Applied Animal Nutrition-I

MEASUREMENT OF PASTURE CONSUMPTION AND DIGESTIBILITY IN GRAZING ANIMALS

• It is essential to know the quantity of forage a grazing animal consumes from the pasture or a range and the nutritive value of the pasture. So initially pasture grasses were harvested and digestion trials were conducted in the stall. This method was not correct since the grazing animals have a tendency of selective grazing. Subsequently the grazing animals were harnessed with faeces collection bags and faeces voided in 24 hours was determined. This can provide total dry matter voided.
• Pasture grasses were harvested and fed in the stalls to determine digestibility coefficients. From these two figures the total dry matter intake (DMI) of the animals was calculated.

• It is difficult to obtain, the representative sample of forage actually eaten by the grazing animal and quantitative collection of faeces by faeces bag. Therefore markers have been used for both the determination of digestibility of pasture herbage and DMI through grazing. 
• Digestibility can be determined through use of an internal indicator.
• Faecal output is measured concurrently by using an external marker and intake is calculated as follows.
• Normally chromic oxide is fed in a capsule to the grazing animals and the number of grab samples of faeces are taken at different time interval to determine the average concentration of the indicator per unit weight of faeces.

• For example: A grazing animal was fed 2 g of Cr₂O₃ in a capsule  per day.  Find out the forage intake and its DM digestibility.                

	% Composition
DM	Lignin(Internal Indicator)	Cr2O3(External Indicator)
Forage 20	0.05	-
Forage 15	0.10	0.1

Solution

 

Use of markers

• Measurement of digestibility coefficients without total faecal collection
• Measurement of herbage intake in grazing animals            
• Markers are used for quantifying the rate of passage and extent of digestion in different segment of the gut.
• Rare earths (Lanthanam,Samarium,cerium,ytterbium and dysprosium) may be used as reliable markers of particulate phase of digesta.
• Polyethylene glycol (PEG), Chromium, EDTA and Cobalt EDTA are liquid phase markers in ruminant studies.