Effect of dried avocado meal as a replacement for concentrate on the performance of sheep fed a basal diet of grass hay

Abule Guye^1,2, Ajebu Nurfeta¹, Sintayehu Yigrem¹ and Adugna Tolera¹

¹ School of Animal and Range Sciences, College of Agriculture, Hawassa University, P.O. Box 05, Hawassa, Ethiopia
² Department of Animal Production and Technology, College of Agriculture and Natural Resource,Gambella University P.O. Box 126, Gambella, Ethiopia
guyeabule@gmail.com

Abstract

The objective of this research was to evaluate the effect of avocado fruit meal as a replacement for wheat bran (WB) in a concentrate mixture on performance of sheep fed a basal diet of natural grass hay. Thirty yearling male sheep with an average initial body weight of 19.74±1.41 kg (Mean ± SD) were grouped into six blocks of five sheep in each block. The treatments were: 0 % avocado fruit meal (AFM0), 20 % avocado fruit meal (AFM20), 30 % avocado fruit meal (AFM30), 40 % avocado fruit meal (AFM40), 50 % avocado fruit meal (AFM50) in concentrate mixture. Three hundred grams of concentrate were offered to each sheep in each treatment group. Natural grass hay was offered ad libitum. The feeding trial lasted for 78 days followed by 7 days of digestibility trial. Carcass evaluation was conducted at the end of digestibility trial. The hay dry matter (DM) and organic matter (OM) intake for AFM50 was lower (p<0.05) than the other treatments except AFM40, which had similar (p>0.05) value with AFM50. Moreover, AFM50 had lower (p<0.05) total DM and OM intake compared with other treatments except AFM40 which was similar with AFM50. The crude protein (CP) intake for AFM0 was greater (p<0.05) than AFM50, but similar with other treatments. The average daily gain and feed conversion efficiency were similar (p>0.05) among the treatments. The DM, OM, CP, neutral and acid detergent fiber digestibility were similar (p>0.05) among treatments. The slaughter weight for AFM20 was greater (p<0.05) than that of AFM40 and AFM50, while AFM0 and AFM30 had an intermediate value. The empty body weight, hot carcass weight, dressing percentage and rib eye area were similar (p>0.05) among treatments. In conclusion AFM up to a maximum of 40 % could be used to replace wheat bran without a negative effect on the growth performance of sheep.

Key words: carcass, digestibility, male sheep, productive performance, whole avocado fruits

Introduction

Animal production in African countries is affected by the low level of feed supply (Amata, 2014). The increasing consumption of animal products will give rise to a vast demand for animal feed. Use of fruits and vegetables by-products can contribute to the supply of animal feeds; improve feed deficiency and also mitigate environmental problems by converting these wastes to useful human food (Manju et al 2015). Moreover, it has been reported that the use of fruit and vegetable by-products helps to reduce feed shortages and pollution of the environment (Yitbarek 2019). Fruit and vegetable processing by-products can be used in farm animal nutrition as functional feed for the production of food products of improved quality (Kasapidou et al 2015).

Avocado waste is obtained after processing avocado fruit for food and other applications. Avocado waste containing peels and seed has unique chemical structures and supported biological activities (Ramadan and Farag 2022). The peel and seed had low content of lipids compared to the avocado pulp and the mineral components were greater in the avocados peel (Daiuto et al 2014). However, the pulp had low content of phenolic as well as antioxidant activity compared to the avocado peel and seed (Daiuto et al 2014). The whole dried avocado fruit meal was reported to contain 32.3% dry matter, 3.3% ash, 14.3% crude fiber, 49.1% ether extract and 9.2% crude protein (Franquez et al 2017).

Waste products from the avocado (avocado residues) processing industries and that which is unsuitable for the market have the potential to be included in animal diets. Organic matter digestibility and in situ dry matter and crude protein degradability of avocado meal waste products indicated that the in vitro organic matter digestibility of avocado meal was 54.3% and could be used as ingredients in the diets of ruminants (Skenjana et al 2006). The effective and efficient utilization of fruit and vegetable wastes will reduce the cost of animal feeding there by increasing farmers' profits (Wadhwa et al 2013).

Feeding blocks containing 14.8% avocado wastes (pulp and peel) was reported to improve milk fat content (De Evan et al 2020). In sheep feeding the inclusion of whole dried avocado meal up to maximum of 10% did not have a negative impact on productive behavior, feed intake and daily weight gain (Bugarin et al 2021). There is little information as to the effect of avocado meal on ruminant growth performance, digestibility coefficient and carcass characteristics when fed as a supplement to natural grass hay as ad libitum with avocado meal replacing wheat bran.

As it known feed availability, quality and price are some of the major constraints affecting livestock production and productivity. Crop residues and agro-industrial by-products are widely utilized under different production systems. Such by-products are avocado pomace and rejected avocado fruit during processing of avocado to produce oil. Avocado pomace and rejected avocado fruit which is not suitable for human consumption are causing pollution to the environment. It is important to use these by-products for animal feeding in countries where there are critical feed shortage such as Ethiopia. That will reduce the use of wheat bran which is getting very expensive from time to time.

Therefore, the use of avocado wastes was necessary for decreasing shortages of feeds. Despite large production of fruits and vegetables in Ethiopia, the use of these by-products as animal feed was not common. There was little information on the utilization of avocado by-products and avocado which was not suitable for processing on animal performance. Therefore, the aim of this study was to evaluate the feeding value of avocado residues as a replacement for wheat bran in sheep feeding.

Materials and methods

Description of the study areas

The study was conducted at Hawassa University, College of Agriculture, which is situated at 275 km southwest of Addis Ababa. It is located between 6°83' to 7°17' N and 38°24' to 387°72' E, at an altitude of 1750 m above sea level. It receives mean annual rainfall of 955 mm and has an average annual temperature of 20°C (Haben et al 2020).

Feed preparation

Rejected Avocado fruit was purchased from Yirgalem Agro-industrial Park and transported to the College of Agriculture. Then the discarded avocado fruit including the stone was chopped and dried under the shed until it get dried completely and then milled for further use. Wheat bran, noug seed cake and common salt were purchased from the local market. Natural pasture hay was purchased from Sululta, near to Addis Ababa.

Experimental animals, experimental design and treatments

Thirty male sheep with an average age of yearling were purchased from the local market. The age of animals was identified through dentition and oral history. Soon after arrival at the experimental station, they were ear tagged. They were treated with D-ivermectin against internal parasites and external parasites. The sheep was quarantined for 21 days to get accustomed to the new environment. The animals were closely observed for the incidence of any ill health and disorders during the preliminary period. Then the sheep were adapted to the treatment diets for 15 days before the start of actual data measurement. The animals were kept in individual pens with adequate floor space and equipped with feeding and watering troughs. The concentrate was made of 67% wheat bran and 33% noug seed cake. The experiment consists of five treatments using different proportion (%) of avocado fruit meal and wheat bran (0:100; 20:80; 30:70; 40:60; 50:50 on DM basis) supplemented with a basal diet of natural grass hay (ad libitum) (Table 1). Molasses and urea were used to make the diet isocaloric and isonitrogenous. Also, common salt was added to all treatments diets.

Feed intake and body weight measurements

Three hundred grams of the supplement was offered in equal halves at 8: 00 and 16 hours. Hay was provided ad libitum (20 % refusal). Daily feed offered and refusals was collected and weighed from each treatment throughout the experimental period. Daily mean feed intake was measured as differences between offered and refused. The initial body weight of the animal was determined after two consecutive weighing, and the average of the two was taken as initial weight. The body weight of each animal was taken every ten days. The daily body weight gain was calculated as the difference between final body weight and initial body weight divided by number of feeding days. The feed conversion efficiency of the experimental animals was determined by dividing the average daily body weight gain per day to the amount of feed consumed per day.

All sheep were used to determine the digestibility of experimental feeds. The digestibility trial was conducted at the end of the feeding trial. In the digestion trial, each sheep was fitted with fecal collection bags for three days of acclimatization period to fecal collection bags prior to collection period of seven consecutive days. The amounts of feed offered were similar to the growth experiment. Feed offered and refused was weighed. Representative samples were taken for offer and refusal and bulked for the seven-day collection period. Feces was weighed for individual sheep daily and 20% was taken and stored at -20^OC for seven days. At the end of the fecal collected period, it was thawed under room temperature overnight and subsampled for each sheep.

The samples were dried at 65^OC for 48 hours and then milled for chemical analysis. On a daily basis, fecal samples for each sheep was taken and dried at 105^OC overnight for dry matter determination.

Finally, digestibility of each nutrient was calculated using the following equation:

Carcass characteristics

At the end of the feeding and digestibility trial, four experimental animals from each treatment was randomly selected and fasted overnight then slaughtered. Slaughter weight (SW) was taken 30 minutes before the slaughter. Empty body weight (EBW) of every sheep was computed by subtracting digesta weight from slaughter weight. Hot carcass weights (HCW) and rib eye (longissimus dorsi) area were measured. The carcass was partitioned into hind and forequarter between 9th and 10th ribs. The rib was chilled overnight in a deep freezer. The cross-sectional area of the ribeye muscle (longissimus dorsi) was traced first on plastic paper after it was cut at the 11^th and 12^th ribs perpendicularly to the backbone (Yirdaw et al 2017). The rib-eye area was traced on graph paper and computed using a planimeter (model series 20). The rib-eye area value was the mean of the left and right sides.

Dressing percentage had calculated on the bases of slaughter and empty body weight using the formula: Dressing Percentage = (Hot carcass weight/ slaughter body weight) × 100

Chemical analysis of the feeds

The chemical analysis of samples of feeds and feces during feeding trials were conducted at Hawassa University, College of agriculture in the animal nutrition laboratory. The samples were dried at 65^oc for 48 hours and ground to pass through a 1mm sieve. Ash, dry matter and crude protein were determined according to AOAC (1990). The Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), Acid detergent Lignin (ADL) were determined according to Van Soest and Robertson (1985).

Statistical analyses

The data was subjected to analysis of variance (ANOVA) using the General Linear Model (GLM) procedure of SAS 9.4 version. Tukey test was employed for separation of treatment means and a significant difference was declared at p<0.05.

The model was

Yij = µ + ti + bj + eijk,

Where, Yijis the response variable, µ=is the overall mean, ti=is the treatment effect, bj =is the block effect and eijk is a random error.

Results

Chemical composition

The chemical composition of the experimental feeds is given in Table 2. Hay and avocado fruit meal were poor in CP content, while wheat bran and NSC contained high CP content. The NDF and ADF content for hay and noug seed cake were high compared with other feeds.

Feed intakes, body weight change and feed conversion efficiency

Daily total dry matter, nutrient intake and body weight change of sheep fed avocado fruit meal as a replacement to wheat bran is shown in Table 3 and 4. The hay DM and OM intake for AFM50 was lower (p<0.05) than the other treatments except AFM40, which had similar (p>0.05) value with AFM50. The lowest (p<0.05) total DM intake was for AFM50, except AFM40. Moreover, AFM50 had lower (p<0.05) DM and OM intake compared with other treatments except AFM40 which is similar with AFM50. The CP intake for AFM0 was greater (p<0.05) than AFM50, but similar with other treatments. The average daily gain and feed conversion efficiency were similar (p>0.05) among the treatments (Table 4).

Apparent digestibility

The DM and nutrient digestibility of Arsi bale sheep fed avocado fruit meal as a replacement to wheat bran is shown in Table 5.The dry matter, organic matter, crude protein, neutral and acid detergent fiber were similar (p>0.05) among the treatments.

Carcass characteristics

The carcass traits of the Arsi bale sheep fed whole avocado fruit meal as a replacement to wheat bran is presented in Table 6. The slaughter weight for AFM20 was greater (p<0.05) than that of AFM40 and AFM50, while AFM0 and AFM30 had an intermediate value. The empty body weight, hot carcass weight, dressing percentage and rib eye area were similar (p>0.05) among treatments.

Discussion

Chemical composition

The mean CP content of AFM in the present study was lower than the value reported in previous studies (Franquez et al 2017; Uchenna et al 2017). Similarly, the CP and EE contents of avocado pulp and peels were greater than the present study (De Evan et al 2020) which might be due to the avocado variety, structure (pulp, seed and peel) and location. However, Okoruwa et al (2015) showed that the CP and EE of avocado seed meal were lower than the present study. The mean EE content of AFM reported by Franquez et al (2017) was greater than the values obtained in the present study. AFM has moderate fiber content, with NDF content lower than that of wheat bran and noug seed cake. The mean NDF, ADF and ADL content of avocado meal (in oil extracted residues) reported by Skenjana et al (2006) was greater than the value obtained in the present study.

Feed intakes, body weight change and feed conversion efficiency

The lower hay DM, OM and CP intake for AFM50 compared to AFM0, AFM20 and AFM30 could be due to higher AFM content in AFM50 with higher ether extract (EE) content in AFM50 compared with other treatments which might have caused lipid oxidation and rancidity that can depress feed intake. Similarly, the lower total DM and OM intake for AFM50 compared to AFM0, AFM20 and AFM30 could be due to higher EE content in AFM50 than in the other treatments. However, the higher CP intake for AFM0 compared to AFM50 could be due to differences in the type of protein supplied by wheat bran and the lower EE content in AFM0. The oxidation of high levels of avocado lipids in diets with a high proportion of avocado waste (mixture of pulp and peels) can cause off flavours and reduce palatability (De Evan et al 2020). The current findings are similar with that of Lemus et al (2020) who reported higher levels of avocado flour in the diet decreased feed intake of male sheep compared to the control. Belanche et al (2022) indicated that 20% inclusion of avocado seed replacing cereal grain (corn and wheat bran) did not affect feed intake of goat and sheep.

The similarity in average daily gain and feed conversion efficiency indicated that avocado fruit meal have the potential to replace wheat bran in sheep feeding in areas where wheat bran is not available. De Evan et al (2020) indicated that the final body weight of dairy goat fed avocado pulp and peel mixture was low compared to the control, which is not similar to the present finding.

Apparent digestibility

The similarity in dry matter, organic matter, and crude protein, neutral and acid detergent fiber digestibility have shown that avocado fruit meal has a potential to replace wheat bran and does not affect rumen microbial efficiency digestibility of the diet in sheep feeding. However, Okoruwa et al (2015) indicated that digestibility of dry matter and crude protein were significantly higher in a diet containing 25% avocado seeds compared to diets consisting of 0 and 20 % avocado seeds replacing guinea grass for West African male sheep . Belanche et al (2022) reported that the inclusion of 20% avocado seed meal replacing cereal grains (corn and wheat bran) did not affect apparent digestibility of the diet of sheep, which is in line with the present finding.

Carcass characteristics

The lower slaughter weight for the male sheep supplemented with AFM40 and AFM50 compared to male sheep supplemented with AFM0 could be due to the lower total DM intake in AFM40 and AFM50. However, the similarity in empty body weight, hot carcass weight, dressing percentage and rib eye area observed across the treatments shows the potential of AFM to replace wheat bran in the diet of sheep without affecting carcass performance of the sheep. Therefore, inclusion of AFM for sheep feeding is a feasible option to diversify feed resource base, reduce feed cost and decrease the undesirable effect of avocado wastes disposal problems. Similarly, Marcos et al (2020) reported that including the pulp-peels mixture in the formulation of multi-nutrient blocks for goat feeding is important for decreasing of environmental contamination affected by avocado wastes.

Conclusion and recommendation

Replacement of above 40% of wheat bran with avocado fruit meal (AFM) in the diet of Arsi-Bale male sheep resulted in reduced hay and total DM intake. However, there was no significant effect of AFM level on average daily gain, feed conversion efficiency, and digestibility coefficient among the treatments. Also, slaughter and empty body weight, hot carcass weight, dressing percentage and rib eye area were similar with the control. Therefore, it can be concluded that AFM can replace up to 40 % of wheat bran in the diet of sheep without adverse effects on feed intake, digestibility, and body weight gain and carcass characteristics. Further research is recommended to evaluate the quality of meat as well as a long period of storage of AFM.

Acknowledgments

We thank Hawassa University thematic research project for providing financial support for the study.

Conflict of interest

The authors verify that they do not have any competing of interest.

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