1. The responses of units in the ventral cochlear nucleus in anesthetized guinea pigs have been measured to best-frequency tones, noise bands geometrically centered around the unit best frequency, and noise bands asymmetrically positioned around the best frequency. 2. Each unit isolated was characterized using peristimulus time histograms (PSTHs) to best-frequency tones at 20 and 50 dB suprathreshold, frequency-intensity response areas and rate-versus-level functions in response to best-frequency tones and wideband noise. The data reported here are derived from full analyses of 5 chopper units and 17 onset units. The onsets were divided into onset-I (OnI), onset-L (OnL), and onset-C (OnC) by the criteria described by Winter and Palmer: the PSTHs of OnI units show only an onset response, OnL units respond with a single spike at onset followed by a low level of sustained activity, and OnC units have PSTHs with one to four onset peaks and low levels of sustained discharge. 3. In response to geometrically centered noise bands of constant spectral density, the discharge of chopper units and one OnI unit increased over a relatively narrow range of bandwidths, corresponding to the equivalent rectangular bandwidth calculated from their response area, and then became constant. In contrast, OnL and OnC units showed increases in discharge rate with noise bandwidth over very wide ranges of bandwidth. The growth of the discharge rate with noise bandwidth was approximately linear on double logarithmic axes and therefore could be described by a power function with an exponent of 0.37. This relation held even for noise levels near threshold. 4. When noise bands with constant spectral density (at the input to the earphone) were presented with one edge fixed at the unit's best frequency, the discharge rate of most chopper units and the one OnI unit increased over a narrow range of bandwidths and then became constant. This pattern was observed irrespective of whether the second edge of the noise was progressively increased above, or decreased below, the best frequency. For two of the chopper units, in which lateral inhibitory sidebands could be demonstrated, increasing the noise bandwidth led first to increases and then to decreases in the discharge rate as the noise energy impinged upon the sideband. The chopper units act like energy detectors with a filter corresponding to their single tone response area, but, for some units, with the addition of inhibitory sidebands. 5. For the OnL and OnC units, increasing the noise bandwidth above or below best frequency caused progressive increases in the discharge rate over wide ranges of bandwidth. These increases occurred even for low noise spectral densities. The growth in discharge rate for these onset units was well fitted at all spectral density levels by power functions: one above best frequency and one below. At levels of the noise 40 dB above the unit threshold, the point at which the discharge rate reached 90% of its maximum was, on average, about 2 octaves below best frequency and...

Livestock production in South Africa contributes substantially to food security. It is also a topic of public debate because of lack of knowledge and wrong information. This article aims to provide information on the worth and impact of the livestock sector; information and statistics providing a baseline to guiding sustainability towards 2050. Seventy percent of agricultural land in South Africa can be utilized only by livestock and game and species are found in all provinces with high concentrations in the eastern higher rainfall regions. Statistics in 2010 indicate 13.6 million beef cattle, 1.4 million dairy cattle, 24.6 million sheep, 7.0 million goats, 3 million game species (farmed), 1.1 million pigs, 113 million broilers, 31.8 million layers and 1.6 million ostriches. The gross value of livestock products increased by 185% from 1995/2000 to 2006/2010. In relation to field crops and horticulture, livestock products increased their position from 42% to 47% of gross agricultural value. The main reason was a rise in the value and demand for livestock foods, particularly meat. Livestock foods contribute 27% of the consumer food basket on a weight basis. Consumption of livestock foods resembles that of developing countries with meat consumption being 50 -90 g/capita/day, milk and dairy products 120 -130 g /capita/day and eggs 15 -20 g/capita/day. Since this is the average for the country with consumption by the rich and poor often differing tenfold, consumption of livestock foods by the poor is of concern, given the many health attributes of livestock foods. The livestock sector in South Africa is a major role player in the conservation of biodiversity through a variety of welladapted indigenous and non-indigenous breeds and rare game species. It has also shown commitment to rangeland/ecosystem conservation through conservative stocking rates, with several studies and observations reporting improvement in the condition of the natural resource. The sector has always been a major employer, but employment rate has declined steadily since 2000 because of increased minimum wages, fewer commercial farmers and increased property size. Some 245 000 employees with 1.45 million dependants, in addition to dependants on communal land and emerging farms, are employed on 38 500 commercial farms and intensive units with wages amounting to R 6 100 million (South African rand). Livestock farming is the backbone of the socio-economy and provides the sustenance of most nonmetropolitan towns and rural communities. ________________________________________________________________________________

1. The frequency threshold curves (FTCs) of 91 single units in the cochlear nucleus of the anesthetized guinea pig were measured using a conventional single-tone paradigm and a two-tone paradigm designed to elucidate the frequency extent of two-tone facilitation in onset units (On). Units were classified according to existing classification schemes into primary-like (n = 3), chopper (n = 23), and three onset groups: OnI (n = 12), OnC (n = 29), and OnL (n = 24). Histological reconstructions show onset units to be widely distributed within the ventral cochlear nucleus in a manner generally consistent with its tonotopic organization. 2. The FTCs of onset units differed in their minimum thresholds, the steepness of their high- and low-frequency cutoffs, and their sharpness of tuning as quantified by the quality factor at 10 dB (Q10dB) above best frequency (BF) threshold values. There was considerable overlap in the sharpness of tuning between onset units and auditory nerve fibers, as indicated by the distribution of Q10dB values in the octave around 10 kHz: onset units had Q10dB values of 3.56 +/- 1.38 (SD), compared with 6.3 +/- 2.48 for auditory nerve fibers. The tuning of chopper units was similar to that of auditory nerve fibers (5.52 +/- 1.46). 3. Seventy-five percent of onset units showed some degree of facilitation (a threshold reduction) when their FTCs were measured in the presence of BF tones 4 dB below BF threshold. The frequency extent of such facilitation was variable, with a maximum of 6 octaves around the BF. In extreme cases facilitation could be measured when the BF tone was as low as 30 dB below BF threshold. 4. In 17% of onset units, suppressive effects were evident, as shown by noncontiguous frequency regions of facilitation. These suppressive effects might be a reflection either of suppression in the auditory nerve input or of a direct inhibitory input to the onset units. The strength of this effect suggests that inhibition is a likely explanation, consistent with the finding in previous morphological studies of profuse synapses with pleomorphic vesicles on multipolar cells. 5. FTCs of chopper and primary-like units measured in the presence of BF tones showed little facilitation. The facilitation that was observed in chopper units was confined to a narrow region around BF and disappeared when the facilitatory tone was lowered to 4 dB below BF threshold. 6. These data support the hypothesis that onset units, but not chopper or primary-like units, receive excitatory inputs from auditory nerve fibers with a wide range of BFs. However, the frequency range of facilitation and the magnitude of the threshold facilitation varied from unit to unit, suggesting that the off-BF inputs from auditory nerve fibers are not evenly distributed or equally effective in all units.

1. We examined the temporal and mean rate discharge characteristics of 514 single units recorded extracellularly from the dorsal cochlear nucleus (DCN) of anesthetized guinea pigs. A mean rate response area (receptive field) was measured for the majority of units in this study. Each response area was placed in one of seven categories (type I to type V and the intermediate types I/III and IV-T) as defined by previous workers. The shape of the best frequency (BF) rate-level function has been used to aid in the distinction between type IV and type IV-T units, and the classification of type II units is based on their relative response to noise and tone bursts. 2. The threshold of single units was normalized to the cochlear action potential (CAP) threshold (a negative relative threshold indicates that the unit's threshold was more sensitive than the corresponding CAP threshold). There were significant differences (P < 0.05; 1-way analysis of variance--Duncan test) between the mean relative thresholds of type IV units (-12 dB) and those of type I (-6.52 dB), type II (-3 dB), and type I/III units (-4.25 dB). There were also significant differences between the relative thresholds of types III and IV-T and those of types I/III and II. 3. Rate-level functions at a unit's BF were divided into groups according to shape and degree of nonmonotonicity. Six units responded with a decrease in firing rate at all suprathreshold sound levels. However, most units increased their discharge rate over approximately the first 20 dB above BF threshold. Units were further subdivided by the change in slope 20 dB above BF threshold. The majority of units (60%) showed monotonic increases in discharge rate with sound level: some rate-level functions clearly resembled the sloping saturation rate-level functions observed in intermediate-threshold auditory nerve fibers. An unexpected finding was the relatively large number of nonmonotonic rate-level functions (40%). Among a relatively homogenous group of projection neurons (predominantly type IV and pause/build units) with nonmonotonic rate-level functions, the range of "best intensities" (the sound level evoking the highest discharge rate) was < 50 dB. This range of best intensities is narrower than found in higher auditory nuclei. 4. Units were also classified by their temporal activity pattern in response to suprathreshold BF tones. The most common pattern identified is the pause/build pattern (n = 294). This temporal activity pattern has been associated with the principal output neuron of the DCN, the fusiform cell. Our definition of pause/build units includes units with an almost constant steady-state discharge rate. Nonmonotonic rate-level functions were observed in 42% (99 of 233) of pause/build units. A measure of discharge regularity (the SD of the interspike interval/mean interspike interval: coefficient of variation, CV) revealed that the majority (82%) of units classified as pause/build and with steady-state discharge rates > 75 spikes/s (n = 142) were characterized by regular dischar...