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.

The evaluation of n-alkane concentrations in herbage and faeces is the basis of a methodology that yields precise estimates of herbage intake. Established chemical analysis procedures for the determination of n-alkane concentrations in herbage and faecal samples involve an elaborate sequence of steps utilizing n-hexane as solvent for both the liquid-liquid extraction of n-alkanes from the sample and the solid-phase separation of n-alkanes in the extract. Composites of herbage and faecal samples from studies with sheep provided the experimental material used to evaluate a series of modifications which would simplify and reduce the workload involved in the chemical analysis. The results show that a less hazardous chemical, n-heptane, can replace n-hexane at all stages of the analytical procedure. They also show that evaporation of the sample extract and redissolving it prior to the separation of the n-alkanes, using a silica gel column, is unnecessary and that the volume of solvent used can be reduced. Procedures for saponification of samples prior to extraction can also be simplified as the process can be run overnight involving a slow build-up of temperature to 90 °C. The gain in precision from processing samples in duplicate was negligible and it would be more appropriate to invest extra efforts on an increased number of experimental animals. The results snowed that the workload and cost of using the n-alkane technique to estimate herbage intake can be reduced substantially.i M T R o n i i r n n M Results relative to the simplification of the various IN1KUUUL11U1N s t e p s i n v o l v e d j n t h e c h e m i c a i a n a i y s i s f or the The n-alkane technique has been shown to provide estimation of n-alkane concentrations in herbage and accurate and precise estimates of herbage intake faeces are reported here (Mayes et al. 1986;Vulich et al. 1991a). However, T h e a n a l y t i c a l proce dures used by Vulich et al. application of the technique, as currently developed, ( 1 9 9 1 a) f o r t h e determination of n-alkane concentrato large-scale studies of variation in intake among t i o n s i n herbage and faecal samples involved the individual animals would involve a considerable saponification of the material in order to convert workload. The resources required for (i) the prep-e s t e r s t 0 t h e corresponding alcohols and potassium aration and administration of doses of the marker n-s a l t s o f t h e a c i d s a n d t h u s facilitate extraction and alkane, (n) herbage and faecal sampling and (in) the p ur i fica tion of the hydrocarbon fraction. Samples processing and chemical analysis of individual w e r e subsequently subjected to liquid-liquid extracsamples, would be prohibitive for large-scale experi-t i o n ( L L E ) involving the addition of n-hexane (C 6 ) ments. Simplification of the technique in each of these a n d w a t e r . The higher polarity of alcohols and salts aspects, without sacrificing accuracy and precision, is ( re i at i ve to that of n-alkanes) allows both to be an important go...

1991). Effect of litter size on herbage intake at pasture by ewes and their progeny. AbstractThirty-four mature ewes (17 rearing twins and 17 rearing singles) were used to examine the effect of litter size on herbage intake at pasture by ewes over the course of lactation; intake by their lambs during weeks 13 to 15 of lactation was also evaluated. Daily organic matter intake (OMI) was estimated using the n-alkane technique. Ewes and lambs rotationally grazed 19 X 0-15-ha paddocks during the experimental period which extended from week 2 of lactation to weaning at week 15 of lactation. Sward conditions were maintained steady throughout with daily OM allowance per ewe varying between 4-6 and 5-7 kg and dry matter digestibility between 763 and 858 g/kg DM. Throughout lactation OMI and OMI per kg body weight were higher for twin-rearing ewes (P < 0-05) than for ewes rearing singles: 2-50 and 2-26 kg/day, and 38 and 32 g/kg per day, respectively. Intake reached a maximum on weeks 6 to 7 of lactation. From weeks 13 to 15 of lactation, OMI and OMI per kg body weight for single-and twin-reared lambs were 1 -09 and 1-14 kg/day, and 31 and 36 g/kg per day, respectively. The combined food intake per dam-offspring unit for weeks 13 to 14 of lactation for a ewe plus her single lamb was 2-8 kg OM per day compared with 4-3 kg OM per day for a ewe plus her two lambs. The repeatability of average weekly intake by ewes was 0-39 over the course of lactation and 0-40 for lambs over the 13 to 15 week period. Repeatability estimates for ewes increased slightly when data from weeks 3 to 7 and weeks 13 to 14 was analysed separately (0-42 and 0-53, respectively).

Milk consumption was estimated for crossbred suckled calves from birth to weaning during 2 years. Breed groups utilized were Aberdeen Angus (A) and Charolais (C) sires on Fl Angus-Hereford (and their reciprocals) dams in the 1st year and in the 2nd year, sires A and Nelore (Bos indicus) (N) were used on the same type of dam. The weigh-suckle-weigh technique was employed twice a day to estimate milk consumption on a weekly basis. Estimations were adjusted by least-squares for the effects of genetic group, week of estimation, and their interaction, with sex of calf and calf and cow weights in the week of estimation as covariables. Then a non-lineal regression equation of the form: y = b0Wb1e -b2b2W was fitted for each individual, where y = milk consumption and W = week of estimation. Curves for A and C were very close in their shape, but with a greater consumption (P < 0·01) for C. For the 2nd year, there were differences among A and N both in the shape of the curve and in consumption at the peak of lactation (P < 0·01). Differences in time to peak lactation were also found: for A calves, it was week 9, for C calves week 10 and for N calves week 3·8. The N group showed a sharper decline in persistency than the other groups, suggesting different patterns in milk consumption.

S U M M A R YHerbage intake estimation, using the n-alkane technique, requires the determination of the ratio of 'dosed' to 'natural' n-alkane concentrations in faeces. The present study was designed to evaluate the accuracy and precision of intake estimates based on the analysis of pooled samples of total daily faecal output and those derived from rectal grab samples.Wether lambs maintained in individual metabolism crates, offered fresh herbage ad libitum and dosed daily with 120 mg of n-dotriacontane (C 32 ), were used. Actual intake was recorded daily and samples of total faecal output were retained either for individual analysis or to produce 6-day composites by pooling representative amounts of material from each day's faecal output. Different pooling strategies were evaluated: a constant volume of fresh faecal material from each day or a constant weight (or constant volume) of dried and ground material from each day's faecal output. In addition, daily rectal grab samples, obtained at the same time each day, were pooled using a constant daily volume of fresh faeces. Herbage intake was estimated using the ratios of faecal concentrations of n-hentriacontane (C 31 ) or n-tritriacontane (C 33 ) relative to that for C 32 .Similar patterns of effects were observed for intake estimates derived from the C 31 : C 32 and C 33 :C 32 n-alkane ratios for the different faecal sample types. Comparisons based on intake estimates derived from the use of the C 33 : C 32 ratio showed that there were no significant differences between actual intake and estimates based either on the mean of daily samples or on the different composites of total daily faecal output. Intake estimates based on the analysis of composites of total daily faecal output were consistently lower (c. 3 %) than those based on the analysis of daily faecal samples. A difference of this magnitude is expected, based on the algebraic relationship between the mean of a ratio of two variables (e.g. faecal concentrations of C 33 and C 32 ) and the ratio of the corresponding means. Intake estimates derived from the use of rectal grab samples, taken 3 h after the daily dose was given, yielded a proportionate overestimation of actual intake of 006 (P < 010). No significant differences were detected in the precision of intake estimates derived either from individual daily samples, composites of total daily faecal output, or composites of rectal grab samples, although the latter yielded the lowest precision.It is concluded that faecal samples can be pooled on a gravimetric or a volumetric basis over several days with negligible loss in precision of intake estimates. Such pooling greatly reduces the workload and costs involved in using the n-alkane technique. Sampling and analytical errors associated with the technique were found to be very small, and the processing of faecal samples in duplicate would result in a negligible increase in the precision of intake estimates. The need for further evaluation of rectal grab sampling under grazing conditions is highlighted. I N T...