The effect of dietary fat and metabolizable energy supply on milk protein concentration of dairy cows

Jon Moorby, Richard J. Dewhurst, Cledwyn Thomas, Marsden Stuart

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To investigate the effect of dietary fat and metabolizable energy (ME) on milk protein concentration, an experiment was carried out using 12 multiparous early-lactation Holstein-Friesian dairy cows. Three diets were offered in a complete Latin-square change-over design, based on ad libitum access to grass silage. One of three concentrates was offered at a rate of 12 kg/day, each formulated to supply one of two levels of ME (12·1 and 13·6 MJ/kg dry matter (DM)) and one of two levels of fat (31 and a mean of 88 g acid hydrolysis ether extract per kg DM): low energy, high fat (LEHF); low energy, low fat (LELF); and high energy, high fat (HEHF). The concentration of milk protein was significantly higher from animals offered the LELF concentrate (32·5 v. a mean of 31·2 (s.e.d. 0·45) g/kg, P < 0·05), because of lower milk yields (31·0 v. a mean of 33·4 (s.e.d. 0·63) kg/day, P < 0·05). Animals offered the HEHF concentrate produced the highest yields of milk protein but their milk had the lowest concentrations of fat (32·5, 34·4 and 31·9 g/kg for LEHF, LELF and HEHF respectively; s.e.d 1·07; P < 0·05 for difference between LELF and HEHF). Silage DM intake was significantly increased by animals offered the LEHF concentrate (9·1, 8·6 and 8·7 (s.e.d. 0·19) kg/day, P < 0·05 for differences between LEHF and the other two concentrates). Urinary purine derivative excretion, used as an index of microbial protein supply, was highest from animals offered the LELF and HEHF concentrates, which both supplied similar amounts of fermentable ME. It is hypothesized that increased de novo synthesis of fatty acids on the low fat diet reduced the availability of glucose for lactose synthesis, leading to reduced milk yields and hence increased milk protein concentrations.

Original languageEnglish
Pages (from-to)1-8
Number of pages8
JournalAnimal Science
Issue number1
Publication statusPublished - Aug 1998


  • Dairy cows
  • Dietary fat
  • Metabolizable energy
  • Milk production
  • Milk protein


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