THE EFFECT OF DIETARY ZINC LEVEL AND SOURCE ON YEARLING BULL GROWTH AND FERTILITY

To study the effect of dietary zinc level and source on bull gr o wth and fertility, 325 yearling Angus bulls were allotted by weight into six pens (three pens of heavy and three pens of lightweight bu l ls). The three supplemental zinc (Zn) treatments were 1) 40 ppm inorganic Zn all supplied by Zn sulfate (ZnI); 2) 40 ppm Zn with 1/3 supplied by Zn proteinate and 2/3 suppl ied by Zn sulfate (ZnPI); and 3) 60 ppm ZnI all supplied by Zn sulfate (ZnHi). Initial and final liver biopsies (10 per pen) were collected and analyzed for zinc concentration. Individual weights and scrotal circumferences also were recorded at the start a nd conclusion of the trial. Bull s intended for public sale (n=167) had their semen collected and evaluated for motility and morphological ab n ormalities. Bulls with percent normal sperm cell counts of less than 70% or with motility scores less than fair (moti lity scores = poor, fair, good, very good) were considered classification deferred (CD). Followin g 126 days of treatment, ZnHi bulls had a greater (P=.058) percent change in liver Zn concentration th an ZnI, but similar increases to ZnPI. No difference s in bull ADG or percent change in scrotal circumference were detected. ZnPI and ZnHi bulls had a higher (P<.05) percent of normal sperm cells than ZnI bulls. ZnPI and ZnHi treatments had fewer (P<.05) CD bulls than ZnI. In all fertility measures observed , bulls receiving the Zn proteinate/Zn sulfate combination at 40 ppm had improved semen quality when compared to bulls supplemented with 40 ppm Zn sulfate.

The effect of dietary zinc level and source on yearling bull growth and fertility The effect of dietary zinc level and source on yearling bull growth and fertility

Abstract Abstract
To study the effect of dietary zinc level and source on bull growth and fertility, 325 yearling Angus bulls were allotted by weight into six pens (three pens of heavy and three pens of lightweight bulls).The three supplemental zinc (Zn) treatments were 1) 40 ppm inorganic Zn all supplied by Zn sulfate (ZnI); 2) 40 ppm Zn with 1/3 supplied by Zn proteinate and 2/3 supplied by Zn sulfate (ZnPI); and 3) 60 ppm ZnI all supplied by Zn sulfate (ZnHi).Initial and final liver biopsies (10 per pen) were collected and analyzed for zinc concentration.Individual weights and scrotal circumferences also were recorded at the start and conclusion of the trial.Bull s intended for public sale (n=167) had their semen collected and evaluated for motility and morphological abnormalities.Bulls with percent normal sperm cell counts of less than 70% or with motility scores less than fair (motility scores = poor, fair, good, very good) were considered classification deferred (CD).Following 126 days of treatment, ZnHi bulls had a greater (P=.058) percent change in liver Zn concentration than ZnI, but similar increases to ZnPI.No difference s in bull ADG or percent change in scrotal circumference were detected.ZnPI and ZnHi bulls had a higher (P<.05) percent of normal sperm cells than ZnI bulls.ZnPI and ZnHi treatments had fewer (P<.05)CD bulls than ZnI.In all fertility measures observed , bulls receiving the Zn proteinate/Zn sulfate combination at 40 ppm had improved semen quality when compared to bulls supplemented with 40 ppm Zn sulfate.

Summary
To study the effect of dietary zinc level and source on bull gr owth and fertility, 325 yearling Angus bulls were allotted by weight into six pens (three pens of heavy and three pens of lightweight bu lls).The three supplemental zinc (Zn) treatments were 1) 40 ppm inorganic Zn all supplied by Zn sulfate (ZnI); 2) 40 ppm Zn with 1/3 supplied by Zn proteinate and 2/3 suppl ied by Zn sulfate (ZnPI); and 3) 60 ppm ZnI all supplied by Zn sulfate (ZnHi).Initial and final liver biopsies (10 per pen) were collected and analyzed for zinc concentration.Individual weights and scrotal circumferences also were recorded at the start a nd conclusion of the trial.Bull s intended for public sale (n=167) had their semen collected and evaluated for motility and morphological ab n ormalities.Bulls with percent normal sperm cell counts of less than 70% or with motility scores less than fair (moti lity scores = poor, fair, good, very good) were considered classification deferred (CD).Followin g 126 days of treatment, ZnHi bulls had a greater (P=.058) percent change in liver Zn concentration th an ZnI, but similar increases to ZnPI.No difference s in bull ADG or percent change in scrotal circumference were detected.ZnPI and ZnHi bulls had a higher (P<.05) percent of normal sperm cells than ZnI bulls.ZnPI and ZnHi treatments had fewer (P<.05)CD bulls than ZnI.In all fertility measures observed , bulls receiving the Zn proteinate/Zn sulfate combination at 40 ppm had improved semen quality when compared to bulls supplemented with 40 ppm Zn sulfate.

Introduction
The important role of Zn in male fertility has been realized for some time.Recently, however, the use of "minerals" in livestock nutritio n has gained considerable interest from commercial and purebred producers alike.The generic term "organic mineral" is used to descr ibe any of the three forms of protected minerals availabl e in the feed industry: chelates, proteinates, and complexes.The support for their use stems from research studies and field experience that sugges t ing that organic minerals are more biologically available than inorganic forms.Nevertheless, controlled experiments continue to produce conflicting results.Our study investigated the potential use of organic Zn as Zn proteinate in growing bull diets.Growth , sexual maturation, and fertility were compare d when bulls were supplemented with either inorganic (Zn sulfate) or organic Zn sources .Additionally, a third treatment, consisting of inorganic Zn at an increased level, was incl uded to answer the important question: will increased levels of the less expensive inorganic Zn achieve the same benefits as organic Zn?

Experimental Procedures
Yearling Angus b ulls (n=325) were allotted by weight into six pens of similar size resulting in three pens of heavy-and three pens of lightweigh t bulls.One of three supplemental zinc treatments consisting o f 1) 40 ppm, all supplied by Zn sulfate (ZnI); 2) 40 ppm Zn with 1/3 supplied by Zn proteinate and 2/3 supplied by Zn sulfate (Zn PI); or 3) 60 ppm, all supplied by Zn sulfate (ZnHi).Each Zn treatment was given to cattle in two pens, one heavy-and one lightweight, fo r 126 days.Initial and final liver biopsie s (10 per pen) were collected and analyzed for Zn concentration via inductively couple d plasma spectroscopy.Individual bull weights and scrotal measures also were recorde d at the start and conclusion of the trial.One person measured all scrotal circumferences at each time period.Se men from bulls intended for public sale (n=167) was collected by electro-ejaculatio n and evaluated for motility and morphological abnormalities prior to the conclusio n of the study .Bulls with fewer than 70% norma l sperm cells or with motility scores of poor (moti lity scores = poor, fair, good, very good) were considered classification deferred (CD).

Results and Discussion
Following 12 6 days, ZnHi bulls had greater (P=.058 ) increases in liver Zn concentration than ZnI, but w ere similar to ZnPI treatments 1.2,and 20.6 ppm fo r ZnI,ZnPI,and ZnHi,respectively).No difference s in ADG or change in scrotal circumference were detected (Table 1).ZnPI and ZnHi treatments had a higher (P<.05) percent of normal sperm cells and, consequently , fewer CD bulls than the ZnI treatment .In all fertility measure s we studied, bulls receiving the Zn proteinate/Zn sulfate combination at 40 ppm rated highest, followed by those receiving Zn sulfate at 60 ppm, and lastly by those receiving Zn sulfate at 40 ppm.
These data support the importance of dietary Zn in male fertility.The use of organic Zn in growing bull diets may improve subsequen t fertility measures.
However, inorganic Zn at an increased lev e l also improved fertility.For growing bulls, the NRC-recommende d level of 30 ppm in the diet may be too low.Further studies that investigate higher levels of Zn both in the organic and inorganic forms are merited.

Table 1 . Effect of Zinc Level and Source on Yearling Bull Growth, Sexual Maturation, and Fertility
ZnI = 40 ppm Zn as Zn sulfate; Z n PI = 40 ppm Zn, 2/3 as Zn sulfate and 1/3 as Zn proteinate; and c ZnHi = 60 ppm Zn as Zn sulfate.