Recently, the USDA released minimum class and component prices in the Federal Milk Marketing Orders (FMMOs) during the month of August. Average milk protein value for that month was $4.44 per pound, about 3 times greater than milkfat value ($1.63 per pound). Putting that into perspective, at current prices, increasing a tenth on the milk protein concentration on a 90-pound herd would improve daily income by 40 cents per cow, or $146 per cow per year.
Providing the right amount of amino acids to the udder for milk protein synthesis is the main objective of a feeding program. Since ruminal microbial protein is similar to the amino acid composition of milk protein, maximizing microbial protein synthesis in the rumen is the most effective approach to boost milk protein production. This article discusses three feeding management practices and nutritional strategies for improving milk protein yield and content.
1. Grinding corn more finely
Ground corn is the most economical way for feeding corn grain to dairy cows. However, offering coarse- versus fine-ground corn may drastically affect cow performance. An Italian study evaluated the effects of corn particle size on milk protein production. The researchers fed two total mixed ration (TMR) diets based on dry hay forage (36.4% on dry matter [DM] basis) and course- or fine-ground corn (30% on DM basis) with a mean geometric particle size equal to 978 and 511 microns, respectively.
Although milk yield (73 pounds per day), 3.5% fat-corrected milk (69 pounds per day) and milkfat content (3.2%), were not affected by corn particle size, fine-ground corn improved milk casein (2.57% versus 2.48%) and milk crude protein content (3.31% versus 3.18%).
Moreover, fine-ground-corn-fed cows spent more time below the 5.5 pH threshold (61 versus 15 minutes per day) and had an average daily variation in reticular pH characterized by a lower minimum pH (5.72 versus 5.95) and a higher pH range (0.94 versus 0.79). These results show that feeding fine-ground corn (smaller than 500 microns) improves ground-corn utilization and milk protein synthesis, but special attention should be placed on the supply of effective fiber to avoid subacute ruminal acidosis.
2. Avoiding sorting behavior
Dairy cows selectively consume their rations, generally sorting in favor of finer particles and rejecting longer particles, mainly dry forages. DM content of the diet, particle size of forages, frequency of push-ups, number of feedings, weighback and competition at the feedbunk are the main factors affecting sorting behavior.
A study published recently in the Journal of Dairy Science showed the association between sorting behavior and milk protein production. The researchers evaluated feeding behavior in lactating Holsteins at the University of Guelph, Kemptville Campus Dairy Education and Innovation Center. Particle size distribution in the offered diet was 8% long particles (greater than 19 millimeters), 53.5% medium particles (8 – 19 millimeters), 29.1% short particles (1.18 – 8 millimeters) and 9.4% fine particles (less than 1.18 millimeters).
Cows sorted against long particles and in favor of short and fine particles. On average, intake of the longest particles, expressed as a percentage of the predicted intake, was 78% (ranging from 45% to 103%). Milk production on the group was 90.6 pounds per day with 3.81% fat and 3.3% protein. The authors found negative associations between feed sorting and milk composition: for every 10% increase in sorting against long particles, milk protein contents decreased by 0.04 percentage units.
3. Feeding sugars
Feed co-products such as molasses, whey, almond hulls, bakery meal and citrus pulp that are rich in sugar. A meta-analysis published recently in The Professional Animal Scientist reported the positive effects of additional dietary sugar in milk protein production. A meta-analysis is the statistical procedure for combining data from multiple studies. The authors used data obtained from 21 scientific papers, including 85 treatments in which sugar was added to the diets at different levels.
Although milk protein content was not affected by feeding sugar (3.11%), daily protein yield increased lineally from 2.18 pounds in cows not receiving additional sugar to 2.20, 2.24 and 2.27 pounds in cows fed diets including 1.5-3, 3-5 and 5-7 (% of diet dry matter) added dietary sugar. Interestingly, high-producing cows (producing more than 74 pounds of milk per day) showed greater responses to added sugar. While low-producing cows (producing less than 74 pounds per day) increased protein yield by 0.11 pounds per day when were fed 5% to 7% dietary sugar, milk protein production in high-producing cows improved by 0.2 pounds per day. In summary, milk protein production was greater when cows were supplemented with 5% to 7% of sugar.
The increment in milk protein yield observed in these studies suggests a possible improvement in rumen microbial protein synthesis. Thus, composition and physical characteristic of the TMR can affect the yield and concentration of milk protein and dairy profitability.
Fernando Diaz is a dairy nutritionist at Dellait. Email Fernando Diaz.