Abstract
The objectives of the current research are to quantify the effects that increased dietary Zn during late gestation and early lactation has on ewe and progeny body weights, serum and milk minerals, and somatic cell count. Within Rambouillet (WF) and Hampshire (BF) breeds, ewes were ranked by BW and randomly assigned down the rank into 1 of 2 treatment groups: Control (n = 34, 37 mg Zn/kg DM, ≈1×NRC) and Zn treatment (n = 37, 113 mg Zn/kg DM, ≈3×NRC). Treatments were delivered via a ZnSO4-fortified alfalfa pellet fed at a rate of 0.45 kg/d DM from a RFID-activated automated feeder from d 108 ± 10 of gestation to d 30 post-lambing. Ewe BW were recorded at d 0, 29, lambing, 30 post-lambing, and weaning. Lamb BW was recorded at lambing, d 15, 30, and weaning. Serum samples were taken from ewes and lambs at 18 ± 4 h post-lambing and analyzed for mineral concentrations. Maternal trace mineral transfer efficiency were calculated by dividing lamb serum values by their respective dam’s serum value and expressed as a percentage. Ewe milk was collected twice weekly. Milk was analyzed for mineral content (d 0, 10, and 30 of lactation) and SCC (d 3–5, 6–9, 10–12, 13–16, 17–19, 20–23, 24–26, 27–29, or 30–32). Ewe and lamb BW was not influenced by Zn treatment (P > 0.19). Ewe serum Zn and maternal transfer efficiency did not differ between control and Zn treatment ewes (P ≥ 0.47). There was a treatment × breed type interaction for lamb serum LogZn (P = 0.04), where BF lambs within Zn treatment had greater serum LogZn (0.63 ± 0.32) than WF lambs (-0.37 ± 0.27; P = 0.04), but breeds did not differ within lambs in the Control treatment group. Milk Ni and Zn was greater for Zn treated ewes than control ewes (P < 0.01), but Mg and P concentrations were greater for control ewes (P ≤ 0.02). Control and Zn treated ewes did not differ in LogSCC through the first 30 d of lactation (P = 0.68) nor did they differ at weaning (P = 0.48). White face and BF ewes LogSCC did not differ at weaning (P = 0.09), but for the first 30 d of lactation BF (5.79 ± 0.06) had greater LogSCC than WF ewes (5.54 ± 0.06; P < 0.01). Day of lactation impacted ewe SCC (P < 0.01), with peak SCC between d 6 and 9 which began to decline as lactation progressed. Current Zn recommendations appear to be adequate for ewe and lamb growth during late gestation and early lactation, but results suggest litter size and breed nuances. Milk Zn is also increased with dietary Zn above NRC recommendations, while further interactions with milk Ni, Mg, and P occur. Additionally, longitudinal values of SCC throughout lactation may inform preventative intervention strategies for cases of sub-clinical mastitis since peak SCC is within the first 9 d post-lambing.
Effects of dietary Zn on ewe milk minerals and somatic cell count1
