Trends in goat research, a review

Abstract

The present review covers the main topics related to goats for the last two years. The main topics were pathology, reproduction, milk and cheese production and quality, production systems, nutrition, hair production, drugs knowledge and meat production. Especially energy use by goats in different conditions and the role of somatic cell count in intramammary infections and milk and cheese quality are discussed. Goat research needs progress rapidly to reach the level of knowledge of other species like cattle or sheep, especially in milk and meat production.

Keywords:

• goat
• research
• milk
• meat
• hair

1. Introduction

The number of goats is increasing worldwide and they are becoming increasingly important around the world for a variety of reasons. Basically, there are two major production systems, although hundreds of different variations exist. Meat production is the most extended system and usually is in combination with land management (pastoralism) in developing countries. On the other hand, milk (cheese) production occurs in developed countries and usually is dependent on feedstuff. The aim of this article is to review the recent interests of researchers in this field throughout the world.

2. Pathology

Goats, especially dairy goats, are animals under stress. Thus diseases and syndromes related to stress have been discussed in the literature. Corbera et al. (2009) reported a case of transient tracheal collapse associated with bronchopneumonia in a three-week-old goat, but the pathogenesis remains unclear. The same research group (Vilar et al. 2010) observed a case of dystocia and mummification of a co-twin foetus in a nine-year-old pregnant Spanish ibex (Capra pyrenaica hispanica) that was a direct result of capture procedures. In reference to infectious diseases, Tripathi and Stevenson (2010) focused on Mycobacterium avium subspecies paratuberculosis. These authors studied the genetic relationship between cow and goat strains in India related to European strains.

Nowadays, the relationship between nutrition and pathology plays a central role in the goat research trends. Celaya et al. (2010) observed how the inclusion of heather (Calluna vulgaris, Erica spp.) and/or oats (Avena sativa) affects the parasite resistance and performance in goats. These authors conclude that the combination of both supplements contributes to reduced gastrointestinal nematode parasitism and increases goat performance.

3. Reproduction

Control of the goat reproductive cycle is an important research field nowadays. The use of hormones will be not allowed in the future in Europe and new drugs are being tested. Dutt et al. (2010) tried to use a combination of Murraya koenigii and Aegle marmelos on resumption of fertility in anoestrous goats, with promising results. In the same field, Valencia et al. (2010) investigated the effect of male exposure on luteolytic activity, concluding that during the reproductive season, the introduction of the buck to a group of cyclic goats does not exert a luteolytic effect and consequently does not anticipate the next oestrus. Zarazaga et al. (2010) observed the melatonin concentrations in the two jugular veins and the relationship with the seasonal reproductive activity in goats. The authors concluded that melatonin is highly variable between jugular veins in the same individual and absolute and relative amplitudes of melatonin concentrations are not linked to the seasonal breeding activity in Mediterranean goats.

In trying to understand how goat reproduction is controlled, genomics plays an important role. Thus, Wang et al. (2010) cloned the cDNA encoding the hnRNP K gene in goats. The hnRNP K gene expressions were detected in the uterus, ovary, mammary gland, kidney and muscle, but not in the heart, pituitary and thalamencephalon. This indicates that the hnRNP K gene was mainly expressed in the urogenital system and may influence the reproductive ability of goats.

4. Milk and cheese production and quality

Milk production is a subject of special interest in developing countries; breeds from abroad are being imported and the milk production is studied in tropical and subtropical conditions. Thus, Gaddour et al. (2009) use the gamma function to fit the lactation curve of local goat pure breeds and crosses under southern Tunisian conditions. Similar research has been carried out in well-known breeds like Murciano-Granadina (Menendez-Buxadera et al. 2010). New strategies are being developed to increase milk production without the use of hormones. Veliz et al. (2009) used photoperiod manipulation and observed that increased post-partum photoperiod during winter months in northern Mexico substantially increased milk production in Saanen goats, which might constitute a management strategy for dairy goat producers to increase milk yield in Mexico. Mastitis is always a hot topic due to the milk yield reduction produced by intramammary infections (IMI). Goat research in this area is especially important due to different somatic cell count (SCC) biological behaviour in this specie. Koop et al. (2010b) investigated the relationship between IMI and milk yield, observing that milk yield losses caused by sub-clinical udder infections are limited in goats, and that SCC cannot be used to estimate the magnitude of these losses. McDougall et al. (2010) observed similar non-definitive results by the use of CMT California Mastitis Test in goats and the relationship between SCC and mastitis. Working in the same field, Koop et al. (2010a) investigated the relationship between standard plate count, coliform count, Staphylococcus aureus presence, SCC and total bacteria count (BactoScan) in bulk tank milk. The staphylococcal count was correlated to SCC (r=0.40), total bacteria count (r=0.51) and standard plate count (r=0.53). Barth et al. (2010) investigated the evolution of SCC, lactoferrin and NAGase in the milk of infected and non-infected udders of dairy goats, observing that experimental results supported the approach to monitor mastitis in goats by means of Lf or NAGase instead of SCC. Looking for new biomarkers for mastitis in goats, Tangorra et al. (2010) tried to use milk electrical conductivity to evidence the mastitis status in dairy goats, observing that the average of the 20 highest electrical conductivity half udder values recorded within milking in early lactation and the highest half udder 20 value within goat and milking in mid-lactation could be potentially used in monitoring udder health of dairy goats.

With milk synthesis still being a hot topic in goat milk production, huge differences have been found between cow (where the knowledge is greater) and goats. Ben Chedly et al. (2010) studied how the disruption of cell junctions induces apoptosis and reduces synthetic activity in the lactating goat mammary gland, concluding that these experiments suggest that disruption of mammary epithelium integrity was associated with both reduced synthetic activity and apoptosis induction in the mammary gland at the transcriptional level. Cebo et al. (2010) investigated the major proteins of the goat milk fat globule membrane, observing huge differences with cow milk and in their opinion their observations strongly support the existence of a singular secretion mode previously hypothesised in the goat.

The goat cheese sector is developing and the fat-free philosophy in the current society is influencing the goat sector. Sánchez-Mácías et al. (2010b) investigated the physicochemical properties of full-fat, reduced-fat and low-fat artisan-style goat cheese. These authors concluded that as fat was reduced in milk, cheese yield decreased and protein and moisture percentages increased in cheese. Ripened (for 28 days) low-fat cheese displays higher fracturability, hardness, cohesiveness and masticability values than full fat cheese, and was also less elastic and yellow than full fat cheeses. Using the sensorial approach will improve the knowledge of these kinds of cheeses. The influence of SCC on goat cheese quality is a hot topic. Much is known about ewe and cow cheese, but not much information is available on goats. Thus, Chen et al. (2010) observed how SCC affects the yield, sensory quality and fatty acid profile of semi-soft cheese, concluding that SCC in goat milk did not affect the yield of semi-soft cheese but did result in inferior sensory quality of aged cheeses. New devices for SCC measure like DCC from DeLaval have been presented and tested by Sánchez-Macías et al. (2010a), observing the effects of storage temperatures on the SCC in goat milk. Big efforts have been made by scientists to describe, in depth, the local products. Serhan et al. (2010) describe the changes during ripening in a Lebanese cheese to protect the product through knowledge.

New tools, such as genomics and proteomics, are being used in goat milk production. Zidi et al. (2010) studied the relationship between the stearoyl-CoA desaturase 1 gene and milk fatty acid composition in Murciano-Granadina goats, observing an association between the two, which might be explained by the global effects that stearoyl-CoA desaturase 1 exerts on mammary gland lipid metabolism through the down-modulation of key transcription factors. Safayi et al. (2010a) studied, using genomic tools, the mammary remodelling in primiparous and multiparous dairy goats during lactation. These authors observed differences in genes between primiparous and multiparous goats, but it was not possible to identify any specific genomic factor(s) that could account for the differences between primiparous and multiparous goats with respect to mammary development and mammary epithelial cells. The same research group investigated the effect of continuous lactation on mammary remodelling during the late gestation and lactation, reporting that the continuously lactating gland resembled a normally lactating gland in an advanced stage of lactation (Safayi et al. 2010b). The relationship (genetic and environmental) between milk yield and kidding interval was investigated by Montaldo et al. (2010), who summarised that the presence of unfavourable genetic relationships between milk yield and kidding interval indicates a need to include reproductive performance as a selection criterion in dairy goats.

Milking frequency repercussions on mammary gland biology have been studied by Bequette and Douglass (2010). These authors studied how the frequency of unilateral milking altered leucine metabolism and amino acid removal by the mammary gland in lactating goats, concluding that the manipulation of milk protein output by altering milking frequency was associated with long-term, local (gland-specific) regulation of mammary blood flow.

The measurement of the composition of goat milk composition is currently under study because scientists are looking for newer, easier and cheaper methods to measure this. In this vein, Rukke et al. (2010) compared different calibration methods for determination of protein using ultraviolet spectroscopy.

5. Production systems

The study of production systems has been a hot topic during the last 50 years, but nowadays the study of production systems in developing countries has captured the interest of researchers worldwide. A good example of this situation is the Najari and Gaddour study (2010), where the goat productivity was evaluated in two different production systems: pastoral and oases systems.

Morphometry is still a useful tool for animal science. Yakubu et al. (2010) use multivariate analysis to observe distribution differences in three agro-ecological zones in Nigeria. The authors observed relatively low morphometric distances as well as intermingling between the three goat populations, indicating that they are homogenous and share similar genetic identities. These findings could aid to understand which are the necessities relative to their conservation and formulation of appropriate breeding and selection strategies. To describe new breeds in developed countries is an important topic due to the pressure of selected breeds on local breeds being really high. Martini et al. (2010) carried out a complete zootechnical study of Garfagnina goats in Italy whose milk could be potentially used for human with special requirements.

The Animal Science group from Universidad Autónoma de Barcelona is still working on electronic identification. Carné et al. (2010) compare different systems (electronic leg tags, rumen boluses and electronic ear tags) in dairy goats, observing that electronic leg tags were not adequate for the identification of goat kids under six months of age. The same group in combination with Animal Science group of Universidad de Las Palmas studied the possibility of using mini-boluses for early identification of goat kids with promising results (Castro et al. 2010).

6. Nutrition

Big efforts have been developed to understand the rumen physiology and environment. Thus, Wang et al. (2009) investigated the crude protein and starch degradation in goat rumen in different feedstuffs. Modern nutrition is the basis for improving goat production in developing countries using their own feedstuff or feed resources and is usually poorly studied by developing countries. Lopez et al. (2010) study the relationship between the physical forms of alfalfa on methane production in Murciano-Granadina goats, observing differences between long or chopped alfalfa and differences in the combination with corn or barley. This is one of the major nutrition research topics for the future.

Energy expenditure has been an important topic for the last few years. The E Kika de la Garza group (Beker et al. 2009) have greatly improved the study of the energy expenditure of goats in pasture by studying how it is influenced by stocking rate (SR), breed and stage of production. The same research group (Beker et al. 2010) completed the energy studies by observing the activity energy cost for different types of goats as well as a breed of sheep. More research is necessary to understand how goats in different environments and production systems use the energy. Tovar-Luna et al. (2010a) study the effects of stage of lactation and dietary concentrate level on energy utilisation by Alpine dairy goats, concluding that despite differences in nutrient requirement expressions, observations of this study supported National Research Council recommendations of the energy requirements of lactating dairy goats. Tovar-Luna et al. (2010b) studied the combined effects of stage of lactation and level of feed intake on energy utilisation by Alpine dairy goats, concluding that the level of feed intake can have substantial effect on estimates of energy utilisation by lactating dairy goats.

Nutrition in the last few years has been focused on the search for new vegetal species to feed goats. Alamer (2009) reports the use of Foeniculum vulgare Mill in dairy goats, using Rhodes grass diets as a control, with no differences between diets for milk yield, milk production efficiency, milk composition and feed intake. Other authors (Kamalak et al. 2010) investigated the use of young, old and senescent leaves of Arbutus andrachne, concluding that the A. andrachne tree could be considered moderate quality forage for sheep and goats. However, senescent leaves are only low-quality forage. In the same way, Ben Salem et al. (2010) discussed the use of Atriplex nummularia to feed goat and sheep.

New strategies of goat nutrition have been implemented. Molina-Alcaide et al. (2010) studied the effects of partial replacement of concentrate with feed blocks on nutrient utilisation, microbial N flow, and milk yield and composition in goats, observing good results when feed blocks were used but reduced milk yield. The philosophy ‘from farm to fork’ can be applied to the goat sector nowadays. Pereira et al. (2010) tried to modify milk quality by adding castor or licuri oil to the goats’ diet. Observing the sensory analysis results, a low acceptability was observed for milk from goats supplemented with castor oil, but licuri oil supplementation led to higher acceptability scores for flavour and odour of goat milk.

Betaine has played an important role in goat milk production in the last few years. Trying to understand the role of oral betaine in goat milk production, Fernandez et al. (2009) used two groups of 30 goats to determine the effects of added betaine, but no significant differences between groups were observed for milk yield, chemical composition and somatic cells count in milk. Betaine-supplemented diets increased relatively the proportions of short chain fatty acids.

The relationship between nutrition and physiology has also played an important role in the last few years. Thus, Schonhusen et al. (2010) studied the morphology, the proliferation and ribonucleic acid and fractional protein syntheses in the small intestinal mucosa of young goats fed on soy protein-based diets with or without amino acid supplementation, concluding that soy protein feeding resulted in changes in intestinal growth associated with effects on intestinal RNA and protein synthesis, but that were not ameliorated by amino acid supplementation.

7. Hair production

Although hair (cashmere) production is a minor production in the goat sector, in some regions it is of great importance. The Lan et al. (2009) study provided evidence that supports the influence of the insulin growth factor binding protein-3 (IGFBP-3) gene on cashmere yield, which might be at least partially dependent on age and circulating levels of prolactin in Inner Mongolia White cashmere goats.

8. Drugs knowledge

Nowadays, new knowledge in drugs is coming in goat science. Verma et al. (2009) reported the pharmacokinetics of florfenicol using intravenous and intramuscular administration. Antibiotic presence in milk is becoming an important research topic because antibiotic resistance in humans is increasing. Comunian et al. (2010) investigated the use of Delvotest Accelerator in goat and ewe milk. The main results consisted of very low percentages of false positive and no interactions with the lactation phase were observed. Goat milk displayed a higher detection ability than ewe milk. The pharmokinetics of Difloxacin were studied by Marin et al. (2010), especially the milk excretion, observing that a 15 mg/kg dose of difloxacin would appear to be effective against S. aureus isolated from mastitic goats’ milk with minimum inhibitory concentrations ≤0.25 mg/L.

9. Meat production

In developing countries goat meat production is very important and scientists are currently trying to adjust the predictive method to their local breeds. Najari et al. (2010) studied the best adjustment for goat kid growth for local breeds in Tunisia. Crossbreeding is an important tool to adapt meat production in different environments. Khalil et al. (2010) studied the growth, carcass and meat composition traits in crossing animals from Saudi Arabia with Damascus goats. The main results were that heterosis estimates obtained in this experiment are of considerable importance, particularly for growth and carcass components, while those estimates related to meat quality traits were of little importance.