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Impact of water-soaking on the nutrient composition of UK hays
  1. S. J. Mack, BSc(Hons) BVetMed(Hons) CertAVP(EM) MRCVS1,
  2. A. H. Dugdale, VetMB MA, DVA, DipECVAA MRCVS2,
  3. C. McG. Argo, BSc, BVSc, PhD, DipECAR, MRCVS3,
  4. R. A. Morgan, MA VetMB CertAVP(EM) DipECEIM MRCVS4 and
  5. C. M. McGowan, BVSc PhD, DEIM, DipECEIM, MRCVS5
  1. 1The Philip Leverhulme Equine Hospital, School of Veterinary Science, University of Liverpool, Neston, Wirral CH64 7TE, UK
  2. 2The Philip Leverhulme Equine Hospital, School of Veterinary Science, The University of Liverpool, Leahurst Campus, Neston, Wirral CH64 7TE, UK
  3. 3Department of Obesity and Endocrinology, Institute of Ageing and Chronic Disease, The University of Liverpool, Leahurst Campus, Neston, Wirral CH64 7TE, UK
  4. 4The Queen's Medical Research Institute, University of Edinburgh, 47 Little France Cresent, Edinburgh, Scotland EH16 4TJ, UK
  5. 5Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, The University of Liverpool, Leahurst Campus, Neston, Wirral CH64 7TE, UK

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EQUINE metabolic syndrome (EMS), defined as obesity, insulin resistance and an increased risk of laminitis, is becoming increasingly recognised as an important condition with serious welfare implications (Frank and others 2010). Dietary restriction is critical for the management of EMS, and using a low starch and sugar content diet has been shown to improve insulin sensitivity in overweight and obese horses and ponies (Dugdale and others 2010, Argo and others 2012). Feeding hay with a non-structural carbohydrate (NSC) content of <10–12 per cent dry matter (DM), equivalent to approximately 8–10 per cent DM water-soluble carbohydrate (WSC), has been advised for EMS cases (Frank 2009, Frank and others 2010). Feeding hay with a low (4 per cent) or moderate (10 per cent) NSC content has been shown to induce lower insulinaemic and glycaemic responses compared with hay of high NSC content (17 per cent) (Borgia and others 2011). McGowan and others (2013) demonstrated that restricted daily energy provision in the form of soaked hay promoted weight loss and improved insulin sensitivity in horses and ponies with EMS.

Soaking hay has been recommended as a practical method to reduce the caloric content of hay for the management of conditions such as EMS (Frank and others 2010). There is, however, limited evidence on the effect of soaking hay on its nutrient composition. Studies that have assessed the effects of soaking on the energy and nutrient composition of hay have been inconsistent and contradictory (Warr and Petch 1992, Cottrell and others 2005, Longland and others 2011). This study investigated the effects of water-soaking on the nutrient composition of hays soaked under controlled (study 1) and uncontrolled (study 2) conditions.

Study 1 involved the collection of 10 fresh hay samples, each from different bales from the same batch of mixed meadow hay from the North West of England. Four samples were analysed as ‘fresh hay’ samples. The remaining six hay samples were soaked in a haynet overnight for 16 hours in British summer 2011 (mean ambient temperature 14.1°C, sd 2.2°C). Fresh and postsoaking samples were drained of water and oven dried at 80°C (until constant mass) prior to analysis.

Study 2 involved the collection of hay samples from seven, randomly selected owners of horses diagnosed with EMS. Owners provided a dry fresh sample of hay and a sample from the same hay bale recovered from the haynet postsoaking after their normal soaking routine. Samples were collected during British autumn 2012 (mean ambient temperature 11.9°C, sd 1.9°C). Soaking conditions were not controlled, but the owners were advised to soak hay for 8–16 hours. Postsoaking samples were drained of water and then immediately submitted with the corresponding ‘fresh hay’ sample to be oven dried on the same day at 80°C (until constant mass) prior to analysis.

Dried hay samples from both studies were submitted to a commercial laboratory (DairyOne Equi-Analytical, Ithaca, New York, USA) for nutrient analysis by near infrared reflectance spectroscopy (NIR) and mineral analysis using a Thermo IRIS Advantage HX or ICAP 6300 Inductively Coupled Plasma (ICP) Radial Spectrometer after microwave digestion. Statistical analyses were carried out using SPSS V.19 and GraphPad Prism 16. Data were assessed for normality using a Kolmogorov–Smirnov test (P>0.05). A Student's t test was used to compare means of normally distributed data, and Mann-Whitney U tests were used for data that were not normally distributed. Statistical significance was set at P<0.05.

Data from studies 1 and 2 were not significantly different, therefore hay samples were pooled for further statistical analyses (11 fresh hay and 13 postsoaking hay samples) (Table 1). Combined mean soaking time in water (n=13) was 14.5 hours (sd 2.1 hours). Concentrations of NSC, WSC and simple sugars in hay DM were significantly depleted following soaking with a mean reduction of 50.11 per cent, 51.41 per cent and 57.14 per cent, respectively (Fig 1). Total ash content (mean reduction of 40.61 per cent) and concentrations of the measured macrominerals and sulphur were also markedly depleted postsoaking (Table 1; Figs 2 and 3). The ratio of calcium:phosphorus was increased postsoaking due to the greater loss of phosphorus than calcium. This should be considered when feeding soaked hay to growing or high-level exercise horses. There was no significant reduction in crude protein (CP) content with soaking hay. A significant increase in acid detergent fibre and neutral detergent fibre was observed in the postsoaking samples secondarily to the loss of DM with soaking hay.

TABLE 1:

Mean±sd of NIR analyses of hay represented as a percentage of hay dry matter (DM) for dry (fresh) hay (n=11) and postsoaking hay (n=13)

FIG 1:

Bar chart showing mean±sd for non-structural carbohydrate (NSC), water-soluble carbohydrate (WSC) and simple sugars in samples of dry (fresh) hay (n=11) and postsoaking hay (n=13). There was a significant reduction in NSC, WSC and simple sugars (P<0.001)

FIG 2:

Bar chart showing mean±sd for reduction of calcium, phosphorus and magnesium in samples of dry (fresh) hay (n=11) and postsoaking hay (n=13). There was a significant reduction in calcium (P<0.05), phosphorus (P<0.001) and magnesium (P<0.01) following soaking

FIG 3:

Bar chart showing mean±sd for reduction of potassium, sodium, chloride and sulphur in samples of dry (fresh) hay (n=11) and postsoaking hay (n=13) There was a significant reduction in potassium (P<0.001), sodium (P<0.05), chloride (P<0.001) and sulphur (P<0.01)

In this study, soaking hay produced a consistent decrease in NSC and WSC content. The mean soaked hay NSC content of 9 per cent was below the range of 10–12 per cent currently advised for feeding EMS cases (Frank 2009, Frank and others 2010). The WSC postsoaking mean of 8.45 per cent was within the range of 8–10 per cent advised (Frank 2009, Frank and others 2010).

The results of this study contrast with that of previous reports in that the results were both more consistent and the mean decrease in WSC (51 per cent) was greater. Longland and others (2011) assessed the leaching of WSC and protein from nine UK hay samples, soaked for 16 hours at a mean water temperature of 8°C. Despite a 27 per cent mean WSC decrease (range 6–54 per cent), the WSC content of seven out of the nine hays remained above the suggested upper limit for EMS of 10 per cent DM. The NSC content was not reported. A range of UK hay types were included in the study by Longland and others, which may account for the difference. Warr and Petch (1992) found a 30–48 per cent loss of WSC content for three samples when hay was soaked for 12 hours. Similar to the current study, CP content was not affected significantly by soaking (Longland and others 2011), and in both previous studies, minerals were not analysed.

In conclusion, soaking hay for a mean of 14.5 hours (sd 2.1 hours) led to a significant and consistent reduction in NSC and WSC content postsoaking. On this basis, it is likely that the consumption of soaked hays would elicit decreased glycaemic responses that could aid in the dietary management of EMS. However, individual analysis of different hay types is advised to determine the soaked NSC prior to feeding. The CP content of hay was not altered by soaking, but the mineral content of the hay was significantly decreased. This study has demonstrated that soaking effected a marked loss of water-soluble macrominerals but had no measurable effect on micromineral composition. Given this loss of water-soluble minerals, it is recommended that a feed balancer product is used to compensate for minerals lost in the soaking process where deficits exist relative to recommended dietary intakes.

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Footnotes

  • Provenance: not commissioned; externally peer reviewed

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