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Milk Components
• Fat– Content– Fatty acid profile
• Crude protein– Content– True protein vs NPN
• Lactose
• Minerals and vitamins
• Several nutritional factors affect the composition of milk of dairy cows:
– Energy intake (Mcal of NEL)
– Energy source• CHO• Lipids
– Protein intake– Protein degradability and quality– Interactions between protein and energy– Amino acids– Minerals: Na, K (DCAD)– Feed additives (Niacin, fibrolytic enzymes)
Milk Fat
• Forage:Concentrate ratio
• CHO:
– NDF
– Effective NDF
– Physically effective NDF
– Ruminal digestibility of NDF
– NFC
• Composition of the NFC: sugars, starch and pectin
• Ruminal degradability of starch
• Ionophores
• Fat supplementation
• Lack of RDP (fiber digestibility and
buffering effect)
• Dietary buffers
Theories
• Low fat diets
• Acetate deficiency
• B-OH-butyrate deficiency
• High rumen molar concentration of
propionate: Insulin theory (glucogenic theory)
• Vit. B12 deficiency
• Trans fatty acids
Effect of TFA infusion on milk yield and composition
Gaynor et al. 1994 Romo et al. 1995
Cis Trans Cis Trans
Fat infused, g/d 750.0 750.0 620.0 620.0
TFA infused, g/d 0.0 306.0 0.0 257.0
Milk, kg/d 46.3 47.0 34.5 33.9
Milk Trans-C18:1, % 3.1 8.0 1.7 14.0
Milk composition, %
Fat 3.3 2.6 4.1 3.2
Protein 3.0 3.1 3.2 3.1
Effect of forage level and buffer addition on milk composition
Diet Rumen
pH Duodenal TFA, g/d
Milk TFA, %
Milk TFA, g/d
Milk Fat, %
60% forage, no buffer
6.13 61 3.1 33 4.09
60% forage, buffer
6.15 57 2.9 33 4.22
25% forage, no buffer
5.83 120 5.8 56 3.42
25% forage, buffer
6.02 66 2.9 33 3.91
05
101520253035404550556065707580
g/1
00g
Control4.1%
High Corn2.0%
Control3.3%
High Corn1.8%
Control3.6%
High Corn1.6%
Effect of Forage:Concentrate Ratio on Milk Fat % and Milk Fatty Acid Composition
SCFA, g/100g LCFA, g/100g
Mechanism of Action of Mechanism of Action of Trans FAFA
• Milk fat suppression: reduced SCFA (De Novo
synthesis)
• Trans fatty acids depress milk fat in 48 to 72 hs
• Preliminary data from Maryland (Piperova et al.,
1998):
– Acetil CoA Carboxylase activity decreased (61%)
– Fatty acid synthase activity decreased (54%)
– Acetil CoA Carboxylase mRNA decreased (55%)
Nutritional Causes of Milk Fat Suppression
• Inadequate NDF• Inadequate physically effective NDF (particle
size)• Poor NDF digestibility• Forage source: buffering capacity• Excessive amounts of NFC• Excessive amounts of RDS• High fat diets
• Fat sources with highly unsaturated FA profile– Yellow grease, oils
• Interactions between fat source and forage source (binding sites)– Alfalfa hay vs corn silage
• Protein supplements with high PUFA content– Fish meal, blends of marine by products
• Lack of RDP (fiber digestibility & buffer effect)• Lack of buffers
Milk Protein
• NEL intake
• Forage:Concentrate ratio
• Amount of fermentable CHO (RDS)
• Dietary CP level
• Amino acid profile of the protein flowing to the
duodenum
• Dietary fat
Effect of Varying the Ratio Forage:Concentrate on MilkComposition
Ratio Forage:Concentrate
Item 80:20 65:35 50:50 35:65
Milk, kg 20.80 21.60 22.30 23.40
Composition, %
Protein 3.11 3.12 3.22 3.26
Fat 3.83 3.72 3.68 3.33
Lactose 5.28 5.33 5.33 5.55
Adapted from Macleod et al. (
Effect of Grain Processing on Milk Protein Content
Diet
Cows (Studies) DRS SFS SRC SFC P <
RD Starch, % 52 76 71 81 0.01
92 cows (4) 2.99 3.06 0.11
358 cows (14) 2.95 3.02 0.01
92 cows (4) 2.99 2.92 0.01
Adapted from Theurer et al. (1999) and Santos (2000).
Effect of Isocaloric Infusions of Propionate or Acetate in the Duodenum, orGlucose in the Rumen on Milk Protein Content
Treatment
DRS + DP DRS + RG SEM P < Reference
Milk Protein, % 2.99 3.18 0.01 0.03 Aquino-Ramos,1996
DRS + DA SFS + H2O
Milk Protein, % 2.85 2.91 0.04 0.50 Aquino-Ramos,1996
DRS + DP DRS + RG
Milk Protein, % 2.72 2.88 0.03 0.08 Wu et al., 1994
Effect of Grain Processing on Plasma Insulin
12.66
10.38
6
7
8
9
10
11
12
13
14
uIU
/ml
Insulin
SFS SRC
• Data from 832 blood samples from 32 cows (Santos et al., 2000)
P < 0.05
Effect of Duodenal Infusion of Amino Acids and InsulinTreatment on Milk Protein Synthesis of Dairy Cows
Treatment
Item Water BC Water+I BC+I Insulin
P <
DMI, kg/d 26.2 27.6 25.1 25.2 0.08
Milk, kg/d 26.5b 27.5b 28.3ab 29.8a 0.05
Protein, % 3.29b 3.31b 3.52a 3.66a 0.01
Protein, g/d 867b 895b 995a 1080a 0.001
Adapted from Mackle et al. (1998).
• Diets with more fermentable energy increase milk protein:– Increase flow of microbial protein
– increase molar concentration of propionate
in the rumen
– increase blood insulin
Dietary Protein and Milk Protein
• Low efficiency of N utilization for milk protein
synthesis (< 30%)
• Sprndly (1986): No relationship between dietary
CP content and milk protein concentration
• Emery (1978): correlation between dietary CP and
milk protein content (r2=0.35)
– The effect of higher CP diet is associated with
greater DMI and total energy intake
Chemical Scores of Protein Sources in Relationship to Milk Protein (Chandler, 1989).
Protein Source His Phe Leu Thr Met Lys Arg Val Ile Trp
Ft. Meal 11 59 66 59 23 13 32 38 32 29
C.G. Meal 67 100 100 60 100 18 36 48 40 30
DDG + Solubles 74 84 72 63 81 24 42 53 38 45
Brewers Grains 56 100 83 65 78 34 53 65 74 87
Alfalfa Meal 69 100 55 80 60 46 50 66 51 100
M&B Meal 64 64 46 59 49 55 76 48 36 32
Meat Meal 67 65 46 59 49 58 76 51 36 39
SB Meal 89 100 56 74 56 70 89 60 55 75
F. Meal 77 69 58 68 100 80 59 59 47 71
B. Meal 100 100 93 86 45 91 33 70 10 76
Microbes 90 97 54 100 97 100 79 66 61 99
Comparison of Nitrogen Flow to the Duodenum of Cows Fed SBM ora High RUP Supplement (14 Studies with 27 comparisons)
Treatment Difference
Item SBM RUP g/d % P <
N intake, g/d 469.1 463.6 - 6.5 - 1.4 0.67
Flow to duodenum, g/dMicrobial N 275.6 240.2 - 35.4 - 12.85 0.001
NANMN 201.1 248.9 47.8 23.77 0.002
NAN 474.3 486.7 12.4 2.61 0.31
EAA 1,102 1,159 57.0 5.17 0.11
Lys 230.5 138.7 - 91.8 - 39.83 0.14
Met 45.11 46.54 1.43 3.17 0.42
Summary of Studies Comparing SBM with all RUP Sources
Milk FCM Fat % Protein %
- 0 + - 0 + - 0 + - 0 +
TOTAL 8 103 25 4 94 11 21 99 9 28 95 6
Santos et al. (1998)
Dietary Fat and Milk Protein
• Negative relationship between dietary fat and
milk protein concentration
• Independent of fat source
• Increased efficiency of amino acid extraction
• Supplying more fermentable CHO or high quality
RUP partially overcomes milk protein depression
Effect of Dietary Fat on Mammary Blood Flow
Treatment
Mammaryblood flow
RC-LF AC-LF RC-HF AC-HF Fat
P <
L/h 937.8 911.6 860.5 854.1 0.65
L/kg milk 912.8 854.5 756.9 724.6 0.07
Cant et al. (1993)