MILK PRODUCTION AND NUTRIENT UTILIZATION RESPONSES TO REDUCED DIET-CRUDE PROTEIN LEVEL AND METHIONINE SUPPLEMENTATION FOR DAIRY COWS

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

Dept. of Animal Prod., Fac. of Agric., Mansoura Univ., Mansoura

MILK PRODUCTION AND NUTRIENT UTILIZATION RESPONSES TO REDUCED DIET-CRUDE PROTEIN LEVEL AND METHIONINE SUPPLEMENTATION

FOR DAIRY COWS

(With 7 Tables)

By A.A. GABR; M.K. EL-BANNA*, M.A. EL-HARAIRY;

A.E. EI-SAYED** and M.B. ABOUL-ELA * Animal Prod. Res. Institute, Dokki, Giza, Egypt. ** El-Mansoura for Agric. Develop. Dairy Farm.

(Received at 21/3/2006)

إستجابة الأبقار الحلابة من إنتاج اللبن ومکوناته والقيمة الغذائية لعليقه

منخفضة البروتين مع إضافة الميثيونين المحمي أحمد عبد الرازق جبر،مصطفي قطب البنا،مصطفي عبد الحليم الحرايري،

علي السيد القدور السيد،محمد بدر الدين أبو العلا الغرض من هذا البحث هو دراسة مدي تأثير إضافة الحامض الأميني الميثيونين المحمي للعليقة المنخفضة في مستوي البروتين الخام بدون التأثير السلبي على إنتاج اللبن ومکوناته وکذلک القيمة الغذائية للعليقه ومدي الإستفادة منها. أجريت هذه الدراسة علي ۲۸ بقره هولشتين فريزيان حلابة عالية الإدرار. قسمت الحيوانات إلى أربعة مجاميع متناسقة، المجموعة الأولي: غذيت علي عليقه منخفضة في البروتين الخام (۱۹٫۹% على أساس المادة الجافة)، المجموعة الثانية: نفس عليقة المجموعة الأولي بالإضافة إلي الميثيونين المحمي، المجموعة الثالثة: خذيت على مستوى عالي من البروتين (۱۹٫۳%)، المجموعة الرابعة:

نفس عليقة المجموعة الثالثة بالإضافة إلى الميثيونين المحمي. أضيف الميثيونين بمقدار۱۲جم /بقره يوم بحيث يعوض مقدار النقص المحسوب نظريا والناجم عن خفض مستوي البروتين الخام. إضافة الميثونين المحمي للعليقة المنخفضة في مستوي البروتين أعطي تأثيرة إيجابيا على إنتاج اللبن ومحتواة من البروتين وکذلک أحدث تحسن في کفاءة تحويل العليقه والإستفاده من بروتينه وإنخفضت تکلفة العليقة لکل واحد کجم تبن وخاصة في مراحل الحليب الأولي ولم يختلف معنويا في تأثيره عن بقية المعاملات في مراحل الحليب المتأخرة. زيادة مستوي بروتين العليقه عن ۱۹٫۹% تسبب في زيادة معنوية في ترکيز نيتروجين يوريا الدم واللبن. وبذلک تکون التغذية على أساس المحتوي من الأحماض الأمينية فضلا عن المحتوي من البروتين الخام نظام غذائي مقبول لتحسين الأداء الإنتاجي لماشية اللبن عالية الإدرار مع الأخذ في الاعتبار التأثير السيادي لأسعار المکون البروتيني في العليقة والبحث

31:

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

عن أعلي معدل ربح عن طريق تکوين عليقه أقل تکلفة وکذلک تقليل تلوث البيئة بالنيتروجين المنبعث في البول والروث.

SUMMARY

This study was carried out to determine whether the addition of rumen protected Met to ration formulation allowed a reduction in dietary crude protein (CP) without jeopardizing total milk or milk protein yields. Twenty-eight multiparous Holstein-Friesian cows, in a commercial dairy herd, were randomly assigned to the trial. Rations differed in percentages of CP level (H, 19.3% or L, 16.9%), with or without supplementation by protected methionine. Milk yield was recorded individually at each milking and milk samples were taken during the experimental period. In addition, four digestion trials were conducted on three cows of each group to evaluate the digestibility coefficients of used diets using Acid Insoluble Ash technique. No effects of pMet supplementation or interactions between CP levels and methionine supplementation were detected on any of the parameters measured for digestibility coefficients of nutrient. In early lactation stage, milk production response to pMet supplementation was greater with the low level of CP diets compared with the high level (2.00 vs. 0.300 kg/d, respectively). The pMet supplementation by CP level interaction was significant for protein concentration, while it was not significant for fat and lactose concentration during early and mid lactation period. Every one percentage unit increase in dietary CP above 16.9%, MUN concentrations were, in average, increased 2.2, 2.0, and 1.6 mg/dl in early, mid, and late lactation, respectively. The feed and N utilization efficiencies were improved by feeding low CP diets supplemented with pMet in early lactation. Cows fed diets reduced in CP level had a reduction in cost of feed per kg milk in various stages of lactation. In early lactation stage, feeding diets supplemented with pMet reduced the cost of feed per kg milk by 0.04 L.E. It could be concluded that, a reduction in dietary protein to 16.9% and supplemented with protected AA, particularly the first limiting AA, is an acceptable new nutritional strategy for improving productive performance in dairy cattle and may be used as an approach for reformulating lactating cows rations based on AA profile rather than CP as simple or metabolizable protein. This strategy, with prevailing feed prices, could be compatible with maximum profit and a moderate amount of nitrogen excretion to the environment.

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

Key words: Crude protein, rumen-protected methionine, lactating cows.

INTRODUCTION

Overfeeding of CP to obtain maximum milk yield is common in the dairy industry today, increasing feed cost, decreasing the efficiency of nutrient utilization (Tamminga, 1992), and contributing to higher levels of N in the waste (St-Pierre and Thraen, 1999). Dairy cattle secrete roughly 25 to 35% of the N consumed as milk N, and almost all the remaining N is excreted in urine and feces (Chase, 1994). Most urinary N is excreted as urea (Broderick, 2003) and may be lost as ammonia into the environment (Van Horn et al., 1994). In Egypt, many of the applied strategies for meeting the nutritional requirements of high producing dairy cows may lead to feed diets with CP in excess. Dairy producers often feed CP over recommendations of NRC to early postpartum cows for higher milk peak. Close management of dietary protein is needed to maximize profits and to minimize risk of environmental damage caused by excessive nitrogen excretion in urine and feces. One possible way of reducing urinary N excretion is by reducing the amount of dietary CP fed to the cow. Decreasing dietary CP from 18.4 to 15.1% linearly decreased urinary N expressed as grams per day or as a percentage of N intake (Broderick, 2003). Unfortunately, dietary CP reduction also decreased milk production by 1.1 K/d (Broderick, 2003) and milk protein yield by nearly 100g/d (Kalscheur et al., 1999).

Methionine has been reported to be the first-limiting AA for milk yield and milk protein production (Bach et al., 2000). Under the assumption that dairy cattle require a certain amount of duodenal methionine to maximize production, the primary objective of this experiment was to verify the hypothesis that a lower protein diet with supplemented methionine would support milk and milk protein production as much as a higher CP diet.

In an experiment where treatments comprised two levels of CP high (19.3%) or low (16.9%) with or without protected methionine addition (by a dose designated to compensate the theoretically calculated deficiency level of methionine resulting from reducing dietary CP), the hypothesis would be supported by an interaction with supplemental methionine, improving performance and efficiency of the lower CP diet with less effect on the higher CP diet.

33

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

MATERIALS and METHODS Experimental design and treatments

Twenty-eight multiparous lactating Holstein-Friesian cows were used in the study. The cows were housed in a free-stall barn belong to El-Mansoura for Agriculture Development Dairy Farm. The cows were 20 +3 days post-calving and blocked into four similar groups, based on parity, average daily milk yield from the 7 through the 20th day of lactation. Cows were randomly assigned to one of four treatments. Group 1 (16.9B): received low CP level (16.9% on DM basis) diet, group 2 (16.9M): received low CP level (16.9% on DM basis) diet supplemented with pMet, group 3 (19.3B): received high CP level (19.3% on DM basis) diet and group 4 (19.3M): received high CP level (19.3% on DM basis) diet supplemented with pMet. The trial lasted for 220 days as experimental period.

Chemical compositions of feedstuffs (Table 1) of the experimental rations (barseem, corn silage, cottonseed meal; decorticated, soybean meal, wheat bran, and calcium soap of FA's) were analyzed according to A.O.A.C. (1984). Cows were fed Total Mixed Ration (TMR), ad libitum, (Table 2) that was based on a good quality of corn silage and soybean meal. The offered feed was calculated daily based on the weight of the refusals during the previous day (approximately 5% of the offered feed), which were measured each morning. Equal portions of the rations were fed at 0800, 1400, and 1700 h. The CP level was regulated by the concentrates, mostly SBM and cottonseed meal.

The NRC (2001) software was used to calculate the required amount of protected methionine (pMet) to be added and compensate partially the theoretically calculated deficiency level of methionine resulting from reducing dietary CP to the level 16.9% CP.

Protected Methionine (Smartamine M, 78% post-ruminally release of Met, Adisseo animal nutrition, France) supplementation to TMR at a rate of 12 g/cow/d was top-dressed and then mixed by hand into the TMR for each cow once daily at morning offered portion of TMR to ensure that the protective coats of Smartamine M was not destroyed by mechanical mixing.

All cows were milked three times daily. Milk yield was recorded individually at each milking for three days per week. Daily and weekly milk yield averages were calculated for each cow. The periods from wk 3 to 12 and from wk 13 to 21 were considered as the early and mid stage of lactation, respectively.

34

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

Sampling

The TMR was routinely sampled once biweekly for each diet, composited monthly, and frozen for later analysis of 3-mo pooled samples. Milk samples were collected at each milking from all tested cows at wk 3, 8, 12, and 18 of lactation. Samples of different milkings of the day were composited and preserved using potassium dichromate until analyzed for TS, SNF, lactose, protein, and fat by infrared analysis with a Fossmatic, Milk Scan System (Foss Electric, Hillerød, Denmark) and urea N (MUN) using a colorimetric procedure (Crocker, 1967). Digestion trials

At wk 18 of lactation period, four digestion trials were conducted on three cows of each group to evaluate the nutrient digestibility coefficient of used diets. The previous period of the study was considered as a preliminary period, followed by eight days as a collection period. Feed intake was individually recorded; Feces samples were collected directly from the rectum twice daily. The collected amount of feces was thoroughly mixed, and a sample was frozen for chemical analysis. Acid Insoluble Ash (AIA) technique was used as an internal marker to measure the digestibility coefficients of used diets and was determined according to Van Keulen and Young (1977). Proximate chemical analysis of TMR and feces samples were carried out for dry matter (DM), crude protein (CP), crude fiber (CF) and ash according to

the standard methods outlined by A.O.A.C. (1984). Acid ether extract (AEE) in calcium soap of FA's, TMR, and feces were determined by modified method, as was described by (Abo-Donia et al. 2003). Calculation and Statistical analysis:

The N utilization efficiency was calculated as follows: The N utilization efficiency = Milk N (kg) /feed N (kg) x 100 Milk N (kg) = (average milk yield, kg x (milk protein %/100))/6.38 Feed N (kg) = (average DMI X (CP % in the ration/100))/ 6.25

The crude protein in milk has a different multiplier (N x 6.38) than in feed (N X 6.25) because milk protein contains a differen proportion of N (15.7%), while in feed about 16%. The cost of feed per 1 kg milk was calculated based on the following: Cost of pMet (L.E./day) = 0.13 (L.E./1g) x 12 (g/cow/ day) = 1.56 L.E./ cow/ day Cost of pMet/1kg DM = Cost of pMet (L.E./day)/ average DMI (kg) for each group Cost of 1kg dry matter = 1.55 L.E. for high dietary CP level and 1.35 L.E. for low dietary crude protein level (calculated based on farm data).

35

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006 The data obtained were statistically analyzed using SAS computer program (SAS, 1996).

The following mode was used for analyzing data of daily average milk yield, contents and yields of milk total solids (TS), solids not fat (SNF), lactose, protein, and fat, milk urea nitrogen (MUN) concentration, and digestibility coefficients of nutrient through the studied period:

Yijk = u + Pi+ S; + PS.ij + eijk Where: u = overall mean, Pi = effect of the ith CP level and i=1(low CP level) or 2 (high CP level), S;= effect of jth pMet supplementation where j= 1(non-supplemented) or

2 (supplemented) PSij = the interaction between CP level and pMet supplementation, eijk = common error term

The differences among means were tested using Duncans (Duncan, 1955) Multiple Range Test.

RESULTS

The apparent digestibility coefficients of nutrients, except for EE, (Table 3) was reduced (P <0.01) for cows fed diet with low CP compared with those fed diet with high CP. No effects of pMet supplementation or interactions between CP levels and methionine supplementation were detected on any of the parameters measured for digestibility coefficient of nutrients.

Cows fed diet (16.9% CP) supplemented with pMet (16.9M) produced daily milk yield numerically higher than those fed high level of crude protein without (19.3B) or with (19.3M) pMet during early, Mid, and late lactation (33.7 vs. 33.1 and 33.4, 38.7 vs. 38.3 and 38.6, 23.5 vs.23.2 and 22.9 kg/d, respectively, Tables 4, 5, and 6).

As indicated in Tables 4, 5, and 6 pMet supplementation significantly (P<0.01) increased daily milk yield in early lactation period, but in mid or late stage of lactation it did not; as similar as CP level did. It is worthy noting also that the production response to pMet supplementation was greater with the low level of CP diets compared with the high level (2.00 vs. 0.300 Kg/ d, respectively). Milk protein percentages (Tables 4, 5, and 6) were similar in groups 16.9M and 19.3B through the different stages (early, mid, and late) of lactation (2.7, 2.6, and 2.7, respectively). Supplementing the basal diets of lactating cows with pMet increased (P<0.01) percentage of protein in milk. Moreover, responses were consistent across dietary CP level (CP X pMet

36

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

interaction, P<0.05). Supplementing 19.3B or 16.9B with pMet increased milk protein content 0.2 percentage unit. As shown in Tables 4, 5, and 6, pMet supplementation of the basal diets had no effect on milk fat content during the early and mid stage of lactation. In the late stage of lactation, adding pMet to 16.9B or 19.3B increased (P<0.01) milk fat content. No differences across treatments were detected in percentage of lactose throughout the full lactation. The percentages of TS and SNF in milk were significantly increased (P<0.01) by pMet supplementation in mid and late lactation.

The present results (Table 4, 5, and 6) indicated that for every one percentage unit increase in dietary CP above 16.9%, MUN concentrations were, in average, increased 2.2, 2.0, and 1.6 mg/dl in early, mid, and late lactation, respectively.

Table 7 shows that the feed efficiency (average kilograms of milk per average kilograms of dry matter intake) was improved by feeding diets supplemented with pMet in early lactation. Furthermore, the highest value of feed efficiency (1.48) was recorded in group 2 (16.3M). N utilization efficiency was improved by feeding diets supplemented with pMet in various stages of lactation). However, it is worthy noting that the rate of improvement in N utilization efficiency was a diminished response by advance in days in milk, given its highest value in early lactation and the lowest value was recorded in late stage of lactation. The cost of feed per kg milk was reduced by 0.04 L.E. in cows fed diets supplemented with pMet at early stage of lactation.

Table 1: Chemical composition of feedstuffs

Chemical analysis Feedstuffs

DM OM CPCF AEE NFE Ash

---------------% of DM ---------- Barseem

21.72 90.52 10.68 11.46 0.78 67.599.48 Corn silage

34.33 89.959.35 33.56 3.06 43.98 10.05 Corn grain, dry

88.00 98.82 8.75 2.61 4.32 83.14 1.18 Cottonseed meal, decort.

90.00 91.00 47.41 10.11 5.56 27.92 9.00 Soybean meal, 44% CP

87.00 92.53 50.578.39 1.72 31.84 7.47 Wheat bran

88.00 93.18 13.65 12.50 4.55 62.49 6.82 Calcium soaps of FA's*

97.00 82.51

82.51* - 17.49 Di-calsium phosphate

97.00 Limestone, ground

94.10 Salt

94.02 Sodium bicarbonate

95.01 Vitamin & mineral premix

97.63 - *EE in Calcium soap of FA's was determined as Acid Ether Extract (AEE). Chemical compositions of Di-calcium phosphate, Limestone, Salt, Sodium bicarbonate, and Vitamin & mineral premix were cited from NRC, 2001.

37

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

Table 6: Effects of crude protein level and methionine supplementation

on milk yield and its composition in late lactation.

2.5

2.7

4.6

11.9

Dietary treatments 16.9%CP 1 19.3%CP

Effect (P-value) Item

16.9B 16.9M 19.3B19.3M CP Met CP x Met Milk yield, Kg/d

23.4

23.5 23.2

122.9 0.580 0.699 0.226 Milk composition, %

Protein

2.9 0.0001

0.0001

0.738 Fat

3.6

2.7 3.7 0.0001

0.0001

0.0001 Lactose

4.5

4.6 4.6 0.861 0.614 0.871 Total Solids (TS)

12.1 12.2 12.4 0.0001 0.0001 0.850 Solids Not Fat (SNF) 8.3

9.5 8.7 0.0001 0.0001 0.866 Milk component, gd

Protein

585.0 634.5 626.4 664.1 0.0001 0.0001

0.673 Fat

842.4 869.5

626.4

847.3 0.0001 0.0001 0.0001 Lactose

1053.0 1081.0 1067.2 1053.1 0.458 0.669 0.805 Total Solids (TS) 2784.6 2843.5 2830.4 2839.6 0.021 0.371 0.752 Solids Not Fat (SNF) 1942.2 1974.0 2204.0 1992.3 0.010 0.198

0.786 MUN?, mg/dl

18.8 18.0 | 22.

6 2 2.0 | 0.0001 0.0001 0.311 Treatments:16.9B = Basal diet (16.9%CP); 16.9M = Basal diet (16.9%CP) + pMet; 19.3B= Basal (19.3%CP); 19.3M=Basal (19.3%CP) + pMet. ?MUN= Milk Urea Nitrogen.

Effect: CP= main effect of CP; Met = main effect of methionine; CP x methionine interaction.

Table 7: Feed and economical efficiencies for various groups of

cows**.

Group

pMet

CP level

Item

HIL

22.8

1.11

22.8

1.46 19.6 1.09 23.7 1.62 25.0 0.98

18.2 1.29 20.0 1.22

227 1.44 21.3 0.96 23.9 1.61 23.3 0.86

DMI (kg/d)

22.7

22.5 22.9 22.6

22.9 Early Milk (kgkg DMI

1.40 1.48

1.47

1.46 1.36 1.47 N utilization efficiency 20.24 23.13 20.16 21.47 18.4 22.5 Cost of feed/ kg milk 0.96 0.96 1.05

1.07 1.03 DMI (kg/d)

23.5 23.9 24.0 23.8 23.8 23.9 Milk (kg) kg DMI 1.63 1.62 1,60 1.62 1.61 1.62 Mid

N utilization efficiency 23.56 24.40 21.06 23.05 23.9

24.4 Cost of feed/ kg milk 0.83 0.87

0.97 0.99

0.94 DMI (kg/ d)

18.2 18.1 17.9 18.4 18.3 18.1 Late Milk (kg) kg DMI 1.29 1.30 1.30 1.24 1.27

N utilization efficiency

18.631

20.32 17.76 18.32 19.1 20.3 Cost of feed/ kg milk 1.05 1.10 1.19 1.31 1.14 1.18 ** Group 1: received low CP level (16.9% on DM basis) diet non-supplemented with pMet,

Group 2: received as that of group 1 diet, but supplemented with pMet, Group 3: received high CP level (19.3% on DM basis) diet non-supplemented with pMet,

Group 4: received as that of group 1 diet, but supplemented with pMet, O=nonsuplemented, 1= supplemented, H=high CP level and L=low CP level.

0.90

1.28

18.2 1.27 19.4 1.09

40

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

DISCUSSION

Apparent Digestibility of Nutrients

This study showed that, except for EE, digestibility coefficients of nutrients was significantly improved by increasing dietary CP diet. Ha and Kenelly (1984) have suggested that higher apparent digestibility of DM and CP at higher dietary CP concentrations result from a combination of improved microbial fermentation and greater digestion in the gastrointestinal tract. Supplementation of pMet had no effect on digestibility coefficient of nutrients. These results are consistent with those reported by Vazquez-Anon et al. (2001), who reported no improvement was observed in nutrient digestibility when liquid methionine was added to the diet. In agreement with these results, Blum et al. (1999) reported that supplementation with different types of pMet did not affect nutritive value. Lactation Responses

Supplementation of pMet increased daily milk yield mainly in early lactation period, as similar as high CP level did. This may be attributed to the challenge in diet formulation in achieving the desired concentration of methionine by relying solely on feed protein supplements during early lactation period; the period in which dry matter intake is relatively low and the level of milk production progressively increases. In agreement with the results of this study, others have noted that Met was limiting for milk yield, especially in early lactation cows (Samuelson et al., 2001; Noftsger and St. Pierre, 2003). However, the present finding disagrees with previous reports (Leonardi et al., 2003) that have reported a lack of significant effect of pMet supplementation on milk production, especially when corn silage in the ration was the main forage. Possible explanations for these inconsistent responses are the variable doses used in the studies, the strategies that by which pMet was used, the quantity of CP in the diet, the nature of the supplemental protein source, particularly its AA contents, and the level of milk production.

The production response to pMet supplementation was greater with the low level of CP diets. This finding agrees with that reported by NRC (2001). Who concluded from a number of reviews that production response to pMet supplementation were greater when CP level approximates the normal levels (14 to 18 percent) than when it was lower or higher.

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

Supplementing the diet of low CP level with pMet increased milk protein percentage to the same level produced from cows fed diet with high CP level. These results are similar to those reported by both of Misciattelli et al., (2003), Socha et al., (2005). According to these authors, pMet supplementation increased milk protein content during early- and mid-lactation when the main source of protein was soybean meal. During early and mid lactation, cows have a greater demand for Met to meet the demands of high milk yield and, consequently, the dietary Met content is expected to be deficient in the low level CP diet, but in late lactation, these demands decline as milk yield decreases. So, added Met might partially compensated the shortage of dietary Met resulting from decreasing CP level in the diet during early and mid lactation, whereas it had no revenue when was supplemented to the low CP diet in late lactation that might be originally sufficient in Met content. Literature summaries confirm that responses to postruminal lysine (Lys.) and methionine (Met.) supplementation are greater when basal levels of Lys and Met in Rumen undegradable protein (RUP) are low rather than high, when cows are in early rather than mid or late lactation, and in high- producing cows rather than low producing cows (Rulquin and Verite, 1993; NRC, 2001). pMet supplementation had no effect on milk fat and lactose content during the early and mid stage of lactation. These results are in consistent with those reported in most researches (Pacheco-Rios et al., 1999; Leonardi et al., 2003). The increases in TS content observed during mid and late lactation are mainly attributed to the increases in milk fat and protein concentrations during those periods, while that observed in SNF percentage may be due to the increase in milk protein content.

Cows fed high CP diets had greater concentrations of milk urea nitrogen (MUN) and plasma urea nitrogen (PUN; data not shown), probably due to the higher N intake on the diet. Similar results were reported by Leonardi et al. (2003), who found an increase of 3.8 mg/dl of milk urea nitrogen when dietary protein increased by 2.7-percentage unites. Hutjens and Barmore (1995) suggested that MUN in the range of 12 to 17 mg/dl would indicate optimal balance of RDP and ruminally fermentable energy. Therefore, elevated MUN above the upper level of this range may indicate excess protein has been fed to the dairy cow for her given level of production (Jonker et al., 1998). Others have also noted that MUN had a positive relationship with levels of dietary CP (Frank and Swenson, 2002) and dietary CP content was the best single predictor of MUN (Nousiainen et al., 2004). The primary field

42

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

application of these results is that elevated MUN, above target levels, would indicate that excess protein is being consumed. Reformulating the diet with a lower protein concentration could reduce MUN concentration. Feed efficiency:

Feed efficiency is a measure of how well cows convert the nutrients they eat into products. In the current study, the feed efficiency was determined as milk (Kg) / dry matter intake (Kg), milk nitrogen/ intake nitrogen, and cost of feed per kg milk. Supplementing the diet of low CP level with pMet improved the feed efficiency. The N utilization efficiency gives an index of feed protein utilization, and should likely go in the opposite direction that MUN values go. N utilization efficiency was improved by feeding diets supplemented with pMet. Which may indicate that feeding dietary CP level close to NRC recommendations and supported with adjusted amount of pMet is an acceptable nutritional strategy for improving feed efficiency and N utilization efficiency in dairy cattle. The cost of feed per kg milk was reduced in cows fed diets supplemented with pMet at early stage of lactation, but in mid and late stage of lactation it increased by the same value, which may indicate that the supplementation of pMet is profitable in early lactation, but not profitable in mid or late stage of lactation. Although, increasing of dietary CP level increased milk production in the current study, cows fed diets reduced in CP level had a reduction in cost of feed per kg milk in various stages of lactation. This may indicate that the point of maximum profitability is likely to be at a dietary protein concentration below that needed for maximum milk production.

Collecting all the results together, Cows receiving 16.9% CP plus pMet (16.9M), consumed the same amount of DM, produced numerically more average daily milk, same milk protein content, reduced in cost of feed per kg milk in various stages of lactation and converted dietary N to milk N with a higher gross efficiency when compared to cows receiving 19.3% CP. These results suggested that 16.9M were similar, if not superior, in nutritive value to 19.3B.

In conclusion, the results obtained in the present study indicate that close management of dietary protein is needed to maximize profits. Furthermore, feeding dietary CP lowered to the level that achieves the optimal concentration of MUN with supplementation of pMet to compensate for low dietary CP level, as that in group 2, (16.9M) improved feed and N utilization efficiencies and reduced the cost of feed per kg milk. It could be an acceptable new nutritional strategy for

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

improving productive performance and may be used as an approach for reformulating lactating cows rations based on AA profile rather than CP as simple or metabolizable protein.

REFERENCES

Abo-Donia, F.M.A.; Ibrahim, S.A., El-Shabrawy, H.M. and Salama,

A.M.A. (2003): Milk production and composition of Friesian crossbred cows fed rations containing different sources of energy. The 9th Scientific Conference on Animal Nutrition

October 2003-Horgada. (507). Association of Official Analytical Chemists (A.O.A.C), (1984): Offi

Methods of Analysis. 12th ed. AOAC, Arlington, VA. Bach, A.; Huntington, G.B.; Calsamiglia, S. and Stern, M.D. (2000): BE Nitrogen metabolism of early lactation cows fed diet with two

different levels of protein and different amino acid profiles. J.

Dairy Sci. 83: 2585-2595. Blum, J.W.; Bruckmaier, R.M. and Jans, F. (1999): Rumen-protected A methionine fed to dairy cows: bioavailability and effects on

plasma amino acid pattern and plasma metabolite and insulin

concentrations. J. Dairy Sci. 82: 1991-1998 Broderick, G.A. (2003): Effects of varying protein and energy levels on

the production of lactating dairy cows. J. Dairy Sci. 86:1370 BE1381. Chase, L.E. (1994): Environmental considerations in developing dairy

rations. Pages 56-62 in Proc. Cornell Nutr. Conf. Feed Manuf.,

Rochester, NY. Cornell Univ., Ithaca, NY. Crocker, C.L. (1967): Rapid determination of urea nitrogen in serum or

plasma without deproteination. Am. J. Med. Technol. 33: 361

365. Duncan, D.B. (1955): Multiple range and multiple F test. Biometrix 11:

1-42. Frank, B. and Swenson, C. (2002): Relationship between content of

crude protein in rations for dairy cows and milk yield, concentration of urea in milk and ammonia emissions. J. Dairy

Sci. 85: 1829-1838. Ha, J.K. and Kennelly, J.J. (1984): Effect of protein on nutrient

digestion and milk production by Holstein cows. J. Dairy Sci.

67: 2302-2307. Hutjens, M.F. and Barmore, J.A. (1995): Milk urea test gives us another

tool. Hoard's Dairyman. May 25, p. 401.

44

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

Jonker, J.S., Kohn, R.A. and Erdman, R.A. (1998): Using milk urea

nitrogen to predict nitrogen excretion and utilization efficiency

in lactating dairy cattle. J. Dairy Sci. 81: 2681-2692. Kalscheur, K.F.; Vandersall, J.H.; Erdman, R.A.; Kohn, R.A. and

Russek-Cohen, E. (1999): Effects of dietary crude protein concentration and degradability on milk production responses of early, mid, and late lactation dairy cows. J. Dairy Sci. 82:

545-554. Leonardi, C.; Stevenson, M. and Armentano, L.E. (2003): Effect of two

levels of crude protein and methionine supplementation on

performance of dairy cows. J. Dairy Sci. 86: 4033-4042 Misciattelli, L.; Kristensen, V.F.; Vestergaard, M.; Weisbjerg, M.R.;

Sejrsen, K. and Hvelplund, T. (2003): Milk production, nutrient utilization, and endocrine responses to increased postruminal lysine and methionine supply in dairy cows. J. Dairy Sci. 86:

275-286. National Research Council (NRC, 2001): Nutrient requirements of dairy

cattle. (7th rev. ed.). National Academy Press, Washington, DC,

USA. Noftsger, E. and St-Pierre, N.R. (2003): Supplementation of methionine

and selection of highly digestible rumen undegradable protein to improve nitrogen efficiency for milk production. J. Dairy Sci.

86: 958-969. Nousiainen, J.; Shingfield, K.J. and Huhtanen, P. (2004): Evaluation of

milk urea nitrogen as a diagnostic of protein feeding. J. Dairy

Sci. 87: 386-398. Pacheco-Rios, D.; McNabb, W.C.; Hill, J.P.; Barry, T.N. and

Mackenzie, D.D.S. (1999): The effects of methionine supplementation upon milk composition and production of

forage-fed dairy cows. Can. J. Anim. Sci.: 235-240. Rulquin, H. and Verite, R. (1993): Amino acid nutrition of dairy cows:

Production effects and animal requirements. Page 55 in Recent Advances in Animal Production, Proc. 27th Univ. Nottingham Feed Manufacturer's Conf., P. C. Gainsworthy, ed. Nottingham

University Press, Nottingham, UK. Samuelson, D.J.; Denise, S.K.; Roffler, R.; Ax, R.L.; Armstrong, D.V.

and Romagnolo, D.F.J. (2001): Response of Holstein and Brown Swiss cows fed alfalfa hay-based diets to supplemental methionine at two stages of lactation. J. Dairy Sci. 84: 917-928.

Assiut Vet. Med. J. Vol. 52 No. 109 April 2006

SAS User's Guide: Statistics. (1996): Version 5 Edition. SAS Inst., Inc.,

Cary, NC. Socha, M.T.; Putnam, D.E.; Garthwaite, B.D.; Whitehouse, N.L.;

Kierstead, N.A.; Schwab, C.G., Ducharme, G.A. and Robert, J.C. (2005): Improving intestinal amino acid supply of pre-and postpartum dairy cows with rumen-protected methionine and

lysine. J. Dairy Sci. 88: 113-1126. St-Pierre, N. and Thraen, C.S. (1999): Animal grouping strategies,

sources of variation, and economic factors affecting nutrient

balance on dairy farms. J. Anim. Sci., 77 (Suppl. 2): 72-83. Tamminga, S. (1992): Nutrition management of dairy cows as a

contribution to pollution control. J. Dairy Sci. 75: 345-357. Van Horn, H.H.; Wilkie, A.C.; Powers, W.J. and Nordstedt, R.A. (1994):

Components of dairy manure management systems. J. Dairy

Sci. 77: 2008-2030. Van Keulen, J. and Young, B.A. (1977): Evaluation of acid-insoluble ash

as natural marker in ruminant digestibility. J. Anim. Sci. 44:

262-266. Vazquez-Anon, M.; Cassidy, T.; McCullough, P. and Varga, G.A.

(2001): Effects of aliment on nutrient digestibility, bacterial protein synthesis, and ruminal disappearance during continuous culture. J. Dairy Sci. 84: 159-166.