Impacts of dietary zinc concentrations on lamb feedlot performance1

© The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Transl. Anim. Sci. 2020.4:S6–S10 doi: 10.1093/tas/txaa087


INTRODUCTION
Zinc is one of the most abundant minerals in the body with functions related to immune function and growth performance (Suttle, 2010). However, previous research regarding optimal dietary Zn concentrations has provided varied results observed with average daily gain (ADG), feed efficiency, feed intake, and body weight (BW; Phillips, 1990;Berrie et al., 1995;Fadayifar et al., 2012). Additionally, the effect of a combination of Zn sources (Zn amino acid complex w/ ZnSO 4 ) fed at dietary concentrations that meet or exceed NRC requirements in fine-wool feeder lambs has been evaluated to a lesser extent.
Coccidiosis results from a parasitic infection by Eimeria, and adverse impacts are mitigated by use of anticoccidial drugs (USDA-APHIS, 2001). During internal development, Eimeria spp. multiply inside intestinal cells of lambs. Many host cells are destroyed by Eimeria parasites before an oocyst is produced and excreted within the feces, leading to marked intestinal damage (Bangoura and Bardsley, 2020). As a result, small intestine function can be impaired, which affects nutrient utilization and ultimately lamb feedlot performance (Chartier and Paraud, 2012).
Few studies have evaluated the impact of dietary concentration of trace mineral supplementation on coccidia infection in lamb feedlot settings. Provision of trace minerals have decreased intestinal parasite burden in Se supplemented sheep (Hooper et al., 2014) and improved intestinal barrier function in broilers (Zhang et al., 2012) and Crohn's disease patients supplemented with Zn (Sturniolo et al., 2001), illustrating the role of trace minerals to maintain intestinal health and function. Therefore, strategic Zn supplementation may reduce Eimeria oocyst excretion, lessen intestinal damage, and improve overall performance in lambs and optimal levels may differ from recommendations (NRC, 2007). Thus, optimizing Zn concentrations in feedlot diets may be one means of improving lamb performance while simultaneously providing better protection to coccidia infection. The objectives of this study were to identify the impacts of Zn concentrations in a lamb finishing diet on performance and fecal oocyst load. We hypothesized that increasing dietary Zn concentrations would improve lamb feedlot performance and reduce fecal oocyst counts.

University of Wyoming (UW) Institutional
Animal Care and Use Committee approved all experimental protocols in this project (#20190813WS00386-01).
Translate basic science to industry innovation S7 Zinc supplementation effects on feeder lambs

Animal Selection and Management
Commercial Rambouillet lambs (n = 33; aged 4 mo) of the same sire were selected from the UW flock and stratified by sex and weight into three treatment groups of 11 lambs (43.9 ± 1.0 kg). Lambs were fed a diet fortified with an 80:20 combination of a ZnSO 4 and Zn amino acid complex (ZnAA; Zinpro Corp.; Eden Prairie, MN, United States) at three different dietary concentrations (treatment, TRT) which met or exceeded current recommendations. Treatments (Table 1) consisted of a corn and soybean hull-based diet with Zn fortified pellet fed at: 1) 1× NRC requirements (450 mg Zn/ kg grower pellet; 1NRC), 2) 2× NRC requirements (900 mg Zn/kg grower pellet; 2NRC), and 3) 3× NRC requirements (1,350 mg Zn/kg grower pellet; 3NRC). Each of these values fell below the NRC (2007) maximum tolerable level for sheep when fed at 10% of the diet.

Animal Performance
Each group was placed into a dry-lot pen (12 × 5 m) equipped with a GrowSafe feeder (GrowSafe Systems Ltd, Airdrie, AB, Canada) to collect individual feed intake and allowed to acclimate for 10 d. Residual feed intake (RFI) was calculated as the difference between actual and expected feed intake, where actual feed intake was regressed on ADG and metabolic midweight to estimate expected feed intake (Cammack et al., 2005). Start and end BW were measured as a 2-d average on d 0 and 63, respectively, and BW were also recorded on d 14, 28, 42, and 56.

Fecal Collection and Analysis
Fecal samples were collected on d 0, 14, 28, 42, and 63 following the protocol described by Bauman et al. (2016) and analyzed for parasite stages. Quantification of Eimeria spp. oocysts was performed using a modified quantitative McMaster method (Gordon and Whitlock, 1939), and differentiated based on available species descriptions (Vercruysse, 1982;Rommel, 2000;de Macedo et al., 2019).

Statistical Analyses
The GLIMMIX and analysis of variance procedures of SAS (V. 9.4; SAS Inst. Inc., Cary, NC) were used to analyze feedlot performance traits. The main effects of gain:feed (G:F), ADG, and dry matter intake (DMI) were initially analyzed within TRT, period (d 0 to 11, 11 to 42, and 42 to 63), and TRT × period. Start and end BW and RFI were analyzed within TRT over the entire 63 d trial. Total fecal oocyst counts and counts of major pathogenic Eimeria species (E. ahsata, E. bakuensis, E. crandallis, and E. ovinoidalis) were log 10 transformed then analyzed within TRT, day, and TRT × day. Interactions were removed if no statistical tendencies were detected (P > 0.10).

Feedlot Performance
There was a TRT × period interaction for DMI (P < 0.001), but no interaction was detected for ADG or G:F (P ≥ 0.15; Table 2). A period effect was observed for ADG and G:F (P ≤ 0.04). Lamb ADG and G:F increased by 17% and 29%, respectively, between d 11 to 42 and 42 to 63 across all TRT groups (P < 0.05). Start and end BW, ADG, and RFI did not differ by TRT (P > 0.46). However, DMI was 12% and 9% greater (P = 0.02) for 2NRC and 3NRC compared with 1NRC, respectively.

Fecal Oocyst Counts
A statistical tendency for the TRT × day interaction ( Fig. 1) was evident for total fecal oocyst count, E. bakuensis, and E. ovinoidalis (P ≤ 0.08). All TRT groups had similar d 0 transformed total fecal oocyst counts, indicating similar initial Eimeria load. On d 14 and 28, 1NRC had lower Trait least-squares means within an effect are different (P < 0.05).

Lamb Growth
Investigations into the benefits of feeding Zn beyond NRC requirements have shown divergent results (Phillips, 1990;Berrie et al., 1995;Page et al., 2020). Still factorial equations to estimate Zn requirements are dependent on level of production (NRC, 2007; BW, ADG, and wool production) and have not been exhaustively evaluated in U.S. finewool sheep when fed an 80:20 combination of a ZnSO 4 and ZnAA complex. Although DMI was increased with higher Zn inclusion levels, ADG and G:F were unaffected. Still, Page et al. (2020) did not detect any differences in feed intake or efficiency in developing fine-wool rams. These contrasting results may in part be attributed to developing rams fed an alfalfa based diet supplemented with a ZnAA complex or ZnSO 4 (Page et al., 2020), whereas in the present study feedlot lambs were on a high concentrate ration and supplemented with a combination of the same ZnSO 4 and ZnAA complex.

Coccidiosis Incidence and Severity
Few researchers have investigated the impact of dietary Zn concentrations on Eimeria spp. In broilers, Bun et al. (2011) reported no effects of dietary organic Zn levels on ADG or DMI. However, effects of organic and inorganic Zn sources on Eimeria infections in goat kids have shown reduced oocyst shedding in unsupplemented and Zn oxide supplemented kids compared with Zn chelate and Zn lactate supplemented kids (Strnadová et al., 2011). Of 156 tested fecal samples in the present study, only 4.5% had total fecal oocyst counts less than 100 oocyst per gram (opg) and 11.5% of samples contained more than 10,000 opg, suggesting that coccidiosis spreads easily in an infected population of lambs and can pose a persistent problem. While there was a TRT × day interaction of transformed total fecal oocyst count, E. bakuensis, and E. ovinoidalis, the impacts of Zn supplementation remain unclear. Even if not all observed reductions of Eimeria spp. oocyst excretion were statistically supported, the trend of reduced oocyst counts was obvious for 1NRC compared with 2NRC or 3NRC. Since all Eimeria spp. oocysts are products of intracellular parasite multiplication, a decrease in oocyst counts likely reduces intestinal damage and is beneficial for the lamb. Stronger effects may be observed in a setting with occurrence of more severe coccidiosis, and future experimental infection trials may help elucidate the effect of Zn concentrations on Eimeria spp.

IMPLICATIONS
Zinc has many relationships with immune function and animal performance, yet few studies have investigated the impact of dietary Zn concentrations on feedlot lamb performance. The present study has helped fill this void of knowledge and identified current NRC recommendations appear adequate when assessing ADG, G:F, RFI, and BW with DMI being affected. This study was novel to previous studies looking at different dietary Zn concentrations and sources because an 80:20 ZnSO 4 :ZnAA complex was supplemented to fine-wool feeder lambs. Specifically, our data show that DMI was affected by Zn concentration, however no other feedlot performance trait was impacted. Additionally, log 10 transformed counts of E. bakuensis and E. crandallis were lower for 1NRC compared with 2NRC and 3NRC lambs. Therefore, these results indicate some benefits of Zn supplementation at 1×, 2×, and 3× NRC recommendations to feedlot lambs, albeit increasing dietary Zn concentrations did not improve many performance measures. Results pertaining to Eimeria infections should be interpreted judiciously since they were obtained from a single study in a naturally infected, housed-feeding scenario. Still, future efforts to quantify Eimeria spp. response to dietary zinc levels warrant further investigations.
Conflict of interest statement. Mention of trade names and commercial products was solely stated to provide specific information and does not imply recommendation or endorsement. The authors confirm that the research was conducted in the absence of commercial or financial relationships that could have influenced the outcome of the study.