1549
Effects of supplemental rumen-protected methionine and histidine on performance of lactating dairy cows
Objectives were to determine the effects of rumen-protected methionine (MET) and histidine (HIS) on lactation performance. Twenty-seven multiparous and sixteen primiparous dairy cows blocked by parity, milk production, DIM and breed were assigned a treatment in a randomized complete-block design. Cows were fed a covariate diet for 10 days followed by 4 weeks of experimental diets. Treatments were: 1) control diet (CON; formulated for 50.5 g MP MET), 2) CON + encapsulated MET (EM; 18 g of product, +10.8 g MP MET), 3) CON + spray-freeze MET (SFM; 33 g of product, +10.8 g MP MET), 4) SFM + encapsulated HIS (SFMH; 120 g of product, +10.1 g MP HIS). Diets were formulated using AMTS (Version 3.4.7.1). The control diet was balanced to contain 14.7% CP (91% of MP requirements) and maintained a LYS:MET ratio of 3.46:1. Addition of MET products reduced the LYS:MET ratio to 2.85:1. The control diet was created as a single batch in a vertical mixer and rumen-protected amino acids were added to CON at the Data Ranger to create treatments. Amino acid supplementation did not affect DMI, milk yield, feed efficiency, milk protein content or yield. Milk fat concentration and yield were greater (P < 0.05) for CON compared with EM and SFM. Differences in MUN among EM, SFM, and SFMH may be related to rumen digestibility of the products. Addition of rumen-protected MET or HIS for cows fed a 14.7% CP diet did not alter production performance.
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Treatment |
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Item |
CON |
EM |
SFM |
SFMH |
SEM |
Contrast1 |
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DMI, kg/d |
27.99 |
27.69 |
26.85 |
27.28 |
0.70 |
--- |
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Milk, kg/d |
35.30 |
35.31 |
35.10 |
35.20 |
0.75 |
--- |
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ECM, kg/d |
38.07 |
36.69 |
36.25 |
35.75 |
0.89 |
--- |
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ECMFE |
1.38 |
1.33 |
1.37 |
1.34 |
0.03 |
--- |
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Fat, % |
4.03 |
3.76 |
3.64 |
3.80 |
0.14 |
A |
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Fat, kg/d |
1.40 |
1.30 |
1.25 |
1.28 |
0.06 |
A |
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Protein, % |
3.27 |
3.23 |
3.29 |
3.29 |
0.05 |
--- |
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Protein, kg/d |
1.15 |
1.11 |
1.14 |
1.14 |
0.03 |
--- |
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MUN, mg/dL |
10.00 |
9.97 |
10.63 |
10.94 |
0.13 |
b, d |
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1Contrasts: A = CON vs. EM + SFM; B = EM vs. SFM; D = EM + SFM vs. SFMH. Uppercase = P < 0.05, lowercase = 0.05 < P < 0.10. |
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Keywords: histidine, metabolizable protein, methionine, rumen-protected amino acid