Serum mineral concentrations in relation to estrus and conception in beef heifers and cows fed conserved forage

Small, J. A., Charmley, E., Rodd, A. V. and Fredeen, A. H. 1997. Serum mineral concentrations in relation to estrus and conception in beef heifers and cows fed conserved forage. Can. J. Anim. Sci. 77: 55–62. A study was undertaken to examine serum mineral concentrations in relation to estrus and first service conception (FSC) in beef cattle fed conserved forage. Blood samples were taken from yearling nulliparous heifers, and suckled 2-yr-old primiparous heifers and multiparous cows at first service which occurred within 12 h of observed standing heat and 21 d after. Serum was analyzed for calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K), sulfur (S), sodium (Na), iron (Fe), copper (Cu), manganese (Mn), zinc (Zn) and boron (B) concentrations by ICAP. Heifers were fed in four groups based on parity and given 3.0 and 2.5 kg hd d–1 of a grain supplement, respectively, plus free-choice grass hay (1.71% K; 0.20% P; 8% protein; 41% ADF). Cows were individually fed ad libitum (21 g kg–1 body weight) grass-legume silage (2.82% K; 0.35% P; 14% protein, 34% ADF). Heifers and cows gained body weight over the breeding season and at turnout had body condition scores of 5 to 6 for heifers and 6 to 7 for cows. Rates of FSC were 53% (10/19), 48% (10/21) and 64% (18/28) for nulli-, primiand multiparous groups, respectively. Serum Ca, Na, S, Cu, Fe, Zn and Mn did not differ (P > 0.05) between FSC groups, but Na and Cu were higher (P < 0.05) at estrus than at day 21, especially in nulliparous heifers. Concentrations of serum Mg were low (< 0.74 mmol L–1) and K high (> 4.5 mmol L–1) in heifers and cows but in nulliparous heifers only, serum Mg and K were lowest (P < 0.05) at estrus for those that conceived. Serum B concentrations were generally higher (P < 0.05) in animals that conceived especially on day 21 when B concentrations were higher (P < 0.05) than at estrus. Serum P concentrations were high (> 3.5 mmol L–1), but highest in animals that conceived especially on day 21. It is concluded that P and B may be dietary factors limiting first service conception in beef cows fed conserved forage.