Effect of live weight at slaughter on the carcass characteristics of intensively fattened Martinik sheep fed sugar cane supplemented with pea flour

Fourty Ovin Martinik lambs weighing on average 20.2 ± 3.0 kg LW (4 months) were reared indoors and were fed chopped whole sugar cane supplemented with Pisum sativum (12-14% diet). Feed intake was measured daily and lambs were weighed each week. The fattening period lasted 117 days. Four groups were categorized according to liveweight at the end of fattening (slaughter weight, SW): 28, 30, 33 and 36 kg. Five representative lambs per SW group were slaughtered according to the European procedure. Carcass weight, yields and scores were recorded. Carcass cuts and fat were weighed.

Intake, average daily gain (ADG) and cold carcass weight (CCW) significantly (P<0.05) increased with SW group from 71.2 to 74.8 g DM.kgW^-0.75, from 105 to 146 g.d^-1 and from 12.6 to 16.5 kg , respectively. The CC yield was high (62%) and did not significantly differ from one SW class to another. Conformation scores remained satisfactory around 4, regardless of the group. All the anatomical regions of the carcass consistently (P<0,05) increased in weight. Regardless of carcass weight, the distribution of prime cuts seemed to be similar with about 19% and 35%for the shoulder and leg proportion, respectively. The internal fat scores varied significantly but only by one point from the lighter to the heavier carcasses. The weight of internal fat tissues increased relative to the carcass weight and represented only 7% of the CCW. No significant effect was observed on fat cover scores which remained at a very satisfactory level of 3 on 5 points-scale.

These preliminary results provide an incentive for breeders and butchers and could encourage the development of the mutton sector on native animal and local feed resources. It seems possible to increase the growth, improve the feed efficiency and to obtain well-conformed and heavier carcasses, with no apparent detrimental effect on the carcass fat.

Introduction

The rational exploitation of local feed resources and indigenous breeds (Rodriguez and Preston 1997) is receiving increasing attention in tropical areas as a means to meet the growing challenge for productivity and sustainability. In the Islands of the French West Indies (FWI), the use of non conventional feeds (Geoffroy et al 1991) and the improvement the Creole genotypes (Naves et al 2001) are fundamental components in adapted and productive systems, as is being studied in the Creole pig integrated farming system (Xandé et al 2007).

Sheep production in the FWI is centred on the Martinik breed (Ovin MartiniK, OMK; Vertueux et al 2006). Compared to breeds found in Europe, the OMK is classified in the lightweight sheep category with average carcass weight of 9-12 kg. Resulting in the demand of the local sector (farmers as well as butchers), for heavier and well conformed carcasses.

In this region pasture grazing is the most common type of rearing (Mahieu et al 1997), and tropical forages are of moderate feeding value even when intensively cultivated (Aumont et al 1991), consequently, a limiting factor in animal production. Previous studies in Martinique have reported growth level of g.d^-1 for grazing lambs (Mahieu et al (1997).

High-energy feed intake is necessary to obtain high fattening performances (Santos-Silva and Vaz Portugal 1991; Ramirez et al 1995; Mahgoub et al 2000). According to Preston and Murgueitio (1992) sugar cane (SC) products can be promoted as a sustainable energy-rich alternative to the cereal coarse grains. SC is considered as the main producer of biomass among perennial crops and is interesting for its tolerance to drought and resistance to pest and diseases. It is considered as a valuable feedstuff in many tropical countries where there is an existing sugar cane industry because the technologies for cultivation are known by a number of farmers. The whole plant can be used (Preston and Leng 1979; Lallo et al 1991; Le Diep Long Bien 1999).

The objective of this paper was to assess the fattening performances and carcass characteristics of OMK lambs fed a local feedstuff such as chopped whole sugar cane CWSC. Given that research on CWSC emphasized the important role of nitrogen, starch and oil (Preston and Leng 1979), “Pisum sativum” was used in this initial experimental phase to supplement the CWSC. Results on the digestibility trial will be analysed in another paper.

Materials and methods

This study was carried out at the Animal Production Unit of the INRA Research Centre in Guadeloupe, which is a humid tropical island in the Caribbean (16° 1’ N, 61° 6’ W). The experimental farm in question is located in the driest area of the island, where annual rainfall averages 1280 mm.

Experimental design, diets and animals

Entire male lambs of the "Ovin Martinik" genotype were used for the different experiments. Fourty lambs weighing on average 20.2 ± 3.0 kg LW (4 months) were reared indoors after a 3 week-period of adaptation after weaning. The basal diet was chopped whole sugar cane (CWSC). The sugar cane was harvested daily and then chopped and distributed ad libitum (15% refusals) once a day. The nitrogenous supplement was commercial pea flour which made up 12-14 % of diet. This commercial flour of peas (Pisum sativum) was constituted from the dry grains of peas that was ground. The animals received the pea flour at 6.30 am. The basal diet was distributed thereafter. The chemical composition of the CWSC and the feed supplement are given in Table 1.

Table 1. Ingredients of the different components of the diet, chemical composition, per kg DM
Variables	Dry matter, g	ME, MJ	CP, g	NDF, g	ADF, g
Whole sugar cane*	290	8.49	27	473	304
Pisum sativa**	860	13.0	259	167	76
* Aumont et al 1991; ** INRA 1989

Feed intake was measured from Monday to Friday for the entire length of the trial. The fattening period lasted 117 days and the lambs were weighed each week. Descriptive statistics (Table 2) underlined the variability among the animals.

Table 2. Live weight (LW, kg), average daily gain (ADG, g.d^-1) of the fattening Ovin Martinik lambs fed chopped whole sugar cane (ad libitum) supplemented with pea flour (12-14% diet)
Item	n	Mean	SD	CV, %	Minimum	Maximum
Birth weight, kg	40	3.3	0.6	18	2.4	4.5
ADG at weaning, g.d^-1	40	136	14	10	118	166
Age at the beginning, d	40	132	10	8	113	142
LW at the beginning, kg	40	20.9	2.0	10	17.7	22.5
LW at the end, kg	40	32.1	3.3	10	27.6	38.7

Four groups were categorized according to liveweight at the end of fattening (slaughter weight, SW): 28, 30, 33 and 36 kg.

Slaughtering procedure and carcass measurements

Five representative lambs per SW group were allotted according to their weight at weaning and at the beginning of the experiment. Lambs were weighed the day before slaughter when fasting, and the next day just before slaughter. After bleeding, the full digestive tract was removed, weighed and then separated by compartment. The peritoneal fat was removed and weighed. Dressed carcasses were weighed within 1 h (hot carcass weight: HCW), and then chilled for 24 hours at 4°C, and then weighed again (cold carcass weight: CCW). The day after slaughter, each cold carcass was rated (from 1 to 5) according to conformation, internal and external fat based on a lightweight lamb grid (OFIVAL, 2005). The perirenal fat was removed and weighed. The carcass was then cut in half lengthwise and the left side of the cold carcass was cut up as described by Boccard and Dumont (1955) and all of the pieces (shoulder, neck, ribs, loin, breast, leg) were weighed.

Data calculations and statistical analyses

Empty body weight (EBW) was computed by subtracting the weight of the gut content from the slaughter weight. Commercial dressing out was calculated as the ratio of hot carcass weight on live weight at slaughter (HCW/LW) while cold carcass yield was the weight of cold carcass related to the empty body weight (CCW/EBW). Data were analysed using general linear model (Minitab V14.2 software) with slaughter weight as the main effect in the general model.

Results and discussion

Fattening performances

The lowest weight lambs (group 28 kg) ate significantly less than the others (Table 3).

Table 3. Growth performances and carcass traits of Ovin Martinik lambs fed chopped whole sugar cane supplemented with pea flour according to the live weight (LW) at slaughter
Group of LW at slaughter	28 kg	30 kg	33 kg	36 kg
Results obtained upon 40 lambs (10 per group)
Average daily gain, g.d^-1	105^a ± 23	118^b ± 28	129^c ± 27	146^d ± 27
ADG/LW , ‰	4.8^a ± 0.9	5.1^ab ± 1.0	5.4^b ± 1.1	5.8^b ± 1.1
Intake, g DM.kgW^-0.75	71.2^a ± 2.1)	73.5^b ± 2.8	75.0^b ± 2.0	74.8^b ± 1.5
Feed conversion ratio	7.6^a ± 1.6	7.5^a ± 1.1	7.3^a ± 1.5	6.8^b ± 1.1
Results obtained upon 20 lambs (5 per group)
Fasted slaughter weight, kg	28.0^a ± 0.7	29.8^b ± 0.8	31.8^c ± 1.0	35.8^d ± 1.6
Empty body weight, kg	20.2^a ± 0.7	21.7^b ±1.3	23.2^b ± 0.5	26.8^c ± 1.1
Hot carcass weight, kg	13.0^a ± 0.5	14.2^a ± 0.7	15.0^b ± 0.5	17.2^c ± 0.8
Chilled carcass weight, kg	12.6^a ± 0.5	13.3^a ± 0.9	14.3^b ± 0.5	16.5^c ± 0.9
CC yield*, %	62.6 ± 0.4	61.6 ± 4.6	61.5 ± 2.0	61.6 ± 1.0
HC yield**, %	46.6^a ± 1.0	47.6^a ± 1.5	47.1^a ± 2.0	48.2^b ± 0.9
^a,b,c,dMeans within the same row with different superscripts differ significantly (P<0.05) * CC yield = CCW/EBW ** HC yield = HCW/SW

It appeared that WCSC had a very satisfactory intake level, probably the addition of the pea flour as a source of both starch and protein had improved its digestibility as observed by Preston and Leng (1979). Lower levels of 350 to 500 g DM was reported by Lallo et al (1991) with hair sheep (25 to 32 kg LW) fed WCSC supplemented with a good level of protein.

Significant (P<0.01) differences in ADG were observed within the SW groups (Table 3). The OMK lambs are a native tropical sheep which are not yet selected for this trait and a large variability still appeared in the experimental groups. The variability in live weight at the beginning of the trial was about 15-20%, similar trend of variability (individual differences) was also observed for the growth throughout the study (20%), probably reflecting the genetic growth potential of this breed (OMK). Nevertheless, a diet based on an energy-rich source, such as sugar cane, is also a contributing factor for intensive fattening of this breed. The performances obtained for these experimental lambs are about 27 to 45% higher than values for tropical lambs-fed grass alone (Wildeus 1991; Mahieu et al 1997; Mahgoub et al 2000). However, higher values were observed (up to 200 g.d^-1) for the same genotype (Archimède et al 2007) or with other tropical sheep fed with high-energy rations (Pineda et al 1998; Kawas et al 2007). Given that the initial LW differed between groups, the ratio of ADG (g) to initial live weight (kg) was used to obtain the relative performance value which varied from 4.8 ‰ to 5.8 ‰. These figures are within the wide range of values (4.0‰ to 8.8‰) reported for other tropical sheep (Lallo et al 1991; Ramirez et al 1995; Madhavi et al 2006). These results seemed to indicate that there is still room for the improvement of the growth potential of this particular breed.

Values of feed conversion ratio (FCR; Table 3) were similar within the first three groups of weight class while it lowered with the heaviest lambs probably related with their high growth potential. The values approximating 7.5 could indicate a relative good feeding level with our experimental ration even with a high proportion of WCSC as basal diet. Much higher values (9 to 12) were observed by Mahgoub et al (2000) with Omani lambs, whose ration consisted of 60% forage, Wildeus et al (2007) with hair sheep fed 100 % alfafa hay or Madhavi et al (2006) with Nellore lambs fed neem seed cake based complete diets. Some works have reported lower values (5.7 to 4.1) but they were obtained with rations of a higher concentrate inclusion ratio (Pineda et al 1998; Kawas et al 2007; Archimede et al 2007). The FCR is a trait of economic importance and should be improved by a better feeding management.

Carcass characteristics

The carcass weight significantly increased (from 13 to 16 kg) as expected with the class of LW at slaughter (Table 3). The cold carcass yield, approximately 62%, does not significantly differ from one LW class to another (Table 3) as reported by Santos-Silva and Vaz Portugal (1991). However, these values are higher than other tropical sheep (48%, Mahgoub et al 2000; 44%, Guttierez et al 2005; 52%, Kawas et al 2007; 56%, Madhavi et al 2006), an encouraging conclusion for these preliminary intensive fattening experiments with OMK sheep.

Conformation scores remain satisfactory around 4, regardless of the group (Table 4).

Table 4. Internal fat tissues and quality scores of carcass of Ovin Martinik lambs fed chopped whole sugar cane supplemented with pea flour according to live weight (LW) at slaughter
Group of LW at slaughter	28 kg	30 kg	33 kg	36 kg
Omental fat, g	285^a ± 91	350^b ± 63	375^b ± 54	435^c ± 140
Kidney and channel fat, g	245^a ± 82	395^b ± 108	332^b ± 26	375^b ± 124
Total internal fat*, % CCW	6.3^a ± 1.6	7.5^b ± 0.9	6.4^a ± 0.7	6.5^a ± 2.0
Internal fat score (1-5)	2.5^a ± 1.0	4.3^b ± 0.9	3.5^b ± 0.6	3.5^b ± 1.7
External fat score (1-5)	3.0 ± 0.0	3.0 ± 0.0	3.3 ± 0.5	3.5 ± 0.6
Conformation score (1-5)	3.5^a ± 0.6	4.0^b ± 0.8	4.0^b ± 0.8	4.0^b ± 0.5
Color** (1-4)	2.5^a ± 0.6	3.0^b ± 0.0	3.0^b ± 0.0	3.0^b ± 0.0
^a,b,cMeans within the same row with different superscripts differ significantly (P<0.05) * Total internal fat = omental fat + intestinal fat + kidney and channel fat ** (dark red = 4; red = 3; rose = 2; pale rose = 1)

All the anatomical regions of the carcass consistently (P<0,05) increased in weight (Figure 1).

Regardless of carcass weight, the distribution of prime cuts seemed to be similar with about 19% for the shoulder proportion. The leg proportion represents 35% of the carcass and varies on the same scale with well-conformed genetic sheep breeds (32 to 36%) studied by Laville et al (2002). OMK lambs seem to present cut proportions that are higher than the values recorded by Gutiérrez et al (2005) in Mexico or by Madhavi et al (2006) in India, although it is difficult to compare cutting techniques.

The internal fat scores varied significantly by one point from the lighter to the heavier carcasses (Table 4). In fact, the weight of the peritoneal and kidney fat tissues increased relative to the carcass weight. It is obvious that they represented only 6.5 to 7.5% of the CCW meanwhile very higher values are reported (Laville et al 2002). Similarly, no significant effect was observed on fat cover scores which remained at a very satisfactory level of 3.2 on 5 points-scale.

Conclusions

Acknowledgements

The authors would like to thank J Gobbardhan, G Gravillon, and W Troupe for their technical help. They are grateful to L Onyeka for English corrections of the manuscript. This study was supported by the “Region Martinique”, the "Region Guadeloupe" and the “European Community” (FEOGA).

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