Variations in milk composition during lactation were studied in normal and mastitic dairy cows from 2 seasonally calving herds in northern Victoria. Milk yields, somatic cell counts (SCC), and concentrations of lactose, fat, total protein (TP), casein protein (CP), non-casein protein (NCP), sodium, potassium, and calcium varied considerably as lactation progressed. The basic patterns of change over lactation were similar whether cows were healthy or mastitic (SCC >3 x 105 cells/mL milk). Milk from mastitic cows had higher concentrations of TP, NCP, and sodium, but lower concentrations of fat, lactose, CP, and potassium, than milk from healthy cows, although differences were not consistently significant. The activity of the milk protease, plasmin, was positively correlated with log10SCC in both herds.
Thirty dairy cows in early lactation were individually fed in stalls on high quality pasture (Lolium peuenne, Dactylis glomerata and Trifoliium repens) and given either formaldehyde-treated casein or untreated casein at 1000 g/day. Nitrogen content and apparent digestibility of herbage nitrogen was 2.8 and 70.4% respectively. Treated casein significantly increased the yield of milk by 13 % and milk protein by 15 % although neither supplement affected milk composition. High-producing cows showed a greater response to formaldehyde-treated casein, with increases in milk yield of 0.5 �0.14 kg per kg increase in level of milk production. Increases in milk synthesis were associated with increased efficiency in utilization of nutrients and not with changes in pasture intake. The results support the hypothesis that formaldehyde-treated casein provided more protein for duodenal digestion and thereby increased the supply of essential amino acids which were limiting milk production. It is concluded that milk synthesis in cows fed solely on high quality pasture in early lactation is limited by the amount of protein absorbed post-ruminally.
Rate equations are derived to describe the interaction with an ensemble of atoms of a number of optical fields having arbitrary polarizations. The fields drive transitions between two manifolds of levels, each manifold consisting of magnetically degenerate fine and hyperfine levels. The rate equations are written in an irreducible tensor notation using a coupled tensor basis for the fields' polarizations, which significantly simplifies the equations. Validity conditions for the rate equations are discussed, an expression for the friction force of laser cooling is given, and specific values for elements of the coupled-basis polarization tensor are tabulated. PACS number(s): 42.65.k, 32.80.t, 42.50.VkIn considering the interaction of radiation with matter, it is sometimes possible to obtain rate equations for atomic-state populations [1]. For example, the optical Bloch equations for a "two-level" atom interacting with a radiation field can be reduced to rate equations if the atomic-state coherence between the two levels decays or oscillates at a rate which is much larger than that at which the atomic-state populations evolve. The two-level approximation is inadequate if one wishes to include e6'ects relating to magnetic-state degeneracy or radiatively induced coupling between fine and hyperfine levels within the electronic-state manifolds. In this paper, we derive rate equations that describe a situation in which optical fields of arbitrary polarization drive transitions between two manifolds of levels, each manifold consisting of a number of fine and hyperfine levels. In deriving these equations, we introduce a coupled polarization-tensor basis which facilitates the calculation. DENSITY-MATRIX EQUATIONSThe density-matrix equations describing the system of interest have been given previously [2,3], but we present them here to make this paper self-contained and to introduce the notation [4]. We consider the interaction of several radiation fields with an ensemble of "active" atoms. The incident laser fields drive transitions between a ground-state manifold characterized by quantum numbers LG (total orbital angular momentum), SG (total spin angular momentum), JG (coupling of LG and SG ), I (total nuclear-spin angular momentum), G (coupling of JG and
A novel method to calculate the reflectance of light from a turbid medium is presented. The method takes an approach similar to that of the Beer-Lambert law, where the intensity of light is attenuated by an exponential factor involving the path length and the absorption coefficient. Due to scatter, however, there are many path lengths; in the present method all possible path lengths are weighted by their probabilities and summed over. A path length probability density is derived by considering a photon random walk through the medium. The result is a simple expression for the reflectance based on the physical properties of the medium.
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