Letters

Editor's note: The AVJ welcomes letters from members in all areas of the profession on matters of importance to you. Please keep them brief ‐ to meet our space constraints. Letters will be subject to minimal editing procedures. Subject to letters complying with the AVJ's legal responsibilities, they will not be censored. Nor will individuals or groups waging'‘campaigns’ be permitted to abuse these pages. If submitting a letter intended for publication, kindly identify it as such. Letters to the Editor can be sent by mail, fax or e‐mail at the contact points listed at the start of the News Section. Writers may use a pseudonym to protect their identities ‐ but must supply the Editor with verifiable names and points of contact.     

Concentration of plasma testosterone in adult roosters of a low-weight strain

The levels of blood-plasma testosterone were studied in the adult light bodied strain cocks. Blood was sampled (1 ml) from the wing vein by means of a heparinized syringe six times within a 24-hour interval. The plasma obtained by centrifugation was kept in a refrigerator at a temperature of --18 degrees C. Testosterone was determined by the radioimmunological method. The testosterone levels were significantly higher (P less than 0.001), 18.8 nmol/l on the average, in the blood samples taken during the dark period of the day (10 o'clock p.m., 2 and 6 o'clock a.m.) than in the samples taken in the light part of the day (8 and 10 o'clock a.m., 2 o'clock p.m.) when the average concentration of the studied hormone was 10.7 nmol/l of plasma. the lowest levels of testosterone were recorded in the morning and the highest values were recorded late in the evening (10 o'clock p.m.). The differences in the levels of the hormone between sampling terms indicate that the testosterone level in adult animals shows diurnal variances. It was found by the study of the concentration of testosterone in the blood plasma of the same individuals within short intervals of time (30-60 min) that testosterone secretion in adult cocks had a pulsatory manner. The evaluation of hormone levels should include not only the diurnal variances but also the pulsatory manner of testosterone secretion.     

美国目前和未来的保育猪饲养方案

在过去的20年内美国的猪产业发生了翻天覆地的变化。多址生产系统对畜群的健康和控制断奶仔猪链产生了极大的作用。然而一个成功的断奶仔猪营养方案其基本原则对于任何日龄断奶的仔猪来讲都是相似的。可以归纳成三点：①在断奶时,仔猪尽可能的体重大;②尽可能快的将日粮从复合日粮转化为简单日粮;③重点关注保育仔猪管理。此外,在美国过去的10年通过遗传选育的手段,使窝产仔数大约增加了1.5头,仔猪断奶的日龄也相应地增加到平均为19~23 d。当每头母猪产仔数增加以后,由于初生活仔数的增加,有更多体重轻的仔猪出生,这将是生产者所面临的挑战。因此,对生产者来说,了解影响初生体重轻的仔猪一生的生产性能以及收益的因素是非常必要的。     

Sampling strategies and screening of chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.) germplasm for salt tolerance

Six hundred accessions of chickpea (Cicer arietinum L.) landraces and its wild relatives from 28 different countries, available at Australian Temperate and Field Crops Collection (ATFCC) were screened for tolerance to salt under greenhouse conditions using three sampling strategies; (1) random sampling of 200 accessions from different countries, (2) restricted random sampling of 200 accessions from geographical regions with salinity problems and high diversity (Middle East and West & South Asia) and (3) as for strategy 1 but with a reduced representation of accessions from the geographical regions used in strategy 2. Degree of salt tolerance was based on necrosis scores and shoot biomass reduction relative to unstressed controls at harvest after subjecting stressed plants to salt treatment from 21 to 42 days after sowing. There was a wide variation in salinity tolerance determined by both measures. For sampling strategies 1, 2 and 3 respectively; 24, 28 and 14% of accessions were salt tolerant. Accessions from the middle east and south Asian (regions with salinity problem, a long history of chickpea cultivation and high diversity) gave a higher probability (P < 0.01) of getting salt tolerant accessions.     

Long term fertilization effects on ‘Rio Red’ grapefruit yield and shape on a heavy textured calcareous soil

Fertilizer recommendations for citrus production on heavier textured, calcareous soils increase with the age of the tree up to 168 kg N ha⁻¹ year⁻¹ from a soluble source in one or two applications. Such practices may be inefficient and could cause detrimental effects on fruit quality. A variety of fertilization practices are used in South Texas, and additional evaluation is needed. Rates and sources of nitrogen (N), phosphorus (P), and a commercial program consisting of both a soil component containing organic acids and a foliar component were evaluated on grapefruit production for 6 years. Increasing rate of N application increased leaf nutrient concentration, grapefruit yield, and affected fruit shape as indicated by a decrease in the equatorial:polar diameter (E:P) ratio. Since the response to increasing N application by the E:P ratio was linear while grapefruit yield was quadratic, high N application has a negative effect on fruit shape beyond the level of increasing total yield. Phosphorus application had no effect on any parameter measured, even though soil testing indicated soil P levels were below those at which a P response would be expected. Comparisons between granular 21-0-0 applied broadcast and liquid N-32 injected in a band in the soil at the drip line showed an increase in the number of fruit per tree, but no differences in yield. The ‘Actagro’ program greatly improved available soil P levels and increased the juice brix:acidity ratio, but did not affect grapefruit yield. Phosphorus availability may therefore be a factor in improving grapefruit juice quality. The soil profile within the citrus root zone was found to contain large amounts of inorganic N, but availability of this residual N was limited since yield responses occurred at the N application rates applied in this study. The amount of N contained in the fruit harvested was a small fraction, roughly 5–10%, of the residual amount in the soil. While N uptake in the fruit increased with N fertilizer application, the increase in N taken up relative to the amount applied averaged 42%.