Fortifying native pasture hay with molasses–urea mixtures improves its digestibility and nutrient intake by weaner sheep

Animal Feed Science and Technology 119 (2005) 259–270

Fortifying native pasture hay with molasses–urea mixtures improves its digestibility and nutrient intake by weaner sheep Sean M. Miller∗ , Gordon Lennie, Derek Clelland Department of Agriculture, Goose Green, Falkland Islands Received 28 March 2003; received in revised form 25 November 2004; accepted 25 November 2004

Abstract Weaner ewes were fed poor quality native pasture hay fortified with molasses–urea solutions, and a 42-day indoor metabolism study was conducted to determine forage intake and nutrient metabolism. Low quality native pastures in the Falkland Islands restrict sheep productivity, and methods to improve the value of this resource have been requested by local farmers. Fortification solutions used in the study comprised molasses at either 70 g/kg (LM) or 200 g/kg (HM) on a dry basis (w/w), and with or without additional nitrogen (N, 3.5 or 7 g/d), phosphorus (P, 2 g/d) and sulphur (S, 1.5 g/d). Dry matter (DM) digestibilities of the HM + N fortified hays were higher than the LM-fortified hay (P < 0.05). DM intake of hay was almost doubled by the addition of HM + LN (3.5 g/d) or HN (7 g/d) compared to LM-fortified hay (P < 0.05). Addition of N and P to the hay improved N and P balances of sheep (P < 0.05), and improved the apparent digestibilities of these nutrients. Microbial crude protein (MCP) production was estimated by purine derivative excretion and tended to be higher (P = 0.08) for Nsupplemented diets. N supplementation was reflected in higher (P < 0.05) plasma urea levels for supplemented sheep. The improved nutritive value of molasses–urea fortified native pasture hay may

Abbreviations: N, nitrogen; P, phosphorus; S, sulphur; DM, dry matter; ME, metabolisable energy; CP, crude protein; NPN, non-protein nitrogen; MCP, microbial crude protein; DOMI, digestible organic matter intake; OMD, organic matter digestibility; DOMD, digestible organic matter in the dry matter ∗ Corresponding author. Present address: South Australian Research and Development Institute, Struan Agricultural Centre, P.O. Box 618, Naracoorte, SA 5271, Australia. Tel.: +61 8 8762 9194; fax: +61 8 8764 7503. E-mail address: [email protected] (S.M. Miller). 0377-8401/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2004.11.014

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represent a practical opportunity for Falkland Islands’ farmers to increase the productivity of local sheep. © 2004 Elsevier B.V. All rights reserved. Keywords: Urea; Molasses; Native-pasture hay; Microbial crude protein; Falkland Islands

1. Introduction Poor quality native white-grass (Cortaderia pilosa) pastures are the dominant forage resource of the cool maritime rangelands of the Falkland Islands. The 650,000 sheep that constitute the Islands’ wool industry are reliant on these pastures for their complete nutriment. However, the sheep are subjected to deficiencies of energy, rumen degradable protein and P for as many as 9 months of the year (Miller, 2002). For Falklands’ farmers to increase the prosperity of their wool-based farming systems, methods are required to address the prolonged nutritional restrictions suffered by the national flock. Conserving native white-grass pasture as hay is not an option previously considered by farmers due to its poor quality; the metabolisable energy (ME) and crude protein (CP) contents of white-grass vary seasonally across the range 5.6–7.4 MJ/kg and 36–101 g/kg, respectively (Davies et al., 1971; McAdam, 1986; Davies, 1988; Miller, 2002). Elsewhere, it has been shown that poor quality native pasture hays can be conserved and fortified with molasses–urea solutions to improve their value for sheep (Stephenson et al., 1984, 1988). If successful in the Falklands, this system could be used to supplement sheep simply with energy, rumen degradable protein and P, whilst increasing the efficiency of utilisation of the native pasture resource. The principals supporting molasses–urea supplementation of roughage diets for ruminants are well founded (Pate, 1983; Winks, 1984). Molasses is a palatable source of fermentable carbohydrates, typically has relatively high concentrations of calcium, potassium and sulphur, but contains relatively little crude protein (Curtin, 1983). Consequently, supplemental nitrogen is commonly provided as non-protein nitrogen (NPN), and generally as urea. Considered individually, molasses and urea serve complementary purposes. The fermentable carbohydrates in molasses promote higher populations of rumen microbes (Foreman and Herman, 1953) and the high digestibility of the soluble carbohydrates in molasses contribute to increased dry matter digestibility of the whole diet. However, as the level of molasses increases in the diet, the digestibility of low quality roughages reduces proportionally as a consequence of lowered protein digestibility (Herrera et al., 1981; Martin et al., 1981). The inclusion of urea in molassessupplemented diets provides additional N in situations where rumen ammonia becomes limiting. Using these principals, the following study evaluated the potential to use native pasture hay fortified with molasses–urea solutions as supplements for weaner sheep in the Falkland

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Islands. A metabolism study examined the effect of fortifying hay on the DM intake and digestibility of the diet, and nutrient balances in young sheep.

2. Materials and methods 2.1. Experimental design, sheep and diets Twenty-three Polwarth × (Polwarth × Corriedale) female weaner sheep were selected from a flock grazing a native pasture since birth and used in a 42-day metabolism study (Fig. 1). This pasture was dominated by white-grass (in excess of 80% on a DM basis), and subordinate grass species included Poa pratensis, Poa annua, Festuca magellanica and Agrostis capillaris. There are no legumes in Falklands’ native pastures. The ewes were approximately 5-months-old at the commencement of the study and weighed (±S.E.) 27.5 ± 0.43 kg. The ewes were dosed with an anthelmintic capsule (Extender Junior, Nufarm, NZ) immediately prior to the study commencing. Ewes were held in individual pens (3 m × 1.5 m) for the duration of the study and liveweight was monitored on a weekly basis. Chaffed native pasture hay was fed ad libitum for the first 7 days. Hay was cut from a white-grass dominant pasture at Brenton Loch, East Falkland, chaffed using a garden mulching machine (Alko, UK) and fed to the ewes each morning at 09:00 h. Daily samples of the hay were kept for nutrient analysis. During the second half of the pre-treatment period, from days 8 to 14, molasses (112 g DM) was mixed into the chaffed hay fed daily to halt the rapid weight loss that occurred during the first week. Daily DM intake from days 8 to 14 was used to stratify the ewes, and 20 ewes were randomly allocated to one of 4 treatment groups. Treatments were: (i) native pasture hay with 70 g/kg molasses (LM); (ii) hay with 200 g/kg molasses and 3.5 g N (HM + LN); (iii) hay with 200 g/kg molasses and 7 g N (HM + HN) and (iv) hay with 200 g/kg molasses and 7 g N, 2 g phosphorus (P) and 1.5 g sulphur (S, HM + HNPS). All molasses weights are reported on a DM basis. The P and S supplement was administered as an oral drench each day. Dicalcium phosphate and ammonium sulphate were used as sources of P and S, respectively. Urea provided supplemental N and was dissolved in the molasses each day. For groups that received additional P and S, the 7 g of supplemental N was provided by urea and ammonium sulphate. Molasses was mixed with water at a ratio of 3:1 (v/v) in order to easily mix the solution with the chaffed hay.

Fig. 1. Timeline for the metabolism study with sheep fed native pasture hay.

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Immediately prior to feeding, the molasses + water + N solution was thoroughly mixed with the hay, and the fortifying solution was rapidly absorbed by the feed and uniformly distributed through the hay. Sufficient feed was offered to the ewes to maintain orts at approximately 100 g/d. Daily orts were collected and bulked for each ewe for analysis. Urea was introduced to the N-supplemented groups gradually over 7 days (days 14–21). 2.2. Urine and faecal output A 7-day urine and faeces collection period commenced 21 days after treatment began. Total faecal and urine output was determined during the collection period in order to quantify the effects of treatments on feed digestibility, nutrient balances, apparent nutrient digestibilities and microbial crude protein (MCP) production by the rumen microflora. Urethral catheters were used to determine urine production by four randomly chosen ewes from each of the four treatment groups (16 ewes in total) over a 48-h period (Perez et al., 1996). Subsequently, creatinine concentrations were determined in the urine and creatinine excretion coefficients were established for each ewe using this data. Urine output was then estimated for a further 5 days from the concentration of creatinine in subsequent spot samples (Faichney et al., 1995). The spot samples were bulked for the 5 days of collection. Approximately, 2 mL of 0.1N hydrochloric acid was placed in the collection bags to acidify the urine (below pH 3.0). The bags were emptied every 8 h and the samples were bulked and frozen until analysis for creatinine, N, P and S. An intramuscular injection of oxytetracycline (Terramycin 200 mg/mL, Pfizer, UK) was administered to each ewe at 1 mL/10 kg of body weight at the time of catheterisation, and again following removal of the catheter as a prophylactic to prevent bladder infections. Faecal output was determined using dosed, even chain-length alkanes as faecal markers. Each ewe received a controlled-release capsule containing 1 g of n-dotriacontane (C32 ) and 1 g of n-hexatriacontane (C36 , Captec, NZ) 7 days prior to the collection period. Rectal grab samples were obtained from each ewe at 8-h intervals on each of the 7 days of the collection period and bulked for each ewe. Faecal output was estimated using the dilution of dosed C36 in the faeces as an internal marker (Dove and Mayes, 1996). A faecal recovery coefficient for C36 of 0.781 was used based on previous estimates for its recovery from sheep consuming native pasture in the Falklands (Miller, 2002). Digestible organic matter intake (DOMI) was calculated using organic matter digestibility (OMD) estimated during the 7-day collection period. Venous blood (10 mL) was collected from each ewe by jugular venipuncture into evacuated, heparinized tubes (Vacutainer, Becton Dickson, UK) on a weekly basis. 2.3. Analytical methods N, P, S and ash composition were determined for hay, molasses, faeces and urine samples. Faeces and forage were dried to a constant weight at 70 ◦ C, and milled in a bench-top hammermill (Culatti, Italy) through a 1 mm screen. N in samples was determined by Kjeldahl digestion (MAFF, 1986, method 48). The acid digests were analysed using a Tecator auto N analyser (1030 Kjeltec auto analyser). P analyses were performed using the method described by Cavell (1955), and outlined in (MAFF, 1986, method 58). S was determined turbidimetrically (MAFF, 1986, method 72) with the aid of a Pye Unicam SP6-550 UV–vis

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spectrophotometer. Dried samples of forage and faeces were ashed in a muffle furnace at 550 ◦ C for 3 h, and the ash remaining after incineration was weighed. In vitro DM digestibility was estimated for hay and molasses by near infra-red reflectance spectroscopy using a FOSS-NIR Systems Model 5000 spectrophotometer. Calibration equations were derived from and monitored by samples analysed by the pepsin–cellulase dry matter disappearance method (Tilley and Terry, 1963). Concentrations of alkanes in hay and faeces were determined by high-pressure liquid chromatography (Mayes et al., 1986). The botanical composition of the hay was determined from the alkane profile of dried feed samples using the diet selection calculator EatWhat (Dove and Moore, 1995). Blood samples were centrifuged at 2000 rpm for 10 min, and plasma was aspirated from the sample and frozen at −20 ◦ C until analyses could be performed. Inorganic P and urea concentrations in plasma were analysed using kits (Randox, Crumlin, Northern Ireland; catalogue # PH1016 and UR 445) and a Pye Unicam 8630 kinetics spectrophotometer. Creatinine, uric acid, xanthine, hypoxanthine and allantoin were determined in urine samples by high-pressure liquid chromatography (Balcells et al., 1991), and yield of MCP calculated as described by Chen et al. (1992). 2.4. Statistical analyses The statistical package Systat 5.03 (Wilkinson et al., 1992) was used to examine relationships within data. Means for diet effects were analysed as a completely randomised design using analysis of variance (ANOVA), and analysis of covariance methods (ANCOVA) where appropriate. Individual least squares means were compared using Tukey’s HSD test. Standard errors in the text (S.E.) estimate the variance within a group. Standard errors reported in tables of means (S.E.) represent the residual variance in the ANOVA.

3. Results The native pasture hay contained 280 g/kg green white-grass leaf, 700 g/kg dead whitegrass leaf and 20 g/kg small fern (Blechnum penna-marina). CP concentration of the hay varied from 56 to 60 g/kg on a DM basis, with a general mean (±S.E.) of 58 ± 0.06 g/kg. P and S contents of the hay were 0.48 ± 0.026 g/kg (range 0.42–0.59 g/kg) and 1.21 ± 0.114 g/kg (range 0.64–1.84 g/kg), respectively. Ash content of the hay was 78.4 g/kg. In vitro DM digestibility of hay was 0.428. ME content was estimated from DM digestibility using the equation of Freer et al. (1997), and was 5.8 MJ/kg. Sugar beet molasses (Tate and Lyle, UK) was used to fortify the hay and contained 65 g/kg CP, 0.88 g/kg P, 7.25 g/kg S and 164 g/kg ash on a dry matter basis. The intention was to feed the ewes hay for the 14-day pre-treatment period and stratify the animals for allocation to treatment groups on the basis of DM intake during this period. However, weight loss was rapid for the first 7 days (Table 1) and necessitated a change in feeding strategy to avoid further critical weight loss. Therefore, molasses was added to the hay; 112 g of molasses DM improved (P < 0.05) DM intake of the hay, from 210 to 294 g/d, and halted liveweight loss.

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Table 1 Dry matter (DM) intake of native pasture hay and liveweight (LW) change of sheep during the 14-day pre-treatment perioda Days 1–7 (hay only)

Days 8–14 (hay + 112 g molasses DM)

S.E.b

Intake of hay (g DM/d)* (g DM/kg0.75 LW/d)*

210 a 18.2 a

294 b 26.2 b

17.7 1.43

LW change (g/d)

−437 a

28 b

31.7

a b ∗

Within a row, means with different letters differ significantly. Residual standard error. P < 0.05.

During the 28-day treatment period, intake of fortified native pasture hay was greater (P < 0.05) for ewes consuming HM + LN and HM + HN diets than ewes fed the LM diet (Table 2). In addition, fortification with HM and N increased the contribution of dry hay to the diet consumed by the ewes, by 80–90% (P < 0.05). DOMI was lower (P < 0.05) for ewes consuming LM diet than for the three groups fed HM diets. The differences in liveweight change between groups were not significant for the 27-day treatment period. During the treatment period, DM intake of the LM diet was similar to the intake of hay during the pre-treatment period (201 g/d versus 210 g/d). DM intake of the hay component of the HM diets tended to be greater than, but was not significantly different to intake of the hay + 112 g molasses during the pre-treatment period. Daily consumption of molasses Table 2 Dry matter (DM) intake, apparent dry matter and organic matter digestibility (DMD, OMD), apparent digestible organic matter in the dry matter (DOMD) and digestible organic matter intake (DOMI) and liveweight (LW) changes of weaner sheep fed molasses-treated native pasture hay with or without N, P and S supplements during the 7-day collection period, and the whole of the treatment period (days 15–42)a Diet

7 Day collection period Intake of fortified hay (g DM/d)* Apparent DMD (g/kg) OMD (g/kg) DOMD (g/kg) DOMI (g DM/d)*

LM

HM + LN

HM + HN

HM + HNPS

S.E.b

238 a 441 443 405 96 a

414 b 584 583 527 218 b

439 b 562 559 505 222 b

359 ab 486 492 445 160 ab

48.1 84.6 84.1 77.4 34.2

381 b

387 b

356 b

36.2

476 b 41.6 b

483 b 44.2 b

445 b 41.5 b

44.8 4.13

251 b 16

244 b 16

198 b −91

45.4 33.5

Whole of treatment period (days 15–42) Intake of dry hay (g DM/d)* 201 a Intake of fortified hay (g DM/d) 216 a 20.7 a (g DM/kg0.75 LW/d)* DOMI (g DM/d)* LW change (g/d) a b ∗

88 a −88

Within a row, means with different letters differ significantly. Residual standard error. P < 0.05.

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by sheep fed HM diets during the treatment period was approximately two thirds of that consumed during the pre-treatment period (71–77 g/d versus 112 g/d DM). DM intake and DOMI for ewes fed LM diet during the 7-day urine and faeces collection period was significantly lower (P < 0.05) than ewes fed HM + LN and HM + HN diets. Using the in vitro analyses of molasses and hay, DM digestibilities of the LM- and HM-fortified hays were estimated at 0.457 and 0.510, respectively. Apparent DM digestibility for the LM diet was similar to the in vitro estimate. Apparent DM digestibility of HM + LN and HM + HN diets tended to be higher than the in vitro estimate of HM-fortified hay (0.584 and 0.562 versus 0.510). Apparent DM digestibility, OMD and digestible organic matter in the dry matter (DOMD) did not differ significantly between diets during the 7-day urine and faeces collection period, however values for HM + LN and HM + HN diets tended to be higher than for the LM diet. Actual DM intake, faecal output determined by C36 and urine output calculated using creatinine excretion coefficients were used to estimate N, P and S balances. Mean creatinine excretion rate for ewes was 181.7 ± 12.57 ␮mol/h, and varied across the range from 75.9 to 264.1 ␮mol/h between individuals. N balances were improved in the three groups that were fed N in conjunction with HM (P < 0.05, Table 3). Apparent N digestibility was also improved in these groups (P < 0.05). N digestibilities tended to be higher for HM + HN and Table 3 Nitrogen (N), phosphorus (P) and sulphur (S) balance, apparent N, P and S digestibility, faecal and urine excretion of N, P and S and total purine derivatives (PD) excreted by sheep and microbial crude protein (MCP) supplied by native pasture hay treated with molasses, or molasses plus ureaa Diet S.E.b

LM

HM + LN

HM + HN

HM + HNPS

Nitrogen Balance (g/d)* Apparent digest (g/kg)* Excreted in faeces (g/d) Excreted in urine (g/d)*

−3.33 a 135 c 1.75 3.54 a

1.14 b 644 b 2.87 3.65 a

0.80 b 741 ab 2.78 7.77 b

1.11 b 779 a 2.28 6.45 b

Phosphorus Balance (g/d)* Apparent digest (g/kg)* Excreted in faeces (g/d)* Excreted in urine (g/d)*

−136 a −1033 a 265 a 55 a

−15 a 11 a 295 a 31 a

−27 a −114 a 296 a 8a

637 b 442 b 1234 b 371 b

88.1 211.8 56.3 46.3

Sulphur Balance (g/d) Apparent digest (g/kg)* Excreted in faeces (g/d) Excreted in urine (g/d)

77 349 c 338 146

310 585 ab 577 297

219 527 b 561 446

739 675 a 686 683

227.4 43.4 105.5 123.9

Total PD (mmol/d) MCP yield (g/d) MCP yield (g/kg DOMI)

3.44 14.9 141

5.25 26.4 132

8.94 47.6 192

6.09 31.4 183

a b ∗

Within a row, means with different letters differ significantly. Residual standard error. P < 0.05.

0.720 40.8 0.439 0.724

0.884 5.17 29.9

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Fig. 2. Plasma urea concentrations in blood samples from sheep fed native pasture hay treated with 70 g/kg molasses (䊉), or fortified with 200 g/kg molasses and supplemented with 3.5 g/d N (
), 7 g/d N (), or 7 g/d N with 2 g/d P and 1.5 g/d S ()a , where a = On each collection day, means with different letters differ significantly (P < 0.05).

HM + HNPS diets, however only HM + HNPS fed sheep recorded significantly higher N digestibility (P < 0.05) compared to the HM + LN fed sheep. Both groups that received HN excreted more (P < 0.05) N in their urine. The improved N status of the sheep supplemented with LN and HN was reflected in elevated plasma urea concentrations in blood samples collected during the study (Fig. 2). On days 20 and 35 of the study, ewes that received N supplements had higher plasma urea concentrations (P < 0.05) compared to those not supplemented with N. On day 35, ewes fed the HM + HN diet had higher plasma urea levels (P < 0.05) than ewes fed the LM diet, and ewes that consumed the HM + LN diet. P balance, apparent digestibility and excretion were similar for groups that consumed the LM diet, or HM + LN and HM + HN diets. However, provision of 2 g/d P (HM + HNPS) improved P balance and apparent P digestibility (P < 0.05). Only the ewes supplemented with P exhibited positive balances. In addition, faecal and urine excretion of P was higher (P < 0.05) for HM + HNPS fed sheep. Plasma inorganic P concentrations fell similarly in all groups of ewes during the pre-treatment period (P < 0.05), however the significant improvements in P digestibility and balance for the group supplemented with P were not observed as higher plasma concentrations of inorganic P, and there were no significant differences between groups for plasma inorganic P during the study. Although all groups of ewes exhibited similar S balances and S excretion rates, S digestibilities differed significantly between groups. Ewes from all three groups fed HM diets experienced higher S digestibilities (P < 0.05) than ewes fed the LM diet. Sheep fed the HM+HNPS diet apparently digested S better (P < 0.05) than sheep fed the LM and HM + HN diets. Allantoin was the most abundant purine derivative in urine for all sheep (data not shown) and tended to be higher (P = 0.08) for sheep fed the HM + HN and HM + HNPS diets com-

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pared to those that consumed the LM diet. Concentrations of uric acid, xanthine and hypoxanthine in urine were similar for each diet. Ewes fed the HM + HN diet tended to yield more (P = 0.08) MCP than ewes fed the LM diet. MCP yield as a proportion of DOMI did not differ significantly between diets, but tended to be highest for HM + HN and HM + HNPS diets.

4. Discussion Fortification of native pasture hay with molasses and urea was an effective method to improve the nutritive value of the forage, that without supplements was a sub-maintenance feed. The effects of fortification on the positive liveweight status for sheep fed HM + LN and HM + HN diets were mediated by an increase in DOMI and a tendency towards improved digestibility of both the whole diet and the native pasture hay itself. Examination of the in vitro nutritional quality of the pasture hay suggested that both energy and CP were limiting nutrients. When fed as unfortified hay or LM-fortified hay, these deficiencies were expressed as rapid liveweight losses. However, for the LM diet particularly, the efficiency of MCP production tended to be within the normal range of values for temperate forages (SCA, 1990), and the value was higher than anticipated considering its apparent poor quality. At these efficiencies, it is unlikely that the ewes would have responded to the additional rumen degradable N provided with the hay in the HM + HN diets and would have limited the potential for the NPN to increase the efficiency of MCP production. Moreover, the relationship between plasma urea and rumen ammonia established by McMeniman (1990) suggests that in the present study, rumen ammonia concentrations for the ewes fed the LM diet had declined to approximately 70 mg/L towards the end of the experimental period, and remained within the range that are required for adequate ruminal fermentation (60–80 mg/L, Satter and Slyter, 1974; Satter and Roffler, 1976; Pisulewski et al., 1981; SCA, 1990). Consequently, despite the low DM intake of the LM diet, energy rather than dietary protein was the first limiting nutrient. Although not significant, the tendency towards higher DM digestibility and OMD for hays fortified with HM was consistent with previous studies in which it is suggested that molasses supplementation increases overall diet digestibility, due to the contribution of digestible OM from molasses, albeit reducing the digestibility of the roughage itself (Brannon et al., 1954; Herrera et al., 1981; Hugh-Jones and Peralta, 1981; Martin et al., 1981). The value of urea for increasing MCP yield could not be isolated from the effects of the increased supply of dietary OM provided by the molasses in the HM diets. The increased MCP yield for ewes fed HM diets was indicative of the additional supply of digestible OM with this supplement compared to LM diet, and both the molasses and the additional hay consumed contributed to the additional DOMI. Nevertheless, the discrepancies between apparent and implied DM digestibilities for the HM + LN and HM + HN diets of 0.074 and 0.052 g/kg, respectively, and the 80% higher MCP yield for the HM + HN diet compared to HM + LN fed sheep, could be interpreted as a synergistic influence of urea on the digestion of the whole diet. Since NPN supplements can improve rumen digestion of low quality forages (Van Soest, 1982; Huston and Pinchack, 1991), it is likely that a proportion of the supplemental N from urea contributed to improve rumen fermentation and promote the tendency towards higher DM digestibilities of HM + N diets.

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The N balance data suggested that 3.5 g/d was sufficient to place the ewes in a positive N balance and that provision of 7 g/d N was no more beneficial for liveweight change, DM digestibility and DM intake than 3.5 g/d N. Moreover, when extrapolated on a whole-of-diet basis, the CP provided by the HM + LN diet was approximately 68 g/kg DM and was similar to the 70 g/kg generally accepted as the minimum to maintain rumen ammonia levels above the threshold 60–80 mg/L concentration required for adequate rumen function (SCA, 1990). That the additional N supplied in the HN diets was excreted in the urine at significantly higher rates than by LN fed sheep suggests that dietary energy was limiting conversion of NPN to MCP under these conditions, and further supports the conclusion that the LN treatment was adequate to complement the additional DOM provided by the HM-fortified hay. The low faecal P concentrations for ewes without an additional P supplement (mean = 1.42 g/kg) were less than the 2 g/kg recommended as an indicator of P deficiency (Belonje, 1978; Belonje and Van den Berg, 1980). Although plasma inorganic P concentrations did not reflect this P imbalance, it is likely that long term feeding of the hay without a P supplement would lead to the development of a chronic P deficiency, associated bone problems, and reduced feed intake (Gartner et al., 1982). Consequently, an appropriate fortification solution for native pasture hay would be based on the provision of 200 g/kg molasses to improve palatability and energy supply, and supplying 3.5 g/head/d N and 2 g/head/d P to support positive N and P balances. The benefit of the additional N and P in the hay if fed as a supplement for weaner sheep consuming native pasture would be to assist in alleviating the rumen degradable protein and P deficiencies previously reported for Falklands’ weaner sheep during autumn, winter and spring (Miller, 2002). 4.1. Implications Weaner sheep grazing native pasture in previous paddock studies (Miller, 2002) consumed approximately twice as much pasture DM/d compared to the ewes fed the HM diets in the present pen study. Nevertheless, the housed ewes consumed similar quantities of white-grass, as hay (mean = 375 g/d), compared to weaner sheep that grazed white-grass from native pastures during early winter, early and late spring, and autumn (303, 363, 289 and 444 g/d, Miller, 2002). Under strong seasonal influences, sheep grazing at pasture are able to supplement their intake of white-grass with other more nutritious species. However, the period during which the contributions made by these supplemental species provide growth opportunities for sheep is limited to approximately 3 months each year. Fortifying native pasture hay with HM + LN provided a nutritionally superior forage to untreated hay, and LM-fortified hay, and was as much as 26% more digestible than whitegrass leaves (Miller, 2002). Consequently, the productivity of weaner sheep could be improved if the treated hay was used as a supplement to native pasture where white-grass is a major component of the diet, and at least partial substitution of the fortified hay for poorer quality standing white-grass could be expected. Whilst this study has shown that molasses–urea fortified hay can be used as a maintenance diet for weaner sheep when provided as the sole forage, the practical and economic value of harvesting and fortifying needs to be further assessed when fed as a supplement for sheep grazing native pasture.

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Acknowledgements The Falkland Islands Government funded this work on behalf of Falklands’ farmers. We thank Prof. Neil McMeniman (University of Queensland) for advice on methods and comments on early drafts of the manuscript, Peter Flinn and Suzanne Dalton (Department of Primary Industries, Victoria) for the NIR analyses of plant material, and Dr. Nick Edwards (South Australian Research and Development Institute), Dr. Robin Dynes and Simone Martin (CSIRO Division of Animal Production) for assistance conducting and interpreting the alkane analyses.

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