- Email: [email protected]
Efficiency of utilisation of different diets with contrasting forages and concentrate when fed to sheep in a discontinuous feeding pattern
Available online at www.sciencedirect.com
Livestock Science 119 (2008) 77 – 86
www.elsevier.com/locate/livsci
Efficiency of utilisation of different diets with contrasting forages and concentrate when fed to sheep in a discontinuous feeding pattern R. Kaur ⁎, K.S. Nandra, S.C. Garcia, W.J. Fulkerson, A. Horadagoda M.C. Franklin Laboratory, University of Sydney, Camden, NSW-2570, Australia Received 7 September 2007; received in revised form 6 March 2008; accepted 6 March 2008
Abstract The effects of feeding different levels of forages and concentrate, in a discontinuous feeding pattern, on the efficiency of feed utilisation and rumen function were studied using rumen fistulated sheep. Experiment 1 was a 4 × 4 latin square design to determine the whole tract digestibility and rumen characteristics of diets comprising 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate (energy-dense dairy pellets) with the rest of the diet being a combination of fresh short rotation ryegrass (Lolium mutiforum) and conserved (lucerne hay and maize silage) forages. In Experiment 2, the rumen degradation characteristics of feed ingredients were determined using the nylon bag technique. Daily dry matter intake (either expressed as g/kg LW or g/kg W 0.75) was 10% lower (p = 0.03) for the C15 diet compared with C25, C35 and C45 diets. The apparent in vivo digestibility of dry matter (DM) for C15 diet was 4% higher (p = 0.04) than the C35 and C45 diets which may be attributed to the high quality of the forage (ryegrass) used. Fibre digestibility decreased as proportion of concentrate in the diet increased. However, this was unlikely due to changes in the rumen fermentation pattern, as neither pH (6.1 ± 0.23) nor ammonia concentration (24.4 ± 6 mg/dl), were different (p N 0.05) among diets. Instead, the lower fibre digestion was most likely the result of different type and proportion of fibre among diets, as total rumen degradability and rate of fibre degradation in the rumen were higher (p = 0.001) for ryegrass than for other feedstuffs. There was no significant difference in total nitrogen balance and urinary allantoin excretion among diets, which indicated similar total microbial protein synthesis (MPS). The asynchrony observed, for N and energy availability in the rumen for different diets using Sinclair et al. [Sinclair, L.A., Garnsworthy, P.C., Newbold, J.R., Buttery, P.J., 1993. Effect of synchronizing the rate of dietary energy and nitrogen release on rumen fermentation and microbial protein synthesis in sheep. J. Agric. Sci. 120, 251–263] equation, was due to the feeding pattern used in this study leading to excess of N in relation to total organic matter digested in the rumen. In conclusion, feeding concentrates in the diets as PMR with conserved forages in a discontinuous feeding pattern may be valuable to develop feeding strategies in a pasture based system for high producing dairy cows without affecting the rumen system. Crown Copyright © 2008 Published by Elsevier B.V. All rights reserved. Keywords: Forage(s); Concentrate; Rumen parameters; Fibre digestion; Microbial protein synthesis
1. Introduction
⁎ Corresponding author. Tel.: +61 2 9351 1709; fax: +61 2 46552374. E-mail address: [email protected] (R. Kaur).
Forages are the primary source of nutrients for ruminant animal production, but in order to achieve high production/cow at the farm level more supplementary
1871-1413/$ - see front matter. Crown Copyright © 2008 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2008.03.001
78
R. Kaur et al. / Livestock Science 119 (2008) 77–86
feed is needed in the form of high energy-dense concentrates (Garcia and Fulkerson, 2005). In the Australian dairy industry, for instance, the use of concentrates has increased substantially over the past few years (Fulkerson and Doyle, 2001). Concentrates are used more frequently to address the large variation in seasonal pasture growth, variability in rainfall within the year, the desire to exploit the genetic production potential of animals and the price incentives provided by milk processors to produce milk at times of low pasture growth (Garcia and Fulkerson, 2005). However, when fed twicea-day at milking, the response to feeding high amounts of concentrates is low (Fulkerson et al., 2000; Walker et al., 2001) likely due to the adverse influence on rumen environment. In this regard, feeding high levels of concentrates, over short periods during milking, causes decrease in rumen pH leading to a decrease in fibre digestion (Dixon and Stockdale, 1999). However, the effect of a drop in rumen pH is likely to be dependent on the type of fibre being fed; thus, more rapidly digested fibre is less likely to be affected than slowly degraded fibre. Poore et al. (1990) found that concentrate level in the diet has more influence on the passage rate of low (wheat straw), than of high, quality forage (lucerne hay). Similarly, Grant (1994) noted a greater reduction in fibre digestibility of bromegrass hay than lucerne hay when rumen pH was lowered in vitro through addition of raw sorghum starch. Many studies have looked at the effects of the ratio of forage to concentrate on dry matter intake and digestive function in sheep using complete diets (e.g. Carro et al., 2000; Valdes et al., 2000), or supplementing concentrates to grazing dairy cattle (e.g. Fulkerson et al., 2006). However, less work has been undertaken on feed efficiency, rumen characteristics and synchrony of diets varying in the proportion of fresh pasture, conserved forages (and therefore changing the fibre type) and concentrates typically fed to dairy cows. It is commonly accepted that levels up to about 35% concentrate do not adversely affect fibre digestion. However, even diets with over 35% concentrate will not necessarily affect fibre digestion, as this will depend on other factors such as fibre type, frequency and method of feeding the extra concentrate (Garcia and Fulkerson, 2005). Thus, feeding the extra concentrate as partial mixed ration (PMR) is less likely to affect rumen pH and therefore fibre digestion. In addition, this practice can result in better nitrogen to energy synchronisation in the rumen in comparison to the traditional concentrate/grazing system. This is because the relatively longer periods that occur in the latter system between feeding concentrates to cows in the dairy and grazing are avoided. We used rumen fistulated
sheep to test the above hypothesis that there is no effect of increased levels of concentrate in the diet on rumen pH but MPS can be improved when fed as PMR in a discontinuous feeding pattern. The use of sheep as a model is supported by several authors (e.g. Thomas and Campling., 1977; Aerts et al., 1984) who reported small differences between sheep and cattle in terms of feed utilisation and rumen degradability characteristics (Nandra et al., 2000). It has also been reported (Doreau et al., 2000) that difference between sheep and cattle is evident only when diets with N60% concentrate are fed. Recently, the development of a new support system to feed dairy cows in the UK (Feed into Milk) has concluded that differences between cows and sheep (in terms of ME supply), were minimal (Thomas, 2004). 2. Materials and methods Two experiments were conducted using rumen-fistulated Border Leicester castrate male sheep (with average weight of 55 ± 1.3 kg) housed in individual metabolism crates in a temperature controlled animal house. In Experiment 1, four diets with different forage to concentrate ratio were fed in a latin square design to determine the digestibility coefficients, rumen characteristics and allantoin excretion, as a measure of microbial protein synthesis (MPS). In Experiment 2, the rumen degradation characteristics of the different feed ingredients used in Experiment 1 were determined. 2.1. Experiment 1 2.1.1. Animals and diets The metabolic crates were designed so that the animals had enough space to sit and stand freely. The animals had free access to drinking water and separators were attached to the floor of the crates to collect faeces and urine. The four diets offered ad libitum comprised 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate (dairy pellets) with the remaining of the diet
Table 1 Chemical composition (g/kg DM); and metabolisable energy (ME) in MJ/kg DM of different feed ingredients used for the formulation of different diets Chemical composition (g/kg DM)
Pellets
Ryegrass
Lucerne hay
Maize silage
Organic matter Crude protein Neutral detergent fibre Acid detergent fibre Hemicellulose Water soluble carbohydrates In vitro DMD (%) Metabolisable energy (MJ/kg DM)
863 204 161 71 95 66 81.7 11.1
839 261 409 234 191 143 76.8 11.2
888 220 378 299 89 34 67.0 9.7
933 63 484 297 199 27 61.3 9.6
R. Kaur et al. / Livestock Science 119 (2008) 77–86
79
made up of short rotation ryegrass, lucerne hay (Medicago sativa) and maize silage (Zea mays). The chemical composition of the feed ingredients is shown in Table 1. The four dietary treatments were randomly allocated to 4 animals over 4 replicates in a latin square design. The proportion; and chemical composition of each diet is shown in Table 2.
Table 3 Feeding schedule followed for the in vivo apparent digestibility trial in sheep fed diet with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate
Time of feeding
C15
C25
C35
C45
2.1.2. Intake and digestibility measurement Each of the four experimental periods comprised a 15-day adaptation period followed by a 5 day sampling period. Rumen fluid was collected at the end (6th day) of each sampling period. Animals were weighed twice at the beginning and end of each experimental period. As we were interested in representing diets fed to dairy cows, the timing of the feeding was varied to mimic actual feeding times of dairy cows in a typical situation on a dairy farm (Table 3). Residual feed and faeces were collected and weighed every day, dried at 60 °C for 48 h in a fan-forced oven and then bulked over the period. Urine was collected each day and 10% H2SO4 added to prevent degradation of allantoin and loss of volatile N. Daily urine outputs were diluted with water to constant weight (4 kg) for subsequent analysis.
7:00 A.M. 8:00 A.M. 1:00 P.M. 2:00 P.M. 3:00 P.M.
50% C 100%PMR 50% C 0 RG
50% C 100%PMR 50% C 0 RG
25% C 70%PMR 25% C 30%PMR RG
25% C 70%PMR 25% C 30%PMR RG
2.1.3. Rumen fluid samples Rumen fluid was collected at the end of each sampling period through the rumen fistulae using a suction pump at 0, 1, 2, 3, 4, 6, 8, 10, 13 and 14 h of feeding. About 20 ml of the rumen fluid was removed and analysed immediately for pH using a WP-90 waterproof specific ion-pH-mV temperature meter (made by TPS Australia). The fluid was then strained through two layers of cheese cloth and acidified with 4 drops of concentrated H2SO4 (98%) to prevent loss of volatile N. Samples were then frozen (−20 °C) for subsequent ammonia analysis. Ammonia was determined colorimetrically by the phenol-hypochlorite reaction adapted from the method of McCullough (1967). Table 2 Diet composition (% total DM); chemical composition (g/kg DM); and metabolisable energy (ME) in MJ/kg DM of diets with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate Diet (% Concentrate) C15
C25
C35
C45
Diet composition (% DM) Concentrate Ryegrass Lucerne hay Maize silage
15 75 5 5
25 50 10 15
35 40 10 15
45 30 10 15
Chemical composition (g/kg DM) Organic matter Crude protein Neutral detergent fibre Acid detergent fibre Cellulose Hemicellulose Water soluble carbohydrates Metabolisable energy (MJ/kg DM)
850 240 374 216 161 172 120 11.0
864 213 355 209 154 158 96 10.7
866 207 331 193 140 148 88 10.8
869 201 306 177 126 139 80 10.9
Diets
C = concentrate (pellets); PMR = partial mixed ration that includes pellets, lucerne hay and maize silage; and RG = ryegrass. 100% PMR = 50% pellets + 100% lucerne hay + 100% maize silage. 70% PMR = 35% pellets + 70% lucerne hay + 70% maize silage. 30% PMR = 15% pellets + 30% lucerne hay + 30% maize silage.
2.2. Experiment 2 2.2.1. Animals and diets Six rumen fistulated sheep were used to measure the in sacco degradation characteristics of organic matter (OM), nitrogen (N) and NDF in the concentrate, pasture, lucerne hay and maize silage. Animals were fed a basal diet comprising 25% pellets, 50% ryegrass, 15% lucerne hay and 10% maize silage at maintenance level, which represented approximately the average composition of the four diets used in Experiment 1. Due to physical limit to include all bags from the four feeds, two feeds were tested in three sheep and the other two feeds in another three sheep. 2.2.2. Degradation kinetics and synchrony index For the degradability studies, samples of ryegrass and maize silage were taken fresh and chopped into 1 cm length, samples of chaffed lucerne hay and pellets were taken as such. Approximately 8–10 g of pellets or lucerne hay and 10–20 g of maize silage or ryegrass was placed in dacron bags (80 × 120 mm, 36– 38 mm pores). Seven bags per test feed were inserted in the rumen of the fistulated sheep. The bags containing pellets (protein sample) were withdrawn after 2, 4, 8, 16, 24, 48 and 72 h, while bags containing ryegrass, maize silage and lucerne hay (forage samples) were withdrawn after 3, 6, 9, 16, 24, 48 and 72 h to allow time for complete asymptote degradation. As minimal difference was observed between 48 and 72 h degradation, forage samples were not incubated for 96 h. After removal from the rumen, bags were rinsed under cold water, and then washed for 30 min on a cold rinse cycle in a washing machine. The value at time zero was obtained by washing one bag in triplicate containing the test feed without incubation in the rumen. Bags were dried at 60 °C in a fan-forced oven. Disappearance of dry matter (DM), N or NDF was measured as the loss of weight of the bag contents at each incubation time. The data obtained were then fitted to a model based on McDonald (1981) as per Eq. (1): P ¼ A þ B 1 eCt ð1Þ
80
R. Kaur et al. / Livestock Science 119 (2008) 77–86
where ‘P’ is the cumulative amount degraded at time ‘t’, A is the initial intercept or amount ‘degraded’ at time zero (soluble fraction), B is the degradable part of the insoluble fraction and C is the fractional rate of degradation of fraction ‘B’. The effective degradability (Ed) was calculated as per Orskov and McDonald (1979) using the Eq. (2): EdðkÞ ¼ A þ ð BC Þ=ðC þ k Þ⁎exp½ðC þ k Þ⁎t0
ð2Þ
where ‘A’ represents the rapidly degradable component (%), ‘C’ is the rate constant from time t0 onward (% h− 1), ‘B’ is the water insoluble but potentially degradable fraction (%) and ‘k’ is the passage rate (% h− 1). The hourly quantity of N to OM degraded for each ingredient from each feeding time was calculated as the difference between the N to OM degraded at successive hours and allocated to the appropriate hour of the day. From the hourly quantity of N and OM degraded, a synchrony index (SI) of N to OM was calculated as described by Sinclair et al. (1993) as per Eq. (3): qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2 N=OMÞ X ð25hourly 24 25 ð3Þ 25 124 where 25 = 25 g of N/kg of OM truly digested in the rumen, which is assumed to be the optimal ratio (Czerwaski, 1986). An SI of 1.0 represents perfect synchrony and values less than 1.0 represents a degree of asynchrony. 2.3. Chemical analysis Feed and residual samples; faecal samples; residual samples in the nylon bags; were analysed individually for DM content by drying at 60 °C for 48 h in a fan-forced oven. Ground samples (1 mm screen) were analysed for: OM after igniting in a muffle furnace at 600 oC for 3 h; N using a Leco FP-428 analyzer (Leco Corp., St. Joseph, MO, USA); ADF using the method of Van Soest (1963); and NDF using a modification of Van Soest (1963) with both amylase and amylopectin enzymes. Metabolisable energy (ME) was calculated using Eq. (4) (SCA, 1990). MEðMJ=kg DMÞ ¼ ½0:17 DMD ðkÞ 2:0
ð4Þ
where DMD is the in vitro DM digestibility (%DM). The water-soluble carbohydrate content of feeds was determined using an autoanalyser using a modification of the method of Smith (1969). Allantoin excreted in the urine was calculated by the method of Chen and Gomes (1992). Digestible OM fermented in the rumen (DOMR) was estimated from the digestible organic matter intake (DOMI) and rumen degradability of each ingredient (determined in Experiment 2) using Eq. (5). X Intakei Edi ðat 0:05Þ kOMi ð5Þ Total dry matter intake where i relates to individual ingredient (pellets, ryegrass, lucerne hay and maize silage).
2.4. Statistical analysis Statistical analyses were performed using GENSTAT 9 (Lawes Agricultural Trust, 1983). In Experiment 1, all the data were analysed in latin square design using ANOVA to examine the differences between animal, period, and diet, except that rumen pH and ammonia concentration were analysed using REML procedure to test the effects of period, animal, sampling time and diet. The model used for analysis was: Yijkl ¼ x þ Di þ Pj þ Ak þ Tl þ eijkl Where: Yijkl is independent variable (pH or ammonia concentration); Di (i=1, 2, 3, 4) is the fixed effect of diet; Pj ( j= 1, 2, 3, 4) is the period effect; Ak (k =1, 2, 3, 4) is the animal effect; Tl (l= 0, 1, 2, 3, 4, 6, 8, 10, 13, 14), and eijkl is the random error. In Experiment 2, data were analysed in complete randomised design using ANOVA.
3. Results 3.1. Chemical composition Pasture (ryegrass) had a comparable level of metabolisable energy (ME, 11.2 vs 11.8 MJ/kg DM) to pellets, but a higher content of crude protein (CP, 26% vs 20%), neutral detergent fibre (NDF, 41% vs. 16%), and aciddetergent fibre (ADF, 23% vs. 7%). Diet C15 had 75% ryegrass and therefore ryegrass reflected mostly the nutrient content of the diet. The ME value was not significantly different among diets ( p = 0.08, See Table 2). 3.2. Intake and in vivo digestibility The intake and in vivo digestibility coefficients of the different diets is presented in Table 4. Dry matter intake expressed as g/kg W 0.75 ( p = 0.03) or as g/kg live weight was 10% higher ( p = 0.05) for C25, C35 and C45 than for C15. The digestible organic matter intake (DOMI) and digestible organic matter fermented in the rumen (DOMR) were 6–7% higher (p b 0.01 and p = 0.02) for C25 and C45 diets (mean = 952 and 581 g/kg DM/day) than for C15 and C35 diets (mean = 885 and 549 g/kg DM/day), respectively. The in vivo apparent digestibility of DM was higher ( p = 0.03) for C15 compared to diets with N 35% concentrate. The digestibility of ADF was 22% higher ( p = 0.01) for the C15 diet compared to the average of all other diets while the NDF digestibility was significantly different for most diets, being 19% higher ( p b 0.01) for C15 (0.75) in comparison to C35 and C45 diets (0.63). The hemicellulose digestibility also followed the same pattern as NDF but the differences between diets were not significant ( p = 0.22).
R. Kaur et al. / Livestock Science 119 (2008) 77–86
81
Table 4 Dry matter intake and digestibility coefficients (in vivo) in sheep fed diets with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate Diet C15
C25
C35
C45
sed
p value
Daily Intake Dry matter (g/kgLW) Dry matter (g/kg W0.75) DOMI (g/kg DM) DOMR (g/kg DM)
20.5a
23.0b
22.6b
22.5b
0.74
0.05
55.8a
62.6b
60.7b
60.9b
1.72
0.03
886.9a 967.6b
884.7a
938.0b
17.6 b0.01
558.8a 590.3b
539.7a
572.2b
11.8
0.02
In vivo digestibility coefficients Dry matter Acid detergent fibre Neutral detergent fibre Hemi cellulose
0.76a 0.67a
0.75abc 0.60b
0.73bc 0.56b
0.73bc 0.93 0.53b 2.82
0.75a
0.68b
0.63c
0.63c
1.9 b0.01
0.79
0.78
0.68
0.71
5.2
0.03 0.01
0.22
where DOMI = digestible organic matter intake and DOMR = digestible OM fermented in the rumen. Values in the same row with different letters differ significantly (p b 0.01).
3.3. Rumen pH and ammonia concentration Mean (±se) daily rumen pH was similar (p = 0.95) for all the diets (6.1 ± 0.2), whilst within day changes in rumen pH were related to the time of feeding (Fig. 1a). In the morning, the drop in pH was less after feeding concentrate and immediately after feeding PMR, pH rose to 6.32 (average of four diets), while the fall in pH was high after feeding concentrate in the afternoon. The rumen pH was numerically lowest for C35 (5.44) and C45 (5.54) diets at about 2 h after feeding ryegrass in the afternoon even though 30% PMR was fed in these diets compared to no PMR fed for diets C15 and C25. There was a steady increase in pH observed for all diets after 5 h of feeding ryegrass. Mean daily concentration of ammonia (mg/dl) was not significantly different (p = 0.61) among diets (24.4 ± 6.0) nor was significant (p = 0.74) the interaction between diet and time. Similar to pH, changes in rumen ammonia were related to time of feeding with a marked decline in ammonia concentration after feeding concentrate in the morning and a sharp rise in ammonia concentration after feeding ryegrass in the afternoon (Fig. 1b). The ammonia concentration was as low as 5.9 mg/dl and as high as 40.7 mg/dl in rumen fluid for C15 diet.
Fig. 1. (a) Rumen pH and (b) rumen NH3 concentration (mg/dl) at different times after feeding (‐‐‐‐‐) 15%, (●) 25%, (▲) 35% and (■) 45% concentrate. Arrows indicate time of feeding concentrate (C), partial mixed ration (PMR) and ryegrass (RG).
3.4. Nitrogen balance and microbial protein synthesis Table 5 shows the results of N balance and allantoin excretion in urine as a measure of microbial protein synthesis (MPS). Nitrogen intake expressed on live weight basis was not significantly different among diets ( p = 0.23). The total Table 5 Nitrogen balance (g/kg live weight per day) and allantoin excretion (mg/d per kg live weight and mmol/day) in sheep fed diets with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate Diet
N intake (g/kg LW/day) Urinary N (g/kg LW/day) Fecal N (g/kg LW/day) N balance (g/kg LW/day) Allantoin (mg/kg LW/day) Allantoin (mmol/day)
C15 C25 C35 C45 sed
p value
0.79 0.21 0.19 0.39 31.8 11
0.23 0.47 0.63 0.79 0.55 0.12
0.79 0.21 0.17 0.41 30.6 11
0.76 0.19 0.17 0.40 30.1 9.7
0.73 0.18 0.16 0.39 33.3 11.6
0.03 0.02 0.01 0.03 2.34 0.65
82
R. Kaur et al. / Livestock Science 119 (2008) 77–86
excretion of nitrogen (when corrected on live weight basis) was similar among all the diets ( p = 0.22), urinary excretion being 51% and faecal excretion being 49%. Nitrogen retention was similar among all diets ( p = 0.79) with average retention of 53% of the total N intake. Allantoin excretion was not significantly different among diets, even after correcting by live weight ( p = 0.55). 3.5. Rumen degradability and Synchrony Index The in sacco degradability parameters of OM, N and NDF for different feed ingredients used are shown in Table 6 and the degradability of DM and NDF in relation to incubation time in the rumen are given in Fig. 2. The water insoluble, but potentially degradable, fraction of OM and N were significantly higher ( p b 0.001) for ryegrass than other ingredients leading to higher potential degradability and higher effective degradability (Ed at 0.05/h = 75.1% and 81.8%, respectively). The degradation of NDF was higher ( p b 0.001) for ryegrass indicated by its 86.9% degradability within 24 h and higher rate of degradation (13.4%/h). The potential degradability and
Table 6 Degradability parameters; water soluble component (A), water insoluble component (B), rate of degradation (C), effective degradability (Ed)% at outflow rate of 0.05/h for different feed ingredients Feed ingredients
A (g/g)
B (g/g)
C (/h)
Ed (0.05/h, g/g)
Organic matter Pellets Ryegrass Lucerne hay Maize silage s.e. P value
b
0.36 0.20c 0.29a 0.39b 0.02 b0.001
0.53 0.76c 0.42a 0.44ab 0.04 b0.001
0.056 0.158c 0.111ac 0.034b 0.03 0.01
0.74 0.75b 0.56a 0.56a 0.15 b0.01
Nitrogen Pellets Ryegrass Lucerne hay Maize silage s.e. P value
0.29c 0.22d 0.37a 0.72b 0.02 b0.001
0.66c 0.77d 0.60a 0.19b 0.02 b0.001
0.056 0.235 0.102 0.019 0.079 0.22
0.67c 0.82d 0.75ab 0.80bd 0.16 b0.001
0.012b 0.134c 0.077a 0.026b 0.017 0.001
0.27a 0.61b 0.24a 0.22a 0.23 b0.00
Neutral detergent fibre Pellets − 0.179b Ryegrass − 0.105c Lucerne hay − 0.023a Maize silage − 0.09a s.e. 0.029 P value 0.003
b
1.18c 1.04c 0.44a 0.76b 0.09 0.002
ab
b
Values in the same column (for each different variable) with different letters differ significantly ( pb0.001 and p b or = 0.01).
Fig. 2. (a) DM and (b) NDF degradation of rye grass (‐‐‐‐‐), lucerne hay (■), maize silage (●) and pellets (▲).
effective degradability (at 0.05/h) of NDF for ryegrass was 93.1% and 60.6% which was significantly higher ( p b 0.001) than other feed ingredients.
Fig. 3. Daily variation in the ratio of degradable nitrogen to rumen degradable organic matter (N: OM) after feeding (‐‐‐‐‐) 15%, (●) 25%, (▲) 35% and (■) 45% concentrate. Arrows indicate time of feeding concentrate (C), partial mixed ration (PMR) and ryegrass (RG).
R. Kaur et al. / Livestock Science 119 (2008) 77–86 Table 7 Average daily ratio of ERDP and FME, ratio of rumen degradable N to rumen degradable organic matter (N:OM) and synchrony index in sheep fed diets with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate Diet C15 ERDP/FME ratio N:OM ratio Synchrony Index
C25 a
18.5 53a 0.29
C35 b
16.0 47b 0.36
C45 c
14.8 45c 0.36
d
13.6 43d 0.37
sed
p value
0.15 0.35 0.03
b0.001 b0.001 0.09
ERDP is effective rumen degradable protein and FME is fermentable metabolisable energy. Values in the same row with different letters differ significantly (p b 0.001).
Significant differences (p b 0.001) were observed among diets in the hourly ratio of N to OM degraded in the rumen (Fig. 3). In the morning, before feeding, the ratio of N to OM degraded in the rumen was well above 25 (optimum level for MPS according to Sinclair et al., 1993) for all diets except C15, which increased after feeding and was above the optimum level throughout the day. Synchrony Index was similar (p = 0.09, mean = 0.35) among diets. All these diets were significantly different (p b 0.001) for the average daily ratio of N to OM degraded in the rumen (Table 7). Effective rumen degradable protein (ERDP) to fermentable metabolisable energy (FME) ratio, calculated using in sacco degradation characteristics of N and OM in the rumen (see Table 7), was significantly different (p b 0.001) among diets. The ratio was above the ideal value of 11 required for MPS (AFRC, 1993). 4. Discussion Our study was unique as it was mainly focused to see the effects of increased levels of concentrate in the diet, when fed as PMR in a discontinuous feeding pattern, on feed efficiency, rumen parameters and synchronisation of energy and N in the rumen. Overall, we can say that inclusion of concentrate at 45% level of the diet (both fed separately and as PMR) did not influence rumen pH or MPS and the decrease in dry matter and fibre digestibility were related with the type and amount of fibre in the diet. The total DM intake of sheep on the C15 diet was lower in comparison with sheep fed C25, C35 and C45 diets. This has been previously reported by numerous workers in both sheep and cattle (Mould et al., 1983; Kolver and Muller, 1998; Dixon and Stockdale., 1999). In the present study, the higher intake by sheep fed the C25, C35 and C45 diets may have been due to higher proportion of concentrate in the diets in comparison
83
to C15. This is possible as cows offered concentrate usually replace part of the pasture (substitution); if substitution rate is b1, then total DMI will be higher in supplemented animals than non-supplemented ones (Dixon and Stockdale, 1999). The lower DM and fibre digestibility of diets with high level of concentrate could be due to the less proportion of high quality pasture (ryegrass) in general and specifically its (ryegrass) NDF degradability (Effective Degradability of 61% at 0.05/h), which is reflected in the overall high digestibility of C15 diet and explains the decline in rumen degradability of fibre as the proportion of concentrate in the diet increases (Fig. 2b). Further, the type of fibre in the diet also accounts for the difference in fibre degradation of the diets. If we quantify the effect of fibre degradation of each ingredient within the diets by considering an outflow rate of 0.05/h, 88% of total fibre was digested in the rumen for diet C15 within 24 h compared with 50% digested for diet C45. Thus, the combination of more fibre (more ryegrass in the diet) and higher fibre digestibility (fibre type, see Fig. 2b) resulted in nearly twice as much fibre digested in the rumen for C15 than the other diets. Further, Faichney (1993) related low fibre digestion with an increase in retention time in the rumen that decreases the rate of passage of digesta to the abomasums (See also Garcia and Fulkerson, 2005). These factors may influence DM intake because of passage rate is one of the most important factors influencing DM intake (Offer and Nixon, 2000; Poppi et al., 2000). Another possible explanation for the lower fibre digestion in diets with N 25% concentrate is an associative effect of starch digestion on fibre digestion (Wales and Doyle, 2003). In fact previous studies (Orskov, 1987; Beever, 1993) have suggested that feeding rapidly fermentable concentrates favours the growth of amylolytic bacteria resulting in low rumen pH and adversely affecting the growth of cell wall digesting bacteria and, thus, the rate of fibre digestion. However, in our study, the rumen pH was not significantly different among diets therefore it is unlikely that rumen pH could have affected rumen microbes. In fact, the relationship between pH and fibre digestion is more important with diets containing fibre of lower digestibility. “Garcia and Fulkerson (2005) reported that the digestion of fibre in high quality pasture was probably less affected by a drop in pH than poor quality pasture or TMR, as significant amounts of plant cell wall can be digested in the rumen even when pH is slightly below 6 for most of the day." This is confirmed by our study, in which fibre digestion was very high (particularly for ryegrass) despite the fact that rumen pH was below 6.0
84
R. Kaur et al. / Livestock Science 119 (2008) 77–86
from 4 pm to 9 pm Thus the fibre digestibility may be not affected by rumen pH but by other factors such as the amount of fibre in the diet; time and frequency of feed delivery; type and level of concentrates; and social and feeding behaviour (Garcia and Fulkerson, 2005). In the present study, the crude protein degradability of ryegrass was 99% at 24 h with an effective degradability (Ed at 0.05/h) of nitrogen for ryegrass being 82% compared with 67% for pellets. van Vuuren et al. (1992) and Garcia et al. (2000) have reported N degradabilities greater than 80% for fresh ryegrass with a high N content and 82% for high quality fresh oats, res>pectively. This higher degradation of protein in the diets led to higher ammonia concentration in the rumen. It has been known for a long time (Johns, 1955) that ammonia concentration can exceed 40 mg/dl in animals fed fresh pasture. In our present study, the mean ruminal ammonia concentration (24.4 ± 6.0 mg/dl) was usually above the level of 5 mg/dl (reported by Satter and Slyter, 1974) as the possible minimal concentration for optimum microbial protein synthesis using the in vitro technique and the 6.1 mg/dl (reported by Odle and Schaefer, 1987) as optimum for corn-based diets using in vivo studies. In fact, it is likely that the minimum concentration of ammonia will be a dynamic figure which depends on the rate of degradation of carbohydrates (Garcia et al., 2000). The higher degradation of nitrogen and higher ammonia concentration led to increased excretion of N in urine and faeces. Although the retention of N was nearly one half of the total N intake on all diets, the higher total excretion of N is of environmental concern. There is also energy expenditure to eliminate this excess N as urea which is evaporated as ammonia and nitrous oxide causing environmental pollution. The concentration of allantoin (mean=11±0.65 mmol/d) excreted was not significantly different (p = 0.12) among diets suggesting similar total MPS for all diets. Values were similar to those reported by Chen et al. (1992) for sheep with bodyweight of 54 to 55 kg and DMI of 966 to 1237 g/d (mean = 11.8 ± 0.87 mmol/d). Several studies (Carro et al., 2000; Trevaskis et al., 2001) reported increase in MPS by supplementing concentrates or highly fermentable carbohydrates. In the present study increase in MPS was expected with increase in the proportion of concentrates, but similar MPS among all diets indicates that high quality ryegrass too had substantial amounts of fermentable organic matter (indicated by high WSC content) along with nitrogen to promote optimal microbial growth. Nolan and Dobos (2005) also suggested that fresh forage diets that are usually high in protein and soluble carbohydrates promoted the growth of rumen bacteria.
All these results are in line with those by Garcia et al. (2000) who reported similar MPS for heifers receiving 100% fresh forage (oats) or partially (30%) replaced with corn and barley grain. Rooke and Armstrong (1989), Herrera-Saldana et al. (1990) and Sinclair et al. (1993) have reported increases in MPS with an improved degree of synchrony in the availability of N and non structural carbohydrates (NSC) in the rumen. In our study, there was asynchrony observed between the diets due to the time and pattern of feeding. Illius and Jessop (1996); and Trevaskis et al. (2001) also suggested that the level and pattern of intake determined the extent of asynchrony. Further, asynchrony between N and energy supply may be due to both excess and deficits of N in relation to energy available, or to an excess / deficiency of energy in relation to N available. In our study, microbial growth was not limited by N availability because, (i) ammonia production was well above the recommended level, (ii) the ratio of N to OM degraded in the rumen was also above the level of 25 (suggested optimum for MPS by Sinclair et al., 1993), and (iii) the ratio of ERDP to FME was above the ideal value of 11 required for MPS (AFRC, 1993). This means that more protein was available from the forage in the rumen than what microbes could utilise for their growth (Fulkerson et al., 2007). Normally, when N availability is in excess in the rumen, ammonia is absorbed through the rumen wall and appears as urea in the plasma and as it is continually recycled back to the rumen, it may overcome periods of shortage of N (Illius and Jessop, 1996). In the present study, Synchrony Index was calculated using different fermentation rates of individual feed ingredients using nylon bags, and that would have caused differences between treatments in respect to the ratios and total amounts of energy and N released into the rumen over time. This is supported by Kolver and Muller (1998) who suggested that when treatments differ in their ingredient composition, the degree of energy and N synchronization may be confounded by other ruminal effects inherent to specific ingredients. Further, in sheep, the concentration of allantoin excreted in relation to total purine derivatives may vary from 60% to 85%; uric acid from 9% to 25%; xanthine and hypoxanthine from 4% to 13%, depending upon dry matter intake and body weight (Chen et al., 1992). For this reason, the sum of four compounds, instead of allantoin alone should be used as a parameter to measure microbial protein supply. Accepting the differences in regards to excretion of allantoin in urine of sheep and cattle, still we can consider that the present study will be useful to develop
R. Kaur et al. / Livestock Science 119 (2008) 77–86
feeding strategies by selecting amount, time and pattern of feeding the concentrate supplementation in a pasture based system for high producing dairy cows. 5. Conclusion Our present study has revealed that concentrates when fed at 35 to 45% level as PMR, in a discontinuous feeding pattern, does not influence rumen pH, although the decrease in dry matter and fibre digestibility was due to the lower proportion of fibre of high quality ryegrass in the diet. The lack of synchrony between N and energy observed in this study may be due to imbalance of N and energy due to the different pattern of feeding, but results suggest that this did not limit MPS. In nutshell, this study will help to develop feeding strategies for the efficient use of supplemented concentrates in a discontinuous feeding pattern in a pasture based system for high producing dairy cows without affecting the rumen system. Further research to increase the dry matter intake and reducing the nitrogen excretion with such diets is warranted. Acknowledgement The authors express their thanks to Dr. Idris Barchia for his valuable suggestions for the statistical analysis. References Aerts, J.V., De Boever, J.L., Cottyn, B.G., De Brabander, D.L., Buysse, F.X., 1984. Comparative digestibility of feedstuffs by sheep and cows. Anim. Feed Sci. Technol. 12, 47–56. Agricultural and Food Research Council, 1993. Energy and Protein Requirements of Ruminants. CAB International, Wallingford, Oxon, UK. Beever, D., 1993. Rumen function. Quantitative Aspects of Ruminant Digestion and Metabolism. CAB International, Cambridge, UK. Carro, M.D., Valdes, C., Ranilla, M.J., Gonzalez, J.S., 2000. Effect of forage to concentrate ratio in the diet on ruminal fermentation and digesta flow kinetics in sheep offered food at a fixed and restricted level of intake. Anim. Sci. 70, 127–134. Chen, X.B., Gomes, J.J., 1992. Estimation of Microbial Protein Supply to Sheep and Cattle Based on Urinary Excretion of Purine Derivates—An Overview of the Technical Details. International Feed Resources Unit, Rowett Research Institute, Aberdeen, UK. (Occasional Publication). Chen, X.B., Chen, Y.K., Franklin, M.F., Ørskov, E.R., Shand, W.J., 1992. The effect of feed intake and body weight on purine derivative excretion and microbial protein supply in sheep. J. Anim. Sci. 70, 1534–1542. Czerkawski, J.W., 1986. An Introduction to Rumen Studies. Pergamon Press, Oxford, U.K. Dixon, R.M., Stockdale, C.R., 1999. Associative effects between forages and grains: consequences for feed utilisation. Aust. J. Agric Res. 50, 757–773.
85
Doreau, M., Grimaud, P., Michalet-Doreau, B., 2000. Undernutrition and Digestion in Ruminants. (Personal Communications). Faichney, G., 1993. Digesta flow. Quantitative aspects of ruminant digestion and metabolism. CAB International, Wallingford, UK. Fulkerson, W.J., Hough, G., Goddard, M.D., 2000. The productivity of Friesian cows: effect of genetic merit and level of concentrate feeding. Final report to the Dairy Research and Development Corporation: Melbourne, Vic. Fulkerson, W.J., Doyle, P., 2001. The Australian Dairy Industry. Department of Natural Resources and Environment, Victoria. Fulkerson, W.J., Nandra, K.S., Clark, C.F., Barchia, I., 2006. Effect of cereal-based concentrates on productivity of Holstein–Friesian cows grazing short-rotation ryegrass (Lolium multiflorum) or kikuyu (Pennesitum clandestinum) pastures. Livest. Sci. 103, 85–94. Fulkerson, W.J., Neal, J.S., Clark, C.F., Horadagoda, A., 2007. Nutritive value of forage species grown in the warm temperate climate of Australia for dairy cows: grasses and legumes. Livest. Sci. 107, 253–264. García, S.C., Santini, F.J., Elizalde, J.C., 2000. Sites of digestion and bacterial protein synthesis in dairy heifers fed fresh oats with or without corn or barley grain. J. Dairy Sci. 83, 746–755. Garcia, S.C., Fulkerson, W.J., 2005. Opportunities for future Australian dairy systems: a review. Aust. J. Exp. Agric. 45, 1041–1055. Grant, R.J., 1994. Influence of corn and sorghum starch on the in vitro kinetics of forage fiber digestion. J. Dairy Sci. 77, 1563–1569. Herrera-Saldana, R., Gomez-Alarcon, R., Torabi, M., Huber, J.T., 1990. Influence of synchronising protein and starch degradation in the rumen on nutrient utilisation and microbial protein growth. J. Dairy Sci. 73, 142–148. Illius, A.W., Jessop, N.S., 1996. Metabolic constraints on voluntary intake in ruminants. J. Anim. Sci. 74, 3052–3062. Johns, A.T., 1955. Ammonia concentrations in the rumen of sheep. N. Z. J. Sci. Tech., Sect. A 37, 323–331. Kolver, E., Muller, L.D., 1998. Performance and nutrient intake of high producing Holstein cows consuming pasture or a total mixed ration. J. Dairy Sci. 81, 1403–1411. Lawes Agricultural Trust, 1983. Genstat for Windows. Version 4.1. Numerical Algorithims Group, Oxford. McCullough, H., 1967. The determination of nitrogen in whole blood by a direct colorimetric method. Clin. Chem. Acta. 17, 297–304. McDonald, I., 1981. A revised model for the estimation of protein degradability in the rumen. J. Agri. Sci. 96, 251–252. Mould, F.L., Orskov, E.R., Mann, S.O., 1983. Associative effect of mixed feeds. I. Effects of type and level of supplementation and the influence of the rumen fluid pH on cellulolysis in vivo and dry matter digestion of various roughages. Anim. Feed. Sci. Technol. 10, 15–30. Nandra, K.S., Dobos, R.C., Orchardc, B.A., Neutzed, S.A., Oddyb, V.H., Cullisc, B.R., Jonesa, A.W., 2000. The effect of animal species on in sacco degradation of dry matter and protein of feeds in the rumen. Anim. Feed Sci. Technol. 83, 273–285. Nolan, J.V., Dobos, R.C., 2005. Nitrogen transactions in ruminants. In: Dijkstra, J., Forbes, J.M., France, J. (Eds.), Quantitative Aspects of Ruminant Digestion and Metabolism. CAB International, Cambridge, UK, pp. 177–206. Odle, J., Schaefer, D.M., 1987. Influence of rumen ammonia concentration on the rumen degradation rates of barley and maize. Br. J. Nutr. 57, 127. Offer, N.W., Nixon, D.J., 2000. Factors affecting outflow rate from the reticulo-rumen. Nutr. Abstr. Rev. 70, 833–844. Ørskov, E.R., 1987. The Feeding of Ruminants: Principles and Practice. Chalcombe Publications, England.
86
R. Kaur et al. / Livestock Science 119 (2008) 77–86
Orskov, E.R., McDonald, I., 1979. The estimation of protein degradability in the rumen from incubation measurement weighted according to the rate of passage. J. Agric. Sci. 92, 499–503. Poore, M.H., Moore, J.A., Swingle, R.S., 1990. Differential passage rates and digestion of neutral detergent fiber from grain and forages in 30, 60 and 90% concentrate diets fed to steers. J. Anim. Sci. 68, 2965–2973. Poppi, D., France, J., McLennan, S.R., 2000. Intake, passage and digestibility. Feeding Systems and Feed Evaluation Models. CAB International, London. Rooke, J.A., Armstrong, D.G., 1989. The importance of the form of nitrogen on microbial protein synthesis in the rumen of cattle receiving grass silage and continuous intrarumen infusions of sucrose. Br. J. Nutr. 61, 113–121. Satter, L.D., Slyter, L.L., 1974. Effect of ammonia concentration on rumen microbial production in vitro. Br. J. Nutr. 32, 199. SCA, 1990. Feeding Standards for Australian Livestock, 2nd Edn. PWS-Kent, Boston. Sinclair, L.A., Garnsworthy, P.C., Newbold, J.R., Buttery, P.J., 1993. Effect of synchronizing the rate of dietary energy and nitrogen release on rumen fermentation and microbial protein synthesis in sheep. J. Agric. Sci. 120, 251–263. Smith, D., 1969. Removing and analysing total non-structural carbohydrates from plant tissue. Winsconsin Agricultural Station. Research Report 41, 1–11. Thomas, S., Campling, R.C., 1977. Comparisons of some factors affecting digestibility in sheep and cows. J. Br. Grass. Soc. 32, 33–41. Thomas, C., 2004. Feed into Milk. A New Applied Feeding System for Dairy Cows. Nottingham University Press, UK.
Trevaskis, L.M., Fulkerson, W.J., Gooden, J.M., 2001. Provision of certain carbohydrate-based supplements to pasture-fed sheep, as well as time of harvesting of the pasture, influences pH, ammonia concentration and microbial protein synthesis in the rumen. Aust. J. Exp. Agric. 41, 21–27. Valdes, C., Carro, M.D., Ranilla, M.J., Gonzalez, J.S., 2000. Effect of forage to concentrate ratio in complete diets offered to sheep on voluntary food intake and some digestive parameters. Anim. Sci. 70, 119–126. Van Soest, P.J., 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. Assoc. Agric. Chem. J. 46, 829–835. van Vuuren, A.M., Krol-Kramer, F., van der Lee, R.A., Corbijn, H., 1992. Protein digestion and intestinal amino acids in dairy cows fed fresh Lolium perenne with different nitrogen contents. J. Dairy Sci. 75, 2215–2225. Wales, W.J., Doyle, P.T., 2003. Effects of grain and straw supplementation on marginal milk-production responses and rumen fermentation of cows grazing highly digestible subterranean clover pasture. Aust. J. Exp. Agric. 43, 467–474. Walker, G.P., Stockdale, C.R., Wales, W.J., Doyle, P.T., Dellow, D.W., 2001. Effect of level of grain supplementation on milk production responses of dairy cows in mid-late lactation when grazing irrigated pastures high in paspalum (Paspalum dilatatum Poir.). Aust. J. Exp. Agric. 41, 1–11.
Livestock Science 119 (2008) 77 – 86
www.elsevier.com/locate/livsci
Efficiency of utilisation of different diets with contrasting forages and concentrate when fed to sheep in a discontinuous feeding pattern R. Kaur ⁎, K.S. Nandra, S.C. Garcia, W.J. Fulkerson, A. Horadagoda M.C. Franklin Laboratory, University of Sydney, Camden, NSW-2570, Australia Received 7 September 2007; received in revised form 6 March 2008; accepted 6 March 2008
Abstract The effects of feeding different levels of forages and concentrate, in a discontinuous feeding pattern, on the efficiency of feed utilisation and rumen function were studied using rumen fistulated sheep. Experiment 1 was a 4 × 4 latin square design to determine the whole tract digestibility and rumen characteristics of diets comprising 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate (energy-dense dairy pellets) with the rest of the diet being a combination of fresh short rotation ryegrass (Lolium mutiforum) and conserved (lucerne hay and maize silage) forages. In Experiment 2, the rumen degradation characteristics of feed ingredients were determined using the nylon bag technique. Daily dry matter intake (either expressed as g/kg LW or g/kg W 0.75) was 10% lower (p = 0.03) for the C15 diet compared with C25, C35 and C45 diets. The apparent in vivo digestibility of dry matter (DM) for C15 diet was 4% higher (p = 0.04) than the C35 and C45 diets which may be attributed to the high quality of the forage (ryegrass) used. Fibre digestibility decreased as proportion of concentrate in the diet increased. However, this was unlikely due to changes in the rumen fermentation pattern, as neither pH (6.1 ± 0.23) nor ammonia concentration (24.4 ± 6 mg/dl), were different (p N 0.05) among diets. Instead, the lower fibre digestion was most likely the result of different type and proportion of fibre among diets, as total rumen degradability and rate of fibre degradation in the rumen were higher (p = 0.001) for ryegrass than for other feedstuffs. There was no significant difference in total nitrogen balance and urinary allantoin excretion among diets, which indicated similar total microbial protein synthesis (MPS). The asynchrony observed, for N and energy availability in the rumen for different diets using Sinclair et al. [Sinclair, L.A., Garnsworthy, P.C., Newbold, J.R., Buttery, P.J., 1993. Effect of synchronizing the rate of dietary energy and nitrogen release on rumen fermentation and microbial protein synthesis in sheep. J. Agric. Sci. 120, 251–263] equation, was due to the feeding pattern used in this study leading to excess of N in relation to total organic matter digested in the rumen. In conclusion, feeding concentrates in the diets as PMR with conserved forages in a discontinuous feeding pattern may be valuable to develop feeding strategies in a pasture based system for high producing dairy cows without affecting the rumen system. Crown Copyright © 2008 Published by Elsevier B.V. All rights reserved. Keywords: Forage(s); Concentrate; Rumen parameters; Fibre digestion; Microbial protein synthesis
1. Introduction
⁎ Corresponding author. Tel.: +61 2 9351 1709; fax: +61 2 46552374. E-mail address: [email protected] (R. Kaur).
Forages are the primary source of nutrients for ruminant animal production, but in order to achieve high production/cow at the farm level more supplementary
1871-1413/$ - see front matter. Crown Copyright © 2008 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2008.03.001
78
R. Kaur et al. / Livestock Science 119 (2008) 77–86
feed is needed in the form of high energy-dense concentrates (Garcia and Fulkerson, 2005). In the Australian dairy industry, for instance, the use of concentrates has increased substantially over the past few years (Fulkerson and Doyle, 2001). Concentrates are used more frequently to address the large variation in seasonal pasture growth, variability in rainfall within the year, the desire to exploit the genetic production potential of animals and the price incentives provided by milk processors to produce milk at times of low pasture growth (Garcia and Fulkerson, 2005). However, when fed twicea-day at milking, the response to feeding high amounts of concentrates is low (Fulkerson et al., 2000; Walker et al., 2001) likely due to the adverse influence on rumen environment. In this regard, feeding high levels of concentrates, over short periods during milking, causes decrease in rumen pH leading to a decrease in fibre digestion (Dixon and Stockdale, 1999). However, the effect of a drop in rumen pH is likely to be dependent on the type of fibre being fed; thus, more rapidly digested fibre is less likely to be affected than slowly degraded fibre. Poore et al. (1990) found that concentrate level in the diet has more influence on the passage rate of low (wheat straw), than of high, quality forage (lucerne hay). Similarly, Grant (1994) noted a greater reduction in fibre digestibility of bromegrass hay than lucerne hay when rumen pH was lowered in vitro through addition of raw sorghum starch. Many studies have looked at the effects of the ratio of forage to concentrate on dry matter intake and digestive function in sheep using complete diets (e.g. Carro et al., 2000; Valdes et al., 2000), or supplementing concentrates to grazing dairy cattle (e.g. Fulkerson et al., 2006). However, less work has been undertaken on feed efficiency, rumen characteristics and synchrony of diets varying in the proportion of fresh pasture, conserved forages (and therefore changing the fibre type) and concentrates typically fed to dairy cows. It is commonly accepted that levels up to about 35% concentrate do not adversely affect fibre digestion. However, even diets with over 35% concentrate will not necessarily affect fibre digestion, as this will depend on other factors such as fibre type, frequency and method of feeding the extra concentrate (Garcia and Fulkerson, 2005). Thus, feeding the extra concentrate as partial mixed ration (PMR) is less likely to affect rumen pH and therefore fibre digestion. In addition, this practice can result in better nitrogen to energy synchronisation in the rumen in comparison to the traditional concentrate/grazing system. This is because the relatively longer periods that occur in the latter system between feeding concentrates to cows in the dairy and grazing are avoided. We used rumen fistulated
sheep to test the above hypothesis that there is no effect of increased levels of concentrate in the diet on rumen pH but MPS can be improved when fed as PMR in a discontinuous feeding pattern. The use of sheep as a model is supported by several authors (e.g. Thomas and Campling., 1977; Aerts et al., 1984) who reported small differences between sheep and cattle in terms of feed utilisation and rumen degradability characteristics (Nandra et al., 2000). It has also been reported (Doreau et al., 2000) that difference between sheep and cattle is evident only when diets with N60% concentrate are fed. Recently, the development of a new support system to feed dairy cows in the UK (Feed into Milk) has concluded that differences between cows and sheep (in terms of ME supply), were minimal (Thomas, 2004). 2. Materials and methods Two experiments were conducted using rumen-fistulated Border Leicester castrate male sheep (with average weight of 55 ± 1.3 kg) housed in individual metabolism crates in a temperature controlled animal house. In Experiment 1, four diets with different forage to concentrate ratio were fed in a latin square design to determine the digestibility coefficients, rumen characteristics and allantoin excretion, as a measure of microbial protein synthesis (MPS). In Experiment 2, the rumen degradation characteristics of the different feed ingredients used in Experiment 1 were determined. 2.1. Experiment 1 2.1.1. Animals and diets The metabolic crates were designed so that the animals had enough space to sit and stand freely. The animals had free access to drinking water and separators were attached to the floor of the crates to collect faeces and urine. The four diets offered ad libitum comprised 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate (dairy pellets) with the remaining of the diet
Table 1 Chemical composition (g/kg DM); and metabolisable energy (ME) in MJ/kg DM of different feed ingredients used for the formulation of different diets Chemical composition (g/kg DM)
Pellets
Ryegrass
Lucerne hay
Maize silage
Organic matter Crude protein Neutral detergent fibre Acid detergent fibre Hemicellulose Water soluble carbohydrates In vitro DMD (%) Metabolisable energy (MJ/kg DM)
863 204 161 71 95 66 81.7 11.1
839 261 409 234 191 143 76.8 11.2
888 220 378 299 89 34 67.0 9.7
933 63 484 297 199 27 61.3 9.6
R. Kaur et al. / Livestock Science 119 (2008) 77–86
79
made up of short rotation ryegrass, lucerne hay (Medicago sativa) and maize silage (Zea mays). The chemical composition of the feed ingredients is shown in Table 1. The four dietary treatments were randomly allocated to 4 animals over 4 replicates in a latin square design. The proportion; and chemical composition of each diet is shown in Table 2.
Table 3 Feeding schedule followed for the in vivo apparent digestibility trial in sheep fed diet with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate
Time of feeding
C15
C25
C35
C45
2.1.2. Intake and digestibility measurement Each of the four experimental periods comprised a 15-day adaptation period followed by a 5 day sampling period. Rumen fluid was collected at the end (6th day) of each sampling period. Animals were weighed twice at the beginning and end of each experimental period. As we were interested in representing diets fed to dairy cows, the timing of the feeding was varied to mimic actual feeding times of dairy cows in a typical situation on a dairy farm (Table 3). Residual feed and faeces were collected and weighed every day, dried at 60 °C for 48 h in a fan-forced oven and then bulked over the period. Urine was collected each day and 10% H2SO4 added to prevent degradation of allantoin and loss of volatile N. Daily urine outputs were diluted with water to constant weight (4 kg) for subsequent analysis.
7:00 A.M. 8:00 A.M. 1:00 P.M. 2:00 P.M. 3:00 P.M.
50% C 100%PMR 50% C 0 RG
50% C 100%PMR 50% C 0 RG
25% C 70%PMR 25% C 30%PMR RG
25% C 70%PMR 25% C 30%PMR RG
2.1.3. Rumen fluid samples Rumen fluid was collected at the end of each sampling period through the rumen fistulae using a suction pump at 0, 1, 2, 3, 4, 6, 8, 10, 13 and 14 h of feeding. About 20 ml of the rumen fluid was removed and analysed immediately for pH using a WP-90 waterproof specific ion-pH-mV temperature meter (made by TPS Australia). The fluid was then strained through two layers of cheese cloth and acidified with 4 drops of concentrated H2SO4 (98%) to prevent loss of volatile N. Samples were then frozen (−20 °C) for subsequent ammonia analysis. Ammonia was determined colorimetrically by the phenol-hypochlorite reaction adapted from the method of McCullough (1967). Table 2 Diet composition (% total DM); chemical composition (g/kg DM); and metabolisable energy (ME) in MJ/kg DM of diets with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate Diet (% Concentrate) C15
C25
C35
C45
Diet composition (% DM) Concentrate Ryegrass Lucerne hay Maize silage
15 75 5 5
25 50 10 15
35 40 10 15
45 30 10 15
Chemical composition (g/kg DM) Organic matter Crude protein Neutral detergent fibre Acid detergent fibre Cellulose Hemicellulose Water soluble carbohydrates Metabolisable energy (MJ/kg DM)
850 240 374 216 161 172 120 11.0
864 213 355 209 154 158 96 10.7
866 207 331 193 140 148 88 10.8
869 201 306 177 126 139 80 10.9
Diets
C = concentrate (pellets); PMR = partial mixed ration that includes pellets, lucerne hay and maize silage; and RG = ryegrass. 100% PMR = 50% pellets + 100% lucerne hay + 100% maize silage. 70% PMR = 35% pellets + 70% lucerne hay + 70% maize silage. 30% PMR = 15% pellets + 30% lucerne hay + 30% maize silage.
2.2. Experiment 2 2.2.1. Animals and diets Six rumen fistulated sheep were used to measure the in sacco degradation characteristics of organic matter (OM), nitrogen (N) and NDF in the concentrate, pasture, lucerne hay and maize silage. Animals were fed a basal diet comprising 25% pellets, 50% ryegrass, 15% lucerne hay and 10% maize silage at maintenance level, which represented approximately the average composition of the four diets used in Experiment 1. Due to physical limit to include all bags from the four feeds, two feeds were tested in three sheep and the other two feeds in another three sheep. 2.2.2. Degradation kinetics and synchrony index For the degradability studies, samples of ryegrass and maize silage were taken fresh and chopped into 1 cm length, samples of chaffed lucerne hay and pellets were taken as such. Approximately 8–10 g of pellets or lucerne hay and 10–20 g of maize silage or ryegrass was placed in dacron bags (80 × 120 mm, 36– 38 mm pores). Seven bags per test feed were inserted in the rumen of the fistulated sheep. The bags containing pellets (protein sample) were withdrawn after 2, 4, 8, 16, 24, 48 and 72 h, while bags containing ryegrass, maize silage and lucerne hay (forage samples) were withdrawn after 3, 6, 9, 16, 24, 48 and 72 h to allow time for complete asymptote degradation. As minimal difference was observed between 48 and 72 h degradation, forage samples were not incubated for 96 h. After removal from the rumen, bags were rinsed under cold water, and then washed for 30 min on a cold rinse cycle in a washing machine. The value at time zero was obtained by washing one bag in triplicate containing the test feed without incubation in the rumen. Bags were dried at 60 °C in a fan-forced oven. Disappearance of dry matter (DM), N or NDF was measured as the loss of weight of the bag contents at each incubation time. The data obtained were then fitted to a model based on McDonald (1981) as per Eq. (1): P ¼ A þ B 1 eCt ð1Þ
80
R. Kaur et al. / Livestock Science 119 (2008) 77–86
where ‘P’ is the cumulative amount degraded at time ‘t’, A is the initial intercept or amount ‘degraded’ at time zero (soluble fraction), B is the degradable part of the insoluble fraction and C is the fractional rate of degradation of fraction ‘B’. The effective degradability (Ed) was calculated as per Orskov and McDonald (1979) using the Eq. (2): EdðkÞ ¼ A þ ð BC Þ=ðC þ k Þ⁎exp½ðC þ k Þ⁎t0
ð2Þ
where ‘A’ represents the rapidly degradable component (%), ‘C’ is the rate constant from time t0 onward (% h− 1), ‘B’ is the water insoluble but potentially degradable fraction (%) and ‘k’ is the passage rate (% h− 1). The hourly quantity of N to OM degraded for each ingredient from each feeding time was calculated as the difference between the N to OM degraded at successive hours and allocated to the appropriate hour of the day. From the hourly quantity of N and OM degraded, a synchrony index (SI) of N to OM was calculated as described by Sinclair et al. (1993) as per Eq. (3): qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2 N=OMÞ X ð25hourly 24 25 ð3Þ 25 124 where 25 = 25 g of N/kg of OM truly digested in the rumen, which is assumed to be the optimal ratio (Czerwaski, 1986). An SI of 1.0 represents perfect synchrony and values less than 1.0 represents a degree of asynchrony. 2.3. Chemical analysis Feed and residual samples; faecal samples; residual samples in the nylon bags; were analysed individually for DM content by drying at 60 °C for 48 h in a fan-forced oven. Ground samples (1 mm screen) were analysed for: OM after igniting in a muffle furnace at 600 oC for 3 h; N using a Leco FP-428 analyzer (Leco Corp., St. Joseph, MO, USA); ADF using the method of Van Soest (1963); and NDF using a modification of Van Soest (1963) with both amylase and amylopectin enzymes. Metabolisable energy (ME) was calculated using Eq. (4) (SCA, 1990). MEðMJ=kg DMÞ ¼ ½0:17 DMD ðkÞ 2:0
ð4Þ
where DMD is the in vitro DM digestibility (%DM). The water-soluble carbohydrate content of feeds was determined using an autoanalyser using a modification of the method of Smith (1969). Allantoin excreted in the urine was calculated by the method of Chen and Gomes (1992). Digestible OM fermented in the rumen (DOMR) was estimated from the digestible organic matter intake (DOMI) and rumen degradability of each ingredient (determined in Experiment 2) using Eq. (5). X Intakei Edi ðat 0:05Þ kOMi ð5Þ Total dry matter intake where i relates to individual ingredient (pellets, ryegrass, lucerne hay and maize silage).
2.4. Statistical analysis Statistical analyses were performed using GENSTAT 9 (Lawes Agricultural Trust, 1983). In Experiment 1, all the data were analysed in latin square design using ANOVA to examine the differences between animal, period, and diet, except that rumen pH and ammonia concentration were analysed using REML procedure to test the effects of period, animal, sampling time and diet. The model used for analysis was: Yijkl ¼ x þ Di þ Pj þ Ak þ Tl þ eijkl Where: Yijkl is independent variable (pH or ammonia concentration); Di (i=1, 2, 3, 4) is the fixed effect of diet; Pj ( j= 1, 2, 3, 4) is the period effect; Ak (k =1, 2, 3, 4) is the animal effect; Tl (l= 0, 1, 2, 3, 4, 6, 8, 10, 13, 14), and eijkl is the random error. In Experiment 2, data were analysed in complete randomised design using ANOVA.
3. Results 3.1. Chemical composition Pasture (ryegrass) had a comparable level of metabolisable energy (ME, 11.2 vs 11.8 MJ/kg DM) to pellets, but a higher content of crude protein (CP, 26% vs 20%), neutral detergent fibre (NDF, 41% vs. 16%), and aciddetergent fibre (ADF, 23% vs. 7%). Diet C15 had 75% ryegrass and therefore ryegrass reflected mostly the nutrient content of the diet. The ME value was not significantly different among diets ( p = 0.08, See Table 2). 3.2. Intake and in vivo digestibility The intake and in vivo digestibility coefficients of the different diets is presented in Table 4. Dry matter intake expressed as g/kg W 0.75 ( p = 0.03) or as g/kg live weight was 10% higher ( p = 0.05) for C25, C35 and C45 than for C15. The digestible organic matter intake (DOMI) and digestible organic matter fermented in the rumen (DOMR) were 6–7% higher (p b 0.01 and p = 0.02) for C25 and C45 diets (mean = 952 and 581 g/kg DM/day) than for C15 and C35 diets (mean = 885 and 549 g/kg DM/day), respectively. The in vivo apparent digestibility of DM was higher ( p = 0.03) for C15 compared to diets with N 35% concentrate. The digestibility of ADF was 22% higher ( p = 0.01) for the C15 diet compared to the average of all other diets while the NDF digestibility was significantly different for most diets, being 19% higher ( p b 0.01) for C15 (0.75) in comparison to C35 and C45 diets (0.63). The hemicellulose digestibility also followed the same pattern as NDF but the differences between diets were not significant ( p = 0.22).
R. Kaur et al. / Livestock Science 119 (2008) 77–86
81
Table 4 Dry matter intake and digestibility coefficients (in vivo) in sheep fed diets with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate Diet C15
C25
C35
C45
sed
p value
Daily Intake Dry matter (g/kgLW) Dry matter (g/kg W0.75) DOMI (g/kg DM) DOMR (g/kg DM)
20.5a
23.0b
22.6b
22.5b
0.74
0.05
55.8a
62.6b
60.7b
60.9b
1.72
0.03
886.9a 967.6b
884.7a
938.0b
17.6 b0.01
558.8a 590.3b
539.7a
572.2b
11.8
0.02
In vivo digestibility coefficients Dry matter Acid detergent fibre Neutral detergent fibre Hemi cellulose
0.76a 0.67a
0.75abc 0.60b
0.73bc 0.56b
0.73bc 0.93 0.53b 2.82
0.75a
0.68b
0.63c
0.63c
1.9 b0.01
0.79
0.78
0.68
0.71
5.2
0.03 0.01
0.22
where DOMI = digestible organic matter intake and DOMR = digestible OM fermented in the rumen. Values in the same row with different letters differ significantly (p b 0.01).
3.3. Rumen pH and ammonia concentration Mean (±se) daily rumen pH was similar (p = 0.95) for all the diets (6.1 ± 0.2), whilst within day changes in rumen pH were related to the time of feeding (Fig. 1a). In the morning, the drop in pH was less after feeding concentrate and immediately after feeding PMR, pH rose to 6.32 (average of four diets), while the fall in pH was high after feeding concentrate in the afternoon. The rumen pH was numerically lowest for C35 (5.44) and C45 (5.54) diets at about 2 h after feeding ryegrass in the afternoon even though 30% PMR was fed in these diets compared to no PMR fed for diets C15 and C25. There was a steady increase in pH observed for all diets after 5 h of feeding ryegrass. Mean daily concentration of ammonia (mg/dl) was not significantly different (p = 0.61) among diets (24.4 ± 6.0) nor was significant (p = 0.74) the interaction between diet and time. Similar to pH, changes in rumen ammonia were related to time of feeding with a marked decline in ammonia concentration after feeding concentrate in the morning and a sharp rise in ammonia concentration after feeding ryegrass in the afternoon (Fig. 1b). The ammonia concentration was as low as 5.9 mg/dl and as high as 40.7 mg/dl in rumen fluid for C15 diet.
Fig. 1. (a) Rumen pH and (b) rumen NH3 concentration (mg/dl) at different times after feeding (‐‐‐‐‐) 15%, (●) 25%, (▲) 35% and (■) 45% concentrate. Arrows indicate time of feeding concentrate (C), partial mixed ration (PMR) and ryegrass (RG).
3.4. Nitrogen balance and microbial protein synthesis Table 5 shows the results of N balance and allantoin excretion in urine as a measure of microbial protein synthesis (MPS). Nitrogen intake expressed on live weight basis was not significantly different among diets ( p = 0.23). The total Table 5 Nitrogen balance (g/kg live weight per day) and allantoin excretion (mg/d per kg live weight and mmol/day) in sheep fed diets with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate Diet
N intake (g/kg LW/day) Urinary N (g/kg LW/day) Fecal N (g/kg LW/day) N balance (g/kg LW/day) Allantoin (mg/kg LW/day) Allantoin (mmol/day)
C15 C25 C35 C45 sed
p value
0.79 0.21 0.19 0.39 31.8 11
0.23 0.47 0.63 0.79 0.55 0.12
0.79 0.21 0.17 0.41 30.6 11
0.76 0.19 0.17 0.40 30.1 9.7
0.73 0.18 0.16 0.39 33.3 11.6
0.03 0.02 0.01 0.03 2.34 0.65
82
R. Kaur et al. / Livestock Science 119 (2008) 77–86
excretion of nitrogen (when corrected on live weight basis) was similar among all the diets ( p = 0.22), urinary excretion being 51% and faecal excretion being 49%. Nitrogen retention was similar among all diets ( p = 0.79) with average retention of 53% of the total N intake. Allantoin excretion was not significantly different among diets, even after correcting by live weight ( p = 0.55). 3.5. Rumen degradability and Synchrony Index The in sacco degradability parameters of OM, N and NDF for different feed ingredients used are shown in Table 6 and the degradability of DM and NDF in relation to incubation time in the rumen are given in Fig. 2. The water insoluble, but potentially degradable, fraction of OM and N were significantly higher ( p b 0.001) for ryegrass than other ingredients leading to higher potential degradability and higher effective degradability (Ed at 0.05/h = 75.1% and 81.8%, respectively). The degradation of NDF was higher ( p b 0.001) for ryegrass indicated by its 86.9% degradability within 24 h and higher rate of degradation (13.4%/h). The potential degradability and
Table 6 Degradability parameters; water soluble component (A), water insoluble component (B), rate of degradation (C), effective degradability (Ed)% at outflow rate of 0.05/h for different feed ingredients Feed ingredients
A (g/g)
B (g/g)
C (/h)
Ed (0.05/h, g/g)
Organic matter Pellets Ryegrass Lucerne hay Maize silage s.e. P value
b
0.36 0.20c 0.29a 0.39b 0.02 b0.001
0.53 0.76c 0.42a 0.44ab 0.04 b0.001
0.056 0.158c 0.111ac 0.034b 0.03 0.01
0.74 0.75b 0.56a 0.56a 0.15 b0.01
Nitrogen Pellets Ryegrass Lucerne hay Maize silage s.e. P value
0.29c 0.22d 0.37a 0.72b 0.02 b0.001
0.66c 0.77d 0.60a 0.19b 0.02 b0.001
0.056 0.235 0.102 0.019 0.079 0.22
0.67c 0.82d 0.75ab 0.80bd 0.16 b0.001
0.012b 0.134c 0.077a 0.026b 0.017 0.001
0.27a 0.61b 0.24a 0.22a 0.23 b0.00
Neutral detergent fibre Pellets − 0.179b Ryegrass − 0.105c Lucerne hay − 0.023a Maize silage − 0.09a s.e. 0.029 P value 0.003
b
1.18c 1.04c 0.44a 0.76b 0.09 0.002
ab
b
Values in the same column (for each different variable) with different letters differ significantly ( pb0.001 and p b or = 0.01).
Fig. 2. (a) DM and (b) NDF degradation of rye grass (‐‐‐‐‐), lucerne hay (■), maize silage (●) and pellets (▲).
effective degradability (at 0.05/h) of NDF for ryegrass was 93.1% and 60.6% which was significantly higher ( p b 0.001) than other feed ingredients.
Fig. 3. Daily variation in the ratio of degradable nitrogen to rumen degradable organic matter (N: OM) after feeding (‐‐‐‐‐) 15%, (●) 25%, (▲) 35% and (■) 45% concentrate. Arrows indicate time of feeding concentrate (C), partial mixed ration (PMR) and ryegrass (RG).
R. Kaur et al. / Livestock Science 119 (2008) 77–86 Table 7 Average daily ratio of ERDP and FME, ratio of rumen degradable N to rumen degradable organic matter (N:OM) and synchrony index in sheep fed diets with 15% (C15), 25% (C25), 35% (C35) and 45% (C45) concentrate Diet C15 ERDP/FME ratio N:OM ratio Synchrony Index
C25 a
18.5 53a 0.29
C35 b
16.0 47b 0.36
C45 c
14.8 45c 0.36
d
13.6 43d 0.37
sed
p value
0.15 0.35 0.03
b0.001 b0.001 0.09
ERDP is effective rumen degradable protein and FME is fermentable metabolisable energy. Values in the same row with different letters differ significantly (p b 0.001).
Significant differences (p b 0.001) were observed among diets in the hourly ratio of N to OM degraded in the rumen (Fig. 3). In the morning, before feeding, the ratio of N to OM degraded in the rumen was well above 25 (optimum level for MPS according to Sinclair et al., 1993) for all diets except C15, which increased after feeding and was above the optimum level throughout the day. Synchrony Index was similar (p = 0.09, mean = 0.35) among diets. All these diets were significantly different (p b 0.001) for the average daily ratio of N to OM degraded in the rumen (Table 7). Effective rumen degradable protein (ERDP) to fermentable metabolisable energy (FME) ratio, calculated using in sacco degradation characteristics of N and OM in the rumen (see Table 7), was significantly different (p b 0.001) among diets. The ratio was above the ideal value of 11 required for MPS (AFRC, 1993). 4. Discussion Our study was unique as it was mainly focused to see the effects of increased levels of concentrate in the diet, when fed as PMR in a discontinuous feeding pattern, on feed efficiency, rumen parameters and synchronisation of energy and N in the rumen. Overall, we can say that inclusion of concentrate at 45% level of the diet (both fed separately and as PMR) did not influence rumen pH or MPS and the decrease in dry matter and fibre digestibility were related with the type and amount of fibre in the diet. The total DM intake of sheep on the C15 diet was lower in comparison with sheep fed C25, C35 and C45 diets. This has been previously reported by numerous workers in both sheep and cattle (Mould et al., 1983; Kolver and Muller, 1998; Dixon and Stockdale., 1999). In the present study, the higher intake by sheep fed the C25, C35 and C45 diets may have been due to higher proportion of concentrate in the diets in comparison
83
to C15. This is possible as cows offered concentrate usually replace part of the pasture (substitution); if substitution rate is b1, then total DMI will be higher in supplemented animals than non-supplemented ones (Dixon and Stockdale, 1999). The lower DM and fibre digestibility of diets with high level of concentrate could be due to the less proportion of high quality pasture (ryegrass) in general and specifically its (ryegrass) NDF degradability (Effective Degradability of 61% at 0.05/h), which is reflected in the overall high digestibility of C15 diet and explains the decline in rumen degradability of fibre as the proportion of concentrate in the diet increases (Fig. 2b). Further, the type of fibre in the diet also accounts for the difference in fibre degradation of the diets. If we quantify the effect of fibre degradation of each ingredient within the diets by considering an outflow rate of 0.05/h, 88% of total fibre was digested in the rumen for diet C15 within 24 h compared with 50% digested for diet C45. Thus, the combination of more fibre (more ryegrass in the diet) and higher fibre digestibility (fibre type, see Fig. 2b) resulted in nearly twice as much fibre digested in the rumen for C15 than the other diets. Further, Faichney (1993) related low fibre digestion with an increase in retention time in the rumen that decreases the rate of passage of digesta to the abomasums (See also Garcia and Fulkerson, 2005). These factors may influence DM intake because of passage rate is one of the most important factors influencing DM intake (Offer and Nixon, 2000; Poppi et al., 2000). Another possible explanation for the lower fibre digestion in diets with N 25% concentrate is an associative effect of starch digestion on fibre digestion (Wales and Doyle, 2003). In fact previous studies (Orskov, 1987; Beever, 1993) have suggested that feeding rapidly fermentable concentrates favours the growth of amylolytic bacteria resulting in low rumen pH and adversely affecting the growth of cell wall digesting bacteria and, thus, the rate of fibre digestion. However, in our study, the rumen pH was not significantly different among diets therefore it is unlikely that rumen pH could have affected rumen microbes. In fact, the relationship between pH and fibre digestion is more important with diets containing fibre of lower digestibility. “Garcia and Fulkerson (2005) reported that the digestion of fibre in high quality pasture was probably less affected by a drop in pH than poor quality pasture or TMR, as significant amounts of plant cell wall can be digested in the rumen even when pH is slightly below 6 for most of the day." This is confirmed by our study, in which fibre digestion was very high (particularly for ryegrass) despite the fact that rumen pH was below 6.0
84
R. Kaur et al. / Livestock Science 119 (2008) 77–86
from 4 pm to 9 pm Thus the fibre digestibility may be not affected by rumen pH but by other factors such as the amount of fibre in the diet; time and frequency of feed delivery; type and level of concentrates; and social and feeding behaviour (Garcia and Fulkerson, 2005). In the present study, the crude protein degradability of ryegrass was 99% at 24 h with an effective degradability (Ed at 0.05/h) of nitrogen for ryegrass being 82% compared with 67% for pellets. van Vuuren et al. (1992) and Garcia et al. (2000) have reported N degradabilities greater than 80% for fresh ryegrass with a high N content and 82% for high quality fresh oats, res>pectively. This higher degradation of protein in the diets led to higher ammonia concentration in the rumen. It has been known for a long time (Johns, 1955) that ammonia concentration can exceed 40 mg/dl in animals fed fresh pasture. In our present study, the mean ruminal ammonia concentration (24.4 ± 6.0 mg/dl) was usually above the level of 5 mg/dl (reported by Satter and Slyter, 1974) as the possible minimal concentration for optimum microbial protein synthesis using the in vitro technique and the 6.1 mg/dl (reported by Odle and Schaefer, 1987) as optimum for corn-based diets using in vivo studies. In fact, it is likely that the minimum concentration of ammonia will be a dynamic figure which depends on the rate of degradation of carbohydrates (Garcia et al., 2000). The higher degradation of nitrogen and higher ammonia concentration led to increased excretion of N in urine and faeces. Although the retention of N was nearly one half of the total N intake on all diets, the higher total excretion of N is of environmental concern. There is also energy expenditure to eliminate this excess N as urea which is evaporated as ammonia and nitrous oxide causing environmental pollution. The concentration of allantoin (mean=11±0.65 mmol/d) excreted was not significantly different (p = 0.12) among diets suggesting similar total MPS for all diets. Values were similar to those reported by Chen et al. (1992) for sheep with bodyweight of 54 to 55 kg and DMI of 966 to 1237 g/d (mean = 11.8 ± 0.87 mmol/d). Several studies (Carro et al., 2000; Trevaskis et al., 2001) reported increase in MPS by supplementing concentrates or highly fermentable carbohydrates. In the present study increase in MPS was expected with increase in the proportion of concentrates, but similar MPS among all diets indicates that high quality ryegrass too had substantial amounts of fermentable organic matter (indicated by high WSC content) along with nitrogen to promote optimal microbial growth. Nolan and Dobos (2005) also suggested that fresh forage diets that are usually high in protein and soluble carbohydrates promoted the growth of rumen bacteria.
All these results are in line with those by Garcia et al. (2000) who reported similar MPS for heifers receiving 100% fresh forage (oats) or partially (30%) replaced with corn and barley grain. Rooke and Armstrong (1989), Herrera-Saldana et al. (1990) and Sinclair et al. (1993) have reported increases in MPS with an improved degree of synchrony in the availability of N and non structural carbohydrates (NSC) in the rumen. In our study, there was asynchrony observed between the diets due to the time and pattern of feeding. Illius and Jessop (1996); and Trevaskis et al. (2001) also suggested that the level and pattern of intake determined the extent of asynchrony. Further, asynchrony between N and energy supply may be due to both excess and deficits of N in relation to energy available, or to an excess / deficiency of energy in relation to N available. In our study, microbial growth was not limited by N availability because, (i) ammonia production was well above the recommended level, (ii) the ratio of N to OM degraded in the rumen was also above the level of 25 (suggested optimum for MPS by Sinclair et al., 1993), and (iii) the ratio of ERDP to FME was above the ideal value of 11 required for MPS (AFRC, 1993). This means that more protein was available from the forage in the rumen than what microbes could utilise for their growth (Fulkerson et al., 2007). Normally, when N availability is in excess in the rumen, ammonia is absorbed through the rumen wall and appears as urea in the plasma and as it is continually recycled back to the rumen, it may overcome periods of shortage of N (Illius and Jessop, 1996). In the present study, Synchrony Index was calculated using different fermentation rates of individual feed ingredients using nylon bags, and that would have caused differences between treatments in respect to the ratios and total amounts of energy and N released into the rumen over time. This is supported by Kolver and Muller (1998) who suggested that when treatments differ in their ingredient composition, the degree of energy and N synchronization may be confounded by other ruminal effects inherent to specific ingredients. Further, in sheep, the concentration of allantoin excreted in relation to total purine derivatives may vary from 60% to 85%; uric acid from 9% to 25%; xanthine and hypoxanthine from 4% to 13%, depending upon dry matter intake and body weight (Chen et al., 1992). For this reason, the sum of four compounds, instead of allantoin alone should be used as a parameter to measure microbial protein supply. Accepting the differences in regards to excretion of allantoin in urine of sheep and cattle, still we can consider that the present study will be useful to develop
R. Kaur et al. / Livestock Science 119 (2008) 77–86
feeding strategies by selecting amount, time and pattern of feeding the concentrate supplementation in a pasture based system for high producing dairy cows. 5. Conclusion Our present study has revealed that concentrates when fed at 35 to 45% level as PMR, in a discontinuous feeding pattern, does not influence rumen pH, although the decrease in dry matter and fibre digestibility was due to the lower proportion of fibre of high quality ryegrass in the diet. The lack of synchrony between N and energy observed in this study may be due to imbalance of N and energy due to the different pattern of feeding, but results suggest that this did not limit MPS. In nutshell, this study will help to develop feeding strategies for the efficient use of supplemented concentrates in a discontinuous feeding pattern in a pasture based system for high producing dairy cows without affecting the rumen system. Further research to increase the dry matter intake and reducing the nitrogen excretion with such diets is warranted. Acknowledgement The authors express their thanks to Dr. Idris Barchia for his valuable suggestions for the statistical analysis. References Aerts, J.V., De Boever, J.L., Cottyn, B.G., De Brabander, D.L., Buysse, F.X., 1984. Comparative digestibility of feedstuffs by sheep and cows. Anim. Feed Sci. Technol. 12, 47–56. Agricultural and Food Research Council, 1993. Energy and Protein Requirements of Ruminants. CAB International, Wallingford, Oxon, UK. Beever, D., 1993. Rumen function. Quantitative Aspects of Ruminant Digestion and Metabolism. CAB International, Cambridge, UK. Carro, M.D., Valdes, C., Ranilla, M.J., Gonzalez, J.S., 2000. Effect of forage to concentrate ratio in the diet on ruminal fermentation and digesta flow kinetics in sheep offered food at a fixed and restricted level of intake. Anim. Sci. 70, 127–134. Chen, X.B., Gomes, J.J., 1992. Estimation of Microbial Protein Supply to Sheep and Cattle Based on Urinary Excretion of Purine Derivates—An Overview of the Technical Details. International Feed Resources Unit, Rowett Research Institute, Aberdeen, UK. (Occasional Publication). Chen, X.B., Chen, Y.K., Franklin, M.F., Ørskov, E.R., Shand, W.J., 1992. The effect of feed intake and body weight on purine derivative excretion and microbial protein supply in sheep. J. Anim. Sci. 70, 1534–1542. Czerkawski, J.W., 1986. An Introduction to Rumen Studies. Pergamon Press, Oxford, U.K. Dixon, R.M., Stockdale, C.R., 1999. Associative effects between forages and grains: consequences for feed utilisation. Aust. J. Agric Res. 50, 757–773.
85
Doreau, M., Grimaud, P., Michalet-Doreau, B., 2000. Undernutrition and Digestion in Ruminants. (Personal Communications). Faichney, G., 1993. Digesta flow. Quantitative aspects of ruminant digestion and metabolism. CAB International, Wallingford, UK. Fulkerson, W.J., Hough, G., Goddard, M.D., 2000. The productivity of Friesian cows: effect of genetic merit and level of concentrate feeding. Final report to the Dairy Research and Development Corporation: Melbourne, Vic. Fulkerson, W.J., Doyle, P., 2001. The Australian Dairy Industry. Department of Natural Resources and Environment, Victoria. Fulkerson, W.J., Nandra, K.S., Clark, C.F., Barchia, I., 2006. Effect of cereal-based concentrates on productivity of Holstein–Friesian cows grazing short-rotation ryegrass (Lolium multiflorum) or kikuyu (Pennesitum clandestinum) pastures. Livest. Sci. 103, 85–94. Fulkerson, W.J., Neal, J.S., Clark, C.F., Horadagoda, A., 2007. Nutritive value of forage species grown in the warm temperate climate of Australia for dairy cows: grasses and legumes. Livest. Sci. 107, 253–264. García, S.C., Santini, F.J., Elizalde, J.C., 2000. Sites of digestion and bacterial protein synthesis in dairy heifers fed fresh oats with or without corn or barley grain. J. Dairy Sci. 83, 746–755. Garcia, S.C., Fulkerson, W.J., 2005. Opportunities for future Australian dairy systems: a review. Aust. J. Exp. Agric. 45, 1041–1055. Grant, R.J., 1994. Influence of corn and sorghum starch on the in vitro kinetics of forage fiber digestion. J. Dairy Sci. 77, 1563–1569. Herrera-Saldana, R., Gomez-Alarcon, R., Torabi, M., Huber, J.T., 1990. Influence of synchronising protein and starch degradation in the rumen on nutrient utilisation and microbial protein growth. J. Dairy Sci. 73, 142–148. Illius, A.W., Jessop, N.S., 1996. Metabolic constraints on voluntary intake in ruminants. J. Anim. Sci. 74, 3052–3062. Johns, A.T., 1955. Ammonia concentrations in the rumen of sheep. N. Z. J. Sci. Tech., Sect. A 37, 323–331. Kolver, E., Muller, L.D., 1998. Performance and nutrient intake of high producing Holstein cows consuming pasture or a total mixed ration. J. Dairy Sci. 81, 1403–1411. Lawes Agricultural Trust, 1983. Genstat for Windows. Version 4.1. Numerical Algorithims Group, Oxford. McCullough, H., 1967. The determination of nitrogen in whole blood by a direct colorimetric method. Clin. Chem. Acta. 17, 297–304. McDonald, I., 1981. A revised model for the estimation of protein degradability in the rumen. J. Agri. Sci. 96, 251–252. Mould, F.L., Orskov, E.R., Mann, S.O., 1983. Associative effect of mixed feeds. I. Effects of type and level of supplementation and the influence of the rumen fluid pH on cellulolysis in vivo and dry matter digestion of various roughages. Anim. Feed. Sci. Technol. 10, 15–30. Nandra, K.S., Dobos, R.C., Orchardc, B.A., Neutzed, S.A., Oddyb, V.H., Cullisc, B.R., Jonesa, A.W., 2000. The effect of animal species on in sacco degradation of dry matter and protein of feeds in the rumen. Anim. Feed Sci. Technol. 83, 273–285. Nolan, J.V., Dobos, R.C., 2005. Nitrogen transactions in ruminants. In: Dijkstra, J., Forbes, J.M., France, J. (Eds.), Quantitative Aspects of Ruminant Digestion and Metabolism. CAB International, Cambridge, UK, pp. 177–206. Odle, J., Schaefer, D.M., 1987. Influence of rumen ammonia concentration on the rumen degradation rates of barley and maize. Br. J. Nutr. 57, 127. Offer, N.W., Nixon, D.J., 2000. Factors affecting outflow rate from the reticulo-rumen. Nutr. Abstr. Rev. 70, 833–844. Ørskov, E.R., 1987. The Feeding of Ruminants: Principles and Practice. Chalcombe Publications, England.
86
R. Kaur et al. / Livestock Science 119 (2008) 77–86
Orskov, E.R., McDonald, I., 1979. The estimation of protein degradability in the rumen from incubation measurement weighted according to the rate of passage. J. Agric. Sci. 92, 499–503. Poore, M.H., Moore, J.A., Swingle, R.S., 1990. Differential passage rates and digestion of neutral detergent fiber from grain and forages in 30, 60 and 90% concentrate diets fed to steers. J. Anim. Sci. 68, 2965–2973. Poppi, D., France, J., McLennan, S.R., 2000. Intake, passage and digestibility. Feeding Systems and Feed Evaluation Models. CAB International, London. Rooke, J.A., Armstrong, D.G., 1989. The importance of the form of nitrogen on microbial protein synthesis in the rumen of cattle receiving grass silage and continuous intrarumen infusions of sucrose. Br. J. Nutr. 61, 113–121. Satter, L.D., Slyter, L.L., 1974. Effect of ammonia concentration on rumen microbial production in vitro. Br. J. Nutr. 32, 199. SCA, 1990. Feeding Standards for Australian Livestock, 2nd Edn. PWS-Kent, Boston. Sinclair, L.A., Garnsworthy, P.C., Newbold, J.R., Buttery, P.J., 1993. Effect of synchronizing the rate of dietary energy and nitrogen release on rumen fermentation and microbial protein synthesis in sheep. J. Agric. Sci. 120, 251–263. Smith, D., 1969. Removing and analysing total non-structural carbohydrates from plant tissue. Winsconsin Agricultural Station. Research Report 41, 1–11. Thomas, S., Campling, R.C., 1977. Comparisons of some factors affecting digestibility in sheep and cows. J. Br. Grass. Soc. 32, 33–41. Thomas, C., 2004. Feed into Milk. A New Applied Feeding System for Dairy Cows. Nottingham University Press, UK.
Trevaskis, L.M., Fulkerson, W.J., Gooden, J.M., 2001. Provision of certain carbohydrate-based supplements to pasture-fed sheep, as well as time of harvesting of the pasture, influences pH, ammonia concentration and microbial protein synthesis in the rumen. Aust. J. Exp. Agric. 41, 21–27. Valdes, C., Carro, M.D., Ranilla, M.J., Gonzalez, J.S., 2000. Effect of forage to concentrate ratio in complete diets offered to sheep on voluntary food intake and some digestive parameters. Anim. Sci. 70, 119–126. Van Soest, P.J., 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. Assoc. Agric. Chem. J. 46, 829–835. van Vuuren, A.M., Krol-Kramer, F., van der Lee, R.A., Corbijn, H., 1992. Protein digestion and intestinal amino acids in dairy cows fed fresh Lolium perenne with different nitrogen contents. J. Dairy Sci. 75, 2215–2225. Wales, W.J., Doyle, P.T., 2003. Effects of grain and straw supplementation on marginal milk-production responses and rumen fermentation of cows grazing highly digestible subterranean clover pasture. Aust. J. Exp. Agric. 43, 467–474. Walker, G.P., Stockdale, C.R., Wales, W.J., Doyle, P.T., Dellow, D.W., 2001. Effect of level of grain supplementation on milk production responses of dairy cows in mid-late lactation when grazing irrigated pastures high in paspalum (Paspalum dilatatum Poir.). Aust. J. Exp. Agric. 41, 1–11.