Serum and milk mineral concentration and milk yield of beef cows of three breed types

Abstract

Sixteen Hereford x Holstein (HH), 25 Hereford x Jersey and 27 Hereford (H) cows 7 to 12 yr of age grazed native and improved pastures as a single group in two experiments. Cows were mated to one of two Charolais bulls over a 3 mo breeding season. Cow serum and milk mineral concentrations, milk yield, milk protein, fat and somatic cell count, ultrasound measurements over the 12th rib and over the rump, weight and height measurements and calf weight and height were recorded during each experiment Milk yield was estimated by machine milker (MM) in early to mid-lactation (1.5 to 5 mo) and at weaning (7 mo) in Exp. I, and by MM and weigh-suckle-weigh procedures at an average of 36, 130 and 190 d of lactation in Exp. II. Cow breed group x month of grazing interactions were observed for serum Mg concentrations (P < .02) at weaning in Exp. I, and for serum K concentrations (P < .04) summarized across months in Exp. II. Otherwise, cow breed groups responded similarly in serum K, Ca, inorganic P, Mg and Zn concentrations to month of grazing (P > .10). Hereford x Holstein produced 2.6 kg*d^-1 more milk (P < .05) than H with HJ intermediate in Exp. I, and 1.59 kg*d^-1 more milk (P < .05) than H with HJ intermediate in Exp. II. Hereford x Holstein and HJ cows weaned calves that were 23 and 13 kg heavier (P < .05), respectively, than H cross calves in Exp. I, and 21 and 15 kg heavier (P < .05), respectively, than H cross calves in Exp. II. These data indicate that within the range of serum mineral concentrations observed in these experiments, serum concentrations of K, Ca, inorganic P, Mg and Zn are of no value in determining a sub-clinical mineral deficiency that would result in a reduction in milk yield. While grazing native and improved pastures, calf weight weaned expressed as a function of reproductive success favored HH and H cows in Exp. I, and HH and HJ cows in Exp. II.