Feeding for Milk Components: Brief Overview

Dr. Bill Weiss, Professor and Extension Dairy Specialist, Department of Animal Sciences, The Ohio State University

          Current milk markets are putting a higher value on milk fat and a lesser value on milk protein which is opposite of the historical norm of protein being more valuable. Significant variation exists in both milk fat and milk protein concentrations among herds. Much of this variation is genetics, but a substantial amount is likely nutritional.  A survey of the Mideast Federal Order conducted by Penn State (https://extension.psu.edu/milk-components-understanding-milk-fat-and-protein-variation-in-your-dairy-herd) found that milk fat averaged about 3.76% but based on the reported standard deviation, 16% of herds sold milk with greater than 4.1% fat and 16% of herds sold milk with less than 3.4% fat. Some of the high testing herds were probably colored breeds, but breed cannot account for all the high testing herds. The average protein concentration of milk sold in that order was 3.05%, but 16% of herds had milk protein concentrations greater than 3.3% and 16% of herds had protein concentrations less than 2.9%. Concentrations of milk components are important, but the milk check is based on yields of components, not concentrations. Nutritional modifications that increase the concentrations of milk components but decrease their yields are not something you want to do.

          Increasing energy intake from starch usually increases both the concentration and yield of milk protein.  This can be accomplished by replacing fiber with starch (as long as you do not cause ruminal acidosis), by maintaining starch concentrations but improving forage quality so cows eat more, or by maintaining starch concentrations but replacing some forage fiber with byproduct fiber so that cows eat more. Over a wide range of energy intakes, the effect on milk protein yield and concentration was linear.  Perhaps surprisingly, dietary protein concentrations do not have a large impact on milk protein yield or concentration. In a study from Ohio State, increasing dietary crude protein from 13 to 17.5% increased milk protein concentration and yield; however, the effect was not linear and once dietary protein concentration reached 16%, it had no effect on milk protein. Most diets fed to lactating cows are usually at least 16% crude protein. Feeding supplemental rumen-protected (RP) amino acids can increase milk protein. Most studies report that feeding RP-methionine at about 20 grams/day increases milk protein with an average increase of about 3% in both yield and concentration of protein. Responses to other amino acids are less consistent. Feeding supplemental fat often decreases milk protein percentage but usually maintains or increases milk protein yield.

          Milk fat is more responsive to nutritional modifications than is milk protein. Starch has the opposite effect on milk fat as it does on milk protein. The effect starch has on milk fat yield depends on the type of forage in the diet. When alfalfa silage made up more than about 55% of the forage in the diet (the rest being corn silage), starch in the range of 22 to 30% did not have much effect on milk fat yield (starch was from dry ground corn and corn silage). As the concentration of alfalfa silage decreased below 55% and the concentration of corn silage increased, starch had a greater negative effect on milk fat yield. At the highest corn silage concentration tested (75% of the forage as corn silage and 25% as alfalfa), milk fat yield decreased linearly as starch increased from 22 to 30% of the diet. The generally positive effect alfalfa has on milk fat is caused in large part by the minerals in alfalfa.  Increasing the dietary cation-anion difference [DCAD calculated as: (dietary sodium + potassium) – (dietary chloride + sulfur), where minerals are expressed as milliequivalents per kilogram of diet] linearly increases milk fat concentration and yield. On average, the DCAD concentration in alfalfa is about 3 times greater than that of corn silage. Sodium bicarbonate, potassium carbonate and other buffers increase DCAD and often increase milk fat yield.

          Feeding more forage usually increases milk fat concentration but may not increase milk fat yield. If forage is not highly digestible or you feed too much forage fiber and dry matter intake decreases, milk fat yield often decreases. High forage diets can support high yields of milk fat, but their quality must be good. Replacing starch with byproduct fiber can increase milk fat percentage and yield when diets are high in corn silage and have more than 25 to 27% starch.

          Feeding supplemental fat usually increases milk fat yield, but the response is dependent on the type of fat fed. Based on a meta-analysis published in the Journal of Dairy Science in 2012, increasing dietary fat concentration 2 or 3 percentage units by feeding calcium soap similar to Megalac, oilseeds, or prilled fat increased milk fat yield by 0.1 (oilseeds) to 0.18 (soaps) lb/day, whereas supplementing tallow had no effect on milk fat yield. The gain in milk value caused by increased milk fat yield will need to be tempered if the fat supplement reduces milk protein yield.

          In summary, nutritional modifications can affect milk component yields. Unfortunately, several of the dietary changes affect milk protein and fat in different directions. Because of the high market value of milk fat currently, diets should emphasize increasing milk fat yield at the potential expense of reduced milk protein yields. This will change as milk markets change.