caa a22 4500 386323011 CHVBK 20180307111633.0 cr unu---uuuuu 161130e198811 xx s 000 0 eng 10.1079/BJN19880131 doi S0007114588001333 pii (NATIONALLICENCE)cambridge-10.1079/BJN19880131 Importance of body tissues as sources of nutrients for milk synthesis in the cow, using 13C as a marker [Elektronische Daten] 1. The proportions of carbon in individual milk constituents derived from feed and body tissues in dairy cows, were estimated by taking advantage of the natural variations which occur in the ratio, 13C:12C present in C3- and C4-plant species. 2. Four cows, which had previously grazed C3 plants (ryegrass (Lolium spp.) and white clover (Trifolium repens)), were accustomed to indoor feeding on a ration of C3-plant material (cut pastures and barley meal). The ration was then changed abruptly to one of C4-plant material (paspalum (Paspalum dilatatum) hay, maize silage and meal) for a period of 8 or 9 d in early and again in late lactation. 3. During early lactation it was estimated that 54% of the C in milk fat was derived from the body fat reserves of high genetic merit cows. Corresponding values for casein and lactose were 34 and 24% respectively, if it is assumed they were derived from body protein reserves. In contrast steam-volatile fatty acids in milk fat were almost entirely derived from dietary sources. 4. The proportional contribution of body-tissue C to individual milk constituents varied considerably between animals, possibly associated with genetic merit or the size of the body reserves available for mobilization. 5. In late lactation, when cows were close to energy and protein balance, contributions of body-tissue C to milk fat, casein and lactose ranged up to 19, 19 and 8% respectively. 6. Estimates of endogenous losses of C in faeces averaged 12 and 9% in early and late lactation respectively, and corresponding values for endogenous urinary C were 23 and 15%. Copyright © The Nutrition Society 1988 Wilson G. F. Department of Animal Science, Massey University, Palmerston North, New Zealand Mackenzie D. D. S. Department of Animal Science, Massey University, Palmerston North, New Zealand Brookes I. M. Department of Animal Science, Massey University, Palmerston North, New Zealand Lyon G. L. Institute of Nuclear Sciences, DSIR, Lower Hutt, New Zealand British Journal of Nutrition Cambridge University Press 60/3(1988-11), 605-617 0007-1145 60:3<605 1988 60 BJN https://doi.org/10.1079/BJN19880131 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1079/BJN19880131 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Wilson G. F. Department of Animal Science, Massey University, Palmerston North, New Zealand NATIONALLICENCE 700 1- Mackenzie D. D. S. Department of Animal Science, Massey University, Palmerston North, New Zealand NATIONALLICENCE 700 1- Brookes I. M. Department of Animal Science, Massey University, Palmerston North, New Zealand NATIONALLICENCE 700 1- Lyon G. L. Institute of Nuclear Sciences, DSIR, Lower Hutt, New Zealand NATIONALLICENCE 773 0- British Journal of Nutrition Cambridge University Press 60/3(1988-11), 605-617 0007-1145 60:3<605 1988 60 BJN CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge