Effects of dietary Zn on ewe milk minerals and somatic cell count

Authors: PAGE, CHAD - University Of Wyoming; Murphy, Thomas - Tom; Taylor, Joshua - Bret; JULIAN, ALEXIS - University Of Wyoming; WHALEY, JAELYN - University Of Wyoming; WOODRUFF, KELLY - University Of Wyoming; HUMMEL, GWENDOLYNN - University Of Wyoming; DEMARCO, CLAUDIA - Federal University Of Pelotas; LAVERELL, DYLAN - University Of Wyoming; CUNNINGHAM-HOLLINGER, HANNAH - University Of Wyoming; RULE, DANIEL - University Of Wyoming; STEWART, WHIT - University Of Wyoming

Submitted to: Journal of Animal Science
Publication Type: Proceedings
Publication Acceptance Date: 5/19/2020
Publication Date: 11/30/2020
Citation: Page, C.M., Murphy, T., Taylor, B., Julian, A., Whaley, J., Woodruff, K., Hummel, G., DeMarco, C., Laverell, D., Cunningham, H., Rule, D., Stewart, W. 2020. Effects of dietary Zn on ewe milk minerals and somatic cell count [abstract]. Journal of Animal Science. 98(Supplement 4):213-214. https://doi.org/10.1093/jas/skaa278.394.
DOI: https://doi.org/10.1093/jas/skaa278.394

Interpretive Summary: Feeds for livestock are commonly deficient in micro- and macro-minerals, and zinc (Zn) is one that is often below required levels in the Western United States. Zinc is essential for reproduction, gene expression, wool growth, and immune function in sheep. Research in cattle has reported that increasing dietary Zn may increase milk Zn and decrease the incidence of clinical and subclinical mastitis, which is a common disease affecting the mammary gland of ewes. This experiment utilized both wool and meat type ewes and fed half at currently recommended and half at 3 times recommended dietary Zn for 6 weeks prior to and 4 weeks after lambing. Ewe milk samples were collected twice weekly for 30 days after lambing and analyzed for somatic cell count (SCC), an indicator of intramammary infection, and trace mineral element concentration. Results indicated that increased dietary Zn effectively increased Zn concentration in milk. However, feeding Zn at above recommended levels had no effect on milk SCC. Still, results provide longitudinal values of SCC throughout lactation which may inform other preventative intervention strategies for control of mastitis.

Technical Abstract: The objectives of the current study were to evaluate the effects of increased dietary Zn fed at approximately 3 times NRC recommendations on milk Zn concentrations and mammary health by quantifying milk somatic cell count (SCC). 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 = 45, 37 mg Zn/kg DM, ˜1×NRC) and Zn treatment (n = 44, 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 approximately 6 wk before to 4 wk after lambing. 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). Single-bearing ewes had greater Ca, Mg, and P (P = 0.04) than multiple-bearing ewes. Day of lactation influenced milk Mg, P, and Zn (P < 0.01) and values generally decreased as lactation progressed. Milk Zn was 1.7-fold greater (P < 0.01) for Zn treatment than Control ewes. Milk Ca, Mg, and P were greater for Control than Zn treatment (P = 0.02) ewes. A breed × litter size effect was detected for LogSCC (P = 0.02). Single-bearing WF ewes had lower LogSCC than multiple-bearing WF ewes (5.36 ± 0.09 vs 5.74 ± 0.07; P < 0.01) but litter size did not affect BF ewe LogSCC (5.80 ± 0.08 vs 5.79 ± 0.09; P = 0.92).. Day of lactation impacted ewe SCC (P < 0.01), with peak SCC between d 6 and 9 which began to decline as lactation progressed. Control and Zn treated ewes did not differ (P = 0.28) in SCC. In conclusion, dietary Zn above NRC recommendations resulted in greater milk Zn. 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.