Advanced bull test evaluation: bridging superior feed efficiency with optimal reproductive development and semen quality


Testing bulls for productive performance provides crucial information to be used to select superior breeding stock. Traditionally, commercial bull test evaluations focused on average daily gain and scrotum circumference. A more comprehensive performance test could also include measurement of feed intake, ultrasound for body composition and an in-depth evaluation of their reproductive capacity. Productive performance traits are used to determine feed efficiency (i.e. residual feed intake, RFI), which is a tool to improve profitability of the beef industry. Additionally, appropriate reproductive evaluation is important for a successful cow-calf sector. Our studies i,ii suggest that measures of fertility in young bulls were negatively related with improved feed efficiency.

Consequently, there is a need to identify bulls with both improved feed efficiency and desirable reproductive capacity. To achieve this goal, a series of complementary assessments of feed efficiency and reproductive capacity are being tested at the Elora Beef Research Center (University of Guelph), including:

  • testis ultrasound images
  • infrared imaging of the scrotum
  • blood plasma analysis

These assessments are aimed to more precisely assess sexual development and also evaluate the viability of decreasing the duration of the productive performance evaluation through the indirect assessments of feed efficiency.

Testicular Ultrasound

Testicular ultrasound can be used to assess testicular development and scrotum skin thickness. As a bull matures, the cellular content of the seminiferous tubules (area of sperm formation) increases, and the fluid content decreases. As a result, the pixel intensity of the testes increases, indicating that the bull is approaching sexual maturity. Our results are indicating that bulls with improved feed efficiency have lower testes pixel intensity (delayed sexual maturity) than bulls with lower feed efficiencyii (Figure 1). Testicular ultrasound can also be used to measure scrotal skin and fat thickness, which are associated with thermoregulation of the testes, influencing semen quality.

Diagram showing bull testes ultrasound and image results as well as semen analysis

Figure 1. Testes ultrasound and semen quality evaluation. A: Ultrasound probe placed on the testis for scanning. B: High-pixel intensity testis ultrasound image. C: Low-pixel intensity testis ultrasound image. D: Semen motility corresponding to sexual maturity.

Infrared Imaging of the Scrotum

Uniform temperature gradation of the scrotum is crucial to ensure good semen quality. Temperature patterns of the scrotum are evaluated using infrared imaging that allows visualization of the scrotum thermal profile. Abnormal scrotal temperature patterns are associated with reduced sperm quality (Figure 2). Less feed efficient bulls had larger temperature variation at the base of the scrotum, suggesting a better capacity for thermoregulation and subsequently reduced sperm abnormalities.

Infrared images of bull testes showing heat distribution

Figure 2. Infrared imaging patterns of the scrotum. A: Scrotum with normal patterns as noted by the gradual (layered) cooling observed from the top towards the base of the scrotum. B: Scrotum with abnormal temperature patterns as noted by the random temperature distribution. The thermographically normal scrotum has lower abundance of sperm abnormalities.

Semen Evaluation

Semen is collected using electro-ejaculation and evaluated for sperm motility patterns (total motility and progressive motility) using computer-assisted sperm analysis. Total motility is defined as sperm that display any type of movement and progressive motility refers to sperm that swim forward in a straight line. Semen evaluation also includes assessment of sperm morphology abnormalities, Figure 3.

Four black and white photos of sperm with arrows pointing to sperm abnormalities

Figure 3. Sperm abnormalities associated with decreased fertility. A: Normal sperm B: Detached head. C: Midpiece defect. D: e. Proximal droplet, f. Pyriform head.

Blood Plasma Analysis

Blood levels of sexual hormones change across the sexual development in bulls. Immature bulls have high levels of gonadotropin releasing hormone (GnRH) and Anti-Müllerian Hormone (AMH), and low levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone. As the bull matures, AMH production decreases and LH and FSH levels increase, stimulating testosterone production by the testes. In addition, triiodothyronine (T3) and osteocalcin are involved in the male reproductive function. T3 is involved in testosterone production by the testes.

Our preliminary results indicate that bulls with improved feed efficiency had lower T3 levels, suggesting an association between T3, fertility, and feed efficiency in bulls. Osteocalcin is a bone-derived hormone found to regulate energy metabolism and male fertility in mice. Osteocalcin stimulates production of testosterone by the testes. Apparently, T3 favors osteocalcin production, suggesting that osteocalcin may act as an indicator of both reproductive function and feed efficiency in bulls (Figure 4). This remains to be confirmed in beef cattle.

Blood analytes can also be useful for indirectly assessing feed efficiency, which could facilitate the assessment of feed efficiency in situations where the actual measurement of feed efficiency is not possible. We observed that levels of specific blood analytes differ in cattle diverging in feed efficiency, such as higher aspartate-aminotransferase and lower carbon dioxide in cattle with improved feed efficiency.

Sexual development and maturity of a bull

Figure 4. Sexual development and maturity of a bull. Suggested mechanisms of action of key hormones on testosterone production. FSH: follicle stimulating hormone, GnRH: gonadotropin releasing hormone, LH: luteinizing hormone, T3: triiodothyronine and TSH: thyroid secreting hormone.

Text Explanation: Sexual development and maturity of a bull


This study will provide information to support the implementation of complementary assessments to the breeding soundness evaluation of bulls, and indirect assessment of feed efficiency. This will contribute to the ultimate goal of ensuring the competiveness of the Ontario beef industry.

Next Steps

A future project at the Elora Beef Research Center will use bulls sourced from the Elora herd, the New Liskeard Agricultural Research Station and Ontario beef producers to expand on this work. Stay tuned!


The financial and in-kind support of Ontario Ministry of Agriculture and Rural Affairs, Beef Farmers of Ontario, Agriculture and Agri-Food Canada, Beef Cattle Research Council, Alberta Beef Producers, University of Guelph and Beef Improvement Opportunities are greatly appreciated.


i Awda, B.J., Miller, S.P., Montanholi, Y.M., Vander Voort, G., Caldwell, T., Buhr, M.M.Swanson, K.C. 2013. The relationship between feed efficiency traits and fertility in young beef bulls. Canadian Journal of Animal Science. 185-192.

iiFontoura, A.B.P., Montanholi, Y.R., Diel de Amorim, M., Foster, R.A., Chenier, T., Miller, S.P. (2015). Association between feed efficiency, sexual maturity and fertility related measures in young beef bulls. Animal. (in review).

iiiGonano, C., Montanholi, Y., Schenkel, F., Smith, B., Cant, J., Miller, S. 2014. The relationship between feed efficiency and the circadian profile of blood plasma analytes measured in beef heifers at different physiological stages. Animal. 1-15.

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