Introduction
Goats change their feeding behavior according to the availability of forages and concentrates and they are more versatile than other domestic. For these reasons, goats can adapt to different conditions, ranging from desert to grassland.
The mouth of feeders is similar to that of wild intermediate feeders, so they are efficient at picking their food, since the upper lip is mobile and this help the tongue activity. Daily ruminal activity of goat is intermediate between that of wild selective ruminants, which have a simpler rumen and ruminate frequently, and grass eaters, which spend less time feeding (Van Soest, 1994).
Goats have a greater ability to reduce feed particles size chewing in comparison with sheep indeed a comparative study showed that the total number of ingestive jaw movements (eating) did not differ between species but goats had finer particles size in their ingestive boli than sheep (Hadjigeogiou et al 2003).
The chewing activity involves a reduction of feed particle size and consequently an increase in the surface area for rumen microbial attack in the rumen of goats, there is often high ammonia concentration even when diets in proteins are used. This may be due to (i) no water intake which limits ammonia dilution and (ii). Good efficiency n recycling urea from the blood to the rumen due to the high permeability of rumen epithelium to urea. The amount of recycled urea varies from 0.4 to 9.7 gram per day depending on N intake and animal physiological status and can provide 20% of the rumen degradable protein requirements of goats (Brun- Bellut et al 1991).
Goats feeding activity is highly selective. Goats when gazing grassland prefer plant with high dry mater (DM) and protein content and when fed in manger are able to be very selective, tasting the feed and choosing first the most palatable parts in particular, goats have a preference for concentrates. Thus decreasing forages intake when concentrates are available and showing great ability in avoiding rumen acidosis (Abijaoude et al 2000).
It is well known that goats have a great capacity to utilize the fiber components of diets. When fed low quality diets (high in fiber and low in protein content) they have high DM intake and fiber digestibility than sheep (Domingue et al 1991). The difference in the digestive capacity goats and sheep narrow when diets are characterized by high content of good quality forage and good nutrient balance.
In conclusion when considering the goat as an intermediate feeder, goats (i) are good selective feeder, (ii) have an efficient chewing and rumen activity, (iii) are able to efficiently utilize diets rich in fiber but also diets rich in concentrates and starch, being quiet resistant to rumen acidosis and (iv) can tolerate low water intake. In addition goats can adopt to either poor pastures or rich and balanced diets. For these reason goats can be reared not only in extensive systems but also in intensive farm systems where usually specialized dairy goat’s breeds and utilized.
All of these characteristics of goats should be taken in consideration when formulating diets goats should not be considered as small cattle.
Feeding strategies
The choice among the different feeding strategies for goats in intensive farms is based on flock size and level of intensification of the farm. It is necessary to reach a compromised between managerial choices and nutrient requirements of goats for example utilization of a total mixed ration (TMR) can be the best choice to satisfy to the nutrient requirements of highly productive flaks. However it can be too expensive for small and medium sized farm especially due to the high cost of the TMR mixer.
The aim of the different feeding systems for goats is to satisfy nutrient requirement and consequently to guarantee good health reproduction and production of the animal. However in order to achieve that many problem have to be solved especially regarding feed supply techniques considering the economic and managerial aspects. To different situation are discussed: (i) where goat’s diets are composed of hay and concentrates and (ii) large farms where the feeding system is based on a TMR.
Traditional Feeding Systems
In this case the techniques and the timing use to supply hay silages and concentrates and the quality of the leads have a fundamental effect on the response of the animal. In this system it is the common that concentrate and raw material come from the market while hay and silage and normally produced on the farm in many cases, it is possible that the nutrient composition of concentrates does not complement that of hay properly. As a consequence the final ration does not fully satisfy the nutrient requirements of goats. Since the animal feed industry offers different types of concentrates especially with different crude protein (CP) contents, it is not difficult to choose proper feedstuffs for the farm but it is important to adopt the protein content of the ration to the protein requirements of goats. If the N content of the ration is too high milk urea and urine N content increase without increasing mil protein as demonstrated by Bava et al (2001) and Arieli et al (2005).
Hay should be fed before concentrate in order to avoid and excessive decrease of rumen PH, due to fast rumen degradability of non-fiber carbohydrates (NFC) of the concentrates. More ever it is better to offer small daily meals of concentrates to avoid a drop in PH especially when low quality forages are offered and when high doses of concentrate need to be given to achieve high milk production. It is advisable to use concentrate as pellets. In order to avoid selection and pulmonary disease caused by dust that can occur when the particle size of the feed stuffs is too small, it could be useful to include in the diet a pellet formulated for protein mineral and vitamin supplementation and maize as an energy source to reduce the cost of the ration. Maize as reported below can be given as whole grain without detrimental effect on DM digestibility.
Among the forages, the utilization of Lucerne as hay are pellets is very common in temperate area. This forage is characterized by higher protein content (more than 16% CP on a DM basis) and lower neutral detergent fiber (NDF) concentration than permanent pasture hay. Moreover it has a high content of soluble fiber with high degradability which together with its low NDF content has a positive effect on rumen fill and DM intake. For all these reason Lucerne is considered a valuable forage for feeding goats.
Total Mixed Rations
The well-known advantage of TMRs are that (i) all ingredients are weighted and mixed together, (ii) the rations can be easily balanced to cover the nutrient requirement of the flock and actual intake and refusals can be easily monitored: (iii) the composition of the rations tends to be constant in time and (iv) selection by the animals and dustiness are reduced when silages or wet raw material are included. In the case of TMRs made only of dry ingredients, water could be added to avoid the dustiness. If the rations is not prepared every day, water can be replaced by molasses, useful for palatability and also to increase the sugar content of the diet without increasing excessively, the humidity and guaranteeing an optimal conservation of the TMRs.
Complete diets ensure that goats receive the proper proportion of carbohydrates and N at each meal (Giger-Reverdin and Sauvant, 1991). More ever, the TMR masks unpalatable feeds, such as certain by-products, it is easily managed and its preparation can be completely mechanized.
Maltz et al (1991) reported that a TMR feeding system was superior to feeding the different dietary ingredients separately in terms of daily milk yield, milk fat and milk protein content, and feed conversion ratio of dairy goats.
Finally, a TMR can improve rumen function, due to the advantages associated with simultaneous feeding of roughage and concentrate. In fact, when TMR and tradional diets were compared, Saanen Lactating goats fed TMR had higher rumen acetate/propionate ratio than animals fed traditional forage plus concentrate diets (acetate/propionate ratio % 3.5 versus 2.7, respectively). More ever, ruminal PH was significantly higher for the TMR diet than for the tradional one in the sampling performed before feeding and too 2 and 5h after feeding % 6.67, 6.5, 6.55 versus 6.32, 5.98, 5.95 for TMR and traditional diet, respectively (Rapetti, unpublished data).
The use of a TMR system normally requires high investments for mixer wagon and distribution equipment (e.g. tractor, silos and feed driveway). These investments are justified only on large farms where many goats are reared.
Usually the principle ingredient of TMR is silage, for both cattle and goat rations.
When the TMR is a mixture of dry ingredients without silages, it can be purchased directly from the market or prepared by the farmer. The TMRs available on the market might be convenient for farms where not enough forages can be cultivated. The use of commercial TMRs can encourage the implementation of this advantages feeding system without requiring high additional investments in machinery, labour and so on. However, the disadvantage is the high and variable price of TMR diets purchased directly from the market.
With the use of dry TMRs, special attention must be paid to the particle size of the feeds used, especially for hay. Goats are able to select large particles (grain, pallets and forages) and less- small particles (dust, meals and broken pallets), in particular when the diet offered is abundant (Fernandez and Sanchez-Seiquer, 2003).
Roughages for Dairy Goats in Intensive Systems
Like all ruminants, the goat is primarily a forage consumer. Forage are the principal source of fiber but they might not completely satisfy the nutrient requirement of high producing lacting goats. Many authors have indicated that high quality forage could satisfy the needs for production 2.5-3 Kg of daily milk yield. To support mil yield over 3 kg per day it is necessary to compliment a forage based diet with proper amount of concentrates (Massen et al 1991) mainly to cover energy requirements but also protein mineral and vita min requirements.
The forage per concentration rations an important factor when balancing diets. Diets with the following forage per concentrate ratio were fed ad libitum in a Latin square design: 70:30 (F70), 50:50 (F50), 30:70 (F30), permanent pasture hay was produced on the farm while concentrate was purchased from the market. Dieting NDF concentration 41.5, 47.9 and 54.4 % on a DM basis for the diets F30, F50 and F70 respectively. The DM intake of the high concentrate diet (F30) was about 11 and 21% higher than that of F50 and F70 diets respectively. The high intake of concentrate increased milk production but did not reduce milk fat content. These data confirm that goats are less sensitive than cows to diet with low fiber in term of milk fat depression (Calderon et al 1984). These results are also in agreement with those of Sauvant et al 1987 who concluded that for diets with forage per concentrate ratio 20:80, the goats nutritional energy status is a more important factor than the relative proportion of the forage in the ration. It is important to highlight that the milk fat per protein ratio was lower than 1 for all tested diets. This was probably due to the genetic characteristic of the goats used and the climatic conditions (beginning of the summer) during the trial characterized by the high temperature and high humidity which decreased milk fat production. The renneting properties of the milk and curd firmness were not significantly affected by the forage per concentrate ration of the diet.
Milk efficiency of the diets expressed as the ratio of milk yield to DM intake was highest for the F50 diet (1.40) and similar between F70 and F30 diets (1.37) and 1.38 respectively. The milk efficiency of the F70 diet was mainly due to the low concentration of this diet while that of the F30 diet was due to the conversion of part of the metabolizable energy into body fat instead of milk as resulted from the energy balances determined by means of indirect calorimetry. Fed diet with increasing amount of concentrates (from 20 to 65% of concentrates) had high milk yields when fed a diet with 50% concentrates.
Based on the results of both trials reported above (reported et al 1997: Goetsch et al 2001), It is possible to conclude that in mid-late lactation diets too rich in concentrates may not influence milk production positively and may also cause an excessive fattening of dairy goats. With the risk of metabolic disorder during the transition period. Therefore since it is important to monitor body fatting during productive and reproductive stages of the animals, the evolution of body condition score should be more often practiced in goat farms.
The quality of forages is very important in intensive systems and should be carefully evaluated especially. When they are purchased from the market. If forage quality is poor a large amount of concentrate needs to be supplied in the diet this increases not only feeding costs but also the risk of metabolic disorders.
The importance of forage quality in intensive feeding system was studied in a trial in which maize silage and Italian ryegrass silage were compared in lactating Saanen goats (Crovetto et al 1994) intake of ryegrass silage was lower than fiber digestibility of ryegrass silage was higher than that of maize silage, its nutritive value was high. As a consequence the two diets caused similar effect on milk production. Also autumn-winter serials silage could be good products for dairy goats because of their high productivity in terms of quantity and quality. It is important to remember that the correct stage to harvest whole crop silage is when the grain has reached its full size and weight, but before it becomes hard, and this coincides with dough and milk dough stages ( D Urso et al 1989). At these stages the DM of plants is greater than 30% by contrast if the DM is lower than 30% the forage needs to be pre-wilted before ensiling.
Importance of feed physical form
The physical form of dietary particles is very important for the digestive function of ruminants because it influences, (i) chewing activity and salivary production, (ii) rumen microbial activity, (iii) together with particle density rumen feed passage rate and (iv) milk production and milk fat percentage.
Fiber sources like roughage grains are vegetable byproducts influence the particle sizr of the diet. To underline the importance of fiber function some authors have define the effectiveness of a dietary fibers source as the ability to stimulate chewing activity and to maintain milk fat percentage and fat corrected milk production (Grant 1997).
Particle size is defined by the length and diameter of particles. Length plays a role in rumination and feed intake. Welch (1982) demonstrated that particles that were too long did not pass from the rumen and reduced hay intake permanently. By contrast finally grown forage particles from hay are silage decreased rumination time and ruminal PH and increased ruminal propionate production (Grant et al 1990). Due to reduction of chewing activity (Kuehn et al 1997, Andrighetto et al 1998).
Particle size can be measured by either dry-sieving are wet-sieving (sieving associated with water sprayed on the sieves) through calibrated screens arranged by decreasing mesh size (screen size) from top to bottom. Wet-sieving tends to sort particles according to length while the dry method tends to salt them according to cross sectional diameter. Since the rumen is a wet system and due to the fact that soaking the feed in water dissolves most of the finally divided non-cell-wall matter, wet methods of sizing particles in feeds should be favored (Van soest 1994).
Feed particle size can also be measured in vivo by quantifying the chewing activity of the animal with (i) the visual observation method with fixed observation intervals (e.g., at 5 min) and (ii) electronic measurements. The automatic electronic devices utilized a bit recorder that identifies jaw movements eating ruminating swallowing and accessory movements. By using specific software it is than possible to calculate the number of chees, the total time for each activity (eating and rumination), the number of boli, the number of remastications per bolus etc. a comparative study between goats and sheep in which chewing activity was measured using electronic equipment showed that goats were more able to reduce long forage particles into smaller particles than sheep. More ever while both species had similar faecal particle size, goats spend less time per day masticating and performed fever chews during both ingestion and rumination than sheep, demonstrating goats to have a more efficient and chewing activity ( Hadjigeorgiou et al 2003).
Unprocessed Cereal Grains and By-Products
Besides roughages particle size is also influenced to a lesser extent by whole grains and vegetable by products defined as non-forage fiber sources by Grant 1997.
Cereal grains are the main source of starch in ruminant diets and can be supplied in different physical forms (i.e. meal rolled flaked expended depending on the mechanical and thermal treatment they receive. The aim of these treatments is to increase rumen microbial degradation rate on the starch present inside the kernels. Which is the main energy source for microbes in cereal grains it is well known that if treated cereal grains are supplied in large amounts, there is an increased risk of rumen acidosis with negative consequences such as (i) growth of lactic bacteria (ii) inhabitation of cellulolytic bacteria (iii) decrease of rumen fiber degradability (iv) reduction of volatile fatty acids production and (v) decrease of milk fat content. Therefore it is an important to regulate the inclusion of treated grains in the diets and moderate the physical treatments.
A good and cheaper alternative could be to include whole grains instead of processed grains in goat rations. Some studies (Nicholson et al 1971, Weston 1974) indicated that cattle utilized whole grains only partially there chewing activity is insufficient to break all kernels so a great amount of them pass into the reticule-rumen unfermented and are found in the faeces as whole grain. However goats and sheep are more able to utilize whole grains compared with cattle (Orskov 1979).
To evaluate the importance of the physical form of grains are digestibility trial was conducted in which lactating Saanen goats were fed either a diet with whole maize grain 800 gram/day per head or a diet containing the same quantity of maize meal (Rapetti and Bava 2004). Starch digestibility was lower for whole grain than for ground grain diets (94.2 versus 97.8%, P<0.05), while DM intake and milk yield were higher for the whole grain diet (2295 versus 2162 gram DM per day p<0.10, and 4570 versus 4075 gram milk per day, p<0.05, for whole grain and meal grain diets respectively). More ever only a few whole kernels were found in the faeces of goats fed whole maize grain probably due to the higher ruminating activity of these goats compared with the group fed the maize meal diet (328 versus 262 min per day p=0.079 Rapetti unpublished data 2003). In addition the decrease of rumen PH observed for H after feeding. In relation to that measured at feeding time was lower for the whole maize (-0.10) than for the maize meal (-0.52) based diets. The NDF digestibility was positively affected by the inclusion of the whole maize (44.8 versus 39.7 % for whole grain and meal diet respectively p<0.10), confirming the result obtained by Orskov and Fraser 1975, in sheep fed supplements made of either whole or processed barley.
Even if in many cases by-products are included in the ration to compliment the supply of energy and protein given by roughages, they often have high fiber concentration. By-products such as sugar beet pulp or soybean hulls have a slightly lower content of digestible energy than cereals but due to the high NDF concentration they positively influence rumen fermentations and PH especially when diets rich in starch are used (Bava 2000). By-products are convenient because they (i) can be easily purchased from the market (ii) are easy to store, move and supply and (iii) generally do not require particular machinery or equipment.
Despite the similarity in NDF concentration forages and By-products provide different amount of effective fiber. In particular by-products have lower particle size than forages and this influences chewing activity. In addition the fiber of certain by-products (beet pulps, soy hulls) has a very high degradation rate (Vansoest 1994). Thus diets with a high proportion of these by-products and low content of forages can be rich in fiber with high degradation rate and of small particle size. This would induce at the same time high passage rates and consequently limited rumination and salivary production. In this regard the literature in dairy cattle show that it is possible to substitute up to 30-40% of total dietary NDF content with NDF from by-products (Beauchemin et al 1991, Grant 1997, Zhu et al 1997).
The utilization of by-products are concentrates rich in fiber in substitution of roughages could be useful also for dairy goats considering the high adoptability of this ruminant species to different diet. This hypothesis was tested our research group on lactating Saanen goats in two experiments (Bava et al 2001, Rapetti et al 2005). In the first experiment, the goats were fed two diets throughout the entire lactation or traditional silage based diet and a non-forage diet. In the second trial goats were fed three diet. Feed particle size was determined with the wet-sieving method. In both trials are chewing activity was measured continuously with an electronic instrument in the 2nd one. The two non-forage diets contained byproducts (Cottonseed expeller, coconut meal, and sugar cane molasses, sugar beet pulp, grape cake skins and palm kernel meal) and whole seeds ( cotton seed and maize grain). In experiment 1 the main particle size of non-forage diet was smaller than that of control diets. Infect only 22% of particle of this diet had diameters greater than 4mm. in 2nd trial the physical effective NDF was lower for the non-forage diet in comparison with the other diet 31.1, 27.1 and 24.8% on DM basis for hay-based diet, fresh grass-based and non-forages diet respectively. Indeed, in this experiment the eating and ruminating activity were not significantly different between the nn-forage diet and forage based diets probably due to the inclusion of whole seed sugar beet pulp and cracked carob beans in the non-forage diet. In the first trial the non-forage diet had a higher DM intake and lower digestibility than the control diet probably due to its high content of fiber sources with small particle size. By contrast in the 2nd study the non-forge diet characterized by a high NFC concentration had a lower DM intake but higher digestibility than the hay based diet.
In the first trial milk fat content was significantly higher for the non-forage diet (4.21%) than for the forage diet (3.63%), (average for the whole lactation), while milk yield was not significantly influenced by treatments (3548 versus 3357 gram per day for forage and non-forage diet respectively). In this case the high milk fat concentration of the non-forage diet could partially be explained by its higher dietary fat concentration. By contrast in the 2nd experiment the milk fat content was lower for the non-forage than for the grass based diet with the hay based diet having intermediate value. The result obtained in these experiments suggest that in ration for high producing lactating goats part of forage fiber can be substituted with by-products fiber with negative effect on chewing and rumen activity and milk yield. These data are in agreement with those reported by other authors (Sanz Sampelayo et al 1998). In conclusion when choosing forage substitute for goats diets there particle size should be large enough to stimulate chewing activity and their acid detergent fiber and acid detergent lignin dietary contents should not be excessively high in order to avoid negative effect on diet digestibility.
Nitrogen Feeding of Dairy Goats
Nitrogen metabolism in ruminants is different from that of other mammals, because of the essential contribution of ruminal microbes. In fact, microbial synthesis in the rumen provides most protein supplied to the small intestine of ruminants, according for more than 50% of the total metabolizable protein supply. More ever, microbial protein are the main source of limiting essential amino acids, such as lysine and methionine, for the animal. The total amount of microbial protein flowing to the small intestine depends on the availability and efficiency of use of nutrients by ruminal bacteria (Bach et al 2005). Rumen N availability depends on the degradation rate of protein, while the efficiency of use of N by bacteria depends on energy availability. If sufficient energy is available in the rumen, amino acids (derived from protein degradation) can be transaminated or used directly for microbial synthesis is largely affected by the supply of adequate amounts of rumen-fermentable carbohydrates to be used as an energy source. However, an excessive amount of carbohydrates in the diet can decrease rumen PH and negatively affect the growth of cellulolytic bacteria dietary DM intake and milk production.
In highly producing ruminants, microbial protein can cover only part of the amino acids and requirements. For the reason, as milk yield increase, it is necessary yo increase the intestine supply of amino acids from rumen-un degradable protein (RUP).
However, increasing the supply of RUP does not assure an increase in animal performance, because it will be highly affected by the concentration, type and digestibility of the essential amino acids supplied by the RUP source.
Many studies have described the effects of the substitution of soybean meal with high-RUP sources, such as heat and chemically treated soybean meal maize gluten meal, distiller’s grains and brewer’s grains, on the production of milk by dairy cows, as summarized by Santos et al (1998). Their reviews showed that milk yield of RUP-rich diets was significantly higher than that of soybean meal-based diet is only 17% of the comparison. Positive effects of RUP on milk yield were obtained mostly using fishmeal and treated soybean meal.
The increase of RUP content of the diet might not have positive effects on milk yield in goats either, as demonstrated by some researchers (Burn-Bellut et al 1990; Lu et al 1990) who used meal or bone meal as RUP sources. Similar results were registered in another experiment, carried out on Saanen goats in mild lactation (97 days of milk on average), with two diets with different RUP content (35 and 40% of CP), obtained with a partial substitution of soybean meal with treated canola meal. Milk yield (average 3454g/day), milk CP (average 2.97%) and casein N (average 72.8% of total N) content did not differ between the two diets (Rapetti, unpublished data).
Information regarding the amino acids requirements of dairy goats in scarce. Semptey (1996), cited by Rousselot (1997), suggested including 2.2% of digestible methionine and 6.8% of digestible lysine, on the basis of total digestible protein (PDI), in the diets of goats. These values are lower than those reported for cows (2.5 and 7.3% for digestible methionine and lysine respectively) (Rulquin et al 1993).
To reach high levels of digestible methionine and lysine in the diets for goats in most cases it would be necessary to include rumen protected amino acids. However the addition of ruminal protected amino acids does not guarantee positive effect as observed in a specific experiment in which the addition of rumen protected lysine and methionine did not influence milk yield and equality of Saanen goats (Rapetti et al 1999). A possible explanation of these results could be related to the fact that mammary uptake of lysine and methionine seem to be effected not only by supply but also by mammary synthetic capacity, since mammary tissue is capable of extracting these amino acids according to its needs independently of arterial supply (Madsen et al 2005).
Conclusion
Goats can easily adopt to intensive feeding system. They can tolerate high amounts of concentrates rich in starch but also diets with high amount of forage due to their efficiency in chewing and selecting the feeds of the diet. In intensive feeding system, TMR are advantages to balance nutrient supply and to reduce feed selection. More ever goats are able to eat and efficiency utilize diets without forages as long as the particle size of ration and its fiber level are carefully balanced.
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————————————————————————————————————————————– Author: Ali Hassan Shabbir
MSc (Hons) Agricultural Economics, Institute of Agricultural and Resource Economics,
University of Agricultural Faisalabad, Pakistan.
Email: [email protected]
