Relationship of herd average somatic cell count and spontaneous recovery from subclinical mastitis

The rate of spontaneous recovery from subclinical mastitis was evaluated in 56 Kansas. DHI herds participating in the Somatic Cell Count (SCC) program. Herds were classified as low (>300,000) or high (>600,000) based on herd sec average. Comparisons between low and high SCC-herds were made for each cow's ability to recover from a subclinical case of mastitis (>600,000 SCC). Low-SCC herds had a rate of spontaneous recovery that was more than three times greater than that of high-SCC herds. Average SCC of cows with subclinical mastitis was similar in low and high herds J as well as the average sec of cows following spontaneous recovery. Results illustrate the importance of monitoring monthly sec reports. Proper attention to good procedures of milking management includes: attention to milking techniques, proper function of milking equipment, and attention to sanitation and housing conditions. As a result, herds with low SCC tests will have higher production and fewer subclinical cases of mastitis

Nutrient requirements of dairy cattle revised

The 1988 National Research Council's (NRC) Nutrient Requirements of Dairy Cattle have been revised. Adjustments have been made in the recommended requirements for net energy for lactation (NEL); crude protein (CP); calcium (Ca); phosphorus (P); and vitamins A, D, and E. In addition, suggestions are made for using undegraded intake protein (UIP) and degraded intake protein (DIP) for diet formulation

Milk urea nitrogen: a nutritional management tool

Milk urea nitrogen (MUN) analyses can be used to evaluate the nutritional status of dairy herds and for fine tuning the feeding program. MUN values \u3e18 mg/100 ml indicate that dietary protein is being wasted and feed costs could be reduced with ration adjustments. Higher than desired MUN values also indicate the need for additional undegradable intake protein (UIP; bypass protein) in the ration. High MUN values can also indicate the need for more nonstructural carbohydrates (NSC) in the diet. MUN readings \u3c14 mg/100 ml indicate dietary crude protein deficiencies or too much UIP in the ration. Reduced milk production or low milk protein tests can occur when feeding rations that produce low MUN tests. Poor reproductive performance may be the result of feeding rations that produce high MUN measurements. Conception rates may be reduced as much as 20 percentage points when MUN is \u3e18 mg/100 ml.; Dairy Day, 1996, Kansas State University, Manhattan, KS, 1996

MF890

Edward P. Call & James R. Dunham, A guide to successful AI, Kansas State University, September 1992

Earthquake Slip Between Dissimilar Poroelastic Materials

A mismatch of elastic properties across a fault induces normal stress changes during spatially nonuniform in-plane slip. Recently, Rudnicki and Rice showed that similar effects follow from a mismatch of poroelastic properties (e.g., permeability) within fluid-saturated fringes of damaged material along the fault walls; in this case, it is pore pressure on the slip plane and hence effective normal stress that is altered during slip. The sign of both changes can be either positive or negative, and they need not agree. Both signs reverse when rupture propagates in the opposite direction. When both elastic and poroelastic properties are discontinuous across the fault, steady sliding at a constant friction coefficient, f, is unstable for arbitrarily small f if the elastic mismatch permits the existence of a generalized Rayleigh wave. Spontaneous earthquake rupture simulations on regularized slip-weakening faults confirm that the two effects have comparable magnitudes and that the sign of the effective normal stress change cannot always be predicted solely from the contrast in elastic properties across the fault. For opposing effects, the sign of effective normal stress change reverses from that predicted by the poroelastic mismatch to that predicted by the elastic mismatch as the rupture accelerates, provided that the wave speed contrast exceeds about 5–10% (the precise value depends on the poroelastic contrast and Skempton's coefficient). For faults separating more elastically similar materials, there exists a minimum poroelastic contrast above which the poroelastic effect always determines the sign of the effective normal stress change, no matter the rupture speed.Earth and Planetary SciencesEngineering and Applied Science

MF789REVISED

James R. Dunham & John F. Smith, Characteristics of Low Somatic Cell Count (SCC) Herds, October 1985

Earthquake ruptures with thermal weakening and the operation of major faults at low overall stress levels

We model ruptures on faults that weaken in response to flash heating of microscopic asperity contacts (within a rate-and-state framework) and thermal pressurization of pore fluid. These are arguably the primary weakening mechanisms on mature faults at coseismic slip rates, at least prior to large slip accumulation. Ruptures on strongly rate-weakening faults take the form of slip pulses or cracks, depending on the background stress. Self-sustaining slip pulses exist within a narrow range of stresses: below this range, artificially nucleated ruptures arrest; above this range, ruptures are crack-like. Natural earthquakes will occur as slip pulses if faults operate at the minimum stress required for propagation. Using laboratory-based flash heating parameters, propagation is permitted when the ratio of shear to effective normal stress on the fault is 0.2–0.3; this is mildly influenced by reasonable choices of hydrothermal properties. The San Andreas and other major faults are thought to operate at such stress levels. While the overall stress level is quite small, the peak stress at the rupture front is consistent with static friction coefficients of 0.6–0.9. Growing slip pulses have stress drops of ∼3 MPa; slip and the length of the slip pulse increase linearly with propagation distance at ∼0.14 and ∼30 m/km, respectively. These values are consistent with seismic and geologic observations. In contrast, cracks on faults of the same rheology have stress drops exceeding 20 MPa, and slip at the hypocenter increases with distance at ∼1 m/km

Thermo- and Hydro-mechanical Processes along Faults during Rapid Slip

Field observations of maturely slipped faults show a generally broad zone of damage by cracking and granulation. Nevertheless, large shear deformation, and therefore heat generation, in individual earthquakes takes place with extreme localization to a zone <1–5 mm wide within a finely granulated fault core. Relevant fault weakening processes during large crustal events are therefore likely to be thermal. Further, given the porosity of the damage zones, it seems reasonable to assume groundwater presence. It is suggested that the two primary dynamic weak- ening mechanisms during seismic slip, both of which are expected to be active in at least the early phases of nearly all crustal events, are then as follows: (1) Flash heating at highly stressed frictional micro-contacts, and (2) Thermal pressurization of fault-zone pore fluid. Both have characteristics which promote extreme localization of shear. Macroscopic fault melting will occur only in cases for which those processes, or others which may sometimes become active at large enough slip (e.g., thermal decomposition, silica gelation), have not sufficiently reduced heat generation and thus limited temperature rise. Spontaneous dynamic rupture modeling, using procedures that embody mechanisms (1) and (2), shows how faults can be statically strong yet dynamically weak, and oper- ate under low overall driving stress, in a manner that generates negligible heat and meets major seismic constraints on slip, stress drop, and self-healing rupture mode.Earth and Planetary SciencesEngineering and Applied Science

Earthquake Ruptures with Thermal Weakening and the Operation of Major Faults at Low Overall Stress Levels

We model ruptures on faults that weaken in response to flash heating of microscopic asperity contacts (within a rate-and-state framework) and thermal pressurization of pore fluid. These are arguably the primary weakening mechanisms on mature faults at coseismic slip rates, at least prior to large slip accumulation. Ruptures on strongly rate-weakening faults take the form of slip pulses or cracks, depending on the background stress. Self-sustaining slip pulses exist within a narrow range of stresses: below this range, artificially nucleated ruptures arrest; above this range, ruptures are crack-like. Natural quakes will occur as slip pulses if faults operate at the minimum stress required for propagation. Using laboratory-based flash heating parameters, propagation is permitted when the ratio of shear to effective normal stress on the fault is 0.2–0.3; this is mildly influenced by reasonable choices of hydrothermal properties. The San Andreas and other major faults are thought to operate at such stress levels. While the overall stress level is quite small, the peak stress at the rupture front is consistent with static friction coefficients of 0.6–0.9. Growing slip pulses have stress drops of ~3 MPa; slip and the length of the slip pulse increase linearly with propagation distance at ~0.14 and ~30 m/km, respectively. These values are consistent with seismic and geologic observations. In contrast, cracks on faults of the same rheology have stress drops exceeding 20 MPa, and slip at the hypocenter increases with distance at ~1 m/km.Earth and Planetary SciencesEngineering and Applied Science

Preventive health programs for dairy cattle

Always consult your veterinarian when making vaccination decisions. The most common errors are failing to give booster immunizations and doing so at the incorrect time. Animal comfort is a greater determinant of production than vaccinations, and to receive the full benefits of nutrition, genetic, and management programs, cow comfort must be maximized. This does not lessen the need for balanced rations that allow the immune system to respond efficiently to vaccines. More is not necessarily better. The best vaccination program for a dairy includes vaccines for the most probable infectious pathogens possibly found in the herd. This combination is different for each production unit based on disease problems and management practices that can be identified by your herd practitioner.; Dairy Day, 1996, Kansas State University, Manhattan, KS, 1996