Effect of recombinant bovine somatotropin on the reproductive efficiency of beef cows subjected to differently timed-artificial insemination protocols

This study aimed to verify the reproductive efficiency of beef cows treated with recombinant bovine somatotropin (rbST). Study 1, Bos indicus cows were distributed (three groups). The control group (CG) was subjected: on day zero (d0), the animals received a CIDR and oestradiol benzoate (EB); on (d8, CIDR was removed, and PGF2α and oestradiol cypionate (EC) were administered; on d10, timed Artificial Insemination (TAI) was performed; on d45, pregnancy diagnosis was made. The rbST on d0 group (bST0G) was subjected to an identical protocol as CG, except for the addition of 250 mg rbST on d0. The rbST on d8 group (bST8G) was subjected to the same protocol as bST0G, except that the rbST was administered on d8 rather. In study 2, the animals followed the same design which was used in Bos taurus cows. The follicular growth rate (FGR) was calculated between d8 and d10. In study 1, pregnancy/artificial insemination (P/AI) did not differ among the treatments. FGR in bST8G was higher than in other groups. In study 2, bST0G showed higher Pregnancy/Artificial Insemination (P/AI) (p < .05) when compared with other groups. bST0G showed a different FGR (p < .0001) than the other groups. In conclusion, rbST (Bos indicus cows) did not increase P/AI, but it did promote follicular growth when administered on d8; the rbST administered on d0 improved P/AI (p < .05) and the FGR in Bos taurus cows.

Transcriptional changes in the peripheral blood leukocytes from Brangus cattle before and after tick challenge with Rhipicephalus australis

Background

Disease emergence and production loss caused by cattle tick infestations have focused attention on genetic selection strategies to breed beef cattle with increased tick resistance. However, the mechanisms behind host responses to tick infestation have not been fully characterised. Hence, this study examined gene expression profiles of peripheral blood leukocytes from tick-naive Brangus steers (Bos taurus x Bos indicus) at 0, 3, and 12 weeks following artificial tick challenge experiments with Rhipicephalus australis larvae. The aim of the study was to investigate the effect of tick infestation on host leukocyte response to explore genes associated with the expression of high and low host resistance to ticks.

Results

Animals with high (HR, n = 5) and low (LR, n = 5) host resistance were identified after repeated tick challenge. A total of 3644 unique differentially expressed genes (FDR < 0.05) were identified in the comparison of tick-exposed (both HR and LR) and tick-naive steers for the 3-week and 12-week infestation period. Enrichment analyses showed genes were involved in leukocyte chemotaxis, coagulation, and inflammatory response. The IL-17 signalling, and cytokine-cytokine interactions pathways appeared to be relevant in protection and immunopathology to tick challenge. Comparison of HR and LR phenotypes at timepoints of weeks 0, 3, and 12 showed there were 69, 8, and 4 differentially expressed genes, respectively. Most of these genes were related to immune, tissue remodelling, and angiogenesis functions, suggesting this is relevant in the development of resistance or susceptibility to tick challenge.

Conclusions

This study showed the effect of tick infestation on Brangus cattle with variable phenotypes of host resistance to R. australis ticks. Steers responded to infestation by expressing leukocyte genes related to chemotaxis, cytokine secretion, and inflammatory response. The altered expression of genes from the bovine MHC complex in highly resistant animals at pre- and post- infestation stages also supports the relevance of this genomic region for disease resilience. Overall, this study offers a resource of leukocyte gene expression data on matched tick-naive and tick-infested steers relevant for the improvement of tick resistance in composite cattle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08686-3.

Coat score. A possible explanation for the zebuine selective sweep located on bovine chromosome 5: 47,670,001-48,100,000 bp

Over 65% of the world's cattle population resides in warm areas where heat stress conditions limit the breed of European taurine cattle. Composite breeds were developed to retain the main traits of both parental breeds. The skin plays a central role in animal response to heat stress. Research on the genetic architecture of skin traits has identified genes and regions related to warm resistance skin features. The aim of this study was to determine whether the indicine proportion accounted for coat type or whether there were genes of large effect segregating in Brangus. Bulls (n = 108) were genotyped using microarrays and their coat score and hair length were evaluated. Indicine-taurine genome-wide composition was estimated and GWAS was performed. Although significant correlations between indicine proportion and traits were not observed, four windows of SNPs on BTA4 and BTA5 explained more than 2% of the trait variance. The GWAS for coat score in summer showed the main peak on BTA5:46,941,446-48,030,219 bp, accounting for 4.65% of the variance. Our results suggest that the variation in coat score and undercoat hair length in Argentinian Brangus bulls is associated with the presence of some particular gene variants, rather than with the whole indicine genetic content.

Vaginal bacterial community composition and concentrations of estradiol at the time of artificial insemination in Brangus heifers

The knowledge surrounding the bovine vaginal microbiota and its implications on fertility and reproductive traits remains incomplete. The objective of the current study was to characterize the bovine vaginal bacterial community and estradiol concentrations at the time of artificial insemination (AI). Brangus heifers (n = 78) underwent a 7-d Co-Synch + controlled internal drug release estrus synchronization protocol. At AI, a double-guarded uterine culture swab was used to sample the anterior vaginal tract. Immediately after swabbing the vaginal tract, blood samples were collected by coccygeal venipuncture to determine concentrations of estradiol. Heifers were retrospectively classified as pregnant (n = 29) vs. nonpregnant (n = 49) between 41 and 57 d post-AI. Additionally, heifers were classified into low (1.1 to 2.5 pg/mL; n = 21), medium (2.6 to 6.7 pg/mL; n = 30), and high (7.2 to 17.6 pg/mL; n = 27) concentration of estradiol. The vaginal bacterial community composition was determined through sequencing of the V4 region from the 16S rRNA gene using the Illumina Miseq platform. Alpha diversity was compared via ANOVA and beta diversity was compared via PERMANOVA. There were no differences in the Shannon diversity index (alpha diversity; P = 0.336) or Bray-Curtis dissimilarity (beta diversity; P = 0.744) of pregnant vs. nonpregnant heifers. Overall, bacterial community composition in heifers with high, medium, or low concentrations of estradiol did not differ (P = 0.512). While no overall compositional differences were observed, species-level differences were present within pregnancy status and estradiol concentration groups. The implications of these species-level differences are unknown, but these differences could alter the vaginal environment thereby influencing fertility and vaginal health. Therefore, species-level changes could provide better insight rather than overall microbial composition in relation to an animal's reproductive health.

Evidence of positive selection towards Zebuine haplotypes in the BoLA region of Brangus cattle

The Brangus breed was developed to combine the superior characteristics of both of its founder breeds, Angus and Brahman. It combines the high adaptability to tropical and subtropical environments, disease resistance, and overall hardiness of Zebu cattle with the reproductive potential and carcass quality of Angus. It is known that the major histocompatibility complex (MHC, also known as bovine leucocyte antigen: BoLA), located on chromosome 23, encodes several genes involved in the adaptive immune response and may be responsible for adaptation to harsh environments. The objective of this work was to evaluate whether the local breed ancestry percentages in the BoLA locus of a Brangus population diverged from the estimated genome-wide proportions and to identify signatures of positive selection in this genomic region. For this, 167 animals (100 Brangus, 45 Angus and 22 Brahman) were genotyped using a high-density single nucleotide polymorphism array. The local ancestry analysis showed that more than half of the haplotypes (55.0%) shared a Brahman origin. This value was significantly different from the global genome-wide proportion estimated by cluster analysis (34.7% Brahman), and the proportion expected by pedigree (37.5% Brahman). The analysis of selection signatures by genetic differentiation (F st ) and extended haplotype homozygosity-based methods (iHS and Rsb) revealed 10 and seven candidate regions, respectively. The analysis of the genes located within these candidate regions showed mainly genes involved in immune response-related pathway, while other genes and pathways were also observed (cell surface signalling pathways, membrane proteins and ion-binding proteins). Our results suggest that the BoLA region of Brangus cattle may have been enriched with Brahman haplotypes as a consequence of selection processes to promote adaptation to subtropical environments.