title: Effects of decreasing metabolizable protein and rumen-undegradable protein on milk production and composition and blood metabolites of Holstein dairy cows in early lactation.
abstract: This study was conducted to evaluate the effects of decreasing dietary protein and rumen-undegradable protein (RUP) on production performance, nitrogen retention, and nutrient digestibility in high-producing Holstein cows in early lactation. Twelve multiparous Holstein lactating cows (2 lactations; 50 ± 7 d in milk; 47 kg/d of milk production) were used in a Latin square design with 4 treatments and 3 replicates (cows). Treatments 1 to 4 consisted of diets containing 18, 17.2, 16.4, and 15.6% crude protein (CP), respectively, with the 18% CP diet considered the control group. Rumen-degradable protein levels were constant across the treatments (approximately 10.9% on a dry matter basis), whereas RUP was gradually decreased. All diets were calculated to supply a postruminal Lys:Met ratio of about 3:1. Dietary CP had no significant effects on milk production or milk composition. In fact, 16.4% dietary CP compared with 18% dietary CP led to higher milk production; however, this effect was not significant. Feed intake was higher for 16.4% CP than for 18% CP (25.7 vs. 24.3 kg/d). Control cows had greater CP and RUP intakes, which resulted in higher concentrations of plasma urea nitrogen and milk urea nitrogen; cows receiving 16.4 and 15.6% CP, respectively, exhibited lower concentrations of milk urea nitrogen (15.2 and 15.1 vs. 17.3 mg/dL). The control diet had a significant effect on predicted urinary N. Higher CP digestibility was recorded for 18% CP compared with the other diets. Decreasing CP and RUP to 15.6 and 4.6% of dietary dry matter, respectively, had no negative effects on milk production or composition when the amounts of Lys and Met and the Lys:Met ratio were balanced. Furthermore, decreasing CP and RUP to 16.4 and 5.4%, respectively, increased dry matter intake.
authors.affiliation: Department of Animal Science, Isfahan University of Technology, Isfahan 84156, Iran. Electronic address: ha.bahramiyekdangi@ag.iut.ac.ir.
authors.forename: H
authors.initials: H
authors.lastname: Bahrami-Yekdangi
authors.affiliation: Department of Animal Science, Isfahan University of Technology, Isfahan 84156, Iran.
authors.forename: M
authors.initials: M
authors.lastname: Khorvash
authors.affiliation: Department of Animal Science, Isfahan University of Technology, Isfahan 84156, Iran.
authors.forename: G R
authors.initials: GR
authors.lastname: Ghorbani
authors.affiliation: Department of Animal Science, Isfahan University of Technology, Isfahan 84156, Iran.
authors.forename: M
authors.initials: M
authors.lastname: Alikhani
authors.affiliation: Department of Animal Science, Isfahan University of Technology, Isfahan 84156, Iran.
authors.forename: R
authors.initials: R
authors.lastname: Jahanian
authors.affiliation: Department of Animal Science, University of Gorgan, Gorgan 49138-15739, Iran.
authors.forename: E
authors.initials: E
authors.lastname: Kamalian
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001806:Blood Urea Nitrogen; D002417:Cattle / Q000254:growth & development / Q000502:physiology*; D004044:Dietary Proteins / Q000378:metabolism*; D004063:Digestion; D005260:Female; D007774:Lactation; D008892:Milk / Q000737:chemistry* / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism*
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen
keywords: blood metabolite; crude protein; milk production; rumen-protected methionine