Effects of natural rainfall and spontaneous heating on voluntary intake, digestibility, in situ disappearance kinetics, passage kinetics, and ruminal fermentation characteristics of tall fescue hay fed to growing steers

Relatively little is known about the combined effects of spontaneous heating and natural rainfall on the feeding value of ‘Kentucky 31’ tall fescue (Festuca arundinacea Schrieb.) hay infested with the fungal endophyte Neotyphodium coenophialum (Morgan-Jones & Glenn, Bacon, and Hamlin comb. nov.). A digestion trial utilizing a 4 × 4 Latin square design was initiated to determine the effects of both natural rainfall before baling and spontaneous heating during storage on the voluntary intake, digestibility, in situ disappearance kinetics, and ruminal fermentation characteristics of tall fescue hay consumed by four 227 ± 20.5 kg steers. The four tall fescue hays utilized in this experiment were baled at 99 (low, L), and 225 g/kg (high, H) moisture prior to rainfall, and at 246 g/kg moisture after a 23 mm rainfall event (H–R) and at 93 g/kg moisture after a total accumulation of 72 mm of rain (L–R). Daily voluntary intake of the total diet, and dry matter (DM) and organic matter (OM) intakes of hay (g/kg body weight) were greater (P ≤ 0.032) for steers consuming hays baled without rainfall prior to baling than for those receiving rainfall during the wilting period. However, hays altered by rain had greater (P ≤ 0.033) apparent digestibilities of DM, OM, NDF, and ADF than did hays baled without rainfall. Effective in situ disappearance of DM and N was poorer (P ≤ 0.033) for hays altered by rainfall, spontaneous heating, or both (H, H–R, and L–R) than for L hay, but effective NDF disappearance was not affected by treatment (P ≥ 0.361). Ruminal fermentation characteristics and passage kinetics varied little between the four diets. Although hay receiving no rainfall had slightly better characteristics of nutritive value and in situ degradation than hays altered by rainfall, apparent total tract digestibilities were higher for hays altered by rainfall. While depressed total tract digestibilities in hay baled without rainfall were clearly associated with higher voluntary intakes, statistically significant decreases in ruminal or total tract retention times could not be established clearly.