Developing a ruminal physiologically based model for the evaluation of dietary structural effectiveness in high-yielding dairys cows (Entwicklung eines ruminal-physiologischen Modells zur Bewertung der Strukturwirksamkeit von Rationen bei Hochleistungsmilchkühen)
Zusammenfassung der Projektergebnisse
The main objective of this research project was to develop physiologically-based, easy-to-use models to assess and predict the physical effectiveness and adequacy of dietary fibre in highyielding dairy cows. Statistical modelling approaches were used to model crucial physiological responses of dairy cattle such as chewing activity, rumen pH course, fibre degradation, dry matter (DM) intake, and production performance to different variables including physical, chemical and starch-degrading characteristics of the diet, and relate them to the assessment of dietary fibre adequacy in dairy cows. Extensive research data, comprising a wide range of feeding regimens, were used for parameterization and calibration purposes of the models. A stochastic sensitivity analysis was performed to evaluate the magnitude of ruminal pH fluctuations, determine the risk of sub-acute rumen acidosis (SARA), and relate it to the derivation of adequate amounts of physically effective neutral detergent fibre (peNDF) in the diet of dairy cows. Determination of the threshold for SARA, in this research, is a crucial aspect both in physiological terms for the determination of SARA itself, and, most importantly, for the estimation of adequate amounts of peNDF in the diet required to prevent SARA and the related consequences on low milk production performance of dairy cows. Results of this study showed that in order to minimize the risk of SARA the following events should be avoided: 1) a daily mean ruminal pH lower than 6.16, and 2) a time length in which ruminal pH is < 5.8 longer than 5.24 h/d, whereas fibre degradation was depressed when this time duration is longer than 5.01 h/d. It was suggested that to minimize the risk of SARA and depression of fibre degradation in dairy cows, the time period in which ruminal pH is < 5.8 for more than 5 - 5.24 h/d should be avoided. Modelling data revealed that as the content of peNDF expressed inclusive of particles > 1.18 mm (peNDF>1.18) or the ratio between peNDF>1.18 and rumen-degradable starch from grains in the diet increased up to 31.2 ± 1.6% (DM basis) or 1.45 ± 0.22, respectively, so did the daily mean ruminal pH, of which a asymptotic plateau was reached at a pH of 6.20 to 6.27. Further, our study revealed that for the prevention of depression in fibre degradation average amounts of 31.2% peNDF inclusive particles > 1.18 mm (i.e., peNDF>1.18) or 18.5% peNDF inclusive particles > 8 mm (i.e., peNDF>8) in the diet (DM basis) are required. As expected, our modelling demonstrated that besides peNDF also the amount of degradable starch of grains is important to determine dietary fibre adequacy and prevent the depression of ruminal pH. It was determined that about 15% of rumen degradable starch from grains (i.e., 3.8 kg per day for cows consuming about 25 kg DM/d) in the TMR (DM basis) may be considered as a general optimum to assure normal rumen conditions and digestion. Because the ruminal degradability of starch from forages showed a high variation, their inclusion in the model of this study was not possible. This aspect should be considered in the development of future models after some more research data will be available in the future. It was also demonstrated that the capabilities of peNDF>1.18 and peNDF>8 in expressing physical effectiveness of the diets were similar when they were used to predict some variables such as ruminal pH, indicating that they can be used similarly to predict the risk of SARA. However, their effects differed for the prediction of some other physiological variables such as chewing and rumination activity, and DM intake level, indicating that peNDF>8 is a better determinant of physical fill in the reticulorumen. Thus, peNDF>8 can express the effectiveness to stimulate rumination better than peNDF>1.18, hence demonstrating that these units of peNDF cannot be always used interchangeably. In terms of improvement of the accuracy to assessing dietary fibre adequacy, it is suggested that the content of peNDF required to stabilize ruminal pH and maintain milk fat content without compromising milk energy efficiency can be arranged based on grain or starch sources included in the diet, feed intake level and days in milk of the cows, using the equations developed in this research. In conclusion, a level of about 30 to 33% peNDF>1.18 or 14.9% (10.9 to 18.8%) peNDF>8 in the diet may be considered as the general optimal one to minimize the risk of ruminal disorders without impairing important production responses in high-yielding dairy cows.
Projektbezogene Publikationen (Auswahl)
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2007. A simulation model to evaluate the risk of subacute ruminal acidosis in high-yielding dairy cows fed total mixed rations ad-libitum. Proc. 13th International Conference of Production Diseases in Farm Animals (Ed. M. Fürll), Leipzig, Germany, p. 160
Zebeli, Q. and W. Drochner
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2008. Modeling dietary fiber adequacy in dairy cows based on responses of ruminal pH and milk fat production to diet composition. Journal of Dairy Science 91:2046-2066
Zebeli, Q., J. Dijkstra, M. Tafaj, H. Steingass, B.N. Ametaj, and W. Drochner
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2009. Determining fiber requirements in dairy cows by modelling digestive responses to dietary physically effective NDF. Journal of Dairy Science 92 E-Suppl. 1:584 (American Dairy Science Association Joint Annual Meeting, July 12-16, Montreal, Quebec, Canada)
Zebeli, Q., D. Mansmann, H. Steingass, W. Drochner, and B.N. Ametaj
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2010. A practical model to estimate the requirements for physically effective fibre (peNDF) in dairy cows. Proc. 64th Congress of German Society for Nutrition Physiology. March 9-11, 2010, Göttingen, Germany
Zebeli, Q., D. Mansmann, B.N. Ametaj, H. Steingass, and W. Drochner
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2010. A statistical model to optimize the requirements of lactating dairy cows for physically effective neutral detergent fibre. Archives of Animal Nutrition 64:265–278
Zebeli, Q., D. Mansmann, B.N. Ametaj, H. Steingass, and W. Drochner
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2010. Balancing diets for physically effective fibre and ruminally degradable starch: A key to prevent rumen acidosis and increase productivity of dairy cattle. Livestock Science 127:1-10
Zebeli, Q., D. Mansmann, H. Steingass, and B.N. Ametaj
