Ian W. Purvis

Evaluation of visual implant elastomer and alphanumeric internal tags as a method to identify juveniles of the freshwater crayfish, Cherax destructor

In the last few years there has been an increasing interest in using traditional animal breeding techniques to improve important traits such as growth rate in freshwater crayfish. However, a major impediment to such programs is an inability to reliably identify individuals or family groups for long periods because of the non-retention of external tags through ecdysis. Visual implant elastomer (VIE) and visual alphanumeric (VIalpha) internal tags have proven useful in identifying finfish and amphibians. We evaluated the suitability of these two internal tags as a method to identify yabby (Cherax destructor) juveniles. Both tags proved useful in identifying juveniles between 0.1 and 4.6 g, with the VIE having the higher retention rate of the two tags (up to 92%, as opposed to 79% for the VIalpha tag). Mortality, as a direct consequence of tagging juveniles with the VIE and VIalpha tags was 13% and 11%, respectively. The ability to reliably identify C. destructor juveniles will increase the efficiency of selective breeding programs for this species by allowing individuals and family groups to be pooled in growth experiments, thereby decreasing the impact of confounding environmental effects.

New ways of measuring intake, efficiency and behaviour of grazing livestock

Wireless sensor networks (WSN) offer a novel method for measuring important livestock phenotypes in commercial grazing environments. This information can then be used to inform genetic parameter estimation and improve precision livestock management. Arguably, these technologies are well suited for such tasks due to their small, non-intrusive form, which does not constrain the animals from expressing the genetic drivers for traits of interest. There are many technical challenges to be met in developing WSN technologies that can function on animals in commercial grazing environments. This paper discusses the challenges of the software development required for the collection of data from multiple types of sensors, the management and analyses of the very large volumes of data, determination of which sensing modalities are sufficient and/or necessary, and the management of the constrained power source. Assuming such challenges can be met however, validation of the sensor accuracy against benchmark data for specific traits must be performed before such a sensor can be confidently adopted. To achieve this, a pasture intake research platform is being established to provide detailed estimates of pasture intake by individual animals through chemical markers and biomass disappearance, augmented with highly annotated video recordings of animal behaviours. This provides a benchmark against which any novel sensor can be validated, with a high degree of flexibility to allow experiments to be designed and conducted under continually differing environmental conditions. This paper also discusses issues underlying the need for new and novel phenotyping methods and in the establishment of the WSN and pasture intake research platforms to enable prediction of feed intake and feed efficiency of individual grazing animals.

Definition of a breeding objective for commercial production of the freshwater crayfish, marron (Cherax tenuimanus)

This study tested the hypothesis that profitability of commercial marron production would be increased by the development of a rapidly growing strain that has a large tail, a proportional claw size, and a high survival, food conversion efficiency, reproductive rate, and fecundity. A profit equation was developed for commercial marron production, and expressed as function of the production characteristics associated with maintenance of the broodstock (growth rate, survival, food conversion efficiency, reproductive rate, and fecundity), incubation of the eggs and hatchlings (survival), rearing of the juveniles (growth rate, survival, and food conversion efficiency), and grow out of the marron (growth rates of the carapace, tail, and claws, survival, and food conversion efficiency). Economic values were estimated for these characteristics when profit was set to zero, and the sensitivity of selection response to potential errors in these estimates was analysed. The results showed that profit was increased by a genetic increase in the growth rate of the juveniles, growth rates of the carapace and tail of the marron, survivals of the broodstock, eggs and hatchlings, juveniles, and marron, food conversion efficiencies of the broodstock, juveniles, and marron, and the reproductive rate and fecundity of the broodstock. By contrast, profit was decreased by a genetic increase in the growth rate of the broodstock, and a genetic increase in the growth rate of the claws of the marron, given that there was a smaller claw weight to carapace weight ratio that was ideal. Growth rate of the tail of the marron was the most economically important characteristic. Its economic value (per genetic standard deviation improvement) was between 4.7 and 11.6 times larger than an improvement in the growth rate of the carapace, survival of the marron, and growth rate of the claws. In turn, growth rate of the tail was between 30 and 7900 times more important than the food conversion efficiency of the marron, and the characteristics associated with the broodstock, eggs and hatchlings, and juveniles. The sensitivity analysis indicated that response to selection was not sensitive to potential errors in the magnitude of the economic values. These results demonstrate that breeding programs for commercial production should concentrate on the improvement of those characteristics associated with the marron, with emphasis on the growth rate of their tail. They also suggest that the economic values are suitable for implementation in breeding programs, even when future production systems and market conditions are uncertain. The hypothesis tested in this study was supported. Profitability of commercial marron production would be increased by the development of a rapidly growing strain that has a large tail, a proportional claw size, and a high survival, food conversion efficiency, reproductive rate, and fecundity.

Eggs and hatchlings of the freshwater crayfish, marron (Cherax tenuimanus), can be successfully incubated artificially.

Abstract The objective of this study was to test whether marron eggs and hatchlings can be incubated artificially with high levels of survival. Marron eggs were collected from 30 gravid females. The eggs from each female were divided into two replicate groups, and each replicate group was incubated separately within an artificial incubator until the eggs had hatched and developed into independent juveniles. Eighty-nine percent of the eggs hatched and developed into independent juveniles, while the variation in survival between replicate female groups was not significant. These results demonstrate that the artificial incubator was a suitable replacement for the maternal care provided by the female marron after spawning, and that a uniform environment existed within the incubator. The success of the artificial incubation technique enables experiments to be carried out on eggs and hatchlings independent of the females, under a common and controlled environment, and with many separate treatment groups.

Precision of estimating individual feed intake of grazing animals offered low, declining pasture availability1

Measurement of intake of individual grazing animals remains one of the fundamental challenges to improving efficiency of livestock production. The use of wireless sensor networks (WSN) shows potential for this purpose and requires benchmark data to underpin the necessary algorithm development. This study aimed to provide benchmark data and enable improved precision in estimating pasture intake when pasture availability is low and declining. Each of 10 Angus steers with a mean liveweight ± s.d. of 326 ± 46 kg was randomly allocated to an individual grazing plot. The plots comprised a monoculture of Italian ryegrass (Lolium multiflorum cv. Surge), with estimated initial pasture biomass availability ≤1100 kg DM/ha, provided at three levels of pasture availability (low, medium and high), achieved by varying plot sizes (0.2, 0.3 and 0.4 ha). Pasture intake was estimated using two pasture disappearance-based techniques (rising-plate meter and capacitance meter) using regression equations of daily pasture biomass estimates over an 11-day pasture intake period, and two chemical marker-based techniques (dosed n-alkanes and chromic oxide). Both pasture disappearance-based techniques showed high variability in estimating pasture biomass, with mean coefficients of variation between repeated-measurements of 28% for the capacitance meter and 44% for the plate meter, although daily biomass measurements over the duration of the study using the two devices were highly correlated (r = 0.82). Mean pasture intake estimates across all four techniques ranged from 3.4 to 10.7 kg DM/day. The estimates of pasture intake differed between techniques but not between biomass availability treatments. Mean of pasture intake estimates made using the plate meter were consistently higher than for the other three techniques. The correlation coefficients between the intake estimates determined using the pasture disappearance-based techniques, and between their rankings, were 0.61 and 0.58, respectively. Intake estimates obtained using pasture disappearance and the chemical marker methods were not correlated apart from between chromic oxide and the plate meter (r = 0.51). Further refinement of these techniques and more studies over a wider range of pasture conditions are needed. It is critical to understand the limits within which each of the pasture intake methodologies will produce reliable results that can then be used as benchmark data for the development of predictive algorithms using WSN.

Pregnancy scanning can be used as a source of data for genetic evaluation of reproductive traits of ewes

Reproductive traits generated from mothering up lambs to ewes (n = 59 603 records) were compared with data resulting from pregnancy scanning (n = 46 663 records), to examine the consistency between the two data sources for deriving specific reproductive traits and to estimate genetic parameters. The reproductive traits considered were fertility (FERT: 0/1) of ewes joined, total litter size (LSIZE: lambs born), the number of lambs surviving at weaning (LSIZEW: lambs weaned) and the percentage of lambs surviving (LSURV = LSIZEW/LSIZE) for ewes that lambed, along with the composite traits number of lambs born (NLB) and number weaned (NLW) for ewes joined. Corresponding trait values were derived from pregnancy scan data (FERT_S, LSIZE_S and NLB_S) for comparison, and were classified as inconsistent if the trait values did not match from scanning and lambing records. Data were obtained from four flocks, representing different time frames, locations, management and breeds or bloodlines. Each flock recorded scan data separately from lambing outcomes. Genetic parameters were estimated separately within each flock. Average levels of inconsistency between scan- and lambing-data values varied between 4.6% and 14.8% across flocks, tending to be highest (9.1–18.5%) for litter size of ewes scanned with multiple fetuses, and lowest (0.29–7.3%) for assignment of fertility. Inconsistencies did not have a significant impact on estimates of trait heritabilities, suggesting recording errors were independent of genetic merit. In three flocks, the genetic correlations (ra) between comparable traits derived from the different data sources were not different from unity (ra ≥ 0.99) even when phenotypic correlations (rp) were lower (rp ≥ 0.84). In the flock with the highest inconsistency rate between data sources, the range in ra varied between 0.60 (fertility) and 1.0 (litter size). Therefore, pregnancy scan data can be directly substituted for reproductive traits traditionally based on lambing data, but attention should be paid to ensuring accuracy of the data sources used. Scan data also provide no information on lamb-survival outcomes after birth, so does not constitute complete data on reproductive outcomes. Genetic evaluation systems might also benefit from fine tuning for scale-induced effects (due to litter size) on parameters to improve the accuracy of across flock prediction of breeding values for reproductive traits.

The Contribution of Naturally Occurring Food Items to the Diet of Bidyanus bidyanus When Fed Differing Formulated Diets

Fish raised in ponds and fed formulated feed also have access to naturally occurring food items. The contribution of these food items to growth of Bidyanus bidyanus was investigated by assigning fish to four treatments: in diet 1, caged fish were fed a high protein feed (52% CP); in diet 2, caged fish were fed a medium protein feed (30% CP); in diet 3, caged fish received no feed; and in diet 4, uncaged fish received no feed. Survival between caged treatments was similar (88%–96%), and fish performed best when fed a high-protein feed. Modelling of C and N stable isotope ratios showed formulated pellets provided 12% to 84% of the growth of fish fed diet 1 or 2, while invertebrates provided between 4% and 74%. The majority of growth of fish in diet 3 was from zooplankton (54%–76%) and invertebrates for fish in diet 4 (6%–94%). Implications for low intensity production of B. bidyanus are discussed.