Browsing by Author "Baudracco, Javier"

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    Effects of feeding level and genetic merit on the efficiency of pasture-based dairy systems : field and modelling studies : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2011) Baudracco, Javier
    The objective of this thesis was to develop and validate a dynamic and stochastic whole-farm model that can predict physical and economic performance of pasture-based dairy systems; explore interactions between cow genetic merit, feeding level (supplementation and stocking rate) and market prices; and be applied to both ryegrassbased and lucerne-based pasture dairy systems. The effects of, and interactions between, stocking rate (SR), supplementation and genetic merit of cows on grazing dairy systems were reviewed, approaching both the physical and economic impact of these factors. The performance of strains of Holstein- Friesian cows in experiments from Ireland, Australia and New Zealand was summarised, and a meta-analysis that explores the relationship between herbage allowance and herbage intake was included. The development of the whole-farm model was completed in three steps. Firstly, a model was developed and validated that predicts herbage intake at grazing for dairy cows with or without supplementary feeding and that combines physical, metabolic and ingestive constraints. Secondly, an animal model that predicts energy intake, milk yield and live weight change of a single cow at grazing (e-Cow model) was developed and validated. This model also integrates the above intake model, a mammary gland model and a body lipid change model. The e-Cow model, which is available as a web-based version, combines nutritional and genetic drives to control energy partitioning within the cow. It also accounts for genetic differences between cows and is sensitive to genotype by environment interactions. The third and final step was the development and validation of a stochastic and dynamic whole-farm model that predicts physical and economic performance of grazing dairy systems (e-Dairy model). Both the e-Cow and the e-Dairy models simulate the performance of individual cows on a daily basis and were developed using Visual Basic programming language. The validation of the whole-farm model (e-Dairy) was conducted for ryegrassbased dairy systems using existing data from a 3-year farmlet experiment comparing five levels of SR (2.2 to 4.3 cows/ha) conducted in New Zealand, with cows offered 0.15 t dry matter (DM) supplement/cow/year. The validation of the model for lucernebased dairy systems was performed with data from a 2-year farmlet experiment designed and completed as part of the current research. This experiment compared three levels of SR (1.6 to 2.6 cows/ha) for cows offered 1.8 t DM supplements/cow/year in Argentina. An indigestible intake marker developed from a purified enriched lignin (LIPE®) was used to estimate individual herbage intake for a short-period within the farmlet experiment. Stochastic simulations (n=200) using the whole-farm model (e-Dairy) suggest that for ryegrass-based New Zealand dairy systems (ratio $/kg milk to $/kg supplement of 1.1 ± 0.31), the increase in SR from 2.8 to 3.5 cows/ha together with an increase in imported supplements from 0.15 to 1.45 t DM/cow/year can be profitable only when milk price is higher than $NZ5.5/ kg MS ($US4.1). Simulations for lucerne-based dairy systems in Argentina (ratio $/kg milk to $/kg supplement of 1.8 ± 0.55), suggest that the increase in SR from 1.6 to 2.6 cows/ha, with a fixed amount of imported supplements per cow at 1.8 t DM/cow/year would increase operating profit across the range of milk prices tested ($US 3.3 ± 0.84/kg MS). The e-Dairy model can be used to explore the effects and interactions of feeding level and genetic merit of cows for grazing dairy systems with differing calving patterns as well as evaluating the trade-offs between profit and the associated risk. It could also potentially be used, after further development, to simulate the genetic evaluation of cows and bulls under different selection objectives and selection schemes such as progeny tests for bulls.
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    Effects of stocking rate and supplementation on the productivity and profitability of Argentine dairy systems : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Animal Production at Massey University, Palmerston North, New Zealand
    (Massey University, 2006) Baudracco, Javier
    Dairy production in Argentina is based on grazed pastures, with the inclusion of supplements as a secondary source of feed. The average milk production per hectare in Argentine dairy farms is low and this affects the profitability of the farms. The low efficiency of production per hectare appears to be associated with low stocking rate and low utilisation of the cheapest source of feed, which is grazed pasture. Data reviewed in the present study suggested that stocking rate (SR) and the amount of imported feed are factors with significant influence on dairy farm productivity and profitability in Argentina, as is also the case in New Zealand and Australia. Stocking rate, expressed as the number of cows per hectare, is a simplification of the relationship between feed demand and feed supply. This relationship can be better expressed as kilograms of live weight per tonne of dry matter total feed supply, defined as comparative stocking rate. The aim of this thesis was to quantify the effects of comparative SR and supplementation (imported feed) on the productivity and profitability of Argentine dairy farms. A simulation model was developed to predict pasture dry matter (DM) intake and the harvesting efficiency of grazing dairy cows in Argentina (Chapter 3). In validation tests, using data from cows grazing lucerne in Argentina and ryegrass-clover in Ireland, the model predicted satisfactorily. Following this, a simulation model was developed to predict milksolids (MS) production and live weight (Lwt) change of Argentine Holstein cows in grazing dairy systems, given a determined intake of metabolisable energy (Chapter 4). Finally, a whole-farm simulation model called the Argentine Dairy System Model (ADSM) was developed (Chapter 5). by integrating the models developed in Chapter 3 and 4, together with a pre-existent economic model for Argentine dairy farms. Model validation was conducted by comparing results from the model against data form eight Argentine dairy farms. The accuracy of model predictions was satisfactory. Twenty-two dairy systems were tested with ADSM, in order to allow the effects of comparative SR and supplementation to be explored. The cow type used was the Argentine Holstein (550 kg Lwt and 6.8% MS content). The present study suggests that the low MS production of Argentine dairy farms could be increased by increasing both comparative SR and the amount of supplements imported into the farm. Model predictions indicated that MS production per hectare would be maximised at a comparative SR of approximately 100 kg Lwt/t DM, economic farm surplus ($US/ha) at 90 kg Lwt/t DM, and return on assets at 80 kg Lwt/t DM. Additionally, the model predicted that cows stocked at a comparative SR of about 80 kg Lwt/t DM will neither increase nor decrease Lwt change over a complete season (lactating and dry periods). These results suggest that the optimum comparative SR, in terms of both economic and sustainable physical performance for the Argentine Holstein cows seems to be around 80 kg Lwt/t DM. Annual pasture utilization values were 70%, 76%, and 81% for comparative SRs of 80, 90, and 100 kg Lwt /t DM, respectively. At the milk payout and concentrates price used in this study, it would be profitable to increase the amount of imported feed up to 3.6 t DM per hectare, provided that SR is simultaneously increased, in order to achieve pasture utilisation of 70% or higher. A dairy system with 8.6 t DM/ha/year produced on-farm, importing 3.6 t DM concentrates per year and stocked at 81 kg Lwt/t DM (1.8 cows/ha) would be able to utilise 71% of pasture and produce 626 kg MS/ha/year, which is about two-fold the average MS production of Argentine farms. Changing either the price of milk or the cost of concentrates by 10% did not alter the relative profitability of the different systems.