Effect of Supplementing Heat Stressed Dairy Cows with Electrolytes on Milk Yield, Composition, and Blood Metabolites

Abstract Text: The objective of this study was to determine the effect of supplementing electrolytes from -21 to 30 DIM to heat stressed cows on DMI, MY, and blood metabolites. A total of 104 Holstein and Jersey, cows and heifers, were utilized between August-September, 2012, and August-November, 2013. Prior to calving, all cows and heifers were fed ryegrass baleage in the AM and TMR in the PM (CON) or the same base ration plus 270g of electrolyte (E+, Bovine Bluelite, TechMix, Inc; MN) providing balanced electrolytes (0.55% Ca; 0.30% P; 9.60% NaCl; 8.25% K; 0.14% Mg). Post-calving, CON cows were fed standard TMR and E+ cows received the same TMR plus 270g of Bovine Bluelite. DMI, MY, rectal temperature, and respiration rate were monitored daily; while blood metabolites, body weight, condition score and frame (withers height, hip height, and heart girth) were measured weekly. Orts and feedstuffs were sampled weekly and subjected to proximate analysis. Milk samples were taken weekly and analyzed for fat, protein, solids, lactose content, and SCS. Blood samples were taken via jugular venipuncture, further analyzed for pH, HCO3, tCO2, pCO2, Anion Gap, Na+, K+, and Cl-, using an onsite IDEXX Blood Gas Analyzer, and for hematocrit utilizing a micro centrifuge. DMI was not different among treatments, however, during 2013 dry cows consumed more than in 2012 (8.33 vs. 7.09 kg/d; P<0.0001). Cows fed E+ had lower MY than CON cows (29.64 vs. 34.99 kg/d; P=0.0042). Holstein cows averaged greater MY than Jerseys (36.45 vs. 28.18 kg/d; P<0.0001) but despite this expected breed effect, MY for CON and E+ cows only differed between Holsteins (40.90 vs. 32.00 kg/d, respectively; P<0.0001), not between Jerseys (29.08 vs. 27.29 kg/d, respectively; P=0.6084). Milk composition was not affected, however, E+ cows had increased fat content (P<0.001) weekly for the first four weeks, whereas CON cows decreased (P<0.001) until week two. Respiration rate (57.12 vs. 55.30 bpm; P= 0.1197) and rectal temperature (38.7 vs. 38.7 °C, respectively; P=0.9853) were not influenced by treatment, but Holstein cows had greater respiration rates than Jerseys (58.63 vs. 53.78 bpm, respectively; P<0.0001). No differences were observed in blood metabolites, nor in body weight change and condition score, except for withers height which was greater for CON cows (133.40 vs. 130.75 cm, respectively; P=0.0170). Electrolyte supplementation did not increase MY, nor affect any of the other measured variables in the present study.

Keywords: Dairy, Electrolyte, Transition