Intake, Digestion, Passage Rate and Serum Prolactin in Growing Dairy Steers Fed Endophyte-Infected Fescue with Noninfected Fescue, Clover or Wheat Straw

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Abstract
Growing Holstein steers were used in two Latin-square experiments to determine the effects of supplementation of endophyte-infected fescue hay diets with other forages on intake, digestion, passage rate and serum prolactin concentration. In Exp. 1, five steers (average weight of 186 kg) were fed ad libitum amounts of endophyte-infected and noninfected fescue hays (I and NI, respectively) of similar quality in 0:1, 1:3, 1:1, 3:1 and 1:0 proportions. Total dry matter (DM) intake as a percentage of body weight (BW) linearly decreased .0055% for each 1% increase in dietary I (P<.05). Dry matter intakes with 100% I and 100% NI diets were 2.13 and 2.72% of BW, respectively. Total tract digestion of neutral detergent fiber (NDF) increased linearly (P<.05) with increasing I (66.0, 65.9, 66.3, 68.1 and 69.6%). Ruminal passage rate of particulates changed linearly (P<.05) and quadratically (P<.10) as I in the diet increased (3.5, 3.4, 2.6, 2.8 and 2.8%/h), while serum prolactin concentration and rectal temperature decreased linearly (P<.05). In Exp. 2, four steers (average weight of 137 kg) were given ad libitum amounts of wheat straw (WS) or .73% of BW of clover hay (C) at 0800 and free access to either I or NI at 1600. Total intake as a percentage of BW was greatest for C with NI (3.04), intermediate for WS with NI (2.70) and lowest for C with I (2.30) and WS with I (2.23; P<.05). Fescue intake (percentage of BW) was lowest (P<.05) for C with I (1.56) and higher (P<.05) for WS with NI (2.63) than WS with I (2.12); fescue intake for C with NI (2.33) was intermediate (P>.10) to WS with NI and WS with I. The results are interprete Rd to indicate that increasing the dietary level of I depressed intake linearly and markedly. Intake of diets high in I appears to be lower than can be explained only by ruminal-fill factors. When animals that are consuming basal I diets are provided access to nontoxic, high-quality forage, changes in intake may differ from those with basal diets of nontoxic forage. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science