Evaluating Sugarcane Diets for Dairy Cows Using a Digestion Model

To eliminate unnecessary feeding trials, a mechanistic model of sugarcane digestion was used in the search for suitable supplements to improve milk production. Milk production simulated by the model was compared with data observed in four feeding trials published in the tropical literature where crossbred dairy cows were fed sugarcane/urea diets with different types of supplements. The predicted effects of the supplements on the ruminal microbial population, concentrations of ammonia and volatile fatty acids were also compared with the published results in one experiment. The model indicated the nutrient most limiting milk production for the different feeding situations. The addtion of Leucaena to the basal sugarcane/urea improved the availability of amino acids and long-chain fatty acids, with energy becoming the limiting factor. Supplementation with rice bran increased the availability of energy and long-chain fatty acids, but amino acids then became the limiting factor. Supplementation with both Leucaena and rice bran further improved the milk yield, but availability of energy now limited milk production. Supplementation with Leucaena increased milk production more than supplementation with king grass. The main reason for this increase was increased amino acid absorption due to increased microbial outflow. In all feeding situations, the average difference between the predicted milk production and that observed experimentally was 0.57 kg/d (ranging from 0.08 to 1 kg/d).     

Modelling dairy cattle feeding in the South-East region of Brazil

Computer modelling techniques were applied to study the structure of traditional dairy farms in the South-East region of Brazil and to help define research priorities and policies. Animal feeding is considered the principal factor affecting dairy cattle performance in the study. Knowledge of animal nutrition and feed supply from Brazilian and other literature was synthesized in two mathematical models. One model deals with the optimization of resources used in supplementary feeding for dairy cows under grazing; the other predicts dairy cow performance under a range of feeding conditions imposed by changes in the level of supplementation, stocking rate and calving date. Both models are empirical in nature. The modelling approach shows itself to be a useful means of defining research priorities and making recommendations on practical aspects of dairy cow feeding and management.     

Soft tissue sarcomas and mast cell tumours in dogs; clinical behaviour and response to surgery

OBJECTIVE: To characterise the types of canine soft tissue sarcoma and mast cell tumour treated surgically at the University Veterinary Centre, Sydney. To evaluate the success of surgical treatment of these tumours and identify variables predictive of local recurrence and survival. To establish whether conclusions drawn from previous international studies are applicable to the University Veterinary Centre, Sydney, dog population and vice versa. DESIGN: Clinical presentation and results of surgical excision of 54 soft tissue sarcomas and 70 mast cell tumours affecting the trunk and limbs of dogs at the University Veterinary Centre, Sydney, between 1989 and 2001 were reviewed retrospectively. RESULTS: Cross-bred dogs and Rhodesian Ridgebacks were at significantly greater risk of developing soft tissue sarcomas, and Boxers, Australian Cattle Dogs and Staffordshire Bull Terriers were at significantly greater risk of developing mast cell tumours than other breeds. Fine needle aspiration biopsy yielded a correct diagnosis in 62.5% of soft tissue sarcomas and 96% of mast cell tumours. Local recurrence was encountered after surgical excision in 7.4% of soft tissue sarcomas and 7.3% of mast cell tumours. Metastasis occurred in 6% of soft tissue sarcomas and 12% of mast cell tumours. The most significant risk factors for local recurrence were contaminated surgical margins (soft tissue sarcomas) and histological grade (mast cell tumours). Due to the low number of animals experiencing metastasis, no conclusions could be drawn about significant risk factors. CONCLUSIONS: Aggressive surgical management of soft tissue sarcomas and mast cell tumours is associated with a low incidence of local recurrence. The type, location and behaviour of mast cell tumours and soft tissue sarcomas in the population of dogs presented to the University Veterinary Centre, Sydney are similar to those reported by others.     

A dynamic model of N metabolism in the lactating dairy cow and an assessment of impact of N excretion on the environment

Improving N utilization in dairy cows and especially reducing N output in excreta is desirable due to global concerns of agricultural contribution of N to environmental pollution, particularly as ammonia. Data from five N balance experiments were used to develop a dynamic model that was evaluated with independent data. Model predictions of feces, urine, and milk outputs were close to observed values. Statistical analysis showed that 96% of mean square prediction error for feces and urine N output predictions was due to random variation. However, the model tends to overpredict milk N output, especially at higher N intake levels. Evaluation of model predictions for independent experimental observations from Agricultural Development Advisory Service at Bridgets (U.K.) showed good agreement between predicted and observed urine N output (95% due to random variation). However, there was a slight underprediction for fecal N output (14% mean square prediction error due to bias) and overprediction of milk N output (22% of mean square prediction error due to bias). The model predictions of N outputs in excreta were sensitive to changes in energy concentration of the diet. Dietary protein degradability had only a small influence on predicted fecal N output. However, the model was sensitive in its predictions of urine N when protein degradability was varied. Application of the model to assess reduction in ammonia emissions from dairy cows showed that increasing the energy concentration could potentially reduce ammonia emissions by up to 25% per cow. Similarly, reducing CP concentration in the diet to about 16% could reduce ammonia production by 20% and lower degradability of CP to match microbial requirement by 19% per cow. The model is a first step toward a mechanistic approach of nutrient modeling, and it is a valuable method for predicting N excretions and estimating N emissions from dairy systems.     

A variance-covariance structure to take into account repeated measurements and heteroscedasticity in growth modeling

This study proposes a within-subject variance-covariance (VC) structure to take into account repeated measurements and heteroscedasticity in a context of growth modeling. The VC structure integrates a variance function and a continuous autoregressive covariance structure. It was tested on a nonlinear growth model parameterized with data from permanent sample plots. Using a stand-level approach, basal area growth was independently modeled for red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] in mixed stands. For both species, the implementation of the VC structure significantly improved the maximum likelihood of the model. In both cases, it efficiently accounted for heteroscedasticity and autocorrelation, since the normalized residuals no longer exhibited departures from the assumptions of independent error terms with homogeneous variances. Moreover, compared with traditional nonlinear least squares (NLS) models, models parameterized with this VC structure may generate more accurate predictions when prior information is available. This case study demonstrates that the implementation of a VC structure may provide parameter estimates that are consistent with asymptotically unbiased variances in a context of nonlinear growth modeling using a stand-level approach. Since the variances are no longer biased, the hypothesis tests performed on the estimates are valid when the number of observations is large.     

Stable carbon and nitrogen isotopic evidence for ecotonal coupling between boreal forests and fishes

Abstract— As a result of water turbulence effects on boundary layer diffusion resistance and carbon isotopic discrimination, the δ¹³C values (ratios of ¹³C: ¹²C) of attached algae may often overlap those of terrestrial plants, thereby making it impossible to distinguish between the relative importance of these two potential food sources for aquatic animals. The present study used a dual isotope approach (δ¹³C and δ¹⁵N) to refine measurements of the incorporation of allochthonous organic matter into freshwater fishes. The dependence of five species of littoral fishes on terrestrial detritus for part of their energy sustenance was demonstrated. The littoral zones of boreal Canadian Shield lakes are, therefore, not isolated from their surrounding riparian forests in terms of carbon flow as present day timber management guidelines erroneously assume, but instead exhibit a measurable degree of ecotonal land-water coupling. As a result, clearcut logging of riparian forests to the lakeshore edge, permissible by law in most Canadian provinces containing boreal forests, may have to be reassessed as a forest harvesting strategy.     

Spawning dynamics of American shad (Alosa sapidissima) in the St. Lawrence River,Canada–USA

Maltais E, Daigle G, Colbeck G, Dodson JJ. Spawning dynamics of American shad (Alosa sapidissima) in the St. Lawrence River, Canada–USA.
Ecology of Freshwater Fish 2010: 19: 586–594. © 2010 John Wiley & Sons A/S Abstract – The most northerly population of American shad (Alosa sapidissima), located in the St. Lawrence River, is considered vulnerable because of low population abundance and limited spawning habitat located at the upstream extent of the population’s anadromous migration. Here, we aimed to establish the temporal and spatial extent of spawning based on a novel hatch‐date analysis of juveniles. Spawning activity lasted from early May to early July. We found that juveniles captured downstream during the summer hatched later in the year than those captured further upstream. As a result, younger juveniles were distributed somewhat further downstream. In addition, we found significant multimodality in hatch‐date distributions at midstream and downstream sampling stations. Together, these results provide evidence that the 2‐month spawning period involved numerous spawning events that progressed in a downstream direction as the season advanced, rather than being restricted to upstream sites over the spawning season.     

Supercritical fluid extraction/enzyme assay: a novel technique to screen for pesticide residues in meat products.

The novel combination of supercritical fluid extraction (SFE) with an enzyme assay system has been used to screen meat products to detect the presence of pesticides. Analytes are collected in water by expanding supercritical carbon dioxide to atmospheric pressure through a restrictor and into an aqueous phase. The solution is then tested for the presence of pesticide residues by enzyme assay. Two experimental approaches have been used. Alachlor-fortified lard and bovine liver were monitored by static SFE coupled with an enzyme immunoassay. SFE of carbofuran-fortified frankfurters was coupled with an enzyme assay based on cholinesterase inhibition. A major benefit of the SFE/enzyme assay technique over conventional screening techniques is that the analyst is not exposed to organic solvents.