FEEDING FOR MILK COMPOSITION Jos Eduardo Portela Santos

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

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. B 12 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 Co. A Carboxylase activity decreased (61%) – Fatty acid synthase activity decreased (54%) – Acetil Co. A Carboxylase m. RNA 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 P < 0. 05 • 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 (r 2=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