Conventional digestibility trials with steers were conducted to evahutte relationships between actual forage intake and estimated forage intake using the total fecal collection procedure. Actual forage intake of 6 of the 9 forages fed was not accurately estimated by the widely used technique of dividing total fecal output by forage indigestibility estimated by in vitro procedures. This was because 4811 in vitro digestibility poorly estimated in vivo digestibility of 6 forages. Regression equations based on in vivo-in vitro digestibility relationships can reduce but not solve this problem because in vivo processes such as mastication and rumination are bypassed with in vitro techniques. The use of a 36-h microbial digestion period for nongrasses and a 72-96-h microbial digestion period for grasses shows potential to improve in vitro digestibility estimates of cattle in vivo digestibility. Another potential means of improving in vitro digestibility estimates is to select the highest digestibility value from forage or diet snmpies subjected to 36,4&, 60-, 72-, 84 and 96-h microbial digestion periods. Although mechanisms controlling forage intake in ruminants have been described by Ellis (1978) Mertens (1977), Church (1979) Van Soest (1982), and Mertens and Ely (1982), present techniques to measure intake of pasture and range forages by ruminants are laborious, costly, and subject to numerous errors (Cordova et al. 1978, Kartchner and Campbell 1980). The total fecal collection method discussed by Van Dyne (1969) has become the most favored approach for estimating forage intake by domestic ruminants. Although this procedure has been widely used, evaluation of its accuracy is limited (Van Dyne and Meyer 1964). Our objective was to evaluate the total fecal collection/ indigestibility method of Van Dyne (1969) for determining intake. Methods Two independent studies were conducted in 1980 and 1982 at the New Mexico State University farm. Details of each study will be reported separately. Study I Three feeding trials were conducted between May and September of 1980. Steers were fed alfalfa (Me&ago sativu) hay for 3 weeks before each trial. Five Hereford X Angus yearling steers, weighing approximately 340 kg each, were used in each trial. Trials were 14 days long with 10 days for adaptation and 4 days for data collection. Schneider and Flatt (1975: 124) concluded that a 5day adjustment period was adequate to clear previously fed diets from the digestive tract; Dubose and Embry (1956) reported that a 4-day collection period was sufficient to quantify fecal excretion in steers and lambs. Trials were in drylot pens where steers were fed ad libitum individually. Feed intake was determined by conventional handfed methods (Schneider and Flatt 1975:57). Steers were harnessed with fecal collection bags. Total fecal output was measured daily. Forages fed in the 3 drylot trials included milo hay (Sorghum vulgare) that had the heads removed, alfalfa hay, and oat hay (Avena sativu) that contained about 10% alfalfa.
One experiment involving steers fed low-quality grass diets singly and mixed with native forbs, native shrubs, or alfalfa (Medicage sorival.) was conducted to compare the influence of these diets on ruminal fermentation. Native forbs used in our study were a 5050 mixture of scarlet globemallow (Splureralcea coccinea Nutt.) and leatherleaf croton (CrotonpoHsii Lam.); native shrubs were a 5050 mixture of fourwing saltbush (A&*lex canescens [Pursh.D and mountain mahogany (Cercocurpus montanus Raf.). Neither passage rate of indigestible neutral detergent fiber nor fluid passage rate differed (p>.lO) among the 4 diets. Ruminal pH did not differ (J9.10) among diets, and rumhral ammonia concentrations differed (P<.lO) inconsistently among diets, depending on time after feeding. Likewise, total rumhtal volatile fatty acid (VFA) concentrations did not differ (D.10) among diets. Except for butyrate [less (P<.O5) with alfalfa], proportions of individual VFA showed little difference among diets. Based on these data, adding forbs or shrubs with low-quality forage diets appears to elicit few changes in ruminal digesta kinetics and fermentation patterns compared to including alfalfa hay.There is considerable evidence that includingforbs and shrubs in cattle diets improves cattle performance during periods when grasses are dormant and low in quality (Holechek et al. 1989a). Several studies reviewed by Holechek et al. (1989a) show that leaves from forbs and shrubs contain more protein, phosphorus, and cell solubles than do grasses at comparable stages of maturity. In recent digestion trials with cattle , goats (Hunez-Hemandez et al. 1989), and sheep (Rafique et al. 1992), forage intake and nitrogen retention did not differ between palatable range shrubs and alfalfa (Me&ago sutiva L.) hay fed mixed into lowquality grass diets. However, these studies did not evaluate comparative ruminal fermentation characteristics of the shrub and alfalfa diets.Our objectives were to determine passage rate of indigestible, fiber, fluid passage rate, ruminal pH, ruminal ammonia (NH3) concentrations, and ruminal volatile fatty acid (VFA) proportions in beef steers fed a lowquality grass diet singly and in combination with forbs, shrubs, and alfalfa hay. Forbs and shrubs used in our study are common range components in New Mexico, and their use by cattle is well documented. Results from our study should provide a better understanding of how native range forbs and shrubs influence range cattle nutritional status.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.