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Table 1. Dry matter intake (DMI), milk yield, composition, and component yield in first lactation Holstein cows fed diets containing 3 levels of dietary protein from week 2 to 44 of lactation (Reynolds et al., 2016).


14 DMI, kg/d Milk yield, L/d


Milk component, g/kg Fat


Protein Lactose Urea


Milk component, g/d Fat


Protein Lactose


Body weight, kg


Body condition score ECM1 NUE2


, L/d , %


1Energy corrected milk yield. 2


21.3b 28.1b


37.9 32.9 45.5 0.17c


1052b 920b


1281b 606b


3.01ab 29.2b 31.5a


Diet CP % 16


21.3b 29.6a


36.9 33.2 45.2 0.24b


1091a 982a


1342a 606b 2.96b 30.6a 29.5b


Nitrogen use efficiency.


observed have implications for practical applications and nutritional strategies aimed at precision feeding cows at or near requirements for essential amino acid supplies, but cows are resilient, and evidence suggests they are able to tolerate daily fluctuations in diet protein composition. As a ruminant able to recycle nonprotein N to the rumen, the long-term average diet composition appears to determine rate of metabolism and production. In the long-term study at CEDAR the 16% CP diet was ‘optimal’


in many respects, but this was by design. Cows fed lower levels of protein had higher NUE but produced less milk and were less likely to survive three lactations. There was no evidence that higher body energy balance in early lactation when cows were fed lower protein diets improved fertility, as suggested by other research. Cows fed higher levels of protein consumed more feed but did not produce more milk and were the least efficient in terms of dietary nitrogen utilization. Other studies for the project are determining the environmental and economic implications of feeding lower protein diets, as well as the effects of reduced protein concentrations in diets for growing heifers and lactating cows fed diets based primarily on grass silage and grazing.


References


Cantalapiedra-Hijar, G., J. L. Peyraud, S. Lemosquet, E. Molina- Alcaide, H. Boudra, P. Nozière and I. Ortigues-Marty. 2014. Dietary carbohydrate composition modifies the milk N efficiency. Animal: 8:275-85 Lee, C., A.N. Hristov, T.W. Cassidy, K.S. Heyler, H. Lapierre, G.A. Varga, M.J. de Veth, R.A. Patton, C. Parys. 2012. Rumen-protected lysine, methionine, and histidine increase milk protein yield in dairy cows fed metabolizable protein-deficient diet. J. Dairy Sci. 95, 6042–6060.


Lee, C., F. Giallongo, A. N. Hristov, H. Lapierre, T. W. Cassidy, K. S. Heyler, G. A. Varga, and C. Parys. 2015. Effect of dietary protein level and rumen protected amino acid supplementation on amino acid utilization for milk protein in lactating dairy cows. J. Dairy Sci. 98:1885–1902. Mills, J.A.N., L.A. Crompton, A. Bannink, S. Tamminga, J.M. Moorby and C.K. Reynolds, 2009. Predicting methane emissions and nitrogen excretion from cattle. In: Crompton, L.A. and T.R. Wheeler (editors), Proceedings of the forty-first meeting of the agricultural research modellers’ group, J. Agric. Sci. 147, 741. Olmos Colmenero, J. J., and G. A. Broderick. 2006. Effect of dietary crude protein concentration on milk production and nitrogen utilization in lactating dairy cows. J. Dairy Sci. 89:1704–1712. Reynolds, C. K., and N. B. Kristensen. 2008. Nitrogen recycling through the gut and the nitrogen economy of ruminants – an asynchronous symbiosis. J. Anim. Sci. 86 (E. Suppl.): E293-E305. Reynolds, C.K., L.A. Crompton, J.A.N. Mills, D.J. Humphries, P. Kirton, A.E. Relling, T.H. Misselbrook, D.R. Chadwick and D.I. Givens, 2010. Effects of diet protein level and forage source on energy and nitrogen balance and methane and nitrogen excretion in lactating dairy cows. In: Crovetto, G.M. (ed.) Energy and protein metabolism and nutrition. Wageningen Academic Publishers, The Netherlands, pp. 463-464. Reynolds, C. K., L. A. Crompton, D. J. Humphries, and A. K. Jones. 2016. Long term implications of feeding low protein diets to first lactation dairy cows. In J. Skomial, and H. Lapierre (eds.) Proceedings of the 5th International Symposium on Energy and Protein Metabolism, EAAP Publ. No. 137, Wageningen Academic Publishers, he Netherlands, 263-264. Sinclair, K. D., P. C. Garnsworthy, G. E. Mann, and L. A. Sinclair. 2014. Reducing dietary protein in diary cow diets: implications for nitrogen utilization, milk production, welfare and fertility. Animal 8: 262-294. St-Pierre, N. R., and W. P. Weiss. 2015. Partitioning variation in nutrient composition data of common feeds and mixed diets on commercial dairy farms. J. Dairy Sci. 98:5004–5015. Yoder, P. S., N. R. St-Pierre, K. M. Daniels, K. M. O’Diam, and W. P. Weiss. 2013. Effects of short-term variation in forage quality and forage to concentrate ratio on lactating dairy cows. J. Dairy Sci. 96:6596–6609.


FEED COMPOUNDER MAY/JUNE 2018 PAGE 41 P < 18


22.0a 29.7a


37.8 33.4 45.3 0.31a


1112a 986a


1350a 619a 3.09a 30.9a 25.5c


SEM 0.20 0.41


0.53 0.24 0.10


0.003


13.8 10.3 18.9 2.9


0.04 0.32 0.31


Diet


0.013 0.006


0.366 0.321 0.076 0.001


0.008 0.001 0.008 0.003 0.057 0.001 0.001


Week 0.001 0.001


0.001 0.001 0.001 0.001


0.001 0.001 0.001 0.001 0.001 0.001 0.001


Diet x week 0.064 0.003


0.209 0.965 0.857 0.001


0.865 0.032 0.865 0.065 0.215 0.600 0.003


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