Relationships of Body Composition and Fat Partition with Body Condition Score in Serra da Estrela Ewes

Twenty eight non-lactating and non-pregnant adult Serra da Estrela ewes, ranging in body condition score (BCS) from 1 to 4 were used to study the relationships between BCS, live weight (LW), body composition and fat partition. Ewes were slaughtered and their kidney knob and channel fat (KKCF), sternal fat (STF) and omental plus mesenteric fat (OMF) were separated and weighed. Left sides of carcasses as well as the respective lumbar joints were then dissected into muscle, bone and subcutaneous (SCF) and intermuscular fat (IMF). The relationship between LW and BCS was studied using data from 1,396 observations on 63 ewes from the same flock and it was found to be linear. Regression analysis was also used to describe the relationships among BCS and/or LW and weights (kg) and percentages in empty body weight (EBW) of dissected tissues. The prediction of weights and percentages in EBW of total fat (TF) and of all fat depots afforded by BCS was better than that provided by LW. Only the weight of muscle and the percentage of bone in the EBW were more efficiently predicted by LW than by BCS. IMF represented the largest fat depot with a BCS of 1 and 2, whereas SCF was the most important site of fat deposition with a BCS of 3 and 4. Allometric coefficients for each fat depot in TF suggest that the fat deposition order in ewes from this breed is: IMF, OMF, SCF and KKCF. Results demonstrate that BCS is a better predictor than LW of body reserves in this breed and that LJ is a suitable anatomical region to evaluate BCS. (


INTRODUCTION
It is well recognized that, under farm conditions, body condition score (BCS) is an important tool to assess the adequacy of feeding programs, particularly in production systems where the availability of feeds are not constant.Ewes' BCS, first outlined by Jefferies (1961), was adapted by Russel et al. (1969) and tested by these authors in the Scottish Blackface breed.In most studies BCS demonstrate to provide a better prediction of body composition than live weight (LW) (Russel et al., 1969;Teixeira et al., 1989;Sanson et al., 1993) but Frutos et al. (1997) found that LW was more accurate to estimate body composition and fat depots in Churra breed.Between-breed differences in body size and fat partition (Russel et al., 1968 and1969;Taylor et al., 1989) can possibly explain those contradictory results.Therefore, studies on each breed are needed in order to determine which of those parameters are more accurate for the evaluation of body reserves.
The experiment reported here was designed to study the accuracy of BCS, LW, composition of LJ, and sternal fat to estimate body reserves, as well as to characterize fat partition in different BCS, in the Portuguese sheep breed Serra da Estrela, the top sheep dairy breed in Portugal.

MATERIALS AND METHODS
Twenty-eight non-pregnant, non-lactating, adult ewes of mixed ages from Serra da Estrela breed, were drawn from the experimental flock of Estação Zootécnica Nacional and randomly allocated in two groups which were fed with the same diet (mixture of corn silage and corn gluten) but at two different levels, 30% and 200% of maintenance requirements (Agricultural Research Council, 1980), in order to bring them into different BCS.Ewes were housed in two large indoor pens with free access to water and trace mineralized salt during all the experiment.BCS was evaluated by two assessors using the Russel et al. (1969) technique and recorded weekly along with LW.When they attained the prescribed BCS: 1, 2, 3 and 4, ewes were slaughtered, after a 24 h fasting period.
Kidney knob and channel fat (KKCF), sternal fat (STF) and omental plus mesenteric fat (OMF) were separated and weighed.After 24-48 h at 0°C, left sides of carcasses as well as the respective lumbar joints (LJ) (Delfa et al., 1989) were dissected into muscle, bone and subcutaneous (SCF) and intermuscular fat (IMF), which weights were recorded.
The effect of BCS on LW was also studied on a larger sample: 1396 observations on 63 non-lactating, non-pregnant, adult ewes from the same flock as the experimental animals.All BCS and LW assessments were conducted between 9:00 and 10:00 h, before the ewes go out to pasture.
Statistical analysis was performed with the GLM procedure of SAS (SAS Institute, 2003) using the following models: To evaluate the effect of BCS on: (i) LW, (ii) empty body weight (EBW) and (iii) dissected components To evaluate the effects of: (i) BCS on LW, (ii) BCS or LW on dissected components, (iii) dissected components of LJ on the same components in carcasses, and (iv) STF on TF, SF and muscle To evaluate if any improvement was achieved on the prediction of dissected components of carcass using simultaneously LW and BCS To compute allometric coefficient (Huxley, 1932) for each fat depot: log (fat depot) = µ+b 1 ×log (total fat)+e ij For all the variables studied, the variance homogeneity was tested beforehand and those showing deviation from normal distribution were subjected to log 10 or log 10 (y+1) transformation (Steel and Torrie, 1980).

RESULTS AND DISCUSSION
Means, standard deviations and extreme values of LW in each half score of BCS (Table 1) show that, even in nonlactating and non-pregnant animals, ewes with a similar LW can exhibit very different BCS or, in other words, ewes scoring the same BCS may have very different LW.This can probably be justified by different body sizes of ewes in this breed and/or variation in gastrointestinal contents, which are some of the most important factors that make LW difficult to interpret in ruminants (Russel et al., 1971;Hossamo et al., 1986;Jarrige, 1988).
The regression equation between LW and BCS shows that LW increases 11.00 kg per unit change in BCS (LW = 20.893+11.002BCS (R2 0.66, RSD 6.551, SE b 0.213).This result is similar to those observed by Russel et al. (1969), Teixeira et al. (1989) and Sanson et al. (1993, with a 1 to 9 scores scale), for Scottish Blackface, Aragonesa and Western-range ewes, respectively, but is greater than those recorded by Peart (1970), MLC (1983), Caldeira and Portugal (1991), Oregui et al. (1991) and Frutos et al. (1997), in different sheep breeds.Differences were also explained by different body sizes and/or gastrointestinal contents and perhaps by the subjectivity of BCS evaluation (Evans, 1978).Means and standard errors of age, LW, empty body weight (EBW) and dissected components, expressed in weight in half carcasses and as percentages of EBW are summarized in Table 2.No significant differences were found in age, weight of bone and percentage of muscle in EBW, whereas means of all other variables differ significantly (p<0.01).Teixeira et al. (1989) found similar results in the Aragonesa breed, although they recorded significant differences on bone weights between ewes with a BCS lower than 2.50 and equal or higher than 2.50.
Simple regression equations for estimating carcass dissected components expressed in weight (Table 3) and as percentages of EBW (Table 4) from BCS and LW, as well as correlation coefficients among these parameters (Table 5), showed that BCS is a better predictor of body reserves than LW, as was observed in various breeds (Russel et al., 1969;Teixeira et al., 1989;Sanson et al., 1993) but not in Churra (Frutos et al., 1997).Only the weight of muscle and the percentage of bone in the EBW were more efficiently predicted by LW than by BCS.Regression equations developed from weight of bone and percentage of muscle in EBW on BCS and LW did not provided sufficient accuracy.
Inclusion of LW as an independent variable in multiple regressions with BCS (Table 6) slightly improved the efficiency of muscle, SCF, IMF and TF weights estimation but did not afford greater precision over simple regressions with only BCS on the prediction of percentages of dissected components in EBW.
The proportions of the remaining variation accounted for (R² values) by BCS and LW of TF, SCF and IMF weights are slightly greater than those found by Teixeira et al. (1989), whereas for KKCF was slightly smaller.The R² value observed for the prediction of percentage of TF in EBW was greater than that found by Russel et al. (1969).These authors, Teixeira et al. (1989) and Sanson et al. (1993) did also not found any improvement on the efficiency of predictions with the inclusion of LW in multiple regressions with BCS.
Data showing fat partition in TF at different BCS, are set out in Table 7.Only for SCF and IMF significant differences (p<0.01) were found between BCS.IMF represented the largest fat depot with a BCS of 1 and 2, whereas SCF was the most important site of fat deposition with a BCS of 3 and 4. Allometric coefficients (Table 8) for each fat depot on TF suggest that the fat deposition order in ewes from this breed is: IMF, OMF, SCF and KKCF, although the b coefficients of the regression equations between log 10 OMF, log 10 SCF and log 10 KKCF and log 10   TF were not different (p>0.05).Russel et al. (1968) and Teixeira et al. (1989) observed a different order in Aragonesa and Scottish Blackface breeds, respectively, which probably can be explained for a higher potential for meat production of these breeds in relation to that of Serra da Estrela, which is known for its milking aptitude.In fact, it is well recognized that milk breeds tend to deposit more fat in the intra abdominal depots in relation to the carcass depots than meat breeds (Truscott et al., 1983;Ferrell and Jenkins, 1984;Taylor and Murray, 1991).
Muscle is also an important depot as a protein reserve and therefore of energy, available under subnutrition conditions (Bryant and Smith, 1982;Chilliard and Robelin, 1983;Purroy et al., 1989).Mobilization and deposition of muscle may be observed in Table 2, from 7.227 kg with a BCS of 1 until 13.869 kg with a BCS of 4. BCS did not prove to be a good predictor of muscle percentage in EBW (neither did LW) (Table 4) but provided an acceptable estimate of its weight (R² 0.67, RSD 0.071), though LW had a much better efficiency of prediction (R² 0.93, RSD 0.032) (Table 3).
Mean values of dissected components of LJ and the relationship between these components and the same tissues in carcass are depicted in Table 9 and 10.SCF of LJ and TF of LJ (SCF plus IMF of LJ) can also be good predictors of different carcass fat depots as it is shown in Table 11.These relationships among SCF and TF of LJ and carcass fat depots are remarkable similar to those found by Delfa et al. (1989).LJ provided a reasonable estimate of both weights and percentages in EBW of all variables in carcasses.These results, in addition to those presented above on the efficiency of prediction of body composition from BCS, as Jefferies (1961), Russel et al. (1969) and Teixeira et al. (1989) as already stated in other sheep breeds, offer evidence to support LJ as a suitable anatomical region to evaluate BCS in Serra da Estrela breed.
STF was recorded in order to estimate its relationship with body reserves as an eventual alternative anatomical   site (sternal region) to lumbar region to assess BCS.In goats, sternal region was found to provide greater precision on the prediction of body reserves than lumbar or caudal regions (Santucci and Maestrini, 1985;Morand-Fehr et al., 1989;Amaro and Caldeira, 1991).The proportion of remaining variation accounted for by STF on the prediction of TF and muscle weights, and on the percentage of TF in EBW (Table 12), showed that sternal region could eventually be an alternative site to evaluate BCS, although it has revealed to be a poorer predictor of body reserves than LJ.However, it will be important to remember that, under farm conditions (handling chutes), the assessment of sternal region will always be more difficult than that of lumbar region.BCS assessed on the lumbar region demonstrate to be an excellent predictor of body reserves in Serra da Estrela ewes, providing an important tool to assess the adequacy of feeding programs and, consequently, contributing to the improvement of milk production efficiency.

Table 1 .
Means, standard deviations and extreme values of live weight in each half score of body condition score (BCS) Means in the same line with different superscripts differ significantly (p<0.01).SCF: subcutaneous fat, IMF: intermuscular fat, OMF: omental plus mesenteric fat, KKCF: kidney knob and channel fat, STF: sternal fat and TF: total fat.

Table 7 .
Mean values and standard errors of subcutaneous fat (SCF), intermuscular fat (IMF), omental plus mesenteric fat (OMF) and kidney knob and channel fat (KKCF) expressed as percentages in total fat (TF)

Table 9 .
Mean values of lumbar joint (LJ) weight and muscle, subcutaneous fat (SCF), intermuscular fat (IMF) and bone of the LJ expressed in weight and as percentages in LJ

Table 10 .
Prediction equations for estimating muscle, subcutaneous fat (SCF) and intermuscular fat (IMF) in carcass, expressed in weight and as percentages in empty body weight (EBW), from the same tissues in lumbar joint (LJ)