There is a need to exploit methods of digestibility trials that do not require sophisticated facilities and equipment. The measurements involved should be the minimum needed to set up feeding trials.
This will require observing and measuring the livestock response to dietary manipulations based on the available feed resources. This will aid in the identification of several feed resources that are cheap and readily available locally.
Read Also Digestive Anatomy of Ruminants
Methods of In-Vivo Digestibility
Materials used for in vivo techniques are expected to meet a set of digestibility standard conditions. These conditions include animal protocols as well as diet preparations.
1. Animal Protocol
You must prepare the animal according to the breed, treatment, and surgical modifications to be carried out on such animals.
You must remember to seek the approval of the Animal Ethics Committee of your institution. Remember that animals have to be cannulated before you can collect digest.
Certain factors are very important for preparing diet(s) for in vivo digestibility studies. Such factors include feedstuff variety, diet type (compound or single feedstuff), source (commercial or experimental), sample quantity, and sample particle size.
You can do In vivo digestibility studies on ruminal digestion in which digestibility processes in the rumen of a ruminant animal are observed using fistulated steers.
Read Also Nutrient Requirements and Feeding of Ruminants
Several techniques can be applied to in vivo digestibility. They include;
- 1. Direct or total/complete collection
- 2. Difference method
- 3. Regression method
- 4. Indirect method
1. Direct or total/complete collection: This method entails housing the animal in metabolic cages/crates or they can be housed in pens. The animals housed in pens are fitted with collection bags.
The quantity of feed served to the animal is measured and proximate analysis of the feed is carried out and noted. The total feces voided during the experiment are also collected. The dry weight content of the faeces will be determined and proximate analysis carried out on the dry faecal samples.
The calculations involved in the total collection method are as follows;
Digestibility (g/kg) = 𝐍𝐮𝐭𝐫𝐢𝐞𝐧𝐭 𝐢𝐧 𝐟𝐞𝐞𝐝 – 𝐍𝐮𝐭𝐫𝐢𝐞𝐧𝐭 𝐢𝐧 𝐟𝐞𝐚𝐜𝐞𝐬 ×100 / 𝐍𝐮𝐭𝐫𝐢𝐞𝐧𝐭 𝐢𝐧 𝐟𝐞𝐞𝐝
DMD (g/Kg) = 𝐃𝐌 𝐢𝐧 𝐟𝐞𝐞𝐝 – 𝐃𝐌 𝐢𝐧 𝐟𝐞𝐚𝐜𝐞𝐬 ×1000 / 𝐃𝐫𝐲 𝐦𝐚𝐭𝐭𝐞𝐫 𝐢𝐧 𝐟𝐞𝐞𝐝
Where;
DMD = Dry matter digestibility.
DM = Dry matter.
OM (g/Kg) = 𝐎𝐌 𝐢𝐧 𝐟𝐞𝐞𝐝 – 𝐎𝐌 𝐢𝐧 𝐟𝐞𝐚𝐜𝐞𝐬 ×1000 / 𝐎𝐌 𝐢𝐧 𝐟𝐞𝐞𝐝
Where;
OMD = Organic matter digestibility.
OM = Organic matter matter.
DOMD (g/Kg) = 𝐎𝐌 𝐢𝐧 𝐟𝐞𝐞𝐝 – 𝐎𝐌 𝐢𝐧 𝐟𝐞𝐚𝐜𝐞𝐬 ×1000 / 𝐃𝐌 𝐢𝐧 𝐟𝐞𝐞𝐝
Where;
DOMD = Digestible organic matter content.
TDN = DCP + DCF + DNFE +DEE (2.25)
Where;
TDN = Total digestible nutrient.
DCP = Digestible crude proteins.
DCF = Digestible crude fibre.
DNFE = Digestible nitrogen-free extract.
DEE = Digestible ether extract (2.25).
*Note that Digestible organic matter content (DOMD) and Total digestible nutrient (TDN) are used to estimate energy values of feed resources
2. Difference method: This method is used to calculate the digestibility of two types of feeds fed concurrently. This implies that there are no interactions between the digestibility of the two feeds.
There should also be a priori knowledge of digestibility and the feacal dry matter output (DMO) of the basal diet.
Test feed DMD = 𝐓𝐞𝐬𝐭 𝐟𝐞𝐞𝐝 𝐃𝐌𝐈 – (𝐅𝐚𝐞𝐜𝐚𝐥 𝐃𝐌𝐎 – 𝐁𝐚𝐬𝐞 𝐟𝐞𝐞𝐝 𝐃𝐌𝐎) ×1000 / 𝐓𝐞𝐬𝐭 𝐟𝐞𝐞𝐝 𝐃𝐌𝐈
Where;
DMI = Dry Matter Intake
DMO = Dry Matter Output
3. Regression method: Use the regression method to estimate the digestibility of two feeds fed simultaneously. To do this, the animal will be served the two feeds of differing ratios.
Estimates of the digestibility of each of the ratios are determined. A regression model is made fitting the regression of test feed versus digestibility. This is then extrapolated to estimate the digestibility of the test feed.
In conclusion, there are numerous techniques for conducting in vivo digestibility trials depending on the number of feeds (singly or two different types fed concurrently) and the mode of collection of the digesta. In-vivo trials do not require elaborate facilities/equipment to be conducted.
There are four (4) techniques which can be employed for in-vivo trials. Parameters such as digestibility, dry matter digestibility, organic matter digestibility, and total digestible nutrients can be estimated from in-vivo trials.
