Effect of Zinc Chloride or Zinc Sulfate Treatment of Protein Supplement on Milk Production

Abstract

Production response to protein supplements treated with Zn salts to increase rumen escape was evaluated with 27 lactating Holstein cows in a switchback design trial with three treatments. Pelleted supplements fed with corn silage as total mixed rations were: 1) 18% protein, untreated, 2) 15% protein, treated with .5% zinc chloride, and 3) 15% protein, treated with .65% zinc sulfate. Corresponding total mixed rations (TMR) fed ad libitum contained 15, 12.6, and 13% crude protein. Each cow was offered 2.3kg of alfalfa-orchardgrass hay daily. Dry matter intake (DMI) 17.2, 16.8, 17.0 kg/d), DMI as percent of body weight (2.74, 2.68, 2.73%), and milk total solids (10.8, 10.7, 10.6%) were similar, although low for TMR 1 to 3, respectively. Daily milk production and fat percentage were 26.4, 26.5, and 26.2kg and 3.16, 3.21, and 3.26%, respectively. Plasma and milk Zn concentrations (1.15, 1.35, 1.33: 3.68, 4.37, 4.17ppm) were relatively normal despite dietary concentrations of 135, 1386, and 1264ppm. Body weight change, total milk yield, fat percent, FCM, milk protein yield, and SNF produced were similar among treatments. Dietary crude protein intake was highest for total mixed ration 1 but was lower than recommended on all diets as a result of low DMI.