Abstract
The objective of the study was to evaluate the use of n-alkanes to estimate DM intake and digestibility by beef cattle. Six steers were blocked (3 blocks, 2 animals/block) according to the body weight (279±19 kg) and randomly allotted within blocks to two diets (3 steers/diet). A second trial was conducted with the same animals (321±18 kg) after 36 days (d), using a switch back design. The diets consisted of two types of chopped sun-cured hay, alfalfa (Medicago sativa L) hay, or fescue (Festuca arundinacea Schreb) and alfalfa mixture, which were fed in equal amounts to steers. Animals were dosed with C32 and C36 alkanes, employing an intra-ruminal controlled-release device at the beginning of each trial. Hay intake per animal was measured from d 6 to 12 and sub samples were taken for chemical analysis. Rectal samples of feces were taken from each animal once/daily from d 8 to 14, freeze dried, and ground prior to alkane analysis. Alkanes were extracted from ground hay and feces. Feed intake was calculated from the dose rate of C32 alkane and, the herbage and fecal concentrations of adjacent odd (C33 or C31) and even (C32) chain length alkanes. Crude Protein, NDF, ADF, ash concentrations and In vitro dry matter digestibility (IVDMD) were 17.7, 42.2, 28.4, 7.9 and 71.7 for alfalfa, and 12.4, 56.5, 30.4, 6.9 and 69.1% for fescue/alfalfa mixture, respectively. For both diets, intake estimated from C33:C32 ratio was not different from the measured intake, but intake estimated from C31:C32 ratio was lower (p<0.05), than the measured intake for both diets. The average estimated forage intake from C33:C32 ratio was 4.86 and 0.69% below than the measured intake for alfalfa and, fescue/alfalfa mixed diets, respectively. The respective estimates with C31:C32 ratio were 9.59 and 11.33% below than the measured intake. According to these results, alkane C33:C32 ratio is better than alkane C31:C32 ratio for the estimation of intake by beef steers. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 11 : 1564-1568)
Highlights
Use of indigestible plant components as internal markers for estimating intake and digestibility in grazing ruminants gives potential advantages over external markers or other methods
The compounds, n-alkanes are saturated aliphatic hydrocarbons of plant cuticular wax, which have been used as internal markers to estimate the feed intake of grazing ruminants (Dove and Mayes, 1991; Mayes et al, 1994) and the digestibility of herbage mixtures (Dove, 1992)
These synthetic alkanes can be administered to grazing ruminants in different ways and one such method is the intra-ruminal controlled release devices (CRD), which release alkanes in the rumen continuously (Dove et al, 1991)
Summary
Use of indigestible plant components as internal markers for estimating intake and digestibility in grazing ruminants gives potential advantages over external markers or other methods. The compounds, n-alkanes are saturated aliphatic hydrocarbons of plant cuticular wax, which have been used as internal markers to estimate the feed intake of grazing ruminants (Dove and Mayes, 1991; Mayes et al, 1994) and the digestibility of herbage mixtures (Dove, 1992). These n-alkanes are predominantly odd-chain in the range of C25 to C35 and substantially indigestible. These synthetic alkanes can be administered to grazing ruminants in different ways and one such method is the intra-ruminal controlled release devices (CRD), which release alkanes in the rumen continuously (Dove et al, 1991)
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