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Mastitis is one of the most costly diseases to dairy producers around the world with milk yield loss being the biggest contributor to economic losses. The objective of first study of this thesis was to determine the impacts of high somatic cell counts on milk yield loss. To accomplish this, over one million cow data records were collected from Southeastern US dairy herds. The objective of the second study was to determine optimum treatment cost of clinical mastitis by combining two economic modeling approaches used in animal health economics. The last objective of this thesis was to determine how much Southeastern US dairy producers are spending to control milk quality on farm and determine if they understand how milk quality affects them economically. This was accomplished through a collaborative project within the Southeast Quality Milk Initiative.

In experiment I), dry matter disappearance (DMD) and nitrogen disappearance (ND) of raw soybeans (RAW), solvent extracted soybean meal (SBM), heat treated whole soybeans (HT), mechanically extracted soybean meal (MEX), dry extruded soybeans (DEX), and wet extruded soybeans (TEX), were studied in situ for times of 3, 6, 12 and 24 h of rumen exposure. Five gram, air dry, samples were suspended in the rumen of a lactating Holstein cow fed a total mixed ration twice daily. The percent DMD for 24 h was as follows: RAW-85.9; SBM-56.6; HT-39.0; MEX-40.2; DEX-28.0; TEX-43.3. The greatest DMD was observed with RAW and was greater than all others (P<.01), followed by SBM which was significantly greater than all but Raw (P<.01). DEX presented the lowest DMD when compared to all other (P<.01). Percent ND values for 24 h for the soy products were: RAW-90.8; SBM-47.0; HT-32.7; MEX-23.7; DEX-16.5; TEX-23.0. The ND for RAW was significantly greater (P<.01) than all others, while the ND for SBM was similar P>.01) to HT but greater (P<.01) than MEX, DEX and TEX. ND for HT, MEX, DEX and TEX were similar (P>.01). Significant differences were observed in DMD and ND of various soybean products. As expected a high degree of degradation and ND was observed with raw soybeans. The application of heat decreased DMD and ND in SBM and application of greater heat (HT, MEX and DEX) and application of heat with moisture (TEX) resulted in products with lower DMD and lower ND. In experiment II) wheat straw acid detergent fiber (ADF) was subjected to in situ DMD and ND studies. Effects of time (612-24 h) and sample weight (1-2-3 grams) were evaluated. A lactating Holstein cow being fed a mixed ration was used. ADF dry matter (DM) weights (after incubation) expressed as a % of the original sample, were as follows: one gram: 101, 110 and 136; two grams: 99, 106 and 110; and three grams: 97, 110 and 114 for 6, 12 and 24 h respectively. The ADF DM weights of the one and two gram samples were significantly higher (P<.05) for 12 and 24 h than 6 h. When sample sizes were combined for each time, comparisons found 24 h to be significantly higher (P<.01) than 6 h. The DM changes were also reflected and magnified in the % N changes in the ADF residues. The amount of N of the one gram ADF samples increased 32% after 6 h, 122% after 12 h and 287% after 24 h (24>12>6-P<.01), and for two grams 29%-6 h, 97%-12 h and 117%-24 h (24>12>6-P<.05), and for three grams 34%-6 h, 140%-12 h and 142%-24 h (24 and 12>6-P<.01). Potential problems with DM and N contamination of ADF residue with in situ studies were demonstrated with small increases in DM weights and larger increases in N content.