Applicability of Chromogen and Nitrogen as Internal Indicators of Forage Digestibility¹

Abstract

Twelve yearling sheep were fed three forages (alfalfa, bromegrass, and reed canarygrass) cut at various stages of maturity in each of two stall digestion trials during two succeeding years. Four techniques were employed to measure apparent digestibility of forage organic matter in stall trials during each of three 6‐day periods in 1964 and 1965. These included the conventional total collection method (control), the chromogen ratio method, the chromogen fecal‐index using the equation of Reid et al. (18), and the nitrogen fecal‐index using the equation of Lancaster (11). The control mediod indicated that alfalfa and reed canary were significantly more digestible than brome during 1964, but that the three forages were not different in digestibility in 1965. The three indicator methods were also used to estimate digestibility of the same forage species under grazing conditions. Measurements of the digestibility of organic matter consumed by esophageal‐fistulated sheep were made during five 9‐day periods of the 1965 grazing season. None of the indicator methods were useful for predicting absolute values. Also, the chromogen methods gave low relative values for alfalfa, while the fecal nitrogen prediction equation of Lancaster (11) gave low relative values for reed canary. The need for verification of published equations or establishment of local fecal‐ index equations was apparent. The chromogen fecal‐index equation of Reid et al. (18) failed to provide accurate measurements under our conditions primarily because the chromogen ratio technique upon which it is based was apparently invalid, due to low recovery in the feces of alfalfa chromogen and high recovery of grass chromogen.

Evaluation of Reed Canarygrass and Tall Fescue as Spring‐Summer and Fall‐Saved Pasture1

“…Both in vivo digestibility of the forage and voluntary intake (VI) of the grasses by grazing steers were studied. Regressions between fecal N and dry matter (DM) digestibility, determined from concurrent indoor digestion trials with steers fed fresh grass, were used to predict digestibility as grazed (9). Chromic oxide was used to estimate fecal output of grazing steers ( 18).…”

Voluntary intake by grazing steers and digestibility trends of tall fescue and reed canarygrass as summer and fall-saved pasture

“…Indi cators have been widely used both to predict digestibility and to estimate fecal output of the grazing animal. Some of the indicators that have been used are chromic oxide (11); iron oxide (80); certain radio-active isotopes (80); plant chromo gens (38); lignin (43); N (38); fiber, variously determined (98); methoxyl groups (80); silica (84); copper (84); and magnesium (84). More recently, jUn vitro digestibility deter minations on samples taken from esophageal fistulae have been used to estimate digestibility {5, 85.…”

“…This course has been taken primarily because of the difficulty of measuring the factors influencing nutri tive value in the case of the grazing animal (38) . An inves tigation of VI is an important step in attempting to better assess how forages differ in nutritive value.…”

Voluntary intake by grazing steers and digestibility trends of tall fescue and reed canarygrass as summer and fall-saved pasture

“…Indi cators have been widely used both to predict digestibility and to estimate fecal output of the grazing animal. Some of the indicators that have been used are chromic oxide (11); iron oxide (80); certain radio-active isotopes (80); plant chromo gens (38); lignin (43); N (38); fiber, variously determined (98); methoxyl groups (80); silica (84); copper (84); and magnesium (84). More recently, jUn vitro digestibility deter minations on samples taken from esophageal fistulae have been used to estimate digestibility {5, 85.…”

“…In pasture work most experiments have been set up to assess nutritive value by measuring animal production while paying little attention to intake, digestibility, or efficiency of utilization. This course has been taken primarily because of the difficulty of measuring the factors influencing nutri tive value in the case of the grazing animal (38) . An inves tigation of VI is an important step in attempting to better assess how forages differ in nutritive value.…”