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ZINPRO® Zinc Methionine Improved Mammary Tight Junction Integrity

Introduction:

This study was designed to assess the effect of ZINPRO® zinc methionine (ZINPRO) on mammary tight junction (MTJ) integrity in heat-stressed lactating dairy cows.

Experimental Design:

Seventy-two multiparous, lactating Holstein cows were evaluated during two 84-day periods. During the baseline period, cows received 1 of 2 zinc treatments: ZnCl alone or ZnCl + ZINPRO, and were cooled with fans and misters. Diets were maintained during a subsequent environmental challenge when some cows were deprived of access to cooling mechanisms (Cooled or Not Cooled).

Baseline Treatments:

T1: 75 ppm ZnCl; Cooled

T2: 35 ppm ZnCl + 40 ppm ZINPRO; Cooled

Environmental Challenge Treatments:

T1: 75 ppm ZnCl; Cooled

T2: 35 ppm ZnCl + 40 ppm ZINPRO; Cooled

T3: 75 ppm ZnCl; Not Cooled

T4: 35 ppm ZnCl + 40 ppm ZINPRO; Not Cooled

Results:

Baseline phase

At the start of the baseline phase, plasma lactose was similar between Zn treatments; however, as the baseline phase progressed, plasma lactose increased in cows receiving only ZnCl, but remained unchanged in cows consuming ZINPRO (Zn source X day, P = 0.06).

Environmental challenge phase

During the environmental challenge, feeding ZINPRO tended to decrease plasma lactose, P = 0.11.

Cooled cows receiving ZINPRO had lower milk fat % compared to other treatments (Zn treatment X environment, P = 0.04).

Cows deprived of cooling systems were observed to have:

• Decreased feed intake, energy-corrected milk (ECM) yield, milk lactose, and milk solids, P ≤ 0.05

• Increased milk urea nitrogen and vaginal temperature, P < 0.01

• A tendency for increased plasma lactose over time, P = 0.09

Removing cooling systems impaired lactation performance; however, cows receiving ZINPRO® zinc methionine had improved MTJ integrity as evidenced by lower plasma lactose.