The effect of harvest time of forage on carbohydrate digestion in horses quantified by in vitro and mobile bag techniques

• Grass species and harvesting time affect the nutrient content, in vitro and in vivo digestibility of forages measured with the mobile bag technique in horses. This study showed that harvesting time of forage had a larger effect on digestibility than grass species, and that fructans can potentially be digested precaecally.Lay Summary Feedstuffs contain different carbohydrate fractions that are digested in different parts of the gastrointestinal tract of horses. Grass for grazing or harvesting contains variable amounts of structural carbohydrates such as cellulose and hemi-cellulose (named fibres) and nonstructural carbohydrates which in temperate grass species include sugars and fructans (named water soluble carbohydrates (WSC)). This study quantified carbohydrate composition and digestion of six grass species (perennial ryegrass, timothy, smooth bromegrass, tall fescue, cocksfoot, and meadow fescue) harvested at three different times (early, medium, and late) and preserved as hay. In general, fiber content increased as the grasses matured, whereas WSC content varied to a large extent. In vitro fermentation using horse caecal fluid was used to quantify digestion of early and late cut grass samples of all species. Harvest time (early vs. late) had a larger effect on in vitro fermentation compared to the effect of grass species. Early and late harvested perennial ryegrass and cocksfoot were further selected for detailed studies of precaecal digestion in vivo as these species had highest and lowest WSC content. In general, cocksfoot was identified as grass species with low digestibility and low WSC concentration compared to the other species investigated.Carbohydrates in forages constitute an important part of the feed ration for all horses. The aim of the present study was to investigate the effect of harvest time on carbohydrate composition and digestion of various grass species. The experiment was divided into three parts 1) characterization of the chemical composition of experimental feeds (6 grass species: meadow fescue [MF], cocksfoot [CF], perennial ryegrass [PR], smooth bromegrass [SB], tall fescue [TF], and timothy [TI], and 3 harvest times: early, medium, and late first cut), 2) measurements of the in vitro digestion of selected experimental feeds (the 6 grass species, and 2 harvest times [early and late]) measured by in vitro gas production, and 3) in vivo digestion of selected experimental feeds (2 grass species: CF and PR, 2 harvest times [early and late]) measured by the mobile bag technique using caecum cannulated horses. An experimental field was established with plots containing each of the grass species in three replicate blocks. Grass samples were cut between 1200 and 1400 h at 4th of June (early first cut), 17th of June (medium first cut), and 1st of July (late first cut) and analyzed for crude protein (CP), neutral detergent fiber with heat stable amylase and free of residual ash (aNDFom) and water-soluble carbohydrates (WSC). The in vitro fermentation was investigated using the ANKOM RF gas production technique, where feeds were incubated for 48 h using horse caecal fluid as an inoculum. Gas production was modeled, and maximum gas production (MGP) was used to evaluate the potential digestibility of the feeds. Based on the chemical analyses and the in vitro experiment, early and late harvested CF and PR were selected for the in vivo experiment, which was conducted as a randomized 4 x 4 Latin square design including four periods, four horses and four feeds. In general, the CP content decreased whereas the aNDFom content increased as the grasses matured. The content of WSC increased in SB and TI, but decreased in CF, and fructans increased in SB, TI, PR, and TF as they matured. The in vitro MGP showed a clearer difference between harvest times than between grass species. Harvest time had larger effect on digestibility than grass species, and a high precaecal disappearance of the WSC fraction was measured by the mobile bag technique. Cocksfoot was identified as a grass species with potentially low digestibility and low WSC content and could potentially be used more for horses.

Ämnesord

LANTBRUKSVETENSKAPER  -- Husdjursvetenskap -- Husdjursvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Animal and Dairy Sience -- Animal and Dairy Science. (hsv//eng)

LANTBRUKSVETENSKAPER  -- Veterinärmedicin -- Annan veterinärmedicin (hsv//swe)

AGRICULTURAL SCIENCES  -- Veterinary Science -- Other Veterinary Science (hsv//eng)

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