Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/20/2000
Publication Date: 6/20/2000
Citation: BLUMMEL, M.R., GRINGS, E.E. RELATIONSHIP BETWEEN ESOPHAGEAL DIET SAMPLES, CLIPPED FORAGE SAMPLES, AND WEIGHT GAIN OF STEERS. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2000. v. 51. p. 267-271. Interpretive Summary: The decline in forage quality and the resulting decrease in the growth rate of cattle during the late summer grazing season in the Northern Great Plains are well documented. Attempts to counterbalance these effects by supplementation were met with only varying success. Efficient supplementation requires a thorough knowledge of the ruminal fermentation characteristics of the forages. The problem of selective grazing on diverse pasture is frequently addressed by fitting animals with esophageal cannulas from which more representative diet samples can be collected than obtained by clipped forage samples. The objective of the present work was to describe gas production kinetics of esophageal and clipped forage samples and to relate these kinetics to weight gain of steers. Pasture quality and weight gain of steers were measured from May to September. Pasture quality was assessed monthly based on esophageal diet sampling as well as on clipped forage samples. Samples were analysed for conventional chemical variables and 48 h in vitro organic matter digestibility; additionally, kinetics of fermentation were estimated by an in vitro gas production test. Chemical variables esophageal samples were more closely related to weight gain than the respective variables of clipped forage samples. We conclude that forages with high in vitro digestibility, but proportionally low gas production, which indicates high microbial efficiency, support high performance in grazing animals.
Technical Abstract: The relationship between pasture quality and weight gain (WG) of steers was examined monthly from May to September in 1993 and 1994. Pasture quality was assessed by esophageal diet (EDS) and by clipped forage sampling (CFS). EDS and CFS were analysed for chemical parameters and 48 h in vitro organic matter digestibility (IVOMD); additionally kinetics of fermentation were estimated by an in vitro gas production (GP) test. Kinetics of GP were described by exponential and by sigmoidal models. To assess the impact of rumen nitrogen (N) recycling on forage utilization CFS were incubated in N-low and N-rich medium. Monthly WG of steers from May to September were 1.50, 0.92, 0.84, 0.85 and 1.42, 0.91, 0.47 and 0.85 kg/day in 1993 and 1994, respectively. Chemical parameters and IVOMD of EDS were more closely related to WG than the respective parameters of CFS (P<0.01 vs P<0.05). No model of in vitro GP fit all periods. Exponential models fit better (P<0.05) than sigmoidal in early season while the reverse was true for later season. In vitro GP from EDS was positively related to WG (R**2=0.79; P<0.01) while this relationship was only insignificantly positive for CFS incubated in N-low medium. Supplementation with N improved this relationship and up to 70% (P<0.01) of the variation in gain was thus accounted for. The reason for this improvement is seen in underestimation of available N in CFS. Best correlations with WG were obtained by a combination of IVOMD and GP values of EDS and up to 87% (P<0.001) of the variation in WG were thus accounted for. In this model the regression coefficients were positive for IVOMD but negative for GP.