Epsilon Archive for Student Projects

Abstract

The objective of this thesis was to investigate how enteric CH4-reducing feeding strategies affect the protein profile and fatty acid composition, as well as the concentrations of calcium, phosphorus, and potassium, in dairy cow milk. The study evaluated two energy sources, barley and high-oil oats; two protein supplements, rapeseed meal (RSM) and cold-pressed rapeseed cake (RSC); and supplementation with 3-nitrooxypropanol (3-NOP) at levels of 0 and 68 mg/kg dry matter. The dietary treatments had no significant effect on milk fat concentration. Milk fatty acid analysis by gas chromatography indicated potential treatment-related differences in milk fatty composition. However, these results should be interpreted with caution due to limitations of the method, as several fatty acids normally present in milk were not detected and some peaks were likely affected by co-elution. Therefore, a more comprehensive method that captures the complete fatty acid profile is required before any conclusions can be drawn. Protein concentration was higher in milk from cows fed barley compared with high-oil oats, and from cows fed RSM compared with RSC. This indicates that mitigating enteric CH4 emissions by replacing barley with high-oil oats, or RSM with RSC, may not be beneficial if the objective is to increase milk protein concentration. However, dietary supplementation with 3-NOP increased the protein concentration when combined with barley. No effect of diet was observed on whey protein proportion. Replacing RSM with RSC resulted in 25.8% lower proportion of β-CN A1, regardless of energy source. However, the proportion of κ-CN increased by 11.3% when replacing RSM with RSC in combination with high-oil oats. The proportions of αs1-CN increased by 2.9% when supplementing the diet with 3-NOP. Diets did not have any significant effect on proportions of total casein, total β-CN, β-CN A2, or αs2-CN. Replacing RSM with RSC resulted in 3.8% lower milk Ca concentration when combined with barley as an energy source. However, 3-NOP supplementation increased milk Ca concentration by 1.9%. Concentrations of the minerals P and K were 3.2% and 3.1% greater, respectively, in milk derived from cows fed barley compared with high-oil oats.