An evaluation of n-alkanes as markers to estimate dry matter intake, diet selection and solid digesta passage rates in ruminants

• Main Author: Magadlela, Andrew Mtutuzeli
• Published: University of Edinburgh 2001
• Subjects: 636.085
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657187

Study 1 (exp 1, 2, and 3) assessed the use of alkanes for estimating diet composition and intake in lambs. In exp 1, 36 lambs at 30% and 45% of projected mature sizes were used in a factorial design with 2 breeds (Suffolk and Scottish Blackface), two sexes (male and female) and three feed treatments [pelleted lucerne (<i>Medicago sativa)</i> or pelleted ryegrass (<i>Lolium </i>spp) alone or both as a choice] to compare alkane-derived estimates of dry matter intake (DMI) and selected diet with direct measurements. In exp 2, to assess diurnal variation in n-alkane concentration in the gut, 6 restricted and 6 <i>ad libitum </i>fed lambs at 45% mature size were used in a split-plot design to compare the ratios of the amount of dotriacontane (C₃₂) to tritriacontane (C₃₃) in the faeces collected at 4 hourly intervals over a 24 hour period. In exp 3, to evaluate the efficacy of dosing once-daily (cf. twice-daily) with C₃₂, 6 once-daily and 6 twice-daily dosed lambs were used in a split-plot design to compare faecal alkane ratios of C₃₃ to C₃₂. Exp 1 suggested general agreement between measured quantities and those estimated using the alkane technique However, at 30% mature size, for the lambs fed on grass only, dry matter intake was slightly overestimated and for those fed on lucerne and grass as a choice, dry matter intake of lucerne was underestimated. Exp 2 indicated that the ratio of the concentration of C₃₃:C₃₂ in the faeces was not affected by sampling time and thus no diurnal variation irrespective of whether the lambs were restricted or <i>ad libitum</i> fed. Experiment 3 suggested no difference in the ratios of the concentrations of C₃₃:C₃₂ between the two dosing strategies until the fifth day of dosing. Study II used the alkane pair of C₃₆ and C₃₅ to compare the voluntary dry matter intake of <i>Brachiaria decumbens</i> by 8 dry cows, averaging 301 kg liveweight and 8 lactating Criollo cows averaging 320 kg liveweight during the wet season and 8 lactating cows averaging 300 kg liveweight and 7 dry cows, averaging 289 kg liveweight during the dry season of Bolivia. Results suggested that this alkane pair can be used to estimate the dry matter of intake of tropical forages, but if the concentrations of C₃₅ are very low the accuracy of the estimate may be compromised.