experienced by the group. When a bull fails to meet the minimum morphology standards for a satisfactory classification due at least in part to a high proportion of DMRs it is appropriate to reevaluate the bull in as little as two weeks. Not only do DMRs appear fast following an insult, but also if all goes well the numbers of affected sperm will decline rapidly.
Figure 9.16 Distal midpiece reflexes with and without droplet material and detached heads on an eosin‐nigrosin stained smear.
Figure 9.17 Three images all showing distal midpiece reflexes.
Mitochondrial Sheath Defects
Surrounding the inner core of the midpiece the mitochondrial sheath is laid down during spermatogenesis, beginning at the attachment of the midpiece to the sperm head all the way to completion at the annulus on the very distal end of the midpiece. Any disruptions in mitochondrial sheath development can result in one or a few tiny gaps appearing along the length of the midpiece (Figure 9.18). Incomplete development of the sheath at the annulus causes the appearance of larger gaps and a propensity for the tail to break at this point. Mitochondrial sheath defects are usually seen in low numbers, but there have been a few bulls that produced a high percentage of sperm with sheath gaps. Surprisingly, these bulls had normal fertility [2]. A conclusive link between the feeding of gossypol in cottonseed meal to bulls and the occurrence of high numbers of mitochondrial sheath defects has been shown [2, 17]. Despite reports of bulls producing high numbers of affected sperm with apparently normal fertility, mitochondrial sheath defects are considered abnormal; therefore any bulls producing high numbers of these defects should be flagged for further examination, including an investigation of possible causes. The more common occurrence is that of a few mitochondrial sheath gaps being noted in spermiograms – usually in the presence of other sperm defects.
Figure 9.18 Mitochondrial sheath defect.
Accessory Tails
Accessory tails are an uncommon occurrence affecting a small number to as much as 35% of a spermiogram. Closely related to the abaxial tail aberration, accessory tails, multiple tails, and abaxial tails are often present in the same spermiogram [2]. Differing from abaxial tails, however, accessory tails have been shown to have a negative effect on fertility. Accessory tails may be partially obscured by droplet material; therefore the proportion of affected sperm may be underestimated. This defect has been recorded in a number of breeds of cattle and is believed to have a heritable basis [27].
Stump Tail
The stump tail defect (Figure 9.19) is unmistakable, with usually more than 50% of the spermiogram affected. Other sperm will have broken midpieces and midpiece defects. Cytoplasmic droplet material often obscures the stump tail from view. This is believed to be a heritable defect reported in Charolais, Hereford, and other breeds of cattle [2].
Figure 9.19 Stump tail defect.
Dag Defect
The Dag defect is a rare heritable midpiece defect that carries the name of a Jersey bull who produced it in large numbers along with his full brother. The unusual and distinctive name of this defect is often highlighted in the minds of students, leading to a tendency to refer to DMRs as the Dag defect. Differing from the DMR, unique features of the Dag defect include a swollen, disrupted mitochondrial sheath and fractures of the midpiece (Figure 9.20). Oftentimes, midpiece fractures result in coiling of the tail very similar to the DMR. By studying the fractures closely, broken axonemal fibers that can be likened to broken structural cables can be seen. In addition to the Jersey breed, the Dag defect has been reported in the Hereford, Swedish Red and White, and Galloway breeds [2]. Sperm showing the true Dag defect are usually produced in very high numbers. Although very uncommon, a few sperm displaying mitochondrial disruption identical to the Dag defect may be noted in spermiograms, but in the presence of other defects. These defective sperm are called Dag‐like to differentiate their occurrence from the rare, heritable condition where high numbers of sperm express the defect in the absence of any other evidence of an insult to spermatogenesis.
Figure 9.20 Dag defect.
Principal Piece Defects
Coiled Principal Piece
Coiled principal pieces can be found in small numbers on many smears, often with other defects (Figure 9.21). They usually appear at the same time as nuclear vacuoles following an insult to spermatogenesis. Sperm with coiled principal pieces are not capable of normal motility.
Figure 9.21 Coiled principal piece.
Bent Principal Piece
Occasionally, sperm displaying a loop bend in the principal piece with cytoplasmic droplet material trapped in the loop are encountered. The loop begins just past the midpiece, so technically it is not a DMR. Most of the sperm with bent principal pieces are noted in spermiograms where DMRs are present and are believed to have the same origin.
References
1 1 Koziol, J. and Armstrong, C. (2018). Society for Theriogenology Manual for Breeding Soundness Examination of Bulls, 2e. Pike Road, AB: Society for Theriogenology.
2 2 Barth, A. (2013). Bull Breeding Soundness, 3e. Saskatoon, SK: Western Canadian Association of Bovine Practitioners.
3 3 Mosure, W., Meyer, R., Gudmundson, J., and Barth, A. (1998). Evaluation of possible methods to reduce pain associated with electroejaculation in bulls. Can. Vet. J. 39: 504–506.
4 4 Ohl, D. (1993). Electroejaculation. Urol. Clin. North Am. 20: 181–188.
5 5 Stafford, K. (1995). Electroejaculation: a welfare issue? Surveillance 22: 15–17.
6 6 Whitlock, B., Coffman, E., Coetzee, J., and Daniel, J. (2012). Electroejaculation increased vocalization and plasma concentrations of cortisol and progesterone, but not substance P, in beef bulls. Theriogenology 78: 737–746.
7 7 Dziuk, P., Graham, E., Donker, J. et al. (1954). Some observations in collection