Livestock is one of the major sectors of Pakistan’s agrarian based economy. During 2013-14, it contributed almost 55.4% to the agricultural value added and 11.9% to national GDP. In the livestock sector, gross value addition increased from Rs.735 billion to Rs.756 billion; revealing an increase of 2.9% as compared to the previous year. Livestock is considered the best tool for poverty alleviation, as most of the livestock are owned by poor people who live in the rural areas. Pakistan is 4th largest Milk producing country in the World. Its Cattle Population is 33 Million while Buffalo Population is about 30 Million (Economic Survey of Pakistan, 2013-14). Despite large population, per animal production is very low.The low productivity of these animals is because of poor quality feed stuff. Their productivity can be enhanced by feeding them balanced ration.
Growing human population urges the intense need to explore the present livestock resources to fulfill the animal protein requirements. It is impossible unless optimal fodder and forage production is ensured. In Pakistan, low quality fodders coupled with the reduction in the fodder area are the main constraints, which adversely affect the animal production. In future, it is expected that ruminants will be more dependent on forages because readily expanding human population will have direct competition with livestock for edible grains.
Among the problems facing the livestock in the tropics is the low protein tropical grasses and the high cost of alternate sources of protein such as the Soybean and other oil cake. A portion of nitrogen in feeds for ruminants may be provided in the form of simple nitrogen compounds (or0non-protein0nitrogen0NPN) 0that are degraded in the0rumen to release ammonia (NH3), which is used by rumen microorganisms to produce amino acids. The amount of NPN that can be provided is limited. The product which is the urea, when it releases NH3 faster than it can be converted into microbial protein excess NH3is absorbed through the rumen wall, causing toxication.
Protein is often0the0major0limiting0nutrient for ruminants. Protein-rich leguminous forages and vegetable protein supplements are usually expensive or not available.The manufacture0of0urea and0ammonia for use as0fertilizer has been greatly0expanded in0many countries, 0but these compounds0could0not be0used more0widely in feeds for0ruminants. The ability0of0the0micro-organisms0in0the0rumen0of0cattle0and0sheep0to0utilize0urea0sources0to form0true protein0that0can0be converted0to meat0and0milk0by the0animals, represents0an important0contribution0to0man's0food0supply.0Maximizing0microbial0protein0synthesis0and flow0to0the0duodenum0by0reducing the0recycling of0microbial N in the rumen offers a potential0to improve0the production0efficiency0of ruminants.In general, the efficiency of utilization of dietary N by cattle is relatively low under normal production conditions (Castillo et al, 2001) with a global average N-efficiency in cattle estimated at 7.7 % (Van der Hoek, 1998). Urea is used rather inefficiently for production of protein products (Broderick et al, 2009) and due to its wide use in ruminant feeds, may0be0partially0responsible for0the poor N efficiency0in cattle. Low efficiency of utilization of dietary urea has been attributed to the rapid0hydrolysis0to0ammonia (NH3) in0the0rumen0by microbial0enzymes which occurs at a higher rate than its utilization byrumen bacteria, leading to ruminal accumulation and absorption0of0ammonia andsubsequent excretion of0urea in the urine (Golombeski0et0al., 2006; Highstreet0et0al,2010).Furthermore if used above threshold level, the main problem with urea usage is that it can cause toxicity and even death of the animals. Farmers hesitate to use urea as a source of protein, resulting which his animals remain underfed and never achieve the peak production.
Urea0poisoning0is0one0of0the0more0commonly0suspected0toxicities0of0cattle. Urea0is0used as0a source0of non-protein0nitrogen0in feed0supplements.In ruminants,0nitrogen0from0urea is released0in the0rumen as0ammonia0and0can0be0used0by0rumen0micro0flora0to0synthesize protein. This0protein0thenbecomesavailable0to0the0animal0through0the0normal0processes of digestion0and0absorption. However,if0 more0ureaisconsumed0than the rumen organisms can0metabolize, the0ammonia0is0absorbed0from0the0rumen0into0the0blood.Ruminal pHbecame alkaline due to the hydrolysis of urea to0ammonia (Buffalo Bulletin,2002). The ammoniaisthen0converted0back0to urea in0the liver and is0the0excreted by0the0kidneys. This0pathwaycan easily be0overwhelmed,0when excess0ammonia0and urea0circulate0in the blood,0causing0poisoning. Poisoningcanoccur0rapidly0from a few0minutes0to four0hours after0consumption. Suspect0urea0poisoning0if cattle are found0dead close to0the0supplement (H. Parkes et al. 2003).Slow release urea has been shown to affect ruminal fermentation characteristics.Most notably, slow release urea is intended to0reduce0the release rate0of NH3 within the0rumen. Most reports on controlled release urea have shown a reduction in ruminal NH3 concentration when measured (Cherdthonget al, 2011; Huntington etal, 2006b; Taylor- Edwards0et0al, 2009d). This is the reason why slow release urea presents a lower risk for ammonia toxicity than feed grade urea. Ruminal NH3 concentration is often related to ruminal pH, as the protonation of NH3 toNH4+ when ammonia from urea ionizes, can result in an increase in ruminalpH. Consequently, there are reports of higher ruminal pH for animals fed urea than those fed slow release urea (Cherdthongetal, 2011; Taylor-Edwards et al, 2009b)