Location: Forage and Livestock Production Research2013 Annual Report
1a. Objectives (from AD-416):
The long-term objective is to improve understanding of forage-based production systems and genetics that allow ruminant livestock to efficiently consume and convert feedstuffs, primarily forages, in profitable production systems while mitigating negative impacts on the environment. Specifically, during the next five years we will focus on the following objectives. Objective 1: Determine how forage livestock production systems interact with plants, soils, and climate with respect to carbon and nitrogen cycling under forage and grazing systems typical for the southern plains. Sub-objective 1A: Evaluate continuous and management intensive rotational grazing systems on native prairie pastures and quantify cow-calf production traits, animal and plant productivity, input requirements, and carbon (C) and nitrogen (N) dynamics in the soil-plant-animal-atmosphere continuum. Sub-objective 1B: Determine greenhouse gas (GHG) emissions from soil, plant, and animal components of diverse grazing systems. Objective 2: Determine the most efficient ruminant genetic types for forage-based production systems to optimize forage use efficiency. Sub-objective 2A: Determine how frame score affects calf growth rate, carcass quality, and economic returns under different finishing systems. Sub-objective 2B: Evaluate growing and finishing systems for impact on growth rate, carcass quality, and economic returns for sheep of different genetic types. Objective 3: Evaluate feed intake and nutrient use efficiency of beef cattle fed diets varying in proportions of forage and grain in varying environments. Sub-objective 3A: Determine the effect of frame score on intake and feed efficiency of growing cattle in different seasons. Sub-objective 3B: Determine the effect of frame score and dietary metabolizable energy density on intake and feed efficiency of mature cows. Sub-objective 3C: Determine intake, diet nutritive value, and growth rate of stocker calves grazing cool-season annual and perennial forages.
1b. Approach (from AD-416):
The research will focus on improving production efficiency while mitigating the environmental impact of forage-livestock systems by matching animal genetic type to the proper production system and nutritional regime. For objective 1), two farm-scale replicates of two grazing systems on tallgrass native prairie have been established to evaluate the long-term impacts of grazing system on input costs, animal performance, rangeland health, soil ecological function, and plant diversity. Grazing systems consist of either continuously grazed or rotationally grazed under an adaptive management framework. Animal production, forage biomass and species diversity will be monitored. Angus:Brahman F1 cows bred to Charolais bulls will constitute the grazing cow herd. Greenhouse gas (GHG) emissions, particularly methane, will be monitored on two diverse forage resources: 1) native tallgrass prairie and 2) wheat pasture. An eddy covariance flux tower combined with CH4 monitors will be established in each pasture type to calculate CH4, CO2, water, and energy fluxes at 30-minute intervals. Cattle position will be monitored using global positioning devices. Differences in GHG production with and without cattle will be determined. Simultaneously, forage intake, diet digestibility, and methane emissions will be determined using marker systems on a select group of individual animals to assess components of efficiency at the animal scale. Under objective 2, research will be conducted to match finishing system with cattle genetics to optimize biological, economic, and ecological efficiency. Frame score, associated with rate of maturity and reproductive efficiency, will be used to characterize different genetic types. At weaning, calves from each frame score class will be assigned to one of two postweaning treatments: 1) conventional (wheat pasture followed by feedlot), and 2) extended forage followed by a short feedlot phase (30-50 days) if needed]. When finished, calves will be harvested; carcass data, Warner-Bratzler shear, sensory by a trained panel, and fatty acid profile will be determined. Under objective 3, all replacement heifers, and some companion steer herd mates, will be evaluated for feed efficiency at weaning. They will be fed forage-based diets to achieve 1 kg/d gain, and individual daily intake and weight gain will be recorded. After the heifers reach maturity they will again be evaluated as mature, non-lactating cows (5 years of age). Cows will be fed a ration based on Bermudagrass baleage at maintenance for 84 d, weighed at 14-d intervals, and after final body weights are recorded on day 84, offered ad libitum access to the same ration. Efficiency will be determined as the difference in requirements and feed consumed and related to productivity during the first four calf crops.
3. Progress Report:
This was the first year of the project that involved a significant redirection from the former project 6218-31630-005-00D. We have realigned the cow herds to provide the four specific genetic types of calves from which to evaluate different growing and finishing systems, one of which provides farm-finished beef. The moderate framed Angus herd was augmented with a purchase of 35 heifers that match the cattle obtained from the Brooksville, FL, herd. The large-framed modern Angus herd is at full capacity. We discovered that we will have difficulty obtaining the necessary Angus:Brahman F1 heifers that are required each year for replacements, so an alternate plan and pasture resource was devised to generate those animals on location, and more closely control the genetics. However, to do that, part of the Angus herd was diverted so we are short of the Angus base by about 50 cows. The management intensive grazing study is progressing and should produce phase 1 results in a publication by next year. A meeting of the stakeholder group interested in the project is planned for this fall. A significant part of the effort in this project is to evaluate the carbon footprint of beef production systems by monitoring greenhouse gas emissions at different scales. At the pasture scale, one flux tower that monitors sub-hourly change in carbon dioxide (CO2), methane (CH4), water, and energy over a native prairie site has been erected and is collecting data (except for CH4). Another tower is ready to be deployed, but since the wheat fields require several field operations as we initiate a long-term rotational study, the second tower will be deployed in an improved warm-season grass pasture that is predominantly Old World Bluestem. The greenhouse gas research is expanding as the result of an AFRI grant so that we will eventually have four flux sites on location, that include two over wheat (both no-till and conventional tilled), one over native prairie, and one over the improved warm-season perennial pasture. Both the feed efficiency and calf finishing systems research were delayed for a year due to lack of facilities and insufficient number of calves of known genetics. Three research finishing barns were destroyed in May 2011 by a tornado. One is near being restored complete with Calan headgates suitable for individual feed intake, and will be available this fall when the first calves are weaned. We completed field work on three intake trials to determine the cause of depressed gains by cattle on Jose tall wheatgrass compared to wheat pasture. Laboratory procedures have been developed and samples analyses are being initiated. This work will also contribute to a database that will help in calibration of NIRS to predict pasture intake by scanning feces of the grazing animals.
1. Estimated RFI poor indicator of cattle feed efficiency. Feed makes up about two-thirds of inputs costs for a finished beef carcass, and mature cows consume the majority of the feed required to produce that carcass. Therefore, improving feed efficiency in the cow-calf unit is one way to mitigate production costs. Residual feed intake (RFI) is a popular measure of feed efficiency that is independent of body weight, milk production, or growth rate. Several studies have investigated feed efficiency in young, growing cattle, but few have investigated whether RFI in growing heifers is related to her performance and efficiency as a mature cow. Scientists at ARS and colleagues the University of Florida Agricultural Research and Education Center, Marianna, Florida, initiated research to determine whether RFI evaluated as heifers is an indicator of subsequent RFI, overall performance, and temperament as mature cows. Mature cow body weight, condition score, daily gain, milk production, backfat, ribeye area, or RFI was similar among the RFI groups determined as heifers. Also, the rank correlation between efficiency as heifers and the same animals as cows was very low. However, the most efficient heifers ate less, both as heifers and as cows. We conclude that estimating RFI on heifers is a poor indicator of efficiency of those heifers as cows, other than perhaps reducing feed intake.
Black, T.E., Bischoff, K.M., Mercadante, V.R., Marquezini, G.H., Dilorenzo, N., Chase, C.C., Coleman, S.W., Maddock, T.D., Lamb, G.C. 2013. Relationships among performance, residual feed intake, and temperament assessed in growing beef heifers and subsequently as 3-year-old, lactating beef cows. Journal of Animal Science. 91:2254-2263 doi: 10.2527/jas.2012-5242(05032013).