Feed evaluation for dairy cows: Tests on the system proposed in the Netherlands

Livestock Production Science, 4 (1977) 57--67 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

57

FEED EVALUATION FOR DAIRY COWS: TESTS ON THE SYSTEM PROPOSED IN THE NETHERLANDS

Y. VAN DER HONING 1, A. STEG' and A.J.H. VAN ES ',2 ' Institute for Animal Feeding and Nutrition Research "Hoorn", Lelystad (The Netherlands) 2 Department o f Animal Physiology, Agricultural University, Wageningen (The Netherlands) (Received 19 July 1976)

ABSTRACT Van der Honing, Y., Steg, A. and Van Es, A.J.H., 1977. Feed evaluation for dairy cows: tests on the system proposed in the Netherlands. Livest. Prod. Sc£, 4: 57--67. The validity of the new Dutch feed evaluation system for dairy cattle was tested by using the results of energy balance experiments in Wageningen and of Scandinavian feeding trials performed by Frederiksen and Dijkstra. From the digestibility in vivo by wethers or in vitro, the metabolizable energy in the ration was predicted as well as the net energy to be produced. In the latter, the net energy for maintenance was assumed to be 70 kcal/kga/~ metabolic body weight. Prediction of energy in milk and energy balance agreed well with the results of energy balance trials with dairy cows fed on winter rations. For fresh grass a discrepancy was found which is not yet explainable, but further research on this subject is in progress. In the feeding trials, the measured average weight change agreed rather well with the predicted energy balance. Finally, the reliability of these methods for testing this new feed evaluation system is discussed.

INTRODUCTION In T h e N e t h e r l a n d s , f e e d e v a l u a t i o n f o r r u m i n a n t s is b a s e d on K e l l n e r ' s s t a r c h e q u i v a l e n t (SE) s y s t e m . In 1 9 7 7 a n e w s y s t e m will be i n t r o d u c e d , w h i c h is b a s e d o n m a n y e n e r g y b a l a n c e d a t a o f t h e l a s t f e w d e c a d e s . T h e r e a s o n s f o r l e a v i n g t h e SE s y s t e m in f a v o u r o f a n e w n e t e n e r g y s y s t e m , esp e c i a l l y f o r d a i r y c o w s , w e r e r e c e n t l y d e s c r i b e d b y V a n Es ( 1 9 7 5 a ) . T h e a p p l i c a b i l i t y o f t h e SE s y s t e m , w h i c h t o a g r e a t e x t e n t is b a s e d o n n e t e n e r g y f o r f a t t e n i n g , has b e e n c h e c k e d b y several a u t h o r s ( F r e d e r i k s e n , Dijkstra, etc. ) using a S c a n d i n a v i a n f e e d i n g t r i a l t e c h n i q u e . U n d e r t h e c o n d i t i o n s o f t h e s e trials, a n d w i t h t h e r a t i o n s t e s t e d , a g o o d a g r e e m e n t w a s f o u n d bet w e e n t h e p r e d i c t e d a n d o b s e r v e d levels o f p r o d u c t i o n . T h e d e r i v e d f e e d i n g standards based on a requirement for maintenance and milk production witho u t b o d y gain or loss w e r e also t h o u g h t t o b e q u i t e c o r r e c t . E x p e r i m e n t s with groups fed above or b e l o w these standards c o n f i r m e d this conclusion, a l t h o u g h t h i s i n t e r p r e t a t i o n was h a m p e r e d b y t h e l o w p r e c i s i o n o f t h e f e e d i n g

58 trials. Because of the assumptions made, for instance with regard to energy gain or loss, which were measured b y weight changes, the experimental errors were n o t well known (Van der Honing and Rijpkema, 1974). In practice, never theless, the results of feeding trials are thought to be of great value to farmers. The introduction of a new feed evaluation system will raise questions about its reliability under different circumstances. As the system was derived mainly from energy balance data, its applicability to different types of rations was studied first. Secondly, an attempt was made to evaluate this system on the basis of many data from earlier feeding trials. MATERIALS AND METHODS

Energy balance data The digestibility of the components of 70 different rations, each fed to 3--6 lactating cows in energy balance trials, was determined with sheep fed at the maintenance level. For ground and pelleted roughages and concentrates the difference-method was used with 200 g of hay as basic feed. If no trial with the concentrates-mixture was available, its digestibility could be calculated from the average digestibility coefficients of the components of the mixture presented in the Dutch feeding table (CVB, 1970). The digestibility of organic matter in vitro from the roughages according to Tilley and Terry was also available (Van der Koelen et al., 1974). For each ration, the prediction of its metabolizable energy and of the utilization of metabolizable energy according to the new feed evaluation system could be compared with the results of the energy balance trials (3--6 cows in each trial).

Feeding trial data Data a b o u t the ration supplied, the milk produced and the b o d y weight and weight change during the trials, which lasted 8--16 weeks, were collected from 138 different groups with a total of 1370 lactating cows in the first part of the lactation. Of these groups, 78 were in trials conducted by Frederiksen (1931); 60 groups were in trials performed at the Institute of Animal Feeding and Nutrition Research " H o o r n " , most of them described by Dijkstra (Anon., 1971). Using digestibility coefficients from sheep trials, or from the Dutch feeding table (CVB, 1970) it was possible to estimate metabolizable energy intake and the net energy to be obtained from it. This predicted net energy was compared with the total net energy used for milk production, maintenance (related to W3A) and b o d y gain or loss.

59 Calculation o f p r e d i c t e d energetic values

Metabolizable energy, M E (the gross energy, I E, minus energy in faeces, urine and methane), was predicted from digestible nutrients, according to the proposal of Van Es (1975b) as follows: C o n c e n tra tes: ME = a.Dxp + b.DxL + c.DxF + d.Dxx

(1)

in which a, b, c and d have the values 3.8, 9.0, 3.3 and 3.5 kcal/g and D is the digestible nutrient specified by the subscript XP, X L , X F and X X for crude protein, ether extract, crude fibre and N-free extract, respectively. For roughages a more simple formula with only digestible organic matter, D 0, and D x p was used. R o ughages: M E = p.D 0 + q . D x p

(2)

with the values 3.4 and 1.4 kcal/g for p and q, respectively. With very low protein concentration in the feedstuff or when no information on D x p is available, the following formula is used: M E = r.D 0

(3)

in which r has the value 3.6 kcal/g. The digestibility in vivo could be derived from the digestibility coefficient in vitro using one of the following regression equations (Van der Koelen and Dijkstra, 1971). Hay, artificially dried grass: d o (vivo) = 0.763 d O (vitro) + 16.67

(3.1)

Silage: d o (vivo) = 0.777 d o (vitro) + 17.11

(3.2)

Fresh or frozen grass: d O (vivo)= 0.850 d o (vitro) + 11.93

(3.3)

The M E predicted by using formula 1 and 2 or 3 refers to the maintenance feeding level. For feeding at a multiple of maintenance, this value has to be de creased by 1.8% if the feeding level is raised by once the maintenance requirement. In formula: ME (production level) = ME (maintenance) ( 1 - 0 " 0 1 8 ( intake o f M E --1)} 117 W 3A

To compute the metabolizable energy concentration in gross energy (q = 100 ME/IE), the gross energy (IE) of concentrates was calculated as: IE = a . I x p + b . I x L + C . I x f + d . I x x

(4)

60 in which a, b, c and d have the values 5.77, 8.74, 5.00 and 4.06 kcal/g according to Schiemann et al. (1971, p.120), whereas for roughages it was derived from

IE = P'/O

(5)

in which p = 4.8 kcal/g according to the proposal of Blaxter (1974). Energy in milk (LE) for the data from feeding trials was calculated from the q u a n t i t y of milk (L) and the percentage of fat in milk, f% by the formula: L E = u-n(0.4+0.15.f%) (6) in which u has the value 730 kcal/kg of fat-corrected milk and the term 0.4 + 0.15.f% (CVB, 1973) is used to correct the milk to a fat concentration of 4%. Net energy for maintenancewas related to metabolic body size (W3A). In the balance experiments a value of 70 kcal/kg3Awas used, whereas in the feeding trial data, both 70 and 77 were applied, accordingto international usage (Schiemann et al., 1971; Ministry of Agriculture, London, 1975) to increase the figure derived from energy balance data by a safety margin for use in practice. Net energy for production (RE +LE) was calculated from ME according to the proposal of Van Es (1975a), assuming that net energy for maintenance per unit metabolic body weight was a constant: (RE + LE) / W3A = (0.60 + 0.0024 (q--57)) M E / W 3A --c = (0.463 + 0.0024 q) ME/W 3/a --c

(7)

in which c has the value 70 (or 77, only for feeding trial data) kcal/kg 3A. From these figures the energy balance (R E) can be derived and compared with the results of the energy balance experiments or the body weight changes in the feeding trials. In the energy balance experiments the rations always consisted of roughage with an addition of a concentrates-mixture. Roughages were grass hay, silage of grass or maize, grass hay with pelleted artificially dried grass or lucerne, or fresh or frozen grass. In the feeding trials rations of roughage made up with concentrates were also used. Most of the roughages were grass hay or silage from wilted or fresh grass and with or w i t h o u t a preservative; some diets included fodder beets or straw. The usual experimental design of a Scandinavian feeding trial is as follows. With 2--4 groups of cows comparable as to milk production, fat and protein concentrations in milk, live weight and b o d y reserves, an experimental period of about eight weeks, in which different treatments are performed, is preceded and followed by a period of four weeks in which both groups receive the same treatment. Before and after the experimental period the live weight is measured on three consecutive days, whereas during the whole trial the milk production and composition are measured each week on at least four days per week. Body weight change (A W) is calculated as the difference in

61 average weight before and after the experimental period. Normally in these feeding trials an a t t e m p t is made to provide as much feed as necessary to maintain b o d y weight. In some trials, however, the experimental group was fed below or above the generally accepted standards for starch equivalent or digestible protein. Because of the high standards for digestible true protein in some of Frederiksen's experiments, it was not t h o u g h t to be necessary to exclude these trials from our evaluation. We estimated that all groups except one received more than 57 g D x p / k g of milk, which is within the range advised by CVB (1973) in The Netherlands. One group received 53 g Dxp/kg of milk, which may be too low for maintaining milk production. RESULTS In the energy balance experiments the prediction of gross energy intake could easily be checked with the values found in the experiments. For the roughages, using equation (5), the prediction led to an average underestimation of 1.4%, varying from 6.0% to an overestimation of 2.4%. In general, the greatest underestimation was with fresh grass and early-cut hay or silage, whereas an overestimation was found mainly with late-cut hay.

Prediction of metabolizable energy Metabolizable energy intake could be predicted in two ways: method (a) based on digestibility of organic matter in vivo by wethers fed at maintenance and m e t h o d (b) based on digestibility of organic matter in vitro of the roughages as described by Van der Koelen et al. (1974). A regression (see equations 3.1 to 3.3) was used to transform this coefficient into a digestibility figure to be found with sheep. Method (a) was used for concentrates here. The results of these methods are presented in Table I. On average for winter rations the ME predicted is about 1% too low. There is hardly any difference between the digestibility figures from the m e t h o d with sheep or in vitro. For the diets with pelleted forages a slightly lower figure was to be expected (Van der Honing, 1975) from the sheep digestibility m e t h o d than from the in vitro method. With the in vitro m e t h o d the predicted value found for the fresh and frozen grass diets was far too low. Because the reason for the discrepancy between this and the other diets was n o t clear, digestibility studies with cattle and sheep fed with grass from the same origin are in progress. Except for the grass it is concluded that on average the prediction of ME is correct with both methods. For pelleted forages the m e t h o d based on digestibility in vitro is preferable, also for reasons described by Van der Honing (1975). However, the correct prediction of ME of individual feedstuffs cannot easily be tested in this way. Only if there is a marked variation with regard to the proportion of high and low digestible feeds or of roughage and concentrates

62 TABLE I Comparison of predicted metabolizable and net energy with the values measured in energy balance experiments with lactating cows Main roughage in diet

Number of diets

Predicted energetic value as a percentage of measured value Metabolizable energy

Net energy

"sheep . . . .

vitro . . . .

cow . . . .

sheep . . . .

vitro"

Hay (long)

19 av. sd.

98.2 2.5

98.0 2.5

99.1 3.2

97.7 4.4

97.4 3.9

Silage

13 av. sd.

97.3 3.6

96.6 4.1

99.6 2.9

97.0 5.7

96.2 6.1

Pelleted forage

27 av. sd.

99.7 3.1

100.8 3.7

99.0 3.3

99.3 4.2

100.5 4.0

All diets

59 av. sd.

98.7 3.1

99.0 3.8

99.2 3.2

98.3 4.6

98.6 4.8

---

87.9 3.6

101.6 3.2

--

87.4 6.2

Grass fresh/frozen

8 av. sd.

can the p r e d i c t i o n be tested t o s o m e extent. In Fig.1 the results are p r e s e n t e d o f a p l o t o f the d i f f e r e n c e b e t w e e n the p r e d i c t e d and the m e a s u r e d M E against the p r o p o r t i o n o f organic m a t t e r as c o n c e n t r a t e s . No definite t r e n d is f o u n d in the figure e x c e p t for the diets with pelleted forages w h i c h have generally a less negative d e v i a t i o n t h a n t h o s e with h a y or silage in long f o r m . T h u s there is no definite i n d i c a t i o n t h a t roughages are o v e r e s t i m a t e d a n d c o n c e n trates u n d e r e s t i m a t e d or the reverse. P r e d i c t i o n o f n e t e n e r g y in balance trials

The validity o f e q u a t i o n (7) c o u l d be tested b y p r e d i c t i n g t h e n e t energy t h a t h a d t o be f o u n d f r o m the M E m e a s u r e d in e x p e r i m e n t s with c o w s ( " c o w " m e t h o d in Table I). P r e d i c t i o n o f n e t e n e r g y f r o m digestible organic m a t t e r c o u l d be evaluated in t w o steps: (1) p r e d i c t i o n o f m e t a b o l i z a b l e energy (see a b o v e section), and (2) p r e d i c t i o n o f utilisation o f M E (relation as expressed in e q u a t i o n ( 7 ) ) . A d e v i a t i o n o f the p r e d i c t e d M E value f r o m the m e a s u r e d M E m i g h t be (partly) c o m p e n s a t e d b y step 2 w h e n n e t e n e r g y is p r e d i c t e d f r o m digestible nutrients. B o t h steps, including p r e d i c t i o n o f M E b y m e t h o d (a) or (b), were t e s t e d b y using e q u a t i o n (7) t o calculate the p r e d i c t e d n e t e n e r g y f r o m the p r e d i c t e d M E at t h e p r o d u c t i o n feeding level (indicated b y m e t h o d s " s h e e p " and " v i t r o " , respectively). In these calculations the net e n e r g y for m a i n t e n a n c e was a s s u m e d t o be 70 k c a l / k g 3A.

63

llc~ i,tl ],,]~ ,~t p r c d i , l ~ ] !,It

iI'*~H,

•

+

+

o

o~°

o

• 0

+

•

+

•

4o

0 •

0 o

+

0

O ÷

~rJ

I

0 o

+

0

I

o

+ + 00

00

'~/'1

0

0

• g°

I

I

I

I

÷

:LJ:,~,

1~ +M

4 L:L?
I

I

I

I

Fig. 1. Relation between the difference in predicted metabolizable energy, ME, using digestible organic matter in vitro, from measured M~:,and the proportion of concentrates in the diet (organic matter basis).

As shown in Table I the " c o w " m e t h o d resulted on average in an accurate prediction o f net energy, for the winter diets as well as for the grass rations. With the " s h e e p " and " v i t r o " m e t hods of prediction som ew hat greater deviations were found, but this was caused mainly by a difference between predicted and measured ME, rather than a difference in utilization of M E. No direct relationship was f ound bet w e e n the deviation from the measured net energy and the p r o p o r t i o n of concentrates varying from 25 to 73% of I O or the t y p e of roughage in the diet. F r o m these calculations it is concluded t hat the prediction with the proposed feed evaluation system will result on average in only a small difference (less than 2--3%) from the actual energetic value f o u n d in balance trials.

Evaluation with the results o f feeding trials In practice great value is attached to the results of feeding trials with regard to feeding standards and feed evaluation. Although these trials were p e r f o r m e d under conditions very close to those in m any farms in our c o u n t r y , t hey are n o t as accurate as the energy balance experiments because energy balance of the animals has to be derived f r om changes in b o d y weight in the feeding trial and c a n n o t be calculated f r o m C and N-balances as in the energy balance experiments. When the experimental period is n o t t oo short and enough animals

64

are used in each group, the Scandinavian feeding trial may be used to study the utilization of feed if some assumptions about the energetic value of weight changes are made. In Table II the results of the energy balance, calculated with values of 70 and 77 kcal/W 3A for the maintenance requirement, are compared with the weight change during the experiment. The animals were weighed on three consecutive days before and after the experimental period, and so the variation due to differences in gut fill as a result of incidental drinking or loss of faeces or urine will have been excluded partly. Individual variation, moreover, is reduced because an average of 12--14 cows was used in these calculations. On average, and for the separate experiments of Frederiksen and Dijkstra as well, there is good agreement between the energy balance calculated with a maintenance requirement of 70 kcal/kg 3A and the weight change measured in the experiment, although the standard deviation is too high to obtain a perfectly clear conclusion. On the other hand, there is also good agreement between these items in those trials in which feed was supplied above or below standards instead of according to the energetic standards. The correlation coefficient between energy balance and weight change in the Frederiksen material was 0.48 and in the Dijkstra material 0.37, whereas in the total it was 0.41. Although, in general, an energetic concentration of 4000--6000 kcal per kg of body gain or loss is assumed in a dairy cow, it is difficult to obtain this value from our calculations from these feeding trials because the experimental error is high, which will result in increased variation and a less correct figure for energy per kg of weight change. However, a value of 70 kcal/kg 3A gave a better agreement than 77 kcal/kg 3A between weight changes and energy balance predicted. DISCUSSION

Contrary to the feeding trials of Frederiksen and Dijkstra, the energy balance experiments included a greater variability in composition of the ration with regard to different types of forage and the proportion of concentrates in the diet. Hay, silage and processed forages such as pellets, all harvested at different stages of maturity and covering a wide range of digestibilities, were used in rations for dairy cows in various parts of the lactation, and with high and low milk production. Hence the evaluated feeding system, as described before, will be valid over a wide range of rations. This may also be true because the equation describing the utilization of M E was based on many data from experiments performed mainly in Beltsville, Wageningen and Rostock. In addition, the prediction of M E was derived from digestibility data from wethers and dry cows fed at the maintenance level of feeding (Van Es, 1975b). In this evaluation, however, the basic figures used to predict M E of forages, like the digestibility coefficient of organic matter, found from wethers or from fermentation in vitro, are n o t free from errors. The same is true for the digestible nutrients of the concentrates, which were calculated from the average figures of the components in the mixture from the Dutch feeding table.

II

No. o f

3 3 4 3 78

60

85%ofSE* 100%ofSE*

100% of SE 120% of SE

All g r o u p s

All g r o u p s

av. sd.

D av. sd.

F av. sd.

D D

D D

F F F

F F F

Author

aw

32 65 189

--

--

31 186

16 236

68 125

42 169

-- 200 -91

-- 192 23 142

--

(g/day)

981 488 2342

689 594 2477

--

--

375 1166

22 1106

680 1125

369 1719

-- 1614 114

--

--

(kcal/d)

RE(70)

--

--

337 1177

769 1104

5 1129

-- 1072 979

- 2353 -608

-- 1643 -183 1664

-- 1370 -95 1794

(kcal/d)

RE ( 7 7 )

11127 1610

12424 1168

10130 1118

12465 13313

12790 14157

10405 10620 11408

9495 10160 11051

(kcal/d)

LE

33029 3269

35224 2314

31341 2877

35058 39782

33002 38209

28642 31639 36434

27800 31383 36229

(kcal/d)

M~

* F e e d i n g w a s a i m e d a t s u p p o r t i n g a c e r t a i n a m o u n t o f t h e u s u a l s t a n d a r d s f o r s t a r c h e q u i v a l e n t (SE). **In these experiments both protein and starch equivalent standards were the subject of study.

138

5 5 5

80% of SE 100% of SE 120% of SE

Total

6 6 6

groups

Below standards** At standards** Above standards**

Treatment

T h e w e i g h t c h a n g e ( A w ) , p r e d i c t e d e n e r g y b a l a n c e (RE) c a l c u l a t e d w i t h 7 0 a n d 77 k c a l / k g 3A, e n e r g y in m i l k (LE) a n d p r e d i c t e d m e t a b o l i z a b l e e n e r g y (ME) o f 78 g r o u p s o f c o w s in f e e d i n g trials p e r f o r m e d b y F r e d e r i k s e n ( F ) a n d 6 0 g r o u p s b y D i j k s t r a ( D )

TABLE

ol

66

O f c o u r s e , t h e m e a s u r e d m e t a b o l i z a b l e a n d n e t e n e r g y f i g u r e s in t h e b a l a n c e e x p e r i m e n t s a r e n o t f r e e f r o m e r r o r e i t h e r , a l t h o u g h s u c h e r r o r s m a y b e expected to be smaller than those from the earlier mentioned data. Therefore a n a v e r a g e d e v i a t i o n b e t w e e n p r e d i c t e d a n d m e a s u r e d e n e r g e t i c v a l u e s as s m a l l as t h a t f o u n d in T a b l e I s u p p o r t s t h e v a l i d i t y o f t h e p r o p o s e d f e e d e v a l u ation system. T h e e n e r g e t i c f e e d e v a l u a t i o n o f f r e s h grass is n o t c o m p l e t e l y s o l v e d . In p r a c t i c e o n e c o u l d d e c i d e t o i n c r e a s e t h e M E p r e d i c t e d f r o m d i g e s t i b i l i t y in vitro by about 10% to reduce the discrepancy. It will be some time before the e x p l a n a t i o n c a n b e given.

REFERENCES Anonymous, 1971. Lijst van publikaties van Dr. N.D. Dijkstra. Landbouwk. Tijdschr., 83: 309. Blaxter, K . L , 1974. Metabolizable energy and feeding systems for ruminants. Proc. Nutr. Conf. Feed Manuf., Nottingham, pp. 3--25. CVB, 1970. Veevoedertabel. Gegevens over voederwaarde, verteerbaarheid en samenstelling. Centraal Veevoederbureau in Nederland, Wageningen, 69 pp. CVB, 1973. Voedernormen voor de landbouwhuisdieren en voederwaarde der veevoeders (1973). Centraal Veevoederbureau in Nederland, Lelystad, 32 pp. Frederiksen, L., 1931. Varierede foder- og proteinmaengder til maelke produktion. 136 Beretning Fra Fors~bgslab., Kdbenhavn. Ministry of Agriculture, Fisheries and Food, 1975. Energy allowances and feeding systems for ruminants. Tech. Bull., Minist. Agric. Fish. Food, 33. Her Majesty's Stationery Office, London, 79 pp. Schiemann, R., Nehring, K., Hoffmann, L., Jentsch, W. and Chudy, A., 1971. Energetische Futterbewertung und Energienormen. VEB Deutscher Landwirtschaftsverlag, Berlin, 344 pp Van der Honing, Y., 1975. Intake and utilization of energy of rations with pelleted forages by dairy cows. Agric. Res. Rep., Cent. Landbouwpubl. Landbouwdoc., Wageningen, 836, 156 pp. Van der Honing, Y. and Rijpkema, Y.S., 1974. Vergelijking van kunstmatig gedroogd gras met hooi in rantsoenen voor melkvee door middel van een voederproef en energiebalansproeven. Agric. Res. Rep., Cent. Landbouwpubl. Landbouwdoc., Wageningen, 820, 48 pp. Van der Koelen, C.J. and Dijkstra, N.D., 1971. Bepaling van de verteerbaarheid in vitro als hulpmiddel bij de schatting van de voederwaarde van ruwvoeders. Landbouwk. Tijdschr., 83: 494--499. Van der Koelen, C.J., Kemmink, A. and Dijkstra, N.D., 1974. Determination of the nutritive value of roughages by the 'in vitro' digestibility method. Intern rapport, Instituut voor Veevoedingsonderzoek "Hoorn", nr. 70, 20 pp. Van Es, A.J.H., 1975a. Feed evaluation for dairy cows. Livest. Prod. Sci., 2 : 9 5 107. Van Es, A.J.H., 1975b. Discussion paper on energy utilization by ruminants. Mimeographed paper (17 pp).

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RESUME Van der Honing, Y., Steg, A. et V a n Es, A.J.H., 1977. E v a l u a t i o n des a l i m e n t s p o u r les vaches laiti~res: v e r i f i c a t i o n du s y s t 0 m e p r o p o s ~ a u x Pays-Bas. Livest. Prod. Sci., 4: 5 7 - - 6 7 (en anglais). La validit6 du n o u v e a u syst~me d ' ~ v a l u a t i o n des a l i m e n t s p o u r le b~tail laitier p r o p o s ~ aux Pays-Bas, a ~t~ test~e h p a r t i r des r~sultats des bilans ~nerg~tiques mesur~s ~ Wageningen et des essais d ' a l i m e n t a t i o n de t y p e s c a n d i n a v e r~alis~s par F r e d e r i k s e n et p a r Dijkstra. A p a r t i r des m e s u r e s de digestibilit~ in vivo (sur des b~liers) ou in vitro, o n a ~valu~ ia t e n e u r en ~nergie m ~ t a b o l i s a b l e de la r a t i o n , de m ~ m e q u e sa valeur ~ n e r g 6 t i q u e n e t t e p o u r la prod u c t i o n , en a d m e t t a n t u n b e s o m e n e r g e t l q u e d e n t r e t m n de 70 kcal/kg ¼ de p o i d s vif. Les e s t i m a t i o n s ainsi o b t e n u e s p o u r la q u a n t i t ~ d'~nergie secr~t~e d a n s le lait et p o u r le bilan 6nerg~tique, o n t 6t~ en b o n a c c o r d avec les r~sultats des m e s u r e s de bilan ~nerg~tiques des vaches laiti~res r e c e v a n t des r a t i o n s hivernales. Avec l ' h e r b e fraiche l ' a c c o r d ~tait m o i n s b o n ; nouvelles r e c h e r c h e s s o n t e n r o u t e . Dans les essais d ' a l i m e n t a t i o n , les v a r i a t i o n s ( m o y e n n e s ) de p o i d s vifs observ~es o n t 6t6 e n assez b o n a c c o r d avec les valeurs pr~vues du bilan ~nerg& tique. La valeur de ces m ~ t h o d e s p o u r appr~cier le n o u v e a u syst~me d ' ~ v a l u a t i o n des alim e n t s est discut6e. .

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KURZFASSUNG V a n der Honing, Y., Steg, A. u n d V a n Es, A.J.H., 1977. F u t t e r b e w e r t u n g filr Milchk(ihe: Priifung des in d e n N i e d e r l a n d e n v o r g e s c h l a g e n e n Systems. Livest. Prod. Sci., 4 : 5 7 - 6 7 (in Englisch ). Die Giiltigkeit eines n e u e n F u t t e r b e w e r t u n g s s y s t e m s fiir Milchkiihe w u r d e gepriift an Ergebnisse v o n 351 E n e r g i e b a l a n z e n in W a g e n i n g e n u n d v o n 138 s k a n d i n a v i s c h e n F i i t t e r u n g s v e r s u c h e n y o n F r e d e r i k s e n u n d Dijkstra. Es war mSglich d e n G e h a l t a n u m s e t z b a r e r Energie u n d a n N e t t o Energie in der R a t i o n v o r h e r z u s a g e n aus E r g e b n i s s e n fiber die V e r d a u l i c h k e i t bei H a m m e l n ( e t w a E r h a l t u n g s f i i t t e r u n g s n i v e a u ) o d e r fiber die in vitro g e m e s s e n e Verdaul i c h k e i t n a c h Tilley u n d Terry. Dabei w u r d e a n g e n o m m e n dass ffir E r h a l t u n g e t w a 70 kcal N e t t o Energie p r o kg 3/~ K S r p e r g e w i c h t nStig war. Die in dieser Weise v o r h e r g e s a g t e Milchenergie u n d E n e r g i e b i l a n z e n w a r e n in g u t e m E i n k l a n g m i t d e n E r g e b n i s s e n der Bilanzvers u c h e n m i t M i l c h k f i h e n a u f W i n t e r r a t i o n e n (Heu o d e r Silage plus K r a f t f u t t e r ) . Frisches Weidegras gab eine n o c h n i c h t zu erkl~iren Differenz y o n e t w a 10%. Neue V e r s u c h e m i t Gras sind s c h o n geplant. B e r e c h n u n g e n a n E r g e b n i s s e n der F f i t t e r u n g s v e r s u c h e zeigten eine z i e m l i c h g u t e U b e r e i n s t i m m u n g z w i s c h e n der m i t t l e r e n G e w i c h t s i i n d e r u n g u n d d e m n a c h d e m n e u e n B e w e r t u n g s s y s t e m s geschiitzten Energiebilanz. Z u m Schluss w u r d e die Genauigkeit dieser P r i i f u n g s m e t h o d e n des n e u e n F u t t e r b e w e r t u n g s s y s t e m s diskutiert.