The effect of earlier mating and improving fertility on greenhouse gas emissions intensity of beef production in northern Australian herds

Abstract

Approximately 5% of Australian national greenhouse gas (GHG) emissions are derived from the northern beef industry. Improving the reproductive performance of cows has been identified as a key target for increasing profitability, and this higher efficiency is also likely to reduce the GHG emissions intensity of beef production. The effects of strategies to increase the fertility of breeding herds and earlier joining of heifers as yearlings were studied on two properties at Longreach and Boulia in western Queensland. The beef production, GHG emissions, emissions intensity and profitability were investigated and compared with typical management in the two regions. Overall weaning rates achieved on the two properties were 79% and 74% compared with typical herd weaning rates of 58% in both regions. Herds with high reproductive performance had GHG emissions intensities (t CO2-e t–1 liveweight sold) 28% and 22% lower than the typical herds at Longreach and Boulia, with most of the benefit from higher weaning rates. Farm gross margin analysis showed that it was more profitable, by $62 000 at Longreach and $38 000 at Boulia, to utilise higher reproductive performance to increase the amount of liveweight sold with the same number of adult equivalents compared with reducing the number of adult equivalents to maintain the same level of liveweight sold and claiming a carbon credit for lower farm emissions. These gains achieved at two case study properties which had different rainfall, country types, and property sizes suggest similar improvements can be made on-farm across the Mitchell Grass Downs bioregion of northern Australia.

The concordance between greenhouse gas emissions, livestock production and profitability of extensive beef farming systems

“…A combination of commercial modelling packages developed for herd structure optimisation, enterprise economic planning or determining net farm GHG emissions were used to conduct the study. The baseline farm model was calibrated using advice from regional sources and data were collected from an extensive beef enterprise near Longreach in central Queensland (Cullen et al 2015). For equivalence across comparisons, the stocking rate of each scenario was matched with that of the baseline, except for two scenarios where net farm emissions were matched with those of the baseline (leucaena equal emissions (LEE) scenarios, see below).…”

“…Details of the baseline property are documented in Cullen et al (2015); only an overview is given here. The farm consisted of 23 000 ha located 65 km south of Longreach in central Queensland (Qld), Australia (23.44 S,142.25 E).…”

“…Herd management and LW turnoff of the case-study property were considered more advanced than those of other farms in the region due to early joining of maiden heifers and the use of high-fecundity females; thus, data from the case-study farm were used to parameterise the 'early joining' (EJ) and 'high fecundity' (HF) scenarios described below. Details of the case-study farm and the influence of EJ and HF relative to generic management are further described in Cullen et al (2015). The size of the baseline herd was set to 1750 AE (1 adult equivalent = 455 kg steer at maintenance), resulting in an average annual stocking rate of 0.08 AE/ha, which is comparable to the long-term average regional value of 0.13 AE/ha (D. Phelps, pers.…”

“…The majority of steers were sold aged 20 months in August and the remainder aged 31 months in July. The LW of bulls retained on farm was set to 950 kg and surplus bulls were sold at 800 kg LW in March, following Cullen et al (2015). The ratio of bulls to cows was set to 2%; 25% of the number of bulls required each year were purchased and the remainder were home-grown.…”

“…Increasing female fecundity can increase profitability and reduce the emissions intensity of livestock enterprises (Harrison et al 2014b;Ho et al 2014;Cullen et al 2015;Dick et al 2015), mainly because sales of juvenile animals increase relative to the number of adult breeding animals retained on farm (Beauchemin et al 2011;Harrison et al 2014a). The HF scenario assumed the use of cross-breeding with Angus bulls (Bos taurus) to increase weaning rates from Brahman heifers, as well as annual selection for cows with higher reproductive performance by culling on the basis of pregnancy testing.…”