Abstract
Several in vitro experiments, a digestion trial and a growth trial were performed to determine dry matter (DM) and fiber digestibilities, rate and extent of in vitro DM disappearance, ammonia-nitrogen (NH3-N) release, N metabolism variables, intake and average daily gain in sheep fed various combinations of lucerne and caucasian bluestem hay. Dietary treatments were prepared with lucerne replacing bluestem at 0, 25, 50, 75 and 100% of dietary DM. Associative effects between forages were evaluated. In vitro NH3-N accumulation exhibited a cubic response (P < 0.01) to percentage of lucerne at 6 h of incubation. A positive associative effect on NH3-N accumulation was evident at 6 h, with the 25% lucerne substrate having greater NH3-N accumulation compared with the 0 and 100% lucerne substrates. The extent of DM, acid detergent fiber (ADF) and cellulose disappearance, and the rate of DM and neutral detergent fiber (NDF) disappearance, decreased (P < 0.05) linearly as the percentage of lucerne increased. However, the addition of lucerne resulted in a linear increase (P < 0.01) in the rate of in vitro DM digestion early in fermentation (0–24 h).In the digestion trial, DM, NDF, ADF and cellulose digestibilities decreased linearly (P < 0.001) as dietary lucerne level was increased. Nitrogen intake, apparent N digestibility and N balance were found to increase linearly (P < 0.001) with increasing lucerne percentage. Quadratic responses (P < 0.05), indicating that positive associative effects occurred between lucerne and caucasian bluestem, were found for hemicellulose digestibility, apparent N digestibility and percent N retained. Metabolic fecal N was determined to be 5.78 g N kg−1 DM intake and no effect (P > 0.90) was observed on true N digestibility due to increasing lucerne in the diet. Diets varying in lucerne were fed ad libitum to 2 pens of lambs (6 lambs per pen; average initial weight, 20 kg) in a 56-day growth trial. Dry-matter intake increased linearly (P < 0.05) as the percentage of lucerne in the diet increased. Quadratic (P < 0.05) responses to an increasing percentage of lucerne were observed for average daily gain (ADG) and feed to gain ratio.Addition of lucerne to caucasian bluestem hay increased the amount of N and cell solubles available for microbial growth and fiber digestion, resulting in increased intake and animal performance despite decreased digestibility.
Published Version
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