Developing twinning cattle for commercial production

Long-term selection programs in the United States and New Zealand have developed twinning herds. In Nebraska, the United States Meat Animal Research Centre population had a calving rate of 1.56 per parturition in 2004. They have shown that the location of ovulation has an important effect on the success of pregnancy and that ovulations ≥3 are probably undesirable. These cattle have issues associated with calving difficulty and calf survival, which present challenges for commercial application. Intensive management using existing technology and/or future genetic improvement to address these traits are required to realise the potential benefits to beef production systems.

Analysis of high yielding maize production - a study based on a commercial crop

This paper reports on the use of APSIM – Maize for retrospective analysis of performance of a high input, high yielding maize crop and analysis of predicted performance of maize grown with high inputs over the long-term (>100 years) for specified scenarios of environmental conditions (temperature and radiation) and agronomic inputs (sowing date, plant population, nitrogen fertiliser and irrigation) at Boort, Victoria, Australia. It uses a high yielding (17 400 kg/ha dry grain, 20 500 kg/ha at 15% water) commercial crop grown in 2004–05 as the basis of the study. Yield for the agronomic and environmental conditions of 2004–05 was predicted accurately, giving confidence that the model could be used for the detailed analyses undertaken. The analysis showed that the yield achieved was close to that possible with the conditions and agronomic inputs of 2004–05. Sowing dates during 21 September to 26 October had little effect on predicted yield, except when combined with reduced temperature. Single year and long-term analyses concluded that a higher plant population (11 plants/m2) is needed to optimise yield, but that slightly lower N and irrigation inputs are appropriate for the plant population used commercially (8.4 plants/m2). Also, compared with changes in agronomic inputs increases in temperature and/or radiation had relatively minor effects, except that reduced temperature reduces predicted yield substantially. This study provides an approach for the use of models for both retrospective analysis of crop performance and assessment of long-term variability of crop yield under a wide range of agronomic and environmental conditions.

Within- and between-animal variance in methane emissions in non-lactating dairy cows

Several studies on methane (CH4) emissions have focussed on selecting high and low CH4-emitting animals. One challenge faced by this work is the lack of consistency, or repeatability, in animal rankings over time. Repeatability for individual animals over time needs to be high to reliably detect high and low CH4-emitting animals. A possible explanation for the lack of repeatability is a relatively high within-animal variation in daily CH4 emissions, meaning that animals could then change their ranking when compared at different points in time. An experiment was undertaken with four non-lactating dairy cattle to assess the within- and between-animal variation in CH4 emissions over time when measured using the sulfur hexafluoride (SF6) tracer technique. Two contrasting diets were fed to the cattle at maintenance energy levels: lucerne silage (diet 1) and a cereal + lucerne + straw mixed ration diet (diet 2). Daily CH4 measurements were undertaken for 23 days on diet 1 and 30 days on diet 2. There was a significant (P < 0.001) difference between diet 1 and diet 2 in daily CH4 production, with mean (±s.e.) production of 124.3 (11.1) g CH4/day from diet 1 and 169.8 (±11.0) g CH4/day from diet 2. Lower CH4 yield (g CH4/kg dry matter intake) was recorded on diet 1 (22.8 ± 2.0) than diet 2 (32.0 ± 2.0). Cows differed significantly (P < 0.05) from one another in daily CH4 yield (diet 1: cow 1 = 19.4 ± 0.6, cow 2 = 22.2 ± 0.8, cow 3 = 23.2 ± 0.7, cow 4 = 25.4 ± 0.6; diet 2: cow 1 = 26.0 ± 0.7, cow 2 = 36.4 ± 0.7, cow 3 = 29.3 ± 0.7, cow 4 = 36.6 ± 0.7). Variances for daily CH4 yield were smaller for diet 1 (within animal = 6.91, between animals = 6.23) than for diet 2 (within animal = 10.09, between animals = 27.79). Estimates of repeatability (variation between animals/total variation) for daily CH4 yield were 47 and 73% in diet 1 and 2, respectively. Coefficients of variation in average daily CH4 emissions in this experiment ranged from 8 to 18% despite the fact that each animal received the same quantity and quality of feed each day. While further research is required, the high within-animal variability in CH4 emissions measured using the SF6 tracer technique may explain why there has been difficulty in obtaining consistent rankings in CH4 yields when animals are measured on multiple occasions. The results also suggest that the SF6 tracer technique may exaggerate apparent between animal differences in CH4 emissions.

The systematic collection and characterisation of herbaceous forage species for recharge and discharge environments in southern Australia

Australian temperate pasture Genetic Resource Centres (GRCs) co-ordinated a major program to introduce and screen herbaceous forage species. This program aims to expand the environments where such species could reduce recharge and manage discharge for the control of dryland salinity in southern Australia. The sustainability of agriculture, in Australia especially, depends on continued access to new germplasm to enable plant breeders to continue crop and forage improvement. The GRCs supported the selection and identification of promising new legume, grass and herb species as part of a national pasture evaluation program. In total, 671 species and 21 non-species-specific genera were identified as having potential to increase water use profitability of recharge lands and to improve the productivity of saline lands across a diverse range of agricultural environments in southern Australia. Through a series of activities, 201 of these species, representing legumes, herbs and grasses were identified as promising. These were then disseminated for evaluation in a range of environments across southern Australia. The progress of selected species was monitored and germplasm of the most promising 11 species and three leguminous genera was targeted for intensive acquisition and characterisation as the basis for selection and breeding. In addition to the identification and dissemination of promising species of immediate potential, a comprehensive collection of 544 native and exotic, wild and cultivated pasture species was conserved and is now available to service future plant improvement programs.

Diversity of methanogens in ruminants in Queensland

Methane emissions from ruminant livestock represent a loss of carbon during feed conversion, which has implications for both animal productivity and the environment because this gas is considered to be one of the more potent forms of greenhouses gases contributing to global warming. Many strategies to reduce emissions are targeting the methanogens that inhabit the rumen, but such an approach can only be successful if it targets all the major groups of ruminant methanogens. Therefore, a thorough knowledge of the diversity of these microbes in different breeds of cattle and sheep, as well as in response to different diets, is required. A study was undertaken using the molecular techniques denaturing gradient gel electrophoresis, DNA cloning and DNA sequence analysis to define the extent of diversity among methanogens in ruminants, particularly Bos indicus cross cattle, on differing forages in Queensland. It was found that the diversity of methanogens in forage-fed cattle in Queensland was greater than in grain-fed cattle but there was little variability in methanogen community composition between cattle fed different forages. The species that dominate the rumen microbial communities of B. indicus cross cattle are from the genus Methanobrevibacter, although rumen-fluid inoculated digestors fed Leucaena leucocephala leaf were populated with Methanosphaera-like strains, with the Methanobrevibacter-like strains displaced. If ruminant methane emissions are to be reduced, then antimethanogen bioactives that target both broad groups of ruminant methanogens are most likely to be needed, and as a part of an integrated suite of approaches that redirect rumen fermentation towards other more useful end products.

Strategies for control of the redlegged earth mite in Australia

The redlegged earth mite, Halotydeus destructor, continues to be an intractable pest causing damage to most crop and pasture species in southern Australia. H. destructor feed on all stages of plants, but particularly damage seedlings in autumn. Research has aimed to develop new controls based on a better understanding of the biology and ecology of this pest. Chemicals remain the key tool to control H. destructor, despite the recent appearance of resistance to synthetic pyrethroids. A control package, Timerite, has been developed by which a single well-timed spray in spring can prevent H. destructor from developing diapause eggs. Field trials show this strategy provides effective control of H. destructor the following autumn, and protects plant seedlings, although mite populations build up again during winter. Non-chemical control strategies include grazing, the use of tolerant plants such as cereals, resistant legume cultivars and avoiding rotations where favourable host plants are available in the year before growing susceptible crops such as canola. Natural enemies can assist in mite control, and their numbers can be enhanced by methods including increasing landscape features like shelterbelts. Interspecific competition can occur between H. destructor and other pest mites, but the extent to which these interactions influence the structure of pest communities under different management regimes remains to be investigated.

Increased levels of cysteinyl leukotrienes and prostaglandin E2 in gastrointestinal tract mucus are associated with decreased faecal dry matter in Merino rams during nematode infection

Immune-mediated scouring in sheep is a mucosal hypersensitivity response incited by infective larvae of gastrointestinal nematodes in the southern half of Australia and in New Zealand, regions characterised by a Mediterranean, winter-rainfall climate. To gain insights into the underlying mechanism(s), this study investigated the relationship between nematode infection of sheep in pens, faecal dry matter and release of inflammatory mediators in the intestinal tract. Six worm-free, immune rams received a dose of 3000 Trichostrongylus third stage larvae (L3) and 3000 Ostertagia L3 per week for 6 weeks, after which they were euthanased. Three rams acted as uninfected controls. Faecal dry matter was significantly lower in the infected group from the first week of infection until the end of the trial. Concentrations of cysteinyl leukotrienes and prostaglandin E2 were higher in mucus from both the abomasum and the small intestine of infected rams compared with controls. Within the infected group, concentrations of both mediators were higher in mucus from the small intestine than from the abomasum. There were greater numbers of eosinophilic granulocytes and mucosal mast cells in abomasal and small-intestinal tissue sections from infected rams compared with the controls. The results are consistent with the hypothesis that nematode infection causes an inflammatory response in the gastrointestinal mucosa, characterised by increased fluid secretion.

Measurement of greenhouse gas emissions from Australian feedlot beef production using open-path spectroscopy and atmospheric dispersion modelling

Feedlot production of beef cattle results in concentrated sources of gas emissions to the atmosphere. Reported here are the preliminary results of a micrometeorological study using open-path concentration measurements to determine whole-of-feedlot emissions of methane (CH4) and ammonia (NH3). Tunable near-infrared diode lasers were used to measure line-averaged (150–400 m) open-path concentrations of CH4 and NH3. A backward Lagrangian stochastic model of atmospheric dispersion and the software package WindTrax were used to estimate greenhouse gas fluxes from the measured concentrations. We studied typical Australian beef feedlots in the north (Queensland) and south (Victoria) of the continent. The data from a campaign during summer show a range of CH4 emissions from 146 g/animal.day in Victoria to 166 g/animal.day in Queensland and NH3 emissions from 125 g/animal.day in Victoria to 253 g/animal.day Queensland.

Simulation models used for determining food intake and growth of ostriches: an overview

A formal method for determining the amino acid requirements of ostriches, from which a feeding strategy may be developed, requires characterisation of the growth potential of the body and feather proteins of these birds. Allometric equations may then be used to predict the growth of the physical parts of the ostrich, from which the optimal harvest time can be determined. Reasonable estimates of the parameters describing body and feather growth are now available. These values, together with the amino acid composition of the ostrich carcasses obtained at various stages of growth, make it possible to calculate the daily amino acid requirements of an ostrich growing at its potential. Subsequently, when given a description of the feed being offered, the desired food intake can be determined. The constraining effects of feed bulk and high temperatures are not yet well defined, but voluntary food intake in these birds when fed intensively under normal environmental conditions can now be predicted with the use of simulation models, from which it is possible to design a feeding strategy that will optimise performance.

Effects of hormonal growth promotants (HGP) on growth, carcass characteristics, the palatability of different muscles in the beef carcass and their interaction with aging

Effects of hormonal growth promotant (HGP) implantation on liveweight, carcass and meat quality measurements were examined using 80 Angus yearling cattle. After entry to the feedlot, 40 steers and 40 heifers were implanted with Revalor-S (28 mg oestradiol and 140 mg trenbolone acetate) and Revalor-H (20 mg oestradiol, 200 mg trenbolone acetate), respectively. Cattle were slaughtered after 55 and 65 days on feed. Samples from the Mm. longissimus dorsi, biceps femoris (the cap and body portions), gluteus medius (the eye and D portions), infraspinatus and triceps brachii were prepared for sensory testing after aging for 5 and 21 days after slaughter. A total of 854 muscle samples were cooked by grill (601) or roast (253) methods and served to consumers using the Meat Standards Australia taste panel protocols. When adjusted to the same initial liveweight, implantation with Revalor-H and Revalor-S resulted in a 4 and 7% increase in slaughter weight, respectively. Implantation resulted in an increased ossification score in steers (P < 0.05), but not in heifers. There was a significant interaction (P < 0.05) between HGP implantation and days aged for shear force. There was a small effect of HGP implants on compression (P < 0.05), but not on cook loss and intramuscular fat percentage. Muscles differed in their response to HGP implantation (P < 0.05) for tenderness, overall liking and palatability scores. Muscles also differed in their aging rates after slaughter (P < 0.05). The greatest response in sensory scores to HGP implantation was found in those muscles that had the highest aging rates. Possible mechanisms by which muscles differed in their response to HGP implantation are discussed.