Supplementation of Yearling Steers Grazing Fertilized and Unfertilized Northern Plains Rangeland

Supplementation studies were conducted with yearling steers on a silty range site in central North Dakota, where yearly precipitation averaged 380 to 410 mm. The studies were conducted for 3 summers on both fertilized (45 kg N/ha) and unfertilized native pastures. Animal performance was compared to seasonal changes in the chemical composition of pasture samples collected with esophageal-fistulated steers. Chemical composition differences between diet samples from the fertilized and unfertilized pastures were inconsistent, but generally protein was higher and acid detergent fiber lower on the fertilized pasture. Supplementation with barley in the early summer resulted in little benefit, but supplementation with barley in the late summer, especially when pasture digestibility (in vitro) dropped to 50 to 52%, was beneficial on both the fertilized and unfertilized pastures. However, the response was not consistent between years. Barley supplementation appeared to be economically viable, but the feasibility of this practice will vary from year to year, depending on the price of barley relative to the price of steers. The results of protein supplementation were more erratic, possibly because of differences in precipitation patterns and hence plant growth between years. Native rangelands in the Northern Great Plains support good summer weight gains on yearling steers. Therefore, little consideration has been given to use of supplements which might produce still greater and more efficient gains. Rogler and Lorenz (1965) have shown that beef cattle carrying capacity of the Northern Great Plains mixed grass prairie can be approximately doubled with appropriate nitrogen fertilization. However, fertilization was shown to favor the growth of cool-season midgrasses, particularly western wheatgrass (Agropyron smithii), with an associated reduction in the stand of blue grama (Boutelouagracilis), a warm-season shortgrass (Lorenz and Rogler 1972). This shift in species composition alters the seasonal growth pattern and may affect the nutritional value of the grazing animal’s diet. There is limited information available on the chemical composition of native forages in the Northern Great Plains, especially with respect to changes during the grazing season. Information available on the value of supplementing yearling steers grazing native forage is also limited. However, Raleigh (1970) reported positive results from a supplementation scheme developed for use in eastern Oregon. Both crude protein (CP) and energy were supplemented as required to complement the diet of yearling steers grazing crested wheatgrass (Agropyron desertorum). A beneficial effect from energy supplementation of steers grazing spring native range in eastern Colorado has been reported by Denham (1977). These results suggested that CP and/or energy supplementation might also be beneficial to grazing steers in the Northern Plains. Thus the objectives of this study were: (I) to determine the chemiAuthors are research animal scientist and research agronomist, USDA-AR& Northern Great Plains Research Laboratory, P.O. Box 459, Mandan, N.D. 58554. Authors wish toacknowledge Mr. Charles Graham for hisassistance with statistical procedures and Mr. Richard Huppler and Mrs. Margo Dockter for their techncial assistance. Manuscript received May I I, 1980. cal composition of esophageal fistula diet collections taken from fertilized and unfertilized native range throughout the grazing season, and (2) to study the effect of CP and energy supplementation on the performance of yearling steers grazing these rangelands. Materials and Methods Summer supplementation studies were undertaken in 1977, 1978, and 1979 on a Northern Great Plains silty range site in the 380-410 mm rainfall area of central North Dakota. Predominate forage species were western wheatgrass (Agropyron smithii). prairie junegrass (Koeleria cristata), blue gmma (Boutelouagracilis), needleandthread (Stipa comata), green needlegrass (Stipa virid&), and upland sedges (Carex spp.). Big bluestem (Andropogon gerardii) was present in low areas and along intermittent waterways. The experimental site had been previously separated into 2 pastures. The smaller of these (14.2 hectares) had been fertilized annually for 20 years with 45 kg nitrogen per hectare (45-N). This practice was continued during these studies. The other pasture contained 28.4 hectares and had not been fertilized (O-N). The same number of steers were grazed on each pasture based on results of work by Rogler and Lorenz (1965), which demonstrated that a hectare of fertilized rangeland would support twice as many steers as a hectare of unfertilized rangeland. Five esophageal-fistulated steers were used to collect weekly diet samples from each pasture in 1977 and 1978. The 1977 study was conducted from mid-May until mid-September and the 1978 study from mid-May until mid-October. In 1979 diet samples were collected every second week from mid-May to mid-October using 6 esophageal-fistulated steers. Diet samples were collected from both pastures the same day by using the same steers. To avoid a possible pasture bias, samples were collected one week from the 45-N pasture first and the next week from the O-N pasture first, Obioha et al. (1970), reported slight but significant differences in nitrogen level between morning and evening forage samples collected via esophageal fistula. The difference was attributed to differences in grazing selectivity due to hunger. In our study samples were collected from pastures in the morning, with samples collected from the second pasture immediately following the first. Esophageal-fistulated steers were maintained on an adjacent O-N native pasture and were not supplemented. They were kept off feed the night before sampling to facilitate diet collections. Diet samples collected by individual steers were dried to a constant weight at SO“ C in shallow pans in a forced draft oven then ground throught a l-mm screen in a Wiley mill. Chemical analysis included Kjeldahl nitrogen, in vitro digestible organic matter (Tilley and Terry 1963, Moore and Mott 1974), neutral detergent fiber (Van Soest and Wine 1967), acid detergent fiber (ADF) and lignin (Van Soest and Wine 1968). In 1978 and 1979 diet samples from individual steers were processed the same as in 1977. Kjeldahl nitrogen was measured on each sample, but the other chemical analyses were performed on a composite sample for each pasture JOURNAL OF RANGE MANAGEMENT 36(l), January 1963 41 Table 1. Chemical comypition of forage samples collected via esopbagel fiitulated steers during tbe summer grazing season from native range receiving 45-N and O-N (1977). Month IVDOM % Pasture 45-N O-N CP NDF ADF % of D.M. Lignin % of D.M. % of D.M. % of D.M. Pasture Pasture Pasture Pasture Mean 45-N O-N Mean 45-N O-N Mean 45-N O-N Mean 45-N O-N Mean May’ 66.2 62.4 64.3 19.1 12.8 16.0 56.6 66.6 61.6 33.5 46.8 37.2 7.6 6.5 7.0 June 59.7 57.4 58.6 13.4 10.5 12.0 69.4 JO.6 70.0 39.1 44.3 41.7 6.4 8.2 7.3 July 56.6 53.6 55.1 12.7 8.8 10.8 10.6 JO.6 70.6 41.5 44.6 43.0 7.2 7.7 7.4 August 58.2 52.5 55.4 12.2 7.9 10.0 67.3 66.4 66.8 42.2 46.6 44.4 7.4 9.1 8.2 September 60.3 55.9 58.1 16.2 12.6 14.4 64.5 66. I 65.3 39.1 46.8 43.0 6.8 9.6 8.2 mean 60.2” 56.4’ 58.3 14.7” 10.5b 12.6 65.7” 68.lb 66.9 39. I” 44.6b 41.9 7.1’ 8.2b 7.6 ‘Pasture means with the same heading and different superscripts differ significantly (K.05). *Each value isan average of20samples(4dates by5steers)except September, whichcontains only3samplingdatesand May whichcontains 19samplesfor the45-N pastureand I8 for the O-N pasture. ‘Contains June 2 sampling date. for each sampling date. Data wereanalyzed by collection period by using either an arithmetic mean of data from individual diet samples or data from the chemical analysis of a composite sample. equipment to facilitate supplementation when the study was initiated. 1977 Study Twenty yearling Hereford steers weighing approximately265 kg were randomly assigned to either the 45-N or O-N pasture. Five steers on each pasture were then randomly assigned to one of the following treatments: (I) no supplement, or (2) .9 kg dry rolled barley containing 2.7 Meal DE and 119 gm CP. Steers were corralled each morning before 1000 hours CDT and those that received supplement were individually fed. Refused supplement was weighed and subtracted from the amount offered. The experiment was started June 1 and terminated July 22 because of a severe drought and consequent lack of forage, which forced removal of the steers from the pasture. All steers had continual access to a 50-50 mixture of salt and dicalcium phosphate. Weight gains for each pasture, each period, and each year were analyzed separately, then the two years of ES data and the two years of LS data were analyzed as randomized complete blocks. Treatment differences were determined by Duncan’s multiple range test and were considered statistically significant at the 5% level of probability.