Start Date: Oct 10, 2012
End Date: Oct 09, 2017
Sub-objectives 1.A and 1.B: Latin square feeding studies with lactating dairy cows will be performed to test the effects of: 1) different combinations of dietary forage and supplemental protein sources, and 2) the interaction of dietary tannins and crude protein level of the diet as they influence milk production and efficiency of nitrogen use for milk production. Omasal sampling will be performed using triple markers in order to quantify differences among dietary treatments in flow of amino acids (AA) from the rumen (~metabolizable AA supply to the animal). Effects of tannin and protein levels on nitrogen volatilization will also be evaluated using manure samples from this study. Sub-objective 2.A: Studies will explore the relationship of ruminal microflora profile and milk fat depression (MFD) in lactating dairy cows. 1) Cultures of Megasphaera eldenii strains isolated and enriched from cows displaying or not displaying MFD will be used to determine if they differentially metabolize linoleic acid to produce biohydrogenated fatty acids implicated in MFD. 2) Ruminal inocula collected from lactating dairy cows displaying or not displaying MFD on diets designed to induce MFD. M. elsdenii will be quantified in the archived ruminal samples, and ARISA will be used to identify samples containing unidentified bacterium AL383 which has been shown to be negatively correlated with M. elsdenii. The intent is to identify AL383, isolate it, and assess its interactions with M. elsdenii. Sub-objective 2.B: The impact of interactions of cow genome, lactation performance, and accrual of disease events over multiple lactations will be investigated using records of 4000 genotyped cows. Phenotypic data will be used to establish heritability of phenotypes, and adjust phenotypic data for effects of age on increased risk of decreased performance/increased treated disease events. Phenotypic and genotypic data will then be subject to a genome-wide association analysis. Sub-objective 3.A: In vitro fermentations will be used to investigate relationships among nonfiber carbohydrate sources and level and type of protein supply as they alter the profile, amount, and rate of fermentation product formation by ruminal microbes. Batch culture fermentations of less than 8 hours with multiple destructive sampling times will be used to define patterns of substrate disappearance and microbial product appearance. Sub-objective 3.B: The impact of the protein x carbohydrate interactions described in 3.A combined with influence of changing rates of liquid passage and forage sources will be investigated in studies with lactating cows. Latin square studies with 2 x 2 factorial arrangements of dietary protein solubility and a salt concentration will be performed with repeated ruminal sampling to describe rumen function, omasal sampling to determine AA flow from the rumen, and lactation performance measurements. Sub-objective 3.C: A series of in vivo studies with lactating cows will be conducted to explore the effects of dietary components (salts, soluble protein) on ruminal digesta liquid and dry matter (DM) proportions, total digesta weight, liquid passage rate, and water intake.