kg long-chopped lucerne (Medicago sativa) hay/d plus a high-grain diet (ad libitum) (DMD 70 (SE 1)%; 31 g N/kg). CH4 production was measured using confinement-type respiration chambers. Metabolizable energy intake (MJ/d) of cattle fed on Angleton grass (18.4 (SE 2.0)) was lower (P < 0.01) than that for Rhodes grass (54.9 (SE 2.1)), which was lower (P <0.01) than that for the high-grain diet (76.7 (SE 5.8)). CH4 production (g/d) for cattle fed on Rhodes grass (257 (SE 14)) was higher (P < 0.01) than that for cattle fed on both the high-grain diet (160 (SE 24)) and Angleton grass (113 (SE 16)). CH4 conversion rate (MJ CH4 produced per 100 MJ gross energy intake) was not significantly different between cattle fed on Angleton (10.4 (SE 1.1)) and Rhodes (11.4 (SE 0.3)) grass, but was higher (P < 0.01) than for cattle fed on the high-grain diet (6.7 (SE 0.7)). CH4 production (g/kg live-weight gain) was associated (P < 0.001) with both live-weight gain and feed:gain ratio. We conclude that the relationships between CH4 production, energy utilization and live-weight change of cattle fed on tropical forages differ from those of cattle fed on diets based on temperate forages.

Utilization of low-quality roughage by Bos taurus and Bos indicus cattle

: In a number of experiments voluntary food intake of three low-quality roughages, either alone or supplemented with rumen-degradable nitrogen and sulphur and minerals, was measured in Brahman (Bos indicus) and Hereford (Bos taurus) steers. The chaffed hays were Spear grass (Heteropogon contortus) (6.2 g N/kg organic matter (OM)), Pangola grass (Digitaria decumbens) (7.9 g N/kg OM), and Pangola grass (12.0 g N/kg OM). Rumen characteristics relating to rate of fluid outflow from the rumen were also determined. There was no significant difference between breeds in the dry-matter intakes of the unsupplemented diets which ranged from 11.3 to 17.8 g/kg body-weight (BW) by Herefords and from 11.8 to 16.1 g/kg BW by Brahmans. Supplementation of Spear grass with N and S significantly (P less than 0.05) increased intake by Herefords (24%) but not by Brahmans. When the lower-N Pangola grass was supplemented there was a significant increase in intake by both breeds with the magnitude of the response in Herefords (42%) (P less than 0.001) being greater than that in Brahmans (15%) (P less than 0.05). The intakes of both the supplemented Spear grass and the lower-N Pangola diets were significantly (P less than 0.05) greater by Herefords than Brahmans. There was no breed difference in intake when the higher-N Pangola grass was supplemented. Both breeds recorded an 8% intake response to supplementation, although the increase was only significant (P less than 0.05) in Herefords. The mean retention time of fluid in the rumen on the unsupplemented Pangola grass diet of lower N content was 12.7 h in Brahmans compared with 17.5 h in Herefords (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)In a number of experiments voluntary food intake of three low-quality roughages, either alone or supplemented with rumen-degradable nitrogen and sulphur and minerals, was measured in Brahman (Bos indicus) and Hereford (Bos taurus) steers. The chaffed hays were Spear grass (Heteropogon contortus) (6.2 g N/kg organic matter (OM)), Pangola grass (Digitaria decumbens) (7.9 g N/kg OM), and Pangola grass (12.0 g N/kg OM). Rumen characteristics relating to rate of fluid outflow from the rumen were also determined. There was no significant difference between breeds in the dry-matter intakes of the unsupplemented diets which ranged from 11.3 to 17.8 g/kg body-weight (BW) by Herefords and from 11.8 to 16.1 g/kg BW by Brahmans. Supplementation of Spear grass with N and S significantly (P less than 0.05) increased intake by Herefords (24%) but not by Brahmans. When the lower-N Pangola grass was supplemented there was a significant increase in intake by both breeds with the magnitude of the response in Herefords (42%) (P less than 0.001) being greater than that in Brahmans (15%) (P less than 0.05). The intakes of both the supplemented Spear grass and the lower-N Pangola diets were significantly (P less than 0.05) greater by Herefords than Brahmans. There was no breed difference in intake when the higher-N Pangola grass was supplemented. Both breeds recorded an 8% intake response to supplementation, although the increase was only significant (P less than 0.05) in Herefords. The mean retention time of fluid in the rumen on the unsupplemented Pangola grass diet of lower N content was 12.7 h in Brahmans compared with 17.5 h in Herefords (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure of beef cattle to sub-clinical doses of Microcystis aeruginosa: toxin bioaccumulation, physiological effects and human health risk assessment.

Yearling beef cattle were fed 1 x 10(5) cells ml(-1) of toxic Microcystis aeruginosa in their drinking water for a period of 28 d. Feed and water intakes of four control and four treated animals remained unchanged following introduction of M. aeruginosa into the drinking water of the treatment animals, and there were no significant differences in feed and water intakes between control and treated animals. We tested the blood plasma of both control and treated animals twice each week for elevated concentrations of the liver enzymes gamma-glutamyl transferase (GGT), glyceraldehyde dehydrogenase (GADH), amino aspartate transferase (AST) and bilirubin. All tests were negative indicating no measurable liver dysfunction resulting from microcystin intoxication. We also tested for the presence of free microcystin in the liver and blood plasma by HPLC and ELISA and for total microcystin (free+bound) in the liver by GC-MS. If all the ingested microcystin was bioaccumulated within the liver, the concentration would have exceeded 3 microg MCYST-LR g(-1) fresh weight. HPLC and GC-MS analysis of the liver tissue and blood plasma from treated animals failed to detect any microcystins. ELISA analysis of liver tissue extracts from the treated animals indicated microcystin concentrations as high as 0.92 microg MCYST-LR equivalents g(-1) fresh weight although none was indicated in the blood plasma. The microcystin concentrations measured by ELISA in livers of treated animals were more than 1000 times higher than the limit of quantification by HPLC and GC-MS indicating the ELISA results were almost certainly due to cross reactivity with something other than intact MCYST-LR. Based on the detection limits of the HPLC and the per capita daily consumption of beef in Australia, it appears that consumption by beef cattle of water containing M. aeruginosa cell concentrations up to 1 x 10(5)cells ml(-1) for 4 weeks would not produce concentrations of microcystin within the liver or blood plasma that would present an unacceptable risk to human health based on World Health Organization protocols for determining such risks.

Ingestion of toxic Microcystis aeruginosa by dairy cattle and the implications for microcystin contamination of milk.

Microcystin (MCYST) toxins can be produced by the bloom-forming cyanobacterium Microcystis aeruginosa. They are chemically stable compounds and have both acute and chronic effects on the health of mammals, including cattle and humans. Cattle will drink water containing lethal cell concentrations of M. aeruginosa. When cattle consume sub-lethal doses of microcystins, the fate of those toxins is unknown. We provided drinking water containing 1 x 10(5) cells ml(-1) M. aeruginosa (strain MASH01-A19) to four lactating Holstein-Friesian dairy cattle for 21 days to determine if MCYST-LR produced by the cyanobacteria, could be detected in milk produced by the cattle. Cattle consumed up to 15 mg MCYST-LR at an ingestion rate of 1.21 microg kg (live weight) d(-1). Analysis by HPLC and ELISA indicated that no detectable amounts of microcystin from the cyanobacteria were present in the milk obtained from the treated animals. Based on the level of quantitation of the ELISA analyses, the maximum possible concentration in the milk was less than 2 ng l(-1). This is more than three orders of magnitude less that the concentration that could be considered problematic for milk of 0.86 microg l(-1) which we calculated using the World Health Organization derived tolerable daily intake for MCYST-LR and the per capita daily consumption of milk in Australia.

Methane production by cattle in the tropics

The data of Kurihara et al. (1999) have been used in estimating emissions of CH4 of tropical cattle consuming warm season grasses. These data, obtained using Brahman crossbred cattle fed ad libitum on hays of the grasses Dichanthium aristatum (Angleton grass) and Chloris gayana (Rhodes grass), or a grain-based diet, indicated that CH4 yield per intake of gross energy was higher than for cattle eating temperate forages. CSIRO has now discovered a systematic error of þ17% in calculation of these CH4 emission values as a result of an algorithm which used an incorrect chamber volume. The error does not apply to O2 or CO2 data, as these were corrected from gas exchange data resulting from combustion of a known amount of ethanol. Because of the use made of the data of Kurihara et al. (1999) in the Australian greenhouse gas inventories of greenhouse emissions (e.g. National Greenhouse Gas Inventory Committee, 2006), I consider it necessary to correct the public record on behalf of CSIRO. Accordingly recalculations of the pertinent data are presented in Table 1. The relationship between methane production (y, g/d) and dry matter intake (x, kg/d) for the two tropical grasses depicted in Figure 2 of Kurihara et al. (1999) becomes:

Sustained growth promotion, carcass characteristics, and meat quality of steers treated with oestradiol-17β.

The experiment measured the effect of 2 hormonal growth promotion strategies on growth rate, carcass characteristics, and some objective measurements of meat quality of steers. Bos indicus × Bos taurus crossbred steers grazing improved tropical pastures were divided into 3 treatment groups: unimplanted controls, implantation once with a long-acting formulation containing 45 mg oestradiol-17β (Compudose 400, Elanco Animal Health, West Ryde, NSW), implantation every 105 days with a shorter acting formulation containing 20 mg oestradiol-17β (Compudose 100) (4 implantations). Over a 420-day experimental period, steers implanted several times with oestradiol gained significantly (P < 0.001) more weight (279 kg) than those implanted once (251 kg) and the controls (230 kg). Respective carcass weights were 270, 255, and 244 kg. At the same carcass weight, oestradiol treatment had no significant effect on beef yield or carcass fatness. Increased total beef yields from implanted steers were associated with increased carcass weight, rather than significant modification of carcass composition. Treatment had no significant effect on any of the objective measures of meat quality studied, including ultimate pH, peak force, compression, and adhesion.

The effect of the α2-adrenergic agonist, guanfacin, on the energy metabolism of steers fed on low-quality-roughage diets

The effect of the alpha 2-adrenergic agonist, guanfacin, on the energy metabolism, feed intake and live weight (LW) change of steers was studied in three experiments. In the first, the metabolic rate of twelve steers was measured after a 72 h fast. The next day, after a 96 h fast, six steers were injected intramuscularly with 15 mg guanfacin in sterile saline (9 g sodium chloride/l) and six with sterile saline alone, and metabolic rate was measured again. Treatment significantly (P less than 0.01) lowered metabolic rate by approximately 20% (53.9 v. 66.8 kJ/kg per d). In the second experiment twelve steers were fed on long-chopped, low-quality roughage (Pangola grass (Digitaria decumbens) hay) ad lib. for 6 weeks. Six steers were continuously infused through a jugular catheter with 15 mg guanfacin/d (about 40 micrograms/kg LW) in sterile saline. The other six served as controls. There was no significant effect of treatment on feed intake (g dry matter (DM)/kg LW) or the rate of LW loss. Treatment significantly (P less than 0.05) increased the retention time of fluid (17.9 v. 22.1 h) in the alimentary tract. In the final experiment twenty-three steers were divided into four treatment groups and fed on long-chopped, low-quality roughage (Pangola hay). Treated animals were continuously infused with guanfacin at the rate of 20, 40 or 80 micrograms/kg LW per d. Control steers were not infused. At the end of the 6-week feeding period metabolic rate was measured after a 72 h fast. Regardless of dose, guanfacin significantly (P less than 0.01) lowered metabolic rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of guanfacin and nitroprusside on the haemodynamics and oxygen consumption of brahman steers

1. The systemic vascular resistance (SVR) and oxygen consumption of high grade Brahman (Bos indicus) steers were measured before and after treatment with guanfacin and nitroprusside to test whether the decreased whole-body oxygen consumption seen with guanfacin treatment is due to less oxygen consumption by vascular smooth muscle. 2. Guanfacin changed oxygen consumption by -31% but raised SVR by 61%. Nitroprusside had no significant effect on oxygen consumption but changed SVR by -20%. Moreover, with guanfacin, the changes in oxygen consumption and SVR were temporally incongruent. 3. We conclude that the lowered whole-body oxygen consumption caused by guanfacin was not due to decreased consumption by vascular tissue.