Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/1998
Publication Date: N/A
Interpretive Summary: In sunlight, plant leaves make carbohydrate (sugar and starch) from carbon dioxide gas they remove from the atmosphere. Carbohydrate is made faster than the leaves can move it to roots and growing tissues to provide energy. Animals like cattle, sheep, and goats prefer feeds with higher starch and sugar so their preferences for hays harvested at sundown (higher carbohydrate) may be greater than their preference for hays harvested at sunup (lower carbohydrate). A grass called tall fescue was harvested so that each of three cuttings at sundown was followed by cuts the next mornin at sunup resulting in 6 hays. In three experiments sheep, goats, and cattle were offered every possible pair of hays (15 pairs) for a meal. All three animal species preferred hays harvested near sundown. Increased preference was associated with increased carbohydrate and digestibility and decreased fiber.
Technical Abstract: Plants vary diurnally in concentrations of nonstructural carbohydrates (TNC). If ruminants prefer forages with higher TNC then the preference for hays harvested within the same 24-h period may vary. An established field of Tall Fescue (Festuca arundinacea Shreb.) was harvested six times in the vegetative stage. Harvests were paired such that each cutting at sundown (PM) was followed by another the next morning at sunup (AM). We harvested in this manner 3 times resulting in 6 hays. The hays were field dried, baled, and chopped prior to feeding. Three experiments were conducted (Exp. 1, sheep; Exp. 2, goats; and Exp. 3,cattle) utilizing six animals in each case. During an adaptation phase, hays were offered alone as meals. In the experimental phase, every possible pair of hays (15 pairs) was presented for a meal. Data were analyzed by multidimensional scaling and by traditional analyses. Multidimensional scaling indicated that selection was based on a single criteria. Preference for PM hays was greater than for AM hays (p<.01) in all experiments. Increased preference was associated with increased TNC (p<.01) and in vitro true dry matter disappearance (IVTDMD) (p<.01) and decreased fiber (p<.01; NDF, ADF, cellulose, and lignin). Mowing hay late in the day was effective in increasing forage preference.