The vaccination-challenge trial: the gold standard test to evaluate the protective efficacy of infectious coryza vaccines

Infectious coryza is an upper respiratory tract disease of chickens with the major impact occurring in multi-age flocks. We investigated the relationship between the level of antibodies, as detected by a haemagglutination-inhibition (HI) assay, in infectious coryza-vaccinated chickens and the protection against challenge in those chickens. In one experiment, chickens given a single dose of either of two infectious coryza vaccines lacked a detectable HI response to vaccination but showed significant levels of protection 11 weeks after vaccination. In contrast, in chickens given two doses of an infectious coryza vaccine and challenged 3 weeks after the second vaccine dose, there was a strong serological response with 36/40 birds having a HI titre of 1/20 or greater. In this trial there was an apparent relationship between titre and subsequent protection, with none of the 32 chickens with a titre of 1/40 or 1/80 showing any clinical signs and only one of the same group yielding the challenge organism on culture. In contrast, three of the four vaccinated chickens with a HI titre less than 1/5 developed the typical clinical signs of coryza and yielded the challenge organism on culture. Overall, our results suggest that HI titres cannot be regarded as a definitive predictor of vaccine efficacy. We suggest that the vaccination-challenge trial is the gold standard for the evaluation of the immune response to infectious coryza vaccines.

Standard yet unusual mechanisms of long-distance dispersal: Seed dispersal of Corymbia torelliana by bees

Mellitochory, seed dispersal by bees, has been implicated in long-distance dispersal of the tropical rain forest tree, Corymbia torelliana (Myrtaceae). We examined natural and introduced populations of C. torelliana for 4 years to determine the species of bees that disperse seeds, and the extent and distance of seed dispersal. The mechanism of seed dispersal by bees was also investigated, including fruit traits that promote dispersal, foraging behaviour of bees at fruits, and the fate of seeds. The fruit structure of C. torelliana, with seed presented in a resin reward, is a unique trait that promotes seed dispersal by bees and often results in long-distance dispersal. We discovered that a guild of four species of stingless bees, Trigona carbonaria, T. clypearis, T. sapiens, and T. hockingsi, dispersed seeds of C. torelliana in its natural range. More than half of the nests found within 250 m of fruiting trees had evidence of seed transport. Seeds were transported minimum distances of 20-220 m by bees. Approximately 88% of seeds were dispersed by gravity but almost all fruits retained one or two seeds embedded in resin for bee dispersal. Bee foraging for resin peaked immediately after fruit opening and corresponded to a peak of seed dispersal at the hive. There were strong correlations between numbers of seeds brought in and taken out of each hive by bees (r = 0.753-0.992, P < 0.05), and germination rates were 95 ± 5%. These results showed that bee-transported seeds were effectively dispersed outside of the hive soon after release from fruits. Seed dispersal by bees is a non-standard dispersal mechanism for C. torelliana, as most seeds are dispersed by gravity before bees can enter fruits. However, many C. torelliana seeds are dispersed by bees, since seeds are retained in almost all fruits, and all of these are dispersed by bees.

Using automated supplementation systems to meet growth targets for grazing sheep

Remote drafting technology now available for sheep allows targeted supplementation of individuals within a grazing flock. This paper reports results of three experiments. Experiment 1 examined the weight change of Merino wethers allowed access to either lupin grain or whole cottonseed 0, 1, 2 or 7 days/week for 6 weeks. Experiment 2 examined the weight change of Merino wethers allowed access to either lupins or a sorghum + cottonseed meal (CSM) supplement 0, 2, 4 or 7 days/week for 8 weeks. Experiment 3 investigated the relationship between five allocations of trough space at the supplement self-feeders (5–50 cm/sheep) and the weight change of Merino wethers allowed access to lupins 1 day/week for 8 weeks. In all experiments, the Merino wethers had free access as a single group to drinking water and low quality hay in a large group pen and were allowed access to supplement once per day on their scheduled days of access. No water was available in the areas containing supplement, but one-way flow gates allowed animals to return to the group pen in their own time. There was a linear response in growth rate to increased frequency of access to lupins in Experiments 1 and 2, with each additional day of access increasing liveweight gain by 26 and 21 g/day, respectively. Similarly, the response to the sorghum + CSM supplement was linear, although significantly lower (P < 0.05), at 12 g/day. Providing access to whole cottonseed resulted in no significant change in growth rate compared with the control animals. In Experiment 3, decreasing trough space from 50 to 5 cm/sheep had no effect on sheep liveweight change. It was concluded that the relationships developed here, for growth response to increased frequency of access to lupins or a sorghum + CSM supplement, could be used to indicate the most appropriate frequency of access to supplement, through a remote drafting unit, to achieve sheep weight change targets. Also, that a trough space of 5 cm/sheep appears adequate in this supplementation system.

Circulating concentrations of leptin, ovarian follicle number, and oocyte lipid content and active mitochondria, in Zebu crossbred cows maintained on standard or improved nutrition

Zebu (Bos indicus) crossbred beef cows (Droughtmaster) were maintained long-term (16 months) on standard nutrition (SN) or improved nutrition (IN). Cows on IN had better body condition and greater (P<0.05) circulating concentrations of leptin than cows on SN (0.7±0.1n/ml and 1.7±0.1n/ml, respectively). There were no outstanding differences between SN and IN cows in basal number of ovarian follicles (≤4mm, 5-8mm, and≥9mm) and there were also no differences in number of oocytes recovered by oocyte pick-up. Cows on IN had a greater (P<0.05) number of total follicles after stimulation with FSH than cows on SN. Oocytes from cows on IN had greater (P<0.05) lipid content than cows on SN (-0.23±0.16 and 0.20±0.18 arbitrary units, respectively) and oocytes of the former cows also tended to have more active mitochondria, although this was not significant. Cows on IN showed a positive relationship (R2=0.31, P<0.05) between plasma leptin and oocyte lipid content. Lipids are utilized by oocytes during high energy consumptive processes including fertilization and early cleavage. The greater lipid content of oocytes from IN cows could therefore confer a reproductive advantage. The present study has shown relationships between nutrition, body condition, circulating leptin, and oocyte lipid content, but a clear cause-and-effect requires further investigation in the cow. © 2013 Elsevier B.V.

Impact of nitrification inhibitor (DMPP) on soil nitrous oxide emissions from an intensive broccoli production system in sub-tropical Australia

Vegetable cropping systems are often characterised by high inputs of nitrogen fertiliser. Elevated emissions of nitrous oxide (N2O) can be expected as a consequence. In order to mitigate N2O emissions from fertilised agricultural fields, the use of nitrification inhibitors, in combination with ammonium based fertilisers, has been promoted. However, no data is currently available on the use of nitrification inhibitors in sub-tropical vegetable systems. A field experiment was conducted to investigate the effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N2O emissions and yield from broccoli production in sub-tropical Australia. Soil N2O fluxes were monitored continuously (3 h sampling frequency) with fully automated, pneumatically operated measuring chambers linked to a sampling control system and a gas chromatograph. Cumulative N2O emissions over the 5 month observation period amounted to 298 g-N/ha, 324 g-N/ha, 411 g-N/ha and 463 g-N/ha in the conventional fertiliser (CONV), the DMPP treatment (DMPP), the DMMP treatment with a 10% reduced fertiliser rate (DMPP-red) and the zero fertiliser (0N), respectively. The temporal variation of N2O fluxes showed only low emissions over the broccoli cropping phase, but significantly elevated emissions were observed in all treatments following broccoli residues being incorporated into the soil. Overall 70–90% of the total emissions occurred in this 5 weeks fallow phase. There was a significant inhibition effect of DMPP on N2O emissions and soil mineral N content over the broccoli cropping phase where the application of DMPP reduced N2O emissions by 75% compared to the standard practice. However, there was no statistical difference between the treatments during the fallow phase or when the whole season was considered. This study shows that DMPP has the potential to reduce N2O emissions from intensive vegetable systems, but also highlights the importance of post-harvest emissions from incorporated vegetable residues. N2O mitigation strategies in vegetable systems need to target these post-harvest emissions and a better evaluation of the effect of nitrification inhibitors over the fallow phase is needed.