Wool Quality Traits of Purebred and Crossbred Merino Lambs Orally Drenched with Spirulina (Arthrospira Platensisi)

Abstract

The objective of this study was to evaluate the effect of Spirulina supplementation, sire breed and sex on the wool characteristics of purebred and crossbred Merino weaned lambs under a single pasture-based management system. Lambs sired by Merino, White Suffolk, Dorset, Black Suffolk breeds were randomly allocated into 3 treatments – the control group grazing without Spirulina (0 mL), low (100 mL) and high (200 mL) Spirulina groups. All lambs were kept as a single mob in paddocks, grazed for 9 weeks and wool samples analysed. Differences in wool quality between the control and supplemented groups were not significant (P>0.05). However, sire breed significantly (P<0.001) influenced fibre diameter, spinning fineness, comfort factor and fibre curvature with purebred Merinos having superior wool quality than crossbreds. Wethers grew higher quality wool than ewes. Spirulina has a potential as an alternative supplementary bioresource in dual-purpose sheep feeding because it does not compromise wool quality in supplemented weaner lambs.

Key Words:

• Spirulina
• Wool quality
• Merino crossbred
• Supplementation
• Dual purpose

Introduction

Spirulina (Arthrospira platensis) is an edible microalga with potential as an alternative protein-rich lamb supplement due to its high protein content (60-70%; Becker, 2007). Spirulina is also rich in essential vitamins, minerals, fatty acids, amino acids and carotenoids (Table 1). Supplementary feeding with Spirulina has been previously tried with several animal species (Holman and Malau-Aduli, 2013), but to the best of our knowledge, there is presently no published information on the impact of Spirulina supplementation on wool quality traits in dual purpose lambs.

Across Australia, farmers have adopted dual purpose sheep systems with both wool and meat production goals (Rowe, 2010). This objective is generally achieved by mating meat-type rams to a core flock of purebred Merino ewes and exploiting heterosis to optimise lamb growth. Current lamb meat prices are high (Martin and Phillips, 2011), while wool prices are at a historical low (Gibbon and Nolan, 2011). Hence, profitability in dual purpose sheep systems is now mostly driven by lamb growth and early attainment of slaughter weight.

Lamb growth is commonly enhanced through protein-rich supplementation using canola meal, lupins, barley and wheat. Varying and inconsistent reports on the impact of these supplements on wool quality have been reported (Malau-Aduli and Akuoch, 2012; Masters and Mata, 1996). Any decline in wool quality due to supplementary feeding can affect total farm profitability. Therefore, we tested the hypothesis that the oral drenching of grazing purebred Merino and crossbred lambs with Spirulina supplement would not elicit a significant variation and decline in wool quality. The experimental objective was to evaluate the effect of Spirulina supplementation and interactions with sire breed and sex on wool quality traits in purebred and crossbred Merino lambs under a single pasture-based management.

Materials and methods

This study was conducted at the University of Tasmania Farm, Cambridge, Tasmania, Australia. All procedures had the University of Tasmania Animal Ethics approval and were conducted in accordance with the 1993 Tasmania Animal Welfare Act and the 2004 Australian Code of Practice for the Care and Use of Animals for Scientific Purposes.

Animal management and experimental design

A completely randomised experimental design in which 24 weaner lambs with an average live weight of 37.6±5.2 kg and body condition score of 3.1±0.4 at 6 months of age was utilised. The experimental lambs had an inbuilt factorial of 4 sire breeds (Merino, White Suffolk, Dorset, Black Suffolk) and 2 genders (ewes, wethers). Lambs were randomly allocated into 3 treatments (8 lambs per treatment) – the control group grazing and ad libitum drinking water only without (0 mL), or low (100 mL of Spirulina) or high (200 mL) content of Spirulina dissolved in water. The Spirulina was commercially purchased (TAAU, Darwin, Australia) as a powder and dissolved in water utilising a weight:volume ratio of 1 g:10 mL (low) and 2 g:10 mL (high) and the solution delivered to the lambs by oral drenching. Both control and Spirulina supplemented groups of lambs were kept in a single mob and had ad libitum access to the basal diet of ryegrass pastures and crushed barley whose nutrient composition is depicted in Table 2. Lambs in the low and high Spirulina treatment groups were individually drenched daily with Spirulina solution prior to being released with the control group of lambs (also drenched with water only) into paddocks sown with ryegrass pastures. The lambs were allowed 3 weeks of adjustment to the Spirulina drench prior to the experimental phase lasting 6 weeks. At all times, lambs had ad libitum access to clean drinking water.

Wool sampling and analysis

Midside wool samples of approximately 10 cm² were shorn from each lamb by an experienced shearer using Oster-Sunbeam electric shears (Boca Raton, FL, USA; Baxter and Cottle, 1998) at the start and completion of the feeding trial. Samples were accurately catalogued and commercially analysed at the Australian Wool Testing Authority (Melbourne, Australia) using LaserScan equipment (Heath et al., 2006). The wool quality traits assessed were: mean fibre diameter (FD) using LaserScan OFDA, standard deviation (SD), coefficient of variation (CV), comfort factor (CF), spinning fineness (SF), fibre curvature (CURV) and clean fleece yield (YIELD).

Chemical analysis of the basal diet

Dry matter content of the basal diet was determined by drying samples to a constant weight at 65°C in a fan forced oven. Ash content was determined by combusting samples in a furnace at 550°C for 5 h. Neutral and acid detergent fibre contents were measured using an Ankom fibre analyser (ANKOM 220; Ankom Technology, Macedon, NY, USA) (van Soest et al., 1991). Total nitrogen (N) content was measured using the Kjeldahl method (van Soest et al., 1991) and the crude protein estimated by multiplying N by 6.25. Ether extract was determined by the Soxhlet methodology, while in vitro digestibility and metabolisable energy were estimated using near infrared reflectance spectroscopy (Garnsworthy and Unal, 2004).

Statistical analysis

All data were analysed using the ‘Statistical Analysis System’ software package (SAS, 2009). Initially, summary statistics by Spirulina supplementation level, sire breed and sex, were computed with means, standard deviations, and minimum and maximum values scrutinised for any data entry errors or outliers. Subsequently, multivariate analysis of variance in generalised linear model (PROC GLM) and mixed model (PROC MIXED) analyses (SAS, 2009) were used to fit the fixed effects of Spirulina supplementation level, sire breed, sex and their second-order interactions on wool FD, CV, SD, SF, CF, CURV, and YIELD. Sire was fitted as a random effect in the Mixed Model. Significant differences and mean separations were carried out using Duncan’s multiple range and Bonferroni’s probability pairwise comparison tests (SAS, 2009) Pearson correlation coefficients between dependent variables were estimated using PROC CORR (SAS, 2009) with significance determined using Bonferroni’s probability pairwise comparison test (SAS, 2009).

Results

Effect of Spirulina supplementation level, sire breed and sex on wool traits

Spirulina supplementation level had no significant effect on any wool quality trait, compared to the control group (P>0.05; Table 3). However, wethers produced wool with lower FD (P<0.046), SD (P<0.046) and SF (P<0.019) than ewes. Comfort factor was lower in ewes than wethers (79.9±3.31 and 88.1±2.2%, respectively; Table 4).

Merino-sired lambs had lower FD (18.0±0.1 µm), SF (17.1±1.0 µm), CURV (63.5±1.5°/mm) and higher CF (96.2±3.5%) compared to all other sire breeds studied (P<0.001). Among the crossbreds, Black Suffolk-sired lambs had the highest SF (26.1±0.6 µm) and Dorset-sired lambs the least (23.8±0.9 µm; Table 4).

Effect of interactions between Spirulina supplementation level and sex on wool traits

It was evident from Figure 1 that ewes receiving high Spirulina supplementation levels had higher wool YIELD than their wether counterparts (77.2±0.8 and 71.9±1.4% respectively). All other interactions between Spirulina supplementation level and sex were not significant (P>0.05).

Effect of sire breed and sex interactions on wool traits

Black Suffolk-sired ewe lambs had lower CURV than their wether counterparts, 67.8±2.0 and 80.8±3.0°/mm, respectively (P<0.032), as depicted in Figure 2. No other second-order interactions between sire breed and sex reached statistical significance (P>0.05).

Correlations among wool traits

Table 5 shows that there were highly significant relationships (P<0.001) between FD and SF (0.99), CF with both FD (-0.87) and SF (-0.88), FD and CURV (0.39), SF and CURV (0.37), and SD with YIELD (0.29). All other correlations were not significant (P>0.05).

Discussion

Wool growth and quality depend on the type of protein supplement, its nutritional value, and level of supplementation (Malau-Aduli et al., 2009b; Masters et al., 1998; Rowe et al., 1989). Protein-rich supplements vary in amino acid availability thus affecting follicular uptake and wool fibre proliferation (Li et al., 2008). Therefore, increasing amino acid availability within the body-pool by increasing protein-rich supplementation generally results in heightened follicular uptake that favours nutrient partitioning towards faster growth, but also coarser wool fibre synthesis in crossbred lambs (Malau-Aduli and Holman, 2010; Malau-Aduli et al., 2009a). This coarser fibre is characteristic of lesser quality wool (Holman and Malau-Aduli, 2012). However, in this study, there were no observable detrimental effects of Spirulina supplementation on wool quality traits. Spirulina has a lower content of sulphur-containing amino acids compared to other protein-rich lamb supplements (Ciferri and Tiboni, 1985; Volkmann et al., 2008). Methionine and cysteine are sulphur amino acids which are essential for wool proliferation (Liu and Masters, 2003). Cysteine plays a vital role during the differentiation of intermediate filament- and keratin associated proteins during wool synthesis (Plowman, 2007). Furthermore, methionine acts as a source of cysteine in the transulphuration pathway (Liu and Masters, 2003). Spirulina’s relatively minor content of these sulphur amino acids could likely explain insignificant differences in wool traits between the unsupplemented control and Spirulina supplemented group of lambs.

Ewes generally have smaller live weights than wethers (Cam et al., 2010; Holman et al., 2012). This difference could result in considerable variation with other prioritised sinks requiring more of the available amino acids (Rogers and Schlink, 2010). Our sex and sire breed findings were similar to published literature that have demonstrated hormonal differences between sexes (Egan and Russell, 1981; Wallace, 1979) and wool follicle trait variations between sire breeds (Lee and Williams, 1993; Scales et al., 2000) as having major impacts on wool traits. Similarly, the correlations between wool traits is in line with published literature (Notter et al., 2007). The strongly positive correlation between FD and SF is expected as SF is calculated from FD and CV values (Butler and Dolling, 1992; Holman and Malau-Aduli, 2012). Likewise, CF represents the proportion of fibres over 30 µm (Holman and Malau-Aduli, 2012; Wood, 2003) and is a function of FD, thus the strong correlation between CF and FD. However, SF and CF had an antagonistic relationship, hence the negative correlation. The insignificant correlation between CF and YIELD with other wool traits has already been previously reported (Hatcher et al., 2010).

Figure 1. Interaction between Spirulina supplementation level and sex on clean fleece yield (YIELD) of grazing purebred and crossbred Merino lambs. Means (±standard error) within sire breeds with different superscripts are significantly different (P<0.05).

Figure 2. Interaction between sire breed and sex on fibre curvature (CURV). Means (±standard error) within sire breeds with different superscripts are significantly different (P<0.05).

Table 1. Nutrient composition of Spirulina (Arthrospira platensis).

Components	Value
Vitamins and minerals
beta-carotene, µg/100 g	140,000
Total carotenoids, mg/kg	1700
Provitamin A, U kg^–1	2,330,000
B3, mg/kg	130-150
B12, mg/kg	1.5-2.0
Calcium, mg/kg	1200
Magnesium, mg/kg	3300
Sodium, mg/kg	22000
Potassium, mg/kg	26000
Fatty acids, % total
Gamma-linolenic acid	17.1-40.1
Amino acids, % total protein
Methionine	2.05-2.50
Cysteine	0.5-0.9

Table 2. Chemical composition of feed components.

Chemical composition	Feed components
	Spirulina	Barley grain	Ryegrass pasture
DM, g/100 g	96.0	93.2	44.7
NDF, g/100 g DM	32.6	18.5	22.4
NDFn, g/100 g DM	30.3	17.2	20.8
ADF, g/100 g DM	18.3	6.0	23.0
NFC, g/100 g DM	7.9	68.7	43.5
Ash, g/100 g DM	9.5	3.2	11.9
EE, g/100 g DM	5.9	2.0	3.0
CP, g/100 g DM	62.2	8.9	20.8
ME, kJ/100 g DM	1707.5	1723.7	1701.1

DM, dry matter; NDF, neutral detergent fibre; NDFn, nitrogen free NDF; ADF, acid detergent fibre; NFC, non fibrous carbohydrate; EE, ether extract; CP, crude protein; ME, metabolisable energy.

Table 3. Least square means and standard error of Spirulin a supplemented crossbred and purebred Merino lambs’ wool quality traits.

Wool quality trait	Spirulina supplementation level			P
	Control	Low	High
FD, µm	23.7±1.1	24.6±1.3	24.3±1.2	0.687
SD	4.6±0.3	4.4±0.2	16.8±1.2	0.542
CV, %	19.5±0.8	17.8±0.5	5.1±0.8	0.123
CF, %	85.5±3.0	81.8±4.3	84.7±3.5	0.620
SF, µm	22.9±1.0	23.4±1.2	23.0±1.1	0.865
CURV, °/mm	71.4±2.8	71.4±2.3	73.8±2.3	0.657
YIELD, %	75.0±1.4	72.7±1.0	74.6±1.0	0.173

FD, mean fibre diameter; SD, standard deviation; CV, coefficient of variation; CF, comfort factor; SF, spinning fineness; CURV, fibre curvature; YIELD, clean fleece yield.

Table 4. Sire breed and sex least square means and standard error of Spirulina supplemented crossbred and purebred Merino lambs’ wool quality traits.

	Wool quality trait
	FD, µm	CV, %	SD	CF, %	SF, µm	CURV, °/mm	YIELD, %
Sire breed
Black Suffolk	27.2±0.7^a	19.4±0.9	5.3±0.2	74.5±4.3^c	26.1±0.6a	74.3±3.0a	74.2±1.3
Dorset	25.0±0.9^a	18.1±0.7	4.6±0.3	85.4±3.8b	23.8±0.9b	75.2±2.7a	74.1±1.2
Merino	18.0±1.1b	17.0±1.4	4.4±1.1	96.2±3.5a	17.1±1.0^c	63.5±1.5b	75.2±1.7
White Suffolk	26.7±0.4^a	17.7±1.1	4.7±0.2	79.9±2.1b^c	25.3±0.3^ab	75.9±2.5a	72.7±1.0
P	0.001	0.474	0.703	0.001	0.001	0.004	0.399
Sex
Ewes	25.1±0.9^a	18.3±1.0	5.3±0.5a	79.9±3.3b	24.0±0.9a	71.8±1.8	74.8±0.8
Wethers	23.4±0.9^b	17.8±0.4	4.1±0.2b	88.1±2.2a	22.2±0.9b	72.7±2.2	73.4±1.0
P	0.046	0.620	0.046	0.016	0.019	0.721	0.186

FD, mean fibre diameter; CV, coefficient of variation; SD, standard deviation; CF, comfort factor; SF, spinning fineness; CURV, fibre curvature; YIELD, clean fleece yield.

^a-cColumn means within a fixed effect with different superscripts are significantly different (P<0.05).

Table 5. Pearson’s correlation among wool quality traits.

	CV	SD	CF	SF	CURV	YIELD
FD	0.12 (ns)	0.17 (ns)	-0.87^***	0.99^***	0.39^**	0.13 (ns)
CV		-0.27 (ns)	-0.18 (ns)	0.12 (ns)	0.37 (ns)	0.06 (ns)
SD			-0.25 (ns)	0.21 (ns)	-0.07 (ns)	0.29^*
CF				-0.88^***	-0.87 (ns)	0.04 (ns)
SF					0.35^*	0.11 (ns)
CURV						0.21 (ns)

CV, coefficient of variation; SD, standard deviation; CF, comfort factor; SF, spinning fineness; CURV, fibre curvature; YIELD, clean fleece yield; FD, mean fibre diameter. ns, not significant (P>0.05)

*P<0.05

**P<0.01

***P<0.001.

Conclusions

The hypothesis that Spirulina supplementation via oral drenching will not be detrimental to wool quality in grazing purebred and crossbred Merino lambs holds true and should be accepted. The responses of lambs of different sire breeds and sex to Spirulina supplementation in terms of interaction effects on wool traits add to our current knowledge of supplementing crossbred sheep. Finally, there is the need for further investigation into the underlying mechanisms behind our findings, particularly with regard to circulating plasma metabolites and proteomic profiles of supplemented lambs. This would provide a comprehensive understanding of Spirulina’s future applications as a protein-rich lamb feed supplement.

Acknowledgments

This research was funded by grants and scholarships from the Australian Wool Education Trust (AWET) and The University of Tasmania (UTAS). We appreciate the valuable inputs of Chris Gunn and Barrie Wells during the sheep breeding and feeding trials.