Timing of High-Energy Supplementation to Early-Season-Pasture-Forage Fed Continuous Culture

Abstract

A continuous culture study was conducted duplicating the daily meal pattern of pasture-grazed cattle and evaluating the time of two supplements differing in their composition (one complex: SUPP A and one simplistic: SUPP B) on their effects on nutrient digestion and metabolism of ruminal microorganisms. SUPP A contained ingredients containing substantial amounts of both structural and non-structural carbohydrates (NSC), fat, and protein, all having fractions with differing rates of availability. SUPP B’s predominate organic matter ingredients were only corn grain and soybean meal and contained approximately 3% less crude protein than SUPP A. All treatments were fed forage at five distinct times, mimicking forage intake on pasture, with supplements being fed at either a morning (AM) or evening (PM) feeding. The treatments were a) SUPP A fed AM, b) SUPP B fed AM, c) SUPP A fed PM, and d) Supp B fed PM. The results showed that dry matter, organic matter, and NSC digestibility’s were unaffected by supplement type or time of feeding.  Supplement A showed greater fiber digestion than SUPP B, regardless of time of supplementation. The PM feeding decreased the digestion of both neutral detergent fiber and acid detergent fiber in SUPP B with no effect on fiber digestion in SUPP A. Culture pH remained more stable over the 24-hour day with SUPP B feeding than it did with SUPP A feeding while average pH was not affected by supplement or time of feeding. Total volatile fatty acid flow was unaffected by treatment, as were flows of acetic and propionic acids.  Butyric acid flow decreased significantly on both supplements with the PM feeding. As expected, there were fewer total branch chain volatile fatty acids generated with SUPP B. Microbial growth measured in g microbial N flow/day increased for both supplements at the PM feeding. Flow of by-pass feed nitrogen was unaffected by supplement but was lower with PM feeding. Microbial efficiency was increased as a result of the PM feedings. The timing of a large amount of supplementation relative to the timing of daily forage meals can alter the effects seen in continuous culture work and may translate to effects in-vivo systems as well.