A dynamic model for the simulation of cattle herd production systems: 2-An investigation of various factors influencing the voluntary intake of dry matter and the use of the model in their validation

Kahn, Hava E.; Spedding, C. R. W.

doi:10.1016/0308-521x(84)90029-5

Cited by 36 publications

(15 citation statements)

References 14 publications

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“…In the model the upper limit to voluntary intake imposed by the capacity of the digestive system, I ds , is determined from faecal DM output, F DM ,, and the metabolisability of the diet, Q d , Equation 2. The factor 0.82 is the ratio between metabolisability and digestibility of forage diets (Kahn & Spedding, 1984).…”

Section: Methodsmentioning

confidence: 99%

Modelling the long-term consequences of undernutrition of cows grazing semiarid

Richardson¹

2010

SA J. An. Sci.

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________________________________________________________________________________ AbstractUndernutrition of cows grazing semi-arid range as a result of drought or heavy stocking rates reduces prenatal and pre-weaning growth of their calves. A mechanistic model has been developed that simulates the productivity of vegetation and cattle on semi-arid savanna rangeland in southern Africa. When cows are stocked at 0.200 cows/ha instead of 0.123 cows/ha the model predicted that empty body weights of their progeny at birth and weaning would be reduced by 2.9 and 43.8 kg, respectively. If all young animals are stocked at 0.22 animals/ha after weaning, differences in empty body weight at weaning are predicted to persist almost unchanged for a further two years. The model also predicted that undernutrition of cattle aged 21 months would be followed by partial compensatory growth. Comparison of simulated results with data from experiments in Zimbabwe indicates that the model realistically simulates the effects of stocking rate on cattle growth.

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Section: Methodsmentioning

confidence: 99%

Modelling the long-term consequences of undernutrition of cows grazing semiarid

Richardson¹

2010

SA J. An. Sci.

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“…However, with feeds having a low digestibility, the physical limit on intake may be lower than the physiological requirement. Following Conrad et al [4], the physical limit to feed intake is controlled by the rate of passage of undigested material through the digestive tract and the rate is positively related to the digestibility of the feed, where the size of the digestive tract is assumed to be related to the liveweight of the dairy cow, and the stage of lactation [16].…”

Section: Grazing Herbage Intake and Silage Productionmentioning

confidence: 99%

Modelling Productivity and Nitrate Leaching in a Simulated Dairy Farm

Topp¹,

McGechan

2003

Agronomie

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-Dairy farmers are faced with the challenge of balancing trade-offs between productivity, and hence profitability, and protection of the environment. An integrated simulation model of the dairy system has been used to explore impacts of varying fertiliser application rates and stocking densities on these trade-offs. The winter requirement for silage was found to be an important determinant of the carrying capacity throughout the year. Increasing fertiliser application rates tends to increase the carrying capacity and also reduce the degree of variability between years. However, nitrate leaching and denitrification losses increase as fertiliser and stocking rates increase. The losses from a permanent pasture tend to be higher than those observed for ley pastures. Congregation of cows in small areas results in substantial increases in leaching losses and hence increased risk of environmental damage compared to an even spatial distribution over the whole area. The modelling framework provides a tool with which to explore optimum management strategies on a practical dairy farm.systems model / silage production / economic performance / nitrogen leaching Résumé -Simulation de la productivité et des pertes nitriques dans un système d'élevage laitier modélisé. Les producteurs de lait sont confrontés au problème de l'établissement de l'équilibre entre la productivité, et par conséquent la rentabilité, et la préservation de l'environnement. Un modèle de simulation intégré du système laitier a été employé pour étudier l'impact de différentes doses d'engrais et de charge en animaux sur ces équilibres. Les besoins en ensilage pour l'hiver se sont avérés être une cause déterminante de la charge en bétail pour l'ensemble de l'année. L'augmentation des doses d'engrais a tendance à accroître la capacité de charge et à également réduire la variabilité interannuelle. Cependant, les pertes par lixiviation et par dénitrification augmentent avec les applications d'engrais et la charge en bétail. Les pertes à partir des prairies permanentes tendent à être plus importantes que celles observées pour les prairies temporaires. Le groupement des vaches sur des espaces réduits induit des augmentations de pertes par lixiviation et, par conséquent, a de plus grands risques de dommages environnementaux comparativement à une distribution spatiale plus uniforme, couvrant les zones entières. Le modèle fournit un outil qui permet d'explorer les stratégies optimales de gestion en production laitière. modèle de systèmes / production d'ensilage / performance économique / lessivage d'azote

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“…It follows that the ideas developed here may be of value if they are incorporated into dynamic systems designed for use under extensive grazing conditions such as those discussed by Bosman et al (1997), Finlayson et al (1995) and Kahn & Spedding (1984).…”

Section: Extension To Dynamic Systemsmentioning

confidence: 99%

Use of theoretical efficiencies of protein and fat synthesis to calculate energy requirements for growth in ruminants

Roux¹

2014

SA J. An. Sci.

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The main objection against conventional net energy systems is that owing to variation in gain composition and the different energy contents of protein and fat, the efficiency of energy gain cannot be regarded as a growth constant. The present approach shows that the separate accommodation of protein and fat in predicting ruminant nutritional requirements can easily be achieved, since growth energy retention efficiency can be replaced by protein and fat synthesis efficiencies, together with an augmentation of maintenance with the cost of protein turnover. The synthesis efficiency of protein (k PS ) is taken to be k PS = (q L /q M )(6/7), with 6/7 the synthesis efficiency of protein, q L the metabolizability of the diet at an arbitrary level (L) of intake and q M the metabolizability of the diet at maintenance. The correction (q L /q M ) allows for the usual evaluation of ruminant diets at the maintenance level of intake. The synthesis efficiency of fat from fermentation of digestible fibre is k FF = 1.018q M or k FF = 1.287k g , without the necessity of adjustment by q L /q M , since evaluation of metabolizability at maintenance is incorporated in the relationship between k FF and q M and where k g denotes growth energy efficiency. Maintenance estimated from fasting heat production or intake at zero energy retention should be augmented by the cost of protein turnover from (PB/6) ÷ (q L /q M ), with PB/6 = 102.7 kJ/kg (FW) 0.75 per day for cattle and PB/6 = 78.1 kJ/kg (FW) 0.75 per day for sheep, where PB denotes protein breakdown and FW fasted body mass. Alternatively, with knowledge of the degree of protein maturity, body protein turnover can be incorporated in a theoretically derived estimate of protein retention efficiency. The effective energy system can also be improved by employing theoretical protein retention and fat synthesis efficiencies or by equivalently replacing protein retention efficiency by protein synthesis efficiency in conjunction with the augmentation of maintenance heat production by the cost of protein turnover. A comparison between average growth energy efficiencies shows excellent agreement between estimates of the present theory and those of the UK Agricultural Research Council (ARC) and the US California Net Energy System (CNES), with degrees of maturity together with protein and fat gain ratios that seem typical of original experimental conditions. This implies that the present approach should do at least as well as the ARC or CNES, but can be expected to do better with reasonable accuracy in estimating the degree of protein maturity or maintenance augmentation and the composition of energy gain. The relationship between conventional growth energy efficiency and the synthesis efficiency of fat from digestible fibre allows the accumulated information of net energy systems to be transferable to the new methodology.________________________________________________________________________________

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A dynamic model for the simulation of cattle herd production systems: 2-An investigation of various factors influencing the voluntary intake of dry matter and the use of the model in their validation

Cited by 36 publications

References 14 publications

Modelling the long-term consequences of undernutrition of cows grazing semiarid

Modelling the long-term consequences of undernutrition of cows grazing semiarid

Modelling Productivity and Nitrate Leaching in a Simulated Dairy Farm

Use of theoretical efficiencies of protein and fat synthesis to calculate energy requirements for growth in ruminants

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