title: Effect of reducing dietary forage in lower starch diets on performance, ruminal characteristics, and nutrient digestibility in lactating Holstein cows.
abstract: This experiment evaluated the effect of feeding a lower starch diet (21% of dry matter) with different amounts of forage (52, 47, 43, and 39% of dry matter) on lactational performance, chewing activity, ruminal fermentation and turnover, microbial N yield, and total-tract nutrient digestibility. Dietary forage consisted of a mixture of corn and haycrop silages, and as dietary forage content was reduced, chopped wheat straw (0-10% of dry matter) was added in an effort to maintain chewing activity. Dietary concentrate was adjusted (corn meal, nonforage fiber sources, and protein sources) to maintain similar amounts of starch and other carbohydrate and protein fractions among the diets. Sixteen lactating Holstein cows were used in replicated 4×4 Latin squares with 21-d periods. Dry matter intake increased while physically effective neutral detergent fiber (peNDF1.18) intake was reduced as forage content decreased from 52 to 39%. However, reducing dietary forage did not influence milk yield or composition, although we observed changes in dry matter intake. Time spent chewing, eating, and ruminating (expressed as minutes per day or as minutes per kilogram of NDF intake) were not affected by reducing dietary forage. However, addition of chopped wheat straw to the diets resulted in greater time spent chewing and eating per kilogram of peNDF1.18 consumed. Reducing dietary forage from 52 to 39% did not affect ruminal pH, ruminal digesta volume and mass, ruminal pool size of NDF or starch, ruminal digesta mat consistency, or microbial N yield. Ruminal acetate-to-propionate ratio was reduced, ruminal turnover rates of NDF and starch were greater, and total-tract digestibility of fiber diminished as dietary forage content decreased. Reducing the dietary forage content from 52 to 39% of dry matter, while increasing wheat straw inclusion to maintain chewing and rumen function, resulted in similar milk yield and composition although feed intake increased. With the lower starch diets in this short-term study, the minimal forage content to maintain lactational performance was between 39 and 43%.
authors.affiliation: William H. Miner Agricultural Research Institute, Chazy, NY 12921.
authors.forename: E R
authors.initials: ER
authors.lastname: Farmer
authors.affiliation: William H. Miner Agricultural Research Institute, Chazy, NY 12921.
authors.forename: H A
authors.initials: HA
authors.lastname: Tucker
authors.affiliation: William H. Miner Agricultural Research Institute, Chazy, NY 12921. Electronic address: dann@whminer.com.
authors.forename: H M
authors.initials: HM
authors.lastname: Dann
authors.affiliation: William H. Miner Agricultural Research Institute, Chazy, NY 12921.
authors.forename: K W
authors.initials: KW
authors.lastname: Cotanch
authors.affiliation: William H. Miner Agricultural Research Institute, Chazy, NY 12921.
authors.forename: C S
authors.initials: CS
authors.lastname: Mooney
authors.affiliation: Department of Animal Sciences, Michigan State University, East Lansing 48824.
authors.forename: A L
authors.initials: AL
authors.lastname: Lock
authors.affiliation: ZEN-NOH National Federation of Agricultural Co-operative Associations, Tokyo 100-6832, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yagi
authors.affiliation: William H. Miner Agricultural Research Institute, Chazy, NY 12921.
authors.forename: R J
authors.initials: RJ
authors.lastname: Grant
mesh_terms: D000818:Animals; D002417:Cattle; D004032:Diet / Q000662:veterinary*; D004043:Dietary Fiber / Q000008:administration & dosage; D004063:Digestion; D005260:Female; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D007774:Lactation / Q000502:physiology; D008409:Mastication / Q000502:physiology; D000455:Medicago sativa; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D009584:Nitrogen / Q000652:urine; D010316:Particle Size; D011687:Purines / Q000652:urine; D012417:Rumen / Q000378:metabolism* / Q000382:microbiology; D012820:Silage; D013213:Starch / Q000008:administration & dosage; D014908:Triticum; D003313:Zea mays
chemical_list: D004043:Dietary Fiber; D011687:Purines; D013213:Starch; D009584:Nitrogen; C030985:purine
keywords: digestibility; low forage diet; low starch diet; rumen dynamics