Seed contamination in sheep: new investigations into an old problem

Abstract

Seed contamination significantly affects production capacity and animal welfare in Australian sheep flocks and causes considerable financial loss to producers and processors across sheepmeat value chains. Seven grass-weed species contribute to seed contamination in Australia, with barley grass (Hordeum spp.) identified as a key perpetrator. Herbicide resistance and variable dormancy emerging in southern Australian barley grass populations are thought to enhance its capacity for successful pasture invasion, further exacerbating the potential for seed contamination in sheep. The present article reviews the current literature regarding the impact and incidence of seed contamination on sheepmeat production, with particular reference to key grass-weed species prevalence across Australia. Data are presented on a recent incidence of carcass contamination across years, where incidence varied between 11% and 80% from 2009 to 2013, contracting to between 2% and 60% during 2014 and 2015. Key areas requiring future research are defined. Understanding the biology of key grass weeds, historical influences and economic consequences associated with seed contamination in sheep may assist in defining future risks to sheep production and improve weed management. Furthermore, examining more recent data describing the current status of seed contamination across Australia and the associations with causal weed species may aid the development of critical weed-management strategies in highly infested regions, subsequently limiting the extent of future seed contamination.

The Impact of Herbicide Application and Defoliation on Barley Grass (Hordeum murinum subsp. glaucum) Management in Mixed Pasture Legumes

“…The use of conservation tillage practices, continuing climate variability, and the exclusive use of certain herbicides for annual grass control are all likely to facilitate current barley grass invasion across southern Australia, enabling the recent proliferation of highly competitive biotypes [12]. Despite the utilisation of barley grass for livestock fodder during its vegetative phase, efficacious control is crucial to reduce potential for seed contamination in sheep and improve pasture productivity later in the season.…”

Causative factors influencing epizoochorous dispersal of weed seeds by sheep and associated carcass contamination in southern Australia

“…Upon attachment to the coat via the seed awns, seeds can move through the coat to the skin under the influence of animal movement, later penetrating underlying tissues via the sharp seed rachis. Despite reports of seed injury existing in European alpaca and cattle (Hudson et al , 2006; Fischer and Hendrix, 2012) and dogs in South America and Europe (Del Angel‐Caraza et al , 2011; Tetas Pont et al , 2016), the impacts of seed penetration have been most extensively documented in New Zealand and Australian sheep, and include tissue wounds, weight loss, reduced growth rates and carcass damage (Hartley, 1976; Kelly, et al , 2018). Sheep carcass damage from weed seeds is of critical importance in Australia due to Australia's current position as the leading exporter of sheep meat around the world (Behrendt and Weeks, 2019).…”

“…(barley grass) and Bromus spp. (brome grass) have obtained greatest notoriety, due to their sharp seed rachis and long, fibrous awns (Kelly et al , 2018). Furthermore, herbicide resistance (Owen et al , 2015; Shergill et al , 2015), variable dormancy patterns (Fleet and Gill, 2012; Kleemann and Gill, 2013) and adaptation to farming practices in both species (Fleet and Gill, 2012; Recasens et al , 2016) have resulted in the spread of Hordeum spp.…”

“…and Bromus spp. populations across southern Australia (Kelly et al , 2018). Although native to Central and Western Asia, Hordeum spp.…”

“…Rainfall and temperature strongly influence Hordeum and Bromus subspecies distribution across all zones via their impact on phenological development (Cocks et al , 1976; Gill and Blacklow, 1985; Kemp and Dowling, 1991) and are reported as less ubiquitous at high elevations (Kemp and Dowling, 1991). Weather patterns also typically influence annual vegetation by inducing growth under heavy precipitation and warm temperature conditions (Pitt and Heady, 1978) and are suggested to be associated with seed contamination incidence (Kelly et al , 2018), although these relationships currently remain unexplored.…”