Effects of forage type, animal characteristics and feed intake on faecal particle size in goat, sheep, llama and cattle

Animal Feed Science and Technology 208 (2015) 53–65

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Effects of forage type, animal characteristics and feed intake on faecal particle size in goat, sheep, llama and cattle A.R. Jalali a,∗ , M.R. Weisbjerg b , E. Nadeau c , Å.T. Randby d , B.-O. Rustas e , M. Eknæs d , P. Nørgaard a a Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark b Department of Animal Science, AU Foulum, Aarhus University, Tjele, Denmark c Department of Animal Environment and Health, Swedish University of Agricultural Sciences, Skara, Sweden d Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Ås, Norway e Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Kungsängen Research Center, SE-753 23 Uppsala, Sweden

a r t i c l e

i n f o

Article history: Received 9 September 2014 Received in revised form 4 July 2015 Accepted 6 July 2015 Keywords: Animal maturation Dry sieving grass silage NDF lignification Ruminant

a b s t r a c t The effect of forage maturity stage at harvest, animal characteristics and neutral detergent fibre (NDF) intake on mean particle size and particle size distribution in faeces from sheep and cattle fed grass silages was studied (Study I). Models for prediction of faeces characteristics from sheep and cattle and feed characteristics established from Study I were tested on faeces samples from goat, sheep, llama and cattle fed other types of forages (Study II). Study I included 112 faeces samples from 5 trials, and Study II included 90 faeces samples from 3 trials. Animals were fed ad libitum or restrictively with or without concentrate supplementation. The NDF content and acid detergent lignin (ADL) to NDF ratio of the forages ranged from 410 to 660 g/kg of dry matter (DM) and from 0.03 to 0.10, respectively, in Study I, and from 320 to 810 g/kg of DM and from 0.05 to 0.18, respectively, in Study II. The faecal samples were washed in nylon bags with a pore size of 0.01 mm and freeze dried before being sorted into 5 sieving fractions with pore sizes of 2.4–0.1 mm; particles less than 0.1 mm were collected in bottom bowl. The faecal particles were characterized by the arithmetic and geometric mean sizes, most frequent, median and the 95 percentile values. In Study I, the mean faecal particle size increased, and the proportion of small particles (SP; <0.2 mm) decreased with increasing body weight (BW), maturity of forage, ADL/NDF ratio, concentrate to forage ratio (C:F), and NDF intake (p < 0.05). The proportion of large particles (>1 mm) increased with higher BW and NDF intake (p < 0.05). The mean particle size was higher and the proportion of SP was lower in faeces from cattle than from sheep (p < 0.05). In conclusion, increased lignification of forage NDF resulted in increased particle sizes in faeces and this effect was amplified in larger animals. The prediction model established from Study I, on the effect of BW, ADL/NDF in forage, C:F and forage NDF intake on particle size in faeces of grass silage-fed animals in Study I appeared to be valid to predict the geometric mean particle size in faeces from goat, sheep, llama and steers fed other forages e.g., lucerne, dried grass, grass seed straw and whole crop barley silage in Study II. © 2015 Elsevier B.V. All rights reserved.

Abbreviations: ADF, acid detergent fibre; ADL, acid detergent lignin; APS, arithmetic mean particle size; BIC, Bayesian information criteria; BW, body weight; C:F, concentrate to forage ratio; DM, dry matter; GPS, geometric mean particle size; LP, large particles; Mode PS, most frequent particle size; MPS, median particle size; NDF, neutral detergent fibre; NDFI, neutral detergent fibre intake; PDM, particle dry matter; RMSPE, root mean square prediction error; SP, small particles; VAR, variance; VSP, very small particles; WCBS, whole crop barely silage. ∗ Corresponding author. E-mail address: [email protected] (A.R. Jalali) . http://dx.doi.org/10.1016/j.anifeedsci.2015.07.003 0377-8401/© 2015 Elsevier B.V. All rights reserved.

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1. Introduction The particle dynamics affecting passage out of the rumen depend on pools of both large (LP) and small particles (SP) with a suggested critical threshold value of 1.18 mm between the two pools in sheep (Poppi et al., 1980). Faecal particle size reflects the size of particles leaving the rumen (Kennedy, 2005) and is affected by forage maturity (Jalali et al., 2012b) and forage particle size (Jaster and Murphy, 1983). Increased intake causes an increased passage rate (Okine and Mathison, 1991) and reduces the selective retention of LP in the rumen (Van Soest et al., 1988). Van Soest (1994) reported that forage degradability by rumen microorganisms mostly is related to the ADL to NDF ratio, which increases with increasing maturity stage of the forage at harvest. However, advanced forage maturity at harvest causes decreased intake and increased resistance against particle breakdown in the rumen (De Boever et al., 1990). In growing steers fed whole-crop barley silage, the mean faecal particle size increased with advanced forage maturity at harvest (Rustas et al., 2010). According to Fritz et al. (2009), the mean faecal particle size increases with increasing BW, however, the effects of forage and other animal characteristics were ignored. The key animal characteristics affecting feed intake are BW and maturation of the animal (Volden et al., 2011). Many of the previous studies on faecal particle size have been conducted by feeding forages of late maturity stages at harvest with high NDF contents, high ADL to NDF ratios and low digestibilities (Bae et al., 1981, 1983; Poppi et al., 1985; Domingue et al., 1991a). To our knowledge, no other study has analyzed the effects of animal species and maturation, considering a wide range of forage maturity from very early harvested grass to late harvest, forage type and feed intake on the distribution of faecal particle size in sheep and cattle. We hypothesized that animal BW, forage ADL to NDF ratio, proportion of concentrate, and NDF intake are the major factors affecting the mean faecal particle size and that the mean faecal particle size appears as a footprint of the quality of the forage eaten by animal. Hence, the aim was to study effects of harvest time of grass silage, animal characteristics and intake on particle size in faeces to establish models for prediction of faeces characteristics. Further, the aim was to validate the models on different ruminant species fed different forage types of various nutritional qualities.

2. Materials and methods 2.1. Animals, forages and experimental design Study I includes analysis of faeces from sheep and cattle of various maturations fed grass silage harvested at 2–3 different stages of maturity within Trials 1–5 (see Table 1). Study II (Table 2) includes validation of the models to predict faeces characteristics derived in Study I on faeces from 3 trials with different ruminant animals of variable maturation and body size (37–412 kg) fed various forages, such as the non-green grass whole crop barley silage (Trial 6), lucerne and grass-clover silages (Trial 7), hay and grass-seed straw (Trial 8).

2.2. Study I Five trials were selected from ongoing studies with sheep and cattle fed grass silages harvested at different stages of maturity with a minimal supplementation and with other main purposes than faeces characteristics. The particle sizes of 112 individual faeces samples from 5 trials examining young and mature sheep and cattle fed grass silages were compared (Table 1). The BW of the studied ruminant species ranged from 36 to 52 kg in lamb (Trial 4), 75 to 104 kg in sheep (Trial 5), 92 to 125 kg in sheep (Trial 2), 387 to 563 kg in growing bulls (Trial 3) and 517 to 671 kg in dairy cows (Trial 1). The NDF content of the grass silages ranged from 410 g/kg (Trial 1) to 660 g/kg of DM (Trial 4), the DM content from 190 g/kg (Trial 2) to 660 g/kg (Trial 5), the ADL to NDF ratio from 0.03 to 0.10 (Trial 4) and the concentrate to forage ratio from 0.0 (Trials 4 and 5) to 0.48 (Trial 2). Grass maturity was defined from differences in harvest dates. Early harvest in Trials 1 and 2 occurred 14 days before medium harvest. For Trials 3, 4 and 5, early harvest occurred 7, 14 and 10 days before medium harvest and medium harvest occurred 8, 8 and 9 days before late harvest (see Table 1).

2.3. Study II The particle sizes of 90 faeces samples from 3 trials with four ruminating species fed different forage characteristics were used in a test study for predicting the geometric mean particle size values (GPS) of faecal particles by using the model established in Study I (Table 2). The BW of studied animals ranged from 37 to 52 kg in goats, 63 to 83 kg in sheep, 99 to 174 kg in llamas (Trial 8), 66 to 121 kg in sheep (Trial 7) and 337 to 412 kg in growing steers (Trial 6). The NDF content of the different forages ranged from 320 g/kg (Trial 7) to 810 g/kg of DM (Trial 8), the DM content from 360 g/kg (Trial 6) to 920 g/kg (Trial 8), the ADL to NDF ratio from 0.05 to 0.18 (Trial 7) and the concentrate to forage ratio from 0.0 (Trials 7 and 8) to 0.08 (Trial 6). For Trials 1 and 2 early harvest occurred 21 and 11 days before late harvest. One goat fed hay in the second period in Trial 8 was excluded, due to sickness of the animal and associated reduced feed intake.

Table 1 Study I. Trial design, animal characteristics, grass silage characteristics, concentrate to forage ratio (C:F) and NDF intake.a Trial

Trial design

Animal characteristics

1

Latin square

Cattle, 6

Maturation

Mature, lactating

Grass silage characteristics

Harvest

36

Early

Medium

2

Latin square

Sheep, 6

Mature, maintenance

18

Early Medium Medium

3

Randomized block

Cattle, 18

Growing bulls

18

Early Medium Late

Physical form

Unchopped Medium, 55 mm Fine, 24 mm Unchopped Medium, 55 mm Fine, 24 mm Direct, 80 mm Wilted, 80 mm Direct, 80 mm Wilted, 80 mm Wilted, 80 mm

C:F, g DM/g DM (mean ± s.d.)

NDF intake, %BW (mean ± s.d.)

0.31 ± 0.03 0.31 ± 0.02 0.31 ± 0.02 0.35 ± 0.03 0.34 ± 0.04 0.34 ± 0.04

1.18 1.16 1.16 1.25 1.32 1.32

± ± ± ± ± ±

0.10 0.11 0.11 0.12 0.15 0.15

See Supplementary Table S1, Randby et al. (2008)

± ± ± ± ±

0.04 0.04 0.15 0.15 0.15

See Supplementary Table S2, Prestløkken et al. (2008)

References

Fibre NDF, g/kg DM

ADL/NDF, g/g

410

0.063

510

0.075

450

0.059 0.041 0.069 0.069 0.085

0 0 0 0 0.47 ± 0.49

0.39 0.39 0.41 0.41 0.41

0.038 0.038 0.040 0.040 0.055 0.055

0 0.17 ± 0.19 0 0.20 ± 0.22 0 0.19 ± 0.21

0.94 ± 0.16 1.01 ± 0.23 1.03 ± 0.12

See Supplementary Table S3, Randby et al. (2010)

550 550

Chopped, 54 mm Chopped, 54 mm Chopped, 54 mm

480 530 600

4

Randomized block

Sheep, 22

Growing lambs

22

Early Medium Late

Chopped, 20 mm Chopped, 20 mm Chopped, 20 mm

460 600 660

0.032 0.066 0.097

0 0 0

1.16 ± 0.09 1.44 ± 0.06 1.47 ± 0.12

See Supplementary Table S4

5

Completely randomized

Sheep, 18

Mature, late pregnancy

18

Early Medium Late

Unchopped Unchopped Unchopped

450 580 630

0.042 0.067 0.082

0 0 0

1.16 ± 0.23 1.27 ± 0.26 1.33 ± 0.16

Jalali et al. (2012b)

a

A.R. Jalali et al. / Animal Feed Science and Technology 208 (2015) 53–65

Species, number

No. of observations

Intake was restricted in Trial 2 and was ad libitum in Trials 1, 3, 4 and 5.

55

56

Trial Trial design Animal characteristics Species, number

6

Latin square

Cattle, 8

Maturation

Growing steers

Forage characteristics Forage type

Harvest

Factorial

Sheep, 24

Mature, maintenance

8

Crossover

Goat, 6 Sheep, 6 Llama, 6 Goat, 6 Sheep, 6 Llama, 6

Mature, maintenance

a

NDF intake, %BW (mean ± s.d.)

Fibre

NDF, g/kg DM

ADL/NDF, g/g

Unchopped Chopped, 20 mm Unchopped Chopped, 20 mm

480 510 480 510

0.116 0.095 0.140 0.121

0.07 ± 0.01 0.08 ± 0.01 0.08 ± 0.01 0.07 ± 0.01

1.04 1.03 0.97 1.05

Grass-clover

Early Late Early

Chopped, 20 mm Chopped, 20 mm Chopped, 20 mm

345 405 440

0.157 0.172 0.048

0 0 0

0.38 ± 0.03 0.38 ± 0.14 0.53 ± 0.06

Green hay

Medium

Late

0.064 0.064 0.064 0.099 0.099 0.099

0

Grass seed straw

Chopped, 30–40 mm 580 Chopped, 30–40 mm Chopped, 30–40 mm Unchopped 810 Unchopped Unchopped

0.91 1.05 0.74 1.16 1.03 0.62

Whole-crop barley silage

Early Late

7

Physical form

C:F, g DM/g DM (mean ± s.d.)

Lucerne

Intake was restricted in Trial 2 and were ad libitum in Trials 1 and 3.

0

± ± ± ±

± ± ± ± ± ±

0.15 0.10 0.11 0.08

0.24 0.15 0.13 0.17 0.11 0.12

GPS value (mean ± s.d.)

0.28 0.30 0.37 0.36

± ± ± ±

References

0.01 0.02 0.01 0.03

Rustas et al. (2010)

0.19 ± 0.03 0.20 ± 0.03 0.14 ± 0.01

See Supplementary Table S5

± ± ± ± ± ±

Jalali et al. (2012a)

0.14 0.18 0.17 0.17 0.20 0.20

0.01 0.01 0.03 0.01 0.02 0.02

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Table 2 Study II. Trial design, animal characteristics, forage characteristics, concentrate to forage ratio (C:F), geometric mean particle size value (GPS) and NDF intake.a

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2.4. Chemical analysis The DM concentration of feed and orts was analyzed by drying at 60 ◦ C for 24 h. The dried samples were ground through a 1 mm screen using a mill (Kamas Kvarnmaskiner AB, Malmö, Sweden) and analyzed sequentially for NDF and ADL using a FiberCap system with a pore size of 0.01 mm (FOSS Tecator AB, Höganäs, Sweden). The NDF concentration was determined with residual ash with heat-stable ␣-amylase according to Mertens (2002). The ADL concentration was determined as ash free by the modified method described by Van Soest et al. (1991). 2.5. Faecal particle size determined by dry sieving Approximately 15 g of mixed fresh faeces from small ruminating species and 30 g from cattle were washed using a commercial laundry detergent (BIOTEX Color, Blumøller, Denmark) in nylon bags with a pore size of 0.01 mm and freeze dried before dry sieving into 6 fractions as described by Jalali et al. (2012a). Bags containing faeces of cattle were not soaked in a tempered water bath before washing because of the lower DM concentration in faeces of large than of small ruminant species. The proportion of particle DM in faeces DM (PDM) was defined as the residual DM left after washing and freeze drying. The proportion of PDM retained in each sieving fraction was estimated from the weight of particles retained in each fraction. The large particles (LP) were defined as those particles retained on a sieve of 1 mm pore size, as defined by Kennedy (2005). The proportion of small (SP) and very small particles (VSP) was defined as particles passing through sieves of 0.212 and 0.106 mm pore size, respectively. The arithmetic mean particle size (APS) and the GPS were estimated according to Waldo et al. (1971). The most frequent particle size (Mode PS), median particle size (MPS) and 95 percentile values were estimated from gamma distribution functions based on the APS and variance (VAR) values. The VAR values were estimated as the squared deviation of the particle size values for each sieving fraction from the APS weighted by the proportion of particulate matter retained in each sieving fraction, as described by Nørgaard (2006). The estimations of the Mode PS values were only based on sieve fractions with a pore size of less than 1 mm in order to ensure positive Mode PS estimate for all the samples. 2.6. Statistical analysis 2.6.1. Individual trials The models used to test the fixed effects in the 1st to 5th experiment in Study I were as follows: (Trial 1) Yij =  + Hi + Fj + Pl + (HF)ij + Eij

(1)

(Trial 2) Yijk =  + Hi + Cj + Wk + Pl + (HW )ik + Eijk

(2)

(Trial 3) Yij =  + Hi + Cj + Bm + (HC)ij + Eij

(3)

(Trial 4) Yi =  + Hi + Bm + Ei

(4)

(Trial 5) Yi =  + Hi + Ei

(5)

where Yijk = dependent variable,  = overall mean, Hi = effect of maturity stage of forage at harvest (Trials 1 and 2, i = 2; Trials 3–5, i = 3), Fj = effect of physical form of forage (Trial 1, j = 3), Pl = effect of period (Trial 1, l = 3; Trial 2, l = 4), Wk = effect of pre-wilting (Trial 2, k = 2), Cj = effect of concentrate to forage ratio (Trial 3, j = 2), Bm = effect of block (Trial 3, m = 6; Trial 4, m = 3), HFij , HWik , HCij = interactions between the respective variables and Eijk = residual error. In Trial 1 (model 1) the effect of concentrate to forage ratio was tested, but omitted as it was non-significant (p > 0.10). 2.6.2. Study I The characteristics of faeces were statistically analyzed using the Mixed model procedure of SAS (SAS system for windows, release 9.2; Cary, NC, USA) with animal as a random effect. The interactions between animal species, animal maturation and NDF intake per kg BW were tested against metabolic BW and ADL/NDF ratio in forages, but were removed from the final models due to non-significant effects. The final reduced models for animal and diet characteristics were as follows: Yi...o =  + Hj + Sk + M1 + Fm + ˇ1 Kn + ˇ2 No + (HS)jk + (PS)mk + (SM)kl + Ei...o

(6)

Ym...q =  + Fm + ˇ1 Kn + ˇ2 No + ˇ3 Wp + ˇ4 Lq + (WL)pq + Em...q

(7)

where Yi. . .q = dependent variable,  = overall mean, Hj = fixed effect of maturity stage of grass at harvest (j = 3), Sk = fixed effect of animal species (k = 2), Ml = fixed effect of animal maturation (l = 2), Fm = fixed effect of physical form (m = 2), ˇ1 Kn = regression effect of concentrate to forage ratio, ˇ2 No = regression effect of forage NDF intake (NDFI) per kg BW, ˇ3 Wp = regression effect of metabolic BW, ˇ4 Lq = regression effect of ADL to NDF ratio in forage, HSjk = interaction between maturity stage of forage at harvest and animal species, PSmk = interaction between forage physical form and animal species, SMkl = interaction between animal species and animal maturation, WLpq = interaction between BW and ADL to NDF, Ei. . .q = residual error and animal within experiment as a random factor.

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The main differences between the two final models are that model 6 includes maturity stage of forage at harvest and animal species and maturation, whereas model 7 includes forage characteristics (e.g., the ADL to NDF ratio) and animal characteristics (e.g., metabolic BW). Effects of the feeding levels of forage and forage DM content in all trials and of concentrate NDF to total NDF intake in Trials 1, 2 and 3 using concentrate-containing rations were non-significant and removed from the model. The effects of both DM and NDF intakes have been tested using the Mixed procedure in SAS. The effect of NDF intake was kept due to both significant effect and lower Bayesian information criteria (BIC) value as compared to effect of DM intake. The effect of forage NDF content was removed due to confounding effect with forage lignification and also higher BIC value without any effect on the overall p-values from model 7. The residuals in the final models were tested for outliers by using the Cook’s D test with the threshold value of 1 for exclusion of a value. Effects were declared significant at p < 0.05. Paired comparisons were performed using the t-test. The squared overall correlation values for models 6 and 7 were estimated by use of the GLM procedure. All presented correlations were determined using the CORR procedure in SAS (SAS system for windows, release 9.2; Cary NC, USA). 2.6.3. Study II 2.6.3.1. Individual trials – validation. Effects of the feeding levels of forage and forage DM content in all trials and of concentrate NDF to total NDF intake in Trial 6 were non-significant and removed from the model. Faeces characteristics in terms of PDM (% of DM), VSP (% of PDM), LP (% of PDM) and GPS (mm) from animals with BW ranging from 37 to 412 kg in Trials 6–8 were predicted using the models and parameters derived in Study I with model 7, which includes BW. The root mean square prediction error (RMSPE) was estimated as: RMSPE =

 n

i=1

(Ai − Pi )2 /n

The mean bias () and line bias (ˇ1 ) was estimated as: Ai − Pi =  + ˇ1 (Pi − mean (P)) + Ei The relationship between the difference between predicted and observed and the wide range of NDF contents and ADL/NDF ratios of the forages was estimated as: Ai − Pi =  + ˇ2 NDFj + Ei Ai − Pi =  + ˇ3 ADLj /NDFj + Ei where Ai = observedi , Pi = predictedi , Ei = residual error, NDFj = content of NDF in forage and ADLj /NDFj = ADL to NDF ratio in forage. Random effect of animal within experiment was included in the three above models. The statistical analyses were performed using the Mean and Mixed procedures in SAS (SAS system for windows, release 9.2; Cary NC, USA). 3. Results 3.1. Individual trials Advancing stage of grass maturity at harvest increased the PDM (p < 0.01), the most frequent particle size value and the faecal median particle size (p < 0.05; Supplementary Tables S1–S5) in Trials 1–5, the APS and GPS values in Trials 1, 2, 4 and 5 (p < 0.05), the 95 percentile value in Trials 2 and 4 (p < 0.05), the proportion of LP in Trials 1 and 4, and decreased the proportion of SP in Trials 1–5 (p < 0.01) (see Supplementary Tables S1–S4, which correspond to Study I, Trials 1–4, respectively). The APS and GPS values and the proportion of LP in faeces increased when forage at late maturity stage was finely chopped (p < 0.05; Trial 1). 3.2. Study I The statistical model 6 could explain three/fourth of the variation in measured faeces characteristics, ranging for a R2 value of 0.63 for the proportion of LP to an R2 value of 0.95 for the content of DM in faeces. Advancing maturity stages of forages increased the mean particle size and PDM, and decreased the proportion of SP in faeces (Table 3). Forages in a long physical form compared to chopped resulted in a higher proportion of particles smaller than 0.106 mm by 12.6 ± 2.5% (p < 0.001). Increasing the concentrate to forage ratio (g DM/g DM) increased the APS by 0.07 mm and GPS by 0.05 mm and decreased the proportion of SP in faeces by 0.21% (p < 0.001). The mean particle size, faeces DM content, PDM and the proportions of particles smaller than 0.5 mm were significantly affected by an interaction between animal species and stage of forage maturity at harvest and physical form (Table 3). An increase in the intake of forage NDF per kg of BW increased the mean particle size and the proportion of particles larger than 1 mm, and decreased the proportion of faecal particles smaller than 1 mm (Table 3). The mean particle size was higher, and the faeces DM content and the proportion of SP were generally lower in faeces from cattle than from sheep (p < 0.05; Table 4). Growing animals had significantly lower faeces DM content and a higher

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Table 3 Effect of maturity stage of grass at harvest, physical form, concentrate to forage ratio and intake on faeces characteristics, distribution of particles in individual sieving fractions and overall particle size in faeces from model 61 in Study I. Item

Stage of maturity at harvest Early

Abbreviations in model 6 Number of observations

Medium

p-Value =

Intake

Harvest (H)

Physical form (P)

C:F

H×S

P×S

NDFI/BW5 g/kg

Hj 112

Pm

ˇ1 Kn 61

HSjk

PSmk

ˇ2 No 112

2

3

4

p-Value =

50

20

Faeces characteristics, g/kg 212b Faeces DM PDM6 419c

231a 568b

226ab 680a

0.04 0.001

0.001 0.006

0.02 0.1

0.002 0.001

0.001 0.06

−3.04 2.50

0.03 0.5

Sieving fractions, mm pore size, g/kg 248a <0.106 677a <0.212 <0.5 908a 974 <1.0 25 >1.0

189b 586b 884b 974 25

149c 492c 840c 968 31

0.001 0.001 0.001 0.6 0.5

0.001 0.2 0.008 0.9 0.6

0.001 0.001 0.004 0.9 0.8

0.6 0.4 0.001 0.03 0.03

0.001 0.006 0.001 0.3 0.5

−2.88 −10.8 −3.6 −2.2 2.5

0.3 0.006 0.06 0.06 0.03

0.001 0.001 0.001 0.001 1.0

0.4 0.03 0.2 0.8 0.05

0.002 0.001 0.003 0.001 0.2

0.001 0.008 0.04 0.006 0.8

0.1 0.001 0.005 0.8 0.002

0.0012 0.0373 0.0002 0.2 0.0366

0.4 0.02 0.005 0.9 0.006

Overall particle size, mm Mode PS7 GPS8 APS9 MPS10 95% value

42

Late

p-Value =

0.078c 0.175c 0.255c 0.120c 0.971

0.110b 0.200b 0.282b 0.162b 0.966

0.139a 0.230a 0.319a 0.220a 0.968

Yi. . .o =  + Hj + Sk + Ml + Pm + ˇ1 Kn + ˇ2 No + (HS)jk + (PS)mk + (SM)kl + Ei. . .o Effect of physical form of grasses, chopped (n = 82) or unchopped (n = 30). 3 Effect of concentrate to forage ratio (g DM/g DM). 4 S = effect of animal species. 5 Effect of neutral detergent fibre intake per body weight. 6 Proportion of particle DM in faeces DM. 7 Most frequent particle size. 8 Geometric mean particle size. 9 Arithmetic mean particle size. 10 Median particle size. a–c Means within rows without common superscripts differ (P < 0.05). 1

2

Table 4 Effect of animal species and maturation on faeces characteristics, distribution of particles in individual sieving fractions and overall particle size in faeces from model 61 in Study I. Animal species2 (S) 4

Animal maturation (M) Abbreviations in model 6 Number of observations Faeces characteristics, g/kg Faeces DM PDM5

Sheep Growing

1 2 3 4 5 6 7 8 9

Mature

Growing

p-Value = Mature

S

M

RMSE3

R2

S×M SMkl

22

36

18

36

211 508

401 594

142 579

139 541

0.001 0.5

0.001 0.11

0.001 0.01

31 44

0.95 0.86

215 596 916 981 19

173 505 824 944 56

195 530 830 966 33

0.09 0.001 0.001 0.001 0.001

0.2 0.03 0.4 0.7 0.8

0.9 0.02 0.3 0.03 0.02

36 48 23 16 16

0.79 0.89 0.90 0.63 0.63

0.04 0.001 0.001 0.001 0.001

0.4 0.4 0.4 0.5 0.8

0.5 0.05 0.007 0.7 0.01

Sieving fractions, mm pore size, g/kg 199 <0.106 709 <0.212 939 <0.5 998 <1.0 0 >1.0 Overall particle size, mm Mode PS6 GPS7 APS8 MPS9 95% value

Cattle

0.095 0.161 0.202 0.140 0.645

0.108 0.189 0.263 0.150 0.884

0.117 0.236 0.359 0.192 1.273

Yi. . .o =  + Hj + Sk + Ml + Pm + ˇ1 Kn + ˇ2 No + (HS)jk + (PS)mk + (SM)kl + Ei. . .o Sk in model 6. Residual mean square error from model 6. Ml in model 6. Proportion of particle DM in faeces DM. Most frequent particle size. Geometric mean particle size. Arithmetic mean particle size. Median particle size.

0.116 0.221 0.319 0.192 1.072

0.019 0.019 0.032 0.026 0.154

0.69 0.86 0.86 0.74 0.82

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proportion of SP, but no significant difference in the PDM value and the mean particle size was found. However, there was a significant interaction between species and maturity on the faeces DM content, PDM, the proportions of particles smaller than 0.212 and 1 mm, mean particle size and the 95 percentile value (Table 4). 3.3. Linear model for faeces characteristics Table 5 shows the overall effects of size of the animal, lignification of grass silage NDF, concentrate supplementation and intake of silage NDF per kg of BW on the faeces characteristics, the proportion of particles retained in the different sieving fractions and on the overall faecal particle size values using model 7. Increasing the intake of grass silage NDF relative to BW increased the mean particle size in faeces and the proportion of LP (p < 0.05), whereas the DM content in faeces (p < 0.001) and the proportion of SP (p < 0.01) decreased. Increasing concentrate supplementation increased the most frequent particle size (p < 0.001), the GPS (p < 0.05) and the MPS values (p < 0.01), whereas the proportion of SP decreased (p < 0.001). Increasing BW from 40 kg of lamb to 671 kg in dairy cows led to a linear decrease in the DM content of faeces and an increasing 95 percentile value of LP in PDM (p < 0.01). Increasing lignification of NDF in grass silage increased the content of DM in faeces, the PDM value and the most frequent particle size (p < 0.01), whereas the proportions of SP and VSP decreased (p < 0.05). However, there were significant interactions between BW and the ADL/NDF ratio in grass silage for the proportion of PDM in the lower sieving fractions (p < 0.001) and for the mean particle size (p < 0.01). The effect of increasing the ADL/NDF ratio in grass silage on the proportions of PDM in the lower sieving fractions and on the mean particle size in faeces was amplified by increasing BW (see Table 5). The effect of chopping of forage was tested, but not found to be significant and removed from the model. The results indicated positive Pearson correlations between APS and GPS values (r = 0.98), APS and median particle size values (r = 0.96), APS and most frequent particle size values (r = 0.33) and between the proportion of LP or the proportion of large particles retained in the 2.36 mm sieve fraction and the 95 percentile values in faeces (r = 0.92 and 0.93, respectively) both across and within experiments (p < 0.001). The ratios between the R2 values found by use of model 7 and model 6 ranged between 0.38 for the Mode PS to 0.93 for the content of DM in faeces, and with an overall average ratio of 0.64 for all the presented faeces characteristics (Table 5). 3.4. Study II: validation The following prediction equations obtained for grass fed animals in Study I (Table 5) were used to predict faeces characteristics on independent samples from a wide range of ruminant species from small goats to growing steers fed a wide range of different forage types and characteristics in Trials 6–8: PDM = 24.3 + 0.020BWa + 561ADL/NDFb − 0.372BW ∗ ADL/NDF + 11C:Fc − 208NDFI/BWb a

c

b

(8) b

VSP = 0.43 + 0.00015BW − 1.21ADL/NDF − 0.00531BW ∗ ADL/NDF − 0.15C:F − 7.68NDFI/BW a

(9)

c

b

b

LP = 0.0052 + 0.000041BW − 0.276ADL/NDF + 0.000744BW ∗ ADL/NDF − 0.0090C:F + 1.67NDFI/BW a

b

c

b

GPS = 0.0915 + 0.000094BW + 0.085ADL/NDF + 0.0043BW ∗ ADL/NDF + 0.0521C:F + 4.71NDFI/BW

(10) (11)

where PDM = particle DM (% of DM), VSP (% PDM retained in the bottom bowl), LP (large particles; % of PDM), GPS (geometric mean particle size; mm), and a = kg; b = g/g and c = g concentrate DM/g forage DM. Fig. 1a–d shows the relationship between predicted and observed PDM values, VSP, LP and GPS values in faeces from steers and small ruminants (goat, sheep and llama) fed different forage types, respectively. The RMSPE value for the difference between observed and predicted PDM, VSP, LP and GPS values (mm) were 17% of DM, 0.061% of PDM, 0.017% of PDM and 0.028 mm, respectively. The proportions of VLP and LP appeared to be under predicted, and the PDM values appeared to be over predicted in faeces from sheep fed lucerne silage at low level of NDF intake relative to BW. However, there was no significant mean bias or line bias for the predicted values, and the difference between observed and predicted GPS values were not significantly related to the NDF content or the ADL to NDF ratio in the forages fed. However, the PDM values were over predicted at decreasing NDF content (p < 0.001) and at increasing ADF to NDF ratios (p < 0.001) in the forages. On the contrary, the proportions of VSP and LP in PDM were under predicted at decreasing NDF content (p < 0.001) and at increasing ADL to NDF ratios in the forages (data not shown). 4. Discussion 4.1. Study I 4.1.1. Factors affecting mean faecal particle size The effects of forage and animal characteristics and of NDF intake on the overall mean faecal particle size was studied using models 6 and 7. Stage of forage maturity at harvest, animal species and maturity in model 6 were substituted for forage fibre characteristics (i.e., ADL to NDF ratio) and BW in model 7, respectively. The residual mean square error values were increased for all faeces characteristics by 66 ± 22% (mean ± s.d.) by replacing animal species with BW, and forage maturity with the ADL to NDF ratio, when changing from model 6 to 7. The relatively high mean R2 ratio confirmed that we reached

Table 5 Effect of animal size, diet characteristics and intake on faeces characteristics, distribution of particulate matter in individual sieving fractions and overall particle size in faeces from model 71 in Study I. Item

Intercept

Size of animal BW, kg

Diet characteristics p=

gDM/gDM

BW*ADL/NDF

RMSE2

Intake p=

NDFI/BW5 , g/kg

R2 ratio3

p=

p=

ˇ1 Kn

ˇ2 No

WLpq

−0.503 0.1956

0.001 0.16

1195 5610

0.01 0.001

−26.7 110

0.4 0.02

1.082 −3.72

0.4 0.11

−1.873 −2.0879

0.001 0.5

48 78.3

0.93 0.62

Sieving fractions, mm pore size, g/kg 427 <0.106 <0.212 979 1016 <0.5 992 <1.0 5.2 >1.0

0.146 0.149 0.039 −0.04 0.041

0.10 0.3 0.6 0.3 0.2

−1211 −1770 226 303 −276

0.04 0.06 0.6 0.10 0.2

−147 −264 −43.0 10.3 −9.01

0.001 0.001 0.2 0.4 0.5

−5.31 −9.62 −5.23 −0.82 0.744

0.001 0.001 0.001 0.10 0.2

−7.679 −12.47 −6. 18 −1.628 1.672

0.002 0.002 0.001 0.04 0.03

58.1 94.1 45.2 19.4 19.2

0.54 0.62 0.60 0.65 0.66

Overall particle size, mm Mode PS7 GPS8 APS9 MPS10 95% value

0.0 −0.00009 −0.00011 −0.00011 0.00114

0.3 0.2 0.7 0.2 0.008

0.666 0.0853 −0.050 0.899 −2.016

0.008 0.8 0.9 0.04 0.4

0.0513 0.0521 0.0591 0.0890 −0.0079

0.002 0.03 0.10 0.001 0.9

−0.00061 0.00430 0.00436 0.003848 −0.00080

0.5 0.001 0.004 0.002 0.9

0.00135 0.00471 0.00789 0.00132 0.0354

0.2 0.002 0.001 0.4 0.001

1 2 3 4 5 6 7 8 9 10

524 243

0.0325 0.0917 0.1132 0.0552 0.383

Yn. . .q =  + ˇ1 Kn + ˇ2 No + ˇ3 Wp + ˇ4 Lq + (WL)pq + En. . .q Residual mean square error from model 7. R2 model 7/R2 model 6. Effect of concentrate to forage ratio. Effect of neutral detergent fibre intake per body weight. Proportion of particle DM in faeces DM. Most frequent particle size. Geometric mean particle size. Arithmetic mean particle size. Median particle size.

0.028 0.036 0.056 0.041 0.23

0.38 0.55 0.63 0.47 0.70

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Faeces characteristics, g/kg Faeces DM PDM6

p=

ˇ4 Lq

ˇ3 Wp

Abbreviations in model 7

C:F4

Grass silage ADL/NDF, g/g

Interaction

61

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Fig. 1. (a–d) Relationship between predicted and observed (a) particle dry matter (PDM), (b) proportions of very small particles in PDM (VSP) (Bottom bowl, <0.1 mm) % values, (c) proportions of large particle DM (LP) (>1.0 mm) and (d) geometric mean particle size (GPS) in faeces from goat, sheep, llama and steers fed different forage types (Study II). The line y = x is shown.

a relatively high degree of explanation even by use of BW in combination with the forage ADL to NDF ratio in model 7 compared with animal species and harvest times in model 6. This indicates that the fixed effects of animal species and stage of forage maturity from model 6 were well represented by BW and the ADL to NDF ratio in the forage for the GPS value and faecal characteristics by using model 7. 4.1.2. Forage characteristics The mean particle size increased and the proportion of SP decreased with advancing stage of forage maturity at harvest (p < 0.05; Supplementary Tables S1–S4). These results were confirmed when analyzed across experiments in model 6 including stage of forage maturity at harvest, animal species, animal maturation and intake (Tables 2 and 3). The mean R2 value for this model was 0.80 ± 0.11% (mean ± s.d.), ranging from 0.63 for the mode particle size value to 0.95 for faeces DM content. The lower proportion of small particles in faeces with increased forage maturity was in line with the findings by Shaver et al. (1988). This result might be explained by the slower degradation of forage harvested at a late rather than at early stages of maturity (Buxton and Redfearn, 1997). Also within individual experiments, a mean faecal particle size significantly increased due to advancing stage of maturity at harvest (Rustas et al., 2010; Jalali et al., 2012b). Chopping was found to affect the PDM value and to increase the mean particle size in two studies with cattle (Supplementary Table S1; Randby et al., 2008; Rustas et al., 2010) but no significant effect of chopping was found by use of model 6 in sheep. This could be due to confounding effects with other factors, such as ADL/NDF ratio, BW and mostly an interaction between BW and required work to process the forage particles before swallowing during eating. Furthermore, the chopping process may make the forage particles less retainable in the rumen system and thereby increasing mean faecal particle size (Jaster and Murphy, 1983; Zaaijer and Noordhuizen, 2003). Our results indicated that feeding late cut grass with a high ADL to NDF ratio leads to a low proportion of LP in faeces when adjusted to the same intake level as with earlier cut silages, which is in agreement with Jalali et al. (2012b). Our results indicated that feeding more lignified forage results in a higher proportion of PDM compared to feeds with lower ADL to NDF ratio (p < 0.001, Tables 3 and 5; p < 0.01, Supplementary Tables S1–S4). Zaaijer and Noordhuizen (2003) reported that feeding immature forage to cattle lead to a lower DM content in faeces than when feeding mature forages. We found similar results in cattle (Supplementary Table S3) and in other studied ruminant animals by use of model 7 (see Table 5).

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4.1.3. Animal characteristics The higher proportion of SP in faeces of large ruminants compared to small ruminants indicates that the small ruminant species swallow particles of smaller size than do large ruminants due to more particle size degradation during eating (Domingue et al., 1991b) and ruminating (De Boever et al., 1990). Poppi et al. (1980) demonstrated that in sheep fed forage of different maturities, 1–2% of the faeces particles were LP, in line with the range of values presented in Table 4. Adjusting for forage characteristics in model 7 eliminated the correlation between forage characteristics and animal. The higher mean faecal particle size of large ruminant species in our study is in line with the findings of Udén and Van Soest (1982), Clauss et al. (2002) and Fritz et al. (2009). 4.1.4. Intake In both models 6 and 7 the mean faeces particle size and the proportion of LP increased with increasing intake of forage NDF per kg BW. The increases in the proportion of LP relative to SP in faeces with higher NDF intake might be explained by a relatively higher passage rate of LP than of SP and shorter retention time of digesta and lignin in the rumen system (Mudgal et al., 1982). The experimental diets in Study I included grass silages with or without supplementation with small amounts of concentrates. We observed an increasing mean particle size, PDM and a decreasing proportion of SP in faeces due to increasing concentrate supplementation, possibly due to the physical processing of the ingredient feed in the concentrates which are most likely not exposed to further degradation by rumination. The relatively low concentrate to forage ratio (0.49; Table 1) in this study might not be representative for diets with higher proportion of concentrate, low rumen pH and low fibre digestion. Increased NDF intake per kg of BW resulted in increased mean faecal particle size and proportion of LP, a decreased proportion of particles smaller than 1 mm and a decreased DM content in faeces which is most likely due to higher passage rate. The results in this study indicated that the mean particle size and the proportion of SP and LP in faeces were significantly affected by both animal size and forage characteristics, but in different ways. The proportion of LP in faeces was increased by animal BW and NDF intake, whereas the proportion of SP in faeces was decreased by increased forage fibre lignification, and by increased NDF intake and concentrate supplementation. Finally, our model confirmed our hypothesis that the increasing ADL to NDF ratio in grass silage, increasing animal BW and increasing NDF intake are the major factors affecting the faeces characteristics. The most likely mean particle size and proportion of LP in faeces from a ruminant animal can be explained from the BW, ADL/NDF ratio in the grass silage and their interaction, the forage to concentrate ratio and the intake of forage NDF/BW by use of the values shown in Table 5. 4.2. Study II: validation The validation was done on quite different ruminant species fed different diets in order to challenge the developed models. The PDM values decreased and the proportion of VSP increased in all the individual trials due to early harvest and lower ADL to NDF ratio in grass silages (Supplementary Table S5), hay (Jalali et al., 2012a) and whole crop barley silage (Rustas et al., 2010). However, the model 8 appears to over predict the PDM values and model 9 to under predict the VSP values in faeces from sheep fed lucerne silages when using the ADL to NDF ratio as the forage characteristic. The NDF content (g/kg DM) in the grass silage in Study I ranged from 410 to 630 compared with a range from 330 in early harvested lucerne silage to 810 in grass seed straw. However, the model 7 parameterized on faeces from sheep and cattle fed grass silage predicted the PDM, VSP and LP values fairly well in goats, sheep and llamas fed grass hay or grass seed straw with 810 g/kg NDF in DM. Contrary, the models 8, 9 and 10 appeared to overestimate the PDM values and underestimate the VSP and LP values in faeces from sheep fed lucerne silages. The lucerne silages had a combination of low NDF contents of 330–420 g/kg DM and nearly twice the ADL to NDF ratios compared to the grass silages fed in Study I. The size of ruminants species did not affect the PDM value (Tables 4 and 5) which is in line with results found by Jalali et al. (2012a), whereas supplementation with concentrate and feeding early harvested grass silage with decreasing ADL to NDF ratio in Study I decreased the PDM values, and likewise early harvested lucerne silages had lower PDM values compared with later harvest (see Supplementary Table S2). This might be due to increased digestibility leading to higher microbial protein synthesis in the rumen, which further may lead to higher protein content and lower content of undigested NDF in faeces and consequently, a higher protein to NDF ratio in faeces. Forages such as lucerne silage and whole crop barely silage (WCBS) have much higher ADL/NDF content compared with grass silages of similar digestibility, which may explain the over prediction of the PDM from the ADL/NDF ratio. The model was derived from ruminants fed grass silage, and lucerne cell walls differ from grasses with an apparent uneven distribution of the lignification of cell walls in leaves versus stems, which might explain the under prediction of the proportion of VSP in faeces for sheep fed lucerne silages. Kornfelt et al. (2013) observed two peaks on the density distribution of particle length and width values in faeces from cows fed lucerne silages, whereas Jalali et al. (2012a, 2012b) observed only one peak value in faeces from sheep, goat and llama fed grass silage, grass hay and straw, which could be explained by different characteristics of leaf and stem fractions in lucerne. Model 11 appears to be able the address the effect of different forage types and a wide range of forage qualities on the GPS value in faeces from both small and large ruminants, and with a clear demonstration of smaller particles in faeces from small compared to large ruminants, which is in agreement with Clauss et al. (2002, 2010). The PDM value, the proportions

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of particles in the individual sieving fractions and the mean particle size appears as footprints of the quality of the forage eaten after correction for the size of the animal. The effect of body size, diet characteristics and NDF intake on faeces characteristics can be predicted by used of the established models 8–11 and used as reference values in future studies. The derived model 11 predicts the GPS value in faeces from growing steers of 412 kg to be 2 times higher compared with a sheep of 60 kg, when both have an intake of 1.0% NDF of BW from WCBS (Rustas et al., 2010). In addition, the most likely geometric mean particle size and the LP values in faeces can be predicted from animal and dietary characteristics by use of model 11. The predicted values can be used to establish threshold values for faeces characteristics in new studies and in commercial herds. In commercial herds, these threshold values could be combined with simple barn sieving techniques (Nørgaard et al., 2007; Jalali et al., 2012b) to monitor the selective retention of LP in the rumen of intensively fed ruminants. 5. Conclusions Sheep and other small ruminants produce faeces with a higher DM content, a higher proportion of SP and a lower mean particle size compared to cattle. Both animal and dietary characteristics strongly affected the faecal particle size, which increased with increasing BW, forage maturity at harvest, ADL to NDF ratio in forage, concentrate supplementation and forage NDF intake. The proportion of SP decreased and the most frequent particle size increased due to supplementation of concentrate, increased intake of forage NDF and increasing forage maturity at harvest. Furthermore, the effect of increasing ADL/NDF ratio in grass silage on the proportion of SP and on mean particle size appears to be amplified by increasing BW. 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