Effects of lipid supplementation and undegraded intake protein on nutrient metabolism and milk production by lactating cows

David A Carey, Purdue University

Abstract

The high producing dairy cow typically suffers from negative energy balance in the early stages of lactation. Fat can be added to the diet in order to increase energy intake, however, milk protein percentage often is depressed. This research was conducted to examine the effects of added dietary fat on protein metabolism and milk protein percentage in the lactating cow. Diets were formulated with increasing levels of added fat, greater content of undegradable intake protein, and a constant ratio between degradable intake protein and readily available carbohydrate. At the high levels of 6 and 8% added fat, milk yield was decreased 6.5 and 8.7%, respectively, compared with the average for the other treatments. Overall nitrogen metabolism was similar among treatments, however, there was a linear decrease in milk protein yield with added fat in the diet. In comparison to the 0% added fat control treatment, milk protein yield decreased 3.8 and 4.5% for 2 and 4% added fat diets, respectively, versus 6.4 and 10.5% for 6 and 8% added fat diets, respectively. The relatively greater protein yield for the diet containing 4% added fat compared with the 6 and 8% added fat diets prevented a significant depression in milk protein percentage. These results did not conclusively support the concept that increasing ruminally undegradable protein could alleviate depression in milk protein biosynthesis, however, there was an indication that a greater level of undegradable intake protein might provide an increased quantity of metabolizable protein at the small intestine which in turn would increase amino acid supply to the mammary gland. A study was designed to examine the effects of protein supplementation on essential amino acid flow to the small intestine and whether increased quantities of essential amino acids could increase milk production and milk protein yield when cows were fed two levels of added fat. There was reduced essential amino acid flows for the protein treatments containing 5% added fat which likely were due to decreased feed intake and microbial protein synthesis, however, milk production and milk protein yield were similar among treatments. Although there is a pronounced fat effect when diets containing high levels of ruminally undegradable protein or ruminally protected amino acids are fed, it did not appear that metabolizable protein supply in this study was limiting for milk protein synthesis.

Degree

Ph.D.

Advisors

Cecava, Purdue University.

Subject Area

Livestock

COinS