An indoor and a grazing experiment was conducted to determine how estimated feed intake and digestion by grazing goats consuming concentrate, bahaigrass pasture, and mimosa browse changed with body weight (BW), level of supplementation, and forage chemical composition. Twenty four Boer wether goats were assigned in a completely randomized design with repeated measures on the following 3 treatments: concentrate, mimosa browse, and bahiagrass pasture. Internal markers used to estimate both dry matter (DM) digestibility (DMD) and DM intake (DMI) included acid detergent lignin (ADL) and acid insoluble ash (AIA). Marker-derived estimates of DMD and DMI were compared with DMD measured by total fecal collection or directly measured by in vivo feed intake rate. Both ADL and AIA-based markers in mimosa and bahiagrass diets were similar from those derived by in vivo DMD; however, AIA-based marker in concentrate was under-estimated (P < 0.01). These results indicate that ADL and AIA indigestible markers performed similarly to in vivo DMD in mimosa and bahiagrass, although AIA concentration in mimosa seemed to be low compared to others. All markers yielded feed intake estimates that differed from those derived by ADL (P < 0.03), AIA (P < 0.01), and in vitro DMD (P < 0.001) compared to in vivo control, with ADL (P < 0.05) and in vitro DMD (P < 0.01) by period interactions, indicating that estimated intake from ADL and in vitro DMD increased more in mimosa browse diet with time period than in concentrate and bahiagrass diets with that estimated intakes being decreased with corresponding the second period due to lower in vitro DMD (21% to 4%) in second period compared to the first period in both concentrate and bahiagrass diets, respectively. In the present study, mean marker recoveries were higher (P < 0.01) for bahiagrass and mimosa diets than for the concentrate diets for both ADL- and AIA-based markers. It can be concluded that the use of natural markers in ADL and AIA offers advantages over the total fecal collection or direct measurement of in vivo intake methods for digestibility studies. Both ADL and AIA occur in common forages at readily measurable levels and laboratory procedures are not difficult or time consuming. Therefore, both ADL and AIA have possible use in digestibility studies where other methods may not be applicable.
Goats are typically browsing animals; if allowed free access to grazing and browse, they generally obtain 60 to 80% of their diet from browse plants. However, determination of the amount eaten and characteristics of the diet of grazing goats remains one of the most difficult tasks in research. Internal markers have been widely used in site and extent of digestion and for determining dry matter intake (DMI) under grazing conditions, and they include chromium sesquioxide (Cr2O3), rare earth elements such as ytterbium (Yb), and long-chain alkane waxes (C32 and C36) [
Extensive research has been conducted over the years on concentrate supplementation level at pasture for ruminants [
Twenty four 8 month old Boer wether goats (n = 8) were assigned in a completely randomized design with repeated measures on the following 3 treatments: concentrate, mimosa browse, and bahiagrass pasture to evaluate the efficacy of different internal markers for estimating DMD and DMI. Internal markers used to estimate both DMD and DMI included ADL and AIA. Marker-derived estimates of DMD and DMI were compared with DMD measured by total fecal collection or directly measured by in vivo feed intake rate.
Fresh vegetative bahiagrass forage and mimosa browse were grazed by the goats except for concentrate treatment group (confined and fed bermudagrass hay). Animals were confined indoors for a period of 14 days and fed 40:60 soyhull pellet: bermudagrass hay diet on a DM basis. Animals were weighed for two consecutive days, stratified by BW and randomly assigned within Boer breed to one of three production systems: 1) concentrate grain diet containing 40% protein pellets, 40% soybean hulls, and 20% bermudagrass hay; 2) ad libitum consumption of bahiagrass pasture supplemented with 150 g/head/day protein pellets; 3) ad libitum consumption of mimosa browse supplemented with 100 g/head/day of cracked corn. Animals fed the concentrate diet were housed individually in 1.8 m × 2.1 m pens with raised mesh floors. Fresh water and feed were supplied daily. Animals assigned the bahiagrass diet were grazed on 0.8 hectare pasture containing bahiagrass and fed protein pellet once daily. The mimosa browse animals were rotated every two weeks between four mimosa plots (0.4 hectare) with trees trimmed to a height of 1.2 m and fed cracked corn once daily. Body weights were recorded after a four hour withdrawal from feed and water, for two consecutive days every two weeks. The growth period consisted of 14 weeks.
A 0.4 hectare paddock of 6-year-old mimosa was used in this study. Mimosa plants had been planted in rows 1.8 m apart, with about 0.45 m between plants within rows. However, annual mowing in late winter had caused considerable thinning of the stand. The paddock was mown in April, and growth was allowed to accumulate without defoliation for the entire summer. By the end of September, mimosa plants had mostly 5 to 8 stems that ranged between 1.8 and 3 m in length. The Tuskegee University Animal Use Committees approved the animal care, handling, and sampling procedures.
Actual (in vivo) and estimated feed intake and digestibility were measured on eight goats from each treatment group for 10 days. Estimated dry matter (DM) intake (DMI) was calculated as follows using in vitro DM digestibility (DMD) from forage samples [
Total fecal output was measured using fecal bags. Internal markers used to estimate both DMD and DMI included ADL and AIA. Marker-derived estimates of DMD and DMI were compared with DMD measured by total fecal collection or directly measured by in vivo feed intake rate.
Goats were fitted with canvas fecal collection bags and allowed three days to adapt to the bags before initiation of a five day fecal collection period. Fecal collection bags were emptied twice daily. Daily collected feces were weighed, mixed, and a constant percentage (2%) for each animal was taken to be dried at 55oC; this was followed by a 24 hour air equilibration to determine air dried fecal output. Daily fecal samples were pooled relative to the 24 hour air dried fecal output to provide a representative sample of the five day collection period. During the five day collection period, samples of pasture, browse, hay and supplements were taken daily, composited, and subsampled. Samples were ground through a 1-mm screen in a Wiley Mill (Thomas Scientific, Swedesboro, NJ, USA) prior to laboratory analyses.
Pasture, browse, hay and supplement samples were collected weekly during the entire trial, ground through a 1-mm screen in a Wiley Mill and pooled by month for chemical analysis of DM, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), cellulose, ADL and AIA.
Feed samples and fecal samples from the fecal collection period were analyzed for DM and nitrogen determined by the combustion method [
Twenty four Boer wether goats were assigned in a completely randomized design with repeated measures on the following 3 treatments: concentrate, mimosa browse, and bahiagrass pasture .The model included the fixed effects of treatment, sampling week (week 1 and week 2), and treatment × week interaction.
For variables measured repeatedly over the experiment, such as forage chemical composition, digestibility, fecal output and feed intake data, the GLM procedures of SAS was used to asses DMI, DMD, and their interaction [
Chemical composition of feeds and in vitro organic matter digestibility are listed in
Treatment | ||||||
---|---|---|---|---|---|---|
A | B | C | SEM | P-value | ||
Item | Period | Confined | Grazing | Grazing | ||
n | 8 | 8 | 8 | |||
OM | 1 | 91 | 89 | 93.1 | 0.54 | |
2 | 89.9 | 89.1 | 92 | 0.42 | ||
Mean | 90.4b | 92.5a | 89.0c | 0.35 | 0.01 | |
CP | 1 | 15.7 | 10.1 | 17.2 | 0.25 | |
2 | 14.9 | 10.6 | 18 | 0.26 | ||
Mean | 15.3b | 10.4c | 17.6a | 0.16 | 0.001 | |
NDF | 1 | 59.1 | 69.8 | 59.8 | 0.51 | |
2 | 59.1 | 67.6 | 58.9 | 0.58 | ||
Mean | 59.1b | 68.7a | 59.3b | 0.53 | 0.01 | |
ADF | 1 | 34.7 | 34.6 | 42.4 | 0.48 | |
2 | 33.8 | 30.6 | 41 | 0.42 | ||
Mean | 34.2b | 32.6c | 41.7a | 0.47 | 0.001 | |
Lignin | 1 | 6.7 | 9.6 | 23.7 | 0.16 | |
2 | 6.8 | 7.9 | 21.9 | 0.15 | ||
Mean | 6.8c | 8.7b | 22.8a | 0.23 | 0.001 | |
Cellulose | 1 | 27.2 | 24.7 | 18.6 | 0.17 | |
2 | 26.2 | 22.5 | 19.2 | 0.38 | ||
Mean | 26.7a | 23.6b | 18.9c | 0.36 | 0.001 | |
ADL | 1 | 4.1 | 1.78 | 15.2 | 0.53 | |
2 | 6.8 | 3.73 | 15.8 | 1.68 | ||
Mean | 5.5b | 2.8c | 15.5a | 0.43 | 0.01 | |
AIA | 1 | 0.5 | 1.6 | 0.3 | 0.05 | |
2 | 0.8 | 1 | 0.3 | 0.02 | ||
Mean | 0.6b | 1.3a | 0.3c | 0.03 | 0.001 | |
IVOMD* | ||||||
1 | 94.5 | 59.9 | 55.7 | 1.66 | ||
2 | 74.8 | 57.5 | 67.4 | 4.56 | ||
Mean | 84.6a | 58.7b | 61.5b | 2.39 | 0.01 |
*IVOMD, in vitro organic matter digestibility (72 h incubation). 1Treatments A (concentrate), B (bahiagrass pasture), and C (mimosa browse) were supplemented with 800 (treatment A) and 150 (Treatments B and C) g of concentrate. Fresh vegetative bahiagrass forage and mimosa browse were grazed by the goats except for treatment A (confined and fed Bermuda grass hay). ADL = acid detergent lignin; AIA = acid insoluble ash. a,b,cMeans within a treatment or mean grouping without a common superscript letter differ (P < 0.05).
tion of CP, ADF, lignin and ADL were higher (P < 0.001) for mimosa browse than for other diets, but cellulose content and in vitro organic matter (OM) digestibility (IVOMD) were higher (P < 0.01) for concentrate among diets. Average OM, NDF and AIA contents were higher (P < 0.01) for bahiagrass than for other diets.
Estimates of concentrate, bahiagrass and mimosa browse DMD by ADL and AIA-based internal markers were differed among diets (P < 0.001;
Both ADL and AIA-based markers in mimosa and bahiagrass diets were similar from those derived by in vivo DMD; however, DMD estimated from AIA-based marker in concentrate was about 8% under-estimated (P < 0.01). These results indicate that ADL and AIA indigestible markers performed similarly to in vivo DMD in mimosa and bahiagrass in estimating forage DMD, but not in the concentrate, although AIA concentration in mimosa seemed to be low compared to others as recommended by Thonney et al. [
Initial BW (28.5 ± 1.6 kg; data not shown in the text) was similar among diets, but final BW was higher for concentrate (39.6 kg; P < 0.01) than for bahiagrass (32.3 kg) and mimosa browse (36.9 kg) diets. Mean fecal
Items | In vivo | Marker method | ||||
---|---|---|---|---|---|---|
Period | control | ADL | AIA | SEM | P-value | |
Concentrate | 1 | 0.75 | 0.88 | 0.67 | 0.03 | 0.001 |
2 | 0.76 | 0.63 | 0.72 | 0.01 | 0.001 | |
Mean | 0.76 | 0.76 | 0.7 | 0.02 | 0.01 | |
Mimosa | ||||||
1 | 0.75 | 0.75 | 0.77 | 0.01 | 0.39 | |
2 | 0.76 | 0.75 | 0.76 | 0.02 | 0.6 | |
Mean | 0.76 | 0.75 | 0.76 | 0.01 | 0.77 | |
Bahiagrass | ||||||
1 | 0.75 | 0.81 | 0.77 | 0.01 | 0.01 | |
2 | 0.76 | 0.78 | 0.76 | 0.001 | 0.36 | |
Mean | 0.76 | 0.79 | 0.77 | 0.02 | 0.17 | |
ANOVA | ||||||
Diets | Period | Diet x period | ||||
ADL | 0.001 | 0.01 | 0.001 | |||
AIA | 0.001 | 0.97 | 0.55 |
ADL = acid detergent lignin; AIA = acid insoluble ash.
DM outputs were similar (data not shown in text) among concentrate (273.7 g DM), Bahiagras (269.4 g DM) and mimosa browse (273.5 g DM) diets.
All markers yielded feed intake estimates that differed from those derived by ADL (P < 0.03), AIA (P < 0.01) and IVDMD (P < 0.001) compared to in vivo control, with ADL (P < 0.05) and in vitro DMD (P < 0.01) by period interactions (
Sunvold and Cochran [
Marker method | |||||||
---|---|---|---|---|---|---|---|
Items | Period | In vivo Control | ADL | AIA | IVDMD | SEM | P-value |
n | 8 | 8 | 8 | 8 | |||
Dry matter intake1 (DMI), kg/d | |||||||
Concentrate | |||||||
1 | 1.1 | 1.7 | 0.82 | 1.5 | 0.081 | 0.001 | |
2 | 1.12 | 0.7 | 0.9 | 0.99 | 0.087 | 0.001 | |
Mean | 1.11b | 1.25a | 0.85c | 1.23a | 0.057 | 0.001 | |
Mimosa | |||||||
1 | 1.09 | 1.01 | 1.16 | 0.6 | 0.07 | 0.001 | |
2 | 1.12 | 1.16 | 1.07 | 0.87 | 0.065 | 0.001 | |
Mean | 1.11a | 1.11a | 1.10a | 0.73b | 0.049 | 0.001 | |
Bahiagrass | |||||||
1 | 1.09 | 1.51 | 1.26 | 0.7 | 0.052 | 0.001 | |
2 | 1.12 | 1.21 | 0.96 | 0.6 | 0.046 | 0.001 | |
Mean | 1.11b | 1.30a | 1.11b | 0.64c | 0.049 | 0.001 | |
ANOVA | |||||||
Treatment | Period | Treatment × period | |||||
ADL | 0.03 | 0.02 | 0.05 | ||||
AIA | 0.01 | 0.86 | 0.09 | ||||
IVDMD | 0.001 | 0.87 | 0.01 |
1Treatments groups in concentrate, bahiagrass pasture, and mimosa browse were supplemented with 800 (concentrate) and 150 g (bahiagrass and mimosa) of concentrate. Fresh vegetative bahiagrass forage and mimosa browse were grazed by the goats except for concentrate treatment (confined and fed Bermuda grass hay). ADL = acid detergent lignin; AIA = acid insoluble ash. a,b,cMeans within a treatment or mean grouping without a common superscript letter differ (P < 0.05).
Marker | ||||
---|---|---|---|---|
Item | Period | ADL | AIA | SEM |
No of animals | 8 | 8 | ||
Concentrate | ||||
1 | 76.3 | 68.8 | 1.26 | |
2 | 63.6 | 70.1 | 1.25 | |
Mean | 70 | 69.5 | 0.89 | |
Mimosa | ||||
1 | 75.2 | 76.9 | 1.77 | |
2 | 75.2 | 76.5 | 1.76 | |
Mean | 75.2 | 76.7 | 1.25 | |
Bahiagrass | ||||
1 | 81.1 | 76.9 | 1.8 | |
2 | 77.7 | 76.2 | 1.79 | |
Mean | 79.4 | 76.6 | 1.25 | |
ANOVA | ADL | AIA | ||
Diet | 0.001 | 0.001 | ||
Period | 0.004 | 0.97 | ||
Diet × Period | 0.01 | 0.54 |
ADL = acid detergent lignin; AIA = acid insoluble ash.
tions for ADL, indicating that marker recoveries from ADL in concentrate and bahiagrass diets decreased with time.
To further understand the effect of fecal output, they were regressed against estimated DMI for goats fed concentrate, bahiagrass and mimosa browse diets (
As BW increased, total DMI increased linearly for mimosa browse (
It can be concluded that the use of natural markers in ADL and AIA offers some apparent advantages over the
total fecal collection method for digestibility studies. Both ADL and AIA occur in common forages at readily measurable levels and laboratory procedures are not difficult or time consuming. Therefore, both ADL and AIA have possible use in digestibility studies where other methods may not be applicable.
This project was supported by the Sustainable Agriculture Research and Education (SARE) program, which is funded by the US Department of Agriculture-National Institute of Food and Agriculture (USDA-NIFA), the USDA/NIFA Evans-Allen Research Program and Tuskegee University, George Washington Carver Agricultural Research Station.