caa a22 4500 388060328 CHVBK 20180307125118.0 cr unu---uuuuu 161130e199808 xx s 000 0 eng 10.1017/S1357729800009735 doi S1357729800009735 pii (NATIONALLICENCE)cambridge-10.1017/S1357729800009735 The effect of dietary fat and metabolizable energy supply on milk protein concentration of dairy cows [Elektronische Daten] 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 ofmicrobial 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 offatty 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. Copyright © British Society of Animal Science 1998 dairy cows nationallicence dietary fat nationallicence metabolizable energy nationallicence milk production nationallicence milk protein nationallicence Moorby J. M. Grassland and Ruminant Science Department, Scottish Agricultural College, Auchincruive, Ayr KA6 5HW Dewhurst R. J. Grassland and Ruminant Science Department, Scottish Agricultural College, Auchincruive, Ayr KA6 5HW Thomas C. Grassland and Ruminant Science Department, Scottish Agricultural College, Auchincruive, Ayr KA6 5HW Marsden S. Dalgety Agriculture Ltd, 180 Aztec West, Almondsbury, Bristol BS12 4TH Animal Science Cambridge University Press 67/1(1998-08), 1-8 1357-7298 67:1<1 1998 67 ASC https://doi.org/10.1017/S1357729800009735 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1017/S1357729800009735 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Moorby J. M. Grassland and Ruminant Science Department, Scottish Agricultural College, Auchincruive, Ayr KA6 5HW NATIONALLICENCE 700 1- Dewhurst R. J. Grassland and Ruminant Science Department, Scottish Agricultural College, Auchincruive, Ayr KA6 5HW NATIONALLICENCE 700 1- Thomas C. Grassland and Ruminant Science Department, Scottish Agricultural College, Auchincruive, Ayr KA6 5HW NATIONALLICENCE 700 1- Marsden S. Dalgety Agriculture Ltd, 180 Aztec West, Almondsbury, Bristol BS12 4TH NATIONALLICENCE 773 0- Animal Science Cambridge University Press 67/1(1998-08), 1-8 1357-7298 67:1<1 1998 67 ASC CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge