The expected reduction in methane emissions from the Australian beef herd resulting from using bulls identified as being more feed efficient as a result of having a lower residual feed intake (RFI) was modelled, both in a single herd in southern Australia and in the national herd. A gene flow model was developed to simulate the spread of improved RFI genes through a breeding herd over 25 years, from 2002 to 2026. Based on the estimated gene flow, the voluntary feed intakes were revised annually for all beef classes using livestock populations taken from the Australian National Greenhouse Gas Inventory (NGGI). Changes in emissions (kg methane/animal.year) associated with the reduction in feed intake were then calculated using NGGI procedures. Annual enteric methane emissions from both the individual and national herd were calculated by multiplying the livestock numbers in each beef class by the revised estimates of emissions per animal. For an individual adopting herd, the annual methane abatement in year 25 of selection was 15.9% lower than in year 1. For the national herd, differential lags and limits to adoption were assumed for northern and southern Australia. The cumulative reduction in national emissions was 568 100 t of methane over 25 years, with annual emissions in year 25 being 3.1% lower than in year 1. It is concluded that selection for reduced RFI will lead to substantial and lasting methane abatement, largely as a consequence of its implementation as a breeding objective for the grazing beef herd.
Extensive grazing of beef cattle is the principal use of the northern Australia land area. While north Australian beef production has traditionally utilised a low-input, low-output system of land management, recent innovations have increased the efficiency with which beef is produced. Investment to raise efficiency of cattle production by improving herd genetics, property infrastructure, the seasonal feed-base and its utilisation, as well as promoting feedlot finishing can all be expected to reduce the number of unproductive animals and reduce age-at-slaughter. Consequently, these innovations can all be expected to contribute to a reduction in the emissions intensity of greenhouse gases (GHG; t GHG/t liveweight gain). The North Australian Pastoral Company (NAPCO) has adopted these technologies to enhance reproductive and growth efficiency of the herd and has coupled them with changes in other aspects of property operation, such as use of solar energy systems, establishment of introduced perennial pastures and minimum tillage, to achieve production and operational gains, which also reduce the emissions intensity of their pastoral properties. Investments to improve production efficiency have been consistent with both financial and, in principle, environmental objectives of NAPCO. While NAPCO supports the development and implementation of new mitigation strategies, the company requires greater knowledge on pastoral emission levels and clarity on the future position of agriculture in a carbon economy. This information would enable confirmation of current emission levels, modelling of mitigation options and evaluation of the efficacy of potential on-farm carbon sinks. This paper presents NAPCO’s perspective on GHG emissions in the context of its pastoral enterprise, including current and future research and mitigation objectives.
This paper reports on both the individual and combined effects of age and liveweight at first calving (AFC and LWFC, respectively) for Australian Holstein–Friesian heifers on multiple lactation production. One hundred and thirty-five heifers were allocated to 1 of 3 AFC treatments. Within each AFC treatment, heifers were randomly assigned to 1 of 3 LWFC treatments. From 16 weeks of age until first calving, heifers in all groups grazed pasture and were provided with supplementary feed when the quantity and quality of pasture was inadequate to meet growth requirements. Mean AFC and LWFC achieved were 25.1 ± 0.121, 29.9 ± 0.11 and 33.9 ± 0.09 months and 498 ± 4.09, 549 ± 5.40 and 595 ± 5.09 kg, respectively. As AFC increased, total production over the first 3 lactations increased. For each month's delay in AFC an extra 56.7 L milk, 1.78 kg milk fat, 1.45 kg milk protein and 3.23 kg fat + protein over the first 3 lactations was produced but by the third lactation the response was minimal. By end of third lactation the remaining heifers that calved at 25.1 months AFC were producing similar amounts to those that calved at the older AFC. As LWFC increased from 498 to 595 kg, production over the first 3 lactations increased. The response to an extra kilogram increase in LWFC was 4.82 L milk, 0.20 kg milk fat, 0.18 kg milk protein and 0.38 kg fat + protein over the first 3 lactations. The greatest benefit was when LWFC increased from 498 to 549 kg. Increasing LWFC from 549 to 595 kg did not significantly increase milk, milk fat and milk protein yields from the second to third lactation. The combined effects of AFC and LWFC indicated that to reduce the negative effects on production due to decreasing AFC, LWFC would have to increase by 7.2, 2.9 and 2.2 kg for each month decrease in AFC (for milk, fat and protein production, respectively). By the end of the third lactation, only 58 heifers remained in the herd. The number of heifers remaining within the 9 groups ranged from 4 to 10. Increasing LWFC while decreasing AFC reduced the chances of a heifer remaining in the herd but this may have been biased by the feeding regime imposed during lactation. Responses to increasing AFC decreased as the number of lactations increased, indicating that heifers calving at younger AFC produce similar amounts to their older herd-mates by the end of third lactation. Increasing LWFC from 498 to 549 kg had the greatest benefits for yield, indicating a possible maximum LWFC of 549 kg for our study. Therefore, the negative effects due to decreasing AFC can be offset in part, by increasing LWFC. However, on-farm resources and ultimately milk price will determine the choice of combination of AFC and LWFC.
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