Calculations

Question 1

Calculate Digestibility

Answer 1

(Feed - Faeces) / Feed x 100

Question 2

Dry Matter (g/kg)

Answer 2

Initial Sample Weight - Dry Sample Weight x 1000

Question 3

Metabolisable Energy

Answer 3

Digestible Energy - Urine Energy - Gas Energy

Question 4

Net Energy

Answer 4

NE for Maintenance + NE for Production

Question 5

Net Energy for Maintenance

Answer 5

Fasting Metabolism + Fasting Metabolic Rate

Question 6

Apparent Digestible Energy

Answer 6

Gross Energy Consumed - Gross Energy in Faeces x 1000 / Gross Energy Consumed

Question 7

Mobile Bag Digestibility

Answer 7

(Feed in Bag at Start - Feed in Bag at End) / Feed in Bag at Start

Question 8

Metabolic Rate of Animals

Answer 8

Kleiber’s Law = KG^0.75

Question 9

‘K’ - the efficiency of ME usage

Answer 9

K = NE / ME

Question 10

Atwater Factors

Answer 10

• 3.5kcal/g of Protein
• 8.5kcal/g of Fat
  -3.5kcal/g of Carbs

Question 11

Nitrogen Free Extract

Answer 11

100 - (%Water + %Crude Protein + Ether Extract + %Crude Protein + %Ash)

Or

1000 - (Moisture + Ash + Protein + Fibre + Ether Extract)

Question 12

Weende System - Water/Moisture Content

Answer 12

Dry feed sample in hot air oven at 100 degrees Celsius.

DM% = Weight After Drying / Weight Before Drying x 100

Moisture% = 100 - DM%

Question 13

Weende System - Ash Content

Answer 13

Place sample in a furnace at 450 degrees Celsius overnight until a white-grey ash remains.

Ash% = (Weight of Combusted Feed and Basin - Weight of Empty Basin) x1000 / Weight of Feed

Question 14

Weende System - Crude Protein Content

Answer 14

Kjeldahl Method!

Calculate the nitrogen content:

Nitrogen% = (Vol of Dilute Sulphuric Acid x 0.14) / Weight of Sample

Then use that to calculate CP content:

CP% = Nitrogen% x 6.25

Question 15

Weende System - Fat Content

Answer 15

Cover feed sample with acetone, leave for 5mins and pour off. Leave in drying oven for 5mins.

Fat (g/kg DM) = Actual Weight of Sample - (Weight of Flask After Drying - Weight of Flask) / Actual Weight of Sample x 1000

Question 16

Weende System - Fibre Content

Answer 16

Because fibre is composed of cellulose, hemicellulose and lignin, two boiling processes can be used to stimulate the pH conditions of the digestive tract (Soxhlet Method)