Can Infrared Imaging Assess Fertility and Feed Efficiency in Yearling Bulls?

Background

Reproductive success is one of the most important factors affecting the profitability of the cow-calf herd, and bull fertility is a key component for that. Bull fertility is known to be influenced by many factors, such as genetics, nutrition, age, and body composition. Recent research has suggested undesirable associations between improved feed efficiency and fertility traits in young beef bulls. And this is an important issue, since improved feed efficiency is a main objective of beef cattle production systems.

Breeding soundness evaluation (BSE) is an assessment of the reproductive system of bulls that includes the measurement of scrotal circumference (SC) and semen quality. Scrotal circumference is associated with testicle size and sperm production. The uniform temperature distribution of the scrotum is also important to ensure normal sperm production and consequently good semen quality. The temperature patterns of the scrotum can be evaluated using infrared imaging, an effective non-contact technology with proven efficacy for this application. Infrared imaging has also shown potential for assessing feed efficiency, but more studies are needed to define the most appropriate locations to perform this assessment.

The experiment

In order to gain further knowledge about these topics, an experiment was undertaken at the University of Guelph's Elora Beef Research Centre. The objectives of this study were to:

  • Verify the relationship between fertility and feed efficiency;
  • Evaluate the relationship between semen quality and infrared imaging;
  • Further investigate the relationship between infrared imaging and feed efficiency.

A group of 34 yearling bulls were housed in indoor pens equipped with automated feeding stations allowing for measurement of individual feed intake. They were fed a corn based diet on a free choice basis. Animals were weighed and ultrasound assessments (backfat thickness, rib eye area, rump fat thickness and marbling score) were done every 28 days until the end of the 112 day feeding test. The bulls were then slaughtered, at an average of 12.5 months of age. Feed efficiency was evaluated as Residual Feed Intake (RFI), which is defined by animal's actual intake compared with its predicted intake based on its body weight, average daily gain, and middle trial ultrasound traits. Animals which are more feed efficient will have lower RFI values. [RFI = Actual Feed Intake - Predicted Feed Intake]

Girl crouching holding a semen collector under penis of bull.

Figure 1. Semen collection from a yearling bull through electro-ejaculation. Ananda Fontoura is harvesting the ejaculate for further analysis.

At the end of the feeding test, BSE was performed and semen was collected with an electro ejaculator (Figure 1). Infrared pictures were taken at five different body locations (eye, snout, front foot, hind foot and scrotum) (Figure 2), Semen motility, concentration and morphology were analyzed (Figure 2). Ultrasound images of the testicles were also performed (Figure 2) Slaughter and carcass measures were collected at the University of Guelph abattoir. In addition, testis samples were collected at slaughter for histology analysis (Figure 2).

Photos from left to right of A. slide stain of bull semen; B. ultrasound image of bull testicle; C. Infrared image of bull testicle; D. slide of bull sperm

Figure 2. A few examples of techniques for assessing fertility in bulls. A: Testicular histology; B: Ultrasound imaging; C: Infrared thermography; and D: Semen analysis.

What we found

Animals were divided into three feed efficiency groups (high, medium and low-RFI) for statistical analysis. Mean values for the RFI groups are shown in Table 1. There were differences on percentage of normal morphology and tail pathologies for high-RFI and low-RFI groups. However, no differences on SC (P>0.10) were observed across RFI groups, indicating that this assessment must be complemented with the actual microscopic analysis of semen to properly assess bulls' fertility. Less efficient bulls had greater temperature variation on the top portion of the scrotum, which is associated with deleterious effects on semen production. In addition, more feed efficient bulls had higher temperatures at the inner corner of their eyes, a body location never considered before for assessing feed efficiency. No differences among RFI groups for carcass traits were observed (P>0.10). This indicates the appropriateness of the RFI determination employing ultrasound measurements to account for differences on carcass composition. This is important for having the bulls under the same comparison basis (no difference on body composition).

Table 1. Mean values according to the RFI group for each trait*

Traits

High-RFI

(less efficient)

Medium-RFI

(average efficiency)

Low-RFI

(more efficient)

Normal sperm morphology (%) 74.1a,c 69.8c 62.8b,c
Sperm tail pathologies (%) 1.64a,c 3.03c 5.01b,c
Scrotum Top side SD (°C) 1.02a 0.63c 0.81b,c
Eye corner average (°C) 33.33a,c 33.80c 34.20b,c

*a,b,c: values within a row having a different superscript letter differ (P<0.05).

We found a positive correlation (0.48, P<0.01) between normal morphology and RFI, and a negative correlation (-0.48, P<0.05) between tail pathologies and RFI. A positive correlation (0.44, P<0.01) was found between the scrotum top side temperature standard deviation and the percentage of loose head pathologies. Similarly, the bottom side of the scrotum temperature standard deviation is suggested to be associated with fertility, as indicated by the amount of head pathologies (0.32; P<0.10). No associations were observed between infrared images and feed efficiency for the other body locations scanned (snout, foot and scrotum) based on a single infrared scanning. Analysis of the testiclular ultrasound and testis tissue are currently being carried over.

What it means to the Industry

Improved feed efficiency appears to be negatively associated with semen quality in beef bulls. However, infrared imaging could be applied as a complementary technology for the assessment of the bulls' fertility to minimize any negative impact of selecting for feed efficiency. As well, the inner corner of the eye may be a promising body location for assessing feed efficiency based on a single infrared image.

Acknowledgments

Beef Cattle Research Council (BCRC), Agriculture and Agri-Food Canada, Ontario Cattlemen's Association (OCA) and Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs (OMAF and MRA).


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