Halophytes as forages in saline landscapes: Interactions between plant genotype and environment change their feeding value to ruminants

Although the growth of halophytic forages is widely recognised as a means for using saline land and water, factors affecting the utilisation of this biomass by ruminants such as sheep, cattle and goats have received less attention. This review focuses on three factors that affect livestock production using halophytes – biomass production, nutritive value (NV) of the biomass and voluntary feed intake (VFI). Biomass production depends on plant species, genotype, the degree of abiotic stress (salinity, aridity, waterlogging), agronomic management and the interaction between genotypes and the abiotic environment. Production in irrigated systems is about 10-times that of dryland systems. NV relates to the efficiency of nutrient use by animals and is influenced by plant species, genotype and genotype × environment interactions. Halophytes typically contain lower metabolisable energy than traditional forages and most do not have enough energy for liveweight maintenance. Chenopods generally have high crude protein, sulphur and minerals, which are critical to ruminant production, however oxalate, mineral toxicities and induced deficiencies can have adverse effects on animals. Antioxidants that halophytes synthesise to detoxify reactive oxygen species may provide precursors of vitamins A and E, helping to alleviate deficiency and improve meat quality. VFI refers to the amount of feed that can be ingested by grazing animals. It is regulated by complex feedback between the stomach and central nervous system. VFI may be restricted by high concentrations of indigestible fibre, salt, and minerals and toxins, such as oxalate and nitrate. The productivity of saline agricultural systems may be improved by increasing halophyte feeding value. Increasing metabolisable energy is the most important factor. Measurement of relative palatability by grazing animals may assist in identifying genotypes with higher NV