Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2005
Publication Date: 3/1/2006
Citation: Ogden, R.K., Coblentz, W.K., Coffey, K.P., Turner, J.E., Scarbrough, D.A., Jennings, J.A., Richardson, M.D. 2006. In Situ Disappearance Kinetics of Nitrogen and Neutral Detergent Insoluble Nitrogen for Common Crabgrass Sampled on Seven Dates in Northern Arkansas. Journal of Animal Science. 84:669-677. Interpretive Summary: In the southeastern USA, there is a critical need for a summer forage that will better meet the needs of livestock classes with high nutrient demands, such as lactating or developing dairy cattle or stockers. When directly compared with other forages, rates of protein digestion for crabgrass were more rapid than those observed for bermudagrass, and were consistent generally with expectations for higher-quality forages. Although the ruminal protein digestion rates for crabgrass were distinctly slower than the extremely rapid rates observed for the alfalfa hay control, a large proportion of the total pool of protein in crabgrass was immediately soluble, and probably highly degradable in the rumen. This may negate some of the apparent potential for improved efficiency of protein use relative to alfalfa. Previous research has suggested that crabgrass offers clear advantages over bermudagrass with respect to ruminal disappearance kinetics of dry matter and fiber, and appears to be a promising forage alternative to perennial warm-season grasses for livestock producers in the southeastern United States. Generally, the results of this study do not negate this potential, and further work, including intensive measurement of livestock production is clearly warranted.
Technical Abstract: Southern crabgrass [Digitaria ciliaris (Retz.) Koel.] is often an undesirable species in field and forage crops, but visual observations suggest that livestock prefer it to many other summer forages. The objectives of this study were to assess the nutritive value of crabgrass sampled weekly between 11 July and 22 August 2001, and then to determine ruminal in situ disappearance kinetics of N and neutral detergent insoluble N (NDIN) for these forages. A secondary objective was to compare these kinetic estimates for crabgrass with those of alfalfa (Medicago sativa L.), bermudagrass [Cynodon dactylon (L.) Pers.], and orchardgrass (Dactylis glomerata L.) control hays. All kinetic evaluations were conducted with five ruminally cannulated Gelbvieh x Angus x Brangus steers (383 ± 22.7 kg). Concentrations of N for crabgrass decreased in a linear (P 0.002) pattern across sampling dates within leaf-blade, stem, and whole-plant tissues. Conversely, percentages of the total N pool within NDIN and ADIN fractions generally increased over sampling dates in mostly linear patterns. For crabgrass, the immediately soluble portion of the total N pool (fraction A; overall mean = 54.6% of N) was greater (P < 0.001) than for all control hays. Crabgrass exhibited a more rapid N disappearance rate (overall mean = 0.093/h) than bermudagrass (0.046/h; P < 0.001), but the disappearance rate for alfalfa N (0.223/h) was considerably faster (P < 0.001) than for crabgrass. The effective ruminal disappearance of N was greater (P < 0.001) for crabgrass (overall mean = 85.4%) than for the alfalfa (83.3%), bermudagrass (72.3%), and orchardgrass (76.0%) control hays. For alfalfa, the ruminal disappearance rate of NDIN (0.150/h) was more rapid (P < 0.001) than for crabgrass (overall mean = 0.110/h); however, the disappearance rate for crabgrass was faster than both bermudagrass (0.072/h; P < 0.001) and orchardgrass (0.098/h; P = 0.010). Effective ruminal disappearance of NDIN was greater (P < 0.001) for crabgrass (overall mean = 72.0%) than for the bermudagrass (69.0%) or alfalfa hays (50.5%), but there was no difference (P = 0.865) between crabgrass and orchardgrass (72.1%). Although crabgrass forages exhibited concentrations of total N that were comparable to alfalfa and rates of ruminal N disappearance that were less than 50% of those for the alfalfa hay control, improvements in N-use efficiency relative to alfalfa are questionable due to the excessively large fraction A for crabgrass.