2008 Annual Report
A study began spring 2008 to evaluate long-term responses of cattle to fescue toxicosis. Cattle were placed on endophyte-infected or uninfected pastures in June. After more than a month on pasture, they were brought into environmental chambers for testing under the same conditions during controlled heat stress. These tests will identify responses during peak summer heat. They will be returned to pasture and retested under the same heat stress and diet conditions after they have recovered from the summer heat. All animals will have telemetric temperature transmitters for continuous monitoring of core temperature in field and laboratory environments. In additions to normal physiological measurements in the chambers, animals will have tissue and blood samples taken for biochemical analyses and Real-Time PCR.
Cattle exposed to heat stress have reduced feed intake, lower growth and conception rates, panting activity, increased peripheral blood flow, and sweating. Although these effects are well documented, the changes in cellular function and gene regulation are poorly understood. Liver is one of the major organs involved in the regulation of metabolism and heat production. The goal of this study is to investigate the changes in gene regulation in liver of cattle under long-term mild heat stress.
Many of the ongoing field studies are near completion. Samples have been collected, dried and ground, and they are currently being analyzed for ergovaline and total ergot alkaloids. These samples are from studies that determine alkaloid production as influenced by poultry litter, commercial fertilizers, herbicides, as well as concentrations that change throughout the calendar year and during haymaking. Additional samples will be collected and analyzed during 2008; these additional samples determine the influence of silage moisture on alkaloid concentration.
Experiments on minimizing ingestion of ergot alkaloids in tall fescue-based grazing systems are midway to completion. These studies focus on using Bermuda grass, instead of endophyte-infected tall fescue, in early summer to minimize ingestion of ergot alkaloids by stocker cattle. These are long-term, whole-forage systems experiments. Forage samples and animal performance data for 2007 are being analyzed; data for 2008 is still being collected.
ADODR monitoring of this project was accomplished by frequent emails, telephone calls, and on-site visits between ADODR and University of Missouri scientists. Meetings between ADODR and SCA partners were held in College Station, TX (Jan. 2008) and Joplin, MO (Feb. 2008).
2. Toxic tall fescue consumed by cows may result in decreased calf performance: Researchers at the University of Missouri determined the effects of endophyte infection level of stockpiled tall fescue on the performance of lactating, fall-calving beef cows and their calves. Ergot-like alkaloids in toxic tall fescue decreased by approximately 50% from December through February; however, weight loss and body condition of lactating beef cows was still influenced by endophyte infection level. Nursing calves did not show changes in ADG or weaning weight based on the endophyte infection level. These data suggest that fall-calving herds can utilize highly infected tall fescue when stockpiled for winter grazing, with minimal impact on cow performance and no impact on calf gain. (Component 2 of NP 215).