Effects of concentrate crude protein content on nutrient digestibility, energy utilization, and methane emissions in lactating dairy cows fed fresh-cut perennial grass.
Although many studies have investigated mitigation strategies for methane (CH4) output from dairy cows fed a wide variety of diets, research on the effects of concentrate crude protein (CP) content on CH4emissions from dairy cows offered fresh grass is limited. The present study was designed to evaluate the effects of cow genotype and concentrate CP level on nutrient digestibility, energy utilization, and CH4emissions in dairy cows offered fresh-grass diets. Twelve multiparous lactating dairy cows (6 Holstein and 6 Holstein × Swedish Red) were blocked into 3 groups for each breed and assigned to a low-, medium-, or high-CP concentrate diet [14.1, 16.1, and 18.1% CP on a dry matter (DM) basis, respectively], in a 3-period changeover study (25d per period). Total diets contained (DM basis) 32.8% concentrates and 67.2% perennial ryegrass, which was harvested daily. All measurements were undertaken during the final 6d of each period: digestibility measurements for 6d and calorimetric measurements in respiration chambers for 3d. Feed intake and milk production data were reported in a previous paper. We observed no significant interaction between concentrate CP level and cow genotype on any parameter. Concentrate CP level had no significant effect on any energy utilization parameter, except for urinary energy output, which was positively related to concentrate CP level. Similarly, concentrate CP content had no effect on CH4emission (g/d), CH4per kg feed intake, or nutrient digestibility. Cross breeding of Holstein cows significantly reduced gross energy, digestible energy, and metabolizable energy intake, heat production, and milk energy output. However, cow genotype had no significant effect on energy utilization efficiency or CH4parameters. Furthermore, the present study yielded a value for gross energy lost as CH4(5.6%) on fresh grass-based diets that was lower than the widely accepted value of 6.5%. The present findings indicate that reducing concentrate CP content from 18.1 to 14.1% may not be a successful way of alleviating CH4emissions from lactating dairy cows offered good-quality fresh grass, but grazing cows could be offered a low-CP concentrate without compromising energy utilization efficiency. Further research is needed to investigate whether larger differences in dietary CP content may yield positive results.
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.
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Hynes
Animal, Dairy and Food Chain Sciences Division, Centre for Dairy Research, University of Reading, School of Agriculture, Policy and Development, Earley Gate, PO Box 237, Reading, RG6 6AR, United Kingdom.
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Stergiadis
Finance and Corporate Affairs Division, Biometrics and Information Systems Branch, Agri-Food and Biosciences Institute, 18a Newforge Lane, Belfast, BT9 5PX, United Kingdom.
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Gordon
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.
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Yan
D000818:Animals; D002417:Cattle; D004032:Diet / Q000662:veterinary; D005260:Female; D007774:Lactation; D008697:Methane / Q000096:biosynthesis*; D008892:Milk / Q000737:chemistry; D006109:Poaceae / Q000378:metabolism*
D008697:Methane
dairy cow; energy utilization; fresh grass; methane