Estimates Of Herbage Intake Research Articles

Prediction of bite number and herbage intake by an accelerometer-based system in dairy sheep exposed to different forages during short-term grazing tests

The accurate estimation of herbage intake is a key to adequately feed grazing ruminants. Ten dairy Sarda sheep fitted with a halter equipped with an accelerometer (BEHARUM device) were allowed to graze micro-swards of Italian ryegrass (Lolium multiflorum L.), alfalfa (Medicago sativa L.), oat (Avena sativa L.), chicory (Cichorium intibus L.) and a mixture (Italian ryegrass and alfalfa) for six minutes. Accelerometer data and video recordings of behaviour were collected simultaneously. The raw acceleration data were processed to calculate 15 variables: sum, mean, variance and inverse coefficient of variation (ICV, mean/standard deviation) for the X, Y and Z axes and the resultant. A database was created that included the acceleration variables and herbage intake (FMI, DMI, g), intake rate (FMIR, DMIR, g/minute), bite mass (FMBM, DMBM, g) either on fresh (FM) or dry matter basis (DM) and the logarithm of number of bites (LB) and bite rate (LBR) measured during the tests. Partial least square regression analysis (PLSR) was used to verify if acceleration variables could be used as predictors of behavioural traits. The precision and accuracy of PLSR were evaluated implementing the Model Evaluation System, in which predicted values were regressed against observed ones, based on r2 and Dent & Blackie test. The PLSR showed an overall good accuracy (Dent & Blackie test P = ns) and was proven precise for the estimation of LB (r2 = 0.87), LBR (r2 = 0.86), DMI and DMIR (r2 = 0.71). To conclude, BEHARUM can accurately estimate with high to moderate precision number of bites and herbage intake of sheep short term grazing Mediterranean forages.

Estimation of herbage intake and digestibility of grazing sheep in Zhenglan Banner of Inner Mongolia by using n-alkanes.

To reveal the seasonal dynamics of herbage intake, diet composition and digestibility and clarify the relationship of those with herbage nutrient and botanical composition of grazing sheep in Zhenglan Banner of Inner Mongolia, the n-alkane technique was used to test in sheep grazed during June, August and December. The results showed that the sheep mainly ate Fringed sagebrush, Stipa krylovii and Carex in proportions of 33.5, 17.9 and 21.2%, respectively, in spring. In summer, the sheep consumed cleistogenes, Potentilla tanacetifolia, Thyme, etc; the intake of Fringed sagebrush, Carex and Stipa declined. In winter, Fringed sagebrush accounted for 50.1% of herbage intake, and the intakes of Cleistogenes and Stipa krylovii increased to 15.3 and 18.4%, respectively. Herbage intake by the sheep in spring was 1.8 kg DM/d, and digestibility was 71.4%. Herbage intake and digestibility decreased slightly to 1.7 kg DM/d and 68.4% during the summer, respectively and decreased significantly to 1.2 kg DM/d and 36.4% in winter. There were significant correlations between diet composition and CP content in winter, diet composition and botanical composition in summer. A highly positive correlation between herbage intake and digestibility was observed in grazing sheep.

Comparison of methods for estimating herbage intake in grazing dairy cows

Summary Estimation of herbage intake is a challenge both under practical and experimental conditions. The aim of this study was to estimate herbage intake with different methods for cows grazing 7 h daily on either spring or autumn pastures. In order to generate variation between cows, the 20 cows per season were either allocated to low or high stocking rate. At low stocking rate, there were 6.7 and 3.5 cows per hectare during spring and autumn, respectively, and at high stocking rate, there were 8.8 and 4.6 cows per hectare during spring and autumn, respectively. The experiment lasted 16 days in each season, and the herbage intake was estimated twice during each season. Cows were on pasture from 8:00 until 15:00, and were subsequently housed inside and fed a mixed ration (MR) based on maize silage ad libitum . Herbage intake was estimated with nine different methods: (1) animal performance (2) intake capacity, (3) content of 13 C in faeces and diet, (4) 13 C in faeces and diet, and with assumption of 13 C discrimination in the digestive tract, (5) 13 C in faeces and diet, with assumption of 13 C discrimination and in combination with in vitro organic matter digestibility (IVOM), (6) simultaneous use of two internal markers (ingestible neutral detergent fibre (INDF) and acid detergent lignin (ADL)), (7) titanium oxide in combination with IVOM, (8) titanium oxide in combination with INDF and (9) titanium oxide in combination with ADL. Furthermore, grazing time of the individual cows was recorded. The estimated average herbage dry matter intake (DMI) varied from 2.2 kg for the method using the INDF:ADL ratio to 7.6 for the methods using 13 C and intake capacity. There was a low correlation between the different methods. Dry matter intake of herbage was not affected by stocking rate except for the method using titanium oxide and ADL as markers. Milk yield was not affected by stocking rate either. It was concluded that methods based on animal performance, 13 C including discrimination factor or in combination with IVOM as well as methods based on titanium oxide gave similar estimates of the average herbage DMI intake during grazing in systems with indoor concentrate and forage feeding during night.

Modelling preference and diet selection patterns by grazing ruminants: a development in a mechanistic model of a grazing dairy cow, MINDY

The work presented here represents additions to the mechanistic and dynamic model of a grazing dairy cow (MINDY). The additions include a module representing preference and selection, based on two theories, namely, post-ingestive feedback and discomfort. The model was evaluated by assessing its ability to simulate patterns of preference and selection in response to a variety of feeding management. The improvements detailed here enable a realistic simulation of patterns of food selection by grazing ruminants, based on a range of feeding situations from different studies with cattle and sheep. These simulations indicate that the concepts encoded in MINDY capture several of the underlying biological mechanisms that drive preferences and selective behaviour. Thus, simulations using MINDY allow prediction of daily and diurnal patterns of selection based on preference, derived from some post-ingestive feedbacks and total discomfort. Estimates of herbage intake and parallel measurements of ingestive behaviour, rumen function and metabolism in grazing ruminants pose experimental and technical difficulties, and matching these processes to animal preference and selective behaviour is a greater challenge. As a consequence, advances in knowledge of foraging behaviour and dietary choice are slow and costly. On completion of more thorough testing, MINDY can be used as a tool for exploratory mechanistic research, to design and organise experimental programs to address a range of factors that control intake and its ecology, helping advance knowledge faster and at a low cost.

A model of diurnal grazing patterns and herbage intake of a dairy cow, MINDY: Model description

Estimates of herbage intake and parallel measurements of ingestive and digestive behaviors of grazing ruminants pose considerable experimental and technical difficulties, owing to dynamic interactions between the plant, the rumen and the animal. As a consequence, advances in the area have been slow and costly. Model simulations that capture such interactions are critical for research and management decisions involving the grazing process. This work describes MINDY, a mathematical, mechanistic and dynamic simulation model of the diurnal grazing pattern of a dairy cow. MINDY is based on a cluster of three models: (1) Molly (Baldwin, 1995), a model of ruminant digestion and metabolism; (2) a model representing feed consumption as a function of diurnal fluctuations in the internal state of the animal; and (3) a sward structure, herbage quality and grazing behavior model. The objective of the work was to describe the diurnal grazing pattern, including ingestive actions and rumination behaviors, herbage intake, and nutrient supply to the animal in response to the animal's internal state and grazing environment. The model was coded in ACSL and simulations were conducted using ACSLXtreme. In addition to dietary nutrient composition required by Molly, MINDY requires sward surface height and mass, and grazing area offered to the cow. Key sub-model parameters were identified by sensitivity analyses and parameterized using two data sets from mid-lactation Friesian and late lactation Holstein dairy cows breeds under set stock conditions. The parameterized model predicted realistic estimates of ingestive behavior for different cow genotypes managed under set stocking and rotational grazing. It also predicted a realistic number of steps taken while eating and searching and sward defoliation dynamics as well as diurnal fluctuations of digestion and metabolism. Additional evaluations are required and further data may be needed to better define some parameters, but the model offers promise as an heuristic tool for feed intake and grazing process research and as an informative tool for grazing and cow management decisions.

Estimation of herbage intake of Angus heifers from growth rate and milk production selection lines

Herbage intake was measured using n-alkanes (at age 10 and 13 months) and the pre- and post-grazing technique (at age 12 and 14 months) in 80 Angus heifers selected for high (Hi-Gr) or low (Lo-Gr) growth rate or high (Hi-Milk) or low (Lo-Milk) milk production. Average liveweight and estimated herbage intake at 10 months were 240.2±0.4 kg and 3.47±0.1 kg dry matter (DM)/head per day respectively. The respective values at 13 months of age were 287.2±1.9 kg and 6.50±0.36 kg DM/head per day. No differences in estimated herbage intake among the genetic lines were detected using n-alkanes at 10 or 13 months of age. Average liveweight at 12 months of age was 247.1±0.7 kg and mean estimated intakes were 4.86±0.26, 4.17±0.26, 4.37±0.26 and 3.00±0.26 kg DM/head per day for the Hi-Gr, Lo-Gr, Hi-Milk and Lo-Milk lines, respectively. The Lo-Milk line had lower (P<0.05) estimated intake than the other three lines. At 14 months of age, average liveweight was 272.5±0.6 kg and estimated intakes were 6.99±0.18, 6.52 kg±0.18, 6.71±0.18 and 7.28±0.19 kg DM/head per day for the Hi-Gr, Lo-Gr, Hi-Milk or Lo-Milk lines, respectively. Lo-Milk heifers had higher (P<0.05) intakes than heifers from the Lo-Gr and Hi-Milk lines. No statistical difference in intake between the Lo-Milk and the Hi-Gr lines was detected. In general, the Hi-Gr heifers outperformed the heifers from other lines.

The use of n–alkanes and other plant–wax compounds as markers for studying the feeding and nutrition of large mammalian herbivores

The use of n–alkanes and other plant–wax compounds as markers for studying the feeding and nutrition of large mammalian herbivores

Seasonal patterns of diet composition, herbage intake and digestibility identify limitations to performance of weaner sheep grazing native pasture in the Falkland Islands

AbstractThe botanical composition, intake and digestibility of the diet consumed by 1‐year‐old weaner sheep grazing a native white grass plant community in the Falkland Islands was measured in five periods between June 1998 and March 1999. Five different sheep were used in each period. Two methods were used for estimating the botanical composition of the diet: plant cuticle patterns in the faeces of the sheep and the patterns of concentrations of n‐alkanes in the faeces of sheep. These methods were used to predict the concentrations of C32‐ and C33‐alkanes in the herbage to allow the estimation of herbage intake and digestibility using the n‐alkane technique. It was concluded that the n‐alkane technique gave more accurate estimates of diet composition based on the comparison with estimates of nutrient intake derived from liveweight gains of sheep. The dominant pasture species, Cortaderia pilosa, was the predominant species consumed during the cooler periods of the year. In the summer, when the highest liveweight gains of sheep occur, the proportion of fine grass species, including Poa spp., Festuca magellanica and Agrostis capillaris, and herbs and sedges in the diet was highest. Herbage intake was the highest during the summer periods when digestibility was also at its peak. Estimated nutritional deficiencies of metabolizable energy, crude protein, phosphorus and vitamin D3 that limit the growth and development of weaner sheep were evident for up to 9 months of the year. Targeted supplementation regimes that counter specific nutrient deficiencies could be developed on the basis of these results to address critical periods in the growth of young sheep.

Evaluation of the dry matter intake predictions of the Cornell Net Carbohydrate and Protein System with Holstein and dual-purpose lactating cattle in the tropics

Data from three separate experiments were used to evaluate the dry matter intake (DMI) predictions of version 5.0 of the Cornell Net Carbohydrate and Protein System (CNCPS). Experiment 1 was conducted with 12 lactating Holstein cows confined in individual stalls, receiving known amounts of supplements and fresh, chopped Panicum maximum cv Tobiatá grass. Experiments 2 and 3 were conducted with 12 and 13 crossbreed dual-purpose cows rotationally grazing Cynodon nlemfuensis cv Alicia and P. maximum cv Tobiatá grass, respectively, with appropriate supplementation. Pasture intake in the grazing experiments was estimated for an 8-day period using the alkane technique. Model-predicted DMI based on measured feed analyses for the group of animals on Experiment 1 was very close to the observed values, with a mean bias of −0.19 kg DM per day, suggesting that the adjustment of DMI used by the CNCPS model in tropical conditions is accurate for confined lactating animals. The intake predictions by the CNCPS model for the grazing dual-purpose lactating cows were not as accurate. The CNCPS model underpredicted DMI in Experiment 2, and different degrees of accuracy and bias were evident in Experiment 3. For the three experiments, the slope of the regression between observed and predicted DMI was not different from unity, but the intercept was significantly different ( P<0.05) from zero, suggesting a mean bias in the prediction. It should be recognized that accurate intake data on grazing animals is difficult to obtain and errors in the estimation of herbage intake using the alkane method could be contributing to the bias in the predictions by the CNCPS model.

Accuracy of estimates of herbage intake of lactating cows using alkanes: comparison of two types of capsules

A feeding study with fresh forage was completed to evaluate the reliability of the alkane technique for estimating voluntary herbage intake in tropical conditions and compare the accuracy of herbage dry matter intake (DMI) estimates from two types of capsules used to deliver the even chain length alkanes to the rumen. Twelve lactating Holstein cows were housed in individual stalls and separately fed chopped fresh Panicum maximum (cv. Tobiatá) grass twice daily. From days 1 to 15 of the experimental period, six cows were dosed twice daily with a gelatin capsule containing synthetic C 32 alkane. The remaining cows were dosed with a controlled release capsule (CRC) on day 1. Individual intakes were measured daily and herbage intakes were estimated for 5 days using the alkane technique. Herbage intake differed between treatment groups, 6.3 and 8.3 kg DM per day for the gelatin and the CRC group, respectively. A 7-day equilibrium period was sufficient for the marker to reach a steady concentration in the feces for both delivery methods. Regardless of the delivery system used to administer the synthetic marker, estimated herbage intake using the C 33:C 32 alkane pair did not differ from the mean measured intake (mean bias=0.55 kg DM per day for each treatment). No obvious trend for increased recovery with alkane chain length was observed. Concentrations of alkanes in fecal samples collected throughout the day, and the resulting intake predictions, varied diurnally with the highest variation observed with the C 31:C 32 alkane pair. When the C 33:C 32 ratio was used, the least accurate herbage DMI estimate was obtained from the 4.30 h samples, for both delivery methods. The alkane technique has the potential to predict herbage intake of cows in the tropics. Although there were some differences in DMI estimates, the two types of capsules used for the alkane administration performed similarly.

Factors influencing the release rate of alkanes from an intra-ruminal, controlled-release device, and the resultant accuracy of intake estimation in sheep

Two experiments were conducted to evaluate factors influencing the release rate of octacosane (C28) and dotriacontane (C32) synthetic alkanes from controlled-release devices (CRD) inserted into the rumen of sheep, and the resultant accuracy of alkane-based estimates of herbage intake. In the first experiment, estimates of the rate of release of alkanes from CRD suspended in the rumen of 7 rumen-fistulated ewes were obtained by directly measuring the rate of CRD plunger travel. In the second experiment, CRD were administered orally to 24 castrate male sheep to evaluate the effects of level of feeding (1200 v. 600 g DM/day), frequency of feeding (continuous v. once-daily), and number of CRD inserted (1 v. 2) on temporal trends in faecal alkane concentrations and ratios and on the accuracy of estimation of intake. In both experiments, animals were also dosed orally, once daily with paper pellets containing 56 mg hexatriacontane (C36). In Expt 1, linear alkane release from the CRD commenced after a lag period of 2-3 days, at mean rates of 40.1 mg/day (C28) and 41.7 mg/day (C32), close to the desired rates of 40 mg/day. There was no evidence of curvilinearity, and differences in release rate between sheep were small (CV 4.1%). Alkanes attributable to the CRD appeared in faeces after 2-3 days and reached plateau concentrations by 6-7 days. Data are presented to indicate that the release rate was not affected by the removal of CRD from the rumen for measurement, and that the release rates in fistulated (Expt 1) and intact sheep (Expt 2) were similar. In Expt 2, there was no effect of level of feeding on CRD release rates and faecal alkane concentrations were consistent with the differences in faecal output caused by feeding level. As a result, the accuracy with which known intakes were estimated was unaffected by level of feeding. Similarly, there were no effects of feeding frequency on the accuracy of estimated intake, implying that in this study, feeding frequency had no effect on CRD release rates. The administration of 2 CRD to half the animals in this experiment increased faecal concentrations of C28 and C32 and the synthetic : herbage alkane ratios associated with these alkanes [e.g. faecal C32 : tritriacontane (C33)] but these changes were not significantly different from those expected from the release rates estimated in Expt 1. As a result, the accuracy with which known intakes were estimated was not influenced by the number of CRD administered. In both experiments, once-daily dosing with C36 alkane resulted in a more rapid rise in faecal C36 concentrations and faecal C36 : pentatriacontane (C35) ratios to maximal levels (3-4 days), compared with alkanes derived from the CRD (6-7 days), but thereafter, faecal C36 concentrations were much more variable, especially in the fistulated sheep. As a result, intake estimates based on the C36 : C35 alkane pair significantly over-estimated known intakes by 13% (Expt 1) and 8% (Expt 2). Data are presented to indicate that C36 alkane functioned satisfactorily as a faecal output marker and, with C32 : C33 estimates of intake, provided accurate estimates of herbage digestibility. The results indicate that intra-ruminal controlled-release devices provide a satisfactory means of delivering an accurate, daily dose of alkanes for the estimation of herbage intake, faecal output, and digestibility in sheep.

The nutrition of grazing ewes during pregnancy and lactation: a comparison of alkane-based and chromium/in vitro-based estimates of herbage intake

The n-alkane and chromium/in vitro procedures for estimating herbage intake were compared in grazing ewes during late pregnancy, early lactation, and mid-lactation. To ensure differences in herbage intake, the ewes were grazed in 4 plots of phalaris-dominant pasture at 2 levels of stocking: 17.1 ewes/ha and 30.8 ewes/ha. To investigate whether either procedure for estimating herbage intake was influenced by supplement consumption, half of the ewes at each stocking level received 500 g/day air-dry of a pelletted supplement (1 : 1 milled oat grain : sunflower meal). Supplement intakes were estimated using tritiated gypsum as a marker. During intake measurement periods, ewes were dosed twice daily with both alkane capsules and capsules containing chromium sesquioxide. For the last 6 days of the 12-day dosing period, rectal faecal samples were taken twice daily, immediately before the dosing. Over these same periods, wether sheep fitted with faecal collection harnesses were similarly dosed and sampled, and their total faecal output collected to establish the faecal recovery of chromium and the alkanes. Herbage intakes were estimated using the C27/C28, C29/C28, C31/C32, and C33/C32 alkane pairs. Estimates of intake based on the shorter alkane pairs were lower than those estimated with the C33/C32 alkane pair, by amounts which differed between the periods. Evidence is presented that estimates based on the last pair of alkanes (C33/C32) are the most accurate and are also more accurate than those based on the chromium/in vitro procedure. The relationship between these 2 methods for estimating intake was different in mid-pregnancy compared with either stage of lactation. The consumption of supplement did not interfere with any of the methods for estimating herbage intake. Estimates of faecal output based on the use of chromium, C28 alkane, or C32 as an external marker were statistically identical, indicating that the difference between the 2 methods for estimating herbage intake was not related to a failure to accommodate the incomplete recovery of any of the markers used or to the failure of rectal grab samples to be representative of total faeces. Our results indicate that herbage collected by oesophageally fistulated (OF) sheep was representative of that grazed by the ewes and could thus be used to provide the herbage alkane data needed to estimate herbage intake by the alkane method. However, the in vitro digestibility values obtained from the OF samples did not represent the digestibilities actually occurring in vivo. This was the main cause of the observed difference between the 2 methods for estimating intake. Possible reasons for the differences between the in vitro and in vivo estimates of digestibility are discussed.

Comparison of n-alkanes or chromium oxide methods for estimation of herbage intake by sheep

Abstract Herbage intake (HI) was estimated with two procedures: (a) with the n -alkanes method (HI al ), which combines the use of odd-chain n -alkanes, naturally occurring in plants, and dosed even-chain n -alkanes, as internal and external markers, respectively; (b) with the ratio between faecal excretion, estimated with chromium sesquioxide (Cr 2 O 3 ), and the herbage indigestibility, estimated in vitro (HI Cr ). The two techniques were compared in an indoor experiment and under grazing conditions. In the indoor trial, 12 wethers were fed 40 g dry matter (DM) kg −1 BW 0.75 day −1 of one of the following diets: herbage only (diet H); herbage plus maize (diet M; 26% of DM intake); herbage plus maize plus maize gluten meal (diet MG; 13% of DM intake each). Each wether was dosed once a day for 12 days with the external indicators impregnated on paper and inserted in gelatine capsules: n -dotriacontane, C 32 , 600 mg day −1 ; Cr 2 O 3 , 500 mg day −1 . In the second experiment, six adult, lactating ewes grazing the pasture used for the indoor trial were divided into groups of three receiving 700 g day −1 of two different supplements: maize (diet M) or a 50:50 mix of maize and maize gluten meal (diet MG). The external indicators (Cr 2 O 3 and C 32 ) were administered for 8 consecutive days. The trial was repeated four times with the same procedure between 10th and the 40th day after lambing. Recoveries of Cr 2 O 3 , C 32 and herbage n -alkanes ( n -hentriacontane, C 31 , and n -tritriacontane, C 33 ) were incomplete, with lower values for the natural n -alkanes than the dosed n -alkane (Cr 2 O 3 , 94.9 ± 5.5%; C 31 , 86.7 ± 8.7%; C 32 , 89.6 ± 8.5%; C 33 , 85.1 ± 9.9%). Therefore, HI Cr gave an overestimate of the true herbage intake of 5.5% and HI al an underestimate of 3.0%, with a significant discrepancy between methods (803 vs. 733 g organic matter (OM) day −1 ), not affected by diet. In the grazing trial, HI Cr was higher than HI al , but the difference between methods (1503 vs. 1273 g OM day −1 ) was higher than that obtained in the indoor experiment and was influenced by diet (380 g OM day −1 vs. 81 g OM day −1 with diet M and diet MG, respectively). A possible explanation of the different results obtained indoor or at pasture is discussed.

Modification of the analytical procedures for the determination of herbage and faecal n-alkanes used in the estimation of herbage intake

SUMMARYThe 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.

Faecal sampling for the estimation of herbage intake using n-alkanes: evaluation of sample pooling and the use of rectal grab samples

SUMMARYHerbage 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 libitumand dosed daily with 120 mg of n-dotriacontane (C32), 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 (C31) or n-tritriacontane (C33) relative to that for C32.Similar patterns of effects were observed for intake estimates derived from the C31: C32 and C33:C32 n-alkane ratios for the different faecal sample types. Comparisons based on intake estimates derived from the use of the C33: C32 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 C33 and C32) 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 0·06 (P &lt; 0·10). 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 t e 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.

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

SUMMARYTwo 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 n-alkane: 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 C31:C32 and C33:C32 (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 (C32 and C36), the herbage odd-chained n-alkanes (C29, C31, C33 and C36) or those used for the estimation of herbage intake (C31, C32 and C33). 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 C31:C32 and C33:C32 ratios, respectively. The estimates based on C31:C32 and C33:C32 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 C31:C32 and C33:C32, respectively. The results show that the n-alkane technique can provide an accurate and precise estimate of herbage intake.

Effect of administration and ruminal presence of chromic oxide controlled release capsules on herbage intake of sheep

Abstract Measurement of herbage intake by grazing sheep may be simplified if chromic oxide intraruminal controlled release capsules (CRC) are used. Two experiments were conducted to determine whether the ruminal presence of CRC affected voluntary herbage intake. In Experiment 1, conducted indoors with twenty 8-month-old rams offered lucerne chaff ad libitum, faecal output (P < 0.05) and feed intake (P < 0.10) were significantly lower in the 10 sheep dosed with Mark II type CRC, irrespective of their initial liveweight, compared with those which had not been dosed. In Experiment 2, faecal outputs, measured by total collection, of yearling rams with or without Mark III CRC (n = 16/group) were not significantly different. This suggests that sheep dosed with the Mark III capsule, which has a more flexible wing structure and bulbous tip than the Mark II design, should behave in a similar manner to their untreated counterparts in grazing studies and provide unbiased estimates of herbage intake. The suitability ...

The use of dosed and herbage n-alkanes as markers for the determination of herbage intake

SUMMARYThe recovery in the faeces of the n-alkanes of herbage (odd-chain, C27–C35) and of dosed artificial alkanes (even-chain, C28 and C32) was studied in twelve 4-month-old castrated male lambs. The lambs received three levels of cut, fresh perennial ryegrass or a mixed diet of perennial ryegrass (0·70) and a barley-based concentrate (0·30) (500–900 g D.M./day). C28 and C32 n-alkanes (130 mg each), absorbed onto shredded paper, were given once daily for 17 days to test whether the recoveries of herbage and dosed alkanes were similar to enable their use as markers for determining the herbage intake of grazing sheep. Stearic and palmitic acids (130 mg each) were given with the dosed alkanes to half of the animals with the objective of facilitating emulsification of the dosed alkanes within the digestive tract.With the exception of C27 n-alkane, the faecal recoveries of all alkanes were unaffected by diet, feeding level or emulsifying agent. Faecal recovery of odd- chain herbage n-alkanes increased with increasing C-chain length. The recovery of the dosed C28 n-alkane was slightly greater than the recoveries of both C27, and C29 n-alkanes of herbage. The recoveries of the dosed C32 n-alkane and the herbage C33-alkane were the same.The mean herbage intake estimated using C33 and C32 n-alkanes was identical to the actual herbage intake. Other alkane pairs gave slight underestimates of herbage intake ranging from 3·5% for the C28–C29 pair to 7·6% for the C27–C28 pair. No cyclical pattern of n-alkane excretion throughout the day was observed. Examination of daily variations in faecal alkane concentrations indicated that the start of alkane dosing should precede the sampling of faeces by at least 6 days.These results suggest that accurate estimation of herbage intake in grazing sheep is possible from the simultaneous use of dosed C32 and herbage C33 n-alkanes as markers.The method may be particularly useful in enabling unbiased estimates of herbage intake to be made in animals receiving supplementary feed.

A comparison of two methods for the estimation of herbage intake by lactating dairy cows

The herbage Intake of grazing dairy cows can be estimated either directly from measurements made through the animal or alternatively from sward measurements. Of the animal-based techniques, the most widely adopted method used to estimate herbage intake is the faecal output-indigestlbillty ratio technique. More recently, animal energy requirements have been used as a basis to predict herbage Intake. The objective of the present study was to compare the two animal-based techniques for estimating herbage intake.Two experiments were carried out during 1984 and 1985. In Experiment 1 a total of 42 lactacing British Friesian cows were allocated to three grazing treatments. Herbage Intakes were estimated over three twelve-day periods during the experiment. In Experiment 2, 40 cows were allocated to three grazing treatments and Intakes were again estimated over three twelve-day periods. Two methods were used to estimate the herbage Intake of the cows. Method 1 involved the estimation of herbage intake from animal energy requirements using both observed liveweight changes (Method 1a) and liveweight changes calculated from a regression analysis of llvewelghts over the experitmental period (Method 1b). With Method 2 intakes were estimated by the faecal output-indigestibllity ratio technique.

The use of long-chain n-alkanes for estimating intake and digestibility of herbage in cattle

Studies with sheep suggest that accurate estimates of herbage intake can be obtained by using the herbage alkane tritriacontane (C33) and dosed dotriacontane (C32) as markers, since the faecal recoveries of both alkanes have been shown to be very similar. To validate the technique for herbage intake estimation in grazing cattle there is a need to compare in cattle, the faecal recoveries of both herbage and dosed n-alkanes. It has been observed in sheep that the faecal recoveries of n-alkanes increase as their chain lengths increase, suggesting that the recovery of hexatriacontane (C36), an alkane absent from herbage but available commercially at low cost, should be complete. C36 may therefore have potential as a dosed marker for estimation of faecal output. Thus it may .30 be possible to obtain estimates of both herbage intake and diet digestibility in the same individual grazing animal using n-alkanes as markers. The purpose of the experiment described here was to determine the faecal recoveries in cattle of odd-chain n-alkanes from fresh herbage and of C32 and C36 dosed n-alkanes.