Effect of prepartum mineral supplement source on cow colostrum and milk composition was evaluated in mature pregnant Angus (n = 20) and Brangus (n = 20) cows, which were allotted to two mineral supplements containing either inorganic or organic trace minerals in a 2 x 2 factorial design. Mineral supplementation began approximately 90 days before expected parturition and continued through weaning. Colostrum (before calves suckling) and milk (30 days post-parturition) samples were collected by hand-milking and frozen at -4°F for eventual mineral and milk composition analysis. Colostrum analysis (percentage basis) included fat, total protein, total solids, lactose, as-fed ash, moisture and dry matter and somatic cell count. Centrifuged colostrum was analyzed for trace minerals (Co, Cu, Fe, Mn, Mo, Se and Zn). Milk analysis (percentage basis) included fat, true protein, total solids and lactose, plus milk urea nitrogen and somatic cell count.

  • Treatment and breed did not affect colostrum fat (5.06 ± 0.42%), total protein (16.67 ± 0.44%), lactose (2.97 ± 0.08%), dry matter (4.38 ± 0.13%) or somatic cell count (7.4 ± 1.0 X 106 cells/mL).
  • Colostrum total solids were greater for Angus (27.10 ± 0.89%) than Brangus (24.56 ± 0.86%).
  • The Brangus (75.44 ± 0.8%) had greater colostrum moisture than Angus (72.89 ± 0.86%).
  • Colostrum as-fed ash tended to be greater for Angus (1.15 ± 0.03%) than Brangus (1.06 ± 0.03%).
  • Colostrum had no detectable concentrations of Co, Cu, Fe, Mn or Mo. However, Zn was greater for Angus (90.80 ± 2.15 μg/g) than Brangus (79.30 ± 2.15 μg/g).
  • A treatment by breed interaction was observed for selenium colostrum (Angus-organic, 0.86 ± 0.06; Brangus-inorganic, 0.88 ± 0.06; Angus-inorganic, 0.74 ± 0.07; Brangus-organic, 0.72 ± 0.07 μg/g).
  • Treatment and breed did not affect milk fat (1.98 ± 0.23%), true protein (3.07 ± 0.06%), total solids (10.89 ± 0.24%), lactose (5.11 ± 0.06%) and somatic cell count (3.2 ± 1.7 X 105 cells/mL).
  • The milk urea nitrogen was greater for Brangus (12.12 mg/dL) than Angus (9.40 ± 0.75 mg/dL).
 
Results indicate breed had more effect on colostrum and milk composition than prepartum mineral supplement treatment.