Energy and protein supplementation of lactating
dairy cows offered urea treated whole-crop wheat
as the sole forage
J. Hill
a,*, J.D. Leaver
baDepartment of Agriculture and Rural Management, Writtle College,
Chelmsford, Essex CM1 3RR, UK
bDepartment of Agriculture and Horticulture, Wye College, University of London,
Wye, Ashford Kent, TN25 5AH, UK
Received 2 February 1999; received in revised form 30 August 1999; accepted 3 September 1999
Abstract
Whole-crop wheat treated with 40 kg urea/t/DM was examined in two experiments as the sole forage offered ad libitum. The objective was to evaluate the nutritive value of the forage, and the response in milk production to energy and protein supplements. In Experiment 1, 12 Holstein Friesian lactating cows in three 44 Latin squares were offered four concentrates, AÐ6 kg/day of 208 g CP kg/DM, BÐ6 kg/day of 276 g CP kg/DM, CÐ8 kg day of 208 g CP kg/DM and DÐ 10 kg/day of 208 g CP kg/DM. The apparent digestibility of the forage was measured at maintenance and ad libitum levels of feeding with four Holstein Friesian heifers in a changeover design. In Experiment 2, six Holstein Friesian lactating cows in two 33 latin squares were offered, EÐ4 kg/day of a concentrate containing 166 g CP kg/DM, FÐ4 kg/day of 333 g CP kg/ DM (additional soya-bean meal) and GÐ4 kg/day of 329 g CP kg/DM (additional soya-bean meal and fish meal). Digestibility of diets was measured in the same cows by the total collection of faeces. In experiments 1 and 2, respectively, mean in vivo DOMD (g/kg/DM) of urea treated whole-crop wheat was 646 and 738, and mean DM intakes (kg/day) were 14.12 and 18.68. These high forage intakes produced only moderate levels of milk production. Estimated energy balances indicated that on average 48 MJ ME intake in Experiment 1, and 70 MJ ME intake in Experiment 2 could not be accounted for in the ME requirements estimated from measured animal performance. This indicates a low efficiency of utilisation of the digested energy of urea-treated whole-crop wheat. Milk production responses to concentrate level were similar to those observed with other
82 (1999) 177±193
*Corresponding author. Tel.:44-1245-420705; fax:44-1245-420456
E-mail address: jh@writtle.ac.uk (J. Hill)
0377-8401/99/$ ± see front matter#1999 Elsevier Science B.V. All rights reserved.
types of forage. Additional protein in the supplement from fish meal but not from soya-bean meal significantly increased milk yield.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Whole-crop wheat; Forage; Lactating cows; Concentrates
1. Introduction
Whole-crop cereals, harvested at a high dry matter (DM) and conserved with urea have become an attractive alternative to grass or maize silage in the UK. The attractions of annual forage crops (maize or whole-crop cereals) for dairy production are the high yields of DM, the high intake characteristics of conserved forage and the availability of land under an arable (non persistent) crop for disposal of slurry and effluent. The principal
method of conservation of whole-crop wheat harvested at about 500 g DM kgÿ1 is
ensiling with urea (40 kg/t). At lower DM contents the crop can be ensiled.
Several studies have investigated the inclusion of urea treated whole-crop wheat into the forage component of the ration of the dairy cow (Leaver and Hill, 1995; Hameleers, 1998; Sutton et al., 1998). These studies used urea-treated whole-crop wheat to partially replace grass silage or maize silage diets (up to 0.67 in the case of Sutton et al., 1997) with significant increases in DM and OM intake but little effect on milk energy output. Sutton et al. (1997, 1998) investigated the factors which may account for the poor responses of lactating cattle given diets containing urea treated whole-crop wheat. The digestibility of energy, DM and neutral detergent fibre (NDF) in the total diet declined when grass silage was replaced by whole-crop cereals but with no effect on energy retention or excretion via milk, urine or heat. However, the DM content of the whole-crops used in the studies of Sutton et al. (1997, 1998) were unusually high compared with those normally produced in the UK (ranging from 717 to 813 g/DM/kg).
Little has been published on the effect of feeding urea treated whole-crop wheat as the sole forage for lactating dairy cattle or on strategies for effective supplementation of the diet with protein or energy. Hill and Leaver (1991) suggested the total metabolisable
energy (ME) intake (DM intakeME density of the diet estimated from in vitro
digestibility) was not accounted for in the estimated requirements for ME at measured animal production levels. This apparent `loss' of ME might have be associated with the high level of ammonia ingested as part of the forage increasing the requirement for energy to excrete the ammonia as urea. The procedures to estimate the ME content of whole-crop wheat may also explain the over-estimation of ME, or the efficiency of utilisation of ME may be lower than the values accepted in AFRC (1993).The objectives of this study were to examine the nutritive value of urea-treated whole-crop wheat offered ad libitum to lactating cows, and to evaluate the milk production responses to increments of energy and protein in concentrate supplements.
2. Materials and method
The research was carried out at the Wye College Dairy Research Unit.
2.1. Forage production
In Experiment 1 (1989), spring wheat (variety Axona) was grown on a field scale. The crop was drilled into a prepared seed bed at a rate of 200 kg seed per hectare. The field received cattle slurry during the previous autumn amounting to 50 kg nitrogen (N) fertiliser per hectare. In Experiment 2 (1990) a winter wheat (variety Avalon) was sown into a prepared seed bed at a rate of 262 kg seed per hectare. The crop received 222 kg/N/ ha in the spring. Both the crops were grown as commercial grain crops and the spray programme applied included herbicide (isoproturon and mecoprop-potassium), insecti-cide (primicarb) and fungiinsecti-cide (fenpropidin and flutriafol) applications.
In Experiment 1 the crop was harvested at growth stage 85 (mid dough: Zadoks et al., 1974) on 25 August 1989 at 651 g/DM/kg. The harvest yield was 11.7 t/DM/ha (at 8 cm stubble height). In Experiment 2, the crop was harvested at growth stage 86 (hard dough) on 20 July 1990 at 609 g/DM/kg (7 cm stubble height). The harvest yield was 15.1 t/DM/ ha (at 7 cm stubble height).
The crops for storage with urea treatment were cut with a oil-seed rape swather which had a reciprocating blade (1.5 m cut width), reel and side delivery belt. Immediately after cutting the crops were harvested from the swath with a self-propelled precision-chop forage harvester. Prior to ensiling, both the crops were treated with the urea (prilled feed grade) at a rate of 40 kg/t/DM. Application of urea was achieved by spreading the harvested crop on a concrete pad and spreading the urea by hand and then mixing with a buck rake. The
urea-treated forage was then stored in wooden-wall silo (11 m3 m, with a settled height of
treated forage of 1.5 m), sheeted on the sides and top with polythene with tyres placed on top. The whole-crop wheat was stored for 90 days before feeding and was sampled for chemical composition prior to storage and treatment in both experiments. Samples of feed prior to and at feeding were taken and frozen for chemical analysis.
2.2. Animals and management
In Experiment 1, 12 multiparous Holstein Friesian cows and in Experiment 2, 6 Holstein Friesian cows (three primiparous and three multiparous) were used. The mean parities for Experiment 1 and Experiment 2 were 3.5 and 4.1, respectively and the cows were calved 95 and 136 days, and had initial milk yields of 29.2 (22.4±42.0) and 22.8 (18.9±25.4) kg/day, respectively. The initial mean live weights and condition scores of cows for Experiment 1 and 2 were 617 (s.e. 18.8) kg, 2.50 (1.5±3.5), 591 (s.e. 17.3) kg and 2.26 (1.25±3), respectively. In Experiment 1 the cows were housed in cubicles with chopped straw as bedding and received their feeds, individually through Calan Broadbent gates. In Experiment 2, the cows were housed individually in pens, bedded on rubber mats and received their feeds through individual troughs. All the cows in both the experiments were milked twice daily at approximately 06:00 and 16:00 h.
2.3. Experimental treatments and design
The two experiments were based on Latin square designs. In Experiment 1 the cows were allocated according to live-weight, condition score, initial milk yield and stage of
lactation to three 44 latin squares with four 3 week periods per square and four cows
per square. In Experiment 2 the cows were allocated to two 33 latin squares with three,
3 week periods per square and three cows per square. The cows were grouped and allocated to squares according to their parity, live-weight, condition score, initial milk yield and stage of lactation. All cows received urea-treated whole-crop wheat ad libitum as the sole forage.
In Experiment 1, cows were given one of four concentrates. The concentrates were formulated using molassed sugar beet pulp and solvent extracted soya-bean meal. The four concentrate treatments were A, 6 kg/day of 208 g crude protein (CP) per kg/DM; B, 6 kg/day of 276 g CP kg/DM; C, 8 kg/day of 207 g CP kg/DM and D, 10 kg/day of 209 g CP kg/DM. The four concentrate treatments were designed to investigate three possible responses, the substitution effect of concentrate (Treatment A versus C versus D), the effect of increasing energy intake in the concentrate at iso-nitrogenous level of intake (Treatment B versus C) and the influence of crude protein content at iso-energetic level of intake (Treatment A versus B).
In Experiment 2 cows were given one of three concentrates. The concentrates were formulated using molassed sugar beet pulp, solvent extracted soya-bean meal, white fishmeal and pelleted maize gluten. The concentrate treatments were E, 4 kg/day of 166 g CP kg/DM; F, 4 kg/day of 333 g CP kg/DM and G, 4 kg/day of 329 g CP kg/DM. Treatments F and G had the same CP contents but Treatment G contained fish meal to reduce the degradability of protein. The compositional analysis and formulation details for all concentrates offered in the two main dairy cattle feeding trials are given in Table 1. The urea treated whole-crop wheat was offered in one feed per day on an ad libitum basis at 08.00 h and uneaten food was removed 24 h later. The amount of forage offered daily was adjusted by 0.1 above that eaten in the previous 24 h. Concentrates were offered through a separate trough to the urea treated whole-crop and each level of concentrate
Table 1
Concentrate formulation and chemical composition (g kg/DM unless stated otherwise)
Experiment 1 Experiment 2
A B C D E F G
Formulation (kg/t/DM)
Soya-bean meal 202 387 206 205 76 517 74
Molassed sugar beet pulp 798 613 794 795 674 236 414
Maize gluten 250 247 244
Fish meal 268
Chemical composition
Oven DM (g/DM/kg) 864 868 867 865 860 871 883
NDF 317 278 317 316 326 231 248
ADF 224 200 224 223 203 147 150
OM 918 922 917 915 900 895 886
Starch 20 32 20 21 26 53 24
Crude protein 208 276 207 209 166 333 329
NDCD 888 887 889 886 855 884 891
Estimated ME (MJ/kg/DM) 12.7 12.7 12.7 12.7 12.3 12.7 12.8
feeding was offered in two equal meals daily after each milking. In both experiments, a supplement of 100 g/day of mineral/vitamin was included. Each concentrate treatment was offered for 21 days duration, with 15 days of adaptation to the diet and six days of measurement. Water was available at all times throughout the experiments.
2.4. Measurements
Milk yield was recorded at every milking and from those data the individual weekly mean yields of milk were calculated. The composition of milk (fat, protein and lactose concentrations) were determined by near infra-red spectroscopy once weekly on samples of milk taken from morning and afternoon milkings. Live weight and condition score were recorded weekly at the same time of day thereby, reducing factors affecting weight change. The voluntary dry matter intake of cows was determined daily for each individual animal by weighing back refusals the subsequent morning. Samples of forages offered and refused were taken weekly and frozen for chemical analysis. In Experiment 2, blood samples were taken weekly from the jugular vein prior to feeding.
2.5. Apparent digestibility
In Experiment 1, the apparent digestibility of the urea treated whole-crop forage (variety Axona) was measured in four Holstein Friesian heifers of mean initial live weight 555 kg (550±561) at the same time as the lactating cow trial. The design of the experiment was based on a switch-back design with two periods and four animals. Two levels of feeding were applied being maintenance and ad libitum. Each period lasted 21 days with 14 days of adaptation and 7 days of measurement.
The heifers were housed in individual pens, bedded on rubber mats and offered urea treated whole-crop wheat at 08.00 h at the level of feeding designated by the experimental design. For the ad libitum treatment, the level of urea-treated whole-crop wheat offered was adjusted by 1.1 times that ingested in the previous 24 h. The level of urea-treated whole crop wheat offered at maintenance level of feeding was calculated using the method of Agricultural Research Council (ARC, 1980) assuming the metabolisable energy density of the feed was available from estimates of in vitro digestibility. Faeces
were collected from the floor of the pen three times daily, weighed and dried at 608C for
48 h. The dried faecal samples were bulked for the 7 days of collection. Three representative samples of faeces from each animal in each collection period were analysed for ash, neutral detergent fibre (NDF), acid-detergent fibre (ADF) and starch.
In Experiment 2, a similar protocol was used to Experiment 1 but the animals used to determine the digestibility of the diets were the lactating dairy cattle described in the previous section. Faeces were collected four times daily from the pen floor and processed in a similar fashion to digestibility trial in Experiment 1.
2.6. Chemical analysis
Samples of urea-treated whole-crop wheat, taken at offer and as refusals, concentrates and faeces were analysed for oven DM using the method of MAFF (1986). Samples of
urea-treated whole-crop wheat (offered and refused) were also analysed for DM content using the toluene extraction method of MAFF (1986). Total N was determined using a micro-kjeldahl method (MAFF, 1986) with a copper-selenium catalyst. Ammonium N was assessed by micro-distillation (MAFF, 1986). Aqueous extracts from the whole-crop samples were analysed for pH and water soluble carbohydrate (MAFF, 1986). Subsamples of the dried and milled to 1 mm, urea-treated whole-crop wheat, faeces and concentrates were analysed for total ash (MAFF, 1986), NDF and ADF (using the sodium sulphite addition method for NDF; Van Soest et al. (1991)), acid detergent lignin (ADL; Van Soest, 1982), starch (Keppler and Decker, 1984) and digestibility (NDCD; Dowman and Collins, 1982).
Samples of blood were taken from the jugular vein were taken into oxalate fluoride and heparin anticoagulant glass tubes. The samples of whole blood were centrifuged and sera collected. Sera samples were analysed for the concentration of magnesium, phosphorus,
glucose,bhydroxy butyrate, non esterified fatty acids, albumin, globulin and urea using
the methods of MAFF (1984).
2.7. Statistical analysis
Experiments 1 and 2 were based on Latin square designs and therefore the data was subjected to analysis of variance (ANOVA) procedures described by the linear model:
Yijij t "ij
whereYij is the observation at the intersection of theith row and thejth column andbi
represents the row (period) effect,jrepresents the column (animal) effect,(t) represents
the treatment effect (represented in each row or column once) and"ijthe unaccounted error.
In Experiment 1, the response to treatment was estimated on 24 error degrees of freedom (d.f.) with the main effects of treatment (3 d.f.), period (9 d.f.) and animal (9 d.f.) being considered by ANOVA. The effect of squares were removed accounting for 2 degrees of freedom. Similarly in Experiment 2, the effect of squares accounted for 1 degree of freedom, the response to treatment was estimated on 6 error degrees of freedom with treatments (2 d.f.), periods (4 d.f.) and animal (4 d.f.) being considered by ANOVA. Statistical analysis of blood compositional data was performed by ANOVA considering by week effect as well as by treatment, period and animal responses. The data for the digestibility trial associated with Experiment 1 was based on 2 error degrees of freedom. All statistical analysis were performed using SAS version 3 (SAS Institute, 1985).
3. Results
3.1. Feed composition
The formulation and chemical composition of concentrates offered in Experiments 1 and 2 are shown in Table 1. The chemical analysis of urea-treated whole crop wheat before treatment with urea is in Table 2. Although the crops were harvested at similar stages of growth there was a difference (104 g/kg/DM) between the level of NDF (and in
ADF) between the two urea-treated whole-crop wheat forages offered to dairy cattle in Experiments 1 and 2. The difference (117 g/kg/DM) in the predicted digestibility (NDCD) of the forage may be ascribed to the high NDF content of the whole-crop used in Experiment 1 (variety Axona) compared to that used in Experiment 2 (variety Avalon). A small difference between the two varieties in the concentration of starch (14 g/kg/DM) prior to ensiling with urea was observed.
The chemical composition of urea-treated whole-crop wheat offered to and refused by dairy cattle in Experiments 1, 2 and the digestibility trial are shown in Table 3. Urea treatment of the forage led to a substantial increase in the total N content as ammonia-N.
3.2. Voluntary intake
Selection of different components of the diet was observed in all experiments. In the digestibility study, grain was ingested in preference (offered 236 g starch kg/DM versus. Table 2
Chemical composition of wheat forage before treatment with urea (g/kg/DM unless stated)
Experiment 1 Experiment 2
Chemical composition of urea treated whole crop wheat as offered to and refused by dairy cattle and growing heifers (g kg DM unless stated)
Toluene DM (g/DM/kg) 657 599 657 605 634 602 596 587
NDF 455 496 455 489 328 358 339 338
ADF 317 338 317 329 210 236 218 218
OM 937 931 937 936 956 943 951 951
WSC 17 13 17 16 18 15 15 16
Starch 236 147 236 169 251 209 226 227
Crude protein 171 136 171 151 235 196 223 222
Ammonia-N (g/kg/total N) 273 187 273 203 289 196 198 207
pH 8.6 7.5 8.6 7.4 8.8 7.3 7.9 7.9
NDCD 640 590 640 601 773 687 729 736
refused 169 g starch kg/DM; Table 3) to straw and chaff. A similar observation (offered 233 g starch kg/DM versus refused 147 g starch kg/DM) was recorded for lactating cows (Experiment 2) but no evidence of level of feeding of concentrates altering the degree of selection was observed. The effect of type of protein offered as the concentrate supplement (Treatments F versus G; Experiment 2) seemed to have little impact on the degree of selection in the forage crop, and the degree of selection was less in Experiment 2 than in Experiment 1.
The total voluntary DM intakes of lactating cattle were high in both experiments (Table 4). In Experiment 1 the total DM intakes were 32.4, 32.7, 33.4 and 34.3 g/kg/live
weight, respectively (p< 0.01) for treatments A, B, C and D. The mean substitution effect
of the concentrate was 0.59 kg/DM/forage kg/DM concentrate. The mean total DM intakes observed in Experiment 2 were 35.8, 36.7 and 35.5 g kg/live weight for treatments E, F and G, respectively.
3.3. Milk production
The level of milk production in both experiments was low compared to pre-experimental (initial). In Experiment 1 increases in the yield of milk were observed with
increasing level of concentrate energy (p< 0.001; A versus C versus D, Table 4) and in
cattle given concentrates with different levels of energy but equivalent concentrations of
crude protein (p< 0.01; B versus C, Table 4), however no significant influence of level of
crude protein at iso-energetic intake was observed (A versus B). The increase in milk yield as a result of increasing concentrate intake equated to 0.52 kg milk/kg/DM/ concentrate intake.
Table 4
DM intake (kg/day), milk yield (kg/day), milk composition (g/kg, live-weight (kg), live-weight gain (kg/day)
and condition score of lactating cows offered urea-treated whole-crop wheat as the sole foragea,b
Experiment 1 s.e.d. Experiment 2 s.e.d.
A B C D E F G
Forage DM intake 14.85 15.02 13.8 12.81 0.367*** 18.80 19.03 18.21 0.88
Concentrate DM intake 5.21 5.22 6.95 8.68 3.44 3.48 3.53
Total DM intake 20.06 20.24 20.75 21.49 0.369** 22.24 22.51 21.74 0.88
Milk yield 21.3 21.9 22.4 23.1 0.37*** 17.3 17.2 19.0 0.44*
Milk fat 39.2 39.3 40.2 40.0 0.85 46.1 42.7 42.8 1.51
Milk protein 31.8 32.4 32.7 33.1 0.33** 36.8 37.3 36.6 0.41
Milk lactose 47.2 46.7 47.0 47.3 0.42 46.0 45.7 46.9 0.45
Live weight 620 621 623 626 4.25 622 613 612 5.23
Live-weight gain 0.24 ÿ0.05 0.17 ÿ0.01 0.256 0.77 0.70 0.62 0.121
Condition score 2.44 2.56 2.55 2.61 0.127 2.52 2.51 2.58 0.100
aA: 6 kg/day of 208 g CP kg/DM; B: 6 kg/day of 276 g CP kg/DM; C: 8 kg/day of 207 g CP kg/DM; D:
10 kg/day of 209 g CP kg/DM; E: 4 kg/day of 166 g CP kg/DM; F: 4 kg/day of 333 g CP kg/DM; G: 4 kg/day of 329 g CP kg/DM.
b*p< 0.05, **p< 0.01 and ***p< 0.001.
A significant increase (p< 0.01) in milk protein was observed with increasing level of concentrate fed, but no effect of level of crude protein at iso-energetic intake (A versus B) was observed. No significant effect of treatments was observed for the concentration of
fat or lactose in the milk. Significant increases in yields of fat (p< 0.05), protein
(p< 0.001) and lactose (p< 0.05) were observed for level of concentrate feeding.
In Experiment 2 milk yield was increased (p< 0.05) significantly as a result of the
addition of fishmeal to the concentrate diet (Treatment G). There was no effect of type of concentrate on milk composition but yield of protein and yield of lactose showed an
increase (bothp< 0.05) in Treatment G compared with Treatments E and F.
3.4. Live weight change
Estimates of live-weight gain and condition score during each experiment are shown in Table 4. No significant changes in live weight or condition score were observed in all experiments with lactating cows. A significant increase in live-weight gain was observed with heifers offered ad libitum urea treated whole-crop wheat compared to maintenance level of feeding.
3.5. Apparent digestibility
The digestibility coefficients for urea treated whole-crop wheat for both the experiments are given in Table 5. The digestibility of the urea treated whole-crop wheat used in Experiment 1 was evaluated at two levels of feeding, maintenance and ad libitum. There was no effect of level of feeding on the digestibility of DM, organic matter (OM), NDF, ADF, starch or on digestible organic matter in the DM.
In Experiment 2, the apparent digestibility coefficients were calculated from the total apparent digestibility corrected for concentrate digestibility (NDCD). The effect of increasing the level of protein in the diet by addition of fishmeal (treatment E versus G)
was to increase the digestibility of DM (35 g kg/DM; p< 0.05), OM (33 g kg/OM;
p< 0.01), NDF (26 g/kg; p< 0.05), ADF (30 g/kg; p< 0.01), starch (32 g/kg;
Table 5
Apparent digestibility of urea-treated whole-crop wheat (g/kg unless stated) in growing heifers (Experiment 1)
and dairy cows (Experiment 2)a,b
Experiment 1 s.e.d. Experiment 2 s.e.d.
Ad libitum Maintenance E F G
DM 657 659 2.51 745 767 780 6.73*
OM 695 693 2.60 757 772 790 5.62**
DOM (g/kg/DM) 647 645 2.10 723 738 754 6.38**
NDF 603 598 2.90 564 534 538 8.51*
ADF 492 519 3.53 527 519 557 7.66**
Starch 861 857 1.64* 934 948 966 2.01***
aE: 4 kg/day of 166 g CP kg/DM; F: 4 kg/day of 333 g CP kg/DM; G: 4 kg/day of 329 g CP kg/DM.
b*p< 0.05, **p< 0.01, ***p< 0.001.
p< 0.001)and to increase the digestible organic matter in the DM (31 g/kg;p< 0.05). The inclusion of soya-bean meal into the diet had a similar effect to that of fishmeal (Table 5), however, significant differences in digestibility between diets supplemented with concentrates containing soya-bean meal or fishmeal were observed for OM and ADF only.
3.6. Blood analysis
The mineral composition of bovine sera (Mg and P) did not differ significantly from those values reported as `normal' in the literature (Payne and Payne, 1987). Supplementation of the diets with minerals and vitamins ensured the concentrations of P and Mg in sera were maintained as the levels of inorganic P and Mg in urea-treated whole-crop wheat were low (2.35 g/P/kg/DM and 7.23 g/Mg/kg/DM; Table 6). The
concentrations of b-hydroxy butyrate, glucose or non esterified fatty acids were low
suggesting there was no deficit of energy. When the data for the concentrations of non esterified fatty acids were analysed by week after offer of urea-treated whole-crop wheat, a skewed distribution of concentration within time was observed (Fig. 1). When urea treated whole-crop wheat was supplemented with a low level of crude protein via the concentrate (Treatment E), the rate of decline of non esterified fatty acid during the first week of the experimental period was rapid suggesting mobilisation of lipid reserves. The rate of decline in concentration of non esterified fatty acids for the diet supplemented high levels of protein (Treatments F and G) was however significantly less than treatment E. No effect of type of high protein supplementation (Treatment F versus G) was observed.
The concentration of albumin was elevated slightly compared with normal concentrations. The concentration of urea in sera was significantly greater than normal values with concentrations ranging from 9.79 to 11.45 mmol/l. The highest concentration
of urea in sera was observed in lactating cattle offered fishmeal in their diet (p< 0.05;
Table 6). Table 6
Composition of blood sera of cattle offered diets containing urea-treated whole-crop wheat as the sole forage
(Experiment 2)a
Treatment s.e.d
E F G
Magnesium (mmol/l) 0.95 1.02 1.05 0.047
Phosphorus (mmol/l) 1.83 1.68 2.06 0.238
Glucose (mmol/l) 2.80 2.73 2.73 0.091
b-hydroxy butyrate (mmol/l) 0.26 0.21 0.25 0.039
Non esterified fatty acids (mmol/l) 161 119 146 45.7
Urea (mmol/l) 10.34 9.79 11.45 0.761
Albumin (g/l) 37.0 36.6 37.4 0.80
Globulin (g/l) 36.6 36.2 37.3 1.23
aE: 4 kg/day of 166 g CP kg/DM; F: 4 kg/day of 333 g CP kg/DM; G: 4 kg/day of 329 g CP kg/DM.
Fig. 1. Concentration of non esterified fatty acids (umol/l) in blood sera of lactating cows given diets containing urea treated whole crop wheat as the sole forage.
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4. Discussion
4.1. Nutritive value of urea treated whole crop
The addition of urea to harvested whole-crop wheat prior to ensiling restricts markedly the fermentation of the forage during storage (Hill and Leaver, 1998). However, in both experiments the differences between toluene corrected DM and oven DM were higher than expected (29 and 36 g/DM/kg for Experiment 1 and 2, respectively), an observation similar to Tetlow and Mason, 1987. The mean chemical composition of whole-crop used in both experiments were within the range of samples reported in the UK (Adamson and Reeve, 1992). The forage harvested in Experiment 1 for whole-crop production was relatively mature (hard dough stage) and the concentration of NDF and ADL in the dry matter was relatively high (507 g/kg/DM and 41 g/kg/DM; Table 2). The winter sown variety of wheat harvested for whole-crop production in Experiment 2 was harvested at a similar stage of maturity but the concentration of NDF and ADL were substantially lower (403 and 26 g/kg/DM; Table 2). These differences could be ascribed to either a lower degree of lignification of the stem and leaves or an increase in the proportion of leaves in the total DM at harvest. Small differences in the level of starch in the diet were observed between the two experiments. The level of starch in the whole-crop increases as grain fill progresses and to some extent compensates for the increase in NDF and ADL thus leading to a reduced rate of decline in digestibility of the forage when mature (Corrall et al., 1977; Leaver and Hill, 1995).
The mean forage intakes for whole-crop offered in the two trials were high but the substitution effect of concentrates was similar to other conserved forage (0.59 kg/DM/kg/ DM). The voluntary intake and digestibility data were complicated by the animal selecting components preferentially of the forage (Table 3). Selection leads to difficulties in developing models for in vitro and in vivo predictions of feed digestibility. Several authors (Adesogan et al., 1998; Hameleers, 1998) have suggested that the neutral detergent cellulase digestion method may not be a good predictor of digestibility of whole-crop wheat. The mean apparent digestibilities of digestible organic matter for urea-treated whole crop given in Experiment 1 and 2 were 646 and 738 g/kg/DM, respectively reflecting the different proportions of leaf and stem in the forage. The predicted ME contents of the urea treated whole-crop given to dairy cattle in Experiments 1 and 2 were 10.4 and 11.4 MJ/kg/DM respectively according to the method of Givens (1990) viz.
ME MJ=kg=DM 2330:65NDCD0:0157
where NDCD is expressed as g kg/DM.
However, a change in digestibility of diet would occur if grain passage was increased substantially or if selection of dietary components occurred to any great degree. The neutral detergent cellulase digestion method does not consider the composition of feed refused and therefore may well over estimate the metabolisable energy content of the feed. However, there was little difference in the digestibility of urea-treated whole-crop between the NDCD and the in vivo methods employed in this study (Tables 3 and 5).
The apparent starch digestibilities for the whole-crop wheat offered to heifers (Experiment 1) and cows (Experiment 2) were in the range of 857±966 g/kg and greater
than those reported by Castejon and Leaver (1994) and Sutton et al. (1998) but similar to those of Deschard et al. (1987) and Adesogan et al. (1998). The estimated mean losses of starch to faeces for Experiments 1 and 2 were 0.52 and 0.27 kg/day, respectively, which represents a loss of potential ME of about 8 and 5 MJ/ME/day, respectively. Adesogan et al. (1998) examined the digestibility of starch in many samples of whole-crop wheat using sheep. The greater efficiency of sheep to digest starch in cereal grain than cattle (Adesogan et al., 1998) emphasises the need to evaluate such forages with appropriate animals.
4.2. Milk production
Replacement of grass silage diets with urea-treated whole crop wheat has led to increases in milk protein but no increases in yield in primiparous animals with moderate milk yields (Phipps et al., 1992). Several authors (Leaver and Hill, 1995; Sutton et al., 1997, 1998; Hameleers, 1998) have also shown small positive responses in milk composition or yield in multiparous animals given diets containing up to 0.4 of the forage DM as urea-treated whole-crop wheat, but no studies investigated the sole feeding of urea-treated whole crop with differing levels of concentrate. In Experiment 1, the increased supply of metabolisable energy from the total diet as a result of the level of concentrate offered increased significantly the yield of milk and concentration of milk protein (Table 4). Increasing the supply of crude protein via the concentrate but not increasing the level of energy had little effect yield or composition of milk. Similarly in Experiment 2, the effect of type of protein given in the concentrate was to increase yield but not alter composition. The effect on yield of milk in Experiment 2 (fishmeal supplementation via the concentrate; Treatment G) could be ascribed to the increase in digestibility of the diet or the increase in supply.
4.3. Energy and nitrogen balances
The current method of prediction of ME content of urea-treated whole-crop wheat may lead to an overestimation of ME content. The nitrogen balances for the cows were calculated according to AFRC (1993) and based on the requirements of the animal for metabolisable protein. The estimated energy balances in these experiments are shown, with estimated N efficiencies, in Table 7.
Assuming there were no differences in the efficiency of energy utilisation between treatments (according to Sutton et al., 1998), the estimated ME contents of the urea treated whole-crop forage in Experiments 1 and 2 were 6.1 (range 5.0±6.7) MJ/kg/DM and 7.3 (range 7.0±7.4) MJ/kg/DM, respectively. These ME contents of the forage component of the diet were similar to those reported by Hameleers (1998) but lower than Sutton et al. (1998). Changes in live weight were determined after three weeks of feeding but the cows did not gain weight at a rate suggested by the surplus of energy resulting from the total DM intake. Results for digestibility of DM in Experiment 2 especially (high DM digestibility and high starch digestibility) indicate that digestibility is not the explanation for the apparent low ME of urea-treated whole-crop wheat as the sole forage and does not support the interpretation of Sutton et al. (1998). If the ME balances are corrected for the cost of excretion of urea via the urine using the method of NRC (1989),
Table 7
Estimated energy (MJ/day) and nitrogen balance (g/N/day) of lactating cows offered diets containing urea-treated whole-crop wheat as the sole foragea
Experiment 1 s.e.d. Experiment 2 s.e.d.
A B C D E F G
ME intake 210 213 222 234 3.56*** 245 255 251 9.00
ME requirement for milk 103 106 110 114 11.18 96 95 100 6.31
ME requirement for maintenance and change in live-weight 68 59 66 60 0.31 85 82 82 3.91
ME intake - ME requirement 39 48 46 60 3.65** 64 78 69
N intake 553 621 576 597 10.04*** 798 901 871
N requirement for milk 107 111 115 120 2.44** 100 101 109 4.22*
N requirement for maintenance and change in live-weight 179 180 181 182 3.15 158 156 158 3.12
N balance 267 330 280 295 8.38*** 540 644 604 27.1*
N efficiency (N requirement for milk/N intake) 0.193 0.179 0.200 0.201 0.125 0.112 0.125
a*p< 0.05, **p< 0.01 and ***p< 0.001.
J.
Hill,
J.D.
Leaver
/Animal
F
eed
Science
and
T
ech
nology
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(1999)
the surplus in the balance calculation approaches 35 MJ/day for all the dietary treatments. This would suggest there is an effect on efficiency of use of metabolisable energy resulting from a surplus of ammonia entering intermediary metabolism of the cow.
4.4. Blood analysis
The levels of the various substrates which indicate energy status of the cow during
lactation (glucose, b-hydroxy butyrate, non esterified fatty acids) were within normal
levels. This suggests that the influence of sources and level of dietary nitrogen and energy were adequate for the level of animal performance (Miettinen and Huhtanen, 1989). Hypoglycaemia can be observed in cattle given diets containing excessive levels of rapidly fermentable nitrogen sources (Symonds et al., 1981). The elevated concentration of urea in sera is a direct response to the high levels of ammonia and degradable nitrogen in the diet. There was a significant influence of source of dietary nitrogen (fishmeal; Treatment G) on the concentration of urea in sera may reflect an increase in the effectiveness of nitrogen uptake compared to the soya -supplemented diet (Treatment F). The rapid mobilisation of non esterified fatty acid by animals during the early stage of the trial with animals given the low protein supplementation (Treatment E) may suggest the cow might be increasing the available energy supply to reduce the level of dietary nitrogen excess. Where animals were given diets which contained high levels of amino acids (Treatments F and G), the decline in non esterified fatty acids was not as rapid potentially suggesting that more energy was available via digestion of the diet rather than met by a mobilisation of body reserves. This observation is tentatively supported by the apparent digestibility data.
5. Conclusions
Urea-treated whole-crop wheat offered as a sole forage had high intake characteristics in spite of the high content of ammonia nitrogen. In vivo and in vitro (NDCD) digestibility results for whole-crop wheat were similar. Using in vivo digestibility to predict the ME value of the forages led to much higher values than from ME balances of estimated ME minus ME requirements for the measured production levels. This indicates there was a poor utilisation of the digested energy with urea-treated whole-crop wheat.
Supplementation of the forages with different levels of concentrate led to similar responses to those observed with other types of forage. In general increasing the supply of crude protein via the concentrate supplement, but not increasing the level of metabolisable energy intake, had little effect on yield or composition of milk. However, additional protein in the concentrate in the form of fish meal significantly increased milk yield.
Acknowledgements
The authors wish to thank the Ministry of Agriculture, Fisheries and Food, UK, for financial support of this work.
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