Hay and pasture digestibility measured in the laboratory

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Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 4 Western Australia, Series 4

Volume 10

Number 2 1969 Article 10

1-1-1969

Hay and pasture digestibility measured in the laboratory Hay and pasture digestibility measured in the laboratory

D N. Tulloch

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Recommended Citation Recommended Citation

Tulloch, D N. (1969) "Hay and pasture digestibility measured in the laboratory," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 10: No. 2, Article 10.

Available at: https://library.dpird.wa.gov.au/journal_agriculture4/vol10/iss2/10

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HAY AND PASTURE DIGESTIBILITY MEASURED IN THE LABORATORY

By D. N . T U L L O C H , B.Sc, O f f i c e r - i n - C h a r g e , Dairy Laboratory

A recently developed " i n v i t r o " (laboratory) method of determining the digestibility of hay and pastures is giving good results in the Department of Agriculture's Dairy Laboratory.

Until recently, the only way of finding the digestibility of a feed was by using live animals. The hay or cut pasture was fed to several animals over a number of weeks, and during this time, all material consumed and excreted was weighed and analysed. This process is so involved and expensive that its use is confined to a few research projects. This meant that assess- ments of hay and pastures have been mainly based on yield, protein and fibre content. As digestibility of a feed is important, a rapid, cheaper method of its determination is of great value.

The importance of pasture digestibility was emphasised during the recent Aus- tralian Grasslands Conference where a number of agricultural scientists said that digestibility of all new pasture species should be determined before they are made available to farmers. This is, of course, in addition to all the other tests that are now required.

Tilly and Terry, of the Grasslands Research Institute, Hurley, U.K., published a paper in 1963 outlining the "In Vitro Method," showing it to be a simple prac- tical means of determining the digestibility of hay. This laboratory technique is carried out in test tubes under condi- tions designed to be as similar as possible to those to which the foodstuff is subjected when digested by a ruminant.

Method

A sample of the foodstuff to be tested is finely ground then mixed with diluted rumen fluid, which has been extracted

through a fistula from the rumen of a sheep. Test tubes containing a weighed quantity of hay and rumen fluid are then held at 39°C for 48 hours, under condi- tions which exclude all air. The function of rumen fluid is to dissolve the carbo- hydrate and cellulose.

Extracting rumen fluid from the rumen of a sheep

The rumen fluid is then removed and the undissolved material is treated with pepsin for a further 48 hours to dissolve digestible proteins. From the proportion of the sample dissolved, the digestibility is calculated.

The great advantage of the "in vitro"

method is the number of hay samples that can be tested at one time. Results from this method are comparable to those obtained from feeding trials with animals.

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Journal of Agriculture, Vol 10 No 2, 1969

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The only exception is with hay of very low digestibility and here the agreement between methods is not as good.

The Dairy Laboratory has been testing a limited number of hay and pasture samples by the "in vitro" method for several years.

One of the pasture experiments subjected to analysis was a trial conducted at the Denmark Research Station to investigate the effect of length of time between closing a paddock and cutting on the quantity and quality of hay. This gave the following results:—

Perioc

Paddock 6 8 10 12 14 Paddock

6 8 10 12 14

closed before cutting (weeks)

14—

13—

Dry matter yield (cwt. per

acre)

24 10 25-73 29-65 34 85 3 2 0 1 26 81 28 03 39-55 46 57 44 30

In vitro digestibility

(per cent.)

67 8 62 9 63 1 57 5 50 0 62-6 63-4 60-3 50-8 47-1

Digestible dry matter

(cwt. per acre)

16 3 16 2 18 7 20 0 16-0 16 8 17 8 23 9 23 7 20-9

The figures show how rapidly the digestibility of a pasture decreases as the period between closing and cutting in- creases. It can also be seen that after the paddocks had been closed for 10 weeks there was little or no increase in the yield of digestible dry matter in spite of a further increase in yield of dry matter between 10 and 12 weeks.

The results from the digestibility determinations will not only be used in the selection of pasture species but will give valuable information which will help to determine the best methods of pasture management. They will also help to

explain differences in animal production on various pasture systems.

The importance of digestibility in the assessment of pastures is fully appreciated by the Department of Agriculture and new laboratory equipment has been pur- chased which enables up to 80 samples to be tested each week.

Digestibility determinations are made on a range of hay and pasture samples from trials covering many investigations such as grazing management, hay quality and animal production. Results, when fully assessed, will have wide application to farming practice.

The feed sample is f i n e l y g r o u n d and m i x e d w i t h d i l u t e d r u m e n f l u i d , t h e n held f o r 48 hours in a test t u b e

63

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