Effect of variable water intake as mediated by dietary potassium carbonate supplementation on rumen dynamics in lactating dairy cows

Authors: FRALEY, SARAH - Purdue University; Hall, Mary Beth; NENNICH, TAMILEE - Purdue University

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2015
Publication Date: 5/1/2015
Publication URL: http://handle.nal.usda.gov/10113/62041
Citation: Fraley, S.E., Hall, M., Nennich, T.D. 2015. Effect of variable water intake as mediated by dietary potassium carbonate supplementation on rumen dynamics in lactating dairy cows. Journal of Dairy Science. 98(5):3247–3256.

Interpretive Summary: Potassium carbonate is being used as a potassium source in dairy cattle diets. Some performance responses suggest that potassium or potassium carbonate may be changing rumen function in unpredicted ways. The objective of this study was to evaluate the effect of potassium carbonate supplementation on water intake and rumen function. Increasing dietary potassium carbonate and total potassium in the diets of lactating dairy cows increased water consumption and modified ruminal measures in ways suggesting that both liquid and total ruminal turnover were increased as water and potassium intake increased. That could deliver more nutrients to the cow or reduce the amount of feed fermented in the rumen. Knowing that potassium carbonate affects rumen function in this way will help nutritionists better understand likely cow responses to some mineral formulations in dairy cattle diets.

Technical Abstract: Water is a critical nutrient for dairy cows, with intake varying with environment, production, and diet. However, little work has evaluated the effects of water intake on rumen parameters. Using dietary potassium carbonate (Kcarb) as a K supplement to increase water intake, the objective of this study was to evaluate the effect of potassium carbonate supplementation on water intake and on rumen parameters of lactating dairy cows. Nine ruminally cannulated, late-lactation Holstein cows (207±12 days in milk [DIM]) were randomly assigned to 1 of 3 treatments in a replicated 3 x 3 Latin square design with 18-d periods. Dietary treatments (on a dry matter [DM] basis) were: no added potassium carbonate (baseline dietary K levels of 1.67% dietary K [CON]), 0.75% added dietary K (LowK), and 1.5% added dietary K (HighK). Cows were offered treatment diets for a 14-d adaption period followed by a 4-d collection period. Ruminal total, liquid, and DM digesta weights were determined by total rumen evacuations conducted 2 h post-feeding on day 4 of the collection period. Rumen fluid samples were collected to determine volatile fatty acids (VFA) and NH3 concentrations and liquid passage rate. Milk samples were collected twice daily during the collection period. Milk, milk fat, and protein yields showed quadratic responses with greatest yields for LowK. Dry matter intake showed a quadratic response with 21.8 kg/d for LowK and 20.4 and 20.5 kg/d for CON and HighK, respectively. Water intake increased linearly with increasing Kcarb supplementation (102.4, 118.4, and 129.3 L/d) as did ruminal liquid passage rate in the earlier hours post-feeding (0.122, 0.135, and 0.141/h). Total and wet weights of rumen contents declined linearly, and dry weight tended to decline linearly as dietary Kcarb increased, suggesting that the increasing water intake and liquid passage rate with increasing Kcarb increased the overall ruminal turnover rate. Ruminal ammonia concentrations declined linearly as K supplementation increased. As a molar percentage of total volatile fatty acids, acetate increased linearly as dietary K increased, though propionate declined. Increasing dietary Kcarb and total K in the diets of lactating dairy cows increased water consumption and modified ruminal measures, suggesting that both liquid and total ruminal turnover were increased as both water and K intake increased.