FEEDING FOR MILK COMPOSITION José Eduardo Portela Santos VMTRC – UC Davis

Fat Crude protein Milk Components Content Fatty acid profile 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 Trans fatty acids 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

Mechanism of Action of Trans FA 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 Grain Processing on Plasma Insulin Data from 832 blood samples from 32 cows (Santos et al., 2000)

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%) Sprndly (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

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

Conclusions