Seasonal variation in bull semen quality demonstrates there are heat-sensitive and heat-tolerant bulls

Investigating the impact of paternal age, paternal heat stress, and estimation of non-genetic paternal variance on dairy cow phenotype

BACKGROUND

Linear models that are commonly used to predict breeding values in livestock species consider paternal influence solely as a genetic effect. However, emerging evidence in several species suggests the potential effect of non-genetic semen-mediated paternal effects on offspring phenotype. This study contributes to such research by analyzing the extent of non-genetic paternal effects on the performance of Holstein, Montbéliarde, and Normande dairy cows. Insemination data, including semen Batch Identifier (BI, a combination of bull identification and collection date), was associated with various traits measured in cows born from the insemination. These traits encompassed stature, milk production (milk, fat, and protein yields), udder health (somatic cell score and clinical mastitis), and female fertility (conception rates of heifers and cows). We estimated (1) the effects of age at collection and heat stress during spermatogenesis, and (2) the variance components associated with BI or Weekly aggregated BI (WBI).

RESULTS

Overall, the non-genetic paternal effect estimates were small and of limited biological importance. However, while heat stress during spermatogenesis did not show significant associations with any of the traits studied in daughters, we observed significant effects of bull age at semen collection on the udder health of daughters. Indeed, cows born from bulls collected after 1500 days of age had higher somatic cell scores compared to those born from bulls collected at a younger age (less than 400 days old) in both Holstein and Normande breeds (+ 3% and + 5% of the phenotypic mean, respectively). In addition, across all breeds and traits analyzed, the estimates of non-genetic paternal variance were consistently low, representing on average 0.13% and 0.09% of the phenotypic variance for BI and WBI, respectively (ranging from 0 to 0.7%). These estimates did not significantly differ from zero, except for milk production traits (milk, fat, and protein yields) in the Holstein breed and protein yield in the Montbéliarde breed when WBI was considered.

CONCLUSIONS

Our findings indicate that non-genetic paternal information transmitted through semen does not substantially influence the offspring phenotype in dairy cattle breeds for routinely measured traits. This lack of substantial impact may be attributed to limited transmission or minimal exposure of elite bulls to adverse conditions.

Morphometric features, seminal profile and diluters effect on post-thaw semen quality of Munshiganj cattle in Bangladesh

The study investigates morphometric features, seminal profile and post-thaw semen quality of Munshiganj cattle. Morphometric features were measured using measuring tape from 20 Munshiganj cattle while coat color was measured by observing in naked eye. Fresh and post thaw semen quality parameters were analyzed using Computer Assisted semen analyzer (CASA). Coat color of Munshiganj male cattle were creamy white to dull pinkish and female were white to creamy. The mean body weight, body length, hearth girth, height at wither, head length, head width, ear length, ear width, fore leg length, hind leg length, tail length, tail doc circumference, horn length, horn diameter and mouth circumference were 362.80 kg, 137.31 cm, 160.66 cm, 135.21 cm, 50.97 cm, 20.58 cm, 19.75 cm, 9.88 cm, 73.02 cm, 74.84 cm, 106.10 cm, 20.75 cm, 13.60 cm, 16.12 cm and 43.00 cm, respectively. There was significant difference (p < 0.05) between male and female in terms of body weight (418.00 vs 307.60 kg), heart girth (173.74 vs 147.57 cm), head width (22.50 vs 18.67 cm), horn diameter (18.58 vs 13.66 cm) and mouth circumference (46.60 vs 39.40 cm). Average scrotal length was 16.76 cm while scrotal circumference was 32.70 cm. Age had significant effect (p < 0.05) on morphometric characteristics of Munshiganj male and female cattle. On the other hand, season had no significant effect on semen quality. Mean semen volume, sperm concentration, total motile, progressive, static, slow and live spermatozoa were 5.83 ± 0.88 ml, 1510.27 ± 844.07 million/ml, 91.9 ± 2.17 %, 63.80 ± 12.53 %, 8.10 ± 2.17 %, 0.10 ± 0.10 %, 91.38 ± 0.25 %, respectively. On the other hand, sperm head length and width, sperm tail length of Munshiganj cattle were 10.39 ± 0.16 μm, 4.26 ± 0.07 μm, 21.5 ± 0.52 μm, respectively. Individual breeding bull had a significant (p < 0.05) effect on post-thawed motile sperm percentage. Four different diluters (Triladyl, Steridyl, Tris-egg yolk-Citrate and Andromed) were used to compare the effects of diluter on post-thaw semen quality of Munshiganj cattle and found that diluter had no significant effect (p > 0.05) on post thaw semen quality except slow motility and proximal droplet percentages. Munshiganj cattle had a distinctive phenotypic feature with standard quality semen and had no effect of egg yolk free and egg yolk based diluters on post thaw semen quality.

Review: The role of male reproductive tract secretions in ruminant fertility

Male fertility largely depends on the ability to produce sperm that can transmit the paternal information onto the next generation. However, the factors that are critical for sperm function and the subsequent development of healthy offspring are still not completely understood in ruminants. Importantly, sperm function is not completely encoded by germ cell DNA, but rather, depends on sequential acquisition, loss, and modification of elements through interaction with secretions from the testes, epididymides, and accessory glands (collectively termed seminal plasma). In addition, these secretions can play a role in the inheritance of paternal environmental effects by progeny. This is likely achieved directly, by the regulation of sperm epigenetic effectors, and indirectly, by altering the female environment in which the individual develops. This review will provide an overview of the different organs that contribute to seminal plasma in ruminants, and summarise how their secretions shape sperm function and modulate the female reproductive tract. Finally, some consideration will be given to the potential of paternal factors to affect embryo development and offspring health in ruminants.

Review: Genetic mutations affecting bull fertility

Cattle are a well-suited "model organism" to study the genetic underpinnings of variation in male reproductive performance. The adoption of artificial insemination and genomic prediction in many cattle breeds provide access to microarray-derived genotypes and repeated measurements for semen quality and insemination success in several thousand bulls. Similar-sized mapping cohorts with phenotypes for male fertility are not available for most other species precluding powerful association testing. The repeated measurements of the artificial insemination bulls' semen quality enable the differentiation between transient and biologically relevant trait fluctuations, and thus, are an ideal source of phenotypes for variance components estimation and genome-wide association testing. Genome-wide case-control association testing involving bulls with either aberrant sperm quality or low insemination success revealed several causal recessive loss-of-function alleles underpinning monogenic reproductive disorders. These variants are routinely monitored with customised genotyping arrays in the male selection candidates to avoid the use of subfertile or infertile bulls for artificial insemination and natural service. Genome-wide association studies with quantitative measurements of semen quality and insemination success revealed quantitative trait loci for male fertility, but the underlying causal variants remain largely unknown. Moreover, these loci explain only a small part of the heritability of male fertility. Integrating genome-wide association studies with gene expression and other omics data from male reproductive tissues is required for the fine-mapping of candidate causal variants underlying variation in male reproductive performance in cattle.