Effect of plant maturity at harvest of haylage on digestibility and faecal particle size in horses fed forage-dominated diets

Abstract: Time of harvest affects nutritional value and digestibility of haylage since plants are in different developmental stages. The aim of this study was to examine the effect of plant maturity of haylage cut in June, July and August on digestibility and faecal particle size in horses.Forage and faecal samples used for the analysis of apparent dry matter digestibility (DMd) and particle size distribution in faeces were from a feed-study performed in the autumn of 2009. Twelve horses were used in the study, divided into three groups in a change-over experiment. Each group was fed haylage harvested in June, July or August during three periods. Faecal grab samples were taken from each horse and pooled so that one sample represented one horse during one period. In total 36 faecal samples were analysed. Apparent DMd of the different haylage diets was calculated by using the amount of acid-insoluble ash in feed and faeces as an internal marker. The apparent DMd was different in the three haylage diets. June haylage had the highest apparent DMd and August the lowest. There was no difference in apparent DMd among the periods or horses. However, a difference among horses occurred when two horses with outlier values were excluded from the statistical evaluation.Particle size distribution in faeces was measured using stainless steel sieves of different mesh sizes. Particle size distribution in faeces did not differ between horses or periods. Particle size distribution in faeces from horses fed the diet containing haylage harvested in June differed from horses fed July/August haylage in all fractions lesser than 2.0 mm. Faecal particles from diets containing haylage harvested in July and August dominated the middle fractions (0.1 – 2.0 mm). The diet containing June haylage had the largest proportion of faecal particles in the smallest fraction size (<0.1 mm). Fraction size 0.2 mm was the only fraction with a difference between all diets. August haylage dominated followed by July and June haylage. More than 0.7 of the faecal particles were found in the largest fraction size (>2.0 mm).This study confirms that a more mature herbage produces a less digestible forage for horses. A haylage of high DMd gave a higher proportion of faecal particles less than 0.1 mm. A more lignified haylage with lower digestibility results in a higher proportion of faecal particles between 0.1 and 2.0 mm.