Alteration of Milk Composition in Dairy Cows Fed Supplemental Fat

173 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.Research was conducted to develop strategies for alleviating the depression in milk protein percentage that is associated with feeding supplemental fat to lactating dairy cows. In experiment one, it was hypothesized that feeding ruminally protected methionine and lysine would alleviate this depression in milk protein. Feeding supplemental fat increased milk production and decreased milk protein percentage. Supplementing methionine and lysine to the diet diminished the decrease in milk protein percentage when dietary protein was 14.2 or 17.5%. Intake and digestibility of nutrients in the total gastrointestinal tract were not altered by methionine and lysine supplementation. When methionine and lysine were supplemented concentrations in plasma of most other essential amino acids was decreased, nonesterified fatty acids were increased, and glucose and urea N were not altered. In experiment two, the effects of postruminal profile of fatty acids on intake of nutrients, milk production, and milk protein percentage was investigated. Infusing long-chain fatty acids into the abomasum decreased intake of nutrients, milk production, and milk protein percentage. Infusing unsaturated long-chain fatty acids from canola, soybeans, and sunflowers decreased intake of nutrients and milk production more than infusing long-chain fatty acids from a highly saturated (85%) fat and milk protein percentage was decreased to a similar extent. Infusing long-chain fatty acids from canola, soybeans, and sunflowers resulted in similar decreases in intake of nutrients and milk production. It was not possible to determine if a difference in chain length or degree of unsaturation of the long-chain fatty acids or both caused the alterations in intake of nutrients and production of milk components. In experiment three, the effects of supplementing nicotinic acid and fat to diets of dairy cows was investigated. Intake of nutrients, ruminal fermentation characteristics, passage of total nitrogen and nitrogen fractions to the small intestine, and production of milk and milk components were not altered by either fat or nicotinic acid supplementation. These results indicate that the beneficial effects reported in previous experiments from supplementing nicotinic acid to diets that contained fat probably were not obtained because nicotinic acid altered ruminal fermentation.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD