By Derek Cuddeford
University Fellow in the Division of Veterinary Clinical Sciences at the Royal (Dick) School of Veterinary Studies at the University of Edinburgh. He has had a long term research programme investigating the nutrition of horses.Pöttinger AG, Austria.

Apparently clean and well-made hay will contain a large number of respirable particles that can lead to the onset of allergic respiratory disease in horses. Soaking hay can reduce the number of particles but also the nutrient content of the forage. Well-preserved silage is relatively low in respirable allergens. However, ensiling forages has been stated to reduce their voluntary intake by horses and there is some suggestion that certain horses will not eat such material. However, comparisons to date have failed to compare preserved forages on an equal footing in terms of stage of maturity, type of crop, etc.

A recent study reported in Animal Feed Science and Technology (vol.132, pages 66-78) compared the preference of horses for grass conserved as hay, haylage or silage. The crop used was a first cut from a permanent ley comprised mostly of timothy, meadow fescue and a small amount of couch grass. The crop was cut with a Kverneland Taarup 3028 mower conditioner; a dry matter (DM) of 350g/kg was achieved 1 hour after cutting and some of the crop was baled as silage using a high-density Lely Welger AP 730 baler. At 550g/kg DM some more was baled as haylage (low DM) and the remainder baled for hay and haylage (high DM) at 700g/kg; hay bales were barn dried to 870g/kg. Silage and haylage were wrapped with 8 layers of Horsewrap from Trioplast.

Four horses (430-650kg) were kept on summer pasture for 3 months before the experiment and during the study when forages were offered once daily for 2 hours in a stable; 1kg DM of each forage was available simultaneously. Placement of forage containers was randomised from day to day over the 4 consecutive 5 day periods of the study.

Silage was the first choice 72 out of 84 times and it was never left in favour of other forages. Eating time and forage consumption differed significantly (p<0.0001) between forages; the longest eating time and highest consumption was for the silage followed by haylage (low DM), haylage (high DM) and then hay. As expected there was considerable variation between horses and towards the end of the meal the horses alternated between forages more frequently than at the beginning.

The big question that arises out of this work is “why did the horses show a clear preference for the silage”? There are a number of possibilities arising out of differences in:

  1. DM content;
  2. chemical composition;
  3. microbial status;
  4. pH.

DM content

There was a clear difference in DM content of the forages on offer to the horses. Grazing horses will naturally consume low DM forage in temperate zones although at times they may browse and eat high DM forage during periods of drought. Horses fed hay when housed will drink many times during the feeding process and some horses will deliberately wet the hay before chewing it. Horses that demonstrate this behaviour are highly motivated to do it; the behaviour can be extinguished by pre-wetting the hay showing clearly that it is a functional behaviour. Thus, it seems not unreasonable that a horse would prefer low DM forage although there are reports that low DM (340g/kg) clamp silage is not very palatable with intakes as low as 9gDM//kg body weight/day; approximately half that of haylage (670gDM/kg) that was fed to the same animals.

Chemical composition

The same parent material was used for all forages so there were only very small differences in the contents of digestible organic matter, crude protein and neutral detergent fibre. Water soluble carbohydrate content was very different reflecting the extent of fermentation and naturally, was highest in the hay (101g/kgDM). Horses have a “sweet tooth”, a fact exploited by feed manufacturers by the inclusion of syrups/molasses/etc to increase product palatability. Thus, it is interesting that the hay was preferred least and that sweetness per se was not the most attractive feature to the horses in the case of the silage (26g/kgDM); something else was making the silage attractive! There is little information in the literature concerning horse preferences but quite a lot concerning voluntary food intake. Unfortunately the latter data do not compare forages made from the same parent material. Fermentation end products (notably lactic, acetic and butyric acids) in the silage clearly did not adversely affect preference although their concentrations were respectively 31.8, 6.6 and 1g/kgDMm much greater than in either of the haylages.

Microbial status

Differences were small except that there were lactic acid bacteria in the silage (8000x103CFU/g lactobacilli )1 and none in the hay although the reverse was true for enterobacteria but it is hard to imagine that this would have any effect on preference.

pH

This will largely reflect the presence of lactic acid and was 5.81 for the high DM haylage, 5.63 for the low DM haylage and 4.94 for the silage. Whilst there is a relationship between pH and intake of silages by ruminants there is no such data for horses. It is unwise to make across species comparisons and to equate food intake with preference. Clearly, in the study reported, a pH of 4.94 did not negatively affect intake and because haylages generally are conserved at higher pH it is unlikely that pH per se will be important in terms of its effect on food preference.

Conclusion

It is impossible to determine why the horses preferred the hay least but clearly the method of conservation affected horse preference, silage being the “favourite”. Once smelled or tasted it was never left for another forage-one wonders about the nature of the fatal attraction.

1 CFU stands for Colony Forming Unit (bacteriology)

< Back
< Back to Autumn '07 Newsletter
Back to...
Autumn 2007 Newsletter
Haylage for Horses Section