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Effect of supplementation with pelleted citrus pulp on digestibility and intake in beef cattle fed a tropical grass-based diet (Cynodon nlemfuensis)

https://doi.org/10.1016/j.anifeedsci.2005年05月02日0 Get rights and content

Abstract

Citrus pulp is an important by-product for sub-tropical and tropical ruminant animal production. In this study, three steers (average body weight = 324 ± 16 kg) were randomly assigned to three levels of pelleted citrus pulp (PCP) supplementation (0, 1.25, and 2.5 kg animal−1 d−1; as-fed) in a 3 ×ばつ 3 Latin square design to evaluate its effects on forage intake, digestion, and ruminal pH. The basal diet was stargrass (Cynodon nlemfuensis) harvested and chopped every day and fed fresh. Supplementation with increasing amounts of PCP tended (P≤0.10) to result in a linear increase in digestibility of total diet dry matter (DM) and organic matter (OM), but no effects were noticed for digestibility of forage DM or total diet neutral detergent fiber. Forage DM intake decreased linearly (P=0.03) with increasing PCP supplementation, although the decrease tended (quadratic; P=0.08) to be of greater magnitude at the highest level of supplementation. Both a linear increase (P<0.01) and a quadratic trend (greatest increase with first level of supplementation; P=0.09) were also observed for intake of total digestible OM. Average ruminal pH was between 6.6 and 7.2 and was not affected (P=0.29) by supplementation treatment. Although supplementation with PCP depressed forage consumption somewhat, little effect on forage digestion was observed. The provision of digestible OM in the form of supplement was greater than that lost via depressed forage consumption, resulting in an overall increase in energy supply. Our results suggest that high levels of citrus pulp to beef cattle can lower forage intake, but increase total energy intake. High levels of citrus pulp supplementation could be beneficial in combination with forages high in rumen dagradable protein. Systems using grasses with higher ruminally degradable protein content than we used, may benefit from this extra supply of energy which should be tested in a further experiment.

Introduction

The use of by-products for livestock feeding allows us to convert material that has limited application for use as human food into animal protein; ruminants are fundamental elements in that process. Citrus pulp is a by-product feed obtained during the manufacture of orange juice and processing of other citrus fruits (Grasser et al., 1995). Citrus pulp is composed of approximately 250 g pectins kg dry matter (DM; Arthington et al., 2002). Neutral detergent soluble fiber (NDSF) fraction which include pectins, represents 250–440 g kg DM. Additionally, this feedstuff contains between 120 and 400 g of sugars and less than 10 g starch kg DM (Hall, 2000). Pectins are highly digested in rumen (over 980 g kg DM; Titgemeyer et al., 1992, Hall et al., 1998, Arthington et al., 2002). Neutral detergent fiber (NDF) content is 230 g kg DM (NRC, 1996) with a digestibility of 780–840 g kg DM (Miron et al., 2002).
Pelleted citrus pulp (PCP) has been used in some subtropical regions of the United States (Florida, California, Texas; Arthington et al., 2002) and in other areas of the tropical Americas (Rodríguez, 1971, Rodríguez, 1972). In Costa Rica (Central America), use of PCP has been recently introduced (Rojas-Bourrillón et al., 2001). Use of citrus pulp has been associated with positive effects on ruminal fermentation (Pinzón and Wing, 1976), fiber digestion (Miron et al., 2001), and microbial protein synthesis (Ariza et al., 2001). Citrus pulp has been studied as an alternative energy source, replacing some grain in concentrate diets. Positive effects have been reported in dairy cattle (Van Horn et al., 1975, Wing, 1982, Rojas-Bourrillón et al., 2001) and in small ruminants (Fegeros et al., 1995, Aregheore, 2000). Some negative effects (reduced milk yield, milk protein content and yield) were noted in dairy cattle when citrus pulp was compared with other by-products (corn meal and hominy) primarily intended as a source of dietary energy (Leiva et al., 2000). However, the impact of citrus pulp supplementation on forage utilization has not been studied extensively. Such research would be useful in the tropics because of the availability of citrus by-products and because many beef- and dairy-production systems in the tropics depend on grasses and other forage sources for the basal feedstuff. Differences in citrus pulp nutritive value can be expected depending upon production site, citrus variety, proportion of seeds and peel and some compounds (e.g., CaO or Ca(OH)2) used during the dehydration process (Arthington et al., 2002).
The primary objectives of this research were to evaluate the effect of different amounts of PCP supplementation on digestibility, intake, and ruminal pH in a grass-based (Cynodon nlemfuensis) diet fed to beef cattle. Additionally, fecal recovery of acid detergent insoluble ash (ADIA) and indigestible acid detergent fiber (IADF) were measured for the dietary treatments evaluated.

Section snippets

Digestion experiment

The experiment was carried out at an experimental farm operated by the Technological Institute of Costa Rica (San Carlos, Costa Rica, latitude: 10°N, longitude: 84°W). Three ruminally fistulated steers (Charolais ×ばつ Brahman) with an average body weight of 324 ± 17 kg were housed in individual pens (2.0 m ×ばつ 2.0 m) that were covered by a roof but otherwise were subjected to natural environmental conditions (average values for temperature, daylength, and relative humidity were 26 °C, 12 h, and 85%,

Chemical composition of forage and citrus pulp

In general, nutritive value of forage offered (stargrass) was characterized by a low CP content (Table 1), with almost 0.5 being potentially ruminally degradable. Also, characteristic of C4 forages, the stargrass contained relatively high fiber content. The by-product used in this experiment (citrus pulp) also possessed low CP content, almost 0.75 of which was ruminally degradable. The PCP contained relatively moderate amounts of fiber, high content of non-structural carbohydrates, and very

Discussion

The chemical composition of stargrass between 20 and 25 days and at 21 days of regrowth in a rotational grazing system has been reported by Sánchez and Soto (1996) and Rojas-Bourrillón et al. (2001), respectively. Samples in both experiments were collected by the hand-pluck technique and in the same geographic region as our experiment. Some of the values for key chemical constituents reported by these authors were: 125–127 g CP kg DM, 649–738 g NDF kg DM, and 332–400 g ADF kg DM. The forage fed in our

Conclusions

Citrus pulp seemed to be an acceptable supplement choice for ruminants consuming stargrass with moderate to low nutritional quality. Although citrus pulp supplementation was compatible with maintenance of forage digestion and desirable ruminal pH, it was associated with a decline in forage intake. The decline in forage intake was most evident at higher levels of supplementation, however and suggests that caution should be exercised in the choice of supplementation level. Both ADIA and IADF seem

Acknowledgements

The authors express particular gratitude to the following institutions for the financial support provided during this project: Technological Institute of Costa Rica, Kansas State University, MICIT (Ministry of Science and Technology, Costa Rica), and CONICIT (National Council for Scientific and Technological Research, Costa Rica). The senior author also expresses his thankfulness to the Department of Animal Science and Industry of Kansas State University for the assistantship provided during

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