Effects of germination on the energy value of cereal grains for livestock

Abstract

Context Unusually wet weather in eastern Australia during the 2021 spring resulted in prolonged preharvest germination of a large proportion of cereal crops. An estimated 40–45% of wheat grown in New South Wales was downgraded from human consumption to feed-wheat. Similarly, preharvest germination of barley renders it unsuitable for malting or brewing. Aims To investigate the impact of wheat grown in 2021 and of various germination times on the energy value of cereal grain species for different livestock types. Methods Twenty-three samples of wheat harvested in 2021 were evaluated. Three experiments were also conducted with increasing germination times, as follows: (1) grain from wheat, barley and sorghum cultivars were germinated for 0–100 h; (2) sorghum grain was steeped in water and germinated for 5 or 10 days, with different periods of ensiling to simulate grain ‘reconstitution’ as practiced in cattle feedlots; (3) barley, wheat, sorghum and triticale grain was germinated for 0, 20 or 48 h and fed to meat chickens. Experiments 1 and 2 were conducted in vitro, with starch disappearance, starch digestion by animal-derived enzymes and starch fermentation by rumen microbes measured. Key results Short-term germination did not affect grain starch content within a cultivar, increased animal enzyme digestion of starch for barley, but not for wheat or sorghum. Longer germination of sorghum grain for 5–10 days substantially increased starch fermentability, which was further enhanced by anaerobic ensiling. Germination significantly increased the available-energy content of barley grain, but not wheat, sorghum or triticale for meat chickens. Conclusions The energy content of preharvest germinated grains for animals was not decreased, but increased for barley fed to chickens and for sorghum fed to ruminants after 5 days of germination. Implications Feeding preharvest germinated grains to livestock does not reduce energy availability, but may lead to fungal growth and mycotoxin formation.