Influence of Source and Amount of Dietary Protein on Milk Yield by Cows in Early Lactation1

Influence of Source and Amount of Dietary Protein on Milk Yield by Cows in Early Lactation' K. D. CUNNINGHAM,2 M. J. CECAVA,2 T. R. JOHNSON, and P. A. LUDDEN Department of Animal Sciences, Purdue University, West Lafayette, IN 47907

ABSTRACT

diets has had inconsistent effects on yields of milk and milk components. Christensen et al. ( 5 ) reported The purpose of this research was t o examine the similar performance of cows consuming low or high effects of various amounts of CP and RUP on AA flow RUP diets a t two percentages of dietary CP. Heatt o the small intestine and milk yield of lactating dairy treated soybean meal ( S B M ) and combinations of cows. The first trial was a 5 x 5 Latin square design heat-treated SBM and corn gluten meal did not inusing five ruminally and duodenally cannulated mul- crease milk yield in two trials (10).Plausible explatiparous cows, Diets contained chopped alfalfa hay, nations for similar milk yields in those studies (5, corn silage, high moisture corn, solvent-extracted soy- 1 0 ) include 1) RUP interactions with amount of DMI, bean meal, and specially processed soybean meal 2 ) depressed microbial protein synthesis and flow (60.2% RUP). Soybean meal replaced high moisture with high RUP diets, and 3 ) the inability of certain corn t o increase dietary CP from 14.5 to 16.5 or RUP sources to increase the flow of limiting AA. 18.5%,and specially processed soybean meal replaced In the studies of Windschitl ( 2 6 ) and Wattiaw et solvent-extracted soybean meal in diets containing al. (231, increasing the amount of RUP had a nega16.5 or 18.5% CP to provide 6.2, 7.3, 6.7, and 8.3% tive impact on yield because of lower DMI. When RUP. Increasing dietary CP increased the flows of all proteins containing high concentrations of RUP were AA to the duodenum. Increasing dietary RUP in- used t o replace SBM i n diets of lactating cows, creased flows of Arg, His, Lys, Phe, Asp, and Glu t o microbial protein flow to the small intestine the duodenum. In a second trial, 36 cows were fed decreased (15, 221, ostensibly because of reduced diets similar t o those used in trial 1. Increased ruminal availability of substrate for microbial protein amounts of RUP in diets tended t o increase milk yield synthesis. Cunningham et al. ( 8 ) reported a trend because of improved protein status, improved intake toward lower microbial protein flow as high RUP of metabolizable energy, or both. sources replaced 0, 33, 67, and 100% of the RDP i n (Key words: soybean meal, amino acid flow, dairy supplements fed to lactating dairy cows. Quantitative cow) and qualitative requirements for AA that are critical for milk protein synthesis have not been clearly esAbbreviation key: E M = essential AA, N A " = (18);however, Lys and Met are likely limittablished nonammonia, nonmicrobial N, SBM = soybean meal, ing for milk protein synthesis by cows in early lactaSE SBM = solvent-extracted SBM, SP SBM = spetion (18, 19). Consequently, the source of RUP and cially processed SBM. its AA profile are important for optimal supply of potentially limiting AA. When lactating cows were fed INTRODUCTION diets containing SBM, blood meal, feather meal, or a High yielding dairy cows in early lactation cannot combination of feather and blood meals, the duodenal meet postruminal AA requirements with microbial flows of Lys, His, Leu, and Cys were lower for diets protein synthesized in the rumen (16). Supplementa- containing feather meal than for those containing tion of diets with RUP has become commonplace in blood meal ( 2 2 ) . King et al. ( 1 2 ) reported greater the dairy industry. However, increased RUP in the DMI and duodenal flows of Lys for cows fed blood meal than for cows fed corn gluten meal or cottonseed meal. Their finding suggested that diets should be formulated t o contain sufficient RDP to meet Received November 7, 1994. microbial requirements and that RUP should have a n Accepted December 1, 1995. 'Journal Paper Number 14078, Purdue University Agriculture AA pattern that complements microbial AA and opResearch Programs. *Current address: Research and Technology Center, Consoli- timizes postruminal supply of essential AA. Therefore, the objectives of our research were t o examine dated Nutrition, L. C., Fort Wayne, IN 46801-2508. 1996 J Dairy Sci 79520-630

620

PROTEIN SOURCE AND AMOUNT FOR COWS

621

the impact of the amount of dietary protein and RUP on the flow of AA t o the small intestine and on milk yield of cows in early lactation.

Cows were used in a 5 x 5 Latin square experiment. Experimental diets contained chopped alfalfa hay, corn silage, high moisture corn, and protein supplement (Table 1).Diets were formulated t o contain MATERIALS AND METHODS 14.5, 16.5, and 18.5% CP on a DM basis. Within the two higher protein concentrations, diets contained low Trial 1 or high percentages of RUP. High moisture corn was decreased, and soybean protein was increased, to Five multiparous Holstein cows (612 kg) were fitted with permanent ruminal and open, T-type duo- achieve the selected amounts of dietary CP. A 3:l denal cannulas according to procedures approved by (wt/wt) ratio of solvent-extracted SBM ( SE SBM) to the Purdue Animal Care and Use Committee. The specially processed SBM ( SP SBM) was used for the duodenal cannulas were placed proximal t o the bile low RUP diets, and a 1:3 (wt/wt) ratio of SE SBM to and pancreatic ducts and approximately 10 cm distal SP SBM was used for the high RUP diets. The SE to the pylorus. At the onset of the experiment, cows SBM and SP SBM were supplied by Consolidated averaged 32 f 10 DIM. Cows were housed in conven- Nutrition, L. C. (Fort Wayne, IN). The SP SBM was tional tie stalls, equipped with rubber mats and in- produced by a process (patent pending) involving dividual water bowls in a well-ventilated room main- mechanical and chemical treatments that increased tained at 18°C. Cows were milked three times daily at the RUP concentration t o approximately twice that of 0500, 1500, and 2100 h. SE SBM. The RUP concentrations of SE SBM and SP

TABLE 1. Composition of diets fed to lactating cows. Composition

14.5% CP

16.5% CP, Low RUP

16.5% CP, High RUP

18.5% CP, Low RUP

18.5% CP, High RUP

(% of DM)

Ingredient Alfalfa hay Corn silage High moisture shelled corn Soybean meal (SBM) Specially processed SBMl MegalaCB2 Urea Dicalcium phosphate Limestone Magnesium oxide Trace-mineralized salt3 Selenium 200 premix4 Vitamin premix5 Chemical

OM CP RUP NDF

ADF NSC7 NSC:RDP

10.00 40.00 32.05 9.85 4.96 0.45 0.98 0.98 0.13 0.47 0.10 0.03

10.00 40.00 27.25 10.99 3.69 4.96 0.42 0.98 0.98 0.13 0.47 0.10 0.03

10.00 40.00 27.25 3.69 10.98 4.96 0.42 0.98 0.98 0.13 0.47 0.10 0.03

10.00 40.00 22.57 14.59 4.79 4.96 0.40 0.98 0.98 0.13 0.47 0.10 0.03

10.00 40.00 22.57 4.79 14.59 4.96 0.40 0.98 0.98 0.13 0.47 0.10 0.03

93.6 14.4 5.2 33.2 17.1 41.3 4.49

92.7 16.4 6.2 34.0 19.0 38.7 3.80

92.7 16.4 7.3 35.9 21.5 36.6 4.02

93.0 18.4 6.7 39.1 21.8 33.9 2.89

93.0 18.4 8.3 43.2 26.5 31.0 3.07

...

lManufactured by a process to enhance RUP concentration (Consolidated Nutrition, L. C., Fort Wayne, IN). Patent is pending. 2Calcium soaps of long-chain fatty acids with 82.5% approximate fat content (Church and Dwight, Inc., Piscataway, NJ). 3Composition: 98% NaCl, 0.35% Zn, 0.28% Mn, 0.175% Fe, 0.035% Cu, 0.007% I, and 0.007% Co. Wontained 200 mg of S&g of premix. SProvided 88,000 IU of vitamin A, 22,000 IU of vitamin D, and 785 IU of vitamin E/d per cow. 6Estimated from NRC (16)values for forages and high moisture corn and concentrations of RUP (percentage of total CP) in solventextracted soybean meal (29.8%) and specially processed soybean meal (60.2%) determined by in situ ruminal incubation. 7Nonstructural carbohydrate content; NSC = 100 - NDF - ( a s h + CP + ether extract). Journal of Dairy Science Vol. 79, No. 4. 1996

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CUNNINGHAM ET AL.

SBM were 29.8 and 60.2%, respectively, as measured by an 18-h ruminal incubation of the test protein sources. Complete diets were mixed once daily in a horizontal mixer and fed twice daily at 0100 and 1300 h. Orts were taken daily, prior to the 1300-h feeding, and DM of the feed offered was adjusted t o provide 5% orts. Gelatin capsules containing 7.5 g of CrzO3 were administered via the ruminal cannula twice daily a t feeding, and Cr was used as a n indigestible marker to assess DM flow in the gastrointestinal tract. Experimental periods were 13 d: 10 d for diet adaptation, followed by 3 d for sample collection. Procedures for sample collection and analysis were described by Cunningham et al. ( 8 ) . Feed DMI was calculated as the mean DMI for each cow over the last 5 d of each period. Data were analyzed using the general linear models procedure of SAS ( 1 7 ) for a Latin square design. Model sums of squares were separated into effects of cow, period, and treatment. Single degree of freedom contrasts evaluated the linear and quadratic effects of percentage of CP (14.5, 16.5, or 18.5%), amount of RUP (low or high), and the interaction between amount of CP and RUP. When the interaction of CP and RUP was evaluated, means for the 14.5% CP treatment were not included in the analysis. Least squares means for CP and RUP were generated using the least squares option. Effects were considered to be significant at P < 0.05 unless otherwise stated. Pearson correlation coefficients between flows of N and AA a t the duodenum and yield criteria presented in Table 8 were calculated using the CORR statement of SAS ( 1 7 ) .

DHI Laboratory, West Lafayette, IN). Means for these measurements were used for covariant adjustment i n statistical analysis of data collected during the study. m e r the covariant period, cows were adapted to the experimental diets, and measurements were collected for the next 12 wk. The four treatments in trial 2 corresponded to the diets containing low and h g h RUP and 16.5 and 18.5% CP i n trial 1. Tallow was used in place of Megalac@ (Church and Dwight, Inc., Piscataway, N J ) to provide supplemental energy. Diets were mixed and fed once daily for ad libitum consumption. Orts were collected daily, and mean feed DMI was calculated over 7-d periods every 2 wk for the 12-wk trial. Individual feed components were composited monthly, dried (55"C), ground (1-mm screen), and analyzed for DM, OM, ADF, and N contents according to AOAC methods (1) and for NDF according to Van Soest et al. ( 2 1). Milk weights were recorded daily, and samples were collected from six consecutive milkings over a 2-d period every 2 wk. Milk samples were analyzed as described for fat and protein contents. The BW and body condition score were recorded over 2 consecutive d every 2 wk for 12 wk, and means were used for statistical analysis. Data were analyzed using the general linear models procedure of SAS ( 1 7 for a completely randomized design with a 2 x 2 factorial arrangement of treatments. Model sums of squares were partitioned into effects of percentage of CP, amount of RUP, parity, and the interactions. Least squares means for treatments and standard errors, adjusted for covariants, are presented. Significance was declared at P < 0.05 unless otherwise stated.

Trial 2

In trial 2, 36 Holstein cows ( 1 9 multiparous and 17 primiparous) with similar estimated milk yield were used to determine the effects of dietary CP and RUP on lactation performance. Cows were housed in comfort stalls in a temperature-controlled (20°C) barn and individually fed throughout the experiment. During a covariant period, all cows received a common diet based on alfalfa hay, corn silage, high moisture corn, SE SBM, SP SBM, and tallow for 10 d starting a t 28 DIM. The DMI and milk yields were recorded the last 7 d of the covariant period, and the mean was used for covariant adjustment of data collected during the trial. The BW and body condition score [five-point scale; (25)l were measured, and milk samples were collected over 2 consecutive d a t the end of the covariant period. Milk samples were analyzed by infrared spectroscopy for protein and fat contents (Indiana Journal of Dairy Science Vol. 79, No. 4, 1996

RESULTS AND DISCUSSION Trial 1

The composition of diets is shown in Table 1. Alfalfa hay was chopped using a large bale tub grinder (3-cm screen) to aid in diet mixing and consistency. The corn silage and high moisture shelled corn were obtained from the same upright silos throughout the trial to minimize variation between lots. The SE SBM and SP SBM were from two lots; however, lot variation was minimal a s measured by DM, N, and AA content of the lots. The AA content of SP SBM was about 10% lower than that of SE SBM (79.4% vs. 88.7% of total N ) , but the pattern of AA was similar between protein sources. In previous work with SBM that had been processed similarly t o that for the SP SBM used in these trials, Cecava et al. ( 4 ) found that

623

PROTEIN SOURCE AND AMOUNT FOR COWS

57.3 and 30.3% of the N in SP SBM and SE SBM, respectively, escaped ruminal fermentation based on in situ incubation of test proteins. The diets in this trial contained 5.2, 6.2, 7.3, 6.7, and 8.3% RUP (DM basis) for the diets with 14.5% CP; 16.5% CP, low RUP; 16.5% CP, high RUP; 18.5% CP, low RUP; and 18.5%CP, high RUP, respectively. The suggested percentage of RUP in the diets of high yielding cows ranges from 6.2 to 7.0% of dietary DM ( 16). Because protein supplements were substituted for corn to increase CP concentration of diets, the ratio of nonstructural carbohydrates t o RDP declined as dietary CP concentration increased. The ratio of nonstructural carbohydrates to RDP increased as RUP increased because dietary percentages of RDP decreased. The intake, flow to the duodenum, and digestion of OM were unaltered by treatment (Table 2). Keery et al. ( 11) reported significantly higher OM flows t o the duodenum and lower digestion of OM in. the reJiculorumen of steers fed diets supplemented with heat-treated SBM than for those fed diets sup-

plemented with SE SBM. This reduction in OM digestion was related to the increased RUP content of the heat-treated SBM diets, which lowered N digestion compared with SE SBM ( 11).In our study, mean OM flow from the stomach was nonsignificantly higher (0.6 kg/d) for high RUP diets than for low RUP diets, but ruminal digestion was unchanged. Total tract digestion of OM, as a percentage of OM intake, was similar among treatments. Some researchers ( 2 7 ) have reported that ruminally protected SBM products decreased digestion of OM in the stomach and total tract, possibly because of overprotection of the SBM protein or the reductions in OM digestibility that were associated with low RDP intake, or both. The data for N digestion in our study do not indicate overprotection of the SBM protein, as is discussed subsequently. The intakes of NDF and ADF increased as percentages of CP and RUP increased, and those intakes increased more for the diet containing 18.5% CP, high RUP than for the diet containing 16.5% CP, high RUP, which resulted in a trend for an interaction of

TABLE 2. Effects of diet on the digestion of OM, NDF, and ADF in trial 1. Contrast

OM Intake, kg/d Flow at duodenum, kg/d Fecal output, kg/d Apparent ruminal digestion, % of intake True ruminal digestion, % of intake Apparent total tract digestion, % of intake NDF Intake, kg/d Flow at duodenum, kg/d Fecal output, kg/d Ruminal digestion, % of intake Apparent total tract digestion, % of intake ADF Intake, kg/d Flow at duodenum, kg/d Fecal output, kg/d Ruminal digestion, % of intake Apparent total tract digestion, % of intake

14.5% CP

16.5% CP, 16.5% CP, 18.5% CP, Low RUP High RUP Low RUP

18.5% CP, High RUP SEM

17.1 8.2 4.7

16.8 8.2 4.8

16.9 8.8 4.6

16.6 8.2 4.8

18.2 8.7 5.0

51.8

50.6

48.8

50.6

69.2

67.2

63.3

72.6

71.1

8.0 4.6 4.7

CP'

CP x

L

Q

RUP

RUP

0.7 0.5 0.3

NSZ NS NS

NS NS NS

NS NS NS

NS NS NS

51.9

2.7

NS

NS

NS

NS

65.8

66.1

2.4

NS

NS

NS

NS

72.4

71.6

72.4

1.3

NS

NS

NS

NS

8.0 3.7 4.3

7.9 4.2 3.9

8.9 4.6 4.7

10.1 3.8 4.9

0.2

0.002

0.06

NS

0.02 NS

0.06

0.4

0.2

NS

0.06

NS NS

NS NS

43.0

52.8

46.6

46.8

62.7

4.3

NS

NS

NS

0.07

41.0

47.6

50.2

50.0

46.8

2.6

0.01

NS

NS

NS

4.1 2.1 2.5

4.4 2.2 2.4

4.8 2.4 2.2

4.9 2.3 2.7

6.2 2.0 2.8

0.2 0.1 0.2

0.003 NS NS

NS NS NS

0.003

NS NS

0.03 NS NS

50.0

50.9

50.6

52.5

65.4

2.9

NS

NS

NS

0.09

39.4

46.7

53.6

52.2

43.6

3.9

0.06

NS

NS

0.09

1L = Linear; Q = quadratic.

2P > 0.10. Journal of Dairy Science Vol. 79, NO. 4, 1996

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CUNNINGHAM ET AL.

CP and RUP. Ruminal digestion of NDF numerically diets containing 14.5, 16.5, and 18.5% CP, respecincreased as CP increased (nonsignificant). The ru- tively. Increasing the amount of RUP in the diet minal digestibilities of NDF and ADF were higher for lowered ruminal NH3 N concentration, reflecting that the diet containing 18.5% CP, high RUP than for SP SBM was more protected from ruminal degradadiets containing 16.5% CP, high RUP or low RUP, tion than was SE SBM. Despite lower N H 3 N concenwhich resulted in an interaction of CP and RUP. trations for diets containing high amounts of RUP, Improved ruminal digestion of NDF and ADF for the the flow of microbial protein to the small intestine 18.5% CP, high RUP diet might have occurred be- was not affected (Table 4). Consequently, either all cause diets had low concentrations of effective fiber. diets ostensibly met or exceeded microbial requireThe greater intake of NDF and ADF during this ments for NH3 N ( 16), or all diets were deficient in treatment might have improved ruminal conditions ruminally available N H 3 N. The former statement is for fiber fermentation. Apparent digestion of NDF in more likely because diets met or exceeded recomthe total tract was unaffected by treatment and aver- mended allowances for RDP relative to yield of FCM aged 47%, but apparent digestion of ADF in the total [RDP = 9.6% of dietary DM; (1611. Other researchers tract increased as percentage of CP increased. There ( 8 , 22) have suggested the need t o include a source of was a trend for an interaction of CP and RUP for total RDP in diets with high amounts of RUP to maintain a tract digestion of ADF because increasing the amount source of ruminally available N. In the present study, of RUP in diets containing 16.5% CP improved the all diets appeared t o provide sufficient RDP from digestion of ADF, but increasing the amount of RUP SBM and urea to meet the needs of ruminal microorin diets containing 18.5% C P decreased digestion. The ganisms for AA, NH3 N, and peptides for protein reason for this difference is unknown. For most synthesis. Ruminal pH and VFA concentrations were similar studies reported in the literature (2, 10, 13, 151, the source and amount of RUP in diets fed to lactating for all diets (Table 3 ) ; however, the ratio of acetate t o dairy cows appeared to have only small effects on the propionate was decreased by increasing dietary CP digestion of fiber in the stomach and total tract. from 14.5 t o 18.5%. A reduction ( P < 0.05) in molar Ruminal NH3 N concentrations were affected by percentages of acetate and a trend ( P = 0.08) for the percentage of CP and amount of RUP (Table 3 ) . higher molar percentages of propionate were responIncreased ruminal N H 3 N concentrations with in- sible for the lower ratio of acetate to propionate. The creased CP were expected because the dietary percen- molar percentages of butyrate in total VFA increased tages of RDP increased, regardless of the intended as RUP increased, but the molar percentages of aceincreases in RUP. The estimated concentration of tate, propionate, isobutyrate, isovalerate, and valerRDP averaged 9.2, 9.7, and 10.9% of dietary DM for ate were unaffected by treatment.

TABLE 3. Ruminal characteristics in trial 1. Contrast1

cP.2

14.5% CP

16.5% CP, Low RUP

16.5% CP, High RUP

18.5% CP, Low RUP

18.5% CP, High RUP

SEM

L

Q

5.3 5.95 82.3

9.0 5.93 94.7

6.8 5.96 91.7

10.9 5.96 98.8

7.0 5.97 89.9

1.0 0.09 6.1

0.04 NS3

0.01

NS

NS NS NS

57.1 25.8 12.9 0.8 2.5 0.8 2.3

54.3 29.3 12.4 0.8 2.3 0.8 1.9

54.7 27.6 13.5 0.9 2.4 0.8 2.0

55.0 28.3 12.3 0.9 2.6 0.8 2.0

53.9 28.8 13.4 0.8 2.3 0.8 1.9

1.0 1.2 0.5 0.1 0.1 0.1 0.1

0.05 0.08 NS NS NS NS 0.04

NS NS NS NS NS NS NS

NS

RUP

P Ruminal NH3 N, mg/dl PH Total VFA, mM Individual VFA, moVlOO mol Acetate ( A ) Propionate ( P ) Butyrate Isobutyrate Valerate Isovalerate

A:P

'The interaction of CP and RUP was not significant ( P > 0.10). = Linear; Q = quadratic. 3P > 0.10. 2L

Journal of Dairy Science Vol. 79, No. 4, 1996

NS NS

NS 0.04 NS NS

NS NS

625

PROTEIN SOURCE AND AMOUNT FOR COWS

Intake and flow of N and microbial efficiency are reported in Table 4. As anticipated, N intake increased as dietary CP content increased. Cows readily consumed the diets containing SP SBM; therefore, N intake did not differ between diets containing high and low RUP. Keery et al. ( 11) reported lower N intake by cows when supplemental protein was provided by menhaden fish meal rather than by SE SBM or heat-treated SBM. This finding suggests that, in some cases, processed SBM with high RUP content might be superior to animal protein supplements because acceptability by cows was better. Increased percentages of dietary CP increased the flow of N to the duodenum, but the amount of RUP had no effect on total N flow. A considerable amount of N ( 2 0 to 30% of N intake) was not recovered at the duodenum. The reason for the extensive loss of N in the stomach is unknown but might suggest uncoupled ruminal fermentation of carbohydrate and protein. However, amounts of ruminal N H 3 N concentrations and OM disappearance in the rumen were acceptable for cows consuming these types of diets and in this stage of lactation. Furthermore, the quantity of microbial N a t the duodenum was unaffected by dietary CP content

TABLE 4. Effects of diet on the digestion of

or amount of RUP. However, microbial N made up a smaller proportion of NAN flow at the duodenum as the percentage of CP increased. Increased RUP increased the flow of non-NH3, nonmicrobial N (NA") at 16.5% CP, but not at 18.5% CP. We have no explanation for the inconsistent ability of SP SBM t o increase NANMN flow. Bowman et al. ( 3 fed dairy cows SE SBM and SBM treated with sodium hydroxide in diets containing 15 and 17.5% CP. Replacing SE SBM with treated SBM increased the concentrations of RUP for the low CP but not for the high CP diets. They attributed these differences to the amount of CP from test proteins and total CP. In o u r study, supplemental protein from SE SBM or combinations of SE SBM and SP SBM provided 37 to 56% of total dietary CP. Clark et al. ( 6 ) suggested that test protein supply be >35% of total dietary CP when test protein effects on duodenal N flows were to be measured. Therefore, the diets i n the present study should have elicited changes in postruminal flows of N and AA. The failure t o detect significant effects of dietary RUP content on NANMN flow was partly explained by the variation associated with estimates of digesta flow at the duodenum and

N in trial 1. Contrast CP1 RUP

CP x RUP

NS

NS

NS NS

NS NS

NS NS

NS NS

NS NS

NS NS

12 2.7

NS NS 0.0001 NS

NS NS

NS 0.08

170 43.7

15 2.7

0.0004 NS 0,0001 NS

NS NS

0.11 0.08

389 74.3

43 1 74.9

15 1.0

0.0001 NS 0.002 NS

NS NS

NS NS

24.2 18.5

23.7 18.6

2.7 1.5

NS NS

NS NS

NS

14.5% CP

16.5% CP, Low RUP

16.5% CP, High RUP

18.5% CP, Low RUP

18.5% CP, High RUP

SEM

L

N Intake, g/d N Flow at duodenum, Total N

425

478

486

526

575

21

0.0002 NS2

g/d % of N Intake NAN Flow g/d % of N Intake Microbial N dd % of NAN Flow NAMW dd % of NAN Flow Apparent total tract N dirrestion dd 8 of N Intake Microbial efficiency,' g of MN/kg of OMA g of MN/kg of OMT

318 75.5

344 72.7

391 79.4

378 71.6

397 69.4

19 4.2

0.01

NS

316 75.1

342 72.3

389 79.1

376 71.2

395 69.0

19 4.2

0.01 NS

233 72.8

225 65.1

230 58.9

202 53.4

225 56.3

84 27.2

118 34.9

159 41.1

174 46.6

299 70.3

346 72.5

354 72.8

26.1 19.5

26.9 20.0

28.6 21.4

Q

P

NS NS

NS

1L = Linear; Q = quadratic. 2P > 0.10. 3Non-NH3, nonmicrobial N. = Microbial N,OMA = OM apparently digested in the rumen, and OMT = OM truly digested in the rumen.

4MN

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CUNNINGHAM ET AL.

flow of microbial N, which were inherent problems when in vivo methodologies were used t o assess the RUP content of individual feedstuffs. Apparent total tract digestion of N was increased as CP increased but was similar between diets of high and low RUP.The SP SBM used in this study apparently was not overprotected, but digestion of N in the total tract might not be highly correlated with supply of absorbable protein to the intestines. Apparent and true efficiency of microbial protein synthesis were unaffected by percentage of CP or amount of RUP (Table 4). Others have reported lower (26), unchanged ( 4 ) , or increased ( 11) efficiency of microbial protein synthesis when diets contained SBM with low ruminal N degradability. Higher percentages of CP increased the flow of individual AA, essential AA ( EAA) , and nonessential AA (Table 5). These results would be anticipated, based on the summary of Clark et al. ( 6 ) . Those researchers reported that, across a wide range of diets fed t o lactating cows, correlation was high (r2 = 0.82) between N intake and flow of NAN t o the duodenum, of which approximately 80% was AA N. Higher amounts of RUP increased the flow of 6 of the 17 AA

measured, and flow of a n additional 5 AA tended t o be higher ( P < 0.10) for high RUP diets than for low RUP diets. Consequently, flow of EAA and nonessential AA tended ( P= 0.06) to increase as amounts of dietary RUP increased. Cecava et al. ( 4 ) reported that a combination (50:50, wt/wt) of supplemental protein from SE SBM and SP SBM, compared with SE SBM or SP SBM alone, improved AA flow t o the duodenum of growing steers. Windschitl and Stern ( 2 7 ) showed that duodenal flow of AA in dairy cows was highest when supplemental protein was provided by SBM treated with lignosulfonate and that AA flows tended to be higher when diets contained SBM treated with xylose than when diets contained SE SBM. In our study, flow of Lys was increased an average of 13%, and that of Met was increased an average of 8% (nonsignificant) for high RUP diets than for low RUP diets. Although Cecava et al. ( 4 ) reported small changes in duodenal flows of Lys and Met in steers fed SP SBM, Windschitl and Stern ( 2 7 1 reported flow of Lys was 48% higher and flow of Met was 10% higher for diets supplemented with SBM treated with xylose or lignosulfonate than for diets supplemented with SE SBM. Keery et al. ( 11 also

TABLE 5. Effects of diet on the flows of AA to the duodenum in trial 1. Contrast1 AA

14.5% CP

16.5% CP, Low RUP

16.5% CP, High RUP

88.0 44.6 95.6 209.7 124.7 44.8 105.8 107.5 123.9 944.6 152.5 213.6 35.3 320.0 152.7 112.9 114.0 99.2 1200.1 2144.7

106.2 51.4 112.3 235.7 147.1 50.8 123.8 125.2 140.8 1093.3 170.8 258.2 40.1 363.6 173.5 126.1 134.5 114.0 1380.9 2474.1

127.7 59.5 125.6 255.7 171.0 53.5 136.8 134.6 155.8 1220.1 181.2 284.7 43.4 400.0 196.4 135.4 146.2 123.1 1510.4 2730.6

CP2

18.5% CP, Low RUP

18.5% CP, High RUP

SEM

L

Q

110.3 53.8 118.3 244.1 155.1 52.3 129.4 129.7 146.9 1139.8 176.5 265.6 41.7 378.7 192.0 128.9 137.3 118.9 1439.5 2579.4

132.9 61.7 128.9 270.4 171.3 57.4 145.1 139.2 157.9 1264.7 188.6 299.4 46.3 441.5 188.4 146.6 155.1 129.5 1595.4 2860.2

7.7 3.3 6.2 13.0 9.3 2.7 6.6 6.0 7.4 60.5 8.4 12.8 2.6 18.7 11.8 6.8 7.2 6.0 69.7 130.0

0.01 0.01 0.003 0.01 0.008 0.01 0.003 0.003 0.009 0.006 0.01 0.001 0.02 0.005 0.02 0.02 0.005 0.005 0.004 0.005

NS3 NS NS NS

P

( g/d )

'% His I le Leu LYS Met Phe

Thr Val EM4 Ala ASP CYS Glu GlY Pro Ser

% NEAA4 Total AA

'The CP by RUP interaction was not significant ( P > 0.10). *L = Linear; Q = quadratic. 3P > 0.10. 4EAA = Essential AA; NEAA = nonessential AA. Journal of Dairy Science Vol. 79, No. 4, 1996

RUP

NS NS NS NS NS NS NS NS NS NS

NS NS NS NS NS NS

0.01 0.03 0.09 0.10 0.05 NS 0.05 NS 0.10 0.06 NS 0.04 NS 0.02 NS 0.07 0.06 NS 0.06 0.06

PROTEIN SOURCE AND AMOUNT FOR COWS

reported duodenal flow of Lys was 38% higher and flow of Met was 34% higher, for steers fed heated SBM than for steers fed unheated SBM. Altering the proportions of dietary CP and RUP resulted in relatively few changes in the pattern of EAA in duodenal digesta (Table 6 ) . Higher percentages of CP increased the percentages of Arg and Lys, but decreased the percentages of Leu, Met, and Val. High RUP diets increased the percentages of Arg and His, but lowered the percentages of Met and Thr compared with those of low RUP diets. Because microbial N constituted S O % of the total duodenal flows of N and because the pattern of AA in microbial protein was unaffected by treatment in our study (data not shown), dramatic changes would not be anticipated in the AA pattern of duodenal digesta. Compared with the ideal pattern of AA for milk protein synthesis that was suggested by Fox et al. (91, the percentages of Ile, Lys, Met, and His were less than optimal. This result was particularly true for Lys, which constituted 13.5%of EAA; however, Fox et al. ( 9 ) suggested that Lys should constitute 16.3% of EAA in duodenal digesta. These data suggest that additional ruminally protected Lys, Met, or both in the diets of dairy cows might improve milk protein yield, assuming that Lys and Met were limiting AA. Increased amounts of RUP generally increased the flow of AA from feed and endogenous sources (data not shown). Increased dietary RUP content increased the flow of Lys but had little effect on the flow of Met from feed and endogenous protein. This effect occurred because SP SBM was relatively high in Lys (2.7% of DM) but was low in Met (0.5% of DM). Approximately 10, 31, 38, 37, and 39% of the postrumina1 flow of Lys and 24, 39, 42, 43, and 43% of the

627

postruminal flow of Met were of feed and endogenous origin for the 14.5% CP; 16.5% CP, low RUP; 16.5% CP, high RUP; 18.5% CP, low RUP; and 18.5% CP, high RUP diets, respectively (data not shown). Although the effects were small, SP SBM could be used t o improve flows of potentially limiting AA, such as Lys, in the lactating cow. However, postruminal infusion of AA or dietary addition of ruminally protected synthetic AA could alter the pattern of AA more predictably than dietary addition of feedstuffs having high concentrations of RUP. Yields of 4% FCM, milk fat, and milk protein increased as dietary CP increased (Table 7). Increases in yield of milk fat and milk protein occurred because of numerical increases in milk yield and because of increases in the concentration of fat (linear effect) and protein (quadratic effect) as dietary CP content increased. The largest proportion of increase in yields of milk and milk components occurred as CP content increased from 14.5 to 16.5%. Relatively smaller improvements occurred as CP increased from 16.5 t o 18.5%. Increased RUP, especially the diet containing high RUP and 18.5% CP, tended t o increase yields of milk, 4% FCM, milk fat, and milk protein. Yields of milk and milk components tended to increase as dietary RUP content increased, perhaps because of increased flow of the EAA that were critical for milk protein synthesis. Alternatively, when the 18.5% CP, high RUP diet was fed, intake of OM was 8.5% greater (nonsignificant) than the mean intake of other diets. Higher OM intake likely improved the energy status of cows and accounted for the increase in milk yield for the 18.5% CP, high RUP diet because flows of EAA t o the duodenum were similar for the diets containing 18.5% CP and low or high RUP.

TABLE 6. Effects of diet on the pattern of essential AA (EAA) at the duodenum in trial 1. ~

~~~~~~~~~~

Contrast

AA

14.5% CP

16.5% CP, Low RUP

16.5% CP, High RUP

18.5% CP, High RUP

SEM

Ideal pattern2 L

Arg His Ile Leu LYS Met Phe Thr Val

9.2 4.7 10.1 22.3 13.1 4.7 11.2 11.4 13.1

9.8 4.7 10.3 21.5 13.5 4.6 11.3 11.4 12.9

10.4 4.9 10.3 21.0 13.9 4.4 11.3 11.1 12.8

10.4 4.9 10.2 21.4 13.5 4.5 11.5 11.0 12.5

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

9.6 5.8 12.5 17.5 16.3 5.2 9.0 8.7 12.6

1L

18.5% CP, Low RUP (% of EAA) 9.7 4.7 10.4 21.3 13.7 4.6 11.3 11.4 12.9

CP' RUP

Q

CP x RUP

P 0.02

0.09

NS NS

NS NS

0.006 0.05 0.04 0.09

0.02 0.05 006

NS 0.02

NS NS NS

0.004 0.04

NS NS NS

NS3 NS NS

NS NS

0.02

0.003

NS

NS NS NS

0.01 0.09

= Linear; Q = quadratic.

2Estirnated using the Cornel1 Net Carbohydrate and Protein System (9). 3P > 0.10. Journal of Dairy Science Vol. 79, No. 4, 1996

628

CUNNINGHAM ET AL.

TABLE 7. Effects of diet on milk yield in trial 1. Contrast1 14.5%

CP Milk yield, kg/d Milk fat %

dd Milk protein %

dd 4% FCM, kgld 4% FCM:DMI, kg/kg DMI

16.5% CP, Low RUP

16.5% CP, High RUP

18.5% CP, Low RUP

18.5% CP, High RUP

CP2 SEM

L

Q

RUP

33.8

34.0

36.5

35.2

39.3

0.7

NS3

NS

0.10

2.19 744.4

2.46 844.8

2.52 922.4

2.45 857.0

2.51 974.2

0.11 49.9

0.04 0.02

NS NS

NS

2.79 945.7 24.7

2.92 997.2 26.3

3.00 1093.1 28.4

2.94 1041.0 27.1

2.84 1114.4 30.3

0.07 47.0 1.3

NS

0.09

NS NS

NS

0.05 0.04

1.35

1.44

1.56

1.53

1.57

0.07

0.03

NS

0.08 0.10 0.06

NS

'The CP by RUP interaction was not significant ( P > 0.10).

*L = Linear; Q = quadratic. 3P > 0.10.

Milk fat depression was evident for all diets and

was likely the result of low effective fiber intakes caused by fineness of the chopped alfalfa hay. Milk fat concentrations measured by infrared spectroscopy were compared with concentrations determined using the Babcock assay (1); variation was <1%between the two procedures. Efficiency of milk yield was unaltered by amount of RUP, but increases in CP increased the output of 4% FCM relative to DMI. The correlations between the flows of individual AA and of total N to the duodenum, yields of milk and milk protein, and milk protein percentage are shown in Table 8. Yield of milk protein and flows of total N and individual EAA were closely correlated. The correlations between milk protein percentage and flows of EAA and total N were low, and those of milk yield were intermediate. Other researchers (18, 20) observed that the content of milk protein was most sensitive t o AA status, followed by milk protein yield, and total milk yield. In the present study, no single AA appeared t o be clearly limiting because, except for Leu and Ile, the correlation coefficients for individual EAA and milk protein yield were quite high and relatively similar. The low correlation of Ile and milk protein yield was unexpected because the proportion of Ile in duodenal digesta was low relative to the required proportion of Ile in digesta (Table 6 ) , suggesting that Ile might have been limiting for milk protein synthesis. However, Schwab et al. (19) expressed reservations regarding interpretation of test results when requirements for AA were expressed on the basis of ratios of E M in duodenal digesta. One concern was that the required contribution of an individual EAA to EAA at the duodenum would be a Journal of Dairy Science Vol. 79, No. 4, 1996

function of the other EAA in digesta. Consequently, relative excesses of EAA would underestimate the true requirement for an EAA. Also, this approach did not consider potential differences in absorption of an EAA in the intestine. The high correlations of yields of milk and milk protein with flow of total N to the small intestine and the similarity in correlation coefficients for EAA, suggested that the effect of diet on the quantities of N and EAA supplied to the intestines was more critical for yields of milk and milk protein than was the effect of diet on the pattern of EAA in duodenal digesta. Trial 2

Diets fed in trial 2 were similar to those fed in trial 1, except that tallow was used as a supplemental

TABLE 8. Coefficients of determination ( r 2 ) of flows of essential AA and N a t the duodenum to milk yield, milk protein percentage, and protein yield in trial 1. Yield cntena

AA

Milk yield

Protein percentage

Protein yield

'4% His Ile Leu LYS Met Phe Thr Val Total N

0.68 0.67 0.65 0.66 0.66 0.65 0.66 0.65 0.66 0.71

0.29 0.35 0.39

0.78 0.79 0.65 0.66 0.78 0.79 0.80 0.81 0.82 0.83

0.40

0.35 0.33 0.37 0.41 0.42 0.33

PROTEIN SOURCE AND AMOUNT FOR COWS

energy source and, only the diets containing 16.5 and 18.5% CP were fed. "he mean DMI by multiparous cows was 21.8 kg/d, which was 3.3 kg/d higher, on average, than that of the cows in trial 1; mean consumption of primiparous cows was 19.4 kg/d (Table 9). The DMI peaked at wk 10 postpartum, and the pattern of DMI over the course of the trial was unaffected by diet (data not shown). The BW and body condition score of cows were not affected by diet, and no adverse effects on health were related to diet (data not shown). Milk yield was unaffected by percentage of CP but tended ( P = 0.08) to be improved by higher amounts of dietary RUP. The response t o dietary RUP content appeared to be affected by parity and dietary CP concentration. Milk yield increased for primiparous cows fed high amounts of RUP and 18.5% CP, but yield was unaffected by dietary RUP content when diets contained 16.5% CP. Yield of multiparous cows increased when dietary RUP content increased a t 16.5% but not a t 18.5% CP in the diet. The reasons for these interactions were not totally clear, but they might have been related to the relationship of dietary RUP content and DMI. When increased dietary RUP

629

improved milk yield, DMI also increased. Consequently, the impact of RUP on metabolizable protein and milk yield was confounded by effects of dietary RUP content on energy status. Other researchers (3, 10, 1 4 ) have reported no improvement in milk yield of cows fed diets containing SBM with low ruminal degradability compared with those fed SE SBM. Lundquist et al. ( 1 4 reported higher DMI and milk yields when dietary CP increased from 12.3 to 18.0% of DM; however, the amount of DMI in that study was lower than DMI during the present study. For trial 2 of our study and for the study of Bowman et al. ( 3 ) , requirements for metabolizable protein probably were met or exceeded for all diets. CONCLUSIONS

In trial 1, the amount of CP and RUP in diets had only small effects on the pattern of AA in duodenal digesta, and no single AA was clearly limiting for milk protein synthesis. Consequently, when diets contained higher amounts of CP or RUP, the yields of milk and milk components improved, probably because of higher flows of N and EAA to the intestine.

TABLE 9. Covariant-adjusted means for effects of diet on DMI and milk yield in trial 2.

16.5% CP Low RUP

18.5% CP

High RUP

Low

RUP

Contrast

High RUP

SEM

CP

RUP

CP x RUP

P DMI, kg/d All cows Primiparous Mu1tiparous Milk yield, kgld All cows Primiparous Multiparous Milk protein, % All cows Primiparous Multiparous Milk protein, g/d All cows Primiparous Multiparous Milk fat, % All cows Primiparous Multiparous Milk fat, g/d All cows Primiparous Multiparous

20.6 19.9 21.2

21.0 19.7 22.4

20.5 18.5 22.5

20.6 20.5 20.7

0.5 1.0 0.5

NS1

NS

NS

NS

NS

NS

NS

NS NS

35.8 33.2 38.3

38.3 33.6 43.0

36.1 32.6 39.6

38.9 37.0 40.8

1.3 1.1 2.2

NS

0.08 NS NS

NS

NS NS NS

NS NS NS

NS NS NS

NS

NS NS

NS

2.90 2.98 2.82 1034 991 1077 2.51 2.70 2.32 899 906 892

2.90 3.10 2.70 1100 1039 1160 2.38 2.37 2.39 908 795 1021

2.88 2.91 2.84 1033 951 1116 2.50 2.73 2.28 893 878 909

2.85 2.97 2.73 1100 1097 1103

2.68 2.70 2.65 1027 991 1063

0.05 0.07 0.11 43 55 62 0.11 0.15 0.15 55 75 80

NS

NS

NS NS NS NS

NS NS 0.08

NS NS NS NS NS

NS NS NS NS

0.04

NS

NS NS 0.08 NS NS

NS NS

1P > 0.10. Journal of Dairy Science Vol. 79, No. 4, 1996

630

CUNNINGHAM ET AL.

In trial 2, when DMI of cows was higher, there appeared t o be little advantage for increasing the percentage of dietary CP. If the amount of DMI was increased by higher amounts of dietary RUP, as occurred in trial 2, milk yield might be enhanced by an improved supply of metabolizable energy. The results of these studies underscored how DMI can affect the response of lactating dairy cows to dietary concentrations of CP and RUP. ACKNOWLEDGMENTS

The authors express sincere appreciation t o Shourong Ma for laboratory assistance and t o Mike Grott for cow care and collection of samples. Appreciation also is extended to Consolidated Nutrition, L. C. (Fort Wayne, I N ) for partially supporting this research. REFERENCES 1Association of Official Analytical Chemists. 1984. Official Methods of Analysis. 14th ed. AOAC, Washington, DC. 2 Atwal, A. S., and J . D. Erfle. 1992. Effects of feeding fish meal to cows on digestibility, milk production, and milk composition. J. Dairy Sci. 75:502. 3 Bowman, J. M., D. G. Grieve, J. G. Buchanan-Smith, and G. K Macleod. 1988. Response of dairy cows in early lactation to sodium hydroxide-treated soybean meal. J. Dairy Sci. 71:982. 4 Cecava, M. J., D.L. Hancock, and J. E. Parker. 1993. Effects of zinc-treated soybean meal on ruminal fermentation and intestinal amino acid flows in steers fed corn silage-based diets. J. Anim. Sci. 71:3423. 5Christensen, R. A., G. L. Lynch, J. H. Clark, and Y . Yu. 1993. Influence of amount and degradability of protein on production of milk and milk components by lactating Holstein cows. J. Dairy Sci. 76:3490. 6Clark, J. H., T. H. Klusmeyer, and M. R. Cameron. 1992. Microbial protein synthesis and flows of nitrogenous fractions to the duodenum of dairy cows. J. Dairy Sci. 75:2304. 7Cunningham, K. D., M. J. Cecava, and T. R. Johnson. 1993. Nutrient digestion, nitrogen and amino acid flows in lactating cows fed soybean hulls in place of forage o r concentrate. J . Dairy Sci. 76:3523. 8Cunningham, K. D., M. J. Cecava, and T. R. Johnson. 1994. Flows of nitrogen and amino acids in dairy cows fed diets containing supplemental feather meal and blood meal. J. Dairy Sci. 77:3666. 9 Fox, D. G., C. J. Sniffen, J. D. O’Connor, J. B. Russell, and P. J. Van Soest. 1992. A net carbohydrate and protein system for evaluating cattle diets: 11. Cattle requirements and diet adequacy. J. Anim. Sci. 70:3578.

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10 Keery, C. M., and H. E. Amos. 1993. Effects of source and level of undegraded intake protein on nutrient use and performance of early lactation dairy cows. J. Dairy Sci. 76:499. 11Keery, C. M., H. E. Amos, and M. A. Froetschel. 1993. Effects of supplemental protein source on intraruminal fermentation, protein degradation, and amino acid absorption. J. Dairy Sci. 76: 514. 12King, K. J., J. T. Huber, M. Sadik, W. G. Bergen, A. L. Grant, and V. L. King. 1990. Influence of dietary protein sources on the amino acid profiles available for digestion and metabolism in lactating cows. J. Dairy Sci. 73:3208. 13Klusmeyer, T. H., R. D. McCarthy, Jr., J. H. Clark, and D. R. Nelson. 1990. Effects of source and amount of protein on ruminal fermentation and passage of nutrients to the small intestine of lactating cows. J . Dairy Sci. 73:3526. 14 Lundquist, R. C., D. E. Otterby, and J. C. Linn. 1986. Influence of formaldehyde-treated soybean meal on milk production. J. Dairy Sci. 69:1337. 15McCarthy, R. D., Jr., T. H. Klusmeyer, J. L. Vicini, and J . H. Clark. 1989. Effects of source of protein and carbohydrate on ruminal fermentation and passage of nutrients to the small intestine of lactating cows. J . Dairy Sci. 72:2002. 16 National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th rev. ed. Natl. Acad. Sci., Washington, DC. 17 SASS U s e i s Guide: Statistics, Release 6.03 Edition, 1988. SAS Inst., Inc., Cary, NC. 18 Schwab, C. G., C. K. Bozak, N. L. Whitehouse, and M.M.A. Mesbah. 1992. Amino acid limitation and flow to the duodenum a t four stages of lactation. 1. Sequence of lysine and methionine limitation. J. Dairy Sci. 75:3486. 19 Schwab, C. G., C. K. Bozak, N. L. Whitehouse, and V. M. Olson. 1992. Amino acid limitation and flow to the duodenum a t four stages of lactation. 2. Extent of lysine limitation. J . Dairy Sci. 753503. 20 Schwab, C. G., L. D. Satter, and A. B. Clay. 1976. Responses of lactating dairy cows to abomasal infusion of amino acids. J. Dairy Sci. 59:1254. 2 l V a n Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J . Dairy Sci. 74:3483. 22 Waltz, D. M., M. D. Stern, and D. J . Illg. 1989. Effect of ruminal protein degradation of blood meal and feather meal on amino acid supply to lactating cows. J . Dairy Sci. 72:1509. 23 Wattiaux, M. A., D. K. Combs, and R. D. Shaver. 1993. Milk yield and intake of cows fed alfalfa silage-based diets supplemented with undegradable protein. J . Dairy Sci. 76(Suppl. 1):164.(Abstr.) 24Whitelaw, F. G., J. S. Milne, E. R. 0rskov, and J. S. Smith. 1986. The nitrogen and energy metabolism of lactating cows given abomasal infusions of casein. Br. J . Nutr. 55:537. 25 Wildman, E. E., G. M. Jones, P. E. Wagner, R. L. Bowan, H. F. Trout, Jr., and T. N. Lesch. 1982. A dairy cow body condition scoring system and i t s relationship to selected production characteristics. J. Dairy Sci. 65:495. 26 Windschitl, P. M. 1991. Lactational performance of high producing dairy cows fed diets containing salmon meal and urea. J. Dairy Sci. 74:3475. 27 Windschitl, P. M., and M. D. Stem. 1988. Evaluation of calcium lignosulfonate-treated soybean meal as a source of rumen protected protein for dairy cattle. J. Dairy Sci. 71:3310.