Contribution to the study of body development in Merino Precoce lambs, subject to two diets

Contribution to the study of body development in Merino Precoce lambs, subject to two diets

Two groups of twelve Merino Precoce lambs, slaughtered at 25, 30, 35 and 40 kg liveweight were studied to evaluate the effects of two diets with different roughage to concentrate ratios (diet 1 - 60% concentrate + 40% roughage; diet 2 - 40 % concentrate + 60% roughage) on carcass characteristics, chemical composition of muscle and fat and histological traits of muscle. Diet 1 allowed a higher growth rate and a lower feed conversion. Diets had no significant effects on carcass characteristics or chemical composition of muscle and fat. The effects on muscle distribution were significant only for three of the nine muscles considered and the differences were small. As live weight increased, lamb carcasses changed according to the normal pattern of development. Differences on muscle distribution were found for Semimembranosus muscle, that decreased significantly as a proportion of total chemical composition and histological traits of muscle. Lipid concentration of fat tissue, however, increased significantly.

KEY WORDS: Lambs, growth, roughage to concentrate ratio, carcass composition, muscle distribution.

The normal growth pattern of the various animal species may be represented by sigmoidal curving lines, with the exception of Man (Brody 1964). It is also known that weight increase involves great changes in the body composition and that there are priorities in the development of organs, tissues and different body areas. Hammond's works showed that there are two growth gradients, one from the cranial area to the caudal area and the other from the metatarsal area to the pectoral and pelvic arch areas (Prud'hon 1976).

The sequence of priorities in the formation of tissues is very well defined. The nervous tissue is the first to develop followed by the bone, muscular and fat tissues respectively (Wood et al 1980; Butterfield et al 1983a,c and 1984b; Butler-Hogg 1984).

The influence of feed on growth phenomena is not yet well defined. The type of diet may change the body composition within certain limits (Andrews and Orskov 1970), although the effects are influenced by breed (Fortin et al 1981; Robelin 1986) and the level of maturity (Lindsay and Davies 1981). The effects of feed on fat partition are practically unknown, although some authors refer to an increase of energetic concentration which corresponds to an increase in the proportion of subcutaneous fat (Kempster et al 1976a; Murray et al 1974 cit. Sully and Morgan 1982). Feed does not seem to have any effects on muscle distribution (Berg and Butterfield 1975; Fortin et al 1980; Jones et al 1984).

The present work aims at studying some aspects of Merino Precoce lamb development, trying to evaluate the effect of two diets with different roughage to concentrate ratios.

During the trial, animals were fed ad libitum and the group intake was controlled on a daily basis. All lambs were weighed weekly, at the same time and before feeding. Drinking water was supplied ad libitum.

The diet of both groups was based on concentrate feed and wheat straw. The concentrate was formulated with crushed oats (80%) and soyabean meal [44% protein] (15%) complemented with minerals and vitamins. Diets were established in such a way as to have ratios of 60% of concentrate and 40% of straw in the first diet and 40% of concentrate and 60 % of straw in the second one. The feed was presented in the form of "cake". The mean analytic composition is shown in Table 1.

At the beginning of the trial, four slaughter weights were determined: 25, 30, 35 and 40 kg of live weight. Three lambs were slaughtered for each of these live weights and for each diet.

Live weights, weights of hot and cold carcasses and of gastro- intestinal contents were determined for each lamb at the slaughterhouse. The right halves of all carcasses were totally dissected and the weights of muscle, subcutaneous ,intermuscular, pelvic, renal and bone fat were determined.

The following nine muscles were individualized: Infraspinatus, Supraspinatus, Deltoideus, Triceps brachii caput laterale, Triceps brachii caput longum of the foreleg, Gracilis, Sartorius, Semitendinosus and Semimembranosus of the hindleg.

Samples of the Longissimus dorsi muscle were collected at the 6th and 13th dorsal vertebrae level and at the 6th lumbar vertebra level. These samples were conserved in a 10% formol solution for later histological tests (diameters of muscular fibres and adipocytes). The parts of the Longissimus dorsi muscle between the 13th dorsal vertebra and the 6th lumbar, as well as the samples of fat from the pelvic and renal deposits were used for the chemical analysis.

Table 1: Diet Composition

	DIET 1	DIET 2

Dry Matter (%)	82.35	82.05
Crude Protein (%)	8.12	6.30
Crude Fat (%)	3.50	2.70
Crude Fibre (%)	17.00	20.10
Non nitrogenous extracts (%)	47.98	47.70
Ash (%)	5.75	5.25
NDF (%)	36.55	41.50
Metabolizable Energy (MJ/kg DM) *	10.50	9.41
Retained Protein (g/MJ ME) **	4.14	3.60

* Values calculated according to the method proposed by the Agricultural Research Council (1980).
** Calculations according to the following values: 80% of protein degradability in the rumen (Ministry of Agriculture, Fisheries and Food 1975); 80% of starch nitrogen in microbial protein, 70% of the digestibility in the small intestine of microbial starch nitrogen and of feed origin and 75% of the efficiency in using nitrogen apparently digested in the small intestine (Agricultural Research Council 1980).

In order to determine the diameters of muscular fibres and adipocytes histologically, 4 mµ histological cuts were made and Hematocilin-Eosin was used as dye. The method used for measuring was Stiassnie's ocular micrometer (cit. Langeron 1942). Protein contents of muscle were determined by Kjeldhl's method (AOAC 1984).The total lipids of muscle and fat were determined by the method of Summers et al (1965).

Growth and dry matter intake were studied through the adjustment of regressions to the days of trial. The feed conversion factor was estimated based on the accumulated feed intake and live weight values.

The experimental design based on a factorial scheme (2 x 4) using two levels of the diet factor and four slaughter weights allowed the variables of carcass composition, chemical composition of muscle and fat and histological characteristics of the muscle to be studied. Each one of these variables was analyzed using the usual test of variance analysis, having been completed with a test of multiple comparisons when significant differences were found.

Table 2 shows the regressions determined to characterize lamb growth in the two groups. Group 1 lambs had a growth rate which was significantly higher than that of the lambs of group 2. In both cases, growth did not reach the breed potential. In the "Estaçäo Zootécnica Nacional", growth rates superior to 300 g/day were determined in animals of the same breed and sex (unpublished results). The new values may be due to low levels of protein in diets 1 and 2, 8.12 and 6.30% respectively. These values are much lower than those presented in the literature for growing lambs (Church 1972; Orskov et al 1976; Adu and Osinowo 1985).

The highest growth rate in group 1 may be explained through the differences between the energy and protein fractions in feed. The values of diets 1 and 2 were 4.14 and 3.60 respectively for the ratios between the retained protein and metabolizable energy. Orskov (1988) considers that the requirements of 40 kg lambs with a growth rate of 200 g/day are met by feeds with a value of 5.90 for the ratio mentioned above. Therefore, it may be accepted that, in relation to protein, there was an excess of energy intake in both groups, although it was higher in group 2. The physical characteristics of feeds as well as the low contents of nitrogenous substances may have limited protein intake in both groups. As a result, protein intake is the limitant factor of growth. Diet 1, having a higher nitrogen content and being more balanced, allowed greater lamb growth.

The daily intakes of feed and dry matter were analyzed using linear regression. The results are presented in table 3.

Table 3: Analysis of the evolution of daily mean intakes (y) in relation to the number of trial days (x), for the total feed (TF) and dry matter (DM) variables.

	GROUP 1		GROUP 2

Daily intake (TF)
N. obs.	15		15
regression	y=1.012+0.0064x		y=0.896+0.0052x
r	0.83		0.84
GRb	(0.0039	0.0088)	(0.0033	0.0070)
GRa	(0.853	1.172)	(0.775	1.017)

Daily intake (DM)
N. obs.	15		15
regression	y=0.834+0.0053x		y=0.735+0.0042x
r	0.83		0.84
GRb	(0.003	0.0073)	(0.0027	0.0057)
GRa	(0.697	0.971)	(0.632	0.838)

Although the differences between the a and b coefficient figures of the regressions were not significant, a tendency for higher intake in table 3 was verified. This tendency is proved by the means presented in table 4.

Table 5 shows regressions obtained after comparing the total intakes with the increases of live weight, for which the value of b presented the mean conversion rate.

Group 1 shows a conversion rate (7.63) significantly lower than that of group 2 (9.41).

The greatest intake of diets with a higher proportion of concentrate was also verified by Castillo and Elias (1981), Sekine et al (1986) and Hassan and Bryant (1986). These authors used growing animals, as was done in this work. Forage based diets may not meet the requirements of this type of animal. In many cases, intake is regulated by physical phenomena. The composition of diet 1 had a greater proportion of concentrate and the protein to energy ratio was more balanced. Therefore, it may have allowed an increase of the microbial activity and degradation rate of carbohydrate components. We may accept that diet 1 allowed a greater passage rate and thus a greater intake.

Carcass characteristics and composition corrected yield and carcass composition

Carcass composition was studied through variance analyses and results are shown in tables 6 and 7. Table 6 also includes results concerning the corrected yield (weight of the cold carcass/empty live weight).

Table 6: Variance analysis for corrected yield (CY), muscle (M), subcutaneous fat (SF), intermuscular fat (IF) and pelvic and renal fat (PRF).

sw	DIET 1				DIET 2
(kg)	25	30	35	40	25	30	35	40	D	W	DxW

CY	49.9	50.6	50.3	51.6	50.3	49.6	49.2	51.0	NS	NS	NS

M	59.7	56.8	55.2	55.6	55.9	54.8	55.9	56.1	NS	NS	NS

	b	ab	a	ab	ab	ab	ab	a
SF	6.6	8.9	10.9	9.6	7.6	8.3	8.5	10.1	NS	*	NS

IF	9.8	12.3	12.5	12.9	13.5	12.1	12.4	12.9	NS	NS	NS

	ab	b	ab	a	ab	ab	ab	ab
PRF	2.4	2.1	2.6	3.5	2.3	2.2	2.7	3.4	NS	*	NS

Note: sw:slaughter weight; D:diet; W:weight; DxW:interaction between diet and weight.
Significant differences of W£ 0.05 correspond to different indexes.

The corrected yield was neither influenced by the diets nor by the slaughter weight.

According to Kempster et al (1982), yield increases with the increase of carcass fat in animals slaughtered at the same weight. As the diet had no significant effects on the carcass composition, no differences in yield were expected.

In relation to weight, the obtained results are not easy to justify because, according to Geay (1978) and Solomon et al (1980), yield increases as a result of live weight.

Diets did not have significant effects on carcass composition. Group 2 lambs were expected to have carcasses with a greater fat proportion because of the greater fraction of available energy for the synthesis of fatty tissues. Differences in diet composition were probably not sufficient for changes in carcass composition to occur. The obtained results at 25 kg may show that in this phase of development, group 2 lambs were accumulating more fat than group 1 lambs, although differences were not significant.

Table 7: Variance analysis for total fat(TF), bone(B), muscle/bone (M/B) and intermuscular fat/subcutaneous fat(IF/SF).

sw	DIET 1				DIET 2
(kg)	25	30	35	40	25	30	35	40	D	W	DxW

TF	18.8	23.4	25.3	25.9	23.4	22.7	23.6	26.2	NS	*	NS

B	21.2	19.5	19.2	18.1	20.6	21.8	20.1	17.5	NS	*	NS

	ab	ab	ab	ab	ab	b	ab	a
M/B	2.8	2.9	2.9	3.1	2.7	2.5	2.8	3.2	NS	*	NS

IF/SF	1.5	1.4	1.2	1.3	1.7	1.5	1.5	1.3	NS	NS	NS

Note: sw:slaughter weight; D:diet; W:weight; DxW:interaction between diet and weight.
Significant differences for W£ 0.05 correspond to different indexes.

When comparing values now obtained with those presented by Silva (1986) for Merino Precoce lambs which were slaughtered at 30 and 35 kgs of live weight and fed a 16% crude protein concentrate, it is verified that in that case, the carcass muscle values were higher while those of the total fat were lower. This was due to a smaller accumulation in the intermuscular deposit. In the 40 kg case however, the differences annulled themselves. These results are in accordance with those of Andrews and Orskov (1970), which verified a lesser quantity of carcass fat due to the increase of 10 to 20% of crude protein in lambs slaughtered between 16 and 40 kgs of live weight. These authors also verified that the answer had a tendency for curvilinearity, admitting that for greater weights, these differences should be annulled. Similar results were obtained by Lindsay and Davies (1981) in cattle. Therefore the composition of the diets that were used in this trial, namely the low level of protein, may have influenced the growth of the muscular tissue. This effect may have been compensated by greater fat deposition that determined differences in carcass composition in both trials. In the final phase of the trial, there was a greater approach between animal requirements and feed composition.

The greater accumulation of fat in the intermuscular deposit was prematurely formed and this may suggest that a preferential accumulation in the deposit presenting the greatest growth rate during this development stage may correspond to an increase of fat synthesis.

Weight significantly affected fat and bone percentages which increased and decreased respectively. These results reflect normal changes of carcass composition in conditions of continuous growth, due to differences in patterns of development of both tissues.

As far as the muscle is concerned, there was no relative decrease in carcasses as should be expected according to the results of Butterfield et al (1983a) and (1984b) and Kempster et al (1987b). These authors classified this tissue as one of premature formation, although the obtained values are close to isometry. It is accepted that the situation of protein shortage may have influenced the lambs' development at the beginning of the trial. Therefore, the quantity of muscle in carcasses of animals slaughtered at inferior weights did not reach the maximum allowed by the genetic potential. Probably due to the lambs development and the decrease of their protein requirements, at the end of the trial, muscle deposition levels were close to those allowed by the genetic potential of the animals. That is why the proportion of this tissue in carcasses was relatively constant.

During the considered periods, lamb fat deposits were preferentially found in the subcutaneous, pelvic and renal deposits which increased significantly in percentual value. On the contrary, the intermuscular deposit kept constant. Thus, we may confirm the late and early pattern of development of the subcutaneous and intermuscular deposits respectively, as referred by Kempster et al (1976a and 1987b), Simöes and Carmona Belo (1983) and Silva (1986). As far as the pelvic and renal deposits are concerned, results show that there will be a late phase of deposit, as referred by Kempster et al (1987a) and Thompson et al (1987).

The muscle to bone ratio increased significantly with weight, and this is in accordance with Broad and Davies (1981). Yet, the new obtained results are inferior to those referred by Silva (1986) for lambs of the same breed and sex that were slaughtered at the same weight.

Tables 8 and 9 show results concerning the muscle distribution. Values are presented as percentages of the carcass total muscle.

Table 8: Variance analyses for Infraspinatus muscle (M1), Supraspinatus muscle (M2), Deltoideus muscle (M3), Triceps brachii caput laterale muscle (M4) and Triceps brachii caput longum muscle (M5).

sw	DIET 1				DIET 2
(kg)	25	30	35	40	25	30	35	40	D	W	DxW

M1	2.55	2.59	2.57	2.56	2.66	2.51	2.54	2.57	NS	NS	NS

	ab	ab	ab	b	a	ab	ab	ab
M2	2.11	2.23	2.27	2.09	2.55	2.30	2.35	2.29	*	NS	NS

	b	b	b	b	a	ab	ab	ab
M3	0.44	0.49	0.41	0.44	0.57	0.49	0.47	0.53	*	NS	NS

M4	0.88	0.79	0.82	0.94	0.89	0.87	0.82	0.89	NS	NS	NS

M5	3.08	3.02	3.13	2.85	3.42	3.01	3.07	2.86	NS	NS	NS

Note: sw:slaughter weight; D:diet; W:weight; DxW:interaction between diet and weight.
Significant differences for D£ 0.05 correspond to different indexes.

Table 9: Variance analysis for Sartorius muscle (M6), Gracilis muscle (M7), Semimembranosus muscle (M8) and Semitendinosus muscle (M9).

sw	DIET 1				DIET 2
(kg)	25	30	35	40	25	30	35	40	D	W	DxW

M6	0.18	0.21	0.16	0.20	0.22	0.19	0.15	0.21	NS	NS	NS

	a	a	a	a	a	a	a	a
M7	0.91	0.88	0.81	0.85	0.90	0.97	0.96	0.99	*	NS	NS

	a	a	a	a	a	a	a	a
M8	5.97	5.82	5.44	5.11	6.03	5.42	5.10	5.37	NS	*	NS

M9	2.02	2.24	2.18	2.82	2.13	2.50	2.30	2.27	NS	NS	NS

Note: sw:slaughter weight; D:diet; W:weight; DxW:interaction between diet and weight.
Significant differences for D£ 0.05 and W£ 0.05 correspond to different indexes.

As far as diets are concerned, significant differences were found concerning Gracilis, Supraspinatus and Deltoideus muscles. In Gracilis and Supraspinatus muscles however, the test of multiple comparisons did not allow to find differences between individual groups. As far as the Deltoideus muscle is concerned, real differences between the two groups were verified only at 25kg. The differences found were very small and this is in accordance with Fortin et al (1980) and Kempster et al (1976b) who verified that diets with different energetic levels had a minimum effect on the muscle distribution.

As far as the Semimembranosus muscle is concerned, significant differences were found concerning slaughter weights. The proportion of this muscle decreased as a result of the weight increase. These results show that all the considered muscles, except the Semimembranosus one, will have to be classified as muscles of isometric growth. This was confirmed by values obtained for allometric coefficients which are shown in table 10.

The allometric coefficient of the Semimembranosus muscle was significantly inferior to 1, showing that it is of premature formation. This result is in accordance with Taylor et al (1980), Butterfield et al (1983b and 1984a) and Thonney et al (1987).

According to the results of this trial, at this stage of development small differences may be found in lambs muscle distribution, as referred by Butterfield and Berg (1966) in relation to cattle.

Table 10: Allometric coefficients of individual muscles.

	GR. 1	GR. 2	W£ 0.05

Infraspinatus	0.93	0.93	NS
Supraspinatus	0.96	0.77a	*
Deltoideus	0.95	0.83	NS
T. b. caput laterale	--	1.00	--
T. b. caput longum	--	0.62a	--
Gracilis	0.85	1.20	NS
Sartorius	0.99	0.67	NS
Semimembranosus	0.60a	0.75a	NS
Semitendinosus	1.22	1.11	NS

Table 11 shows results of variance analyses which are relative to the chemical composition of muscle and fat.

The diet had no significant effects on chemical parameters of muscle and fat which were analyzed.

According to Lawrie (1966), intermuscular fat is affected by the feeding level just as it occurs with total fat. As the diet did not influence the percentage of total fat, no effects were expected on the lipid percentage of the muscle.

Table 11: Variance analysis for the nitrogen percentage of the muscle (NM), total lipids percentage of Longissimus dorsi muscle (LM) and total lipids percentage of fat (LF).

sw	DIET 1				DIET 2
(kg)	25	30	35	40	25	30	35	40	D	W	DxW

NM	3.00	3.00	3.23	3.23	3.15	3.07	3.30	3.30	NS	NS	NS

LM	2.40	3.30	2.87	2.78	2.93	2.82	3.02	3.03	NS	NS	NS

LF	88.6	88.5	89.1	93.2	88.9	87.0	94.0	90.2	NS	*	NS

Note: sw:slaughter weight; D:diet; W:weight; DxW:interaction between diet and weight.
Significant differences for W£ 0.05 correspond to different indexes.

The chemical composition of the muscle was not significantly affected by weight. The contrary was expected because growth usually means a decrease of muscular water and nitrogen and an increase of the lipid concentration (Lawrie 1975 and 1978). The weight interval considered in the trial may not have been sufficient for differences to occur.

The increase of total lipids percentage of fat tissue is in accordance with Callow (1948) who refers that the lipids concentration of fat tissue is directly related to the total fat of the carcass.

Table 12 shows results of variance analyses concerning histological parameters determined in the muscle.

Table 12: Variance analysis for fibre diameter (FD) and adipocyte diameter (AD).

sw	DIET 1				DIET 2
(kg)	25	30	35	40	25	30	35	40	D	W	DxW

FD(µ)	23.7	22.4	25.0	23.2	22.4	22.5	23.2	21.2	NS	NS	NS

AD(µ)	41.3	41.4	43.6	45.2	42.4	41.4	45.2	46.1	NS	NS	NS

Note: sw:slaughter weight; D:diet; W:weight; DxW:interaction between diet and weight.

Neither diets nor slaughter weights had any significant effects on the analyzed variables.

Moody et al (1980) and Cornforth et al (1980) found no differences in fibre diameters of Longissimus dorsi and Biceps femoris muscles when they evaluated the effect of diets on histological parameters. The new results are in accordance with these authors.

Moody et al (1970) verified that there was an increase of the fibre diameter of the Longissimus dorsi muscle in entire lambs slaughtered between 36 and 54 kg. Yet, they found no differences in castrated lambs. As far as the Semimembranosus muscle is concerned, no differences were found in the fibre diameter in any of the two types of animals. The effect of weight on muscle fibres diameter may depend on the level of maturity reached by muscles used as samples. This depends on the animals level of development at slaughter. In this trial, weight did not led to significant differences in muscular fibres diameter which may probably be related to the high level of maturity of the Longissimus dorsi muscle during the considered stage of development. This is in accordance with Butterfield et al (1983b and 1984a) who classified this muscle as one of early maturity.

The diet had no significant effects on the adipocyte diameter. Although weight had no significant effects on this parameter, there is a tendency for an increase, which is in accordance with results found by Moody et al (1970 and 1980).

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Table 2: Live weight regressions (y) in relation to the number of trial days (x).

	N. obs.	regression	r	GRl

Gr. 1	111	y=22.716+0.176x	0.84	(0.154	0.198)
Gr. 2	144	y=22.344+0.131x	0.85	(0.117	0.145)

Table 4: Mean values of daily intake during trial

	Group 1	Group 2

Daily mean intake of feed/lamb (kg)	1.38	1.19
Daily mean intake of DM/lamb (kg)	1.14	0.98
Daily mean intake of DM/kg W0.75 (kg)	0.086	0.076

Table 5: Regressions of the total feed intake (y) in relation to live weight gain (x)

	N. obs.	regression	r	GRb

Gr. 1	16	y=8.81+7.63x	0.99	(7.18	8.08)
Gr. 2	18	y=61.36+9.41x	0.99	(9.07	9.75)