Six high and 6 low producing cows were fed corn silage, alfalfa hay, corn, and soybean meal diets to evaluate the cow's ability to metabolize energy and N. High producers consumed more feed and gave more milk than low producers. Energy digestibility (.70), conversion of digestible to metabolizable energy (.90), and absorption of N (.70) were not different between groups. For low producers, heat production (249 kcal/kg BW.75) and loss of metabolizable energy as heat (.62) were greater than for high producers (238 kcal/kg BW.75 and .53), suggesting a less efficient intermediary metabolism of the former. Body composition was unaffected by treatment. Body fat mobilized during periods 1, 2, and 3 was replaced during period 4. Change in body energy (fat) and change in energy balance (calorimetric) data were in the same direction, but absolute values did not agree; change in energy as body fat lagged behind change in energy balance determined by calorimetry. Body protein was used in early lactation and was replaced immediately in spite of negative energy balance; this suggests that protein (amino acids) may play a significant role in meeting short-term energy needs during the first few weeks of lactation.

Missouri-96 and Kentucky-31 hays were chopped with a tub grinder containing screens with apertures of 31, 63, or 100 mm in diameter and fed to dairy cows or heifers. Particle sizes (geometric mean diameter) were 1218, 1486, and 1933 micron, respectively, for the 31, 63, and 100-mm treatments. In Trial 1, the six treatments were fed ad libitum to 24 lactating cows; concentrate was offered at 1 kg/2 kg of milk. Dry matter intake and NDF digestibility were greater for Kentucky-31, but there were no other effects of variety. Particle size did not affect DM intake, DM or fiber digestibility, nitrogen partition, milk yield, or milk fat percentage. Crude protein digestibility was greatest for the 63-mm particle size treatment. In trial 2, the six treatments were fed ad libitum to 24 dairy heifers. Intake was greater for the 31 than for the 100-mm treatment but was unaffected by variety. Variety and particle size did not affect DM digestibility, nitrogen utilization, or daily gain. In this study fescue hay chopped through screens having apertures ranging from 31 to 100 mm was without effect on milk yield or composition. Reducing particle size increased intake and nitrogen utilization but not DM or fiber digestibility.

Tall Fescue (Schedonorus arundinaceus) is an introduced cool-season bunch grass that is a vital component of forage systems that support beef cattle production in Missouri and much of the eastern United States. This cool-season grass is known for its high forage yield and resistance to environmental stressors such as drought, pest, and grazing. The resilience of tall fescue to stress is attributed to a symbiotic relationship with the fungal endophyte Epichloe coenophiala, which produces ergot-like alkaloids that can negatively impact livestock performance. Replacement of alkaloid producing tall fescue cultivars, such as K31, has been suggested as a strategy to reduce ergot-like alkaloid consumption by livestock; however, this requires extensive resources and time. It has been reported to cost $250 to $400 per acre to replace tall fescue, with an additional 18 months of no grazing while new species emerge. Most current research efforts have focused on managing tall fescue to reduce toxicity risk by decreasing amounts of alkaloids consumed by livestock. Removing parts of the plant, such as the stems and seedheads, that contain greater concentrations of alkaloids by physical or chemical seedhead suppression has proven to be a successful strategy. A metsulfuron herbicide and nitrogen fertilizer were applied on pastures grazed by stocker cattle for three years to evaluate impacts on toxicity and productivity of the forage system. Metsulfuron herbicide reduced seedhead density by 80 percent and decreased ergovaline production; however, this management strategy also caused a decrease in forage yield. Nitrogen fertilizer recovered forage yield losses due to metsulfuron herbicide. Seedhead reduction in response to metsulfuron has potential for reducing alkaloid exposure when grazing endophyte-infected tall fescue.

Chemical seed-head suppression of endophyte infected tall fescue (Lolium arundinaceum) improves stocker cattle performance but may decrease forage yield. Spring nitrogen application increases tall fescue growth with a concomitant increase in ergot alkaloids, produced by the symbiotic endophyte Epichloë coenophiala. We hypothesized that greater amounts of nitrogen applied to tall fescue would increase forage yield and offset losses in forage production from chemical suppression of seed-heads with metsulfuron without effect on alkaloid concentration. Ninety-six steers (270 ± 20 kg) were randomly assigned to one of sixteen paddocks (1.8 ha) on April 18 and continuously grazed for 57 d. Paddocks were blocked by previous use (n = 4) and randomly assigned to one of four treatments; no metsulfuron, no nitrogen (NEGCON), metsulfuron with 0 (MET0), 67 (MET67), or 134 (MET134) kg/ha of ammonium nitrate, applied March 11. Steers grazing MET0 paddocks were removed 17 d early due to insufficient forage availability. Steer weight, forage yield, forage nutritive value and ergot alkaloids in forage samples were measured monthly. Seed-head frequency and species composition were determined in June. Metsulfuron application reduced (P < 0.01) tall fescue seed-heads by 80%. Metsulfuron decreased (P = 0.03) ergovaline but ergovaline increased (P < 0.01) at each monthly sampling across treatments. Nitrogen had no impact on ergovaline concentration (P = 0.50). Forage yield tended to be least (P = 0.07) for MET0, intermediate for NEGCON and MET67, and tended to be greatest for MET134 (P = 0.08). Steer ADG was not affected by treatment (P < 0.80). Metsulfuron decreased NDF (P=0.02) regardless of fertilization rate. Forage CP increased with fertilization (P < 0.01) and no differences were detected between NEGCON and MET0 (P = 0.45). Species composition was not impacted (P >0.07) by treatment. Metsulfuron decreased seed-head growth and ergovaline concentration in tall fescue. Additional nitrogen fertilizer ameliorated forage yield lost to metsulfuron application but did not impact steer gain.