Starch digestibility in dairy cows how do we handle starch in ration evaluation systems?

Transcription

1 AARHUS UNIVERSITY Starch digestibility in dairy cows how do we handle starch in ration evaluation systems? Martin Riis Weisbjerg Animal Science, AU Foulum, Aarhus University, Denmark WIAS Seminar Development in Ruminant Nutrition, Wageningen University Monday 30 September 2013 in combination with PhD defence of Warner and Spek

2 Ruminant starch digestion VFA Microbial protein 80% of energy Glucose 97% of energy RUMEN VFA 62% of energy SMALL INTESTINE HIND GUT

3 Outline Recent DK studies on starch digestibility How to handle starch in feed evaluation models Suggestion for in vivo approach Major future challenges regarding starch AARHUS UNIVERSITY

4 Starch digestibility in Dairy cows variable! AARHUS UNIVERSITY

5 Maize silage effect of maturity/dm AARHUS UNIVERSITY Jensen et al. 2005, ANIFEE, 118,

6 Corn cob silage Dairy cows Treatment Barley Corn cob silage NaOH wheat SEM P-value Dry matter intake (kg/day) Digestibility (%) DM OM NDF Starch Protein AARHUS UNIVERSITY Hymøller et al. 2013, submitted

7 Rye upcoming in Denmark for feeding, and not just for rye bread Digested starch [g/kg starch intake] Rumen Small instestine Hind gut = =966 Rolled rye NaoH rye AARHUS UNIVERSITY Hellwing et al EAAP Nantes

8 Conclusion - Starch digestibility in dairy cows Starch digestibility variable, also in Danish starch sources Digestibility and rumen degradability of ensiled starch is high AARHUS UNIVERSITY

9 Outline Recent DK studies on starch digestibility How to handle starch in feed evaluation models Suggestion for in vivo approach Major future challenge regarding starch AARHUS UNIVERSITY

10 In vitro in situ vs in vivo - starch kd in vitro (per h) Weisbjerg et al y = x R² = kd in situ (per h) Rumen starch degradability Rumen starch degradability y = 1.39x r = Conclusion Weak correlations between in situ and in vitro kd Effective AARHUS degradability UNIVERSITY- OK correlations for both methods IS k d values unrealistic, however ESD values correlated well In vitro ESD y = 0.385x r = In situ ESD

11 Mobile bag assessment of in vivo starch digestibility Mobile bag disappearance (g/kg) y = 0.88x + 92 R² = 0.19 y = 0.58x R² = In vivo starch digestibility (g/kg) Without RP With RP Conclusion Weak correlations between in vivo and mobile bag digestibilities AARHUS UNIVERSITY Ghoorchi et al. 2012, Animal, 7,

12 Conclusion estimation of starch digestibility No obvious lab method for estimation of starch digestibility Probably because both physical form, processing (heat, ensiling, etc.) and origin (protein matrix?) influence starch digestibility therefore e.g. standardised milling hamper assessment Then, at present, in vivo approach seems most appropriate, as it seems that only the animals can give the right answer! AARHUS UNIVERSITY

13 Outline Recent DK studies on starch digestibility How to handle starch in feed evaluation models Suggestion for in vivo approach Major future challenge regarding starch AARHUS UNIVERSITY

14 Literature data dairy cows 62 publications Observations as treatment means Selection criteria: Lactating dairy cows At least total tract starch digestibility, preferentially rumen, small intestinal and hind gut Starch digestibility Observations Total tract 279 Rumen 173 Small intestine 54 Hind gut 57

15 Database included Nutrient intakes Starch flow (digestibilities) Name of main starch sources (2 main concentrate and 2 main forage sources, if appropriate) Proportion of total starch intake coming from these 4 starch sources In total 21 starch sources

16 Challenge in using in vivo data for lactating cow rations: Most examined rations contain more than one starch source!

17 Data analysis Regression and multiple regression analysis Y = starch digestibility, total or in different digestive compartments Y = starch intake/escape + proportion of starch source 1-21 Y = starch intake/escape Y = proportion of starch source 1-21

18 Main results regression analyses Rumen and total digestibility info on source (name) necessary Small intestinal digestibility positively correlated to rumen degradability source (name) still important Hind gut digestibility source (name) not important - positively correlated to rumen degradability [opposite to hypothesis!!]

19 Digestibilities for individual starch sources

20 Digestibilities - estimated using GLM obs. dig = source digestibility x source prop. of ration total starch Starch source Total tract Rumen Small intestine Hind gut Wheat Starch Corn starch Wheat Oat Faba beans Barley Corn silage (CS) CS high Wheat NaOH Wrinkled pea Corn Sorghum na na Smooth pea Barley NaOH Green = highest, blue=high, purple=low, red =lowest 1 corn silage > 60% of ration starch

21 How can this be used to model starch digestion in practical feed evaluation models? Rumen: k d calculated from in vivo rumen digestibility, and tabulated Small intestine: function of rumen digestibility (if we forget about starch source, problematic with legumes) or use estimates for digestibility of individual sources Hind gut: function of rumen digestibility

22 Approach introduced in NorFor NorFor update - changed starch model A new version of the NorFormodel was released on June 4, called FRC The new update includes a modified calculation of starch digestibilityand a recommendation for individual amino acids. We will come back with more information later on amino acids and focus on starch in this newsletter. However only partly introduced at present, post rumen digestion in NorFor as regressions on rumen escape

23 Outline Recent DK studies on starch digestibility How to handle starch in ration evaluation models Suggestion for in vivo approach Major future challenge regarding starch

24 Major remaining question How does starch pass out of the rumen How to assess starch digestibility in samples where no in vivo data are available ( new starch sources, processed starch, commercial concentrates)?

25 Starch passage!

26 This presentation has been carried out with financial support from the Commission of the European Communities, FP7, KBB and from NorFor It does not necessarily reflect its view and in no way anticipates the Commission s future policy in this area. Innovative and practical management approaches to reduce nitrogen excretion by ruminants