The importance of goat farming in Mexico

The goat population in Mexico is currently 8,791,894¹, most of which is distributed in the states of Zacatecas, San Luis Potosí, Coahuila, Puebla and Oaxaca. All have a traditional cuisine that includes goat meat in dishes such as birria, cabrito, mole de caderas and barbacoa. Specialized meat production or dual-purpose breeds, such as Boer and Nubia, have been developed, but most of the goat population continues to be Creole or local animals, which are descendants of Spanish breeds. Specialized dairy breeds, such as Saanen, French Alpine, Toggenburg and Nubia, are found mainly in the states of Coahuila, Guanajuato, Durango, Jalisco and Chihuahua¹; cheese, cajeta (caramel) and candys are produced from goat’s milk in these states².

Goat farmers in the Bajío region of central Mexico and those in northern Mexico have technified production more than those of the south, such as in the Mixtec and Guerrero regions. This is probably due to the primary focus of production being milk to supply several companies that produce goat dairy products. Even so, regional production systems in Mexico are predominantly heterogeneous, utilize traditional technology, face myriad animal health problems, and suffer from minimal organization among producers and throughout the value chain³.

Goats’ importance as producers of food and valued-added derivatives is more pronounced in arid and semi-arid areas, which is also where human populations tend to be poorer. Goats are capable of utilizing the vegetation found in these areas, making it the preferred livestock for its ability to adapt and produce, even in challenging desert conditions⁴.

Brucellosis

Brucellosis melitensis is the principal etiological agent of brucellosis in goats. It is also the main species of the genus and is considered to be one of the causative agents of human brucellosis, known as Malta fever⁵. Transmission of B. melitensis is principally oral, normally through intake of food or water contaminated with vaginal secretions or the remains of abortions from infected animals. For smooth phenotype brucellae, venereal transmission is not generally accepted as a main route of infection. However, B. melitensis is excreted in the milk and colostrum, suggesting that most latent infections may be contracted through their consumption⁵.

Infected cattle manifest clinical signs that can have substantial financial impacts. In sexually mature females it causes reduced fertility, abortion and decreased milk production. In males it colonizes the reproductive system, causing orchitis and epididymitis. Cases of arthritis have also been reported⁶.

Serological diagnosis of brucellosis in goats is most commonly done with the card test using 3 % B. abortus antigen. Its sensitivity is near 100 %, and it is also simple, inexpensive and practical. However, this test cannot be used in goats vaccinated with Rev 1 at any dose until 8 mo post vaccination. Before eight months the test cannot differentiate between antibodies generated in response to the vaccine and those generated in response to infection. In these cases, techniques such as radial immunodiffusion (IDR) with native hapten are used because they allow differentiation between vaccinated and infected animals⁷.

In Mexico. Brucellosis is the main bacterial zoonosis in the country. Its control relies on diagnosis, identification of infected animals, their elimination, and especially vaccination. Goat farmers (especially in poorer goat farming communities), veterinarians, and slaughterhouse workers are the most vulnerable human populations, but laboratory personnel and consumers of unpasteurized dairy products are also at risk⁵.

Chlamydiosis

Chlamydiosis is an infectious-contagious and zoonotic disease caused by bacteria of the genus Chlamydia. The species that most affects goats is C. abortus, an obligate intracellular bacterium with an asynchronous multimorphic development cycle¹³. It has been reported to affect pregnant women, mainly after exposure to infected goats¹³.

In goats, chlamydiosis is characterized as causing abortions in the last two or three weeks of gestation, or birth of weak offspring¹³. Abortion generally occurs without previous signs, although behavioral changes and vaginal discharges containing a large number of elementary bodies can occur between 24 to 48 h beforehand. Placental lesions develop initially in the hilum of the placentaloma and extend to the intercotyledonary membranes. This leads to destruction of placental tissue which affects nutrient acquisition and hormonal regulation, resulting in premature expulsion of the fetus. Histological changes in the placenta and appearance of lesions typically occur after 90 d gestation¹³.

In Mexico. The first report of isolation of chlamydiosis’ etiological agent in goats was published in 1997¹⁴. Initially considered exotic in Mexico, C. abortus is now viewed as common in goats based on increasing evidence. For example, a 2015 study was aimed at isolating C. abortus in dairy goats from herds with abortion problems in the state of Guanajuato, and developing adequate diagnostic tests for its detection¹⁵. Analysis by ELISA of serum samples and vaginal swabs taken from six goat herds found that 9.60 % of the evaluated animals were seropositive for C. abortus. A PCR analysis using vaginal exudate DNA identified 23.8 % positive animals, and Chlamydia spp. was isolated in 26.98 % of the sampled animals. These three diagnostic methods were complementary, and all were applied in areas where Chlamydia is suspected of causing abortions. The combined results confirmed that this pathogen is present in dairy goat herds in Mexico¹⁵. In a 2016 study, 1,307 serological samples were collected from goats distributed in 14 municipalities in Guanajuato, and analyzed using indirect ELISA. Frequency in females with a history of abortion was 46.62 %, whereas it was 27.13 % in females with at least one parturition that were clinically healthy but lived with females that tended to abort¹⁶. A study done in Culiacán, in the state of Sinaloa, identified the presence of C. abortus in a goat herd with abortion problems, further supporting its presence in the country¹⁷.

Colibacillosis

Colibacillosis is caused by Escherichia coli, and one of the main conditions caused by this bacterium is diarrhea in goat kids. Two main forms of the disease are recognized: enteric and systemic colibacillosis. The enteric form affects animals 2 to 8 d of age in which it causes diarrhea that is usually yellowish white in color, and creamy to almost liquid in consistency, while the kid exhibits weakness, cachexia and dehydration. If not quickly and adequately treated, infected animals can die within 12 h of clinical onset. The systemic, or septicemic, form affects animals between two to 6 wk of age. The bacteria crosses the intestinal or respiratory mucosa and enters the circulatory stream, causing animals to exhibit higher rectal temperature, meningitis and arthritis, but without diarrhea. Infected animals are the most important source of transmission, the most common route being fecal-oral. Reducing exposure to E. coli is attained through proper hygiene and handling practices. Lack of colostrum makes kids more susceptible to diarrhea²¹.

In Mexico. One of the two main causes of mortality in goat kids is diarrhea²². Little research has been done on the pathogenic mechanisms and identification of virulence genes involved in E. coli diarrhea in goats. Most of the strains isolated from animals have been enterotoxigenic E. coli (ETEC), which express adhesins and enterotoxins as pathogenicity factors, and cause neonatal enteritis. Other pathogens isolated from diseased animals include enteropathogenic E. coli (EPEC), which also cause diarrhea, and enterohemorrhagic E. coli (EHEC), a known pathogen in humans²³. The EHEC pathotype O157:H7 infects humans and its reservoirs are ruminants. Fecal contamination of water and other foods, as well as cross contamination during food preparation (with contaminated meat products, surfaces and kitchen utensils), are common infection routes²⁴.

Respiratory disease complex (RDC)

The causes of RDC in goats include the environment, animal condition and the presence of infectious agents such as viruses and bacteria. Kids are particularly susceptible to RDC. The adverse environmental conditions that predispose goats to respiratory problems are sudden changes in climate, overcrowding of animals, inadequate pens, lack of ventilation, accumulation of dust and ammonia, poor protection against drafts and stress from transportation²⁸. Among infectious agents, some viruses are known to be primary agents, particularly the parainfluenza-3 and respiratory syncytial viruses²⁹. The bacteria that can generate RDC include Pasteurella multocida, Mannheimia haemolytica, and Mycoplasma spp., all commonly found in the upper respiratory tract of healthy animals³⁰. When immune system mechanisms become depressed these bacteria colonize the lungs, causing RDC. Various host-related factors can contribute to development of RDC or pneumonia. These include deficient colostrum intake in kids, damage from viruses in the mucociliary clearance system (which causes insufficient bacterial clearance from airways), a depressed immune system, malnutrition, parasitosis, dehydration, etc. When pneumonia occurs, symptoms can range from 40 to 41 ºC fevers, cough, shortness of breath, lack of appetite, mucopurulent nasal and ocular discharge, depression, prostration and death³¹.

In Mexico. Goat producers in Mexico recognize pneumonia as one of the most frequent health problems in herds, but rarely is a diagnosis made or a prevention program implemented²².

Q fever

A worldwide zoonotic disease, Q fever is caused by the bacterium Coxiella burnetii. Its hosts are myriad, and range from domestic (cows, sheep, goats, dogs, cats, rabbits) to wild animals (small rodents, foxes). Most hosts are chronic carriers and do not suffer from the disease, but they excrete the bacteria via urine, feces, milk, and birth by-products such as amniotic fluid, the placenta and abortions. These secretions form aerosols that can transmit the microorganism by air to susceptible human populations³⁶.

In Mexico. Coxiella burnetii is an exotic species in Mexico, and as such has been considered by SADER as a notifiable disease since 1994³⁷. The first serological evidence of this bacterium in animals was reported in the state of Baja California in 1990³⁸, and the first reports of it in humans were from the Comarca Lagunera region³⁹.

Small ruminant lentivirus

Caprine arthritis encephalitis virus (CAEV) and Maedi-Visna virus show genetic, structural and pathogenic similarities; consequently, they have been reclassified as small ruminant lentiviruses (SRLV)⁴¹. In goat production, SRLV can have negative financial impacts directly related to the presence of multisystemic and incurable chronic-degenerative infections. In adult goats, arthritis and mastitis occur, while in kids the viruses manifest in the nervous system during the first months of age⁴². Replication of lentiviruses in mammary gland epithelial cells plays an important role in viral particle transmission. Mononuclear cells and infected macrophages can also be shed through colostrum and milk. Direct contact with aerosolized respiratory secretions, urine, and feces from infected animals are considered sources of infection that can become exacerbated by overcrowding. Water and feed, as well as inadequate disinfection of facilities, machinery and milking equipment, allow the spread of SRLV⁴³.

In Mexico. A seroprevalence study of CAEV in Mexico’s goat-producing regions in 1985 determined that the disease entered the country through import of live breeding animals from the United States⁴⁴. The SAGARPA subsequently classified CAEV as an endemic disease and required mandatory monthly reporting. It was isolated, and sequencing done of the entire genome of a recombinant SRLV belonging to the B1 subtype⁴⁵.

Leptospirosis

Leptospirosis is an infectious disease caused by bacteria belonging to the genus Leptospira. It is distributed worldwide in rural and urban areas with specific climatological and orographic characteristics, natural drainage networks, extensive agricultural areas and seasonal rainfall; these conditions favor the spread of Leptospira spp. Infection with Leptospira affects domestic and wild mammals differently, and cases can range from asymptomatic to acute or chronic infection. This microorganism is eliminated in the urine of infected animals continuously or intermittently, thus contaminating the environment. Acute leptospirosis in goats can cause symptoms such as an increase in body temperature, anorexia, depression, jaundice, and anemia. In its chronic form it causes abortions, mummifications, infertility, premature births and neonatal mortality, all resulting in financial losses⁴⁷. Humans can occasionally host Leptospira spp. When infected they can manifest pathological disorders such as fever, headache, muscle and joint pain, cough, stroke, nausea, vomiting, jaundice, and kidney and liver disorders⁴⁸.

In Mexico. In a study in the state of Veracruz, an analysis of 873 serum samples identified the most frequent serovars to be Wolffi (45.58 %) and Icterohaemorragiae (45.13 %)⁴⁹. In the Lagunera region, an analysis of 802 serum samples showed 60.1% to be seropositive for leptospirosis⁵⁰. In goat herds from the state of Guerrero, 64.26 % of a set of serum samples had antibody titers against at least one Leptospira interrogans serovar⁵¹.

Caseous lymphadenitis

Caseous lymphadenitis is a chronic infectious disease affecting goats caused by the Gram-positive bacterium Corynebacterium pseudotuberculosis, a facultative intracellular pathogen capable of replicating and surviving inside phagocytes. The disease is characterized by presence of suppurative lesions in the lymph nodes, lungs and other internal organs. At a subclinical level the disease manifests in the viscera in the form of abscesses in internal organs (e.g. lungs, liver and mesenteric lymph nodes), and occasionally animals may exhibit chronic pneumonia and progressive weight loss⁵⁵.

Paratuberculosis

Caused by the bacterium Mycobacterium avium subspecies paratuberculosis, paratuberculosis is an infection characterized by chronic regional inflammation in the small intestine of ruminants. Its most frequent signs in goats are a decrease in body condition and weight, declining milk production, loss of stool consistency and diarrhea (only in the terminal phase)⁵⁹. This bacterium has been associated with Crohn’s disease, a chronic disease leading to inflammation and ulceration of the gastrointestinal tract (mainly in the ileum and colon)⁶⁰, although it is not recognized as the main etiological agent.

In Mexico. Paratuberculosis was first identified in goats in a 1983 study that reported a clear clinical picture of the disease, including intestinal lesions such as enteritis and granulomas in mesenteric lymph nodes, presence of M. avium subsp. paratuberculosis in the injured tissues, and antibodies in blood serum⁶¹. Various reports have since addressed seroprevalence, isolation and detection of M. avium subsp. paratuberculosis genetic material in infected animals in various states in Mexico^59,61,62.