Screening two biodegradable polymers in enhanced efficiency fertiliser formulations reveals the need to prioritise performance goals

Enhanced efficiency fertilisers (EEF) may reduce nitrogen (N) losses and improve uptake efficiency through synchronising N release with in-season plant requirements. We hypothesised that EEF formed via matrix encapsulation in biodegradable polymers will improve N use efficiency when compared to conventional urea fertiliser. This hypothesis was investigated for two biodegradable polymer matrices: polyhydroxyalkanoate (PHA), containing 11.6% urea (by mass), and polybutylene-adipate-co-terephthalate (PBAT), containing either 19.4 or 32.7% urea; and two contrasting soil types: sand and clay. Nitrogen availability and form was investigated under leaching conditions (water) with a growth accelerator pot experiment involving a horticultural crop and novel non-destructive three-dimensional scanning to measure in-season biomass development. The PBAT 32.7% formulation enabled greater above ground biomass production at both 50 and 100 kg N ha^-1 equivalent application rates compared to conventional urea. For the sandy soil, plant scanning indicated that improved uptake performance with PBAT 32.7% was probably the result of greater N availability after 25 days than for conventional urea. Two of the encapsulated formulations (PHA and PBAT 19.4%) tended to decrease nitrogen leaching losses relative to urea (P < 0.05 for the red clay soil). However, decreased N leaching loss was accompanied by poorer N uptake performance, indicative of N being less available in these biopolymer formulations. A snapshot of nitrous oxide emissions collected during peak nitrate concentration (prior to planting and leaching) suggested that the biopolymers promoted N loss via gaseous emission relative to urea in the sandy soil (P < 0.05), and carbon dioxide emissions data suggested that biopolymer-carbon increased microbial activity (P < 0.1). Controlled testing of N release in water was a poor predictor of biomass production and leaching losses. The diverse behaviours of the tested formulations present the potential to optimise biopolymers and their N loadings by taking into account soil and environmental factors that influence the efficient delivery of N to target crops. The greater N uptake efficiency demonstrated for the PBAT 32.7% formulation confirms our hypothesis that matrix encapsulation can enable better synchronisation of N release with crop requirements and decrease leaching losses.

Local immune response to larvae of Rhipicephalus microplus in Santa Gertrudis cattle

This study investigated the local immune response at larval attachment sites in Santa Gertrudis cattle with low and high levels of tick resistance. Skin samples with tick larvae attached were collected from Santa Gertrudis cattle at the end of a period of 25 weekly infestations, when the animals manifested highly divergent tick-resistant phenotypes. There was a tendency for more CD3⁺ , CD4⁺ , CD8⁺ , CD25⁺ , γδ T cells and neutrophils to concentrate at larval tick attachment site in susceptible cattle than in resistant cattle but the differences were significant only for γδ T cells and CD4⁺ cells. Most of the cattle developed intra-epidermal vesicles at the larval attachment site but the predominant cell within or around the vesicles was the neutrophil in susceptible animals and eosinophil in the resistant animals. The monoclonal antibodies (mAbs) specific for CD45 and CD45 RO antigens reacted with skin leucocytes from a higher number of susceptible cattle than resistant cattle. Our data suggest that some of the cellular responses mounted at larval attachment site are not involved in tick protection. The mAbs specific for CD45 and CD45 RO directly, or a test for CD45 genotype might be developed as markers of tick susceptibility or resistance.

Predicting nuisance fly outbreaks on cattle feedlots in subtropical Australia

Flies are important arthropod pests in intensive animal facilities such as cattle feedlots, with the potential to cause production loss, transmit disease and cause nuisance to surrounding communities. In the present study, seasonal population dynamics of three important nuisance flies, namely house flies (Musca domestica L.), bush flies (M. vetustissima Walker) and stable flies (Stomoxys calcitrans L.) (Diptera: Muscidae), were monitored on cattle feedlots in south-eastern Queensland, Australia, over 7 years. Musca domestica was by far the dominant species, comprising 67% of the total flies trapped. Models were developed to assess the relationship between weather parameters and fly abundance and to determine whether population trends could be predicted to improve the timing of control measures. For all three species, there were two main effects, namely time-of-year (mainly reflected by minimum temperatures and solar radiation) and rainfall. The abundance of all three species increased with increasing temperature and rainfall, reaching a peak in summer, before decreasing again. Rainfall events resulted in significantly elevated numbers of M. domestica for up to 5 weeks, and for 1 week for M. vetustissima. Peak fly numbers were predicted by the model to occur in spring and summer, following 85–90-mm weekly rainfall. The population dynamics of S. calcitrans were least influenced by rainfall and it was concluded that weather variables were of limited use for forecasting stable fly numbers in this environment and production system. The models provide a useful tool for optimising the timing of fly-control measures, such as insecticide or biopesticide applications, adding to the efficiency of integrated control programs.

Prophylactic and therapeutic efficacy of Australian-registered insecticide formulations against Old World screwworm (Chrysomya bezziana) infestation

OBJECTIVE

To determine the prophylactic and therapeutic efficacy of Australian-registered insecticide formulations against Old World screwworm (OWS) myiases for potential use in screwworm containment and eradication programs.

METHODS

The longevity of protection provided by six insecticidal formulations (subcutaneous ivermectin, doramectin and abamectin, a topically applied aqueous formulation of spinosad, ivermectin controlled-release capsule and a dicyclanil spray-on formulation) was tested using implants of 1st-instar OWS larvae on Javanese thin-tail sheep. Therapeutic efficacy of four formulations (topical ivermectin, chlorfenvinphos/cypermethrin mixture, aerosol spinosad formulation and a formulation containing propetamphos and eucalyptus oil) was tested against 2- and 4-day-old OWS strikes.

RESULTS

Both the ivermectin capsule and dicyclanil spray-on formulation gave 100% protection against screwworm implants for the full 12 weeks of the study. Ivermectin, doramectin and abamectin administered SC all gave 100% protection at 3 days post-treatment, but at 2 weeks the protection had become incomplete. Spinosad dipping did not give complete protection at any time. All four therapeutic treatments gave complete resolution of 2-day-old strikes and topical ivermectin, spinosad and chlorfenvinphos/cypermethrin, but not the propetamphos/eucalyptus oil formulation, gave complete resolution of all 4-day-old strikes.

CONCLUSION

Dicyclanil spray-on and ivermectin capsule formulations, both registered for use in sheep, but not for cattle or other livestock species, gave much longer protection against screwworm implants than the currently recommended SC ivermectin. Pre-emptive action to facilitate rapid deployment of these formulations in the event of a screwworm incursion is urgently needed.

Comparison of the impact of six heat-load management strategies on thermal responses and milk production of feed-pad and pasture fed dairy cows in a subtropical environment

Exposure to hot environments affects milk yield (MY) and milk composition of pasture and feed-pad fed dairy cows in subtropical regions. This study was undertaken during summer to compare MY and physiology of cows exposed to six heat-load management treatments. Seventy-eight Holstein-Friesian cows were blocked by season of calving, parity, milk yield, BW, and milk protein (%) and milk fat (%) measured in 2 weeks prior to the start of the study. Within blocks, cows were randomly allocated to one of the following treatments: open-sided iron roofed day pen adjacent to dairy (CID) + sprinklers (SP); CID only; non-shaded pen adjacent to dairy + SP (NSD + SP); open-sided shade cloth roofed day pen adjacent to dairy (SCD); NSD + sprinkler (sprinkler on for 45 min at 1100 h if mean respiration rate >80 breaths per minute (NSD + WSP)); open-sided shade cloth roofed structure over feed bunk in paddock + 1 km walk to and from the dairy (SCP + WLK). Sprinklers for CID + SP and NSD + SP cycled 2 min on, 12 min off when ambient temperature >26°C. The highest milk yields were in the CID + SP and CID treatments (23.9 L cow^-1 day^-1), intermediate for NSD + SP, SCD and SCP + WLK (22.4 L cow^-1 day^-1), and lowest for NSD + WSP (21.3 L cow^-1 day^-1) (P < 0.05). The highest (P < 0.05) feed intakes occurred in the CID + SP and CID treatments while intake was lowest (P < 0.05) for NSD + WSP and SCP + WLK. Weather data were collected on site at 10-min intervals, and from these, THI was calculated. Nonlinear regression modelling of MY × THI and heat-load management treatment demonstrated that cows in CID + SP showed no decline in MY out to a THI break point value of 83.2, whereas the pooled MY of the other treatments declined when THI >80.7. A combination of iron roof shade plus water sprinkling throughout the day provided the most effective control of heat load.

On-farm Campylobacter and Escherichia coli in commercial broiler chickens: Re-used bedding does not influence Campylobacter emergence and levels across sequential farming cycles

Limitations in quality bedding material have resulted in the growing need to re-use litter during broiler farming in some countries, which can be of concern from a food-safety perspective. The aim of this study was to compare the Campylobacter levels in ceca and litter across three litter treatments under commercial farming conditions. The litter treatments were (a) the use of new litter after each farming cycle; (b) an Australian partial litter re-use practice; and (c) a full litter re-use practice. The study was carried out on two farms over two years (Farm 1, from 2009–2010 and Farm 2, from 2010–2011), across three sheds (35,000 to 40,000 chickens/shed) on each farm, adopting three different litter treatments across six commercial cycles. A random sampling design was adopted to test litter and ceca for Campylobacter and Escherichia coli, prior to commercial first thin-out and final pick-up. Campylobacter levels varied little across litter practices and farming cycles on each farm and were in the range of log 8.0–9.0 CFU/g in ceca and log 4.0–6.0 MPN/g for litter. Similarly the E. coli in ceca were ∼log 7.0 CFU/g. At first thin-out and final pick-up, the statistical analysis for both litter and ceca showed that the three-way interaction (treatments by farms by times) was highly significant (P < 0.01), indicating that the patterns of Campylobacter emergence/presence across time vary between the farms, cycles and pickups. The emergence and levels of both organisms were not influenced by litter treatments across the six farming cycles on both farms. Either C. jejuni or C. coli could be the dominant species across litter and ceca, and this phenomenon could not be attributed to specific litter treatments. Irrespective of the litter treatments in place, cycle 2 on Farm 2 remained Campylobacter-free. These outcomes suggest that litter treatments did not directly influence the time of emergence and levels of Campylobacter and E. coli during commercial farming.

Cattle herd inspections and fly trapping for the detection of the Old World screw-worm fly (Chrysomya bezziana)

OBJECTIVES

To compare the sensitivity of inspections of cattle herds and adult fly trapping for detection of the Old World screw-worm fly (OWS).

PROCEDURES

The incidence of myiases on animals and the number of OWS trapped with LuciTrap®/Bezzilure were measured concurrently on cattle farms on Sumba Island (Indonesia) and in peninsular Malaysia (two separate periods for the latter). The numbers of animal inspections and traps required to achieve OWS detection at the prevalent fly densities were calculated.

RESULTS

On Sumba Island, with low-density OWS populations, the sensitivity of herd inspections and of trapping for OWS detection was 0.30 and 0.85, respectively. For 95% confidence of detecting OWS, either 45 inspections of 74 animals or trapping with 5 sets of 4 LuciTraps for 14 days are required. In Malaysia, at higher OWS density, herd inspections of 600 animals (twice weekly, period 1) or 1600 animals (weekly, period 2) always detected myiases (sensitivity = 1), while trapping had sensitivities of 0.89 and 0.64 during periods 1 and 2, respectively. For OWS detection with 95% confidence, fewer than 600 and 1600 animals or 2 and 6 LuciTraps are required in periods 1 and 2, respectively.

CONCLUSIONS

Inspections of cattle herds and trapping with LuciTrap and Bezzilure can detect OWS populations. As a preliminary guide for OWS detection in Australia, the numbers of animals and traps derived from the Sumba Island trial should be used because the prevailing conditions better match those of northern Australia.

BeefSpecs fat calculator to assist decision making to increase compliance rates with beef carcass specifications: evaluation of inputs and outputs

This study evaluated the BeefSpecs fat calculator, a decision-support system developed to assist the beef industry to increase compliance rates with carcass specifications (weight and fat specifications). A challenge to the BeefSpecs calculator and a sensitivity analysis were used to evaluate the inputs and outputs of BeefSpecs. Five industry datasets (n = 80, 97, 68, 25, and 13 for Datasets 1–5, respectively) of Bos taurus, Bos indicus, and Bos taurus × Bos indicus breeds for steers and heifers were collated to challenge BeefSpecs, and a nine-way factorial matrix (n = 57 600) of input variables was created for the sensitivity analysis. There were no significant (P > 0.05) differences in the mean bias between observed and predicted values in any of the datasets but there were significant (P < 0.01) differences in the unity of slope for Datasets 2, 3, and 5. The root-mean-square error was 1.72, 2.61, 2.87, 2.68, and 2.00 mm for Datasets 1–5. The decomposition of the mean-square error of prediction indicated that most of the error contained in the predictions of all models was of a random nature (94%, 85%, 85%, 95% for Datasets 1–4), except in Dataset 5, which had a 47% proportion of error in the slope component. All datasets indicated little bias (0.13%, 12.19%, 12.69%, 0.60%, and 0.12% for Datasets 1–5) in the model predictions. An analysis of variance with the nine-way factorial matrix on the predicted output of final P8 fat was conducted for the sensitivity analysis. A significant (P < 0.01) four-way interaction of days on feed × frame score × initial liveweight × sex was detected. Final P8 fat was sensitive to measurement error in the inputs of frame score when animals had longer feeding periods (e.g. 180 days) and to initial P8 fat when animals had lower initial liveweights (e.g. 200 kg) and higher frame scores (e.g. 7). For each unit of error in estimating frame score, BeefSpecs predicts final P8 with an error of up to 2.3 mm in heifers and up to 1.7 mm in steers. Error in the estimation of initial P8 fat of 2 mm will result in an error of up to 3 mm in the prediction of final P8 fat. The sensitivity analysis of BeefSpecs input variables (frame score and initial P8 fat) on the prediction of final P8 fat indicates that increasing the accuracy of estimating frame score and P8 fat is an issue that needs addressing.

Evaluation of the impacts of spaying by either the dropped ovary technique or ovariectomy via flank laparotomy on the welfare of Bos indicus beef heifers and cows

The welfare outcomes for Bos indicus cattle (100 heifers and 50 cows) spayed by either the dropped ovary technique (DOT) or ovariectomy via flank laparotomy (FL) were compared with cattle subjected to physical restraint (PR), restraint by electroimmobilization in conjunction with PR (EIM), and PR and mock AI (MAI). Welfare assessment used measures of morbidity, mortality, BW change, and behavior and physiology indicative of pain and stress. One FL heifer died at d 5 from peritonitis. In the 8-h period postprocedures, plasma bound cortisol concentrations of FL, DOT, and EIM cows were not different and were greater (P<0.05) than PR and MAI. Similarly, FL and DOT heifers had greater (P<0.05) concentrations than PR and MAI, with EIM intermediate. Creatine kinase and aspartate aminotransferase concentrations were greater (P<0.05) in FL and EIM heifers compared with the other treatments, with a similar pattern seen in the cows. Haptoglobin concentrations were significantly (P<0.05) increased in the FL heifers compared with other treatments in the 8- to 24-h and 24- to 96-h periods postprocedures, and in cows were significantly (P<0.05) increased in the FL and DOT compared with PR in the 24- to 96-h period. Behavioral responses complemented the physiological responses; standing head down was shown by more (P<0.05) FL cows and heifers to 3 d postprocedures compared with other treatments, although there was no difference between FL and DOT heifers at the end of the day of procedures. At this same time, fewer (P<0.05) FL and DOT heifers and cows were observed feeding compared with other treatments, although in cows there was no difference between FL, DOT, and EIM. There were no significant differences (P>0.05) between treatments in BW changes. For both heifers and cows, FL and DOT spaying caused similar levels of acute pain, but FL had longer-lasting adverse impacts on welfare. Electroimmobilization during FL contributed to the pain and stress of the procedure. We conclude that: i) FL and DOT spaying should not be conducted without measures to manage the associated pain and stress; ii) DOT spaying is preferable to FL spaying; iii) spaying heifers is preferable to spaying cows; and iv) electroimmobilization causes pain and stress and should not be routinely used as a method of restraint.

Prediction of mortality and conception rates of beef breeding cattle in northern Australia

In current simulation packages for the management of extensive beef-cattle enterprises, the relationships for the key biological rates (namely conception and mortality) are quite rudimentary. To better estimate these relationships, cohort-level data covering 17 100 cow-years from six sites across northern Australia were collated and analysed. Further validation data, from 7200 cow-years, were then used to test these relationships. Analytical problems included incomplete and non-standardised data, considerable levels of correlation among the ‘independent’ variables, and the close similarity of alternate possible models. In addition to formal statistical analyses of these data, the theoretical equations for predicting mortality and conception rates in the current simulation models were reviewed, and then reparameterised and recalibrated where appropriate. The final models explained up to 80% of the variation in the data. These are now proposed as more accurate and useful models to be used in the prediction of biological rates in simulation studies for northern Australia.

Preliminary investigation of some physiological responses of Bos indicus heifers to surgical spaying

OBJECTIVE

To determine the value of peripheral blood concentrations of cortisol, creatine phosphokinase (CPK), aspartate aminotransferase (AST), non-esterified fatty acids (NEFAs) and haptoglobin as indicators of welfare in Brahman heifers spayed by either the Willis dropped ovary technique (WDOT) or the flank laparotomy method.

DESIGN

A total of 24, 2-year-old Brahman heifers were allocated to: crush (head-bail) restraint alone (Control, n = 5); crush restraint and ear-punch (Ear-punch, n = 5); crush restraint, WDOT spay and ear-punch (WDOT, n = 9); or crush restraint, elecrtoimmobilisation, flank spay and ear-punch (Flank; n = 5). Cattle were blood sampled frequently to 8 h, and then daily to day 4 and were monitored to 42 days post-procedure. Peripheral blood concentrations of bound and unbound cortisol, CPK, AST, NEFAs and haptoglobin were determined.

RESULTS

Concentrations of plasma bound cortisol peaked in the spayed heifers 3-4 h post-procedure; values in the Flank (1603 nmol/L) and WDOT (1290 nmol/L) groups were similar and significantly greater (P < 0.05) than in the Controls (519 nmol/L). Flank heifers had elevated plasma haptoglobin levels to day 4 postprocedure. Liveweights were significantly lower in the spayed compared with the Control heifers at 21 and 42 days post-procedure, with liveweight gains also significantly reduced at day 21.

CONCLUSIONS

Bound cortisol responses in spayed heifers were elevated to 6 h post-procedure and similar in WDOT- and flank-spayed animals, indicating comparable levels of pain and stress. An inflammatory response, indicated by haptoglobin concentrations, was sustained for longer in Flank than in WDOT spayed heifers, suggesting longer-lasting adverse effects on welfare from flank spaying than WDOT spaying.

Local immune response against larvae of Rhipicephalus (Boophilus) microplus in Bos taurus indicus and Bos taurus taurus cattle

Bos taurus indicus cattle are less susceptible to infestation with Rhipicephalus (Boophilus) microplus than Bos taurus taurus cattle but the immunological basis of this difference is not understood. We compared the dynamics of leukocyte infiltrations (T cell subsets, B cells, major histocompatibility complex (MHC) class II-expressing cells, granulocytes) in the skin near the mouthparts of larvae of R. microplus in B. t. indicus and B. t. taurus cattle. Previously naïve cattle were infested with 50,000 larvae (B. t. indicus) or 10,000 larvae (B. t. taurus) weekly for 6 weeks. One week after the last infestation all of the animals were infested with 20,000 larvae of R. microplus. Skin punch biopsies were taken from all animals on the day before the primary infestation and from sites of larval attachment on the day after the first, second, fourth and final infestations. Infiltrations with CD3(+), CD4(+), CD8(+) and gammadelta T cells followed the same pattern in both breeds, showing relatively little change during the first four weekly infestations, followed by substantial increases at 7 weeks post-primary infestation. There was a tendency for more of all cell types except granulocytes to be observed in the skin of B. t. indicus cattle but the differences between the two breeds were consistently significant only for gammadelta T cells. Granulocyte infiltrations increased more rapidly from the day after infestation and were higher in B. t. taurus cattle than in B. t. indicus. Granulocytes and MHC class II-expressing cells infiltrated the areas closest to the mouthparts of larvae. A large volume of granulocyte antigens was seen in the gut of attached, feeding larvae.

Water and feed intake responses of sheep to drinking water temperature in hot conditions

When live-export sheep from Australia arrive in the Middle East during the northern summer months, they may be offered drinking water at temperatures exceeding 40°C. There is little published research to indicate whether drinking water temperature is important in managing heat stress in sheep or its effect on their health and welfare. Three studies were conducted with Merino wethers in climate-controlled rooms to investigate: (i) responses to drinking water temperatures of 20°C, 30°C and 40°C in a cool (20°C) and hot (40°C) environment, (ii) preferences for drinking water temperature at 20°C or 30°C when in a hot or cool environment and (iii) effects of water restriction when offered hot water (40°C) in a hot environment. Sheep assigned to the hot room had significantly higher respiration rates than those assigned to the cool room. In the cool environment, water intakes were the same when water temperatures were 20°C, 30°C or 40°C; however, when the sheep were given a choice between drinking water at 20°C and 30°C, they preferred (P < 0.05) to drink water at 20°C. In the hot environment, water intake increased as drinking water temperature increased, and sheep preferred to drink water at 30°C rather than 20°C. When the availability of 40°C drinking water was restricted (to ~10% of liveweight) in the hot environment, sheep had higher respiration rates than those offered unlimited water.

High subsoil chloride concentrations reduce soil water extraction and crop yield on Vertosols in north-eastern Australia

Salinity, sodicity, acidity, and phytotoxic levels of chloride (Cl) in subsoils are major constraints to crop production in many soils of north-eastern Australia because they reduce the ability of crop roots to extract water and nutrients from the soil. The complex interactions and correlations among soil properties result in multi-colinearity between soil properties and crop yield that makes it difficult to determine which constraint is the major limitation. We used ridge-regression analysis to overcome colinearity to evaluate the contribution of soil factors and water supply to the variation in the yields of 5 winter crops on soils with various levels and combinations of subsoil constraints in the region. Subsoil constraints measured were soil Cl, electrical conductivity of the saturation extract (ECse), and exchangeable sodium percentage (ESP). The ridge regression procedure selected several of the variables used in a descriptive model, which included in-crop rainfall, plant-available soil water at sowing in the 0.90–1.10 m soil layer, and soil Cl in the 0.90–1.10 m soil layer, and accounted for 77–85% of the variation in the grain yields of the 5 winter crops. Inclusion of ESP of the top soil (0.0–0.10 m soil layer) marginally increased the descriptive capability of the models for bread wheat, barley and durum wheat. Subsoil Cl concentration was found to be an effective substitute for subsoil water extraction. The estimates of the critical levels of subsoil Cl for a 10% reduction in the grain yield were 492 mg cl/kg for chickpea, 662 mg Cl/kg for durum wheat, 854 mg Cl/kg for bread wheat, 980 mg Cl/kg for canola, and 1012 mg Cl/kg for barley, thus suggesting that chickpea and durum wheat were more sensitive to subsoil Cl than bread wheat, barley, and canola.

Preweaning feed exposure and different feed delivery systems to enhance feed acceptance of sheep

Prior exposure of sheep to a novel feed has been shown to expedite the acceptance of that feed later in life. This study was designed to investigate the benefits of early social transmission of feed recognition for productivity and feeding behaviour of sheep in a feedlot. On a research farm near Armidale, Australia, 175 12-week-old Merino × Dorset lambs, together with their dams, were exposed to one of three preweaning treatments: (i) no exposure to feedlot pellets, (ii) offered feedlot pellets on the pasture, or (iii) offered feedlot pellets in feed troughs. The feedlot pellets were offered on two occasions at a rate of 200 g/dam, 1 month before weaning. After weaning, from 18 weeks of age, the lambs were observed for feeding behaviour and their growth during a 50-day feedlot finishing phase. Preweaning exposure to the pellets and the feed delivery system increased the rate of feed acceptance; however, there was no difference in the growth of lambs between the preweaning treatments at the end of the feedlot phase. The difference in percentage of lambs not eating between treatment groups was most pronounced during the first 2 days of the feeding period, with the differences gradually diminishing over the initial week of the feedlot phase. It is considered that differences in feedlot performance due to rate of acceptance of novel feeds are more likely under commercial conditions where pen densities are higher and feed ration transitions may be more rapid.

Effects of Environmental Heat on Conception Rates in Lactating Dairy Cows: Critical Periods of Exposure

Environmental heat can reduce conception rates (the proportion of services that result in pregnancy) in lactating dairy cows. The study objectives were to identify periods of exposure relative to the service date in which environmental heat is most closely associated with conception rates, and to assess whether the total time cows are exposed to high environmental heat within each 24-h period is more closely associated with conception rates than is the maximum environmental heat for each 24-h period. A retrospective observational study was conducted in 25 predominantly Holstein-Friesian commercial dairy herds located in Australia. Associations between weather and conception rates were assessed using 16,878 services performed over a 21-mo period. Services were classified as successful based on rectal palpation. Two measures of heat load were defined for each 24-h period: the maximum temperature-humidity index (THI) for the period, and the number of hours in the 24-h period when the THI was >72. Conception rates were reduced when cows were exposed to a high heat load from the day of service to 6 d after service, and in wk -1. Heat loads in wk -3 to -5 were also associated with reduced conception rates. Thus, management interventions to ameliorate the effects of heat load on conception rates should be implemented at least 5 wk before anticipated service and should continue until at least 1 wk after service. High autocorrelations existed between successive daily values in both measures, and associations between day of heat load relative to service day and conception rates differed substantially when ridge regression was used to account for this autocorrelation. This indicates that when assessing the effects of heat load on conception rates, the autocorrelation in heat load between days should be accounted for in analyses. The results suggest that either weekly averages or totals summarizing the daily heat load are adequate to describe heat load when assessing effects on conception rates in lactating dairy cows.

Relationship between thirty post-thaw spermatozoal characteristics and the field fertility of 11 high-use Australian dairy AI sires

This study determined the relationship between two measures of field fertility of 11 high-use Australian artificial insemination (AI) dairy bulls and thirty standard laboratory assessments of spermatozoal post-thaw viability. The two measures of field fertility used, conception rates (cCR) and non-return rates (cNRR), were both corrected for all major non-bull variables. Sperm viability assessments were conducted on semen collected within the same season as that used to derive the field fertility estimates. These assessments measured sperm concentration, motility, morphology and membrane integrity at thawing, after 2h incubation and after the swim-up sperm selection procedure. Derivations of these measures and in vitro embryo fertilizing and developmental capacity were also determined. The Genstat Statistical Package [Genstat 5 Release 4.2 Reference Manual, VSN International, Oxford, 2000] was used to conduct an analysis of variance on the viability parameters across semen straws and bulls, and to calculate the strength of correlation between each semen parameter, cNRR and cCR in a correlation matrix. Step forward multiple regression identified the combination of semen parameters that were most highly correlated with cCR and with cNRR. The sperm parameters identified as being most predictive of cCR were the percentage of morphologically normal sperm immediately post-thaw (zeroNorm), the number of morphologically normal sperm after the swim-up procedure (nSuNorm), and the rate of zygote cleavage in vitro (Clv); the predictive equation formed by these parameters accounted for 70% of variance. The predictive equation produced for cNRR contained the variables zeroNorm, the proportion of membrane intact sperm after 2h incubation at 37 degrees C (twoMem) and Clv and accounted for 76.5% of the variation. ZeroNorm was found to be consistent across straws and semen batches within-bull and the sperm parameter with the strongest individual predictive capacity for both cCR (P=0.1) and cNRR (P=0.001). Post-thaw sperm parameters can be used to predict field fertility of Australian dairy sires; the calculated predictive equations are particularly useful for identifying and monitoring bulls of very high and very low potential fertility within a group.

Application of sustainability indicators, soil organic matter and electrical conductivity, to resource management in the northern grains region

Sustainability is a multifaceted concept. It is expressed here as 'to ensure that the past and current management and use of natural resources does not diminish their capacity to meet economic, environmental, social and aesthetic needs and opportunities of the present and future generations'. Sustainability indicators can be used to monitor responses in condition and trend as a result of natural resource management. We report here 2 case studies that demonstrate the significance of sustainability indicators in discerning trends in land and water resources in the southern Brigalow (Acacia harpophylla) Belt, a major region of the Queensland Murray–Darling Basin. First, soil organic matter was used as a sustainability indicator of soil productivity, soil aggregation, and its association with soil sodicity since these soil attributes affect infiltration rates, runoff and drainage. The second study involved comparing the trends in stream salinity (electrical conductivity) over 35 years and sustainability indicators for a dominant Vertosol in a region used for cereal cropping. Groundwater level and electrical conductivity of a long-term monitoring bore in the Dalby–Chinchilla region, were also analysed to discern trends in salinity and association of the groundwater with soil and stream salinity. Soil organic matter declined exponentially as the cultivation period for cereal cropping increased. This resulted in a reduction in soil nitrogen supply, and lower grain protein and cereal grain yields. The associated effects were reduced soil aggregation and increased soil sodicity. Electrical conductivity of the soil as well as stream water showed weak but declining trends with time. Groundwater level from the long-term monitoring bore near the stream and groundwater salinity showed significantly declining trends over the 35 years sampling period. Groundwater salinity was similar to the Vertosol electrical conductivity at 240–300 cm depths, suggesting groundwater connectivity to the overlaying soil. Thus, use of sustainability indicators provided a strong association among the various attributes of the landscape. However, it is still a challenge to integrate the various sustainability indicators in a landscape context, integrated over space (spatial and geographical distribution), attributes (quality characteristics) and time (trend).

Possible risk factors on Queensland dairy farms for acaricide resistance in cattle tick (Boophilus microplus)

A case control study was carried out within a cross-sectional survey designed to investigate the management by Queensland dairy farmers of the cattle tick Boophilus microplus. Although 199 farmers were surveyed, data on acaricide resistance were only obtained from 66 farms. Multiple models were used to predict the probability of acaricide resistance associated with 30 putative risk factors. The region of the state in which the farm was located and the frequency of acaricide application were consistently associated with acaricide resistance. The risk of resistance to all synthetic pyrethroids (Parkhurst strain) was highest in Central Queensland and increased when more than five applications of acaricide were made in the previous year, when spray races were used and when buffalo fly treatments with a synthetic pyrethroid were applied frequently. The probability of resistance to amitraz (Ulam strain) was highest in Central Queensland, increased when more than five applications of acaricide were made in the previous year, and decreased on farms when a hand-spray apparatus was used to apply acaricides to cattle. The probability of resistance to flumethrin (Lamington strain) was highest in the Wide Bay-Burnett region.

Nitrogen and environmental factors influencing macadamia quality

Applications of nitrogen fertiliser in macadamia orchards remain high, despite indications that optimum yields and quality are obtained at a lower rate. This 6-year study examined the effect on quality of 230, 690 and 1150 g nitrogen/tree . year, applied in April (floral initiation), in April and June (inflorescence development), in April, June and November (rapid nut growth and premature nut drop), in April, June, November and January (nut maturation/oil accumulation) or monthly. Higher rates of nitrogen increased kernel recovery by 1% in 5 years out of 6. In 1 year only, 4 or more split applications of the medium and high rates of nitrogen increased kernel recovery by up to 1.6%. These increases were insufficient to compensate for depressed yields (17% lower) at high nitrogen. In good years, when yields were above average, kernel recovery tended to be high and in years with poor yields, kernel recovery tended to be low except when nuts were small. Moderate summer—early autumn rainfall of about 100 mm/month was associated with high kernel recovery whereas very heavy rainfall (>200 mm/month) during this period was detrimental. The percentage of first grade kernels was influenced most by season but was negatively correlated with the rate of nitrogen. Impurities, including immature, deformed, mouldy and insect-damaged kernels, were lowest at low rates of nitrogen and highest during wet harvest seasons. Time of nitrogen application had no significant effect on yield, kernel recovery, the percentage of first-grade kernels or impurities. For sustained high yield and quality, 355 g nitrogen, or 0.8 kg urea/tree.year, applied in April—June is indicated. Agronomic and economic advantages of reducing rates of nitrogen applied to macadamia orchards are enhanced by increasingly important environmental considerations. Multiple regression analyses indicated that the rate, strategy and timing of nitrogen application, rainfall, temperature, flushing and litterfall were correlated with kernel recovery and first-grade kernels but more work is needed to elucidate the significance of these factors.

Extent and economic effect of heat loads on dairy cattle production in Australia

OBJECTIVE

To investigate the extent of heat load problems, caused by the combination of excessive temperature and humidity, in Holstein-Friesian cows in Australia. Also, to outline how milk production losses and consequent costs from this can be estimated and minimised.

PROCEDURES

Long-term meteorological data for Australia were analysed to determine the distribution of hot conditions over space and time. Fifteen dairy production regions were identified for higher-resolution data analysis. Both the raw meteorological data and their integration into a temperature-humidity thermal index were compiled onto a computer program. This mapping software displays the distribution of climatic patterns, both Australia-wide and within the selected dairying regions. Graphical displays of the variation in historical records for 200 locations in the 15 dairying regions are also available. As a separate study, production data from research stations, on-farm trials and milk factory records were statistically analysed and correlated with the climatic indices, to estimate production losses due to hot conditions.

RESULTS

Both milk yields and milk constituents declined with increases in the temperature-humidity index. The onset and rate of this decline are dependent on a number of factors, including location, level of production, adaptation, and management regime. These results have been integrated into a farm-level economic analysis for managers of dairy properties.

CONCLUSION

By considering the historical patterns of hot conditions over time and space, along with expected production losses, managers of dairy farms can now conduct an economic evaluation of investment strategies to alleviate heat loads. These strategies include the provision of sprinklers, shade structures, or combinations of these.

Estimation of the effects of buffalo fly (Haematobia irritans exigua) on the milk production of dairy cattle based on a meta-analysis of literature data

Published reports on the effect of buffalo fly Haematobia irritans exigua De Meijere (Diptera: Muscidae) and the closely related horn fly (H. irritans) were examined and analysed using non-linear weighted regression techniques in an attempt to establish the relationship between daily production loss (D), average number of parasites (n) and the average damage per parasite per day (d), and to provide estimates of expected losses in milk yield (MYD) and live-weight gain (LWG) in dairy cattle. A Mitscherlich three-parameter model was used to explain the relationship between the total loss of production attributable to buffalo flies and the average number of flies associated with cattle. This model was significant (P<0.01), with R2 = 20.2% and predicted a threshold number of flies (n = 30) below which no adverse effects would be noted. At a moderate level of infestation (n = 200) dMYD was 2.6 ml/fly/day and dLWG was 0.14 g/fly/day, resulting in estimated daily losses in milk yield (D(MYD)) and live-weight gain (D(LWG)) of 520 ml and 28 g, respectively.

Production effects of cattle tick (Boophilus microplus) infestation of high yielding dairy cows

Forty mid-lactation Holstein-Friesian cows, 100% lot fed, were assigned to four groups for 15 weeks. Two groups of 10 cows were infested each week with a gradually increasing number of Boophilus microplus larvae, while the other two groups were maintained free of ticks. Milk yield and composition (including somatic cell count, SCC), liveweight, dry matter intake, packed cell volume (PCV) and total plasma protein (TPP) were measured throughout the 15 week period. By week 15, control cows produced 2.86 l more milk and 0.14 kg more butterfat each day and had gained 10.6 kg more liveweight than infested cows. Each engorging female tick was estimated to be responsible for the loss of 8.9 ml of daily mild production and 1.0 g of bodyweight over the trial period. Milk composition, PCV and TPP were not significantly affected by cattle tick infestation. The dry matter intake of control cows was 0.83 kg greater than infested cows in week 12.

Mating competitiveness of irradiated flies for screwworm fly eradication campaigns

Should the screwworm fly invade Australia, the sterile insect technique (as used successfully overseas) is currently the only feasible method of eradication. Used in conjunction with chemical control methods, it relies on large numbers of factory-reared, sterilized males competing successfully with wild males for the wild females. However, laboratory and field studies have shown that the processes of mass rearing, irradiation and distribution seriously impair the competitiveness of the sterilized flies. This study collates and analyses the relatively sparse information on the relative mating competitiveness of sterilized screwworm flies, from both controlled experiments and large-scale field studies. A population dynamics example then demonstrates that competitiveness will be a key parameter in the effectiveness and economic feasibility of any future eradication campaign.

Evaluating the risk of the establishment of screwworm fly in Australia

OBJECTIVE

To investigate probabilities of establishment of screwworm fly throughout the year, for several locations around Australia's coastline.

METHODS

A simulation model that predicts the spread and economic impact of an established screwworm fly population was modified to include stochastic survival functions, to investigate the risks of the pest actually establishing in this country. The effects of time of year, climate, vegetation and the number of incoming flies or larvae were investigated for four locations around Australia.

RESULTS

Analysis of variance identified a dominant three-way interaction between site, time, and the number of introduced flies. These probabilities are graphed.

DISCUSSION

In southern areas, as exemplified by Fremantle, the cold winters limit survival. A high probability of establishment exists year round in tropical regions, except in areas around the Gulf of Carpentaria and in the Northern Territory where dry weather mid-year would limit survival. Despite these comparatively lower risks, there were no areas or times where reductions in quarantine efforts could be justified.

Comparison of the predicted impact of a screwworm fly outbreak in Australia using a growth index model and a life-cycle model

The spatial population dynamics of an Old World screwworm fly, Chrysomya bezziana Villeneuve (OWS), outbreak in Australia have been modelled in two ways. The first model uses weekly growth indices derived from climatic data to predict the adult female population. The second is a detailed cohort life-cycle model. Due to technical and time constraints, the growth index model is preferred as the biological component of a much larger bioeconomic model because of its smaller program size and faster execution. In deciding whether adoption of the growth index model would be at the expense of scientific accuracy, the life-cycle model was developed as a yardstick. We showed that the growth index model was a practical and adequate substitution for the OWS life-cycle model and a novel spatial/temporal modelling approach with generic qualities. We elaborate on the previously reported growth index model, describe the life-cycle model and compare the results of both models. In the event of an OWS incursion in northern or eastern Australia, given average climatic conditions, both models predict that most of the suitable range (some 2.3M km2) will be colonized within 4-5 years if an eradication campaign is not attempted. Much of its permanent range would be in tropical and subtropical extensive grazing regions. Where computer or funding resources are restrictive, models incorporating growth indices may prove adequate for spatial population studies of some species.

Productivity of Hereford, highgrade Simmental and Belmont Red beef herds in central Queensland 5. Liveweights and carcass traits of steers

Postweaning liveweights and carcass traits of Hereford, 1/4 Simmental-3/4 Hereford crossbreed, first-cross Simmental-Hereford, highgrade Simmental, and Belmont Red steers were compared from 3 cohorts bred at Brigalow Research Station, Theodore, Queensland. One half of each breed was grown and fattened at Brigalow Research Station, and the other half at a different site in southern Queensland, for each of 3 cohorts. When the mean liveweight of the Hereford steers reached 450 kg, a random selection of all breed groups was slaughtered (light group), while the remainder was slaughtered when the Hereford steers reached 550 kg liveweight (heavy group). Highgrade Simmental steers had higher (P<0.05) liveweights than 114 Simmentals and Herefords at each site in each year at all ages. While highgrade Simmentals were usually heavier than first-cross Simmental-Herefords and Belmont Reds, differences were not always significant. First-cross Simmental- Hereford and Belmont Red steers were usually heavier (P<0.05) than Herefords. Response to higher nutritional levels from provision of forage crop varied according to breed, with highgrade Simmentals showing the greatest liveweight response (268 kg by 27 months) and Belmont Reds the least (164 kg) over contemporaries grazing pasture only. Highgrade Sirnmental steers had the heaviest (P<0.05) carcasses in both slaughter groups (274 and 340 kg, respectively), and there were no significant (P>0.05) differences between Belmont Red and first-cross Simmental-Hereford steers (light group, 263 and 258 kg; heavy group, 318 and 327 kg). The 114 Simmental steers had heavier (P<0.05) carcasses than Hereford steers in both slaughter groups (light, 244 v. 235 kg; heavy, 307 v. 295 kg). Belmont Red carcasses had the greatest rib fat depth for both slaughter groups (6.6 and 8.4 mm), and highgrade Simmental carcasses were leanest (3.3 and 4.1 mm; P<0.05). Carcasses from 114 Simmental and from Hereford steers had similar rib fat depth in both slaughter groups (light, 5.0 and 5.1 mm; heavy, 6.8 and 6.8 mm), while the fat depths on first-cross Simmental-Hereford carcasses were 4.3 and 6.0 mm. Although highgrade Simmental steers yielded the heaviest carcasses, the lack of subcutaneous fat cover may reduce the value of these carcasses, on a unit weight basis. By contrast, Belmont Red carcasses were more likely to meet the range of market specifications for grass-fed carcasses.

Responses to nitrogen, phosphorus and irrigation by grain sorghum on cracking clay soils in central Queensland

The yield and dry matter (DM) responses to nitrogen (N), phosphorus (P) and irrigation in sorghum hybrids E57 and Goldfinger were measured near Emerald, Queensland, on a cracking clay soil (Ug 5.12) deficient in N and P. A raingrown experiment received factorial combinations of 0, 25, 50 and 75 kg N/ha as urea, and 0, 10, 20 and 40 kg P/ha as superphosphate. An irrigated experiment received the same rates of superphosphate in conjunction with 0, 50, 100 and 150 kg N/ha and irrigation applied at 80 mm deficit. Plants were sampled on days 20 (floral initiation), 41 (early booting), 55-57 (anthesis) and 142 (grain harvest). Factors affecting yields on a soil type fairly representative of a large area of the cultivated soils of the Central Highlands were, in decreasing order of importance, N, water and P. Goldfinger initially produced higher DM yields than E57, but E57 produced higher grain yields. Mean grain yields for the 2 hybrids from control plots were 1150 kg/ha (raingrown) and 1190 kg/ha (irrigated). Under raingrown conditions, a grain yield asymptote (1600 kg/ha) was reached with 50 kg N/ha, but rates higher than 150 kg N/ha (2700 kg/ha) would be required to achieve maximum yields under irrigation. Responses to P were smaller, with rates of 10-20 kg P/ha (raingrown) producing maximum yields for both hybrids. Phosphorus rates greater than 40 kg/ha would be required to achieve maximum yields under irrigation. Apparent recovery of fertiliser P was significantly (P<0.05) lower at the highest P rate of 40 kg/ha at anthesis in the raingrown experiment. All other P recoveries either at anthesis or in the grain were not significantly (P>0.05) different. Phosphorus recoveries between the raingrown and irrigated experiments showed little difference. Nitrogen, however, showed much higher apparent recoveries in the irrigated experiment, with no significant (P>0.05) differences between N treatments. A month after harvest the only plots on the raingrown site with an increase in soil nitrate were the 75 kg N/ha treatments; residual values from all other treatments were low.

Effects of udder damage and nutritional plane on milk yield, lamb survival and lamb growth of Merinos

A pen study investigated the effects of udder damage and 3 levels of nutrition (110, 90 and 70% of maintenance requirements) during the pre- and post-natal period on the performance of Merino ewes and lambs. Udder damage (only 1 functional teat) significantly reduced (P< 0.05) estimated daily milk yield of ewes (1 139 v. 963 mL/day), growth rate (180.5 v. 143.7 g/ day) and liveweight of lambs (10.1 v. 8.8 kg) at 4-6 weeks of age. Lamb survival was significantly reduced only in the 70% of maintenance treatment (82.2 v. 64.8%). Nutrition level significantly (P< 0.05) affected ewe and lamb performance. Estimated daily ewe milk yield (1146, 1070 and 938 mL/day), ewe liveweight (40.4, 39.2 and 37.1 kg) at lamb marking, and lamb growth rate (178.1, 169.5 and 138.8 g/day) and liveweight (10.2, 9.6 and 8.6 kg) at 4-6 weeks were significantly higher for ewes fed on 110 and 90% of their requirements than for ewes fed at 70% of their requirements respectively. Lamb survival (89.9%) from ewes fed at 110% of requirements was significantly higher than lamb survival (75.3 and 73.5%) from ewes fed at 90 and 70% of requirements respectively. There was no significant interaction between the level of nutrition and udder damage in any parameter of ewe or lamb performance. Birth weight (3.0 v. 3.8 kg) and survival (49.3 v. 84.2%) were significantly (P<0.01) lower in twins than in single birth lambs. Growth rate of single lambs and single survivors of twins reared as single lambs were similar (167 and 160 g/day respectively); both of these groups grew more rapidly (P< 0.01) than lambs reared as twins (91 g/day). Lamb growth rate was positively correlated with ewe milk yield (r=0.75; P<0.01), ewe weight (r = 0.37; P< 0.01) and lamb birth weight (r = 0.24; P< 0.05). Lamb birth weight and ewe milk yield were also significantly and positively correlated with ewe weight. Male lambs were significantly heavier at birth and grew significantly faster than female lambs.

Studies on liver toxicants. Mixed-function oxidase activities and hemoprotein contents in livers of rats poisoned with bromobenzene

In liver microsomes of rats 5 h after intraperitoneal administration of bromobenzene, the activities of a series of drug-metabolizing mixed-function oxidases, i.e., ketamine and aminopyrine N-demethylases, methylayapanine and methoxybiphenyl O-demethylases, and ethoxycoumarin O-deethylase, as well as glutathione and cytochrome b5 contents were found to be decreased, whereas the activities of microsomal, NADPH-dependent cytochrome c and neotetrazolium reductases as well as cytochrome P-450 were unchanged.

Overview of toxicological studies

Ofloxacin was tested in various toxicological test systems. In common with other 4-quinolone derivatives, ofloxacin caused erosions and eruption of blisters in articular cartilage of immature animals. Such effects have not occurred in adults, and monkeys have tolerated ofloxacin up to 40 mg/kg/day for up to 12 months. Administration of various doses of ofloxacin to rats, dogs and monkeys for 4 weeks or up to 12 months did not cause anaemia. Ofloxacin did not impair male fertility. Pefloxacin, in contrast, caused azoospermia and testicular damage in dogs, and enoxacin caused testicular atrophy in rats and reduced spermatogenesis in dogs. In tests for cataractogenesis, ofloxacin was inactive, and adverse hepatic and renal effects occurred only after doses which were greater than the equivalent therapeutic maximum. Mutagenicity studies were negative. Only a recently conducted unscheduled deoxyribonucleic acid synthesis (UDS) test showed some effects, again at therapeutically non-significant concentrations.

Effects of ammonium metavanadate on rat liver enzymes

Five min after administration of a single, i.p. dose of ammonium metavanadate (5 mg/kg), in rats, liver enzyme activities were measured. Microsomal mixed-function oxidases (except for aminopyrine N-demethylase), glucose-6-phosphatase and alkaline phosphatase were inhibited but lactate, malate, and glycerophosphate dehydrogenases as well as microsomal NADPH2-dependent cytochrome c reductase were unchanged.

Studies on liver toxicants: influence of bromobenzene on hepatic microsomal drug-metabolizing enzymes in the hamster

The effect of bromobenzene on hepatic microsomal drug-metabolizing enzymes was investigated in hamsters after oral applications of 1.5 and 3.0 g/kg body weight. After 1.5 g/kg a decrease of aminopyrine N-demethylase as well as an increase of hepatic hydroperoxide formation occurred. At 3.0 g/kg, most mixed-function oxidases were inhibited with the exception of ketamine N-demethylase, methylayapanine O-demethylase, and coumarin 7-hydroxylase. Hydroperoxide formation was increased but lipoperoxidation was reduced. Neither glucuronyltransferase I nor glucuronyltransferase II were affected by bromobenzene treatment.

Studies on liver toxicants: influence of bromobenzene on hepatic microsomal enzymes in mice

The effect of acute bromobenzene intoxication on drug-metabolizing liver enzymes was studied. After an oral dose of 3000 mg/kg body weight of bromobenzene, the glucuronyltransferases I and II were increased, indicating an enzyme activation by this organic solvent via membrane irritation. The mixed-function oxidases were inhibited with the exception of the ketamine N-demethylase. Microsomal lipoperoxidation was reduced whilst H2O2 formation was unchanged.

Studies on liver toxicants. Influence of bromobenzene on hepatic microsomal enzymes in rats

In acute oral studies, the effect of bromobenzene on hepatic microsomal enzymes was investigated. Neither glucuronyltransferases nor cytochrome c reductase showed significant changes. Most of the mixed-function oxidases studied were inhibited with the exception of ketamine-N-demethylase. The data indicate that bromobenzene or its epoxide acts on cytochrome P-450 but not on all cytochrome P-450 species, and does not affect the reductase and the glucuronyltransferases. Microsomal lipoperoxidation and microsomal H2O2 formation were increased.