title: Water dynamics of dairy cattle as affected by initiation of lactation and feed intake.
abstract: Effects of lactation and feed intake on sizes and half-lives of body water pools were investigated in four Holstein cows in a thermoneutral environment. Various markers were administered, on average, 24 days prepartum (Period 1, feed intake fixed to average of consumption after offered at a rate ensuring 10% refusal), 24 days postpartum (Period 2, restricted to intake in Period 1), and 42 days postpartum (Period 3, feed again offered at a rate ensuring 10% refusal). Total body water decreased from period 1 to 2; however, it did not change as a percent of body weight. Estimated body water half-lives and fluxes for the three periods were 7.5, 3.7, and 2.9 days; and 42, 66, and 87 liters/day. Increased water intake during lactation closely matched water secreted in milk. Empty body water, estimated by a two-compartment, four-parameter model, as a percent of body weight did not change across periods. Lactation and increased feed intake decreased half-life of body water. Plasma volume increased as a percent of body weight because of loss of body weight in early lactation; however, extracellular volume tended to decrease with body weight. Initiation of lactation and feed intake during lactation affect water dynamics of the dairy cow.
mesh_terms: D000818:Animals; D001834:Body Water / Q000378:metabolism*; D001835:Body Weight; D002417:Cattle / Q000378:metabolism*; D004326:Drinking; D004435:Eating; D005260:Female; D006207:Half-Life; D007774:Lactation; D008892:Milk / Q000378:metabolism; D008954:Models, Biological; D011247:Pregnancy