Chapter 15 Diseases of the Mammary Gland
Growth in the small ruminant dairy industry is driving the need for more sheep and goat–specific research and tailored application of milk quality principles and practices to small ruminant production settings. Intramammary infections (IMIs) in dairy operations result in significant economic losses to the producer. Mammary health is critical to young stock performance in food and fiber herds and to overall well-being in small ruminants kept as pets.
Normal Anatomy of the Mammary Gland
The mammary structure of the sheep and goat consists of two functionally and anatomically separate glands (halves), each with one teat. Each half is supported by a medial and a lateral suspensory ligament; in turn, these ligaments branch off as secondary laminae that enter into and support the gland tissue. The medial suspensory ligaments are adhered together and run on midline from the prepubic symphysial tendon to the abdominal tunic. The intramammary groove is formed where the medial suspensory ligaments meet the skin of the ventral udder. The elastic medial ligament should hold the udder high and tight to the abdominal wall above the level of the hocks; heritability of the medial suspensory ligament conformation is 0.33,1 and breeding programs should specifically select against a pendulous udder. The lateral suspensory ligaments run deep to the skin and superficial to the mammary neurovascular and lymphatic structures. The draining supramammary (superficial inguinal) lymph node is located at the dorsocaudal aspect of each gland. The main arterial supply to the udder is from the external pudendal arteries, which emerge from the inguinal rings and can be readily identified by their tortuous path. The paired external pudendal veins, paired branching subcutaneous abdominal veins, and paired perineal veins drain the udder and the supramammary lymph nodes. The gland is innervated by the genitofemoral nerve with superficial contributions from the lumbar cutaneous nerves (cranially) and from the mammary branch of the pudendal nerve (caudally).
Each half of the udder consists of multiple gland lobes that drain into six to nine milk ducts.2 These ducts coalesce to form a gland cistern, which in turn drains into the teat cistern. Furstenberg’s ring, an annular venous structure, forms the demarcation between udder and teat. As in cattle, the teat wall consists of five layers: mucosa, vascular connective tissue, circular and longitudinal muscular layers, and epithelium. A 0.5- to 1.0-cm streak canal at the distal end of the teat connects the teat cistern to the teat orifice and is identified proximately by the rosette of Furstenberg. The streak canal is an important anatomic and physiologic barrier to the udder with its keratin-producing squamous epithelial cell lining and muscular teat sphincter.
Species and operation type significantly influence various aspects of lactation. Dairy goats typically are milked for a 305-day lactation with a 60-day dry period, in a regimen similar to that for dairy cattle. It is common for kids to be hand-reared on pasteurized milk or milk replacer. Dairy sheep have a much steeper lactation curve of approximately 5 months, similar to that for sheep and goats in meat and fiber operations. A common practice in dairy sheep operations is to dam-raise the lambs for the first 1 to 2 months and then switch over to machine milking for commercial milk production, the suckling and suckling-to-milking periods offer some unique challenges with regard to mastitis control. Nutrition, mastitis, and reproduction are the major factors influencing production in all herd types (see Chapters 2 and 8).
Milk volume and composition differ among the dairy species. Compared with milk from goats and cows, sheep milk is highest in fat (7.62%), proteins (6.21%), caseins, and other solids.3 As a result, rennet coagulation time is shortened and curd firmness is improved during cheese production. However, dairy sheep produce less milk volume per lactation period, and genetic potential differs significantly between European and U.S. lines. As a rough average, the East Fresian breed produces approximately 1000 lb of milk per lactation, and the Lacaune lait breed, evaluated on an as-milked basis (excluding milk used to dam-rear the lambs), produces around 650 lb per lactation.
Goat milk frequently is prescribed for milk-intolerant children and adults; 40% of people who cannot digest cow milk will be able to tolerate goat milk.3 Digestibility is facilitated by smaller fat globules and a higher proportion of short-chain fatty acids, such as the appropriately named caproic, caprylic, and capric acids.3 Dairy goats produce more milk volume than that typical for sheep, with component percentages falling between those of cattle and sheep; production volume and components are significantly influenced by breed, herd, and individual genetic potential. Miniature breeds produce a smaller volume of milk with higher fat and protein content. The average milk production in Wisconsin herds for 2008 was 1288 lb/doe, with the top four herds averaging 1510 lb/doe.4 By comparison, the 2009 “honor roll” members of the California Dairy Herd Improvement Association (DHIA) produced as much as 2717 and 603 lb/doe for standard and miniature breed dairy goats, respectively.5
In the standard European breeds, a 3.8% fat content is typical.3 Among the top California operations, fat contents as high as 4.9% and 6.9% were recorded for standard and miniature breeds.5 In one high-volume operation, however, the result of a butterfat test was very low at 2.7%. As in cow milk, milkfat in goat milk can be suppressed by highly fermentable diets (with a carbohydrate-to-forage ratio greater than 2:1), subacute ruminal acidosis, and heat stress. Increasing dietary forage and offering free-choice buffers (e.g., bicarbonate) will help raise measured butterfat content. In the standard European breeds, protein averages 2.9%.3 Among the top California operations protein ranged from 2.61% to 3.96% and 3.91% to 5.0% in the standard and miniature breeds.5
In small ruminants, increased somatic cell counts (SCCs) are associated with increased parity, days in milk, stressors, and onset of estrus, as well as with infection. The contribution of these factors is compounded in a seasonally producing herd. In a survey of 71 U.S. goat dairies, 65% did not meet grade A standards of 1 million cells/mL near the end of their lactation cycle,6 and many had difficulty meeting grade B standards of 1.5 million cells/mL. Apocrine milk production in small ruminants complicates SCC determination because some testing methods will miscount normal DNA-free cytoplasmic droplets; goats produce 10 times more cytoplasmic droplets than sheep.7 The Levowitz-Weber stain used for cattle SCC determinations does not adequately differentiate between leukocytes and cytoplasmic droplets.7 Direct microscopic counts using the pyronin Y methyl green stain is specified by the U.S. reference standard for small ruminant milk, but staining methods and technician competency may vary by laboratory.7,8 With Fossomatic techniques, counts are in good agreement with the reference standard.6,8
Normal somatic cell populations differ dramatically between the species. Neutrophils are the most common leukocyte in both the infected and uninfected caprine mammary gland, making up 74% to 80% of the cell population in late lactation.9 By comparison, the noninfected ovine mammary gland cell population is comparable to that in cattle, being largely composed of macrophages (45% to 85%), with fewer neutrophils (10% to 35%), lymphocytes (10% to 17%), and epithelial cells (2% to 3%); neutrophil numbers increase during infection and are highly correlated with SCC.7,9
The degree to which infection directly correlates with SCC is controversial. Some workers suggest that IMI status is the major variable factoring into SCC.9,10 In one goat dairy, however, although SCC increased with IMI prevalence, 90% of SCC variability relates to factors other than mastitis.11 In both species, higher SCCs in early and midlactation are more likely to indicate infection than equivalent counts in late lactation,2,9 and repeated tests, or comparative samples between udder halves, are more informative than single test points.9 SCC also is moderately heritable, estimated at approximately 0.11 to 0.15 in the larger sheep breed databases. French Lacaune breeders are trying to reduce SCC through selective breeding.9
Bacterial pathogens responsible for clinical and subclinical mastitis in small ruminants are well characterized. Sporadic cases of clinical mastitis most frequently are caused by Staphylococcus aureus, coagulase-negative Staphylococcus spp., Arcanobacterium pyogenes, Corynebacterium, Pasteurella spp., and Pseudomonas spp.9 Outbreaks of clinical mastitis most frequently involve S. aureus, Streptococcus spp. (S. uberis, S. agalactiae, and S. suis), and opportunists such as Aspergillus, Pseudomonas, Burkholderia, and Serratia.9
Numerous studies have identified coagulase-negative Staphylococcus spp. as by far the most important cause of subclinical mastitis in both the ewe (78%) and doe (71%). S. epidermidis and S. caprae are isolated most frequently, although other species are commonly identified.8,9 Shedding of coagulase-negative staphylococci often is cyclic, in inverse proportion to SCC elevation, and may be missed on single culture. From 60% to 80% of cultured strains of coagulase-negative staphylococci are hemolytic; hemolytic strains, and S. epidermidis as a species, tend to cause very high elevations in SCC, whereas other coagulase-negative staphylococcal species may not be obviously associated with an elevated SCC.9 S. aureus is the second most frequently isolated subclinical mastitis agent in the ewe (4%) and doe (8%), whereas Streptococcus spp. and Corynebacterium are less frequently identified.9 Unlike in dairy cattle, gram-negative bacteria are infrequent causes of mastitis in the ewe (3%) and doe (8%).9 Although rarely involved in mastitis, Listeria and Salmonella spp. are worth mentioning owing to their zoonotic potential; Listeria can be shed from clinically normal udders.2
The normal conformation of the udder in both sheep and goats includes the presence of two teats, one on each half of the udder; however, some animals may be identified with three to six teats. Dairy breed organizations (for both goats and sheep) often identify supernumerary teats as a serious disqualification in both sexes and prohibit the surgical removal and subsequent registration of purebred animals with extra teats. In meat animals, less emphasis is placed on teat conformation, and many meat breed animals have supernumerary teats. In some instances, breeders have even advocated the selection of meat breed replacement animals that have four “clean” teats (i.e., fully and separately developed) as a means of increasing productivity.12
As with many conditions in goats and sheep, a variety of lay terms have emerged to describe specific supernumerary teat conformations. A clean teat is a single normally shaped teat with a single teat orifice located at the end of the teat. Teats are then further classified as functional or nonfunctional, on the basis of the presence of a single teat orifice and the ability to produce and excrete milk from that teat. Nonfunctional teats have the potential to interfere significantly with nursing if associated with a separate milk gland that is not drained by the primary teat; in our experience, presence of such teats can lead to udder asymmetry with a slightly increased risk of mastitis. Cluster teats are multiple teats in close proximity to each other but remaining distinctly independent (i.e., not split or bifid). In some instances, two teats will be fused for some or all of their length. These fused teats may have either one or two teat orifices. If the fused portion accounts for less than 50% of the teat length, the teats are referred to as split, whereas teats that are fused for the entire length often are referred to as fishtailed. Both of these teat types have been referred to as bifid teats. In rare instances, more than two teats may be fused together; such large, conglomerate teats are referred to as “Christmas tree” teats because of their multibranched appearance. Animals with supernumerary teats also may have supernumerary mammary glands—a condition referred to as hypermastia.
As mentioned earlier, most dairy breed organizations prohibit the registration of animals with more than two clean functional teats. The breed registry requirements for meat breeds vary widely by registry. The American Boer Goat Association (ABGA) allows registration of animals with up to two functional teats per side (for a total of four) and also allows split teats (in which 50% or more of the teat is separate), with clean teats being preferable. The ABGA considers cluster teats and fishtail teats to be disqualifications.
Bifid (split or fishtailed) teats, when present, sometimes can be associated with and drain two distinct and noncommunicating portions of the mammary gland. In such instances, a thin membranous division along the full length of the teat cistern may be visualized with ultrasonography of the distal teat. For this examination, a 7.5-MHz or higher-resolution probe will provide images of reasonable quality. Use of a probe standoff will facilitate better-quality images; in field situations, submerging the teat in a plastic container of water will suffice for this purpose. For this technique, a small plastic flat-sided storage container is filled with water and then lifted up to the ventral portion of the udder, with the teat submerged in the middle of the container. Coupling gel can then be applied to the probe and the side of the container, and the teat is imaged in the middle of the water bath through the side of the container. In the presence of a membranous division of the teat cistern, a distinct variable-thickness hyperechoic division will be seen extending down the length of the teat cistern dividing the two teats. This finding is of greatest clinical significance when one of the teat cisterns lacks a teat orifice. In such cases, this portion of the gland cannot be emptied of milk and may remain swollen and painful until the gland atrophies, which can take prolonged periods in high-producing animals.
From a production standpoint, the presence of supernumerary teats poses significant management problems. Most obviously, because the milking machine claws have only two teat cups, the presence of more than two functional teats constitutes a practical problem in getting the animals milked. Furthermore, the presence of a split or bifid teat precludes proper placement of the inflation and renders milking by mechanical means impossible on that teat. These issues are less important in meat production operations; nevertheless, supernumerary teats can complicate initial attempts at nursing by newborn lambs or kids, with cluster teats in particular presenting significant challenges for offspring trying to latch on to a functional teat.
Although detailed studies of the inheritance of supernumerary teats in small ruminants are not available, a genetic mode of inheritance has been recognized. Consequently, attention to the teat structure in breeding males and females should be of high priority, and animals with unacceptable teat conformation should be culled. Surgical correction of supernumerary teats, especially those classified as a disqualification, does not address the genetic inheritance of this condition and only prolongs and increases the prevalence of this defect in the breeding population.
In some animals selected for high milk production, milk-secreting tissue may be present in the wall of the teat. Three outcomes are possible relative to the milk produced by such tissue: (1) In some instances, the milk passes through local pores into the teat cistern, with no clinical evidence of presence of this tissue. (2) Alternatively, the milk can pass through skin pores in the external epithelial surface of the teat and be released onto the skin surface, resulting in a “weeping teat.” Because the muscular orifice typical of the teat streak canal is absent, this tissue may be prone to development of retrograde bacterial infections and localized mastitis. Clinically, animals with weeping teats are easily identified by the presence of milk on the lateral external surface, particularly at the time of milking. Owners of affected animals also may report that during hand-milking, their hands become wet with milk. Apart from the aesthetic downside of these lesions and the very occasional associated mastitis, they generally do not pose significant health problems for affected animals. The use of silver nitrate sticks to cauterize these weeping pores has been reported2; however, this procedure may potentially lead to the development of a teat cyst, as described further on. (3) Finally, if no porous passage exists for the milk to move out of the teat wall, a teat wall cyst will develop to contain the accumulating milk. In such cases, the cyst can be readily identified clinically by detection of a focal fluctuant swelling in the teat wall. Teat wall cysts may be as small as a couple of millimeters in diameter up to 1 to 2 cm in diameter. Ultrasonographic evaluation of the teat (as just described for bifid teats) will readily identify a hypoechoic fluid-filled structure located in the teat wall. Aspiration of the cyst, performed using aseptic technique, will confirm the diagnosis.2 In some instances, presence of the cyst may lead to difficulty in placing the teat cup on the teat; however, this problem generally is of limited importance. Perhaps more significant is the occasional teat cyst that results in deformation of the mucosal wall of the teat cistern, with consequent functional outflow obstruction of milk through the teat canal. In such cases, ultrasonography-guided aspiration of the cyst may restore milk flow, and surgical resection of the teat cyst can be performed if warranted.
The mammary gland is supported by three primary attachments: the two lateral suspensory ligaments and the medial suspensory ligament located between the two halves of the udder and oriented in the axis parallel to the animal’s body. These three suspensory ligaments provide the support necessary to hold the udder up tight against the body wall, where it is less likely to be injured. In cases where these suspensory ligaments do not provide sufficient support, the udder will be carried in a more pendulous fashion, with excessive movement and swinging during locomotion. One commonly used rule of thumb is that ideally the udder should be held above the level of the hock in lactating animals.
Poor support of the udder contributes to a variety of potential problems for both the doe or ewe and her offspring. Excessively low carriage of the udder often makes it difficult for newborn lambs or kids to find the teats, because by nature they tend to look up at the base of the udder. Furthermore, as the lambs and kids grow older, a normal nursing posture becomes impossible when teats are close to the ground. In the doe, poor udder support predisposes the animal to injury, bruising, and mastitis. Pendulous udders can experience significant trauma associated with swinging while the animal runs, or more directly when either the doe or ewe or one of her penmates steps on a portion of the udder or teat. Pendulous udders also are more prone to damage during dog attacks or from barbed wire or horns of other animals. With regard to mastitis, the low carriage of the mammary system exposes it to more fecal and environmental contamination from the bedding and predisposes affected animals to some forms of mastitis, including coliform mastitis.
Poor udder conformation generally is considered to be an inherited genetic defect and should be negatively selected for in breeding programs, for the health of both the does or ewes and their offspring. Commercially available nylon mesh udder supports are available when warranted. Alternatively, a mastectomy provides a long-term solution if the animal is being kept as a pet. Because these animals should not be bred, the absence of an udder will not be of significant concern with regard to raising offspring.
Asymmetric udders or uneven udders can occur as both a congenital and an acquired condition. In rare instances, the suspensory ligaments of the udder are attached in an asymmetric fashion, which results in a “twisted” appearance of the udder in relation to the main body axis. In dairy goats, it is relatively common for does to have an asymmetric udder associated with uneven milk production. This situation may be present from the time of parturition or may develop over the course of the lactation period. In some cases this finding may be associated with a subclinical infection with coagulase-negative staphylococci on the side with less milk production, so milk culture of each half performed separately is suggested. If the condition occurs as a herd-level problem, a thorough evaluation of the milking system should be conducted in addition to individual animal milk cultures. Milking system cleaning and disinfection practices should be evaluated, as well as milking claw design and placement during milking. In our own practice, we have observed a herd-level problem with asymmetric udders associated with placement of milking claws from the side, resulting in differential milking rates from the halves and, consequently, differential milk production.
Agalactia is the absence of milk production in an animal that should be producing milk. The two most common causes of this condition are systemic disease and mastitis. In animals with severe systemic disease and decreased feed intake, milk production will drop dramatically and, in some cases, will cease altogether. A good physical exam often will identify the specific systemic disease, and treatment should be focused on correction of the underlying issue. If the duration and extent of the systemic disease are limited in duration and severity, the animal may return to some level of milk production for the remainder of the lactation. If, however, the insult is severe, milk production may not be salvageable for that lactation. A syndrome known as “contagious agalactia” associated with mastitis may be caused by any of several members of the Mycoplasma genus. Many of the organisms considered in the etiology of this syndrome are not routinely found in the United States and are considered the agents of foreign animal diseases; however, Mycoplasma spp. have been identified as a significant cause of mastitis in some U.S. operations and can be associated with decreased or absent milk production. In clinical practice, the presence of agalactia with evidence of abnormal mammary gland secretions or texture should result in inclusion of mastitis (due to any of the organisms discussed later on) on the differential diagnosis list.
Udder edema is a common finding in recently fresh animals, especially primiparous does and ewes. Careful evaluation of an enlarged mammary gland is indicated to differentiate between mastitis and edema. In mastitis, the gland often will be enlarged, may be either very warm or very cold to the touch, and may be painful and typically expresses milk with an abnormal-looking texture or color or with an odor. In edema of other causes, the clinical presentation also will include mammary gland swelling but the milk will be normal. Considerations in the differential diagnosis for udder edema should include trauma, hypoproteinemia, recent parturition (fresh doe or ewe), and dependent edema. A less obvious but nonetheless important possibility is hypoproteinemia associated with intestinal parasitism. In one herd, udder edema was the first clinical sign of hypoproteinemia and resolved after appropriate therapy for the parasitic infection (see Chapter 6).
In most cases, udder edema resolves without treatment in recently fresh animals. Correction of the primary cause of hypoproteinemia generally will result in clinical resolution when this is the cause of udder edema. Diuretics such as furosemide can be used if the udder edema poses a significant risk for trauma or is seen to impede locomotion.
Precocious udder can occur in all small ruminant species but most commonly is observed in nulliparous dairy goats. In these animals, the mammary gland development occurs before breeding or is excessive for the stage of gestation in bred animals. The presence of a precocious udder generally is not cause for concern; however, the udder should be evaluated for texture, heat, and pain, which may be indicative of a mastitis. If heat and pain suggest the presence of an infection, expression of some secretions for bacterial culture often is possible, but the benefit of this procedure must be weighed against the decreased mammary gland protection associated with removing the keratin plug from the teat streak canal. Precocious udders may be asymmetric but should be soft and pliable on palpation. If an infection is confirmed, antimicrobial therapy may be indicated. Although intramammary infusion of an appropriate drug for mastitis therapy may be considered, the very small size of the streak canal may preclude infusion without significant trauma. In such cases, systemic therapy with an antimicrobial with good volume of distribution may be a more effective option. In either case, emphasis on appropriate drug withdrawal protocols is important, because most producers are not accustomed to scenarios involving antimicrobial-associated milk withdrawals at the time of parturition.
Gynecomastia refers to the abnormal development of a mammary system and milk secretion in a male. Three different causes have been identified in small ruminants, particularly goats. In two published reports, the animals had evidence of sex chromosome abnormalities, one with Y chromosome deletions and the other with sex chromatin in the neutrophils.13,14 Gynecomastia also has been reported to occur as the consequence of a familial predisposition associated with high milk production in the maternal line. It is speculated that the affected animals may have higher baseline production of prolactogenic hormones that lead to the abnormal mammary gland development.15 Similarly, animals with endocrine imbalances associated with adrenal tumors may exhibit gynecomastia.16 Finally, excessive mechanical stimulation of the teats associated with simulated milking or nursing appears to be sufficient to elicit mammary gland development with secretion of small volumes of milk.15
In many cases of short-term gynecomastia, the fertility of the buck may not be affected; nevertheless, a full breeding soundness exam is always warranted. When the mammary gland is excessively large, it may interfere with normal cooling of the testicles, with the potential for decrease in or loss of fertility.15 With abnormalities involving the sex chromosomes, the affected animal generally is infertile.
Severe damage to the mammary gland associated with mastitis (bacterial or viral) or trauma may result in fibrosis of the secretory tissue and the loss of function in one or both halves of the mammary gland. In such cases the mammary gland typically appears atrophied and no milk can be expressed from the gland. The situation may resolve spontaneously at the time of the next parturition or may be present for the remainder of the animal’s life. Anecdotally, some practitioners also have utilized chemical (chlorhexidine or iodine) means of “killing” one half of an udder in cases of chronic nontreatable mastitis; however, no published reports have evaluated the safety of this procedure, and the potential exists for adulterated milk from the untreated gland. In naturally occurring cases of “blind halves,” no therapy is required, and the prognosis for returning to normal full production is moderate to guarded.
In some animals, the small size of the streak canal in the teat severely limits flow of milk through the orifice; animals with this condition are routinely referred to as “hard milkers.” This problem may be the result of genetic inheritance of small streak canals or due to trauma or irritation associated with teat end lesions. In severe cases, any of several types of teat knife or bistoury can be used to expand the streak canal opening. The instrument is placed through the streak canal and then removed in such a fashion as to cut the internal portion of the streak canal while minimally cutting the external portion of the canal. This procedure should be performed while the udder is full, to assist in assessing the teat opening size. A second or third cut may need to be performed in severe cases. After surgery the teat ideally should be milked every 20 minutes for 2 hours and then every hour until the next day. Owners should be warned that milking will become more difficult over the next 2 to 3 days owing to swelling, but the surgery should not be repeated until at least 1 week later, when a true assessment of the success can be determined. This procedure does carry significant risk of inducing a mastitis or chronic teat leakage if the surgeon is overly aggressive. In our own experience, some does with small but milkable teat orifices tend to have lower somatic cell counts; however, no controlled studies have been performed to determine the role of teat canal size in relation to mastitis and SCC.
Another consideration in the differential diagnosis with animals that are difficult to milk is the presence of a so-called teat spider or one or more lactoliths. Unlike with tight streak canals, these conditions result in difficult milking as a consequence of partial or intermittent blockage of the canal from abnormal tissue or by calcified concretions. Tissue-associated blockage often is secondary to formation of a mass on a pedunculated stalk that allows its free movement—the teat spider. A concretion termed a lactolith may form within the teat cistern, starting from a particulate nidus or teat gargot, and grow to the point that it can occlude flow through the teat canal. Typically, blockage occurs at the top of the streak canal by a ball valve mechanism.
In cases of blockage palpation of the teat often will reveal a firm pea-size mass that may be movable in the teat cistern. Ultrasound examination can be performed as described in the section “Diagnostic and Therapeutic Procedures” and can reveal the presence of a tissue mass extending from the mucosa surface of the teat cistern. With this type of lesion, two basic forms of therapy have been used: Various forms of teat knives can be introduced through the streak canal and used to macerate the teat spider so that it can be removed in smaller portions.17 Alternatively, a surgical thelotomy may be performed to remove the mass. Anesthetic block is obtained with local infiltration of lidocaine in a circumferential pattern at the base of the teat. For the procedure, a 3- to 4-cm-long incision is made parallel to the length of the teat. A teat cannula should be passed through the streak canal and used to protect the mucosa of the opposite side of the teat cistern during entry. The mucosa surrounding the lesion should be undermined and its edges apposed with monofilament suture17 to prevent excessive granulation tissue from developing and occluding the teat cistern. The submucosa and intermediate layer are closed in a continuous horizontal pattern using resorbable monofilament suture, and the skin is closed with simple interrupted sutures.
The first step in repair of any teat laceration is to consider the prognosis for return to function. Several factors influence the prognosis, including laceration severity (partial-thickness versus full-thickness), laceration site, direction of laceration (parallel versus perpendicular to teat axis), and involvement of complex anatomic structures (streak canal or annular ring). With a full-thickness laceration that penetrates either the teat cistern or gland cistern, the risk of mastitis or elevated SCC is significant. An additional risk with these lesions is the potential for postoperative development of teat fistulas. The likelihood of successful laceration repair generally increases as the laceration moves closer to the base of the teat and when the laceration is oriented parallel to the teat axis.
Preoperatively the animal can be sedated if necessary, and a ring block with 2% lidocaine is performed around the base of the teat, with care taken to avoid the circumferential vein and the teat and gland cistern. If the laceration is full-thickness, some clinicians also place a tourniquet at the base of the teat to minimize interference with surgical visualization by milk from the teat. If necessary, the wound should be surgically debrided, with preservation of as much tissue as possible. Full-thickness lacerations should be closed in three layers.17 First the submucosa is closed using a continuous horizontal pattern that does not penetrate the mucosa, followed by closure of the intermediate layer using a similar pattern, best accomplished with 4-0 monofilament synthetic resorbable suture introduced by a swaged-on taper needle. Finally the skin is closed using 4-0 or 3-0 monofilament suture in a simple interrupted pattern. Postoperatively, the patient should not be subjected to mechanical milking or hand-milking for at least 10 days. Instead, the milk should be passively removed from the teat cistern using a teat cannula. Intramammary antibiotics should be given every other day during this time, and the mammary gland should be closely monitored for signs of mastitis.
Teat fistulas that develop after teat lacerations increase the risk for mastitis in that gland of the udder. Because they do not have a streak canal or sphincter, they are open to retrograde movement of bacteria and often are associated with elevated SCCs or mastitis. When surgical correction of the fistula is warranted, the lesions should be allowed to heal until the fistula is well demarcated and easily visible. The teat should be anesthetized as described previously; then an elliptical incision is made along an axis parallel to that of the teat and around the perimeter of the fistula. Care is taken to minimize the width of the elliptical tissue removed so as to retain as much normal skin as possible for closure. The incision is closed as described for the full-thickness teat laceration.
Radical mastectomy is a treatment for mammary conditions such as gangrenous mastitis not responsive to medical treatment, precocious udder that exhibits inappropriate lactation, or other localized mammary disease. Goats with gangrenous mastitis present with clinical signs of a discolored (dark) udder that is cold, painful, and swollen. The milk usually is blood-tinged. Most animals are affected at 10 to 15 days after kidding. Medical treatment is seldom successful, and chronic mastitis frequently is the end result.18 Mastectomy has proved to be a safe and effective treatment to allow good quality of life in pet animals or in genetically valuable animals to be used as embryo donors, or in natural dams of offspring to be hand-raised.19
A radical mastectomy is performed with the animal in dorsal recumbency under general anesthesia (Figure 15-1). This positioning allows access to more skin for closure with minimal tension. Some veterinary surgeons prefer an elliptical skin incision. The inverted cloverleaf skin incision, however, allows dissection of the skin away from the mammary tissue and identification of the vasculature to allow ligation of the vessels to prevent hemorrhage (Figure 15-2). The arterial blood supply to the mammary gland arises from the external pudendal and perineal arteries. The blood drains from the gland by way of the external pudendal and perineal veins as well as the large subcutaneous abdominal vein. The mammary tissue can be bluntly dissected off the external rectus sheath by fanning of the operator’s hand under the glandular tissue. The skin closure is then done in an X shape, with latex drains placed subcutaneously exiting away from the incision line (Figure 15-3). The dissection leaves abundant dead space, which should be ablated as much as possible by tacking the subcutaneous tissue to the external rectus sheath with absorbable sutures.
Figure 15-1 Three lines of the four that make up the inverted cloverleaf skin incision for mastectomy in a 4-year-old Pygmy doe. This view is from the rear, with the animal in dorsal recumbency. The teats are being held adjacent to each other by an assistant’s gloved hand.
(Courtesy Dr. A.N. Baird, Purdue University.)
Figure 15-2 The external pudendal vein near the right inguinal ring, in the doe shown in Figure 15-1. In this caudal view, the skin has been dissected to the left and the mammary tissue is to the right.
(Courtesy Dr. A.N. Baird, Purdue University.)
(Courtesy Dr. A.N. Baird, Purdue University.)
Partial mastectomy may be performed in the case of unilateral disease. The partial mastectomy is done through an elliptical incision around the teat of the affected gland. Partial mastectomy is technically more difficult to perform because of collateral circulation and different dissection required. Care must be taken in the dissection not to compromise the gland to be left intact.20
An alternative to radical mastectomy in does with gangrenous mastitis is ligation of the mammary vasculature in conjunction with the amputation of the teat. This surgical approach allows drainage of the glandular discharge and ultimately avascular necrosis of the udder. When compared with a traditional radical mastectomy, this method was described as quicker to perform, less expensive, and less stressful to the goat.21 However, the sloughing udder may not be cosmetically pleasing to the owner.
The patient with severe gangrenous mastitis may be an unsatisfactory anesthetic risk. In such cases, one option is to ligate the external pudendal artery and vein as they exit the inguinal canal. This procedure can be performed with use of mild sedation and local anesthesia with the animal in lateral recumbency. After ligation of these vessels, the absorption of toxins from the mammary gland is limited, and the mammary gland will atrophy because the external pudendal artery is the primary vascular supply for the mammary gland of sheep and goats.17
For this procedure, the animal is placed in lateral recumbency, and the area external to the inguinal canal is infiltrated with 2% lidocaine. A skin incision is made over the region, and blunt dissection is used to identify the inguinal canal with both the external pudendal artery and vein exiting it. Each vessel is triple-ligated and incised, leaving two ligatures on the cardiac side. The dead space is minimized using several layers of subcutaneous sutures and the skin is closed in a routine fashion. The clinician also may consider teat amputation after this surgery, in order to facilitate drainage of the mammary gland.17
4. Dietman P., Tranel L. The Wisconsin goat dairy profitability project: 2007 and 2008 results for a select group of Wisconsin goat dairies. Madison, Wisc: Wisconsin Department of Agriculture, Trade and Consumer Protection; 2009. A collaborative project of the Wisconsin Department of Agriculture, Trade and Consumer Protection, Wisconsin Technical College System, University of Wisconsin-Extension, Iowa State University Extension, and Southwest Badger Resource Conservation and Development Council
5. California Dairy Herd Improvement Association: 2009 honor roll (website): caldairygoats.com/cdhiagoats.htm. Accessed February 1, 2011.