1. AOAC (1991) Official methods of analysis (15th ed.). Arlington, VA: Association of Official Analytical Chemists.
2. Apelo SA, Singer L, Ray W, Helm R, Lin X, McGilliard M, St-Pierre N and Hanigan M (2014) Casein synthesis is independently and additively related to individual essential amino acid supply. Journal of Dairy Science 97: 2998-3005.
3. Bahrami-Yekdangi H, Khorvash M, Ghorbani GR, Alikhani M, Jahanian R and Kamalian E (2014) Effects of decreasing metabolizable protein and rumen-undegradable protein on milk production and composition and blood metabolites of Holstein dairy cows in early lactation. Jornal of Dairy Science 97: 1-8.
4. Bahrami-Yekdangi M, Ghorbani G, Khorvash M, Khan M and Ghaffari M (2016) Reducing crude protein and rumen degradable protein with a constant concentration of rumen undegradable protein in the diet of dairy cows: Production performance, nutrient digestibility, nitrogen efficiency, and blood metabolites. Journal of Animal Science 94: 718-725.
5. Bernabucci U, Lacetera N, Baumgard L H, Rhoads R P, Ronchi B and Nardone A (2010) Metabolic and hormonal acclimation to heat stress in domesticated ruminants. Animal 4: 1167-1183.
6. Boisen S, Hvelplund T and Weisbjerg M R (2000) Ideal amino acid profiles as a basis for feed protein evaluation. Livestock Production Science 64: 239–251.
7. Calamari L, Bionaz M, Trevisi E and Bertoni G (2004) Preliminary study to validate a model of animal welfare assessment in dairy farms. Reprints 5th Congr. EURSAFE–Science, Ethics & Society, Ed. Johan De Tavernier & Stefan Aerts, Katholieke Uni. Leuven: 38-42.
8. Calsamiglia S and Stern M D (1995) A three-step in vitro procedure for estimating intestinal digestion of protein in ruminants. Journal of Animal Science 73: 1459-1465.
9. Castillo A, Kebreab E, Beever D, Barbi J, Sutton J, Kirby H and France J (2001) The effect of protein supplementation on nitrogen utilization in lactating dairy cows fed grass silage diets. Journal of Animal Science 79: 247-253.
10. Chouinard P Y, Lévesque J, Girard V and Brisson G J (1997) Dietary Soybeans Extruded at Different Temperatures: Milk Composition and In Situ Fatty Acid Reactions. Journal of Dairy Science 80: 2913–2924.
11. Colmenero J O and Broderick G (2006) Effect of dietary crude protein concentration on milk production and nitrogen utilization in lactating dairy cows. Journal of Dairy Science 89: 1704-1712.
12. Davidson S, Hopkins B, Diaz D, Bolt S, Brownie C, Fellner V and Whitlow L (2003) Effects of amounts and degradability of dietary protein on lactation, nitrogen utilization, and excretion in early lactation Holstein cows. Journal of Dairy Science 86: 1681-1689.
13. Fernández R, Dinsdale R M, Guwy A J and Premier G C (2016) Critical analysis of methods for the measurement of volatile fatty acids. Critical Reviews in Environmental Science and Technology 46: 209-234.
14. Gholami V and Amanlou H (2013) Effect of a reduction of dietary protein on milk production and on blood components of lactating holstein cows during heat stress. Iranian Journal of Animal Science 44: 355-365 (in Persian)
15. Hristov A, Price W and Shafii B (2004) A meta-analysis examining the relationship among dietary factors, dry matter intake, and milk and milk protein yield in dairy cows. Journal of Dairy Science 87: 2184-2196.
16. Huhtanen P and Hristov A (2009) A meta-analysis of the effects of dietary protein concentration and degradability on milk protein yield and milk N efficiency in dairy cows. Journal of Dairy Science 92: 3222-3232.
17. Ipharraguerre I R, Clark J H and Freeman D E (2005) Rumen fermentation and intestinal supply of nutrients in dairy cows fed rumen-protected soy products. Journal of Dairy Science 88: 2879–2892.
18. Ishler V and Varga G (2008) Soybeans and soybean byproducts for dairy cattle. Dairy and Animal Sciences: 1-13.
19. Jahani‐Moghadam M, Amanlou H and Nikkhah A (2009) Metabolic and productive response to ruminal protein degradability in early lactation cows fed untreated or xylose‐treated soybean meal‐based diets. Journal of animal physiology and animal nutrition 93: 777-786.
20. Law R, Young F, Patterson D, Kilpatrick D, Wylie A and Mayne C (2009) Effect of dietary protein content on animal production and blood metabolites of dairy cows during lactation. Journal of Dairy Science 92: 1001-1012.
21. Mulligan F, Dillon P, Callan J, Rath M and O’mara F (2004) Supplementary concentrate type affects nitrogen excretion of grazing dairy cows. Journal of Dairy Science 87: 3451-3460.
22. NRC (2001) Nutrient requirements of dairy cattle. 7th rev. ed: 381.
23. O'Mara F, Murphy J and Rath M (1997) The amino acid composition of protein feedstuffs before and after ruminal incubation and after subsequent passage through the intestines of dairy cows. Journal of animal science 75: 1941-1949.
24. Rees A, Fischer‐Tenhagen C and Heuwieser W (2016) Effect of Heat Stress on Concentrations of Faecal Cortisol Metabolites in Dairy Cows. Reproduction in Domestic Animals 51: 392-399.
25. Reynal S and Broderick G (2005) Effect of dietary level of rumen-degraded protein on production and nitrogen metabolism in lactating dairy cows. Journal of Dairy Science 88: 4045-4064.
26. SAS (1999) STAT user’s guide, release 8.01. SAS Institute, Cary, NC.
27. Tao S and Dahl G (2013) Invited review: Heat stress effects during late gestation on dry cows and their calves. Journal of Dairy Science 96: 4079-4093.
28. Van Keulen J and Young B (1977) Evaluation of acid-insoluble ash as a natural marker in ruminant digestibility studies. Journal of Animal Science 44: 282-287.
29. Van Soest P, Robertson J and Lewis B (1991) Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. Journal of Dairy Science 74: 3583-3597.
30. Wang Y, Jin L, Wen Q, Kopparapu N, Liu J, Liu X and Zhang Y (2016) Rumen Degradability and Small Intestinal Digestibility of the Amino Acids in Four Protein Supplements. Asian-Australasian Journal of Animal Sciences29: 241-249.
31. Wattiaux M and Karg K (2004) Protein level for alfalfa and corn silage-based diets: I. Lactational response and milk urea nitrogen. Journal of Dairy Science 87: 3480-3491.
)