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by Carina Lues, Department of Agricultural Economics, UFS
It is generally known that lucerne is of the utmost importance as fodder (roughage) in the dairy industry, although it also plays a vital role in the beef and mutton industries. However, it is important to know how the values of the different grades of lucerne hay – classified according to the New Lucerne Quality Index (NLQI), as determined by the National Lucerne Trust – differ from each other.
Where, in the past, the quality of lucerne had been graded according to the protein content, nowadays grading is increasingly based on digestibility; in other words, the availability of nutrients in the hay. The protein content of lucerne has no value if it is not available to the animal. The NLQI is based on a frequent regressive with acid-resistant fibre – ash and lignin – because it correlates best with production (quality). The NLQI values of the various grades are shown in Table 1.
It is also general practice to determine the quality of lucerne hay according to colour and leaf content. Although these methods are not necessarily at fault, they do not accurately reflect the real value the hay holds for the animal. Consequently the quality of lucerne hay can be defined as a function of ingestion and digestibility which, together, determine the production potential.
Prime lucerne, as the top grade, results in a high intake because animals find it tasty while being highly digestible at the same time. However, prime grade lucerne could also be “too good” because of the high digestibility. Therefore it is important to keep a fine balance for ruminants between the roughage and concentrates of their diet. The roughage represents the effective fibre content of a ration as it results in a healthy rumen environment by establishing an ideal pH of between 5,5 and 6,5 for the optimal balance between the amylolytic (non-fibre carbohydrate digesting) and cellulolytic (fibre-digesting) bacteria.
Effectively fibre digestion takes place at a pH higher than 6. A major contributing factor to pH-control is the fibre in the diet because it stimulates rumination and consequently leads to the production of more saliva. More saliva serves as a buffer because it resists changes in the pH value.
The digestion of top quality lucerne results in the production of large quantities of fatty acids, which cause the pH in the rumen to drop and this, combined with lower saliva production (as a result of less effective roughage) leads to a lower than optimal pH value. Lucerne hay of too high quality will consequently lead to the lucerne losing its primary role as the functional unit in the diet.
Thus it is recommended that the prime lucerne be mixed with roughage from a lower quality source when included in the diet to ensure efficient rumination and consequently maintain a healthy environment in the rumen.
Grade 1 lucerne, on the other hand, can be included in the diet without the addition of lower quality roughage. The above information is not based on a specific lucerne species, but has been confirmed mostly through research undertaken with dairy cattle.
Please note: It is important to keep in mind that sheep, dairy cattle and beef producing cattle do not function in the exact same manner in spite of all of them being ruminants. Because their production purposes differ, the utilisation of their feed also differs and consequently also the diet they have to be fed. The production potential of the different grades of lucerne hay is better known regarding dairy and beef cattle than sheep.
Due to the above it is important to establish what the influence of the lucerne hay quality is on the digestibility of a complete mixed ration, as well as what its influence will be on the production potential of sheep. An MSc study will soon be undertaken at the University of the Freestate to examine this question.
Should you be interested in garnering further knowledge regarding the functioning the lucerne hay grading system, as well as the process of the optimum utilisation of lucerne hay by livestock, you are welcome to contact the National Lucerne Trust should you wish to attend a lucerne hay-grading course.
Contact the NLT at firstname.lastname@example.org should you need more information.