Abstract

A study was conducted to evaluate the efficiency of compensatory feeding. Twenty-five Arsi bulls (32±4 months) were blocked by weight and randomly allocated to the following feed restriction treatments: ad libitum feeding for the entire period (control), maintenance feeding level (maintenance), 15% body weight loss (-15%), 20% body weight loss (-20%) and 25% body weight loss (-25%). A 91-day period of feed restriction was followed by a 105-day re-alimentation period. No treatment effects was observed on average daily gain (ADG) or feed conversion efficiency (FCE) during the compensatory period, both between control and maintenance feeding levels, and within the restricted treatment groups. Recovery index differed (P<0.01) both between the control and maintenance groups as well as within restricted treatments. Compensation was not complete, perhaps due to the low energy diet or insufficient time for compensation. No treatment effects on any carcass traits were observed between the ad libitum (control) and maintenance level feeding except ingesta (P<0.01) and among (P<0.05) restricted groups (Table 4). Effects of feeding levels linearly decreased slaughter weight (Wt2) and ingesta weight (P<0.05), as well as carcass and lean meat yield (P<0.01). Proportions of lean meat, fat and bone to total carcass and slaughter weight differed (P>0.05) between control and maintenance groups as well as among restricted treatments. Although statistically not significant, compensatory gains, FCE, and lean meat yield for treatments -15, -20 and -25% had increasing tendencies with increasing levels of feed restriction. Therefore, Arsi bulls need longer than 105 days of compensatory feeding for complete recovery of LW losses caused by different levels of restriction in a period of 91 days. The appropriate time of feeding and change in the energy density of the diet by manipulating the roughage and concentrate ratios for complete compensation following different levels of retarded growth along with cost–benefit relationship requires further investigation.

Author Keywords: Arsi bulls; Compensatory growth; Restriction period; Weight; Carcass; Concentrate; Teff straw; Recovery index

Abbreviations: ADG, average daily gain; AOAC, Association of Official Agricultural Chemists; ADF, acid detergent fiber; CP, crude protein; DMI, dry matter intake; EBWt, empty body weight; FCE, feed conversion efficiency; LW, live weight; NRC, National Research Council; NDF, neutral detergent fiber; MAFF, Ministry of Agriculture Fisheries and Food; ME, metabolizable energy; MJ, mega Joules; OM, organic matter; WG, weight gain

Article Outline

1. Introduction

2. Materials and methods

2.1. Study area

2.2. Experimental animals and management

2.3. Carcass evaluation

2.4. Chemical analyses

2.5. Data analysis

3. Results

4. Discussion

5. Conclusions

Acknowledgements

References

1. Introduction

Recent FAO statistics (FAO, 1994) show that Ethiopia possesses 29.5 million head of cattle, the highest in Africa. However, in terms of productivity, Ethiopia lags far behind the world. For example, average carcass weight per animal is 105 kg in Ethiopia, 132 kg in Kenya, 135 kg in Sudan, 231 kg in South Africa, 286 kg in Canada, 313 kg in the US, and 398 kg in Japan (FAO, 1994). What is more concerning is the declining trend of carcass output per animal. FAO (1994) indicates that carcass weight per animal in Ethiopia was 109 kg during 1979/1981, but declined to 105 kg in 1994, while in other countries the trend was to increase. For example, in Kenya, South Africa, Australia and US the improvement was by 4, 35, 44 and 42 kg, respectively, during the same period (FAO, 1994).

Livestock production in Ethiopia depends on natural pasture and crop residues and is largely influenced by availability that fluctuates throughout the year. Obradovic et al. (1975) reported severe weight loss in observations of 90 Borana cattle at the Adami Tulu Government Ranch (Ethiopia) over an 11-month period. This observation, that covered all seasons and grazing conditions, clearly demonstrated that live weight (LW) gain was related to grazing conditions. Forage available by grazing at certain times of the year, especially in January–May, was inadequate resulting in LW losses averaging 74.9 kg per head (Obradovic et al., 1975). A livestock production system survey conducted in the Mid Rift Valley of Ethiopia supported this investigation (Adami Tulu Research Center, unpublished). In this survey, all responding farmers stated that feed was scarce, almost unavailable, during the dry period that extends from December to May. Farmers give priority to supplementing oxen and milking cows. In drier areas, where drought is frequent, weight losses of animals are inevitable. The question is, at what ages and how often, can cattle fall behind normal growth rates without losing their ability to respond to better feeding levels. Knowledge of the factors that influence growth and development of these animals is essential.

Compensatory growth describes the ability of animals to exhibit, after feed restriction, a higher growth rate than unrestricted animals of the same chronological age (Wilson; Allden and O). Compensatory growth is a complex biological event because it is associated with factors such as higher feed intake ( O and Wright), increase in gut fill and high efficiency of feed use ( Carstens et al., 1991), changes in the composition of tissue gained ( Baker et al., 1985) and/or alteration in endocrine status ( Blum et al., 1985). Restricted animals, upon re-alimentation, may regain LW to values similar to those that were not restricted thereby resulting in higher feed conversion efficiency ( Ledger, 1975). The response to compensatory growth may also vary depending on the duration or intensity of under-nutrition before re-alimentation ( Wilson and Osbourn, 1960), and breed type ( Payne and Tesfaye) in which slower maturing type of cattle respond better in terms of compensatory growth after a period of under-nutrition than fast maturing cattle.

Arsi cattle probably evolved from the large group of small zebu in the central highlands of Ethiopia, especially in Arsi, Shoa and Bale provinces. They are small, short and compact with an average height at the withers of 110 cm (Albero and Solomon, 1982). Their average birth weight is 21 kg and average mature weight is 257 kg. Under feedlot conditions, they gain between 554 and 619 g per day with an average carcass weight of 115–155 kg and an average dressing percentage of 50.3 (Jepsen and Creek, 1976). They produce marbled, tender, and palatable meat ( Jepsen and Creek, 1976).

The objective of this experiment was to determine the effect of different levels of feed restriction on growth rate and carcass traits of re-alimented Arsi bulls.

2. Materials and methods

2.1. Study area

The study was conducted at the Adami Tulu Research Center situated in the middle of the Rift Valley in Ethiopia at an altitude of 1650 m above sea level with an annual rainfall of 500–760 mm. The average maximum and minimum temperatures are 27 and 12.7 °C, respectively. The soil is fine sandy loam with sand, silt and clay in the proportion of 34:48:18, respectively.

2.2. Experimental animals and management

A total of 25 Arsi bulls (32±2.3 months) were purchased from surrounding local markets. Animals were quarantined for 21 days and drenched and sprayed against internal and external parasites before the start of the experiment. Bulls were blocked by weight, with five animals per treatment, and randomly assigned to five dietary treatments as follows: ad libitum feeding for the entire experimental period (control), energy maintenance requirement for 91 days followed by ad libitum feeding for 105 days (maintenance), 15% weight loss in 91 days followed by ad libitum feeding for 105 days (-15%), 20% weight loss in 91 days followed by ad libitum feeding for 105 days (-20%) and 25% weight loss in 91 days followed by ad libitum feeding for 105 days (-25%).

The experimental ration was formulated from teff straw, maize grain, noug seed (Guizotia abyssinica) cake and common salt in the DM proportion of 42:32:25:1 during the restriction period. During the re-alimentation period the DM proportion of teff straw, wheat bran, noug seed cake and common salt was 29:53:17:1. The chemical composition of the experimental feeds is in Table 1.

Table 1. Chemical composition of experimental feeds (g/kg DM)a
(<1K)

Bulls were individually penned, fed in concrete feeding troughs and provided with water twice daily. No bedding material was used and there were no plant materials in the pens which the animals could consume. During the restriction period, animals in treatments -15, -20 and -25% were fed below their daily maintenance energy requirements (NRC, 1987) to obtain the desired LW change.

Actual data collection was started after a 21-day adaptation period when the experimental animals were gradually acclimatized to their respective experimental feeds. Data on feed intake and refusals were collected on a daily basis, while live weight changes were measured weekly. Before each weighing, animals were deprived of feed and water for 16 h. Based on actual LW, feed provision was adjusted weekly.

The restriction period of 91 days was selected to simulate a typical time of feed scarcity for the area. Following the restriction period, all animals were fed to appetite for 105 days, after which two animals per treatment were slaughtered for carcass evaluation.

2.3. Carcass evaluation

Two Arsi bulls from each feeding level were deprived of feed and water for 24 h prior to slaughter. Each animal was weighed before slaughter. The entire digestive tract (i.e. esophagus, reticulo-rumen, omasum and abomasum, intestines) was removed with the rumen contents and weighed. The rumen was emptied and the gastro-intestinal tract was weighed separately. Internal organs (i.e. lung, heart, liver, kidney and spleen) and internal fat deposits surrounding the stomach (omental), the intestine (mesentric), fat lining the pelvic arch (channel fat) were also removed. Head, hide, feet including hooves, penis and bladder and tongue were also weighed. The carcass was split into two halves and each half was weighed. The left side was deboned and the bone, lean meat and trimmed fat were separated manually and weighed.

2.4. Chemical analyses

Feeds were analyzed for dry matter (DM), organic matter (OM) and nitrogen (N) using standard procedures 7.003, 7.009 and 2.057, respectively, at AOAC (1990). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined as described by Van Soest and Robertson (1985). NDF was assayed without alpha amylase or sodium sulfite, and expressed on an ash free basis. Metabolizable energy (ME) intake (MJ/kg DM) was estimated by multiplying total DM intake of the various feeds with their respective energy (MJ/kg DM) values using Kearl (1982) and MAFF (1985).

2.5. Data analysis

Data on feed intake, LW change and carcass characteristics were analyzed for treatment differences using the general linear model procedure of the statistical analysis system (SAS, 1999). A single-degree contrast and linear and quadratic contrasts were used to compare treatment effects between control and maintenance feeding levels and within restricted groups, respectively. ADG were estimated by regression of LW against time.

The model used was:

Yij=+Bi+Tj+eij

where Y_ij is the individual observation, the over all mean, B_i the effect of block, T_j the effect of treatment, and e_ij is the random error (unexplained variation assumed normally and independently distributed).

Recovery index was calculated using the formula proposed by Wilson and Osbourn (1960) as:

where IW_c and IW_comp are the weights of the control and the compensatory groups at the beginning of the compensation period, respectively, and FW_c and FW_comp are the weights of these groups after the period of compensation.

3. Results

Mean dry matter intakes (DMIs) of restricted animals (i.e. maintenance, -15, -20, and –25%) during the restriction period were 3.22, 1.40, 1.22 and 1.02 kg per day, respectively. All animals were provided with ad libitum feed during the compensatory period (Table 2). Thus, intake increased to 4.78, 4.26, 4.46 and 4.78 kg per day, respectively, and did not differ among treatments. Estimated ME intake of treatments –15, -20 and -25% during the restriction period were 12.95, 10.5 and 8.79 MJ per day and these increased to 39.63, 41.50 and 44.78 MJ per day during the compensatory period.

Table 2. Feed intake of Arsi bulls during different levels of feed restriction (0–91 days) and re-alimentation periods (92–195 days)
(<1K)
NS: P>0.05.

The LW gain and feed conversion efficiency (FCE) during the restriction period differed (P<0.001), both between control and maintenance feeding levels and within the restricted treatment groups (Table 3). There were no significant treatment effects on ADG or FCE during the compensatory period, either between the control and maintenance treatments or among the restricted groups. There was a linear increase (P<0.01) within restricted groups on the recovery index. The overall LW differed (P<0.05) between control and maintenance treatments. Overall FCE was not significantly (P>0.05) different between animals in the control and maintenance treatment groups, or among restricted groups.

Table 3. Initial and final live weight and average daily gain (ADG) of Arsi bulls during different levels of feed restriction (0–91 days) and re-alimentation periods (92–195 days)
(<1K)
NS: P>0.05.

No treatment effects were observed on any carcass traits measured, except ingesta, which differed between ad libitum (control) and maintenance level feeding (P<0.01), and among (P<0.05) restricted groups (Table 4). There was a linear decrease within restricted treatment groups on carcass and lean meat yield (P<0.01) and slaughter weight and ingesta (P<0.05).

Table 4. Mean carcass yield of Arsi bulls after different levels of feed restriction and re-alimentation growth periods
(15K)
NS: P>0.05.

Proportions of lean meat, fat, and bone yield to total carcass and slaughter weight did not differ between ad libitum and maintenance feeding levels or among restricted groups.

4. Discussion

Feed restriction reduced the LW of the bulls and one bull from the severely restricted group (treatment -25%) died at the beginning of compensatory feeding period, probably due to metabolic disturbances caused by the sudden change in the amount of concentrate offered. It was difficult to manipulate feed restriction to obtain accurate LW losses of -15, -20 and -25%. However, the results were very close to the desired LW losses.

The ME intake of treatments -15, -20 and -25% were raised from 12.95 to 39.63; 10.51 to 41.50 and 8.79 to 4.78 MJ per day, respectively. That, the bulls in the restricted groups did not achieve similar final LW to that of the control group shows that there was incomplete recovery, similar to results of others (Hornick and Abdala, Carstens et al., 1991). However, the rapid LW gain of the previously restricted animals during the compensatory feeding period agrees with Ledger (1975). Lack of complete compensation of LW within 105 days of re-alimentation could also have been due to the severity of the LW losses imposed during the restriction period, which is suggested by reports of Wilson and Osbourn (1960); and Drouilard et al. (1991), in which responses to compensatory feeding varied depending on duration and intensity of under-nutrition before re-alimentation. Severity of nutrient restriction was more important than duration of growth for compensatory growth ( Drouilard et al., 1991). Growth response to additional crude protein may also be poor on a low energy density diet ( Smith and Broster, 1977). Arsi bulls subjected to 25% LW loss during the restriction period performed better than those that lost 15 and 20%, while animals managed on the maintenance feeding level during the restriction period attained 96% recovery ( Fig. 1). This agrees with results from double-muscled Belgian blue bulls managed on a maintenance ration for 123 days of restriction period and a recovery index of 0.94 in 204 days of compensatory feeding (Hornick et al., 1999). However, despite differences in the type of feed and the different environment, Arsi bulls are more efficient in recovering their weight losses, at least compared to the Belgian blue bulls. The negative efficiency of the restricted groups during the restriction period was reversed during the re-alimentation period. Re-alimented treatment groups had higher FCE compared to the control group, and values of total carcass weight obtained for treatments -15, -20 and -25% were far below the result of 115–155 kg reported by Jepsen and Creek (1976) for Arsi cattle. However, animals maintained at the maintenance feeding level during the restriction period had similar carcass yield, higher dressing percentage and higher lean meat than all other groups, including the ad libitum fed groups. This indicates that dry season weight losses should be limited, through proper management and supplementation strategies, to support at least maintenance requirement of animals, to allow greater improvement to beef production in the tropics. The lower performance of animals under treatment 15% compared to the other groups both in terms of total carcass, dressing % and fat yield may be due to their lower DMI relative to other groups.

(15K)

Fig. 1. Weekly live weight of Arsi bulls during growth restriction and compensatory periods.

5. Conclusions

The different restricted planes of nutrition imposed on animals in this study were similar to the natural effects of under-nutrition on animals in the drier parts of the tropics that are caused by seasonal fluctuations in feed availability (Ehoche et al., 1992). Compensatory growth rate, feed conversion efficiency (FCE) and recovery index were broadly proportional to the level of feed restriction. However, slaughter weight, empty body weight (EBWt), total carcass and lean meat yield of these Arsi bulls managed under a maintenance energy feeding regime during the restriction period had relatively similar performance with, and even higher dressing percentage, than the ad libitum fed control group. Arsi bulls, after 91 days of feed restriction below their daily maintenance energy requirement, may not achieve similar compensatory growth similar to their non-retarded counterparts with 105 days of compensatory feeding. Appropriate times of feeding, and changes in the energy density of the diet by manipulating the forage to concentrate ratios for complete compensation following different levels of retarded growth, along with cost–benefit relationships, requires further investigation.

Acknowledgements

The authors are grateful to Osho Tibbesso for his careful technical assistance in data collection. The assistance of Ato Amare Atale and Ato Aklilu Bogale in undertaking the statistical analyses is highly appreciated.

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