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      Some challenges and opportunities for grazing dairy cows on temperate pastures

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          Abstract

          Grazing plays an important role in milk production in most regions of the world. In this review, some challenges to the grazing cow are discussed together with opportunities for future improvement. We focus on daily feed intake, efficiency of pasture utilization, output of milk per head, environmental impact of grazing and the nutritional quality to humans of milk produced from dairy cows in contrasting production systems. Challenges are discussed in the context of a trend towards increased size of individual herds and include limited and variable levels of daily herbage consumption, lower levels of milk output per cow, excessive excretion of nitrogenous compounds and requirements for minimal periods of grazing regardless of production system. A major challenge is to engage more farmers in making appropriate adjustments to their grazing management. In relation to product quality, the main challenge is to demonstrate enhanced nutritional/processing benefits of milk from grazed cows. Opportunities include more accurate diet formulations, supplementation of grazed pasture to match macro‐ and micronutrient supply with animal requirement and plant breeding. The application of robotics and artificial intelligence to pasture management will assist in matching daily supply to animal requirement. Wider consumer recognition of the perceived enhanced nutritional value of milk from grazed cows, together with greater appreciation of the animal health, welfare and behavioural benefits of grazing should contribute to the future sustainability of demand for milk from dairy cows on pasture.

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          Most cited references116

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          Livestock-related greenhouse gas emissions: impacts and options for policy makers

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            Characteristics of plant cell walls affecting intake and digestibility of forages by ruminants.

            Even under the intensive concentrate feeding systems of ruminant animal production in the United States, forages continue to represent the single most important feed resource. Cell-wall concentration and digestibility limit the intake potential and energy availability of forage crops in beef and dairy production. Identification of cell-wall characteristics that should be targets of genetic modification is required if plant breeders and molecular biologists are to successfully improve forages for livestock feeding. As the forage plant cell develops, phenolic acids and lignin are deposited in the maturing cell wall in specific structural conformations, and in a strict developmental sequence. Lignin is the key element that limits cell-wall digestibility, but cross-linkage of lignin and wall polysaccharides by ferulic acid bridges may be a prerequisite for lignin to exert its affect. Lignin composition and p-coumaric acid in the wall are less likely to affect digestibility. Voluntary intake of forages is a critical determinant of animal performance and cell-wall concentration is negatively related to intake of ruminants consuming high-forage diets. Cell walls affect intake by contributing to ruminal fill. A simple model of cell-wall digestion and passage in which ruminal fill is a function of rates of digestion and passage, as well as the indigestible fraction of the cell-wall indicates that cell-wall concentration and rate of passage are the most critical parameters determining ruminal fill. Plant factors that affect rate of passage include those that affect particle size reduction by chewing and those that affect particle buoyancy in the rumen. The latter is primarily affected by 1) the ability of the particulate matter to retain gases, which is probably related to plant anatomy and rate of digestion of the plant tissue, and 2) the rate at which the gas is produced, which is affected by the potentially digestible fraction of the particulate matter and the rate of digestion of this fraction. Increasing rate of digestion should increase rate of passage by diminishing the gas produced and increasing density over time. A reduction in the indigestible cell-wall fraction is beneficial because this will decrease fill and increase digestibility. Animal production and economic benefits from reduced cell-wall concentration and increased digestibility are significant. Because of the high cell-wall concentration and large digestible cell-wall fraction of grasses, reduction in cell-wall concentration would probably be of greater value than improving digestibility in these species. Legumes represent the opposite situation and may benefit more from improvements in the digestibility of their cell walls.
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              Invited review: production and digestion of supplemented dairy cows on pasture.

              Literature with data from dairy cows on pasture was reviewed to evaluate the effects of supplementation on intake, milk production and composition, and ruminal and postruminal digestion. Low dry matter intake (DMI) of pasture has been identified as a major factor limiting milk production by high producing dairy cows. Pasture DMI in grazing cows is a function of grazing time, biting rate, and bite mass. Concentrate supplementation did not affect biting rate (58 bites/min) or bite mass (0.47 g of DM/bite) but reduced grazing time 12 min/d per kilogram of concentrate compared with unsupplemented cows (574 min/d). Substitution rate, or the reduction in pasture DMI per kilogram of concentrate, is a factor which may explain the variation in milk response to supplementation. A negative relationship exists between substitution rate and milk response; the lower the substitution rate the higher the milk response to supplements. Milk production increases linearly as the amount of concentrate increases from 1.2 to 10 kg DM/d, with an overall milk response of 1 kg milk/kg concentrate. Compared with pasture-only diets, increasing the amount of concentrate supplementation up to 10 kg DM/d increased total DMI 24%, milk production 22%, and milk protein percentage 4%, but reduced milk fat percentage 6%. Compared with dry ground corn, supplementation with nonforage fiber sources or processed corn did not affect total DMI, milk production, or milk composition. Replacing ruminal degradable protein sources with ruminal undegradable protein sources in concentrates did not consistently affect milk production or composition. Forage supplementation did not affect production when substitution rate was high. Fat supplementation increased milk production by 6%, without affecting milk fat and protein content. Increasing concentrate from 1.1 to 10 kg DM/d reduced ruminal pH 0.08 and NH3-N concentration 6.59 mg/dl, compared with pasture-only diets. Replacing dry corn by high moisture corn, steam-flaked or steam-rolled corn, barley, or fiber-based concentrates reduced ruminal NH3-N concentration 4.36 mg/dl. Supplementation did not affect in situ pasture digestion, except for a reduction in rate of degradation when high amounts of concentrate were supplemented. Supplementation with energy concentrates reduced digestibility of neutral detergent fiber and intake of N but did not affect digestibility of organic matter or flow of microbial N.
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                Author and article information

                Contributors
                jordana.rivero-viera@rothamsted.ac.uk
                Journal
                Grass Forage Sci
                Grass Forage Sci
                10.1111/(ISSN)1365-2494
                GFS
                Grass and Forage Science
                John Wiley and Sons Inc. (Hoboken )
                0142-5242
                1365-2494
                02 December 2019
                March 2020
                : 75
                : 1 ( doiID: 10.1111/gfs.v75.1 )
                : 1-17
                Affiliations
                [ 1 ] School of Biosciences University of Nottingham Loughborough UK
                [ 2 ] Bristol Veterinary School University of Bristol Langford UK
                [ 3 ] Rothamsted Research Okehampton UK
                [ 4 ] Chalcombe Wickham UK
                Author notes
                [*] [* ] Correspondence

                M. Jordana Rivero, Rothamsted Research, North Wyke, Okehampton, Devon EX20 2SB, UK.

                Email: jordana.rivero-viera@ 123456rothamsted.ac.uk

                Author information
                https://orcid.org/0000-0003-1573-0869
                https://orcid.org/0000-0001-7451-5611
                https://orcid.org/0000-0002-9045-289X
                Article
                GFS12458
                10.1111/gfs.12458
                7028026
                32109974
                7e861016-7664-4ce6-bf95-c56314093dbb
                © 2019 The Authors. Grass and Forage Science published by John Wiley & Sons Ltd.

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 20 August 2018
                : 31 October 2019
                : 01 November 2019
                Page count
                Figures: 4, Tables: 2, Pages: 17, Words: 15690
                Funding
                Funded by: Biotechnology and Biological Sciences Research Council , open-funder-registry 10.13039/501100000268;
                Award ID: BB/J004308
                Award ID: BBS/E/C/000I0300
                Funded by: Natural Environment Research Council (NERC) , open-funder-registry 10.13039/501100000270;
                Award ID: NE/N018125/1
                Funded by: UK's innovation agency, Innovate UK
                Award ID: 105150
                Categories
                Review Article
                Review Article
                Custom metadata
                2.0
                March 2020
                Converter:WILEY_ML3GV2_TO_JATSPMC version:5.7.5 mode:remove_FC converted:18.02.2020

                grazed pasture,grazing management,herbage intake,milk production,milk quality,nitrogen use efficiency

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