title: Timothy hay with a low dietary cation-anion difference improves calcium homeostasis in periparturient Holstein cows.
abstract: The current study was undertaken to evaluate the effects of feeding timothy (Phleum pratense L.) hay differing in dietary cation-anion difference (DCAD) on the capability of cows to maintain calcium homeostasis around parturition. We hypothesized that feeding low-DCAD timothy hay during the prepartum period would induce a mild metabolic acidosis prepartum and improve calcium homeostasis postpartum with no effect on dry matter intake. Forty-one dry pregnant Holstein cows entering their second lactation or greater were used in a randomized complete block design. Timothy hay was obtained from an established timothy stand under a pivot irrigation system. Low-DCAD timothy hay was produced by fertilizing the area between the second and third pivot towers at a rate of 224 kg of CaCl(2)/ha, and control timothy hay (high DCAD) was grown on the area between the fourth and fifth pivot towers of the same field. The chloride concentration was 1.07 and 0.15% on a dry matter (DM) basis, and the DCAD was 1.2 and 21.6 mEq/100 g of DM for the low- and high-DCAD timothy hay, respectively. Experimental diets, containing timothy hay at 63% of dietary DM, were fed ad libitum starting 30 d before the expected calving date. The DCAD values were 1.6 vs. 14.5 mEq/100 g of DM for the low- and high-DCAD timothy-based diets, respectively. At the beginning of the study, urine pH and blood bicarbonate concentration averaged 8.22 +/- 0.06 and 28.5 +/- 0.3 mM, respectively. The low-DCAD timothy diet decreased urine pH compared with the high-DCAD timothy diet on d 21 (7.75 vs. 8.31), d 14 (7.69 vs. 8.22), and d 7 (7.50 vs. 8.19) before calving, and it also decreased the prepartum blood bicarbonate concentration by 2 mM. In addition, cows fed the low-DCAD timothy diet had greater blood ionized calcium concentration prepartum (1.22 vs. 1.19 mM), greater blood ionized calcium concentration at 0 and 8 h after calving, and similar prepartum dry matter intake. These results indicate that timothy hay differing in DCAD affects the acid-base balance of periparturient dairy cows, and that low-DCAD timothy hay improves calcium homeostasis postpartum with no negative effect on dry matter intake.
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, T6G 2P5, Canada.
authors.forename: G B
authors.initials: GB
authors.lastname: Penner
authors.forename: G F
authors.initials: GF
authors.lastname: Tremblay
authors.forename: T
authors.initials: T
authors.lastname: Dow
authors.forename: M
authors.initials: M
authors.lastname: Oba
mesh_terms: D000818:Animals; D000838:Anions / Q000032:analysis*; D002118:Calcium / Q000097:blood*; D002122:Calcium Chloride / Q000008:administration & dosage; D002412:Cations / Q000032:analysis*; D002417:Cattle / Q000502:physiology*; D004032:Diet; D005260:Female; D005308:Fertilizers; D006706:Homeostasis / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D036801:Parturition; D031784:Phleum / Q000737:chemistry* / Q000254:growth & development; D049590:Postpartum Period; D011247:Pregnancy
chemical_list: D000838:Anions; D002412:Cations; D005308:Fertilizers; D002122:Calcium Chloride; D002118:Calcium