190 research outputs found
Does the Feeding Behaviour of Dairy Cows Differ When Fed Ryegrass Indoors vs. Grazing?
Dairy cows eating ryegrass ingest smaller boli when grazing than when fed indoors (93 vs. 142 g; Boudon et al., 2004). To investigate whether this difference in bolus affects feeding behaviour of the cows, an automated system (chewing halters) was used to monitor feeding behaviour of cows given ad libitum access to perennial ryegrass in individual feed troughs (indoor feeding, IF) or at pasture (grazing, GR)
Variation Between Individuals in Voluntary Intake and Herbage Intake of Grazing Dairy Cows
Herbage intake and milk yield of unsupplemented grazing dairy cows are highly variable between animals within a herd (Delaby et al., 2001). The objective of this experiment was to describe the relationship between the individual voluntary intake (VI) of dairy cows measured before turnout and their herbage intake at grazing, at two herbage allowances
Recommended from our members
Potential of legume-based grassland-livestock systems in Europe
European grassland-based livestock production systems
face the challenge of producing more meat and
milk to meet increasing world demands and to achieve
this using fewer resources. Legumes offer great potential
for achieving these objectives. They have numerous
features that can act together at different stages in
the soil–plant–animal–atmosphere system, and these
are most effective in mixed swards with a legume proportion
of 30–50%. The resulting benefits include
reduced dependence on fossil energy and industrial
N-fertilizer, lower quantities of harmful emissions to
the environment (greenhouse gases and nitrate), lower
production costs, higher productivity and increased
protein self-sufficiency. Some legume species offer
opportunities for improving animal health with less
medication, due to the presence of bioactive secondary
metabolites. In addition, legumes may offer an adaptation
option to rising atmospheric CO2 concentrations
and climate change. Legumes generate these benefits
at the level of the managed land-area unit and also at
the level of the final product unit. However, legumes
suffer from some limitations, and suggestions are made
for future research to exploit more fully the opportunities
that legumes can offer. In conclusion, the development
of legume-based grassland–livestock systems
undoubtedly constitutes one of the pillars for more
sustainable and competitive ruminant production systems,
and it can be expected that forage legumes will
become more important in the future
The profile of a narrow line after single scattering by Maxwellian electrons: relativistic corrections to the kernel of the integral kinetic equation
The frequency distribution of photons in frequency that results from single
Compton scattering of monochromatic radiation on thermal electrons is derived
in the mildly relativistic limit. Algebraic expressions are given for (1) the
photon redistribution function, K(nu,Omega -> nu',Omega'), and (2) the spectrum
produced in the case of isotropic incident radiation, P(nu -> nu'). The former
is a good approximation for electron temperatures kT_e < 25 keV and photon
energies hnu < 50 keV, and the latter is applicable when hnu(hnu/m_ec^2) < kT_e
< 25 keV, hnu < 50 keV. Both formulae can be used for describing the profiles
of X-ray and low-frequency lines upon scattering in hot, optically thin
plasmas, such as present in clusters of galaxies, in the coronae of accretion
disks in X-ray binaries and AGNs, during supernova explosions, etc. Both
formulae can also be employed as the kernels of the corresponding integral
kinetic equations (direction-dependent and isotropic) in the general problem of
Comptonization on thermal electrons. The K(nu,Omega -> nu',Omega') kernel, in
particular, is applicable to the problem of induced Compton interaction of
anisotropic low-frequency radiation of high brightness temperature with free
electrons in the vicinity of powerful radiosources and masers.
Fokker-Planck-type expansion (up to fourth order) of the integral kinetic
equation with the P(nu -> nu') kernel derived here leads to a generalization of
the Kompaneets equation. We further present (1) a simpler kernel that is
necessary and sufficient to derive the Kompaneets equation and (2) an
expression for the angular function for Compton scattering in a hot plasma,
which includes temperature and photon energy corrections to the Rayleigh
angular function.Comment: 29 pages, 17 figures, accepted for publication in ApJ, uses
emulateapj.sty, corrects misprints in previous astro-ph versio
Heating of gas inside radio sources to mildly relativistic temperatures via induced Compton scattering
Measured values of the brightness temperature of low-frequency synchrotron
radiation emitted by powerful extragalactic sources reach 10^11--10^12 K. If
some amount of nonrelativistic ionized gas is present within such sources, it
should be heated as a result of induced Compton scattering of the radiation. If
this heating is counteracted by cooling due to inverse Compton scattering of
the same radio radiation, then the plasma can be heated up to mildly
relativistic temperatures kT~10--100 keV. The stationary electron velocity
distribution can be either relativistic Maxwellian or quasi-Maxwellian (with
the high-velocity tail suppressed), depending on the efficiency of Coulomb
collisions and other relaxation processes. We derive several easy-to-use
approximate expressions for the induced Compton heating rate of mildly
relativistic electrons in an isotropic radiation field, as well as for the
stationary distribution function and temperature of electrons. We also give
analytic expressions for the kernel of the integral kinetic equation (one as a
function of the scattering angle and another for the case of an isotropic
radiation field), which describes the redistribution of photons in frequency
caused by induced Compton scattering in thermal plasma. These expressions can
be used in the parameter range hnu<< kT<~ 0.1mc^2 (the formulae earlier
published in Sazonov, Sunyaev, 2000 are less accurate).Comment: 22 pages, 7 figures, submitted to Astronomy Letter
Nitrogen yield advantage from grass-legume mixtures is robust over a wide range of legume proportions and environmental conditions
Coordination of this project was supported by the EU Commission through COST Action 852 ‘Quality legume-based forage systems for contrasting environments‘. A636 contribution to the research leading to these results has been conducted as part of the Animal Change project which received funding from the European Union’s Seventh Framework Programme (FP7/2007-20 13) under the grant agreement no. 266018.peer-reviewedCurrent challenges to global food security require sustainable intensification of agriculture through initiatives that include more efficient use of nitrogen (N), increased protein self-sufficiency through home-grown crops, and reduced N losses to the environment. Such challenges were addressed in a continental-scale field experiment conducted over three years, in which the amount of total nitrogen yield (Ntot) and the gain of N yield in mixtures as compared to grass monocultures (Ngainmix) was quantified from four-species grass-legume stands with greatly varying legume proportions. Stands consisted of monocultures and mixtures of two N2 fixing legumes and two non-fixing grasses.The amount of Ntot of mixtures was significantly greater (P ≤ 0.05) than that of grass monocultures at the majority of evaluated sites in all three years. Ntot and thus Ngainmix increased with increasing legume proportion up to one third of legumes. With higher legume percentages, Ntot and Ngainmix did not continue to increase. Thus, across sites and years, mixtures with one third proportion of legumes attained ~95% of the maximum Ntot acquired by any stand and had 57% higher Ntot than grass monocultures.Realized legume proportion in stands and the relative N gain in mixture (Ngainmix/Ntot in mixture) were most severely impaired by minimum site temperature (R = 0.70, P = 0.003 for legume proportion; R = 0.64, P = 0.010 for Ngainmix/Ntot in mixture). Nevertheless, the relative N gain in mixture was not correlated to site productivity (P = 0.500), suggesting that, within climatic restrictions, balanced grass-legume mixtures can benefit from comparable relative gains in N yield across largely differing productivity levels.We conclude that the use of grass-legume mixtures can substantially contribute to resource-efficient agricultural grassland systems over a wide range of productivity levels, implying important savings in N fertilizers and thus greenhouse gas emissions and a considerable potential for climate change mitigation.European Unio
- …