Urea space and body condition score to predict body composition of meat goats

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Abstract

Yearling Boer × Spanish goat wethers (40) were used to develop and compare body composition prediction equations for mature meat goats based on urea space (US) and body condition score (BCS). Before the experiment, one-half of the animals were managed to have high BW and BCS (1–5, with 1 being extremely thin and 5 very fat) and the others were managed to have low BW and BCS. During the 24-week experiment, initially fat wethers were fed to lose BW and BCS and initially thin wethers were fed to increase BW and BCS. BCS, US, and whole body chemical composition were determined after 0, 12, and 24 weeks. Mean, minimum, and maximum values were 42.1 (S.E. = 1.12), 24.5, and 59.0 kg for shrunk BW; 3.0 (S.E. = 0.11), 1.5, and 4.0 for BCS; 61.3 (S.E. = 1.01), 53.7, and 76.5% for water; 20.2 (S.E. = 1.11), 4.7, and 29.7% for fat; 15.6 (S.E. = 0.19), 13.3, and 18.1% for protein; and 2.9 (S.E. = 0.062), 2.2, and 3.7% for ash, respectively. For water, fat, and ash concentrations and mass, simplest equations explaining greatest variability (with independent variables of US, BCS, and (or) shrunk BW) based on BCS accounted for more variation than ones based on US, although in some cases differences were not large (i.e., water and ash concentrations and mass). Neither US nor BCS explained variability in protein concentration. Equations to predict protein mass based on shrunk BW and US or BCS were nearly identical in R2 and the root mean square error. A 1 unit change in BCS corresponded to change in full BW of 8.9 kg (full BW (kg) = 17.902 + (8.9087 × BCS); R2 = 0.653), fat concentration of 7.54% (%fat = −5.076 + (7.5361 × BCS); R2 = 0.612), and energy concentration of 3.01 MJ/kg (energy (MJ/kg) = 0.971 + (3.0059 × BCS); R2 = 0.615). In summary, BCS may be used as or more effectively to predict body composition of meat goats than US. The primary determinant of BCS, within the range of BCS observed in this experiment, was body fat content.

Introduction

Wuliji et al. (2003) discussed the importance of body composition and, in particular, need for accurate non-terminal measures. Urea space (US) has been used to estimate body composition in cattle (Meissner et al., 1980, Bartle and Preston, 1986, Rule et al., 1986, Bartle et al., 1987, Hammond et al., 1990), sheep (Bartle et al., 1988, Poland, 1991, Galloway et al., 1996), and goats (Arta Putra et al., 1998, Wuliji et al., 2003). This technique is relatively simple though not to the extent to allow routine on-farm use, with employment most likely confined to experimental settings. An even less complex measure is body condition score (BCS) (Edmonson et al., 1989, Honhold et al., 1989, Oregui et al., 1997). BCS is intended to be a subjective estimate primarily of degree of fatness, but also with influence of protein mass. BCS is commonly applied with beef and dairy cattle. For example, NRC, 2000, NRC, 2001 suggested concentrations of fat, protein, and energy for different BCS of cattle, thereby allowing calculation of feed needs to achieve specific increases in BW or energy mobilized for use in lactation or maintenance with BW decreases. However, goats have the ability to deposit considerable fat internally, which might lessen the accuracy with which body composition can be predicted from BCS. Recently, Villaquiran et al., 2005a, Villaquiran et al., 2005b; also available at www2.luresext.edu) described a BCS procedure for goats. Therefore, objectives of this experiment were to develop and compare body composition prediction equations for yearling meat goats based on US and BCS.

Section snippets

Materials and Methods

The experiment was approved by the Langston University Animal Care Committee. Most procedures were described by Ngwa et al. (2006) and, therefore, will only be briefly described here.

In the 5 months preceding the experiment, 21 yearling Boer × Spanish goat wethers were managed to achieve high BW and BCS, and 21 received restricted amounts of feed to produce low BW and BCS. Conditions at the beginning of the experiment are given in Table 1. During the 24-week experiment, initially fat (I-F)

Data summary

As shown in Table 1, there was a considerable range in most variables. BCS indicate that some animals were very thin (e.g., minimum BCS of 1.5), and the highest BCS was 4.0. The range in fat concentration was large, with the minimum 23% of the mean and the maximum 47% greater than the mean. The range in protein concentration was smaller, with the minimum 15% less than the mean and the maximum 16% greater than the mean.

Many of the correlation coefficients in Table 2 were as expected and are in

US

The considerable differences between equations of this experiment to predict body composition from US and those of Wuliji et al. (2003) make readily apparent one of the significant limitations of the US procedure. For most accurate use of US, prediction equations should be developed with animals similar to ones to which they will be applied. However, it is not always possible to directly assess chemical composition. If it is feasible, then determining composition with an adequate number of

Summary and conclusions

Equations to predict body composition of yearling meat goats based on BCS were as or more accurate than ones based on US. Although, neither US nor BCS were useful to predict protein concentration, and water and ash concentrations were not predicted with high accuracy either. BCS accounted for considerable variability in concentrations of fat and energy. Thus, BCS can be useful in determining feed needs or energy mobilized with specific changes in BW. Furthermore, assuming similar ranges in

Acknowledgment

This research was supported by USDA Project Number 2003-38814-13923.

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