CSIRO PUBLISHING
Animal Production Science, 2014, 54, 1263–1267 http://dx.doi.org/10.1071/AN14259
Rumen degradation characteristics of ryegrass herbage and ryegrass silage are affected by interactions between stage of maturity and nitrogen fertilisation rate J. A. H. Heeren A, S. C. Podesta A, B. Hatew A, G. Klop A, H. van Laar A,B, A. Bannink C, D. Warner A, L. H. de Jonge A and J. Dijkstra A,D A
Wageningen University, Animal Nutrition Group, PO Box 338, 6700 AH Wageningen, The Netherlands. Nutreco R & D, PO Box 220, 5830 AE Boxmeer, The Netherlands. C Wageningen UR Livestock Research, Animal Nutrition, PO Box 65, 8200 AB Lelystad, The Netherlands. D Corresponding author. Email:
[email protected] B
Abstract. The objective of this experiment was to evaluate interaction effects between stage of maturity and nitrogen (N) fertilisation rate on rumen degradation characteristics determined with nylon bag incubations of ryegrass herbages and ryegrass silage. Grass herbage (n = 4) was cut after 3 or 5 weeks of regrowth and received a low (20 kg N/ha) or a high (90 kg N/ha) fertilisation rate. Grass silage (n = 6) received a low (65 kg N/ha) or high (150 kg N/ha) fertilisation rate and was harvested at early (~2000 kg DM/ha), mid (harvested 13 days later), or late (harvested 34 days later) maturity stage and ensiled in big bales. All grasses were incubated in the rumen of three lactating rumen-cannulated Holstein Friesian cows. Rumen degradation characteristics of organic matter (OM), N and neutral detergent fibre (NDF) and the extent of effective degradation (ED) were evaluated. In grass herbage, NDF content varied between 390 and 454 g/kg DM and N content between 12.1 and 25.8 g/kg DM. In grass silage, NDF content varied between 438 and 593 g/kg DM and N content between 13.4 and 34.8 g/kg DM. In general, rumen degradation of grass herbage and grass silage decreased with increased maturity, and increased with increased fertilisation rate. Significant interaction between maturity and fertilisation rate was observed for ED of OM, N and NDF, except for ED of N in grass herbage. These results indicate that the effect of the rate of N fertilisation on degradation of nutrients in the rumen of dairy cattle and on nutritional value depends on the grass maturity stage. Additional keywords: cutting stage, dairy cow, degradability, grass roughage, in situ, rate of fertilisation. Received 12 March 2014, accepted 16 May 2014, published online 10 July 2014
Introduction In temperate regions worldwide, grass-based systems of milk production predominate, and grass (either fresh or ensiled) is usually also a major part of the diet in mixed dairy farming systems (Van Vuuren and Chilibroste 2013). Nutrient composition, digestibility and nutritional value of grass is influenced by various management factors including the rate of nitrogen (N) fertilisation and the maturity stage at which grass is grazed, or cut and ensiled. Moreover, improving grass quality and digestibility is an effective mitigation strategy to decrease methane emission per unit milk produced (Hristov et al. 2013; Van Middelaar et al. 2014). In general, a high N fertilisation rate increases DM yield (Rahman et al. 2008; Abbasi et al. 2012) and crude protein (CP) content (Tremblay et al. 2005; Nordheim-Viken and Volden 2009), and reduces DM and water-soluble carbohydrates (WSC) content of grass (Peyraud et al. 1997; Valk et al. 2000; Astigarraga et al. 2002). Nitrogen fertilisation rate increases (Lindberg and Lindgren 1988; Journal compilation CSIRO 2014
Peyraud et al. 1997) or does not affect (Astigarraga et al. 2002; Abbasi et al. 2012) grass neutral detergent fibre (NDF) content. The effect of fertilisation rate on grass degradability characteristics is not consistent (Lindberg and Lindgren 1988; Valk et al. 1996). As to grass maturity, an increased grass maturity stage at cutting results in an increase in NDF concentrations (Silva et al. 2008; Vanhatalo et al. 2009), and a decrease in WSC concentrations (Rinne et al. 2002; Tas et al. 2006) and CP (Yu et al. 2004; Nordheim-Viken and Volden 2009), which affects degradability negatively. Although there is ample information on the effects of either maturity or N fertilisation rate on degradation of organic matter (OM), N and NDF of grass herbage and grass silage in the rumen, little is known about the effect of interaction between maturity and fertilisation rate. The objective of this experiment was to evaluate the interaction effects of stage of maturity and N fertilisation rate on degradation characteristics of grass herbage and grass silage in the rumen of lactating dairy cows. www.publish.csiro.au/journals/an
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Materials and methods Rumen degradation characteristics were determined with nylon bag incubations of fresh ryegrass herbage (n = 4; two rates of N fertilisation and two maturity stages) or ryegrass silage (n = 6; two rates of N fertilisation and three maturity stages) according to the Dutch in situ nylon bag protocol (Tas et al. 2006). Grassland fields were divided into four (for herbage) or six (for silage) similar plots. All plots for grass herbage were initially cut in spring 2012 and received 80 kg N/ha from cattle slurry and 30 kg N/ha from calcium ammonium nitrate (CAN) fertiliser. After 1 month, on half of the plots grass was cut and these plots received on the same day either 20 kg N/ha (low N fertilisation rate) or 90 kg N/ha (high N fertilisation rate) from CAN. Grass from these plots was harvested 5 weeks later (grass herbage 5 weeks of regrowth). The other half of the plots was cut 2 weeks later and also received on the same day either 20 kg N/ha or 90 kg N/ha from CAN. Grass from these plots was harvested on the very same day as the 5-week regrowth grass to obtain grass herbage at 3 weeks of regrowth. All grass was harvested at ~1300 hours. The plots for grass silage received in addition to 80 kg N/ha from cattle slurry either 45 kg N/ha (low N fertilisation) or 115 kg N/ha (high N fertilisation) from CAN fertiliser. All grass silage plots were then cut in May and received either 65 kg N/ha (low N fertilisation) or 150 kg N/ha (high N fertilisation) from CAN fertiliser. Next, grass was harvested at an early (~2000 kg DM/ha; 24 days after previous cutting), mid (harvested 13 days after early stage), or late stage (harvested 34 days after early stage). For all grass silages, grass was cut at ~1500 hours and field wilted for ~24 h before ensiling. Grass was ensiled in big bales (~500 kg each) using 12 layers of stretch plastic and stored outdoors for on average 9 months. Material from each bale was bulked, mixed and subsampled. Grass herbage and grass silage samples were stored in a freezer at 20C. Grass herbage and grass silage samples were incubated (start 0900 hours) according to the all in all out method in 3-fold for 2, 4, 8, 12, 24, 48, 96 and 336 h in three lactating rumen-cannulated Holstein Friesian dairy cows with the approval of the Experimental Animal Committee of Wageningen University, The Netherlands. The cows were 91 38 days in milk and producing 35.5 8.6 kg/day. Cows were fed ad libitum a mixed ration of 50% grass silage (N, 16.6 g/kg DM; NDF, 516 g/kg DM) and 50% maize silage (N, 11.5 g/kg DM; NDF, 397 g/kg DM; starch, 374 g/kg DM). Cows received each day an additional 2 kg of protein-rich concentrate feed (N, 53.0 g/kg), and commercial concentrate feed (N, 29.8 g/kg) according to milk production level up to a maximum of 7 kg. Before incubation, frozen grass herbage and grass silage samples were cut at a length of ~1 cm and nylon bags with an inner size of 10 · 8 cm and a pore size of 40 mm (PA 40/30, Nybolt, Zurich, Switzerland) were filled with ~5 g DM. After incubation, bags were immediately placed in ice water for ~5 min to stop fermentation, and rinsed with tap water. The bags were washed in a washing machine (AEG Turnamat, Nuremberg, Germany) for 40 min in cold water (gentle ‘wool wash’ program without centrifuging) and air-dried for at least 48 h (60C). Dried samples were weighed, pooled to one sample per
J. A. H. Heeren et al.
incubation time per cow, ground through a 1-mm sieve (Retsch, ZN100, Haan, Germany) and analysed in duplicate for DM, ash, N and NDF. The DM was determined by drying to a constant weight at 103C (ISO 6496 1999), and ash by combustion at 550C (ISO 5984 2002). Nitrogen was determined using the Kjeldahl method with CuSO4 as catalyst (ISO 5983-2 2005). NDF was determined by the filter bag technique using heat stable a-amylase in an ANKOM 2000 fibre analyser (Ankom Technology Corporation, Macedon, NY, USA). Rumen degradation characteristics were calculated for OM, N and NDF. Three fractions (all expressed in % of total) were determined: a washout (W) fraction (assumed to be zero for NDF) by the disappearance of material after washing in the washing machine, which is assumed to be rapidly degradable; a truly undegradable fraction (U), which is the asymptote of the degradation curve at infinite incubation time; and a potentially degradable fraction (D) calculated as: 1 W U. The fractional rate of degradation of the D fraction (kd; /h) was calculated using a first-order exponential model including a lag time (Lag; h) (Lag for NDF only) using PROC NLIN in SAS (SAS 2009). The extent of effective degradation (ED; %) was calculated as ED = W + D · kd · e(–kp · Lag)/(kd + kp) (Dhanoa et al. 1999), assuming a fractional passage rate (kp) of 0.045/h. Next, W, U, Lag, kd and ED were analysed for grass herbage and grass silage separately conducting ANOVA with PROC MIXED in SAS (SAS 2009), with cow, maturity stage, N fertilisation rate, and the interaction between maturity stage and N fertilisation rate as independent fixed variables in the model. The Tukey test was used to test pairwise comparisons. Results and discussion Grass herbage In line with previous findings (e.g. Yu et al. 2004; NordheimViken and Volden 2009), the N content was lower, and NDF content was higher, of ryegrass herbage harvested after 5 weeks compared with herbage harvested after 3 weeks (Table 1). In comparison with low N fertilisation, high N fertilisation increased N and NDF content of grass. This increase in N content is in line with other studies (e.g. Nordheim-Viken and Volden 2009). The effect of N fertilisation on grass NDF contents is more variable, and increases in NDF content (Peyraud et al. 1997) or no change in NDF content (Valk et al. 2000) with elevated N fertilisation rates have been reported. In line with results reported in various studies (e.g. Valk et al. 1996; Peyraud et al. 1997), in general more mature grass herbage resulted in decreased degradability characteristics, whereas an increase in the rate of N fertilisation increased degradability (for N only) (Table 2). In particular, harvesting grass at 5 rather than at 3 weeks of regrowth increased the Ufraction and decreased the kd, resulting in lower ED values for late than early grass maturity. However, significant interactions between maturity stage and N fertilisation rate occurred for several degradation characteristics. The ED of NDF decreased upon an increase in maturity, but this effect was more pronounced with low than with high N fertilisation. With low N fertilisation, ED of NDF was 31.4% and 19.3% for early and late maturity, respectively; with high N fertilisation, ED of
Maturity and fertiliser effects on grass degradation
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Table 1. Dry matter (DM), ash, nitrogen (N) and neutral detergent fibre (NDF) content of ryegrass herbage and ryegrass silage at various maturity stages and N fertilisation rates DM (g/kg)
Ash (g/kg DM)
N (g/kg DM)
NDF (g/kg DM)
16.0 25.8 12.1 16.3
390 412 416 454
24.8 34.8 17.8 28.5 13.4 20.6
467 438 484 595 561 593
A,B
Early – Low N fertilisation rate Early – High N fertilisation rate Late – Low N fertilisation rate Late – High N fertilisation rate Early – Low N fertilisation rate Early – High N fertilisation rate Mid – Low N fertilisation rate Mid – High N fertilisation rate Late – Low N fertilisation rate Late – High N fertilisation rate
242 180 248 202 438 436 651 580 760 542
Ryegrass herbage 82 88 65 74
Ryegrass silageC,D 92 104 75 96 64 86
A
Maturity-stage ryegrass herbage: Early, 3 weeks maturity; Late, 5 weeks maturity. N fertilisation rate ryegrass herbage: Low, initially 80 kg N/ha cattle slurry plus 30 kg N/ha N fertiliser, with 20 kg N/ha N fertiliser 3 or 5 weeks before harvest; High, same rates as Low but with 90 kg N/ha N fertiliser 3 or 5 weeks before harvest. C Maturity-stage ryegrass silage: Early, cut at ~2000 kg DM/ha; Mid, cut 13 days after Early; Late, cut 34 days after Early. D N fertilisation rate ryegrass silage: Low, initially 80 kg N/ha animal manure plus 45 kg N/ha N fertiliser, with 65 kg N/ha N fertiliser at the cut preceding harvest; High, initially 80 kg N/ha animal manure plus 115 kg N/ha N fertiliser, with 150 kg N/ha N fertiliser at the cut preceding harvest. B
Table 2. Rumen degradation characteristics of neutral detergent fibre (NDF), nitrogen (N) and organic matter (OM) of four ryegrass herbages at various maturity (M) stages (early or late) and N fertilisation (NF) rates (low or high) Rumen degradation characteristics: kd, fractional degradation rate; Lag, lag time; U, undegradable fraction; ED, effective degradation; W, washable fraction. See footnote in Table 1 for explanation of maturity and fertilisation rates. Within fertilisation rate, values followed by the same lower-case letter are not significantly different (at P = 0.05); within maturity stage, values followed by the same upper-case letter are not significantly different (at P = 0.05) M, early NF, low NF, high
NF, low
M, late NF, high
kd (h) Lag (h) U (%) ED (%)
0.027aX 0.0 15.9aX 31.4aX
0.024aX 0.0 18.4aY 28.4aX
0.019bX 5.2 18.5bX 19.3bX
NDF 0.020bX 0.0 18.4aX 24.9bY
0.0007 1.10 0.43 0.69
