PASTURE DEVELOPMENT IN THE BEEF CATTLE REGIONS OF ARGENTINA

An account is given of the climate, vegetation and native pastures of the beef-cattle regions of Argentina. Though some of these native pastures have a satisfactory carrying capacity, most of them are defective in quality or low in productivity; there is considerable scope for increasing production through the establishment of sown pastures. Trials have been made with a wide range of grasses and legumes, principally of African and European origin. Though the pattern of species to be used in these regions is imperfectly resolved, the authors present a map showing tentative boundaries for temperate, sub-tropical and tropical species. Work to date suggests that pasture development can probably proceed over great areas without the use of fertilizers, and this adds to the attractiveness of pasture programmes. A problem of no less importance than the technical aspects of pasture improvement is that of gaining a greater investment of capital into the development of cattle estancias.     

‘Defence lignin’ and hydroxycinnamyl alcohol dehydrogenase activities in wounded Eucalyptus gunnii

To learn more about lignin formation in response to wounding in trees, we adopted two complementary approaches: (1) microscopic and histochemical studies of the wound response in 3.5‐month‐old Eucalyptus gunnii plantlets and (2) biochemical investigations of hydroxycinnamyl alcohol dehydrogenase activities in wounded 6‐year‐old, field‐grown E. gunnii trees. The first approach revealed that a barrier zone was formed in response to wounding in both ground tissues (cortex barrier and pith reaction zone) and vascular tissues. The barrier zone was barely detectable after 24 h but well‐developed 7 days after wounding. Microscopic analyses indicated that the barrier zone was formed by the reinforcement of cell walls with ‘lignin‐like material’ in both ground tissues and vascular tissue, and that, in addition, the lumen of certain xylem cells (vessels and fibres) were blocked by the deposition of polymeric phenolic material. Histochemical characterization revealed that the lignin‐like material (‘defence lignin’) deposited in ground tissue cell walls and xylem cell blockages was poor in syringyl (S‐type) lignin units and therefore differed from the usual mixed guaiacyl–syringyl (G–S) lignin unit composition of E. gunnii developmental lignin. In contrast, S‐type lignin appeared to be deposited in the cell walls of immature developing secondary xylem cells at a stage when the cell walls of comparable cells from unwounded control stems contained lignin poor in syringyl units. The second approach indicated that two different types of cinnamyl alcohol dehydrogenase activity are induced, and apparently regulated differentially, in response to wounding in E. gunnii trees. Coniferyl alcohol dehydrogenase activity was induced immediately and continued to increase throughout the first 15 days of the 17‐day experimental period, while sinapyl alcohol dehydrogenase activity was first detected at 8 days after wounding and continued to increase throughout the experimental period. The biological roles of the two alcohol dehydrogenase activities are discussed in relation to the formation of defence lignin versus developmental lignin in trees.     

Postmortem diagnosis of preclinical and clinical scrapie in sheep by the detection of disease-associated PrP in their rectal mucosa

Samples of tissue from the central nervous system (cns), the lymphoreticular system (lrs) and the rectal mucosa of a large number of scrapie-exposed sheep, with and without signs of clinical disease, were examined immunohistochemically for evidence of disease-associated prion protein (PrP(d)). The rectal mucosa has received almost no attention so far in scrapie diagnosis, despite its abundant rectoanal mucosa-associated lymphoid tissue, and its accessibility. The scrapie-confirmed cases included 244 with clinical disease, of which 237 (97.1 per cent) were positive in the rectal mucosa, and 121 apparently healthy sheep, of which 104 (86 per cent) were positive in the rectal mucosa. PrP(d) was detected in 86.4 to 91.5 per cent of the other lrs tissues of the healthy sheep examined and in 77.7 per cent of their cns tissues. The stage of infection, therefore, affected the probability of a positive result in the rectal mucosa, whereas the breed, PrP genotype, age and sex had little or no independent effect. Accumulations of PrP(d) were observed in the rectal mucosa and other lrs tissues of vrq/arr sheep with preclinical and clinical scrapie, albeit with a lower frequency and magnitude than in sheep of other PrP genotypes. Western immunoblotting analyses of samples of rectal mucosa gave the characteristic PrP glycoprofile, with a sensitivity similar to that of immunohistochemistry.     

Interactions between metabolic status, pre-breeding protein supplementation, uterine pH, and embrionic mortality in ewes: Preliminary observations

The effect of prebreeding short-term protein supplementation level (PL) and body condition (BC) on fertility rate (FERT,%), uterine pH and embryonic mortality (EMORT,%) in sheep, was evaluated. Multiparous Rambouillet ewes at low BC (LC; n = 6, 62.7 ± 1.7 kg) or high BC (HC; n = 6, 71.9 ± 1.7 kg), received. within BC, one of two levels of ruminally undegradable protein: low (LP, 14 g/ewe per day) and high (HP, 30 g/ewe per day). Once the animals were euthanized, corpus luteum number (CLN), as an indicator of ovulation rate, was registered and uterine horns were irrigated to recover embryonic tissue plus associated membranes as well as to measure uterine pH (UpH). While EMORT-1 considered a nonadjusted relationship between the number of embryos and CLN, EMORT-2 considered an analysis of covariance using CLN as the covariate. The HP-supplemented ewes had the lowest FERT (p=0.06; 100% vs 50%) and the highest EMORT (EMORT-1, 16.6% vs 53.8%, p = 0.08; EMORT-2, 52.0% vs 14.5%, p = 0.07) when compared to the LP-supplemented ewes. Neither BC nor PL affected CLN, CL weight or P₄ release (p > 0.10). While the lowest UpH (p = 0.04) was observed in the HP-supplemented ewes, this group also showed the lowest fertility and the highest embryonic mortality.     

由麻疹思考小反刍兽疫的问题

小反刍兽疫(Peste des petits ruminants,PPR)是山羊、绵羊等小反刍兽类的急性接触传染性疾病,国际上将小反刍兽疫归为A类传染病.目前除非洲、中东和南亚次大陆传播外,在我国周边地区的许多国家和地区也频繁出现流行.因此,该病作为一种重大的跨国动物疫病,也在开始危害我国西藏和其他地区的动物生产和卫生安全[1-2].