Forage quality, defined as the extent to which forage has the potential to produce a desired animal response, is a major determinant of the type of pasture to establish and its overall effect on livestock performance. The quality of forage affects forage intake.
However, forage intake could also be compounded by other factors, such as the amount of forage available, the animal’s intake capacity, performance level, health, genotype and social hierarchy. Environmental factors also affect forage intake, including prevailing temperature and humidity.
Management factors, such as stocking rate, type and level of supplementation, feeding frequency and availability of water and feed also affect forage intake.
Factors affecting forage quality
Forage nutritive value is primarily determined by concentrations of crude protein (CP) and “available” energy in the forage.
Forage quality is affected most by variations in forage genotype, maturity, season and management.
Legumes generally have a higher quality than grasses.
Legumes have higher protein concentrations and a higher intake by livestock due to a higher percentage of rapidly digestible leaves.
- SEASON: Seasonal and yearly variations have their effect primarily through temperature, but day length and light intensity are also important.
The high temperatures increase growth rate (primarily stem growth), hasten plant maturity and increase lignification of the cell wall.
Thus, the primary effect of season and temperature is on the leaf-stem ratio and plant maturity. High temperatures hasten biological processes that decrease forage quality
- POST-HARVEST MANAGEMENT: Post-harvest decrease in hay or silage quality can be minimised by careful management. Postharvest management of hay requires avoiding rain damage and proper curing of hay, to less than 15% moisture.
Leaching of nutrients from weathering decreases forage nutritive value. Therefore, hay bales should be stored under a barn, whenever possible. Post-harvest management of silage involves avoiding rain damage, wilting to 60%-70% moisture when necessary, promptly sealing silos (or wrapping haylage bales) on the day the forage is harvested, and feeding out the silage at a rate that prevents heating.
Growth of yeasts and moulds may also decrease forage nutritive value and acceptability and, therefore, reduce forage intake by livestock.
Additionally, moulds may produce mycotoxins, which can reduce animal performance and cause diseases in livestock and people. To avoid mould growth, silages should be harvested and stored at the recommended moisture concentration.
In addition, silage or haylage plastic should be maintained properly, any holes should be promptly sealed with silage tape. Silage’s density and feed out rate should follow the guidelines above, to prevent mould and heating. Application of additives containing propionic acid or lactobacillus buchneri inoculants can also prevent the growth of moulds.
Compiled by Joshua Kato (editor, Harvest Money) and Dr Jolly Kabirizi (livestock nutritionist consultant)
