Small Ruminant Research 192 (2020) 106235

Available online 5 September 20200921-4488/© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

The effect of a perennial wheat and lucerne biculture diet on feed intake, growth rate and carcass characteristics of Australian lambs

Matthew T. Newell a,*, Benjamin W.B. Holman a,b, Gordon Refshauge a,b, Alexandra R. Shanley c, David. L. Hopkins a,b, Richard. C. Hayes d

a Cowra Agricultural Research and Advisory Station, NSW Department of Primary Industries, New South Wales Cowra 2794, Australia b Centre for Red Meat and Sheep Development, NSW Department of Primary Industries, New South Wales Cowra 2794, Australia c School of Animal and Veterinary Sciences, Charles Sturt University, New South Wales Wagga 2678, Australia d Wagga Wagga Agricultural Institute, NSW Department of Primary Industries, New South Wales Wagga 2650, Australia

A R T I C L E I N F O

Keywords: forage mineral forage quality liveweight perennial polycultures ovine

A B S T R A C T

A pen feeding study was conducted using 10 month old Poll Dorset × Merino ewe lambs to test the effect of perennial wheat forage on growth rates and carcass characteristics in comparison to annual wheat forage. In-dividual lambs (n = 48) were fed one of four diets, namely perennial wheat (PW), annual wheat (W), perennial wheat + lucerne (alfalfa) (PW + L) or annual wheat + lucerne (W + L). Lambs were monitored for 28 days during which daily forage quality, forage mineral content, feed intake and weekly liveweight change were recorded. At the completion of the feeding period all lambs were slaughtered in a commercial abattoir. At 24 h post-slaughter the left hand side longissimus lumborum muscle (LL) was removed and assessed for quality attributes. Feed intake increased over the 28 days with W fed lambs eating a greater amount compared to PW fed lambs. The addition of lucerne to the cereal forage (PW + L and W + L) increased feed intake (P < 0.001) of the lambs. However, there were no independent dietary effects on liveweight, carcass weight, carcass traits, including yield parameters, pH declines or fresh colorimetrics. Both the W and PW diets had potassium (K) concentrations greater than 3%. Sodium (Na) deficiency was greater in the PW diet. This indicated that lambs fed these diets would be exposed to impaired calcium (Ca) metabolism and reduced magnesium (Mg) absorption. The addition of lucerne to both cereal forages increased the intake of Ca and Mg and lowered the tetany index. Preferential selection of lucerne was observed in lambs fed the PW + L diet compared to those fed W + L. However, the Na deficiency was not resolved by the addition of lucerne and the dietary cation-anion difference (DCAD) remained high for all diets. Low Na content and consequential effects of a high K:Na + Mg ratio may have limited the expression of higher growth rates (range 55–110 g per day) from the different diets offered. The high DCAD implies calcium ho-meostasis would be challenged by all diets. This study establishes the value of perennial wheat as a novel forage source as there were no unfavorable effects on lamb carcass parameters, however the mineral imbalances in the forage would need to be managed in the same way as they are presently managed in grazing systems using dual- purpose annual wheat.

1. Introduction

The global effort to perennialize grain production offers an alterna-tive to existing, highly-disturbed annual grain production systems and has the potential to address soil degradation and reduce inputs while maintaining food security (Glover et al., 2010; Duchene et al., 2019). A key component of this redesigned agricultural system is crops grown in combination with plant species from different functional groups as

perennial polycultures, to enhance ecosystem function and increase resource-use efficiency (Hayes et al., 2017; Crews et al., 2018). Peren-nial crops are envisaged as being multifunctional, meaning they serve multiple purposes or they are used for multiple products (Ryan et al., 2018). Hayes et al. (2012) identified the likely deployment of perennial wheat in Australia as a dual-purpose grain and graze crop, but no pre-vious study has tested the suitability of this novel cereal crop for grazing livestock.

* Corresponding author. E-mail address: matt.newell@dpi.nsw.gov.au (M.T. Newell).

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Small Ruminant Research

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https://doi.org/10.1016/j.smallrumres.2020.106235 Received 29 January 2020; Received in revised form 31 August 2020; Accepted 1 September 2020

Small Ruminant Research 192 (2020) 106235

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The benefits of using dual-purpose cereals for improved liveweight gain in sheep production systems has been well documented (Dove and Kirkegaard, 2014). Due to the ability of perennial wheat to produce additional forage in late summer and early autumn (fall) periods (traditional feed gap periods in Australia) compared to annual wheat (Triticum aestivum), the deployment of perennial wheat into an inte-grated cropping/livestock farming system could increase whole farm profitability by up to 38% (Bell et al., 2010). This enables increased pasture utilization within a mixed crop-livestock system and conse-quentially increases livestock carrying capacity. A similar result was demonstrated by grazing the vegetative stage of annual crops, with whole farm productivity increasing by up to 75% (Bell et al., 2010). This latter outcome has promoted an expansion of annual dual-purpose grain crops into traditional livestock areas of the high rainfall zone of southern Australia (Bell et al., 2014; Dove et al., 2015) with a concomitant in-crease in the risk of land degradation via increased disturbance, replacement of perennial based pasture and increased use of synthetic inputs.

Forage of annual grazing cereals are often imbalanced in terms of their mineral content and this, even at a subclinical level, can lead to variable weight gains in grazing livestock (Dove and McMullen, 2009; Masters et al., 2019). In particular, grazing cereals are often unable to supply the high mineral requirement of high-producing classes of live-stock, such as growing lambs or twin-bearing ewes in late pregnancy and early lactation. Excess concentrations of potassium (K), deficient sodium (Na), and the subsequent high K:Na ratio act to impair the absorption of calcium (Ca) and magnesium (Mg). These latter minerals may also be marginal at the required intake of the forage content, and together these effects impair growth and compromise health. Similar mineral imbal-ance has been observed in the forage of perennial wheat derivatives (Newell and Hayes, 2017), but no previous study has assessed their impact on grazing livestock.

The relationship between mineral imbalances in the diet of growing livestock and their carcass characteristics has received little prior research. The paucity of studies published have associated Mg supple-mentation with reduced intramuscular fat (Apple et al., 2000) and higher glycogen content (Lowe et al., 2002) which in turn could impact on pH decline, fresh color and sensory attributes of meat (Gardner et al., 2001). Further investigations in this area are as much a priority for annual dual-purpose cereals as it is for future perennial cereals to ensure that lamb diets not only meet reasonable animal health thresholds, but also do not jeopardize the quality of the end product.

Forage mineral deficiencies in cereals are managed by supplemen-tation using combinations of calcium, magnesium and sodium chloride. Notwithstanding the solution offered by supplementation, there remains uncertainty about the absolute capability of supplements to control metabolic disorders and there is reluctance among some producers to graze cereal crops with high-risk livestock (McGrath et al., 2013). The deployment of perennial cereals, as polycultures of mixed species rather than monocultures, offers a potential alternative. Designing comple-mentary and diverse species mixtures enables interspecific relationships to be exploited, improving the performance of the sward through transgressive over yielding (Jolliffe, 1997; Finn et al., 2013). The in-clusion of legumes with grasses is a key component of mixed swards due to their capacity for biological nitrogen (N) fixation, but also their nutritional value for livestock (Elgersma and Søegaard, 2016; Stergiadis et al., 2018). Legumes also generally accumulate more Ca and Mg than grasses (Juknevicius and Sabiene, 2007; Lee, 2018). As a consequence, a grazing cereal (perennial or annual) system which includes a legume component could negate the need for mineral supplementation and provide a cost-effective means to improve livestock performance and carcass traits. Lucerne (Medicago sativa) has been identified as a prom-ising companion species for perennial cereals because of its persistence, high nitrogen fixation and ability to produce abundant forage (Tautges et al., 2018). Perennial cereals are a novel forage source and, therefore, it is prudent to examine their effects on lamb performance to increase

confidence as an addition to the feed base within the red meat industry. This study had two objectives; i) to establish the suitability of novel perennial wheat material as a forage source for lambs, and ii) to quantify differences in feed intake, growth and carcass traits of lambs fed a pure cereal forage compared to those fed a mixed cereal/lucerne ration.

2. Materials and methods

2.1. Use of animal subjects

Authority to conduct this experiment was approved by New South Wales Department of Primary Industries (NSW DPI) Animal Ethics Committee, Orange (ORA: 18/21/022). All procedures followed the Australian Code of Practice for the Use of Animals for Scientific Purposes.

2.2. Study design

A feedlot experiment was conducted at the NSW DPI Agricultural Research and Advisory Station at Cowra (S33◦48.211′ E148◦42.236′, 385 m altitude). Treatments were one of four diets provided to the lambs that comprised fresh forage of either annual wheat (W), perennial wheat (PW), annual wheat plus lucerne (W + L) or perennial wheat plus lucerne (PW + L). The perennial wheat, line 11955, was a 2n = 56 partial amphiploid that was derived from a cross between T. aestivum x Thinopyrum ponticum [also described as PI 550713 in Cox et al. (2002)] and has been observed to exhibit favorable grain attributes and persists well in the Cowra environment (Larkin et al., 2014; Hayes et al., 2018). The annual wheat, cv. EGA Wedgetail was a dual-purpose winter wheat. The winter active lucerne cultivar, Titan 9 was also used.

The feedlot comprised two rows of 24 pens (48 in total). The four diets were randomly assigned to pens in a spatially adjusted complete block design with 12 replicates, using the experimental design tool DiGGER (Coombes, 2002). Each pen (dimensions: 3m × 12m) housed an individual lamb with access to water and shelter (Fig. 1). A 52 L plastic tub was located at the end of each pen and marked with a colored tag to distinguish the diet allocated to the particular pen. The tub was held in a bracket off the ground and had a cover to exclude rain as much as possible. The tubs were interchanged with each day’s feed ration.

2.3. Forage production

The forages for the feedlot study were produced on a six hectare paddock at the research station, on a Red Chromosol soil (Isbell, 1996). To minimize the effect of variable soil mineral content on forage mineral

Fig. 1. Pen layout used in the feeding study with covered feed bins.

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Small Ruminant Research 192 (2020) 106235

3

concentrations the paddock was subdivided into three blocks. Within each block the three forage types were grown in a further three discrete divisions of approximately equal size. A 0− 10 cm aggregated (45 cores per block) soil sample was collected from each plot and analyzed at the CSBP Soil and Plant Analysis Laboratory, Bibra Lake, Western Australia for Colwell phosphorous (P) and K, sulfur (KCl 40), organic carbon (Walkley-Black), nitrate nitrogen (N), ammonia, electrical conductivity, pH (water & CaCl2), Boron (B, hot CaCl2), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) (after diethylenetriamine pentaacetic acid extraction), exchangeable cations (Exc) [aluminum (Al), Ca, Mg, K and Na] and chloride (Cl) (Table 1).

The lucerne was established in the autumn of 2018. These areas were managed over the following summer and early autumn through a combination of grazing with sheep and tactical mowing to provide a sufficient quantity of fresh, weed-free forage by the beginning of the feeding study.

In the last week of February 2019 the first cereal block was estab-lished. This comprised two equal sized blocks, one containing W and the other PW. Each cereal crop was fertilized with a blend of triple super-phosphate and urea at sowing providing 15 kg/ha N, 19 kg/ha P and 11 kg/ha S. Weed control was achieved through the use of herbicides namely, 118 g/ha of 850 g/L pyroxasulfone and 2 L/ha tri-allate immediately prior to sowing and then 5 g/ha of 600 g/kg metsulfuron and 330 mL/ha of 750 g/L MCPA applied six weeks after emergence. The remaining two blocks were sown in the same manner at fortnightly in-tervals. This was done to ensure the cereal forage was harvested at approximately the same stage of phenological development throughout the study. Supplementary irrigation was provided to all forage types to ensure establishment and sufficient growth for feeding.

2.4. Animals

Poll Dorset × Merino ewe lambs (n = 80), were identified 4 weeks after weaning, at an approximate age of 12 weeks and selected for uniformity with an average liveweight of 28.2 ± 1.9 kg. Ewe lambs were selected for the study for the simplicity of urine collection for mineral excretion measurements. The lambs were selected according to their liveweight and subsequently managed to achieve a growth rate of 50− 70 g/day until the commencement of the pen study. This was ach-ieved by holding the lambs on senesced pastures that consisted of pha-laris (Phalaris aquatica), wild oats (Avena fatua) and couch (Cynodon dactylon) during the summer months. As necessary, ad libitum canola hay (Brassica napus; 700 g/h/d offering 11.1% CP and 7.9 MJME) from February to March 2019, and wheaten hay (700 g/h/d offering 13.8% CP and 11.2 MJME) from March to May 2019 were made available.

To allow for possible compensatory weight gains, in the month prior to the commencement of the pen study, the lambs were exposed to

lucerne pastures (2 weeks) and a forage crop of dual-purpose wheat (cv. Wedgetail), also for two weeks; neither with mineral supplementation. In the week prior to the experiment starting, 54 lambs where selected from the middle of the weight distribution of the original group of 80, to enter the feedlot. Average weight of this final group of lambs was 44.6 ±1.5 kg.

2.5. Feedlot management

The 28 day study included a seven day adjustment phase and began on 15th May 2019. Lambs (n = 48) were allocated to the treatment on the basis of stratified weight, sorted in ascending order and each lamb was allocated to a group in a revolving pattern of allocation to minimize variability between replicates in initial liveweight. A further six animals were kept as spares, held in pens adjacent to the main feeding pens. Of these, three lambs were fed ad libitum W and three ad libitum PW and were used to replace any animal that failed to adjust to the same base cereal forage in the adjustment phase of the study. One animal (PW + L diet) was replaced from the main group of 48 lambs during the first week of the experiment, after which no other replacements were required.

To maintain ad libitum access to the diet and better manage refusals, the amount of feed offered did change during the experimental period. On Day 1 of feeding, the lambs were offered 3 kg (fresh weight) of total ration divided over two feeding times, morning and afternoon, 6 h apart. This was supplied as 3 kg of pure cereal forage (PW or W) or 1.5 kg of cereal plus 1.5 kg of lucerne (PW + L or W + L). In the mixed rations, the lucerne was placed on top of the cereal in the feeding tub and then the full ration was turned by hand 90◦ to allow concurrent access to both forage types. Before each morning feed was delivered, uneaten forage (refusals) were collected. These were subsequently individually weighed, and in the case of the mixed ration, separated into cereal and lucerne components. In this way daily intake of each forage type offered in the diet was calculated. As the first week progressed the rations were increased so that by Day 7 the total ration offered was 5 kg (5 kg of cereal or 2.5 kg of cereal + 2.5 kg of lucerne). In the remaining period of the feeding experiment (21 days), the total forage offered was incre-mentally increased so that during the last week of the experiment 7.5 kg of forage was offered (7.5 kg of cereal or 5.5 kg of cereal + 2 kg of lucerne). This quantity of forage was greater in volume than the capacity of the tubs, so the forage was provided over three feeding times, each 3 h apart, which minimized wastage.

Throughout the experimental period, the forage was cut fresh, daily from the allocated block using a three-point linkage sickle-bar mower. A plastic mat was attached behind the cutter to collect forage. Cut height was set to avoid contact with soil, reduce the proportion of stem har-vested in the cereal forage and avoid any weeds present. Any foreign species were removed at the time of cutting or when preparing indi-vidual rations. In this way foreign species present were kept to a mini-mum and would therefore have nugatory influence on the mineral intake of the lambs.

2.6. Forage sample collection and analysis

Grab samples of each forage type were collected from the daily harvest, weighed and dried at 60 ◦C for 48 h to determine moisture content. Dry matter samples were ground through a 1 mm laboratory mill, dried at 60 ◦C and used to determine acid and neutral detergent fiber (ADF and NDF), crude protein (CP), dry matter digestibility (DMD), ash content, metabolisable energy (ME) and water soluble carbohydrate (WSC) via near infrared (NIR) spectroscopy at the NSW DPI Industries Feed Chemistry Laboratory, Wagga Wagga, NSW (ISO 17025 (NATA)). Random samples were selected and analysed using conventional wet chemistry methods to confirm the estimated values from the NIR cali-bration (AFIA, 2014).

A further set of ground samples were dried at 70 ◦C, ground through a 1 mm laboratory mill and used to determine N, P, S, Cu, Zn, Mn, K, Na,

Table 1 Soil characteristics (0-0.10 cm) of the three forage blocks used in the feeding study.

Block 1 Block 2 Block 3

pH (CaCl2) 5.9 5.6 5.4 pH (H2O) 6.9 6.3 6.3 Nitrate N (mg/kg) 77 93 66 Ammonium N (mg/kg) 5 11 5 Colwell P (mg/kg) 46 56 46 Colwell K (mg/kg) 445 398 343 Sulfur (mg/kg) 8.8 12 8.2 Organic Carbon (%) 1.1 0.8 1.0 Exc. Al (meq/100 g) 0.030 0.018 0.042 Exc. Ca (meq/100 g) 3.18 2.8 3.00 Exc. Mg (meq/100 g) 0.35 0.30 0.34 Exc. K (meq/100 g) 0.98 0.8 0.73 Exc. Na (meq/100 g) 0.03 0.03 0.02 Boron (mg/kg) 0.41 0.36 0.37 Chloride (mg/kg) 2.75 6.85 1.8

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Mg, Ca, B, Fe, Cl and nitrate contents, through nitric acid digestion (Rayment and Lyons, 2011) at the Nutrient Advantage Laboratory Ser-vices, Werribee, Victoria.

Mineral indices were determined as follows. The K:(Na + Mg) ratio was calculated from the percentage of mineral in the dry matter using the formula (K/0.039)/[(Na/0.023)+(Mg/0.012)] (Dove et al., 2016). The tetany index was calculated as (K/0.039)/[(Mg/0.012)+(Ca/0.02)] (Kemp and t’ Hart, 1957) and the dietary cation anion difference (DCAD; meq/100 g) was calculated using the formula (Na/0.023 +

K/0.039)-(Cl/0.0355 + S/0.016) (Takagi and Block, 1991). The Ca:P ratio was calculated from the percentage of each mineral in the diet.

2.7. Liveweight gain

On Day 1 of the feeding study, each lamb was weighed (to 0.2 kg) using an auto-draft weigh scale (PAD500 Swing Gate, Prattley Pty. Ltd., Temuka) and a TruTest XR5000 indicator (Datamars Ltd., Auckland). Liveweight was recorded weekly. On the last day of the feeding study the lambs were re-weighed after a 3 h curfew during which they were held off feed and weighed immediately prior to being transported to a com-mercial Australian abattoir (~ 200 km from the research site).

2.8. Slaughter and carcass evaluation

The experimental lambs were held overnight in lairage and slaugh-tered as a single flock, in accordance with industry practice and sub-jected to medium voltage electrical stimulation (Pearce et al., 2010). Carcasses were trimmed and dressed as per AUS-MEAT specifications (Anonymous, 2005) and thereafter, individual hot carcass weight (HCW) was recorded. The percentage difference between final live-weight, measured after a 3 h curfew off-feed, and HCW was calculated as the dressing percentage (DP).

Interval measures (total: 6) of pH were recorded in the longissimus lumborum muscle (LL) from the left side of each carcass. The first pH measurement was recorded immediately upon entry into the chiller. These were made using a pH meter (WP-80, TPS Pty. Ltd., Queensland), fitted with a polypropylene spear-type gel electrode (IJ-44, Ionode™, TPS Pty. Ltd., Queensland), and calibrated using pH 4.01 and pH 6.86 standards. Sample cores (diameter: 5 mm) for glycogen analysis were removed from the cranial end of the right LL, immediately upon carcass entry into the chiller (~ 20 min post-mortem) and then held frozen at − 80 ◦C to halt further metabolism. A GR knife was used to measure GR (Greville) tissue depth, being the combined muscle and fat depth when measured from the surface of the carcass to the lateral surface of the 12th rib, 110 mm from the midline. All carcasses then remained in situ within the chiller (mean ± standard deviation: 4.8 ± 0.3 ◦C) until ~ 24 h post-mortem, when final pH measurements (pH24) were recorded for both LL and semitendinosus (ST) muscles (pH24). Carcasses were again weighed, to record cold carcass weight (CCW).

Paired LLs were removed from each carcass. On the exposed surface at the 12th rib of the left LL, a metal ruler was used to measure eye muscle width (mm, EMW), eye muscle depth (mm, EMD), and subcu-taneous fat depth (mm, Fat C). Eye muscle area (cm2, EMA) was calculated as EMD × EMW × 0.008 (Hopkins et al., 1992). This same exposed surface was allowed to bloom for 30− 40 min at ~ 4 ◦C before being assessed for fresh colour. Triplicate measures were recorded using a calibrated colorimeter (CR-400 Chroma Meter, Minolta Co. Ltd., Osaka) with an 8 mm aperture and D65/10◦ Illuminant/Observer set-tings. Mean colorimetrics (L*, a* and b*) were reported and also used to calculate chroma and hue values (AMSA, 2012).

2.9. Glycogen content determination

Approximately 20 mg samples were combined with 200 μL of Milli-Q water and incubated in a dry-heat block (set to 100 ◦C) for ~ 5 min, so that temperatures exceeding boiling point and enzymatic processes were

deactivated. These were then homogenized using micro-tube pestles, centrifuged and the supernatant held on ice until analysis. The glycogen content of each sample was quantified as the average of technical du-plicates and in accordance to the colorimetric protocol outlined in the Glycogen Assay Kit Technical Bulletin (MAK016, Sigma-Aldrich Ltd., Missouri). This used a benchtop spectrophotometer (FLUOstar OP-TIMA™, BMG Labtechnologies Pty. Ltd., Victoria,) set to measure absorbance at 570 nm. Data were reported as mmol glycogen per kg of (wet) sample (mmol/kg).

2.10. Statistical analysis

All data were analyzed in Genstat (20th Edition, VSN International Ltd., www.vsni.co.uk) using a base linear mixed model fitted with di-etary treatment as the fixed effect. For the analysis of feed intake and liveweight gains, the additional terms of week of feeding and interaction between week and dietary treatment were included as fixed effects to the base model and pen (animal) as a random effect. The raw pH and tem-perature data were used to calculate the pH decline traits: pH at tem-perature 18 ◦C (pH@Temp18) and temperature at pH 6 (Temp@pH6) (van de Ven et al., 2013). These, and the remaining carcass traits, were analyzed using the base linear mixed model with pen (animal) as a random effect, the analysis of pH24 being the exception as the muscle temperature at the point of assessment was included as an additional random term to the base model. Forage quality and mineral data were analyzed using ANOVA, with pen as the blocking structure and terms for week and diet and their interaction added to the model. All data was analyzed at the 95% significance level (P < 0.05).

3. Results

3.1. Feed intake and mineral content of diets

The daily cereal forage dry matter intake averaged for each week was observed to increase over the four week period of the study (Fig. 2). There was a significant difference in cereal forage consumption (P < 0.001) when offered as a monoculture diet particularly in weeks one and four, with lambs consuming on average 7% more W than PW over the course of the study. The cereal forage component of the mixed diet showed a similar trend; however there were no statistical differences between the PW + L and W + L diets. In contrast, although lucerne was provided ad libitum, total lucerne consumption in the mixed diets decreased over time with a 41% reduction in average daily intake from week 1 to week 4 (Fig. 3). In this instance, there was 16% more of the lucerne component consumed by lambs in the PW + L diet compared to the W + L diet, when averaged over the experimental period (P < 0.001). Total intake differed

Fig. 2. Average daily cereal dry matter intake for each week of the experiment for perennial wheat (PW), annual wheat (W), perennial wheat + lucerne (PW +L) and annual wheat + lucerne (W + L) diets. Predicted means ± standard error (bars) are plotted. Columns with the same superscript are not significantly different (P > 0.05).

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Small Ruminant Research 192 (2020) 106235

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significantly between the treatments (P < 0.001) with less PW eaten compared to all treatments (1.20 kg DM/day). The addition of lucerne to the diets increased mean total intake, with more PW + L and W + L (1.33 kg DM/d vs 1.30 kg DM/d, respectively) eaten compared to W (1.27 kg DM/d). However, the total intake difference between PW + L and W + L was statistically non-significant (P > 0.05).

Average diet mineral concentrations, quality and indices calculated from these data and adjusted for intake over the 28 days of experi-mentation are shown in Table 2. The PW and W diets had concentrations of Na lower than the recommend daily requirement and K concentra-tions well above the maximum dietary concentration (3% DM). The Ca and Mg concentrations for the cereal only forages were marginally higher than the value required for growth in young livestock of 0.28% and 0.09% DM respectively. The tetany index was twice the recom-mended level for both PW and W diets. The DCAD for the PW and W diets was approximately 6 × and 5 × the recommended threshold, respectively.

The addition of lucerne had a significant influence on dietary mineral intake (P < 0.001). When compared to the respective cereal forage, the PW + L and W + L diets had higher Ca concentrations, which lifted the consumption of this mineral above the recommended daily requirement. Na intake was also increased with the addition of lucerne by 140% and 40% respectively in the PW + L and W + L diets. However, irrespective of diet, Na intake remained approximately 87% lower than the recom-mended requirement. The K concentration was significantly lower in the PW + L and W + L compared to the forage cereal alone diets and came to within 0.5% of being under the recommended maximum threshold. In the cereal forage biculture diets the combination of Ca, Na and K halved the tetany index compared to the cereal alone diets reducing the index to below the recommended threshold. DCAD was also reduced by the addition of lucerne, by 31% in the PW + L diet and 25% in the W + L diet when compared to their respective cereal only diet. However DCAD indices for all diets were still well above the suggested threshold (<12 meq/100 g DM (Masters et al., 2018)), The addition of lucerne to the cereal forage also reduced K:(Na + Mg) ratio by 33%, however this index also remained higher than the suggested limit.

For both cereal forages, CP and digestibility (DMD %) were suffi-ciently high and did not impose limits on growth. Energy content was sufficient for the class of lamb offered both PW and W diets, however the addition of lucerne reduced DMD and ME by 3% and 4% respectively in the mixed diets, to below the requirement for a 50 kg lamb growing at 250 g/h/d.

3.2. Growth and liveweight

The liveweight of lambs fed the W + L diet were observed to first decline between weeks 0 and 1 of the feeding trial, before recovering to

Fig. 3. Average daily lucerne dry mater intake for each week of the experiment for perennial wheat + lucerne (PW + L) and annual wheat + lucerne (W + L) diets. Predicted means ± standard error (bars) are plotted. Columns with the same superscript are not significantly different (P > 0.05).

Tabl

e 2

Mea

n fe

ed in

take

, die

tary

con

cent

ratio

n of

cal

cium

(Ca

), m

agne

sium

(M

g), p

hosp

horo

us (

P), p

otas

sium

(K)

, sod

ium

(N

a), s

ulfu

r (S

), ch

lori

de (

Cl),

dry

mat

ter

dige

stib

ility

(D

MD

), ne

utra

l det

erge

nt fi

ber

(ND

F), c

rude

pr

otei

n (C

P), m

etab

oliz

able

ene

rgy

(ME)

and

min

eral

indi

ces r

eflec

ting

risk

of m

iner

al im

bala

nce

(DCA

D, d

ieta

ry ca

tion-

anio

n di

ffere

nce)

. Fig

ures

in b

old

are

outs

ide

requ

ired

lim

its. S

uper

scri

pts w

ith th

e sa

me

lett

er in

the

sam

e ro

w a

re n

ot s

igni

fican

tly d

iffer

ent (

P >

0.05

).

Die

t In

take

(kg

/ D

M)

Ca (

%)

Mg

(%)

P (%

) K

(%)

Na

(%)

S (%

) Cl

(%)

Ca:P

(%

) D

CAD

(meq

/100

g

DM

) Te

tany

in

dex

K:(N

a +

Mg)

ra

tio

DM

D

(%)

ND

F (%

) CP

(%

) M

E (M

J/kg

D

M)

Lam

b Re

quir

ed

Leve

l 1.

59#

>

0.28

#

>0.

09α

>0.

24#

<

3α >

0.06

α >

0.18

α >

0.04

#

1.2#

<

12¥

<2.

2∞

<6δ

40

9.

4#

12.0

#

PW

1.20

b 0.

34c

0.12

b 0.

25b

4.70

a 0.

005d

0.35

b 0.

74b

1.39

c 77

.92a

4.49

a 12

.00a

79.0

b 44

.63a

24.3

b 12

.0b

PW +

L 1.

33a

0.82

a 0.

14a

0.21

b 3.

47b

0.01

2b 0.

31a

0.59

d 4.

24d

53.2

7c 1.

79d

7.41

c 76

.0d

40.1

7c 22

.1d

11.5

d

W

1.27

c 0.

31d

0.12

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M.T. Newell et al.

Small Ruminant Research 192 (2020) 106235

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weights comparable with the other dietary treatments. This was the single point of difference (P < 0.001; Fig. 4) with no other interaction between measurement interval and dietary treatment observed to impact on liveweight. Lamb liveweights were shown to increase consistently as weekly measurement progressed (P < 0.001) and ranged between 55 g/day for the W + L diet to 111 g/day for the W diet. There was no independent dietary treatment effect on lamb liveweights (P >0.05).

3.3. Carcass and pH decline traits

The impact of dietary treatment on lamb carcass traits is shown in Table 3. From this, we can observe that HCW was not impacted by di-etary treatment (P > 0.05). The predicted mean HCW ± standard error was 23.5 ± 0.2 kg across all treatments. Likewise, CCW was not impacted by dietary treatment (P > 0.05) with a predicted mean ±standard error across all treatments of 23.2 ± 0.1 kg. No significant difference in DP was observed between the dietary treatments (mean ±standard error: 49.7 ± 0.2%). These results culminated in the absence of any significant effect of dietary treatment on GR depth (mean ± stan-dard error: 13.0 ± 0.3 mm), Fat C depth (4.33 ± 0.2 mm) or EMA (15.3 ± 0.2 cm2).

Neither the pH@Temp18 (mean ± standard error: 5.90 ± 0.02 U) nor Temp@pH6 (18.4 ± 0.64 U) parameters of LL pH decline were impacted by dietary treatment differences (Table 3; P > 0.05). The LL pH24 values were not impacted by dietary treatment (P > 0.05), the predicted mean ± standard error was found to be 5.51 ± 0.01 U. Likewise, ST pH24 values were not significantly different between the dietary treatments (mean ± standard error: 5.75 ± 0.01 U). Also no significant difference was evident for LL glycogen content, although there was a trend wherein lambs fed PW + L diets had lower nominal levels than those fed the alternative diets. The predicted mean ± standard error glycogen content across all dietary treatments was 181.5 ± 9.4 mmol/kg.

The fresh color results for the LL are shown in Table 3. Based on these, we can observe that no effect of dietary treatment on meat color was found (P > 0.05). The means ± standard errors were: L* (32.8 ±0.2), a* (20.5 ± 0.1), b* (2.4 ± 0.1), hue (0.12 ± 0.01) and chroma (20.7 ± 0.2), across the dietary treatments.

4. Discussion

The development of perennial cereals as dual purpose crops is intrinsic to their profitable deployment within an integrated cropping and livestock farming system (Bell et al., 2010; Hayes et al., 2012). The current study is perhaps the first to investigate the effect of perennial wheat derivatives on animal performance in terms of liveweight gain and carcass characteristics in a lamb finishing system.

4.1. Feed intake and liveweight gain

Despite minor, although statistically significant, differences in intake, diet had a negligible impact on changes in lamb liveweight over time. This was based on the observed liveweight changes across the experimental period and provides an outcome that was somewhat un-expected, because of the mineral imbalances evident between forage types. Generally, growth rate was low for all diets and most likely limited by intake. The mean protein and energy intakes were adequate for a 50 kg, early maturing lamb (8 months old) growing at 250 g/d, although the PW + L and W + L diets were below requirements offering 11.5 and 11.6 MJME/kg DM, respectively. NRC intake estimates (NRC, 2007) for a 50 kg lamb growing at 250 g/d requires 1.59 kg DM/d and the lambs in the present study consumed between 1.3 and 1.5 kg DM in Week 4 only, but that did not correspond with an increase in liveweight gain. Similar observations have been made (Dove et al., 2002; Dove, 2007) and it was in these cases that the mineral imbalances were un-derpinning such low growth rates. However, it remains a possibility that the method of cutting the forage, as opposed to natural grazing habit led to a higher fiber intake, thus slowing digesta flow rate and intake.

4.2. Forage minerals

A limitation for perennial wheat forage is the marginal content of Ca and Mg coupled with deficient Na and excessive levels of K. Similar to the W diet the PW diet offered a tetany index higher than 2.2%, a K: (Na + Mg) ratio more than 6 and a DCAD greatly exceeding 12. Together these factors imply an increased risk of induced hypocalcaemia and hypomagnesaemia in grazing ruminants (Masters et al., 2019; Dove et al., 2016). It should be noted, however, that visual signs of either condition were not observed in lambs over the experimental period.

The addition of lucerne to both cereal forages in the current study increased overall forage intake and increased the available dietary

Fig. 4. The liveweight of lambs fed either perennial wheat (PW), perennial wheat and lucerne (PW + L), annual wheat (W) or annual wheat and lucerne (W + L) diets across a four week period (measurement intervals: 0-4). Predicted means ± standard error (bars) are plotted.

Table 3 Predicted means and standard error (s.e.m.) for carcass yield traits, pH decline parameters and fresh colorimetrics of lambs fed one of four dietary treatments: Perennial wheat (PW), perennial wheat and lucerne (PW + L), annual wheat (W), annual wheat and lucerne (W + L). Please note that all pH decline and fresh colour metrics relate to the longissimus lumborum muscle, with the exception of pH@24 which was also recorded for the semitendinosus muscle (ST).1.

Dietary treatment s.e. m.

p- value

l.s.d. (5%) PW PW +

L W W +

L

Carcass Yield HCW, kg 23.2 23.7 23.9 23.4 0.4 0.393 0.825 DP, % 49.3 49.8 49.7 50.0 0.5 0.587 1.191 CCW, kg 22.9 23.4 23.6 23.1 0.4 0.414 0.822 GR depth, mm 13.6 12.2 13.8 12.5 0.9 0.200 1.762 Fat C, mm 4.1 4.8 3.8 4.3 0.5 0.184 0.932 EMA, cm2 15.6 15.4 15.6 14.8 0.7 0.550 1.346 pH Decline Parameters pH@Temp18 5.88 5.85 5.92 5.96 0.06 0.265 0.112 Temp@pH6 18.60 20.40 18.02 16.68 1.81 0.242 3.654 pH@24 5.51 5.52 5.51 5.52 0.02 0.980 0.042 pH@24 ST 5.75 5.71 5.77 5.75 0.03 0.225 0.055 Glycogen,

mmol/kg 183.7 166.5 181.6 194.3 26.45 0.766 53.93

Fresh Colorimetrics L* 33.10 32.69 32.36 32.85 0.48 0.480 0.969 a* 20.58 20.65 20.67 20.10 0.40 0.437 0.800 b* 2.61 2.49 2.34 2.21 0.34 0.673 0.685 Hue 0.13 0.12 0.11 0.11 0.02 0.682 0.031 Chroma 20.77 20.81 20.82 20.24 0.42 0.441 0.841

1Abbreviations include: l.s.d. = least significant difference; HCW = hot carcass weight; DP = dressing percentage; CCW = cold carcass weight; GR = Grenville; EMA = eye muscle area; pH@Temp18 = muscle pH at 18 ◦C; Temp@pH6 =muscle temperature at pH 6; pH24 = muscle pH at 24 h post-mortem, L* =lightness, a* = redness, b* = yellowness.

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supply of Ca and Mg. However, the concentration of K in the mixed diets remained above the recommended maximum threshold. The availability of Ca is a function of concentration within the forages as well as solu-bility. Absorption is favored by low pH in the rumen, and can be depressed by high K intakes (Bhanugopan et al., 2015). The interaction between inflows of anions and cations (DCAD) into the rumen can cause shifts in the systemic acid-base equilibrium and further affect Ca ab-sorption. The high DCAD of diets in the present study suggests a shift towards more alkaline intestinal fluid, which research has shown can increase the susceptibility of animals to hypocalcaemia through reduced Ca absorption (Bhanugopan et al., 2015; Masters et al., 2019). Concur-rently, high concentrations of K in forages (> 1%) can also interfere with Mg metabolism and reduce absorption in the rumen. Low Mg can lead to increased glycogen depletion during pre-slaughter handling and is implicated in a reduction of meat eating quality (Gardner et al., 2001). The excessive K concentrations of the four diets in the current study is estimated to have reduced Mg absorption by as much as 25% (Suttle, 2010). These factors may have converted the marginal excess of Ca and Mg into subclinical deficiency that may not have been resolved by the addition of lucerne. Further investigation is required to assess concen-trations of these minerals in blood serum and urine of these lambs to indicate their metabolic status over the experimental period.

An interesting finding in the current study was the very low Na concentration in the forage of PW, approximately half the concentration found in the W diet. Hexaploid wheat has low Na concentrations in its tissues due to the action of Kna1 genes associated with the D genome, which actively exclude Na from cells and causes accumulation of K (Gorham et al., 1987). The PW accession used in the current experiment was derived from a cross between bread wheat and the perennial grass Thinopyrum ponticum, a known salt-tolerant species (Nichols et al., 2008). The additional perennial grass chromosomes in the PW accession have been shown to enhance Na exclusion and thereby further reduce Na levels in the leaf compared to wheat (Colmer et al., 2006). Values from the present study showing Na concentrations in PW forage are consistent with previous observations (Newell and Hayes, 2017) and therefore, might be expected in all perennial wheat varieties derived from Th. ponticum. Low Na concentrations could account for the increased con-sumption of lucerne in the PW + L compared to the W + L diet, demonstrating selective grazing behavior whereby the lambs have self-medicated their diet to compensate for the Na deficiency in a portion of their diet (Provenza et al., 2003). However, in the current study the Na content of lucerne was not sufficient to increase overall daily intake and all diets remained deficient in Na. Previous studies have shown the provision of Na supplements resulted in increased liveweight gains of ~ 25% and 14% in lambs grazing pure stands of wheat (Dove and Kelman, 2015) and lucerne, respectively (Champness et al., 2020). The combination of factors from low Na, high K, marginal ME and po-tential limitation of Mg and Ca absorption in all diets in the current study may have limited the ability of lambs in the experiment to achieve higher growth rates.

While lucerne proved not to be the ideal companion species to improve the Na balance in these cereals, intercropping with legumes remains a valid technique to increase the diversity of forage types for grazing ruminants to reduce the risk of imbalanced macromineral intake. Other candidate companion legumes may prove to be more suitable to combine with perennial wheat to improve the mineral bal-ance of the forage. Natrophilic legumes such as white clover (Trifloium repens) and subterranean clover (Trifolium subterraneum) contain higher levels of Na as well as Mg and Ca, coupled with low levels of K (Suttle, 2010; Masters, 2018) and therefore, could provide a more diverse mineral intake to compliment cereal forage.

4.3. Carcass characteristics

The results suggest that there is no detriment to lambs grazing perennial wheat in comparison to annual wheat. Furthermore, all diets

used in the current study produced carcasses of sufficient quality to achieve the requirements outlined in the Australian industry guidelines (MLA, 2016) suggesting that the experimental diets would not have a negative impact on lamb profitability. Therefore, this study establishes the suitability of perennial wheat forage for lamb production. It should be noted that there were substantial variation (error) apparent when comparing the effect of dietary treatment on carcass traits and this could have concealed further differences in terms of carcass characteristics. There was no impact of dietary treatment on pH decline parameters or LL glycogen content, collected immediately post-mortem. This is impor-tant as previous research has associated dietary energy intake as influ-ential on muscle glycogen reserves (Daly et al., 2006; Puolanne and Immonen, 2014; De Brito et al., 2016). These reserves would impact on the post-mortem acidification and muscle pH values – which drive many color, water-holding capacity, and sensory characteristics of lamb meat (Honikel, 2014). This did not prove an immediate concern as fresh color was unaffected by the lamb diets. Additional investigation is nonetheless required to determine if the dietary treatments impact aged lamb meat products in terms of eating quality traits and retail-potential.

5. Conclusion

This study establishes the suitability of perennial wheat as a novel alternative forage source for lambs. There were no negative impacts on lamb carcass yield or meat quality characteristics and therefore this result underpins the potential economic worth of perennial wheat to the red meat industry. Similar to annual wheat, perennial wheat forage exhibited very low Na concentrations which would need to be managed in a grazing system much as annual wheat forage presently needs to be managed. Indeed, the perennial wheat in the present study was shown to contain even lower concentrations of Na compared to annual wheat which is thought to be a consequence of the highly salt-tolerant peren-nial grass Th. ponticum ancestry in that particular line. Whether other wheat relatives that might be used in the development of perennial wheat may have substantially higher concentrations of Na in the forage is a question requiring further research.

The inclusion of lucerne in a biculture diet with perennial and annual cereals improved the Ca and Mg balance in the forage, however their absorption may have been limited by the high concentration of K. There was a suggestion in our data that offering a mixed ration of lucerne and cereal enabled the lamb to preferentially select more legume in their diet in an attempt to balance Na deficiency that was more pronounced in the PW diet. The addition of lucerne also marginally increased forage intake, but without observed greater weight gain. A number of factors, including the very low Na concentrations of the forage, led to low daily growth rates in the present study. It is likely that these low growth rates masked anticipated differences in carcass characteristics. Further research on the mineral status of lamb blood and urine is warranted to determine the effect on mineral metabolism and the presence of any sub- clinical health issue of lambs challenged by these diets.

Declaration of Competing Interest

The authors declare no conflicts of interest and have made equal contributions to the manuscript.

Acknowledgement

This work was supported by the Livestock Productivity Partnership, a collaboration between NSW Department of Primary Industries and Meat and Livestock Australia Donor Company (Project P.PSH.1036. Novel Dual Purpose Perennial Wheats for Grazing).

The authors wish to thank the many other NSW DPI staff that contributed to this study; Lance Troy, Susan Langfield, Kylie Cooley, Neil Munday, Matthew Kerr, David Cupitt, George Carney, Stephanie Fowler, Tharcilla Alveranga and Tracy Lamb. Alexandra Shanley used

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part of this study in her thesis submitted to Charles Sturt University for the Degree of Bachelor of Animal Science with Honours.

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