title: Effects of crude protein level in concentrate supplements on animal performance and nitrogen utilization of lactating dairy cows fed fresh-cut perennial grass.
abstract: Nitrogen pollution of air and ground water from grazing cattle is of increasing concern. Although several studies have investigated mitigation strategies for nitrogen output from dairy cows fed conserved forages and concentrates, similar research on fresh-cut grass in addition to production parameters is limited. The current study, using 3dietary treatments and incorporating 2 genotypes, was designed to evaluate the effects of concentrate crude protein (CP) levels on animal production and nitrogen utilization efficiency (NUE) in lactating dairy cows. Twelve multiparous cows (6 Holstein and 6 Holstein × Swedish Red) were used in a changeover study with three 25-d periods and 3 diet treatments. Low, medium and high CP concentrate [14.1, 16.1, and 18.1%, respectively, dry matter (DM) basis] diets were fed at 32.8% DM intake combined with good-quality zero-grazed perennial ryegrass (18.2% CP, DM basis). Each period consisted of an adaptation phase (18d) housed as a single group, a 1-d adaptation phase in individual stalls, and a 6-d measurement phase with feed intake and feces, urine, and milk output recorded. We observed no significant interaction between cow genotype and concentrate CP level on any animal performance or NUE parameter. Total DM intake, milk yield and composition, and NUE were not affected by dietary treatment. However, increasing concentrate CP level increased (1) N intake by 42g/d and excretion in urine and manure by 38 and 40g/d, respectively, and (2) the ratio of urine N over manure N. Feeding high CP rather than low CP concentrate increased milk urea N (MUN) content by 3.6mg/dL and total MUN output by 1.08g/d. Crossbred cows had lower grass DM intake, total DM intake, total N intake, and energy-corrected milk yield. However, cow genotype had no significant effect on NUE or MUN parameters. Equations have been developed to predict urine N excretion using MUN output as a sole predictor or in combination with dietary CP level. The present study indicated that when grazing cows are fed good-quality pasture, feeding concentrates with a protein content as low as 14.1% may not negatively affect productivity. In addition, reducing concentrate CP concentration may be successful in reducing the urinary N excretion of lactating dairy cattle on pasture-based systems, but further research is needed to investigate the long-term effects of supplementary concentrate CP content on milk production.
authors: Sustainable Agri-Food Sciences Division, Agriculture Branch, Agri-Food and Biosciences Institute, Large Park, Hillsborough, BT26 6DR, United Kingdom; Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, University Road, Belfast, BT7 1NN, United Kingdom.
authors: D N
authors: DN
authors: Hynes
authors: Sustainable Agri-Food Sciences Division, Agriculture Branch, Agri-Food and Biosciences Institute, Large Park, Hillsborough, BT26 6DR, United Kingdom; Animal, Dairy and Food Chain Sciences Division, Centre for Dairy Research, University of Reading, School of Agriculture, Policy and Development, Reading, RG6 6AR, United Kingdom.
authors: S
authors: S
authors: Stergiadis
authors: Finance and Corporate Affairs Division, Biometrics and Information Systems Branch, Agri-Food and Biosciences Institute, 18a Newforge Lane, Belfast, BT9 5PX, United Kingdom.
authors: A
authors: A
authors: Gordon
authors: Sustainable Agri-Food Sciences Division, Agriculture Branch, Agri-Food and Biosciences Institute, Large Park, Hillsborough, BT26 6DR, United Kingdom. Electronic address: tianhai.yan@afbini.gov.uk.
authors: T
authors: T
authors: Yan
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D001835:Body Weight; D002417:Cattle; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins / Q000008:administration & dosage*; D019587:Dietary Supplements; D005243:Feces / Q000737:chemistry; D005260:Female; D007774:Lactation; D016014:Linear Models; D008129:Lolium; D008892:Milk / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D006109:Poaceae
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen
keywords: concentrate protein content; dairy cow; fresh grass; milk production; nitrogen utilization