THE EFFECT OF POTASSIUM AND FAT IN THE EARLY LACTATION ON MILK FATTY ACIDS AND THE NUTRIENT CONTRIBUTIONS AND BIOGAS POTENTIAL OF CO-DIGESTION OF FEEDSTOCKS AND DAIRY MANURE
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This dissertation research focused on the areas of nutrition and nutrient management. Three experiments were conducted with lactating cows to evaluate nutritional strategies to improve the efficiency of milk fat production. A fourth study defined the nutrient contributions and biogas potential of co-digestion of feedstocks and dairy manure. In the first study, 1.74 % potassium was compared to 2.33 % potassium of diet dry matter (DM) to investigate changes in milk fat of lactating dairy cows due to potassium supplementation. Through the 21 days of potassium supplementation, milk fat concentration was significantly increased from 4.03 % to 4.27 %. The fat concentration increase was associated with an increase in C18:1 11 trans. In the second study, ruminally inert fat products of either calcium salts of fatty acid (CAFA) rich in C16:0 and C18:1, or saturated fatty acid (SFA) rich in C16:0 were fed to early lactation multiparious Holstein dairy cows. The CAFA diet increased lactation performance when fed beginning at 45 ± 24 days in milk (DIM) , however, the SFA diet resulted in an increase in milk protein yield with cows when fed beginning at 73 ± 41 DIM. In the third study, ruminally inert fat products of either CAFA rich in C16:0 and C18:1, or SFA rich in C16:0 and C18:0 were fed to multiparious dairy cows starting at 14 ± 2 DIM. When cows were fed a low fat diet of 3.4 ± 0.4 % (DM) ether extract, the SFA diet increased lactation performance before the peak of lactation and during negative energy status. Body condition score change, energy status between different rumen inert fat products, and feed efficiency of 3.5 % fat corrected milk/DMI was not different. Greater nutrient intake was partitioned into lactation performance with the CAFA diet from week 3 to 14 of lactation. The fourth study described the nutrient transformations and flow in an anaerobic digestion system and confirmed that biogas or methane yield could be accurately measured from the ratio of % volatile solids: % total solids.