IntroductionIn 1918Edinintroduced chromic oxide forindirect determination of thc amount of faeces excreted in order to determine the digestibility of a given feed (foddcr). Since then this method has been widely used for that purpose. Thc reliability of the method depends on two factors: (1) the thorough mixing of thc chromic oxide with the ruminal contcnt and a consequent even dispcrsion in the facces, (2) a constant and total discharge of chromic oxide. Several expcriments from the recent years show that these two factors to a very high degree dcpcnd on the number of chromic oxide doses pcr day, the method of dosing, the number of samples taken, site of sample, and the timing of sampling (Davis et al., 1957; Kameoka et al., 1955; Smith & Reid, 1955; Troclscn, 1965).Provided the sampling is done over a period of 7-10 days, reasonably good estimates of chromic oxide contents in the faeces can be obtained, when thc chromic oxide capsules arc given twice a day. With this method several workers have found a 100% recovery rate of the chromic oxide in the faeces (93%-1020/0) dcpcnding on technique and feeding conditions (Claynton, 1962; Davis et al., 1957;Hardison & Reid, 1953; Kane et al., 1952; Smith & Reid, 1955, among others).From quantity of faeces discharged it is possible to calculate either the in ciro digestibility of organic matter (it1 cico-D0h.l) or the feed intake, depending on which of these factors are known.Due to the large random and biased variation in the recovery of chromic oxide often revealed in the cited reports, it is of great importance to test the methods on the prevailing circumstances on which future experiments will be conducted.The objectives of this investigation were to study errors and reliability of the use of chromic oxide capsules in research on feed intake by dairy cows with free access to silage as the main feed.
Material and MethodsEsperiinctit I . The purpose of thc experiment was to dcterniinc thc rccovcryratc of chromic oxidein the faeces based on the total amount of faeces excreted in order to estimate the true amount of facces voided. Four individually fed lactating dairy cows entered thccxpcrimcnt.Evperimetit 2. The purposc of this experiment was to estimate the silagc intake based on the indirectly dctcrmincd amount of Iacces (Cr20,) by using in rilro-DOM and bi viro-DOM, respectively, in the total ration. The experiment was divided into 8 ptriods using 4 lactating cows (Danish Friesian) in each period, making up a total of 32 cows.
It1 vitro-DOM was determined byTilley & Terry's (1963) method, which in 1966 was modified by Frederikscn.
Espcritnoitd feedIn both experiments the feed ration consisted of wilted clovcrgrass silage fed ad libitum, 12 kg fodder sugar beets, and conccntratcs fed according to the milk production. Thc quantity of concentrates was kept at a constant level during the expcrimcntal period.
Sotnplitig leclitiiqiicEach period consisted of a lO-day preliminary period and a 10-day sampling period. During the whole period each cow received orally chrom...
