Comparison of ruminal microbiota, IL-1β gene variation, and tick incidence between Holstein × Gyr and Holstein heifers in grazing system

Abstract

Introduction: The variation in bacterial communities among breeds has been previously reported and may be one of the reasons why Holstein × Gyr dairy heifers have better development in grazing systems in tropical conditions. This study aimed to explore the ruminal microbiota composition, the IL-1β gene variation, tick incidence, and blood parameters of Holstein × Gyr (½ Holstein × ½ Gyr) and Holstein heifers grazing intensely managed Guinea grass (Panicum maximum Jacq. cv. Mombaça).

Methods: Sixteen heifers were divided into two groups consisting of 8 Holstein × Gyr and 8 Holstein heifers. The experimental period was comprised of 3 periods of 21 days. Ruminal samples were taken via the stomach tube technique. The sequencing of the V4 hypervariable region of the 16S rRNA gene was performed using the Illumina MiSeq platform. Counting and collection of ticks were conducted each 21 days. Blood and skeletal muscle tissue biopsies were performed at the end of the experiment.

Results: Firmicutes were the most abundant phyla present in both breed rumen samples and Bacteroidota showed differences in relative abundance between breed groups, with greater values for Holstein heifers (p < 0.05 with FDR correction). The 10 most abundant unique OTUs identified in each breed included several OTUs of the genus Prevotella. Holstein heifers had a greater tick count and weight (9.8 ticks/animal and 1.6 g/animal, respectively) than Holstein × Gyr (2.56 ticks/animal and 0.4 g/animal, respectively). We found nucleotide substitutions in the IL-1β gene that might be related to adaptation and resistance phenotypes to tick infestation in Holstein × Gyr heifers. Blood concentrations of urea, albumin, insulin-like growth factor 1, triiodothyronine, and thyroxine were greater in Holstein × Gyr than in Holstein heifers.

Conclusion: Adaptations in Holstein × Gyr heifers such as ruminal microbiota, tick resistance, nucleotide substitutions in IL-1β gene, and hormone concentration suggest a better energy metabolism and thermoregulation resulting in better performance in tropical grazing systems.

Keywords: Guinea grass; crossbred heifer; heat stress; pasture; rumen microbiology.

Figure 1

Beta diversity was evaluated using two distance matrices (weighted and unweighted UniFrac) and Principal Coordinate Analysis—PcoA as the ordination method. Permanova F-statistic and p-values were calculated and are shown in the PCoA plot. Holstein cattle is represented by red dots and Holstein × Gyr as green dots. Please note that some samples overlap in the plot.

Figure 2

Bacterial community composition at the phylum level (relative abundances > 1.0%) in ruminal samples of Holstein × Gyr and Holstein heifers. ^*Different with p < 0.05 with FDR correction using two-sided White’s non-parametric t-test.

Figure 3

Venn diagram representing the number of OTUs that were shared between the Holstein × Gyr and Holstein breeds and those that appeared exclusively in each group.

Figure 4

Heatmap of OTUs shared between Holstein × Gyr and Holstein with relative abundance above 0.5%.

Figure 5

The plot was generated using the online LEfSe project. The length of the bar column represents the LDA score. The figure shows the microbial taxa with significant differences between the Holsteins × Gyr (green) and Holstein (red; LDA score > 2).

Figure 6

(A) Average tick count (number/animals) per breed and average per period of Holstein × Gyr and Holstein heifers in pasture of Guinea grass (Panicum maximum Jacq. cv. Mombaça). (B) Average tick weight (g/animals) per breed and average per period of Holstein × Gyr and Holstein heifers in pasture of Guinea grass (Panicum maximum Jacq. cv. Mombaça).