Sodium Bicarbonate for Early Lactation Cows Fed Corn Silage or Hay Crop Silage-Based Diets1

Sodium Bicarbonate for Early Lactation Cows Fed Corn Silage or Hay Crop Silage-Based Diets * C. J. C A N A L E 2 and M. R. STOKES Department of Animal and Veterinary Sciences University of Maine Orono 04469 ABSTRACT

To compare the effects of NaHCO3 in diets based on different forage sources, 16 Holstein cows, in a split-plot design, were assigned at 2 d postpartum to a total mixed diet of either 30% hay crop silage:70% concentrate or 40% corn silage:60% concentrate (dry basis) that contained 0 or 1.25% NaHCO3. Over the first 6 wk postpartum, NaHC03 increased milk fat percentage in cows fed the corn silage-based diet. During wk 2 through 6 postpartum, NaHCO3 increased milk yield with the hay crop silage-based diet and tended to decrease milk yield with the corn silage-based diet. Sodium bicarbonate increased digestion of NDF with both forages and increased excretion of urinary nitrogen with the corn silagebased diet. Responses to NaHC03 by cows in early lactation may depend on the nature of the dietary forage component. INTRODUCTION

High concentrate diets contain large amounts of readily fermentable carbohydrate and low amounts of effective fiber. Furthermore, these diets ferment rapidly in the rumen and produce a low rumen pH, which is associated with altered patterns of rumen fermentation, reduced digestibility of fiber, and depressed production of milk fat (6). Such effects can be acute in early lactation when animals are abruptly switched from a prepartum diet of high forage to a postpartum diet of high con-

Received February 25, 1987. Accepted September 10, 1987. 1Maine Agricultural Experiment Station Publication Number 1196. 2 Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802.

1988 J Dairy Sci 71:373-380

centrate. Under these conditions, adaptation to high concentrate feeding has been aided by supplementary mineral salts, primarily NaHCO3. With diets containing corn silage (CS) as the sole or major source of forage, NaHCO3 alone, or with MgO, has increased DM intake and milk production (11, 16, 22), and milk fat percentage or FCM yield (12). Some studies have associated NaHCO3 supplementation with increased rumen fluid pH, increased proportion of rumen acetate relative to propionate, and improved digestibility of DM or fiber (12, 21, 26). In addition, positive responses in later lactation (26) suggest benefits even when rations are not abruptly switched. In some studies with high concentrate diets based on hay crop silage (HCS), alfalfa hay, hay and sugar beet pulp, or grass-legume pasture, NaHCO3 alone or in buffer combinations has not improved DM intake, milk production, or milk composition (7, 10, 14, 19, 23, 27, 28). In one commercial herd where diets were based on alfalfa hay, .8% NaHCO3 reduced milk yield in second lactation and older animals (4). Increased yields of milk constituents have been observed with buffered diets of coastal bermudagrass (17), grass silage (15), and grass hay (19) when control milk fat percentage was depressed by low dietary fiber. Increased milk yields were also reported with NaHCO3 supplementation of an alfalfa hay-based diet in a high producing commercial herd subjected to the additional metabolic stress of milking three times daily (4). Although the effects of buffers have been investigated with diets containing a range of forages and forage mixtures, we were not aware of any reports where effects with different individual forage sources had been compared under the same management system. Our objective was to determine the effects on performance, digestion, and N utilization of early lactation cows when 1.25% NaHCO3 was added to high concentrate diets that

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CANALE AND STOKES

c o n t a i n e d either HCS or CS as t h e sole source o f forage in each diet.

MATERIALS AND METHODS

S i x t e e n H o l s t e i n cows w e r e assigned to t o t a l m i x e d diets consisting o f e i t h e r 30% H C S : 7 0 % c o n c e n t r a t e o r 40% CS:60% c o n c e n t r a t e (DM basis). Cows were assigned to blocks b a s e d o n t h e n u m b e r o f their previous l a c t a t i o n s ; o n e block o f eight cows had previously c o m p l e t e d o n e l a c t a t i o n and t h e s e c o n d b l o c k had completed at least t w o l a c t a t i o n s (average 2.9 lactations). Within blocks, cows were r a n d o m l y assigned t o either a c o n t r o l diet or t o t h e s a m e diet s u p p l e m e n t e d w i t h 1.25% NaHCOa (total diet, DM basis). I n g r e d i e n t and c h e m i c a l c o m p o s i t i o n o f t o t a l m i x e d diets is in Table 1.

Diets w e r e f o r m u l a t e d to b e i s o n i t r o g e n o u s and isocaloric in NE l. As s a m p l e d , d i e t s w e r e similar in NE 1 b u t CP c o n t e n t s d i f f e r e d b y 1 t o 1.3%. Each diet e x c e e d e d n u t r i e n t r e c o m m e n d a t i o n s (18) for cows w e i g h i n g in excess o f 700 kg and p r o d u c i n g 35 k g / d milk w i t h t h e e x c e p t i o n s t h a t A D F and NE 1 w e r e marginally low. Beginning 3 w k p r e p a r t u m , c o w s w e r e f e d 2.3 k g / d g r o u n d c o r n plus HCS to m e e t e n e r g y r e c o m m e n d a t i o n s (18) and w e r e t h e n a b r u p t l y s w i t c h e d at 2 d p o s t p a r t u m to an e x p e r i m e n t a l diet. C o m p l e t e diets w e r e h a n d m i x e d and fed individually o n c e daily at 12 00 h for t h e first 7 wk o f lactation. A n i m a l s w e r e fed ad l i b i t u m t h r o u g h wk 5 o f l a c t a t i o n in a m o u n t s s u f f i c i e n t to p r o v i d e at least 10% refusal• During w k 6 and 7, f e e d o f f e r e d was m a i n t a i n e d c o n s t a n t at t h e m a x i m u m intake a t t a i n e d b y wk 5 in

TABLE 1. Ingredient and chemical composition of total mixed diets (% of dry matter except as noted). Corn silage diets

Hay crop silage diets Item

0% NaHCO a

1.25% NaHCO a

0% NaHCOa

30

40 6.5 18.0 23.6 8.9 1.2 .9 ,6 .10 .20

18.4 16.7 37.1 13.9 91.3 4.48 1,00 .64 1,38 .32 .29 1.63

Ingredients: Hay crop silage Corn silage Ground corn Potato meal Soybean meal Ground oats Legumin 1 Limestone Salt Magnesium oxide Vitamin D premix 2 Sodium bicarbonate

2111 20.7 18.1 6.9 1.4 .7 .7 .12 .24 ...

30 ... 19.7 20.7 18.3 6.9 1.4 .7 .7 .12 .24 1.25

Chemical analysis: Cru de pro tein Acid detergent fiber Neutral detergent fiber Cellulose Organic matter Ether extract Calcium Phosphorus Potassium Magnesium Sulfur Net energy for lactation, a Mcal/kg

17.1 17.3 33.3 13.7 88.6 2.33 .88 .50 1.29 .28 .25 1.61

17.1 18.4 34.4 14.9 89.6 3.25 .81 .50 1.35 .26 .28 1.58

i Dairy mineral mixture with vitamins, Agway Inc., Syracuse, NY. 2 Provided 2.2 × 10 6 IU vitamin Da/kg premix. s Estimated from acid detergent fiber (1). Journal of Dairy Science Vol. 71, No. 2, 1988

1.25% NaHCO3

5.13 18.0 23.8 8.9 1.2 .9 .6 .10 .20 1.25 18.1 16.9 38.7 13.9 90.7 4.52 .98 .67 1.17 .34 .29 1.65

SODIUM BICARBONATE WITH SILAGE DIETS order to minimize variation in fecal output during the digestibility trial, which was conducted during wk 7. A controlled daily photoperiod of 16 h light:8 h dark was maintained in an attempt to reduce variation in milk yield caused by a changing natural photoperiod. Samples of forage and concentrates were taken twice weekly for DM analysis and subsamples were composited for later analysis. The proportion of forage to concentrate, as fed, was adjusted weekly to maintain the appropriate DM ratios of forage:concentrate. Orts were measured daily and sampled twice weekly to determine DM intake. Milk production and feed intake were recorded daily and body weights twice weekly from 2 d postpartum. Beginning 5 d postpartum, milk was sampled at consecutive p.m. and a.m. milkings twice weekly, cornposited in proportion to volume, and analyzed for fat (Babcock procedure), CP (Kjeldahl N X 6.38), and SNF (Golding Bead Test). Fresh rectal grab samples of feces were taken once weekly beginning 5 d postpartum for pH measurement by glass electrode. All cows underwent a 7-d total collection digestibility trial during wk 7 of lactation. Feces and urine were collected as described by (12) except that fecal pans were not lined with polyethylene sheets. A fresh urine sample was taken daily for pH measurement. For digestibility measurements, daily samples of feeds and orts were taken beginning 2 d prior to excreta collection and were composited through d 5 of the collection. Wet subsamples of feeds, orts, and feces were analyzed for DM and CP while the remainder was oven dried at 60°C for 48 h, ground through a 1-mm screen, and stored for later analysis. Dry matter of concentrates and feces was determined by drying at 102°C (2) whereas DM of orts and forages was determined by toluene distillation (8). Crude protein was determined on wet samples of feeds, orts, feces, and urine by Kjeldahl procedure (2). Dried feeds, orts, and feces were analyzed for ADF, NDF, acid detergent lignin (13), gross energy, ash, and ether extract (2). Two composite samples of each forage and concentrate were sent to the New York Forage Testing Laboratory, Ithaca, NY, for determination of mineral composition. Net energy content of total mixed diets were predicted from ADF percentage (1).

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The effects of NaHCO3 in diets based on different forage sources were evaluated in a 2 x 2 factorial arrangement of treatments in a completely randomized block design incorporating a split-plot design over time. Effects of block, forage source, buffer, and their interactions were main plots with week postpartum and its interactions with forage and buffer as subplots. Cow interaction effects were used as the error term to test main effects. Data were analyzed by analysis of variance using the General Linear Model procedure of the Statistical Analysis System (25). Previous lactation mature equivalent 305 d milk production did not significantly contribute to the model (P>.I) when included as a covariable for the analysis of milk yield and composition. Production data are therefore reported as unadjusted least squares means. RESULTS A N D DISCUSSION

Over the first 6 wk of lactation, NaHCO3 increased (P<.09) mean milk fat percentage of cows fed the CS-based diet (Table 2). With the control CS-based diet, milk fat percentage was depressed from wk 2 of lactation and reached a m i n i m u m of 2.4% at wk 6 (Figure 1). Supplementation with NaHCO3 maintained milk fat percentage above 3.45% for the entire experiment and, by wk 6, the improvement in fat percentage approached 50% of the control value (2.42 vs. 3.60). Similar effects were observed when CS-based diets were supplemented with NaHCO3 and/or MgO (12). In cows fed the HCS-based diet, NaHCO3 increased (P<.02) yield of milk by an average of 3.6 kg/d (Figure 2) during wk 2 through 6. In contrast, with the CS-based diet, NaHCO3 reduced milk yield by 3 kg/d during wk 3 through 6. With CS-based diets, NaHCO3 reduced milk yield in early lactation when control milk fat percentage was depressed (12) but increased milk yield when milk fat percentage was normal (11, 30). With the HCS-based diet, total fat yield was not increased because of a nonsignificant reduction in milk fat percentage (from 3.50 to 3.24%) in response to increased milk yield. In short-term studies with s~imilar diets based on 30% HCS (27, 28), DM intake and milk yield were not significantly affected by .4 or .7%

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CANALE AND STOKES

TABLE 2. Effect of sodium bicarbonate on dry matter intake, milk production, and body weight. Hay crop silage

Corn silage

0% NaHCO 3

1.25% NaHCO 3

0% NaHCO 3

1.25% NaHCO 3

Dry matter intake: kg/d % Body weight

17.4 3.15

18.7 3.26

16.4 3.02

19.4 3.37

.29 .05

Yields, kg/d of: Milk Fat CP SNF SCM 3.5% FCM

31.2 1.09 .90 2.70 28.8 31.2

33.9 1.08 .99 2.92 29.9 32.1

35.1 1.00 1.01 3.00 29.4 31.4

33.4 1.21 1.03 3.03 32.3 34.1

.54 .03 .02 .03 .62 .70

3.50 2.91 8.68

3.26 2.97 8.67

2.98 2.95 8.60

3.68 3.12 9.08

Item

Milk composition, %: Fat CP SNF Body weight, kg

550

569

SE

.11 a .03 .03 3.58

574

546

asignificant effect of buffer supplementation with the corn silage diet (P<.09).

N a H C O 3 , b u t milk fat percentage was reduced in r e s p o n s e t o i n c r e a s e d m i l k yield ( 2 7 ) . C o n c e n t r a t i o n s o f N a H C O 3 o f .7 t o 1.4% did n o t i n c r e a s e D M i n t a k e , m i l k yield, o r m i l k f a t p e r c e n t a g e w i t h d i e t s b a s e d o n alfalfa h a y (7,

10, 2 3 ) , h a y a n d s u g a r b e e t p u l p ( 1 4 ) , g r a s s silage (9), o r g r a s s - c l o v e r p a s t u r e ( 1 9 ) . I n c r e a s e d yields o f FCM, solids-corrected milk or milk fat, a s s o c i a t e d w i t h i n c r e a s e d p e r c e n t a g e s o f milk fat or milk S N F have been r e p o r t e d w i t h

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Figure 1. Mean milk fat percentages through 6 wk postpartum of cows receiving diets based on hay crop silage (control - - o - -, 1.25% NaHCO 3 - - • --), and corn silage (control - - D - -, 1.25% NaHCO 3 --

•

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Journal of Dairy Science Vot. 71, No. 2, 1988

21

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11C r.

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2

3

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WEEK POSTPARTUM Figure 2. Mean milk yields through 6 wk postpartum of cows receiving diets based on hay crop silage (control - - o - -, 1.25% NaHCOz - - • - -), and corn silage (control - - D - -, 1.25% NaHCO 3 - - • --). Significant effect of buffer supplementation with the hay crop silage based diet, wk 2 to 6, P<.02.

SODIUM BICARBONATE WITH SILAGE DIETS NaHCO3 supplementation of diets containing coastal bermudagrass (17), grass silage (15), and grass hay (9). Yields of milk were reported to both increase and decrease when two commercial herds were fed alfalfa hay-based diets supplemented with NaHCO3 (4). Buffer supplementation tended to increase ( P < . l l ) mean DM intake of the CS-based diet but had no effect on the composition of nonfat milk components or body weight of animals fed either forage type (Table 2). With the CSbased diet, NaHCO3 improved yields of SCM and FCM by 10 and 8%, respectively, because of a 23% increase in milk fat percentage (from 2.98 to 3.68%) and a 6% improvement in milk CP percentage (from 2.95 to 3.12%). Significant increases in DM intake were observed with 1.2 and 1.5% NaHCO~ in CS-based diets (11, 16), but many studies report no significant changes in DM intake (5, 12, 21, 22, 26, 30). Increases in milk yield of 1.3 to 2.8 kg/d (5, 11, 16, 22, 26) have not always been significant (5, 11). Improvements in milk fat percentage, with resulting increases in FCM yields, have been reported when control milk fat tests were below 3.3% (12, 21, 26) with greatest effects occurring when fat test was below 3.0%. Even w i t h moderately depressed milk fat percentages, NaHCO3 has not always increased milk fat test (22), but in this case, yields of milk fat and FCM were increased due to greater total milk yield. Thus, when milk fat percentages were moderately to severely depressed by feeding a diet low in fiber (with or without CS), NaHCO 3 usually increased milk fat percentage and yields of milk fat and FCM with little effect on DM intake. When fat test was not depressed, as was often the case with diets based on forages other than CS, NaHCO3 has had little effect on milk fat percentage but has increased DM intake and milk yield. Patterns of body weight change over time (Figure 3) were not significantly affected by buffer treatment for either forage. However, relationships were evident between the patterns of weight change, DM intake, and milk yield. Cows fed the unbuffered CS-based diet had the lowest DM intakes through wk 3 of lactation and lost more weight in this period than the other groups. Furthermore, these cows gained more weight than the other groups during wk 3 through 6, at which time these cows also produced the greatest milk yields and the

377

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560

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WEEK POSTPARTUH

Figure 3. Mean body weights through 6 wk postpartum of cows receiving diets based on hay crop silage (control - - o - -, 1.25% NaHCO3 - - • - -), and corn silage (control - - [] - -, 1.25% NaHCOz - -= - -).

lowest milk fat percentages. A similar pattern of body weight loss and milk fatpercentage was observed in cows fed 1% NaHCO3 in a CS-based diet (12). This suggests that rumen fermentation in these animals was characterized by a high proportion of propionic acid, which is associated with severe milk fat depression (6) and with high activities of enzymes involved with adipose tissue lipogenesis (3). Digestion Measurements

Table 3 shows the effects of forage source and NaHCO3 on fecal pH and nutrient digestibility. Apparent digestibility of the CS-based diet was greater than digestibility of the HCSbased diet for cell solubles (P<.10), organic matter (OM), energy, NDF (P<.05), CP, and ether extract (P<.01), but fecal pH did not differ. Fecal pH was not affected by NaHCO3 with either diet, which agrees with other studies where NaHCO3 was added to HCS- or CSbased diets (11, 12, 16, 22, 28, 30). Buffer supplementation of both diets increased (P<.10) digestibility of NDF but did not significantly affect the digestion of other nutrients. With diets based on alfalfa~hay (7, 10) or HCS (27), .25% to 1.2% NaHCO3 did not affect nutrient digestion. However, 1.4% NaHCO 3 increased digestibility of DM, OM, and CP with an alfalfa Journal of Dairy Science Vol. 71, No. 2, 1988

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CANALE AND STOKES

TABLE 3. Effect of sodium bicarbonate on fecal pH and nutrient digestibility. Hay crop silage Item

0% NaHCO 3

Fecal pH 6.24 Apparent digestibility, % of: DM 72.3 Organic matter 72.3 Cell solubles 79:8 Energy 69.8 CP 70.9 Ether extract 61.2 NDF 56.3 ADF 43.8 Cellulose 49.8 Hemicellulose 68.1

1.25% NaHCO 3 6.21 72.3 72.5 79.6 69.8 70.5 65.3 57.7 49.9 55.9 66.4

Corn silage 0% NaHCO~ 6.25 73.6 74.8 82.5 73.3 76.9 83.4 57.9 44.8 50.3 68.4

1.25% NaHCO 3 6.28 73.2 74.8 80.9 72.4 73.6 85.5 61.3 48.8 53.2 70.9

SE .02 .88 .87 b 1.01 a .87 b .97 c 2.07 c .78 bd 1.73 1.91 1.01

a 'b c' Slgnlflcant . . . effects of forage source: a, P<.IO; b, P<.05; c, P<.01. dsignificant effect of buffer supplementation (P<.IO).

h a y - b a s e d diet (23). S o d i u m b i c a r b o n a t e ' s lack o f e f f e c t o n d i g e s t i o n w i t h s o m e alfalfa haybased diets m a y b e d u e to a higher r u m e n pH, w h i c h was r e p o r t e d w i t h t h o s e diets, or t o t h e l o w e r NaHCO3 s u p p l e m e n t a t i o n , since 1.2% NaHCO3 t e n d e d to increase f i b e r d i g e s t i o n (7). Improved digestion of NDF and ADF with NaHCO3 s u p p l e m e n t a t i o n o f CS-based d i e t s has b e e n o b s e r v e d in several studies (12, 21, 26). Increased DM d i g e s t i b i l i t y was r e p o r t e d w i t h a 75% c o n c e n t r a t e a n d 25% CS diet supplem e n t e d w i t h 2% NaHCO3 (20). A r e d u c e d flow o f DM and A D F at t h e d u o d e n u m , a s s o c i a t e d w i t h increased t o t a l t r a c t digestibility o f A D F , was o b s e r v e d in cows fed a 60% c o n c e n t r a t e CS-based diet plus .8% NaHCO3 (29). However, b e n e f i t s were g r e a t e r w h e n MgO was i n c l u d e d in t h e diet. Nitrogen Utilization

Effects o f diet a n d N a H C O 3 o n N u t i l i z a t i o n d u r i n g w k 7 of l a c t a t i o n are in T a b l e 4. U r i n a r y N loss (g/d) was g r e a t e r w i t h t h e CS-based diet (P<.O1), possibly d u e to t h e greater digestibility of CP w i t h this diet. As a p r o p o r t i o n o f N intake, a d d i t i o n a l N was lost in u r i n e ( P < . 0 5 ) w h e n t h e CS-based diet was supp l e m e n t e d w i t h N a H C O 3 . As a result, productive N (milk plus tissue) and tissue N b a l a n c e were r e d u c e d b y NaHCO3 a d d i t i o n ( P < . 0 1 , P < . I O , respectively). S o d i u m bicarJournal of Dairy Science Vol. 71, No. 2, 1988

b o n a t e increased u r i n a r y N losses w i t h a 50% c o n c e n t r a t e CS-based diet (26) b u t h a d n o e f f e c t o n N p a r t i t i o n in cows or steers (12, 20). U r i n e pH was n o t a f f e c t e d b y N a H C O 3 w i t h e i t h e r diet, w h i c h agrees w i t h p r e v i o u s r e p o r t s (10, 11, 28, 30). CONCLUSIONS

A l t h o u g h t h e t w o basal diets were d e s i g n e d to b e very similar in n u t r i e n t d e n s i t y , t h e y were c o n s u m e d in d i f f e r e n t a m o u n t s , p a r t i c u l a r l y in t h e first 3 w k of l a c t a t i o n , a n d possibly prod u c e d d i f f e r e n t m e t a b o l i c states in t h e res p e c t i v e g r o u p s o f animals. S u p p l e m e n t a t i o n w i t h N a H C O 3 m a y t h e n have p r o d u c e d diff e r e n t effects b e c a u s e o f t h e d i f f e r e n t m e t a b o l i c s t a t e s associated w i t h each basal diet. With t h e HCS-based diet, NaHCO3 p r o d u c e d small increases in DM i n t a k e a n d milk yield (7.5 to 8.5%). Because t o t a l f a t yield was u n a f f e c t e d , milk fat p e r c e n t a g e was r e d u c e d b u t yields o f p r o t e i n a n d SNF w e r e increased in t h e same p r o p o r t i o n as milk yield. T h e s e e f f e c t s are c o n s i s t e n t w i t h an increased t u r e e n fluid pH a n d t h e o b s e r v e d increase in f i b e r digestibility. T h e i m p r o v e d f i b e r d i g e s t i b i l i t y m a y also have i n c r e a s e d r u m i n a l a c e t a t e p r o d u c t i o n (21) a n d p r o v i d e d a d d i t i o n a l s u b s t r a t e for m a m m a r y g l a n d o x i d a t i o n , t h e r e b y increasing e n e r g y s u p p l y to t h e u d d e r a n d increasing yields o f t o t a l milk, p r o t e i n , a n d SNF. S u c h an inter-

SODIUM BICARBONATE WITH SILAGE DIETS

379

TABLE 4. Effect of sodium bicarbonate and diet on nitrogen utilization and urine pH. Hay crop silage

Corn silage

Item

0% NaHCO a

1.25% NaHCO a

0% NaHCO a

1.25% NaHCO a

SE

Nitrogen, g/d Intake Milk Urine Feces

524 146 186 153

595 175 194 172

574 176 238 133

621 181 297 163

49.5 !2.7 20.1 a 14.0

Nitrogen, % of intake Urine Milk Tissue Production 1 Urine pH

35.9 27.8 7.2 34.9 8.15

32.8 29.8 7.9 37.7 8.27

41.5 30.7 4.7 35.5 8.16

47.7

29.5 -3.6 25.8 8.19

1.63 c 2.15 2.30 b 1.64 d .05

asignificant effect of forage source (P<.01). b'c'dsignificant forage X buffer interactions: b, P<.I0; c, P<.05; d, P<.01. 1Production = Tissue plus milk.

p r e t a t i o n is c o n s i s t e n t w i t h t h e results o f i n f u s i o n e x p e r i m e n t s w h e r e , over several weeks, a d d i t i o n a l acetic acid either increased prod u c t i o n or halted lactational decline o f milk yield and yields o f p r o t e i n and lactose (24). With the c o n t r o l CS-based diet, energy intake was e x t r e m e l y low and m o s t likely led to m o b i l i z a t i o n of f a t t y acids f r o m a d i p o s e tissue t o s u p p l y energy f o r milk s y n t h e s i s resulting in rapid w e i g h t loss and milk fat d e p r e s s i o n . Supp l e m e n t a t i o n w i t h NaHCO3 i m p r o v e d DM i n t a k e and fat yield and significantly increased milk fat p e r c e n t a g e and a p p a r e n t l y r e d u c e d a d i p o s e tissue m o b i l i z a t i o n and w e i g h t loss (Figure 3). C o n s e q u e n t l y , b l o o d free f a t t y acids m a y have b e e n m a d e m o r e available f o r f a t t y acid synthesis and t h u s led t o increased milk fat p e r c e n t a g e and fat yield. ACKNOWLEDGMENTS

The a u t h o r s t h a n k P. H. K n o w l t o n for skilled t e c h n i c a l assistance, D. B. H a r t k o p f f o r assistance w i t h d i g e s t i o n trials, W. A. H a l t e m a n f o r statistical advice, and A g w a y Inc., Syracuse, NY for partial financial s u p p o r t o f this project. REFERENCES

1 Adams, R. S. 1980. Forage testing service revised regression equations. Pennsylvania State Univ.,

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