Effects of proportion and digestibility of grass-clover silage on milk protein, mineral and fatty acid compositions in Danish Holstein cows

ABSTRACT

The objective of this study was to investigate the effects of proportion and organic matter digestibility (OMD) of grass-clover silage on milk composition. Grass-clover silages with low (LD) or high (HD) OMD were mixed at low (30:70, LP) or high (70:30, HP) proportion (DM basis) with maize silage to arrange 4 total mixed rations (TMR) with a forage-to-concentrate ratio of 60:40. The TMR were fed ad libitum to 36 cows in a 4 × 4 Complete Latin Square design. The proportion × OMD interaction showed that feeding a high proportion of low-digestible grass-clover silage resulted in a higher content of milk urea nitrogen (P < .001). The diets had a minor impact on milk protein and mineral compositions. Decreasing the grass-clover to maize silage ratio from 70:30 to 30:70 improved the nutritional value of milk fat by decreasing the share of saturated and increased the share of unsaturated fatty acids (P < .001).

KEYWORDS:

• Grass-clover silage
• organic matter digestibility
• milk urea nitrogen
• milk minerals
• fatty acids

Acknowledgements

The authors would like to thank Gitte Hald Kristiansen and Rita Albrechtsen (Department of Food Science, Aarhus University, Denmark) for excellent technical assistance; the barn crew at AU Foulum (Tjele, Denmark) for animal care, feeding and milking and Torben Larsen (Department of Animal and Veterinary Sciences, Aarhus University, Tjele, Denmark) for colorimetric analysis of minerals in milk fractions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The study was supported by Aarhus University, Denmark and by the Danish Milk Levy Fund through the two projects entitled ‘Development of a new model to quantify the excretion of nitrogen in urine and faeces in the cattle production’ and ‘Indicators in milk for nitrogen and phosphorus excretion’.