Time Postpartum and Nutritional Plane Affect Colostrum and Transition Milk Trace Minerals in Primiparous Beef Females

Trace mineral concentrations and total yields have been under-studied during the transition of colostrum to milk in beef females, and the effects of late gestational nutrition on these are unknown. Fall-calving crossbred beef heifers (BW: 473 ± 34 [SD] kg; BCS: 5.3 ± 0.4) bred to a single sire were individually-fed 100% (control; n = 12) or 70% (nutrient restricted; NR; n = 12) of metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Diets were based on chopped sorghum sudan hay and supplemented to meet targeted nutritional planes; all females received recommended daily intake of a commercially-available trace mineral and vitamin supplement. Calves were removed immediately post-calving, allowing for complete colostrum and transition milk collection by hand (after 20 USP of intravenous oxytocin) at 1, 12, 24, and 36 h postpartum. Subsamples were frozen for trace mineral determination by inductively coupled plasma mass spectrometry. Data were analyzed with fixed effects of nutritional plane, hour, and their interaction, using repeated measures. Date of treatment initiation, maternal sire, and calf sex (when P < 0.25), were covariates. Post-calving, NR females were 68 kg BW and 2.2 BCS lower (P < 0.001) than controls. Colostrum yield was affected by nutritional plane x hour (P = 0.02), where control females had greater (P = 0.03) yield than NR at 1 h. Copper, manganese, molybdenum, iron, selenium, and zinc concentrations were affected by hour (P < 0.001), but not nutritional plane or nutritional plane x hour (P ≥ 0.14). Manganese and iron concentrations decreased (P ≤ 0.03) at each time point. Molybdenum and selenium concentrations decreased (P ≤ 0.002) from 1 to 24 h. Copper and zinc concentrations decreased (P < 0.001) from 1 to 12 h only. Total selenium was affected (P = 0.02) by nutritional plane x hour, where controls had greater (P = 0.02) total selenium than NR at 1 h. Nutritional plane x hour tended to affect (P ≤ 0.08) total manganese and iron, where both tended to be greater (P ≤ 0.07) at 1 h for controls. Total copper tended to be greater (P = 0.10, main effect) for control than NR. Hour (P < 0.001) affected total copper, molybdenum, and zinc. Total copper decreased (P < 0.001) from 1 to 12 h and increased (P ≤ 0.01) from 12 to 36 h, whereas total molybdenum and zinc decreased (P < 0.001) from 1 to 12 h and increased (P < 0.001) from 24 to 36 h. In general, trace mineral content decreases as colostrum transitions to milk in beef females. Impaired colostrum production caused by poor late gestational nutrition also appears to decrease total colostrum trace mineral yields.