Shearing force, tenacity and In vitro digestibility in mustard (Brassica campestris) at various stages of growth and in different stem portions

The feeding value of forages decreases with advancement of maturity, because of increasing cell wall concentration and lignification. The physical properties of forages are linked with feeding value for ruminants. Measurement of physical characteristics viz. shearing force and tenacity provide assessment of nutritive value of forages as alternative means. Shearing force measures the amount of energy required to fragment plant tissue which can be related with the energy used in mastication. In the present study the samples of mustard plant were collected at 60, 90 and 120 days of growth and whole stem portion was separated, divided into two equal parts i.e. stalk and branch portion and subsequently dried in hot air oven. The shearing force (N), tenacity (g/tex) and IVDMD (%) were measured in each sample. Both shearing force and tenacity of mustard stem increased significantly (p<0.01) with the increase in stage of growth and the IVDMD showed a reverse trend as it decreased significantly (p<0.01) with the age of the stem. The shearing force and tenacity on the other hand were significantly higher (p<0.01) in stalk portion than branch portion. However, the IVDMD was higher (p<0.01) in case of branch portion than that of stalk portion. The coefficient of variation (%) with regard to shearing force ranged form 0.01 to 0.06, whereas quite high coefficient of variation was observed with regard to tenacity ranging from 30.9 to 43.6. It is concluded that both shearing force and tenacity are inversely related with the digestibility and these can be used as physical characteristics in quality evaluation of forages. Further, the shearing force is considered as a better parameter than that of tenacity.