Case study: The effects of dietary zinc concentration and sorce on yearling bull growth and fertility

Professional Animal Scientist, Sep 2002 by Arthington, J D, Corah, L R, Hill, D A

Abstract

Yearling Angus bulls (n = 325) were allotted by BW into six pens of equal size. One of three dietary treatments consisting of 1) dietary Zn at 40 ppm, all supplied by zinc sulfate (ZnS); 2) dietary Zn at 40 ppm with 33.3% supplied by zinc proteinate and 66.6% supplied by ZnS (ZnPS); or 3) dietary Zn at 60 ppm, all supplied by ZnS (ZnHi) was delivered to two pen replicates. Initial and final liver biopsies were collected and analyzed for Zn concentration. Scrotal circumference and BW measures were collected at the start and conclusion of the trial. Semen from bulls intended for public sale (n = 167) was collected and evaluated for motility and morphological abnormalities. Bulls with percent normal sperm cell counts

ppm for ZnS, ZnPS, and Zn Hi, respectively). No differences in scrotal circumference or ADG were detected. Bulls receiving ZnPS had higher (P

(Key Words: Zinc, Bull, Fertility.)

Introduction

The important role of Zn in male fertility has been recognized for many years (9). Research in young rams has shown that Zn deficiency results in a lowered capacity to produce testosterone, resulting in impaired testicular development (12). The influence of Zn deficiency on reproductive failure in man has also been reported (1). In some cases, human males diagnosed with fertility complications have responded favorably to Zn supplementation (6, 21). One of the most commonly reported links between dietary Zn and male fertility is the association between Zn and the functionality of spermatozoa (2, 3, 22). Zinc is an essential component of many enzymes; especially important to male fertility are the Zn-dependent DNAand RNA-polymerases (9). Therefore, it is not surprising that deficiencies in dietary Zn often manifest themselves by retarding the rate and functionality of physiological systems, which are controlled by Zn-dependent enzyme systems.

The use of organic minerals in livestock nutrition has gained considerable interest over the past decade. The term "organic mineral" is commonly used to describe generically any of several forms of trace minerals available in the feed industry; some of these include chelates, proteinates, and complexes. Some studies have suggested that organic Zn in ruminant diets may be metabolized differently upon absorption compared with inorganic Zn (20). Considering the potential link between improved bull reproductive development and Zn, the following study investigates the effect of Zn concentration and source in growing bull diets on subsequent measures of fertility. Measures of growth, sexual maturation, and fertility were compared when bulls were supplemented with either inorganic Zn (zinc sulfate) at 40 and 60 ppm of the total diet or a combination of organic (proteinated) Zn and zinc sulfate at 40 ppm.

Materials and Methods

The animals utilized in these experiments were cared for by acceptable practices as outlined in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (8).

Yearling Angus bulls (n = 325) were stratified by BW and randomly allotted into six pens of similar size. All bulls on test originated from a common ranch and were of a similar genetic background. One of three treatments (two pens per treatment) were formulated to provide targeted concentrations of dietary Zn: 1) dietary Zn concentration of 40 ppm, all supplied by zinc sulfate (ZnS); 2) dietary Zn concentration of 40 ppm with 33.3% supplied by zinc proteinate and 66.6% supplied by ZnS (ZnPS), or 3) dietary Zn at a level of 60 ppm, all supplied by zinc sulfate (ZnHi). The ingredient and nutrient composition of the basal diet is presented in Tables 1 and 2.

Initial and final liver biopsies (n = 10 per pen) were collected using a standard technique (4) and analyzed for Zn concentration via inductively coupled plasma analysis (Jobin Yvon 24 Sequential Computer; Peterson Laboratories, Hutchinson, KS). Briefly, liver samples were dried at 100 deg C for 30 min. Samples were then digested in 1 mL 70% (vol/vol) nitric acid for 5 min at 100 deg C. Cooled samples were then diluted with 7 mL deionized water and analyzed for Zn concentration. Individual bull BW and scrotal measures were also taken at the start and conclusion of the trial. To control between-person variation, the same person collected scrotal measures at each time period.

A breeding soundness examination was conducted on all bulls intended for public sale (n = 167). Semen was collected by electroejaculation and evaluated for motility and morphological abnormalities as described by the Society of Theriogenology (10). Bulls with percent normal sperm cell counts of

Analysis of variance was performed using the GLM procedures of SAS (19) in a completely randomized model. Treatments were delivered to pens; therefore, pen was used as the experimental unit. Comparison of treatment means was performed using least significant differences. Effect of treatment on the frequency of bulls categorized as CD was compared using the FREQ procedures of SAS (19). Differences in percent CD were compared using Fisher's Exact Test.