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Title:   Author  item
                                            Zanton, Geoffreyitem
                                            HEINRICHS, ARLYN - University Of Pennsylvania
  Submitted to: Journal of Dairy Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 12/11/2015
                                    Publication  Date: 3/31/2016
                                    Publication URL: http://handle.nal.usda.gov/10113/62714Citation: Zanton, G.I., Heinrichs, A.J. 2016. Efficiency and rumen responses in younger and older Holstein heifers limit-fed diets of differing energy density. Journal of Dairy Science. 99:2825-2836.Interpretive Summary: Effects of age and dietary energy density were studied in limit-fed Holstein heifers. Rumen responses, digestibility, nitrogen balance, and environmental output were measured. Heifers limit-fed the high-energy density (HED) diet had greater digestibility of dietary organic matter and lower excretion of manure. The efficiency of nitrogen retention was greater for heifers fed the HED diet and for younger heifers. Results also supported the concept of limit-feeding HED diets as a potential means to reduce manure excretion and increase nitrogen efficiency.
                                Technical Abstract: The objective of this study was to evaluate the effects of limit-feeding diets of different predicted energy density on the efficiency of utilization of feed and nitrogen and rumen responses in younger and older Holstein heifers. Eight rumen-cannulated Holstein heifers (4 heifers beginning at 257 ± 7 d, hereafter “young,” and 4 heifers beginning at 610 ± 16 d, hereafter “old”) were limit-fed high [HED; 2.64 Mcal/kg of dry matter (DM), 15.31% crude protein (CP)] or low (LED; 2.42 Mcal/ kg of DM, 14.15% CP) energy density diets according to a 4-period, split-plot Latin square design with 28-d periods. Diets were limit-fed to provide isonitrogenous and isoenergetic intake on a rumen empty body weight (BW) basis at a level predicted to support approximately 800 g/d of average daily gain. During the last 7 d of each period, rumen contents were subsampled over a 24-h period, rumen contents were completely evacuated, and total collection of feces and urine was made over 4 d. Intakes of DM and water were greater for heifers fed LED, although, by design, calculated intake of metabolizable energy did not differ between age groups or diets when expressed relative to rumen empty BW. Rumen pH was lower, ammonia (NH3-N) concentration tended to be higher, and volatile fatty acids (VFA) concentration was not different for HED compared with LED and was unaffected by age group. Rumen content mass was greater for heifers fed LED and for old heifers, so when expressing rumen fermentation responses corrected for this difference in pool size, NH3-N pool size was not different between diets. Total moles of VFA in the rumen were greater for heifers fed LED, whereas these pool sizes were greater for old heifers. Total-tract digestibility of potentially digestible neutral detergent fiber (NDF) was greater in heifers fed LED and for young heifers, whereas the fractional rate of ruminal passage and digestion of NDF were both greater in heifers fed LED. Digestibility of N was greater for heifers fed HED, but was unaffected by age group, whereas the efficiency of N retention was greater for heifers fed HED and for young heifers. Manure output was reduced in heifers fed HED, but the effect was largest in old heifers. Results confirmed previous studies in which young heifers utilized N more efficiently than old heifers, primarily through greater efficiency of postabsorptive metabolism. Results also supported the concept of limit-feeding HED diets as a potential means to reduce manure excretion and increase nitrogen efficiency.


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