Use of n-alkanes for the estimation of herbage intake in sheep: accuracy and precision of the estimates

Abstract

S U M M A R YTwo experiments at Belclare, Co. Galway, in late autumn 1988, evaluated the use of herbage and dosed n-alkanes for estimating herbage intake by sheep. The first experiment examined faecal recoveries of dosed and herbage n-alkanes. The second experiment assessed the accuracy and precision of herbage intake estimates obtained using the n-alkane technique, and tested the effect of supplying n-alkanes to animals either in gelatine-capsules (containing different ratios of nalkane:cellulose fibre) or in pellets prepared from shredded paper onto which the n-alkanes had been adsorbed. Individually penned wether lambs were offered freshly cut herbage ad libitum (+ 10%) and actual dry matter intake was recorded daily. Intake was estimated using the C 31 :C 32 and C 33 :C 32 (natural:dosed) n-alkane ratios.There was no significant effect of n-alkane chain length on faecal recovery rate for either the dosed n-alkanes (C 32 and C 36 ), the herbage odd-chained n-alkanes (C 29 , C 31 , C 33 and C 36 ) or those used for the estimation of herbage intake (C 31 , C 32 and C 33 ). The accuracy and precision of the n-alkane technique for estimating herbage intake were unaffected by whether the dosed n-alkane was supplied in capsules or pellets or by the n-alkane:cellulose fibre ratio in the capsules. The bias in the estimated intake was -8 % ( + 1 • 1 %) and + 3 % (± 1 -2 %) for estimates based on C 31 : C 32 and C 33 : C 32 ratios, respectively. The estimates based on C 3l :C 32 and C 33 :C 32 exhibited similar precision in the estimation of herbage intake, with a R.S.D. of 6% in actual intake when adjusted for variation in estimated intake and a correlation of +0-92 between actual and estimated herbage intake. The C.v. for actual herbage intake was 17%. The repeatability of actual dry matter intake over three consecutive 6-day periods was 0-54 while those of estimated intake were 0-57 and 0-60 for estimates based on C 31 :C 32 and C 33 :C 32 , respectively. The results show that the n-alkane technique can provide an accurate and precise estimate of herbage intake.

Estimation of pasture herbage intake by beef cattle based on n-alkanes as markers

“…04) by about 20% lower than that obtained on the basis of pooled samples. This finding is not consistent with the results reported by Vulich et al [9] who showed that there were no statistically significant differences in estimations of DM intake based on individual or pooled samples.…”

“…The results reported by other authors recommend the use of various pairs of alkanes for the estimation of DM intake by cows. For instance, Smit et al [1] as well as Vulich et al [9] obtained results of high precision using alkanes C 33 /C 32 , while Estermann et al [7] alkanes C 31 /C 32 . Reeves et al [2] recommend that the estimation of DM intake from a pasture dominated by Pennisetum clandestinum should be based on a ratio of alkanes C 33 /C 32 .…”

“…Similarly, Smit et al [1] as well as Reeves et al [2] stated that the n-alkane method is the best for determining the pasture dry matter intake. Vulich et al [9] described its repeatability for the estimation of feed consumption by animals as high, while Estermann et al [7] reported that optimum results were obtained when the samples were collected in the morning hours.…”

The accuracy of intake estimation based on the use of alkane controlled-release capsules and faeces grab sampling in cows

“…Difficulties arise from the labour requirement to hand-manufacture either paper pellets with adhered alkane or gelatine capsules, the correct frequency of dosing and the optimal timing of grab faecal sampling in relation to diurnal variation in alkane excretion [20]. Despite these setbacks results in sheep and cattle appear very promising [20,24,25,29].…”

N-alkanes to estimate voluntary forage intake of cattle using controlled-release capsules

“…Similarly, Dove et al (1989) fed sheep with n-alkanes (C 28 and C 32 ) in the form of gelatin capsules of powder cellulose, previously added with a known amount of n-alkane dissolved with n-hexane or n-heptane, to estimate forage intake. Vulich et al (1991) developed a different method that consisted of mixing n-alkanes with solvents and powder cellulose, resulting in a homogenous suspension that, after being evaporated and dried, was inserted into gelatin capsules. Marais et al (1996) developed another technique in which particles of Pennisetum clandestinum (Hochst.)…”