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CHARACTERIZING CHOLINE NUTRITION AND BIOLOGY IN THE DAIRY COW

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Dairy cows transitioning from gestation to lactation develop fatty liver in response to excessive mobilization of free fatty acids (FA) from stored bodily triacylglycerol (TAG) reserves to meet the increased energy demand of lactation. Rumen-protected choline (RPC) supplementation may increase hepatic phosphatidylcholine (PC) synthesis to promote TAG secretion within very-low density proteins. Dietary FA and one-carbon donors such as choline may influence PC synthesis in cows with implications for health. Choline can also be degraded in the gastrointestinal tract in part to trimethylamine (TMA), which is oxidized in the liver to form trimethylamine N-oxide (TMAO). It has not been well- established in ruminants if FA of varying chain length can modulate hepatic PC production. The evaluation of RPC supplementation at various increasing doses and the quantification of lipoprotein TAG concentration in dairy cows has also not been thoroughly evaluated. The effects of TMAO on dairy cow’s health has not yet been assessed as has been the case in non-ruminants including humans. In study 1, we abomasally infused (i) palmitic acid (PA; 98% 16:0 of total fat), (ii) PA + choline chloride (PA+C; 50 g/d choline ion), (iii) PA + L-serine (PA+S; 170 g/d L-serine), (iv) behenic acid (BA; 92% 22:0 of total fat), and (v) a docosahexaenoic acid algal oil (47.5% DHA of total fat) into 5 late lactation dairy cows. Infusion of DHA increased hepatic PC containing 4 or more double bonds (52 out of 61 PC; e.g., PC-14:0/22:6 or 22:0/20:4), relative to other treatments. Hepatic PC containing saturated FA were lowest for DHA-infused cows. While PA+C increasedhepatic PC with moderate saturation, PA+C decreased highly unsaturated PC when compared to PA. A similar outcome was observed for cows infused PA+S. These data confirm that saturated FA, DHA, and one-carbon donors uniquely modify hepatic PC levels in lactating cows. In study 2, forty-one pregnant, non-lactating, multiparous Holstein cows were feed-restricted to consume ~31% of their net energy requirements for 9 d and fed RPC that provided 0 (control), 6.5, 12.9, 19.4, or 25.8 g/d of choline ions. We observed a significant linear increase in TAG-rich lipoprotein total TAG levels with choline ion supplementation. Majority of PC within the TAG-rich lipoprotein fraction increased linearly with increasing RPC (37 out of 55 PC; e.g. PC 38:5). A similar linear outcome was observed for TAG-rich lipoprotein TAG (106 out of 317 TAG). In liver, RPC increased PC (0 vs. rest; 40 out of 57 PC). Hepatic TAG was lowered by RPC (0 vs. rest; 17.5 vs. 13.6% of tissue DM). Our data support the likelihood that RPC increased hepatic PC synthesis and lipoprotein secretion to prevent liver TAG accrual in dairy cows. In study 3, we assessed the effects of TMAO on dairy cow markers of health and milk production. We continuously intravenously infused TMAO at 0, 20, 40, or 60 g/d for 6 d into eight early lactation Holstein cows in a 4 _ 4 replicated Latin square design. Plasma TAG, FA, and glucose concentrations were not modified by treatment. Serum albumin, total protein, globulin, total bilirubin, direct bilirubin, aspartate aminotransferase, _-glutamyl transferase, and glutamate dehydrogenase concentrations were not modified by treatment. We did not observe any differences in markers of oxidative status: total glutathione, reduced glutathione, oxidized glutathione, and the ratio of reduced: oxidized glutathione within plasma. Glucose tolerance or milk production were not modified by treatment. It appears that TMAO does not impair metabolic health in early lactation cows. Future research should investigate nutritional strategies to maximize choline bioavailability in order to decrease post-ruminal choline degradation.

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143 pages

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2020-12

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McFadden, Joseph W.

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Caudill, Marie A.
Lei, Xingen
Mann, Sabine

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Animal Science

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Ph. D., Animal Science

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Doctor of Philosophy

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dissertation or thesis

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