Intake and apparent digestibility of hay or hay plus concentrate diets determined in horses by the total collection of feces and n-alkanes as internal markers

Abstract

The apparent digestibility of hays plus two commercial mixed feeds containing about 14% and 11.8% crude fiber (CF), respectively as feeds was determined by means of two in vivo digestibility trials, each performed on 4 or 5 saddle horses weighing on average about 550 and 535 kg, respectively, over a 6 day feces total collection period with a previous 14 day adaptation period. The diets were based on a first cut meadow hay – whose digestibility was estimated in each trial – and different percentages of the mixed feeds at a feeding level close to maintenance. The two mixed feeds were rich respectively in a by-product from the citrus fruit industry (citrus pulp) and in a by-product from the apple fruit industry (apple pectin pulp). The forage to concentrate ratio was, respectively, 50:50, 75:25 and 100:0 on a dry matter basis (Diets 1, 2 and 3) in the first trial and, 50:50 and 100:0 (Diets 4 and 5) in the second trial. The apparent digestibility of the dry matter, organic matter, gross energy, and crude protein was measured by the ingesta/excreta procedure and using the most abundant n-alkanes (C 27, C 29, and C 31) as internal markers for all the rations and the hays. No differences were found among the digestibility coefficients obtained by the total collection method or using the different n-alkanes. The use of n-alkanes for digestibility determinations in horses is neither precise nor accurate, but can be advised for free ranging animals, when the total collection of feces is impossible. Taking into account that the accuracy of this later method is comparable, we suggest selecting n-alkanes with a high concentration and the highest fecal recovery; C 29 and C 31 n-alkanes (the first in particular) resulted to be the best choice.