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Title: Utilization of tropical pasture by beef cattle : the Cornell Net Carbohydrate and Protein System (CNCPS) and in situ mineral release in the rumen 
Author: Buck, Kevin
Date: 2007
Abstract: Feed costs comprise the majority of the total production costs born by livestock producers, particularly cattle. Because the relative costs of feed are so great, a dramatic economic impact can be realized by utilizing the cheapest feeds available in the most efficient manner possible. In order to make efficient use of a feed, however, it is necessary for the producer to be able to predict how an animal or group of animals will respond to a given feed or mixed ration. A common method fur predicting this response is the use of computer models. Computer models meant to predict animal performance have been around fur some time, particularly fur cattle. Currently, these models are an integral component of most operations, in both temperate and tropical regions. However, these models have not been validated fur beef production in many tropical regions. Poor production by cattle in tropical regions, even in developed countries, bas been well-documented (Minson and Mcleod, 1970; Stobbs, 1971). Tropical regions differ from temperate regions in that the forages present are often lower in protein and higher in fiber, due to the higher solar intensity and faster growth rate. Also, nutrients in tropical grasses may not be as available to the animal as the same nutrients in temperate grasses, as the higher fiber concentration may bind more of the nutrients. The Cornell Net Carbohydrate and Protein System (CNCPS) is a mechanistic, deterministic, and static model based on the principles of rumen function, microbial growth, feed digestion and passage and animal physiology that was developed to predict requirements, feed utilization and nutrient excretion fur dairy and beef cattle. The system was first presented in a series of fuur papers (Fox et al, 1992; Russell et al, 1992; Sniffen et al, 1992; O'Connor et al, 1993) and has since been continually refined (Ainslie et al, 1993; Tylutki et al, 1994; Fox et al, 1995, 1999; Pitt et al, 1996; Tedeschi et al, 2000a, 2000b, 2001, 2002a, 2002b, 2002c, 2003). There have been several evaluations of the CNCPS model with animal performance data. Kolver et al (1998) used a total mixed ration (TMR) and grazing dairy cows to evaluate the performance of the CNCPS and found the CNCPS underpredicted energy allowable milk production by 2.5% in the animals fed TMR and by 6.8% in the animals fed pasture. Dairy replacement heifers have also been used to evaluate the predictions of the CNCPS. Van Amburgh and coworkers (1998) used both the CNCPS and the 1989 Dairy NRC with 273 Holstein replacement heifers. The CNCPS ME allowable ADO accounted for 86% of the actual ADO. The CNCPS has also been evaluated for tropical cattle production. Lanna et al (1996) measured energy and protein content of empty body weight gain of growing animals and milk production of dual purpose lactating cows. Using actual DMI of feeds that were characterized for carbohydrate content and protein fractions, as well as digestion rates, the CNCPS accounted for 72% of the variation in live weight gain and 71 % of the variation in milk production. Juarez Lagwtes et al (1999) found that, when feeds are properly characterized, an increase in NDF or a decrease in the rate of digestion of NDF, will affect the prediction of milk production of dual-purpose cows by the CNCPS accordingly. In most tropical areas of the world, particularly in undeveloped countries, the primary source of nutrition fur cattle and other ruminants is forage, which is harvested by the animal as live material, as opposed to feed which is harvested by the farmer and provided to the animal, In these areas it is simply not economically practical to provide any large degree of supplementation to the animals. A similar situation can be found in Hawaii. Although the cattle industry in Hawaii is considered by most to be well developed, because of its geographical isolation the importation and delivery of supplements to the animals is often considered impractical and/or too costly. This is in contrast to more well-developed, temperate regions of the world where supplements can be produced locally or imported at lower cost. This inability to supplement is compounded by the fact that tropical grasses are primarily <4 (take in C~ at night), rather than C3 (take in C~ during the day) plants and, consequently, are often lower in soluble carbohydrates and higher in cell wall and lignin components (Van Soest, 1994). Because of this increase in lignin and cell wall, tropical grasses are generally about 15% less digestible than temperate forages (Van Soest, 1994). This decrease in digestibility, along with a decrease in intake (INRA [Institut National de 1a Recherche Agronomique], 1989), can lead to a decrease in nutrients available fur the animal It has been well-documented that animals on tropical grasses typically underperform animals on temperate grasses (Minson and McLeod, 1970; Stobbs, 1971; Kaiser and O'Neill, 1975). In other warm-climate areas, mineral deficiencies have been blamed fur poor production of beef cattle (McDowell and Conrad, 1985). There are extensive records in the literature documenting deficiencies, as well as toxicities, of minerals in both soils and plants (McDowell and Conrad, 1985; McDowell, 1997). Therefore, it is important to be aware of the mineral status of the animals_ Often, only soil and/or plant levels of minerals are assessed in making a decision to supplement, and the level of a mineral in the soil or plant does not necessarily reflect what is available to the animal Additionally, mineral supplements are often expensive and could lead to excess excretion or poor utilization by the animal Therefore, unnecessary supplementation can have a dramatic impact on both economic returns and environmental sustainability, in addition to leading to toxicities. To both ensure adequate nutrition and eliminate unnecessary supplementation, it is necessary to know the levels of minerals present in the forages being grazed and their bioavailabi1ity to the animal. Previous in situ tria1s show that there are differences in rate and extent of mineral release in the rumen between forages (Emanuele and Staples, 1990; Emanuele et al., 1991). Therefore, it is dangerous to draw general conclusions from limited studies and it becomes necessary to determine the rate and extent to which minerals are released from each of the forages in question. It is also of interest how the rate of overa11 dry matter disappearance tracks with the rate of macromineral release in the rumen. It may be the case that dry matter disappearance is much more rapid and complete than mineral release. This may provide clues as to where certain minerals are sequestered in the plant. Also, if there is a close relationship, the procedure fur determining dry matter release is easier, takes less time, and is less expensive. The objectives of the research presented here were to: 1. evaluate the Cornell Net Carbohydrate and Protein System for use in Hawaii beef production, 2. evaluate how changing body size, body condition, level of intake, and forage composition affects the predictions of the Cornell Net Carbohydrate and Protein System, and 3. determine the levels and rates of macrominerals released from tropical forages in the rumen, and their relationship to DM disappearance.
Description: Thesis (M.S.)--University of Hawaii at Manoa, 2007. Includes bibliographical references (leaves 61-66). vii, 66 leaves, bound ill. 29 cm
URI: http://hdl.handle.net/10125/20397
Rights: All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Keywords: Beef cattle -- Feeding and feeds -- Hawaii, Beef cattle -- Nutrition -- Hawaii

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