SERUM MINERAL CONCENTRATIONS IN RELATION TO PARTURITION IN BEEF HEIFERS AND COWS FED CONSERVED FORAGE

A study was undertaken to examine the relationship between serum miner al concentrations and calving ease in beef cattle fed conserved forage . Jugular blood samples were taken from multiparous cows (n = 6) and 2 -yr-old primparous heifers (n = 9) that calved without assistance and 2-yr-old primparous heifers that required assistance with calving (n = 6) on days -7, 0 and +7 after parturition. Sera were analyzed for Ca, P, Mg, K, S, Na, Cu, Zn and B by ICAP and for progesterone by RIA. Fr om 2 mo before and throughout the calving season cattle were given ad libitum round bale grass-legume silage (2.89% K; 3.4% P; 13% CP, 40% A DF; 38% DM). Heifers were also given 0.5 kg hd(-1) d(-1) of a grain su pplement beginning 3 wk before calving. At calving, cows and heifers w ere in moderate body condition (5.26 +/- 0.14 BCS) and heifers had rea ched 85% of mature body weight (475 +/- 26 kg). Serum progesterone con centrations were highest (P < 0.05) at -7 d and dropped below 1 ng mL( -1) at parturition and +7 d. Concentrations of serum Mg, S and K were highest (P < 0.05) whilst concentrations of P, B and Cu were lowest (P < 0.05) at parturition. However, serum Mg and S also differed (P < 0. 05) among calving groups because concentrations were lowest for heifer s with assisted calvings and, serum K concentrations were influenced ( P < 0.05) by interaction between calving group and time because K conc entrations increased at parturition only in cows and heifers with unas sisted calvings. Serum Zn, Ca, and Na were not (P < 0.05) influenced b y calving group or time. It is concluded that Mg, S, K, P, B and Cu me tabolism are involved in the physiology of parturition and Mg, S and K metabolism may be particularly important for calving ease in primparo us beef heifers fed conserved forage.