The effect of molasses nitrate lick blocks on supplement intake, bodyweight, condition score, blood methaemoglobin concentration and herd scale methane emissions in Bos indicus cows grazing poor quality forage

Context The Australian government has approved a greenhouse gas (GHG) offset method that requires cattle to consume nitrate in the form of a lick block. Field studies demonstrating the effectiveness of this methodology have not been previously reported. Aims This experiment was conducted to determine the effects on productivity and health when nitrate lick blocks were provided as a supplement to grazing beef cattle. We hypothesised that beef cattle given access to nitrate lick blocks would have similar productivity compared with cattle offered urea lick blocks. Methods Bos indicus breeding cows (n = 76) grazed a 467-ha paddock near Charters Towers, Queensland, between May and November 2014. A two-way remote automatic drafting system enabled allocation of cattle to different treatments while grazing in a common paddock. Treatments were 30% urea lick blocks (30U), or molasses nitrate lick blocks (MNB). At monthly intervals liveweight (LW), body condition score (BCS), and blood methaemoglobin concentration were recorded. Estimates of individual supplement intake were made on three separate occasions using a lithium marker technique. Results Mean daily supplement intake (±s.e.m.) of 30U (122 ± 13 g) was greater (P < 0.001) than MNB (67 ± 8 g). Lesser MNB intake was associated with greater variability for individual supplement intake, a greater proportion of non-consumers of supplement during July (P < 0.05) and reduced voluntary supplement intake until October (P < 0.001). Increasing MNB consumption during October and November was accompanied by elevated blood methaemoglobin concentration (P < 0.001). It was estimated that cattle offered MNB had insufficient supplementary nitrogen intake throughout the study to resolve rumen degradable nitrogen deficiency from grazed forage. Consequently, cattle provided access to MNB demonstrated conceptus free liveweight loss and lesser BCS compared with cattle treated with 30U (P < 0.001). Conclusion Nitrate lick blocks were ineffective as a dual-purpose non-protein nitrogen supplement and methane mitigant for beef cattle grazing poor quality forage. Further field experiments are required to determine if there may be situations where this GHG offset methodology is efficacious. Implications Caution is advised in implementing GHG mitigation methods that involve the use of nitrate lick blocks.

Managing plasma P concentrations in beef heifers with a slow release vitamin D supplementation

Context In extensive northern grazing systems, supplementation of P is recommended to maximise cattle growth rates and reproduction. Improving the absorption of P for the animal by influencing metabolic pathways has the potential to improve both the productivity and profitability of extensive livestock enterprises. Aims This study evaluated the efficacy of rumen bolus containing 25-hydroxyvitamin D (25OHD), commercially available as Hy-D®, and/or monensin on blood P and Ca concentrations in young cattle. Methods A total of 84 heifers, initial liveweight (mean ± s.e.m.) 184 ± 2.0 kg, were allocated to four groups, dosed with one of four slow release bolus: (1) placebo (control), (2) monensin (120 mg/day), (3) Hy-D® (6 mg/day), or (4) monensin with Hy-D®, and managed on a common unimproved native pasture from August 2012 to February 2013. On four occasions postdosing, liveweight, hip height and body condition scores were recorded, and individual faecal and jugular blood samples were collected. Key results Supplementation with monensin had a significant effect (P < 0.05) on average daily gains for the first 25 days. Interactions between 25OHD and monensin and time × monensin were also significant (P < 0.05). After 188 days, heifers receiving monensin or 25OHD + monensin were 5 and 10 kg heavier respectively, compared with their counterparts in the control and 25OHD groups. Plasma P concentrations at 25 days were 6.6 mg/dL, then increased to between 8.5 and 9.0 mg/dL and maintained this level for up to 109 days with a bolus releasing 6.0 mg/day 25OHD. Conclusions The study demonstrated that sustained and elevated plasma concentrations of both 25OHD and P, compared with control animals, can be achieved. The slow release rumen bolus maintained an elevated plasma concentration of 25OHD, and indicated that a target plasma concentration for 25OHD for increasing P absorption in beef cattle is between 200 and 300 ng/mL. Implications Supplementation of a metabolite of vitamin D influences P metabolism in Brahman heifers under grazing conditions. Integration with standard supplementation practices would optimise growth rates and reproductive performance.

Effect of feeding forage characteristic of wet- or dry-season tropical C4 grass in northern Australia, on methane production, intake and rumen outflow rates in Bos indicus steers

Methane production (MP) from Bos indicus steers fed Chloris gayana hay characteristic of the ‘dry season’ (LQH), and a fresh Urochloa mosambicensis grass (PAS) or a C. gayana hay (HQH) characteristic of the ‘wet’ season was determined. A longitudinal feeding trial incorporated a 42-day covariate period (P1) in which Brahman steers (total n = 12) were fed ad libitum LQH (g/kg DM: crude protein (CP) 25; acid detergent fibre expressed exclusive of residual ash (ADFom) 487; DM digestibility (DMD) 380) followed by a 42-day treatment period where steers (n = 4 in each) were randomly assigned to PAS, HQH or remained on LQH (control). The diet composition in P2 was HQH (g/kg DM: CP 88; ADFom 376; DMD 590), PAS (g/kg DM: CP 90; ADFom 324; DMD 630) and LQH (g/kg DM: CP 31; ADFom 461; DMD 410). For each period, on Days 35–41, individual dry-matter intakes (DMI), rumen fermentation parameters and both fluid and particulate fractional rumen outflow rates were measured. On Days 41 and 42, MP was determined using open-circuit respiration chambers. There were diet effects on MP, DMI, volatile fatty acids, and ammonia-N. Both PAS- and HQH-fed steers had greater MP (g/day; P < 0.05) and DMI (P < 0.05) than did those fed LQH, but a lower MP per kilogram DMI digested. The use of predictive equations compared with measured data confirmed prior observations that MP from tropical grasses in the northern Australian rangelands may be overestimated using the current equations for greenhouse gas accounting.

How feasible is it to replace urea with nitrates to mitigate greenhouse gas emissions from extensively managed beef cattle?

Reducing methane emissions from cattle in Australia will be dependent upon finding a strategy that can be readily adopted by its northern beef industry. The majority of the herd are located in this region and they graze low-quality tropical (C4) pastures, resulting in high methane output. There are few mitigation options that can be readily applied to extensively grazed cattle. The addition of nitrate to the diet of cattle has been shown to reduce methane production and may be an applicable strategy in northern Australia. Nitrogen is often the primary limiting nutrient in low-quality tropical pastures and it is common practice by industry to supplement with urea. Supplying an equivalent dose of nitrogen using nitrate as an alternative to urea has been demonstrated in cattle without adverse impacts upon animal productivity or health. These findings may not be directly applicable to grazing cattle in northern Australian because the diets and feeding management are not representative of the region. Nitrite toxicity can result from feeding nitrates to livestock and there is evidence that the composition of the total diet and feeding pattern influences the risk of toxicity. If nitrate supplementation in grazing beef cattle in northern Australia can be demonstrated to reduce methane and be applied safely, adoption rates will still depend on carbon market pricing. Current modelling suggests that the cost of supplementing beef cows with nitrate in northern Australia would be at least double the cost of urea supplementation.

Mastitis in beef cows and the effects of supplemental β-carotene on milk parameters

Belmont red and Brahman cows (n = 50) were allocated to one of two groups to determine if β-carotene supplementation could reduce the incidence of mastitis and consequently improve calf productivity from birth to weaning. Both groups received a molasses-based supplement ad libitum; the treatment group supplement was fortified with ROVIMIX® β-carotene and ROVIMIX® E50 whereas the control group were provided access to the molasses supplement only. Blood samples were collected from cows pre and post calving and from calves when 84 ± 0.4 days old to measure plasma β-carotene concentration (PCC). Milk samples were collected 7 and 84 days post calving and at weaning and analysed for somatic cell count (SCC) and composition. Supplementation had no significant (P > 0.05) effect on SCC, calf PCC, calf LW gain and LW at weaning. Supplemented cows had significantly (P < 0.05) higher PCC compared with unsupplemented cows (4.9 ± 0.36 v. 3.9 ± 0.24 mg/L, respectively) at weaning. Cows commenced the study in an above-average condition, and combined with unseasonal green forage it is concluded that β-carotene supplementation has no effect on mastitis or calf weaning weight.

Determining the effect of stocking rate on the spatial distribution of cattle for the subtropical savannas

With the commercial development of the global positioning system (GPS), it is now possible to monitor the distribution of free ranging cattle and derive measures to describe landscape use. Animal GPS data can be integrated with a geographic information system (GIS) detailing topography, vegetation, soil type and other landscape features. Combining GPS and GIS information is useful for understanding how animals respond to spatial variability. This study quantified land-type preferences for Brahman cross steers over three time periods, from October 2004 to March 2006 in a replicated trial, under heavy (4 ha/AE; animal equivalent of ~450 kg steer) and light (8 ha/AE) stocking in four, ~105 ha paddocks of subtropical semi-arid savanna near Charters Towers, Queensland, Australia. The grazing trail was conducted at a scale much less than would be found in commercial situations. Consequently, the spatial pattern of cattle reported here may not represent what occurs at a commercial scale and implications are discussed. Results were analysed in terms of the spatial distribution of steers fitted with GPS devices in each of the four paddocks and for each stocking rate to provide insight into cattle distribution and land-type preferences. Steers walked in excess of 6 km per day, regardless of stocking rate, and exhibited diurnal patterns of movement, with peak activity around dawn (0500–0700 hours) and dusk (1800–2000 hours). The spatial distribution of the collared steers was not uniform and appeared to be strongly influenced by the prevailing drought conditions and location of water points within each paddock. A hierarchy of drivers for distribution was identified. With the exception of drinking water location, land subtype based on soil-vegetation associations influenced animal distribution. Preference indices (ŵi) indicated that steers selected sites associated with heavy clay and texture contrast soils dominated by Eucalyptus coolabah Blakely & Jacobs (ŵi = 5.33) and Eucalyptus brownii Maiden & Cambage (ŵi = 3.27), respectively, and avoiding Eucalyptus melanophloia F.Muell. ridges (ŵi = 0.26) and Eucalyptus cambageana Maiden (ŵi = 0.12) on sodosols. The results suggest that spatial variation in cattle distribution within a paddock may be more critical than overall stocking rate in influencing the pattern of biomass utilisation. However, to quantifying the effects of different grazing land management practices on animal distribution on a commercial scale, additional studies in extensive paddocks are required.

A bromochloromethane formulation reduces enteric methanogenesis in cattle fed grain-based diets

Enteric fermentation has been estimated to be responsible for 64.2 Mt CO2-e, or ~16% of Australia’s greenhouse gas emissions (Australian Greenhouse Office 2007). A bromochloromethane (BCM) formulation, previously shown to inhibit methanogenesis, was included in the diet of Brahman (Bos indicus) cross steers, twice daily in three separate experiments, to determine the effect on methane production, daily feed intake, liveweight (LW) gain and accumulation of residues of BCM in edible tissue. In the first experiment, the BCM formulation was fed at rates of 0, 0.15, 0.30, or 0.60 g/100 kg LW, twice daily, for 28 days. Methane production (mean ± s.e.), measured over 11 h after feed was first consumed on day 28, was 0.3 ± 0.13 and 0.1 ± 0.03 L/h for animals treated at a rate of 0.30 and 0.60 g/100 kg LW, respectively. This was significantly less (P < 0.05) than for control animals (4.6 ± 0.46 L/h) and animals treated at a rate of 0.15 g/100 kg LW (2.1 ± 0.28 L/h). The dose rate of 0.30 g/100 kg LW was associated with a decrease in methanogenesis by ~93% compared with the control group and was used in subsequent experiments. The second experiment evaluated the efficacy of the BCM formulation fed at rates of 0 or 0.30 g/100 kg LW, twice daily, for 90 days. Methane production was measured over 24-h periods, on days 30, 60 and 90. For days 30 and 90, methane production was reduced by 60% (P < 0.05) to 4.2 ± 1.82 L/h and by 50% (P < 0.05) to 6.1 ± 0.63 L/h, respectively, for treated animals compared with the control group. The final experiment determined the effect on LW gain and detectable residues in edible tissue, with animals given the BCM formulation at rates of 0 or 0.30 g/100 kg LW, twice daily, for 85 days. Liver, kidney, depot fat and muscle samples collected 1 and 10 days after the last day of treatment had concentrations of BCM that did not exceed 0.015 mg/kg and were less than the temporary maximum residue limit (0.02 mg/kg BCM), which applies to bovine meat, fat and edible offal. There were no significant differences in LW gain (1.4 ± 0.10 v. 1.5 ± 0.07 kg/day), feed conversion ratio (5.7 ± 0.32 v. 5.4 ± 0.09), hot carcass weight (235 ± 5.0 v. 250 ± 6.5 kg) or P8 fat depth (6.4 ± 0.89 v. 8.1 ± 1.15 mm) between control and treated animals. The experiments reported here were completed in 2004 before the Australian Government prohibited the manufacture and use of BCM. It is unlikely that the BCM formulation will be available for commercial use to mitigate livestock methane emissions in Australia. Nevertheless, the study has demonstrated that methane emissions were substantially reduced over a 90-day feedlot finishing period. This indicates that alternative antimethanogens with a similar mechanism of action may have practical commercial relevance.

Effect of different post-weaning growth paths on long-term weight gain, carcass characteristics and eating quality of beef cattle

The effects of post-weaning nutrient restriction on growth, carcass characteristics and beef quality were determined. Belmont Red weaner steers (n = 100) were allocated to an initial slaughter group and 3 treatment groups of 120 days duration: rapid growth, slow growth and weight loss. The average daily gain of the groups were (mean ± s.e.): 0.81 ± 0.02, 0.29 ± 0.02 and –0.22 ± 0.01 kg/day, for the rapid growth, slow growth and weight loss groups, respectively. At the end of the treatment period, rapid growth steers had significantly (P<0.05) heavier carcasses, higher dressing percentages and greater bone mineral contents than those from the weight loss group. Steers from each group were realimented for 192 days at pasture. Average daily gains during this period were 0.39 ± 0.03, 0.52 ± 0.04 and 0.61 ± 0.05 kg/day for the rapid growth, slow growth and weight loss groups, respectively. Ten animals from the rapid growth group were then slaughtered to determine carcass characteristics. The remaining steers were finished at pasture for a further 409 days. During this period there was no significant difference in average daily gain between treatment groups. Steers from the rapid growth group had a significantly greater final weight (531 ± 16.8 kg) compared with weight loss steers (481 ± 14.0 kg). Carcass characteristics, eye muscle area, bone mineral content and objective measures of meat quality for the M. longissimus dorsi and M. semitendinosus did not differ significantly between groups. Shear peak force values for cooked M. longissimus dorsi samples were not significantly different between groups. Clipped meat quality scores for M. longissimus dorsi samples, as assessed by Meat Standards Australia, were not significantly different between treatment groups and indicated consumer acceptability. It was concluded that nutrient restriction in the immediate post-weaning period followed by pasture realimentation did not influence final carcass characteristics or beef quality.

Haematological values of young male rusa deer (Cervus timorensis)

OBJECTIVE

To measure haematological values of clinical significance for rusa deer and provide reference data for farmed animals.

DESIGN

Blood samples were collected regularly from eight male rusa deer from 14 days to 27 months old.

PROCEDURE

Blood samples, collected by venipuncture, were analysed within 6 hours of collection for red cell count, haemoglobin, packed cell volume, plasma glucose, white cell count and differentials.

RESULTS

Haemoglobin concentrations appeared to increase with age and ranged from 6.0 to 20.9 g/dL. Packed cell volume and plasma glucose concentration did not appear to vary with age. White cell counts ranged from 6.3 to 7.0 x 10(9)/L and differential counts indicated neutrophils > lymphocytes > monocytes > eosinophils > basophils. In general, the values for packed cell volume, red cell count, mean cell volumes and mean cell haemoglobin concentrations were within ranges previously reported for captive or sedated rusa deer.

CONCLUSIONS

Physical restraint and resultant stress was sufficient to generate some of the effects previously reported for physically immobilised or agitated deer. The values reported here do not differ greatly from those previously reported for rusa deer and can be used as reference values for clinically healthy young farmed male rusa deer.

An outbreak of malignant catarrhal fever in young rusa deer (Cervus timorensis)

On the basis of clinical signs and histological findings eight 9-month-old male rusa deer (Cervus timorensis) were diagnosed with sheep associated-malignant catarrhal fever. Following a variable course involving rectal temperatures around 40.5 degrees C, depression, inappetence, diarrhoea, corneal opacity and hypopyon all animals died or were euthanased over a 5-week period. Severe multifocal vasculitis, mainly periglomerular and in the arcuate vessels were consistent histological findings which in the past have been adequate to confirm clinical diagnosis of sheep associated-malignant catarrhal fever. A nested polymerase chain reaction test has been used to detect a sheep associated-malignant catarrhal fever PRC product, 238 base-pairs in size, in DNA extracted from lymphocyte preparations. The result supported the diagnosis of sheep associated-malignant catarrhal fever in these deer.