title: Effects of ruminally degradable starch levels on performance, nitrogen balance, and nutrient digestibility in dairy cows fed low corn-based starch diets.
abstract: OBJECTIVE
  This trial was performed to examine the effects of ruminally degradable starch (RDS) levels in total mixed ration (TMR) with low corn-based starch on the milk production, whole-tract nutrient digestibility and nitrogen balance in dairy cows.
  
  
  METHODS
  Eight multiparous Holstein cows (body weight [BW]: 717±63 kg; days in milk [DIM]: 169±29) were assigned to a crossover design with two dietary treatments: a diet containing 62.3% ruminally degradable starch (% of total starch, low RDS) or 72.1% ruminally degradable starch (% of total starch, high RDS). Changes to the ruminally degradable levels were conducted by using either finely ground corn or steam-flaked corn as the starch component.
  
  
  RESULTS
  The results showed that dry matter intake, milk yield and composition in dairy cows were not affected by dietary treatments. The concentration of milk urea nitrogen was lower for cows fed high RDS TMR than low RDS TMR. The whole-tract apparent digestibility of neutral detergent fiber, acid detergent fiber and crude protein decreased, and that of starch increased for cows fed high RDS TMR over those fed low RDS TMR, with no dietary effect on the whole-tract apparent digestibility of dry matter and organic matter. The proportion of urinary N excretion in N intake was lower and that of fecal N excretion in N intake was higher for cows fed high RDS TMR than those fed low RDS TMR. The N secretion in milk and the retention of N were not influenced by the dietary treatments. Total purine derivative was similar in cows fed high RDS TMR and low RDS TMR. Consequently, estimated microbial N flow to the duodenum was similar in cows fed high RDS TMR and low RDS TMR.
  
  
  CONCLUSIONS
  Results of this study show that ruminally degradable starch levels can influence whole-tract nutrient digestibility and nitrogen balance in dairy cows fed low corn-based starch diets, with no influence on performance.
authors.affiliation: College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, China.
authors.forename: Guobin
authors.initials: G
authors.lastname: Luo
authors.affiliation: College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, China.
authors.forename: Wenbin
authors.initials: W
authors.lastname: Xu
authors.affiliation: College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, China.
authors.forename: Jinshan
authors.initials: J
authors.lastname: Yang
authors.affiliation: College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.affiliation: College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, China.
authors.forename: Liyang
authors.initials: L
authors.lastname: Zhang
authors.affiliation: College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, China.
authors.forename: Yizhen
authors.initials: Y
authors.lastname: Wang
authors.affiliation: College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, China.
authors.forename: Cong
authors.initials: C
authors.lastname: Lin
authors.affiliation: College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, China.
authors.forename: Yonggen
authors.initials: Y
authors.lastname: Zhang
keywords: Dairy Cow; Milk Production; Nitrogen Balance; Nutrient Digestibility; Ruminally Degradable Starch