Effect of feedlot regimen on performance and carcass characteristics of Sudan Baggara Zebu cattle

S R Fadol and S A Babiker*

Animal Production Research Centre, P. O. Box 1135 Kuku, Khartoum North, Sudan
sosobitnema@hotmail.com
* Institute for Promotion of Livestock Export, University of Khartoum, Sudan

Abstract

Twenty four Sudan Baggara Zebu bulls were divided into two groups of similar body weight (245kg ± 8.08) and fed molasses based diet for a pre-experimental period of two weeks followed by a feeding period of 12 weeks  At the end of this pre-experimental periods the two animals groups were randomly assigned to the feed management, which was ad libtum feeding (group A) or restricted feeding (group B). Group (A) was offered the diet ad libitum for the whole feeding period. Feeding in group (B) was offered into four interchangeable periods of three weeks each where feed was offered 50% of ad libitum for 3 weeks followed by ad libitum feeding for the next 3 weeks and so on.

There were no differences between the two groups in final weight, total gain and daily gain. Live weight increased linearly in the ad libitum fed but not in the restricted fed bull groups. Daily dry matter intake and total dry matter intake were respectively greater (p<0.00119) and (p<0.0119) in ad libitum fed bulls than in restricted bulls. Slaughter and empty body weights were not different in the two groups. Hot and cold carcass weights were respectively  greater (P<0.0413) and (p<0.0386) in the ad libitum fed group than in the restricted bulls. Muscle percentage was also greater (p<0.00461)) while bone and fat percentages increased slightly in ad libitum fed bulls. Muscle to bone ratio was not different between the two feeding groups. Dressing percentage did not differ between the two groups but the ad libitum fed group dressed slightly heavier than the restricted group. Longissismus dorsi  muscle area was not  different between the two groups. The area of the muscle was 61.07 cm² in carcasses of the ad libitum fed group and 49.15 cm² in the restricted bulls.

The results indicated that non-carcass components showed no significant differences between the two groups except for the weight of head which was heavier (p<0.0362)  in restricted bulls than in ad libitum fed bulls. The wholesale cuts showed no different between the two groups.

Key words: Molasses, program of feeding, tropical

Introduction

Animals in the wild, particularly ruminants but also other herbivores, experience periods of alternating food abundance and scarcity. Even under domestication animals do not always have sufficient food available at particular times to allow a full expression of their genetic potential for growth. In such cases a smooth progression a long the sigmoid- shaped growth curve is disrupted. When this occurs, growth falls below genetic potential. It had been shown in many experiments that when food supplies became abundant after periods of feed scarcity, growth rates accelerated and exceeded those achieved by comparable animals fed well and continuously. This faster rate of growth relative to age has been termed compensatory growth (Wilson and Osbourn 1960). Restriction can be implemented either by limiting the quantity or quality of the diet. The period of restriction must be long enough to ensure adaptation to the lower plane of nutrition in order for compensatory growth to be realized (Ryan 1990).

In countries like Sudan, cereal and sorghum is the staple food for people and the crop is costy to feed ruminants. The country has large livestock population raised mainly on natural pastures and rain fed crop by-products mainly sorghum stalks. The country experiences seasonal rainfall which affects animal growth and development. Sugar cane industry is expanding in Sudan and its processing by-products particularly molasses is little utilized in animal feeding although it is cheaper energy source than energy dense cereals. Use of high molasses diets in intensive systems of cattle fattening has been developed in Cuba (Preston 1972). Some feeding trials utilizing molasses based diets reported that live weight gain of 1.0 kg was achieved by Zebu cattle of Sudan( Eltahir 2003)and 1.3to 1.7 in Brahman steer (Tomkins et al 2004). Thus the technology of molasses based diets for ruminant's production worths transfer to Sudan.       

The objective of this study was to use a diet based on molasses in a regimen of restricted feeding followed by ad-libitum feeding hoping to exploit compensatory growth and reduce  total feed required to finish beef cattle. The effect of this feeding programme on feedlot performance and carcass characteristics was  also assessed.

Material and methods 

Twenty four Sudan Baggara Zebu bulls were used in this experiment. Bulls were purchased from Omdurman local market (Elmoulih) and trekked to Animal Production Research Center, Kuku, Khartoum North. There, they were rested, ear tagged and kept for a pre-experimental period of two weeks followed by a feeding periods of 12 weeks.  The animals were fed on molasses feed composed of 52% molasses, 39% wheat bran, 5% groundnut cake, 3% urea and 1% common salt in addition to sorghum straw. The feed was offered at a ratio of 80% molasses feed and 20% sorghum straw. At the end of the per-experimental period bulls were weighed following an overnight fast except for water and divided into two groups of equal average live weight of (245±8.08kg). Each group was sub-divided into three groups of four animals

The two animal groups were randomly assigned to one of the feed managements, which were ad libtum feeding (group A) or restricted feeding (group B). Group (A) was offered the diet ad libitum for the whole feeding period. Feeding in group (B) was offered into four interchangeable periods of three weeks each. In the first period feed was offered as 50% of ad libitum followed by ad libitum feeding for the next period then 50% of ad libitum for the third period and ad libitum for the last period. All animals had free access to clean water and salt lick.

Animals were individually weighed weekly in the morning before feeding. Rates of gain were calculated from the regression of live weight on time (figure 1).

At the end of the feeding period seven animals from each group were randomly selected for slaughter. Animals destined for slaughter were offered water but not food for 14 hours before slaughter. After dressing and evisceration, the internal organs and offal's were individually weighed. The alimentary tract was weighed and then cleaned of its contents (fill) and reweighed. The weight of fill was subtracted from the slaughter weight to determine the empty body weight.

The carcass was weighed hot and then split along the vertebral column into right and left sides. The left carcass side was weighed hot, and after chill at 7 Cº for 24 hours then jointed into 14 wholesale cuts according to M.L.C (1974). Each cut was then dissected into fat, lean, bone and connective tissue and weighed separately. The total weight of each tissue was pooled to give totals for the side. Samples were taken from Longisimus dorsi muscle following carcass chilling for chemical analysis (A.O.A.C 1980). Meat quality attributes as water holding capacity, cooking loss and meat color were detemined as in Babiker and Lawrie (1983). Statistical analysis was performed according to Student t-test for Windows SatSoft, Inc. (1995).

Result and discussion 

Feedlot performance data presented in table 1 indicated that final live weight, total live weight gain and daily gain of ad libitum and restricted bulls tended to be higher in ad libitum fed ones.

According to figure 1, the regression curves indicated that restricted fed bull group was consistently lower in live weight than  ad libitum fed group. The rate of gain  was lower in restricted fed bull group than in ad libitum fed one . The rate of gain of restricted bulls, following full feeding was initially greater up to the eleventh week and thereafter it declined. This could possibly be due to compensatory growth to that feeding period followed by attainment of mature weight. The fact that R² of restricted bull group was lower than that of ad libitum fed group could be explained by the regimen of feeding in the former group. The slight  reduction in rate of gain of restricted bulls might be explained by the reduction (p>0.0119)in total DM intake. Coleman and Evans (1986)  reported that a period of feed restriction had resulted in a decrease in total amount of feed required to reach a given weight. Sainz et al (1995) restricted intake of calves by 45 % before a period of ad libitum consumption and found that overall average daily gain was reduced and 48 more days on feed were required to reach market weight compared with ad libitum access to feed throughout the feeding period. Knoblich et al (1997) reported that restricted feed intake resulted in rates of gain similar to those achieved with full feeding throughout the entire feeding period. In most situations, restricting intake had reduced rate of gain and increased the time required for cattle to reach market weight. However, this problem was alleviated when a programmed feeding system that achieved step-wise increases in growth was used (Loerch and Fluharty 1998).

Feed conversion efficiency shown in table 1 revealed that restricted bull group was less efficient than ad libitum fed one. This was in agreement with Carstens et al (1991) who did not observe any difference between restricted and control bulls in feed efficiency. Coleman et al (1993) reported that the efficiency of gain was higher for compensating steers with no difference in overall efficiency. Knoblich et al (1997) observed that feed efficiency was improved after a period of feed restriction in limit fed cattle. On the other hand Coleman and Evans (1986) reported that feed conversion efficiency for restricted steers was slightly lower than for control.

Carcass yield and characteristics given in table 2 indicated that slaughter weight and empty body weight were slightly lower in the restricted bull groups than in the ad libitum fed one.

These findings  were in agreement with Schoonmaker et al (2003) who reported no difference in slaughter weight at common back fat thickness in crossbred steers on different feeding regimens ( high concentrate fed ad libitum, high concentrate fed to achieve a gain of either 1.2 kg/day or 0.8 kg/day, or high fiber fed ad libitum). Also Ehoche et al (1992) reported no significant difference among restricted cattle groups and control in empty body weight during subsequent full feeding period.

According to table 2 hot carcass weight, cold carcass weight and cold side weight were greater in the ad libitum fed group than in the restricted bulls. These differences might possibly be due to the heavy empty body weight and to the lighter body components as head, hide, feet, empty alimentary tract and liver of the former group. Knoblich et al (1997) contrasted with this result and reported that there were no difference in hot carcass weight due to feeding system.

Carcass composition of ad libitum fed and restricted bulls indicated greater muscle percentage (p<0.0461) in ad libitum fed than in restricted bulls. Carcass bone and fat increased slightly in ad libitum fed than in restricted bulls. Sainz et al (1995) found that restricted steers were leaner than control steers.  Ehoche et al (1992) reported that a period of feed restriction led to lower lean and fat proportion but higher bone proportion. While Abdalla et al (1988) found that steers under going compensatory growth deposited more fat in the carcass than did control steers. Coleman et al (1993) reported that older restricted steer carcasses were fatter than older control in the finishing phase. Difference in the length of the restricting period might account for these discrepancies (Ryan 1990).

Muscle: bone ratio was not affected by restriction and the difference between the two groups was not significant. Mohamed (1999) reported significantly higher muscle: bone ratio of Sudan Baggara Zebu bulls fed higher dietary energy than those fed lower energy. Muscle to fat ratio was slightly lower in ad libitum fed bull group than in the restricted bull possibly due to increased carcass fat in this group. Hornick et al (1998) reported that muscle to bone ratio was similar between restricted and control animals when slaughter weight was used as a covariate.

The current results indicated that bulls ad libitum fed dressed slightly heavier than the restricted bulls. The difference in dressing percentage for ad libitum and restricted bulls was primary due to difference in the weight of gut fill and other external components as head, skin and four feet. In addition ad libitum fed bulls were fatter than restricted bulls.

Longissismus dorsi  muscle area was greater in bulls fed ad libitum compared with restricted bulls. This agreed with Knoblich et al (1997) who found that there was no difference in rib eye area between restricted and unrestricted bulls. Sainz et al (1995) also reported that Longissimus dorsi muscle area was reduced in steers restricted to 70 % of ad libitum and in the steers fed low concentrate diet in growing phase. Boleman et al (1996) reported that Longissimus dorsi muscle area was influenced by protein level for which high protein diet resulted in larger (p<0.05) Longissimus dorsi muscle area. Mohamed (1999) and Ahmed (2003) found that Sudan Baggara Zebu bulls given higher energy diet had greater Longissimus dorsi muscle area than those given low energy diet.

Body components of restricted and ad libitum fed bulls are given in table 3.

The mean weight of the head was greater (p <0.0362) in restricted bulls than in ad libitum fed bulls. The percentage of body components as hide, four feet, rumen full and empty, omasum full and empty, abomasum full and  empty, gut fill, liver, heart , spleen and blood were slightly  heavier in the restricted bulls. This result agreed with Carstens et al (1991) who found that compensatory growth gain was attributable largely to increased gut fill plus weight of the digestive tract and other internal organs. Murray et al (1977) indicated that the weight of contents of the reticular rumen was greater for steers with restricted intake.  While intestine full and empty, mesenteric fat, omental fat, and kidney fat as well as genitalia, lungs and trachea, diaphragm, pancreas and tail were slightly heavier  in the ad libitum fed bull group. Sainz and Bentley (1997) reported that at the end of the growing phase there were no significant differences in weight of heart, lungs or spleen. Fore-stomach and  intestine, were the highest in the quality-restricted group and lowest in the control.

As seen in table 4 wholesale cuts yield as percent of cold carcass weight of ad libitum fed and restricted bulls were not significantly different.

Cuts as clod, neck,  thin ribs, extended roasting ribs, brisket, hind quarter flank and sirloin  were slightly  higher in add libitum fed bulls; while shin, chuck and blade, thick ribs, leg, thin flank, topside and silverside  and rump were slightly  heavier in restricted bulls. Thus most of the high priced cuts as sirloin, rump, topside and silver and thick flank were obtained from carcasses of restricted bulls. Ahmed (2003) observed similar result and reported that there were no significant differences between different levels of energy and protein in yield of several wholesale cuts except for hind quarter flank, neck, shin, topside and silverside of Sudan Baggara Zebu bulls. Mohamed (1999) using the same type of cattle contrasted with this result and stated that with the exception of extended roasting ribs all other wholesale cuts were heavier in carcasses from bulls given high dietary energy but only thick flank, thick ribs and shin were significantly so.

Meat chemical composition and quality attributes of ad libitum fed and restricted bulls given in table 5 showed no difference between the two bull groups.

Slight increased percentages of fat and sacroplasmic proteins and  color co-coordinates lightness (L), redness (a) and yellowness (b) were found in the meat from ad libitum fed bulls. Water holing capacity was slightly  superior and cooking loss was lower in the meat from ad libitum fed bulls. Lawrie (1990) indicated that water holding capacity increased with increase of fatness. Here ad libitum fed bulls had more muscular fat than restricted fed bulls. Murphy and Loerch (1994) reported a linear decrease in carcass ether extract and in carcass protein when cattle were fed at 100, 90 or 80% of ad libitum. While Knoblich et al (1997) reported that there were no difference in ether extract percentage, carcass protein or water due to finishing system.

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Received 11 January 2009; Accepted 3 December 2009; Published 7 February 2010

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