Effects of crop maturity and cutting height on the nutritive value of fermented whole crop wheat and milk production in dairy cows

Livestock Production Science 81 (2003) 257–269 www.elsevier.com / locate / livprodsci

Effects of crop maturity and cutting height on the nutritive value of fermented whole crop wheat and milk production in dairy cows L.A. Sinclair*, R.G. Wilkinson, D.M.R. Ferguson ASRC, School of Agriculture, Harper Adams University College, Edgmond, Newport, Shropshire TF10 8 NB, UK Received 26 February 2002; received in revised form 3 October 2002; accepted 10 October 2002

Abstract Factors influencing the nutritive value of fermented whole crop wheat (WCW) and effects on milk production in dairy cows were investigated in three experiments. In experiment 1, WCW was harvested at one of two maturities: at a dry matter (DM) content of 296 g / kg, 52 g / kg DM starch (LS) or DM of 371 g / kg, 221 g / kg DM starch (HS). Ninety early lactation dairy cows were split into three groups and fed either LS, HS or a first cut grass silage (G). The WCW was mixed 2:1 on a DM basis with the grass silage. There was no significant effect of dietary treatment on milk production (kg / day) although cows fed the low starch WCW (LS) had the lowest milk protein concentration (mean values of 32.1, 30.7 and 31.6 g / kg for cows fed G, LS and HS, respectively, P , 0.05). Plasma urea levels were significantly lower in cows fed the HS compared with the LS treatment (P , 0.05). In experiment 2, ninety early lactation dairy cows were fed one of three dietary treatments: WCW harvested at a long straw length and supplemented with either a starchy concentrate (LW) or a more fibrous concentrate (LF) or a short straw length and supplemented with a fibrous concentrate (SF). The WCW was mixed 1:1 on a DM basis with first cut grass silage. Increasing the cutting height increased starch concentrations from 232 to 292 g / kg DM and reduced neutral detergent fibre from 433 to 384 g / kg DM in the long and short straw WCW, respectively. There was no significant effect of dietary treatment on milk production, composition or body condition score over the experimental period. The lower plasma non-esterified fatty acid concentration in cows fed LW or SF during week 10 of lactation indicate a more positive energy balance in early lactation on these treatments. In experiment 3 the apparent digestibility of the grass silage, long straw whole crop wheat or short straw WCW fed at maintenance or the long straw WCW fed ad libitum was determined in growing lambs. Digestibility coefficients of the grass silage were significantly higher than those of any of the WCW forages, particularly for the fibre fractions. The digestibility of starch was high in all three WCW treatments and averaged 0.955 kg / kg but was not affected by straw length or feeding level. The improvement in metabolisable energy value (MJ / kg DM) by increasing the cutting height at harvest was small and not significant. Increasing the maturity at harvest and decreasing the length of straw at cutting was also observed to have a small but significant effect on decreasing the aerobic stability of the WCW forages. The results indicate that fermented whole crop wheat can provide a comparable milk production to a good quality grass silage and that harvesting at a later stage of maturity had little effect on milk production

*Corresponding author. Tel.: 144-1952-815-332; fax: 144-1952-810-931. E-mail address: [email protected] (L.A. Sinclair). 0301-6226 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0301-6226(02)00261-0

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although milk protein levels tended to be higher in cows fed the higher starch material. There was little advantage to altering cutting height of fermented WCW on apparent digestibility or by altering supplement composition on milk production.  2002 Elsevier Science B.V. All rights reserved. Keywords: Fermented whole crop wheat; Chemical composition; Digestibility; Milk production

1. Introduction

2. Materials and methods

Whole crop cereals offer the potential of a higher yielding forage than grass silage, which is particularly beneficial in drier climates where grass growth can be low and unpredictable or in climates where alternative forages such as maize are difficult to grow. Much attention has been focussed recently on harvesting whole crop wheat at approximately 550 g / kg dry matter (DM) and adding urea at the rate of 20–40 kg / t DM to prevent fermentation and produce a forage with a pH of approximately pH 7.5–8.0 (Phipps et al., 1995; Sutton et al., 1997, 1998). Whilst urea-treated whole crop wheat has been demonstrated to have higher intake characteristics than grass silage (Phipps et al., 1995) there is generally little effect on milk production or composition (Leaver and Hill, 1995; Phipps et al., 1995). This discrepancy has been attributed to the low digestibility in these higher DM crops, particularly of starch, where approximately 0.20 of intake has been reported to be indigestible (Sutton et al., 1997, 1998). In addition, the high levels of urea that are added at ensiling and the low efficiency of capture of N may represent an inefficiency in animal metabolism and be an environmental problem (Sutton et al., 1998). Ensiling the forage when it is at a less mature stage of development and allowing the crop to ferment avoids the need to add urea at ensiling and the softer grains may be a suitable means of improving animal performance. However, less work has been conducted to evaluate strategies of ensiling and feeding fermented whole crop wheat on the nutritive value and milk production by dairy cows. The objectives of the current series of experiments were to evaluate the effect stage of maturity at harvest and cutting height of fermented whole crop wheat on the nutritive value of the forage and the effects on milk production in early lactation dairy cows.

2.1. Experiment 1: effects of stage of maturity on milk production 2.1.1. Forage production The winter wheat variety Hunter was grown as a conventional cereal crop. The crop was sown at a target seed rate of 220 kg / ha and was top dressed with 167 kg nitrogen (N) per ha in the spring in two split applications. The spray programme consisted of diflufenican and trifluralin in the autumn, flutriafol, chlormequat and choline chloride, metsulfuronmethyl and manganese in May with a further application of tebuconazole and flutriafol and fenpropidin in June. The whole crop wheat (WCW) was harvested at two stages of maturity. The first cut (low starch) was on the 15 July 1996 when the crop was 320 g / kg DM and growth stage 71 (watery ripe; Zadocks et al., 1974) and the second (high starch) on 26 July 1996 at 400 g / kg DM and growth stage 85 (soft dough). Both crops were harvested and chopped directly using a self-propelled forage harvester fitted with a Kemper header and ensiled in two separate Ag-Bags (Ag-Bag International, Warrenton, USA). The crop yield (tDM / ha) was 12.1 and 15.6 for the low and high starch WCW, respectively. The grass silage was a first cut harvested on 13–14 May 1996 from a predominately ryegrass sward that had received 121 kgN / ha in one application on 7 March. An inoculant / enzyme additive (Four Sure: Foursight Agriculture, Shreswbury, UK) was added at harvest and the forage ensiled in a concrete walled clamp. 2.1.2. Animals and experimental procedure Ninety Holstein-Friesian dairy cows were used. One cow was removed during the first week with 89 cows completing the experimental period. Based on recordings taken when the cows were in their fifth

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and sixth week of lactation, the cows were blocked and allocated to one of three treatments according to parity (prima or multi) and calving date (mean6S.D.; 3964.9 days post calving), milk yield (32.766.72 kg / day), liveweight (558665.6 kg) and condition score (2.460.52: East of Scotland College of Agriculture, 1976). The three dietary treatments were grass silage (G), grass silage and low starch whole crop wheat (LS) or grass silage and high starch whole crop wheat (HS). The WCW was mixed with grass silage to provide 2 parts WCW to 1 part grass silage on a DM basis. Animals remained on the dietary treatments for 14 weeks. The cows were housed according to treatment group in cubicles in the same section of an open span building. All cows received a standard dairy cow concentrate (g / kg: 298 rapeseed meal, 225 citrus pulp, 128 rice bran, 80 cottonseed meal, 75 shea nut, 75 molasses, 50 copra, 18 sunflower meal, 11 palm kernel, 15 vegetable oil and 25 minerals and vitamins), a balancing protein concentrate (g / kg 504 rapeseed meal, 145 sunflower meal, 110 soyabean meal, 100 linseed meal, 25 cottonseed meal, 40 Megalac (Volac, Royston, UK) 36 vegetable oil and 40 minerals and vitamins), molassed sugar beet pulp and molaferm 20 (80% molasses, 20% molasses solubles: Rumenco, Burton on Trent, UK). Cows fed the grass silage treatment (G) received on a daily basis 5 kg of the standard concentrate, 2.3 kg of the protein balancer, 3.3 kg of molassed sugarbeet pulp and 1 kg of molaferm 20. Cows on either of the two WCW treatments (LS or HS) received 5 kg of standard concentrate, 3.5 kg of protein balancer, 2.1 kg of molassed sugarbeet pulp and 1 kg of molaferm 20. The diets were formulated to ensure an effective rumen degradable protein (ERDP) to fermentable metabolisable energy (FME) ratio above 11 g / MJ and to provide a supply of metabolisable energy and metabolisable protein to maintain a milk yield of 30 kg / day (AFRC, 1993). This level of production was chosen to reflect the higher yields obtained on many dairy farms that use alternative forages. All diets were fed as a complete diet once daily and sufficient feed was provided such that each group received 0.05 in excess of the ad libitum intake. Differences in the group intakes were made up from adding more of the appropriate forage mixture with the same concentrate level (kg per cow per day) being fed to

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each group. Refusals were collected twice weekly and weighed prior to the morning feed whilst forage samples were taken twice weekly. One sample was oven dried and the ratio of grass silage to whole crop silage adjusted to maintain a ratio of 1:2, respectively, on a DM basis whilst the other sample was frozen and bulked for subsequent analysis. Daily intake was calculated as the quantity of the diet offered minus refusals, assuming that the ratio of concentrates to forage was the same in the diet and the refusals. Cows were milked twice daily at approximately 06:30 and 16:00 h. Milk yield was recorded weekly with samples taken for subsequent analysis of fat and protein. At 6 weeks of lactation and thereafter every 2 weeks, all the cows were weighed and condition scored after an evening milking. Blood samples were taken from the tail vein from a sub-sample of 10 cows per treatment when in their 10th, 16th and 20th weeks of lactation. Blood samples were taken at 11:00 h on each sample date into vacutainer tubes to which either no anti-coagulant or potassium oxalate had been added.

2.2. Experiment 2: effect of cutting height and supplement type 2.2.1. Forage production The winter wheat variety Hunter was grown as a conventional winter wheat crop. The seed grains had been dressed with Pancotine and were sown at a target seed rate of 225 kg / ha. The crop received a top dressing of 172 kg N / ha in the spring in two split applications. The spray programme consisted of flutriafol and metsulfuron-methyl followed by tebuconazole and flutriafol in the spring. The crop was harvested on 28 July 1997 using a self-propelled forage harvester fitted with a Kemper header at a dry matter of 450 g / kg and growth stage 85 (soft dough; Zadocks et al., 1974). The crop was cut at one of two heights; low stubble / long straw (mean6S.D.; 17.9 cm stubble64.70 cm) that represented commercial practice and a higher stubble / short straw (38.2 cm stubble 63.81 cm) that was chosen to minimise straw content whilst avoiding any ears being unharvested. The two treatments were cut on the same day using the same forage harvester and ensiled in two separate Ag-Bags (Ag-Bag International, Warrenton, USA). The average height of the wheat at

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cutting was 87 cm (67.4 cm) and the length of the ears was 10.3 cm (60.62 cm) with the resulting proportion of ears to straw (on a length basis) for the long straw WCW being 0.15 and the short straw WCW 0.21. The crop yield (tDM / ha) was 10.6 and 8.9 for the long and short straw WCW, respectively. The grass silage was harvested on 15 May 1997 from a predominately ryegrass sward that had received 128 kgN / ha in two equal applications on 27 February and 27 March. An inoculant / enzyme additive was added at harvest (Four Sure, Foursight Agriculture, Shrewsbury, UK) prior to ensiling in a concrete walled clamp.

2.2.2. Animals and experimental procedure Ninety Holstein-Friesian dairy cows were used. Based on recordings taken when the cows were in their fifth and sixth weeks of lactation, the cows were blocked and allocated to one of three treatments according to parity (prima or multi), calving date (3964.7 days post calving), milk yield (32.666.43 kg / day), liveweight (546665.4 kg) and condition score (2.060.4). Animals remained on the dietary treatments for 15 weeks. There were three dietary treatment groups: long straw WCW supplemented with sugarbeet pulp as a fibre source (LF), short straw WCW supplemented with sugarbeet pulp (SF) and long straw WCW supplemented with rolled wheat as a starch source (LW). The WCW was mixed with grass silage to provide 1 part grass silage:1 part WCW on a DM basis. All cows received on a daily basis 5.5 kg of a standard dairy cow concentrate (g / kg: 320 rapeseed meal, 177 citrus pulp, 100 wheat, 90 rice bran, 75 palm kernel, 75 copra meal, 75 molasses, 33 linseed meal, 25 vegetable oil, 16 malt culms and 14 minerals and vitamins), 2 kg of a balancing protein mixture (g / kg: 413 soyabean meal, 312 rapeseed meal, 225 fishmeal, 14 vegetable oil and 36 minerals and vitamins), 0.28 kg of Megalac (Volac, Royston, UK) and 1 kg of molaferm 20 (Rumenco, Burton on Trent, UK). In addition, cows fed treatments LF and SF received 2.5 kg / day of molassed sugarbeet pulp whilst those fed LW received 2.5 kg / day of rolled wheat. The diets were formulated to provide a similar nutrient supply (AFRC, 1993). Cow housing, feeding routine and animal measurements were the same as those described for experiment 1. Blood

samples were taken at 11:00 h from a sub-sample of 10 cows per treatment when the cows were in their 10th, 15th and 20th weeks of lactation. Forage samples were taken twice weekly. One sample was oven dried and the ratio of whole crop silage to grass silage adjusted to maintain a ratio of 1:1 on a DM basis. The other sample was frozen and bulked for subsequent analysis.

2.3. Experiment 3: apparent digestibility of WCW harvested at two cutting heights in sheep Sixteen Suffolk cross wether lambs weighing approximately 35.0 kg live weight (W) were allocated to one of four dietary treatments: grass silage offered at maintenance (GS), long straw WCW silage offered at maintenance (LSL), short straw WCW silage offered at maintenance (SSL) or long straw WCW silage offered ad libitum (LSH). All three forages were the same as those used in experiment 2. Feeding level was calculated according to AFRC (1993). All diets were supplemented with minerals and vitamins (Sheep General Purpose, Rumenco, Burton on Trent, UK) at a rate of 15.0 g / day and 7.0 g / day of feed grade urea was mixed with the WCW silage diets in order to ensure that ERDP was in excess of requirements (AFRC, 1993). The animals were housed in individual, slatted floor pens and water was freely available at all times. The experiment was conducted over a 20-day period. During the 10-day preliminary period animals were adapted to the experimental diets and food intake was recorded. During the 10-day collection period animals were fitted with faecal collection harnesses and food intake and faecal output were recorded. Animals were fed twice daily at 07:00 and 16:30 h and the faecal collection bags were changed prior to the afternoon feed. Refusals were recorded daily and animals on treatment LSH were offered 0.10 more than they consumed the previous day. Daily faecal output was recorded and a sub-sample (0.20 of daily output) frozen at 2 20 8C prior to analysis.

2.4. Forage aerobic stability measurements Sub samples (1.0 kg) of the grass silage and whole crop wheat forages used in experiments 1 and 2 were

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weighed into polystyrene boxes fitted with lids (five replicates per treatment) and with external dimensions of 240 3 175 3 185 mm and wall thickness of 25 mm into which holes were bored. The forages were loosely teased out by hand and the boxes placed in a controlled environment room set at 13.0 8C. The temperature was measured daily for a period of 10 days, as an index of microbial activity and aerobic deterioration.

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lysed by analysis of variance for a randomised block design using the model Yij 5 b I 1 t j 1 e ij where b I 5 mean yield for block i and t j 5treatment effect on yield. All analyses were conducted using GENSTAT 5.1 (Lawes Agricultural Trust, 1990).

3. Results

3.1. Experiment 1 2.5. Chemical analysis Weekly forage and concentrate samples were bulked for each month of the experimental period. A sub-sample of the forages and the concentrates and the faecal material was analysed for DM, ash, nitrogen and ammonia nitrogen, starch and water soluble carbohydrates (AOAC, 1990), neutral detergent fibre (NDF) and acid detergent fibre (ADF) (Van Soest et al., 1991) whilst forage samples were also analysed for pH (MAFF, 1986) and volatile fatty acids (Jones and Kay, 1976). The metabolisable energy content of the grass silages was predicted by modified acid detergent fibre whilst that of the concentrates by neutral detergent cellulase and gammanase (AFRC, 1993). Milk samples were analysed for fat and protein using a Milkoscan 303b double beam infra red spectrophotometer. Blood samples were analysed for b-hydroxybutyrate (3-OHB), nonesterified fatty acids (NEFA) and urea-N using a Bayer Technicon RA 1000 auto-analyser. Plasma NEFA concentrations in experiment 1 and urea in experiment 2 were not significantly affected by treatment and have not been presented.

2.6. Data analysis Milk yield parameters, liveweight, condition score and blood parameters were evaluated by analysis of variance for a randomised block design using, when appropriate, milk yield (kg / day) in the 2 weeks prior to blocking as a co-variate. Liveweight change (kg / day) was calculated by regressing liveweight on time. Digestible OM in the dry matter (DOMD), corrected for losses during oven drying and metabolisable energy (ME) were predicted as AFRC (1993). The data for the lamb digestibility trial and the forage aerobic stability measurements were ana-

The chemical analysis of the three forages is presented in Table 1. The DM content (g / kg) of the low starch whole crop wheat was 296 and the high starch whole crop wheat 371 whilst the grass silage had the lowest DM content at 252. Crude protein concentrations were highest in the grass silage with the low starch whole crop forage having a higher crude protein content than the high starch whole crop forage (104 vs. 78 g / kg DM for the low and high starch WCW, respectively). By contrast, the starch levels were 221 g / kg DM in the high starch WCW and 52 g / kg DM in the low starch WCW (Table 1). All three silages had a stable fermentation with pH values of approximately 3.9 and ammonia N levels (expressed as a proportion of total N) of approximately 50 g / kg. By contrast the two fermented whole crops had lower levels of total fermentation acids than the grass silage. Both concentrates had a low content of starch at less than 110 g / kg DM. Intake of concentrates was similar for all three treatments at 9.6 kg DM / day for cows offered treatment GS and 9.7 kg DM / day for those offered either LS or HS. The intake of forage was lowest in cows fed the grass silage (9.0 kg DM / day) and highest in cows fed the high starch whole crop wheat (11.5 kg DM / day) with cows fed the low starch whole crop wheat having an intermediate level of intake (10.7 kg DM / day). There was no significant effect of forage treatment on the average yield (kg / day) of milk, fat or protein or on the average fat concentration (Table 2). By contrast, mean milk protein concentration was lower in cows fed the low starch WCW (LS: P,0.05). There was no significant effect of treatment on average liveweight or condition score or daily liveweight change. Plasma urea concentrations were consistently higher throughout the experimental period in cows

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Table 1 Chemical composition of the grass silage, low starch whole crop wheat (WCW), high starch WCW and concentrates fed to dairy cows in experiment 1 Grass silage

Low starch WCW

High Starch WCW

Standard concentrate

Protein balancer

Dry matter (g / kg)a

252 (15.0)

296 (8.3)

371 (10.1)

889 (5.1)

903 (1.9)

g /kg DM Crude protein Starch Neutral detergent fibre Acid detergent fibre Ash pH Ammonia-N (g / kg total N) Water soluble carbohydrate Metabolisable energy (MJ / kg DM)

201 (15.7) nd b 447 (29.0) 247 (31.1) 85 (7.0) 3.8 (0.13) 37 (0.5) 84 (21.2) 11.7 (0.52)

104 (5.9) 52 (8.1) 595 (4.3) 345 (9.6) 58 (3.0) 3.9 (0.05) 48 (3.0) 54 (3.6) nd

78 (4.8) 221 (25.9) 487 (13.5) 287 (8.3) 51 (1.6) 4.0 (0.09) 51 (4.7) 10 (1.8) nd

218 (3.1) 107 (3.8) 308 (10.4) 182 (2.1) 85 (1.9) nd nd 113 (6.1) 13.2 (0.10)

335 (4.5) 55 (10.0) 276 (14.2) 193 (8.7) 98 (8.5) nd nd 80 (5.3) 13.5 (0.12)

Fermentation acids ( g /kg fresh weight) Lactic 115 (27.1) Acetic 14 (4.1) Propionic 0.2 (0.45) Butyric 0

42 (14.0) 3.8 (4.0) 0 0

17 (3.0) 3.8 (0.8) 0 0

nd nd nd nd

nd nd nd nd

Ethanol (g / kg fresh weight)

10.4 (5.9)

8.0 (1.41)

nd

nd

a b

8.8 (3.56)

Mean (standard deviation of five observations). nd, not determined.

Table 2 Milk yield, composition, liveweight and condition score of dairy cows fed grass silage (GS), low starch whole crop wheat (LS) or high starch whole crop wheat (HS) treatments in experiment 1

Milk yield (kg / day) Fat yield (kg / day) Protein yield (kg / day) Fat (g / kg) Protein (g / kg) Liveweight (kg) Liveweight change (kg / day) Condition score

GS

LS

HS

S.E.D.

Sig

29.8 1.20 0.95 40.9 32.1 577 0.22

30.1 1.22 0.92 40.9 30.7 592 0.29

30.7 1.22 0.97 39.7 31.6 588 0.40

0.65 0.038 0.02 1.06 0.50 12.4 0.097

NS NS NS NS * NS NS

2.29

2.34

2.40

0.106

NS

NS, not significant; *P,0.05.

fed the low starch (LS) compared with the high starch (HS) WCW, with the difference being significant during week 20 of lactation (P,0.05; Fig. 1a). Plasma 3-OHB levels were relatively constant between sampling dates although they were significantly higher in cows fed diet LS during week 20 of

lactation than in those fed either of the other two dietary treatments (P,0.01; Fig. 1b).

3.2. Experiment 2 The chemical analysis of the three forages is

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Fig. 1. Plasma urea (a) and b-hydroxybutyrate (b) concentrations in cows fed diets based on grass silage (GS: d), low starch whole crop wheat (LS: j) or high starch whole crop wheat (HS: m) in dairy cows in experiment 1.

presented in Table 3. The grass silage had the lowest DM content at 233 g / kg whilst cutting height had only a marginal effect on DM content with a value of 446 g / kg for the long straw and 477 g / kg for the short straw WCW. Similarly the crude protein content was approximately the same for both WCW forages (mean value of 102 g / kg DM) and considerably lower than that of the grass silage (168 g / kg DM). However, raising the cutting height of the WCW increased the starch content of the short straw WCW by 60 g / kg DM and reduced the NDF and ADF concentrations by 49 and 42 g / kg DM, respectively, when compared with the long straw WCW. Ammonia-N values were similar for all three forages although the pH of the short straw WCW was the highest of the three forages at pH 4.3 compared with pH 4.2 for the long straw WCW and pH 4.0 for

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the grass silage. The concentration of fermentation acids was lower and the concentration of sugars higher in either of the WCWs compared with the grass silage. The intake of concentrates was the same for all three dietary treatments and averaged 9.3 kg DM / day. The intake of forage was also similar for cows fed any of the three dietary treatments at 9.9, 9.8 and 9.7 kg DM / day for cows fed LF, SF or LW, respectively. There was no significant difference in average milk yield (kg / day) between cows on any of the dietary treatments with a mean milk yield across treatments of 30.2 kg / day (Table 4). Additionally there were no significant differences between treatments in average yield of fat or protein although there was a trend for animals offered diet LF to have the lowest concentration of milk protein. Similarly, animals offered diet LF tended to have the lowest body condition score over the experimental period although daily liveweight change was not significantly affected by treatment. Cows fed either of the diets highest in starch (SF and LW) had significantly lower blood concentrations of non-esterified fatty acids (NEFA) during week 10 of lactation when compared with those offered the long straw WCW supplemented with sugarbeet pulp (LF; Fig. 2a; P,0.05) although there were no significant effects of dietary treatment at either of the other two sampling dates. Plasma 3OHB concentrations tended to be lowest in cows fed the long straw WCW supplemented with wheat (LW) compared with those supplemented with sugarbeet pulp (LF), the difference being significant during week 16 of lactation (P,0.05: Fig. 2b). Animals fed the short straw WCW supplemented with the fibrous concentrate (SF) had plasma 3-OHB concentrations intermediate to those offered LW or LF.

3.3. Experiment 3 During the course of the experiment one lamb on treatment LSH suffered from digestive upsets and as a consequence was removed from the experiment. Lambs offered the WCW silage ad libitum (LSH) had a significantly higher (P,0.01) dry matter intake (59.8 g / kg W 0.75 ) compared with those fed any of the three other treatments (GS, LSL and SSL,

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Table 3 Chemical composition of the grass silage, long straw whole crop wheat (WCW), short straw WCW and concentrates fed to dairy cows in experiment 2 Grass silage

Long straw WCW

Short straw WCW

Standard concentrate

Protein balancer

Dry matter (g / kg)a

233 (8.2)

446 (15.3)

477 (15.0)

876 (6.9)

895 (0.1)

g /kg DM Crude protein Starch Neutral detergent fibre Acid detergent Fibre Ash pH Ammonia-N (g / kg total N) Water soluble carbohydrates Metabolisable energy (MJ / kg DM)

168 (5.5) nd b 402 (12.1) 264 (12.1) 83 (3.0) 4.0 (0.11) 103 (19.6) 17 (2.7) 11.9 (0.31)

100 (5.7) 232 (17.2) 433 (17.3) 266 (14.8) 49 (1.7) 4.2 (0.03) 88 (0.29) 50 (2.68) nd

103 (1.8) 292 (4.3) 384 (19.5) 224 (14.9) 46 (2.4) 4.3 (0.04) 96 (0.53) 64 (5.85) nd

229 (2.1) 101 (13.5) 315 (15.5) 211 (9.1) 86 (1.3) nd nd 166 (25.0) 12.9 (0.06)

476 (10.1) 50 (4.7) 181 (10.0) 124 (3.8) 117 (5.6) nd nd 100 (21.0) 13.0 (0.15)

Fermentation acids ( g /kg fresh weight) Lactic Acetic Propionic Butyric

109 (9.3) 22 (7.6) 1.0 (1.91) 0

28 (1.0) 5 (1.4) 0 2 (1.4)

24 (4.3) 4 (1.5) 0 3 (1.0)

nd nd nd nd

nd nd nd nd

Ethanol (g / kg fresh weight)

27 (1.4)

5 (0.6)

4 (0.5)

nd

nd

a b

Mean (standard deviation of four observations). nd, not determined.

Table 4 Milk yield, composition, live weight and condition score in dairy cows fed long straw whole crop wheat (WCW) and a fibrous concentrate (LF), short straw WCW and a fibrous concentrate (SF) or long straw WCW and a starchy concentrate (LW) in experiment 2

Milk yield (kg / day) Fat yield (kg / day) Protein yield (kg / day) Fat (g / kg) Protein (g / kg) Live weight (kg) Liveweight change (kg / day) Condition score

LF

SF

LW

S.E.D.

Sig

30.3 1.14 0.93 37.8 30.9 579 0.31

30.4 1.16 0.96 38.5 31.5 579 0.34

29.9 1.08 0.93 36.6 31.4 581 0.45

0.92 0.054 0.027 1.60 0.46 11.6 0.082

NS NS NS NS NS NS NS

2.22

2.31

2.29

0.08

NS

NS, not significant.

mean intake across treatments of 36.4 g / kg W 0.75 ; Table 5). The apparent digestibility coefficients for grass silage were significantly higher than those for the WCW silages, particularly for the fibre fractions.

Cutting height and feeding level had no significant effect on the apparent digestibility of WCW silage although raising the cutting height (treatment LSL versus SSL) marginally increased DM, OM, starch and GE digestibility, but reduced NDF, ADF and CP

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Table 5 Feed intake, apparent digestibility and metabolisable energy content of grass silage (GS), long straw WCW (LSL), short straw WCW (SSL) (both at a restricted level) or long straw WCW offered ad libitum (LSH) in sheep in experiment 3 GS Food intake (g DM / kg W 0.75 )

35.8

Apparent digestibility ( kg /kg) Organic matter Crude protein NDF ADF Starch Gross energy

0.758 0.676 0.711 0.678 nd 0.721

DOMD (g / kg) ME (MJ / kg DM)

715 11.44

LSL 37.4

0.650 0.530 0.434 0.375 0.946 0.616 630 10.07

SSL 36.0

0.667 0.529 0.410 0.320 0.962 0.650 647 10.34

LSH 59.8

0.661 0.573 0.450 0.418 0.958 0.633 640 10.23

s.e.d.

P

4.29

**

0.0342 0.0475 0.0594 0.0602 0.0215 0.0360

* * ** ** ** NS

31.5 0.504

NS NS

nd, not determined; DOMD, digestible organic matter in the dry matter; ME, metabolisable energy calculated from DOMD as described by AFRC (1993); NS, not significant; *P,0.05; **P,0.01.

digestibility. No significant differences were observed between silages in the DOMD value and energy content. However, values for the grass silage tended to be higher (P50.08) than those for the WCW silages whilst raising the cutting height (treatment LSL versus SSL) tended to increase the DOMD and the metabolisable energy content of WCW silage by 17 g / kg and 0.27 MJ / kg DM, respectively.

3.4. Forage aerobic stability The effect of time on the temperature of the silages used in experiment 1 is presented in Fig. 3a. Initially all silages had a similar temperature. However, the grass silage heated significantly faster and reached a higher temperature than either of the WCW silages. The high starch WCW reached a maximum temperature 1 day before the low starch WCW although a similar value of approximately 30 8C was recorded for either forage. Increasing the cutting height of the wheat crop at harvest in experiment 2 resulted in a significantly higher maximum temperature of the resulting forage at 22 8C compared with 18 8C recorded for the long straw WCW (Fig. 3b). By contrast, the grass silage had a relatively stable temperature throughout the recording period with an increase only being evident during the final 2 days of measurements.

4. Discussion

4.1. Nutritive value and aerobic stability The DM content of either the low starch or high starch WCW used in experiment 1 were approximately 30 g / kg lower than the values at ensiling. Adogla-Bessa and Owen (1995) and Adesogan et al. (1998) also reported losses in the DM content of fermented WCW at silo opening of approximately 20–50 g / kg when compared with the corresponding values measured at the point of conservation. However, the DM contents of the two whole crop wheat silages used in the current work were similar to the range of 300–380 g / kg reported by Weller (1992) for commercially grown forages. One of the largest effects of delaying the date of harvest of WCW was to increase the content of starch from 52 g / kg DM in the low starch WCW to 221 g / kg DM in the high starch WCW, an increase consistent with that of other studies that have investigated the effect of harvest date on the nutritive value of fermented WCW (e.g., Adesogan et al., 1998; Crovetto et al., 1998; Kristensen, 1992). Increasing the stubble height in experiment 2 was also observed to increase the starch concentration from 232 g / kg DM in the long straw WCW to 292 g / kg DM in the short straw WCW whilst there was a corresponding decrease in the concentration of neu-

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Fig. 2. Plasma non-esterified fatty acid (a) and b-hydroxybutyrate (b) concentrations in cows fed diets containing long straw whole crop wheat supplemented with a fibrous concentrate (LF: d), short straw whole crop wheat supplemented with a fibrous concentrate (SF: j) or long straw whole crop wheat supplemented with a starchy concentrate (LW: m) in dairy cows in experiment 2.

tral detergent fibre. Weller et al. (1995) reported that increasing the cutting height of whole crop wheat harvested at approximately 580 g / kg DM increased the proportion of grain in the forage from 0.48 at a residual stubble height of 10 cm to 0.61 at a residual stubble height of 40 cm. By contrast, studies that have investigated the effect of cereal varieties of differing straw length have reported that the chemical composition of a long straw winter wheat variety (Cadenza) was similar to that of a short straw variety (Hussar) when cut and fermented at a similar stage of maturity (approximately 510 g / kg DM; Adesogan et al., 1998). Despite being ensiled without the use of an

Fig. 3. Temperature changes as an indication of aerobic deterioration using the forages ensiled in (a) experiment 1: grass silage (d), low starch whole crop wheat (j), high starch whole crop wheat (m) and ambient (3); or (b) experiment 2: grass silage (s), long straw whole crop wheat (m), short straw whole crop wheat (j) and ambient (3). Pooled S.E.D. for experiment 1 was 0.77 8C and experiment 2 was 1.23 8C.

additive, the whole crop wheat silages in both experiments 1 and 2 were observed to have good fermentation characteristics as shown by the low and stable pH and low ammonia levels. The effects of additives on the fermentation characteristics of WCW are, however, unclear. Filya et al. (2000) reported that the addition of an inoculant resulted in a lower pH of fermented WCW when the material was wilted. However, there was no significant effect on fermentation characteristics when fresh material, as used in the current experiment, was ensiled (Filya et al., 2000). By contrast, Adogla-Bessa and Owen (1995) concluded that the beneficial effects of an

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inoculant additive were more pronounced in less mature WCW silages. In both experiments 1 and 2 the WCW forages were observed to reach a maximum temperature within 10 days of being exposed, a result in accordance with that of by Adogla-Bessa et al. (1999) who reported that whole crop wheat ensiled at 600 g / kg without the use of an additive was observed to reach a maximum temperature of approximately 30 8C within 10 days of exposure. However, in the current work, increasing the DM content at harvest (experiment 1) and decreasing the straw length (experiment 2) were both observed to have a significant, although relatively small, effect on increasing the rate and extent of temperature increase. The negative effect of increasing the stage of maturity at harvest probably reflects the greater nutrient concentration for fungal and yeast growth in combination with the lower concentration of volatile fatty acids in the high starch WCW (McDonald et al., 1991) whilst the greater proportion of grain to straw and higher water soluble carbohydrate content of the short straw WCW may have contributed to the decreased stability of this material. The large variation in the stability of the grass silages used in experiments 1 and 2, despite the similarity in their gross chemical composition is, however, more difficult to explain.

4.2. Digestibility The high digestibility of starch in WCW at either of the cutting heights when determined in sheep in experiment 2 is in agreement with other studies on fermented or urea-treated whole crop wheat (Adesogan et al., 1998; Deschard et al., 1987; Givens et al., 1993). By contrast, the digestibility of starch in urea-treated WCW in dairy cows has been reported to be between 0.8 and 0.9 kg / kg (Sutton et al., 1997, 1998) and the use of sheep as a model for WCW digestion in dairy cows has been questioned. Sheep are observed to have a greater mastication of the cereal grains which results in a greater disruption of the seed coat and subsequently increases the availability of the starch (McDonald et al., 1995). Additionally the smaller omasal orifice in sheep will reduce the outflow of whole grains from the rumen compared with dairy cows (McDonald et al., 1995) which may contribute to the high digestibility re-

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ported here. The mean digestibility of fibre in WCW reported in the current work of 0.431 kg / kg is lower than the value of 0.504–0.634 kg / kg reported by Adesogan et al. (1998) for WCW cut at DM contents between 330 and 530 g / kg but comparable to the values reported by Crovetto et al. (1998) of 0.529 kg / kg for WCW cut at 290 g / kg or 0.350 kg / kg cut at 360 g / kg. The DOMD (g / kg) value of 630 for the long straw WCW and 647 for the short straw WCW are within the range for fermented WCW of 599–634 g / kg reported by Adesogan et al. (1998), the 576– 704 g / kg reported by Crovetto et al. (1998) and the 620–697 g / kg reported by Weller (1992). However, there have been relatively few reports on the effects of cutting height on the digestibility of fermented whole crop wheat. Theoretical calculations by Weller et al. (1995) indicated that increasing the cutting height of whole crop wheat harvested at a DM content of approximately 380 g / kg from 10 to 40 cm stubble height resulted in a decrease in the modified acid detergent fibre (MADF) from 250 to 195 g / kg DM, resulting in an increase in the calculated ME from 10.6 to 11.2 MJ / kg DM. Comparisons of long straw versus short straw wheat varieties cut at the same stubble height did not, however, result in an increase in the ME (Adesogan et al., 1998). Indeed, the ME value of the long straw WCW was predicted from in vivo digestibility measures in sheep to be 0.5 MJ / kg DM higher than in the short straw variety. In the current work the increase in predicted ME from increasing the cutting height from 18 to 38 cm resulted in a small and non-significant increase in ME of 0.27 MJ kg / DM. It would therefore appear at the DM content used in the current work that the proportion of straw is not a major factor limiting the ME value of the forage.

4.3. Milk production In experiment 1 there was no significant effect of stage of maturity of fermented WCW on milk production or composition when compared with cows fed grass silage. The lack of a significant improvement in milk production due to feeding fermented WCW compared with grass silage is in agreement with a number of other studies (e.g., Kristensen, 1992; Phipps et al., 1995, 1998;

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Hameleers, 1998). The effects of stage of maturity on milk composition are less clear. In the current work, feeding the less mature whole crop wheat resulted in the lowest milk protein percentage. By contrast, Kristensen (1992) reported that a lower maturity WCW resulted in an increase in milk fat percentage with no significant effect on milk protein levels whilst Phipps et al. (1998) reported no significant effect of stage of maturity on milk fat or protein levels. It is important to bear in mind that the grass silage used in experiment 1 was of a high quality, with a predicted ME value of 11.7 MJ / kg DM and crude protein of 201 g / kg DM, and was superior to that used in a number of other experiments that have compared grass silage with fermented whole crop wheat (e.g., Phipps et al., 1995; Hameleers, 1998). In experiment 2 increasing the cutting height of the WCW increased the starch and decreased the fibre content although the net effects on ME supply, as shown by the digestibility study, were predicted to be small and non-significant and did not alter either milk production or composition. Similarly, the replacement of 2.5 kg / day of molassed sugar beet pulp with rolled wheat (treatment LF versus LW) had no significant effect on milk production, composition or body condition score. By contrast, Kristensen (1992) reported that the replacement of 5.2 kg / day of rolled barley with sugarbeet pulp as a supplement to fermented whole crop barley increased forage intake whilst milk fat content was increased and milk protein content decreased although there was no net effect on fat corrected milk yield. Studies using urea-treated whole crop wheat (Leaver, 1996) have reported no significant effect of either a high fibre or high starch and sugar supplement on milk production or composition. Similarly, the use of molasses or ground wheat as a supplement to urea treated wheat was not shown to have any consistent effect on intake, milk production or composition (Sutton et al., 2001). Leaver (1996) concluded that at moderate levels of alternative forage inclusion and at a moderate concentrate input that the source of carbohydrate in the supplement was not influential in altering milk output.

4.4. Blood analysis The levels of blood metabolites measured in

experiments 1 or 2 were generally within the normal physiological range of the dairy cow during lactation (Ward et al., 1995). The lower plasma urea concentrations in cows fed the high starch compared to the low starch WCW in experiment 1 may be attributed to the greater supply of fermentable energy to the rumen and subsequent capture of ammonia by the rumen microbes. Whilst plasma ammonia levels were not monitored in the current work, previous studies have shown that diets that result in high plasma concentrations of ammonia can impair reproduction in cattle (Sinclair et al., 2000a,b) which may indicate a positive effect of feeding more mature fermented WCW. In experiment 2, the lower NEFA and 3-OHB concentrations in cows fed either the long straw supplemented with wheat or the short straw WCW indicates a more positive energy balance in early lactation in cows offered these treatments.

5. Conclusions Whole crop wheat cut at a later stage of maturity had an increased starch and decreased fibre concentration although there was no significant effect of stage of maturity of WCW on milk production. There was also a similar level of performance to feeding WCW to that of cows fed first cut grass silage. Increasing the cutting height of WCW at harvest increased the starch and decreased the fibre concentration although apparent digestibility, when determined in sheep, was not significantly affected. There was also no benefit to increasing the cutting height at harvest or altering the starch to fibre concentration in the concentrate on milk production. However, the lower NEFA levels in cows fed either the long straw WCW supplemented with the higher starch concentrate or the short straw WCW indicate a more positive energy balance in early lactation on these treatments.

Acknowledgements The authors would like to acknowledge the assistance of C. Goulding, I. Bell, R. Moore and C. Hughes. This study was funded by the Milk Development Council.

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