Growth performance and carcass characteristics of south african mutton merino fed diets with different levels of macadamia oil cake or baobab seed cake

Resource poor rural communities in South Africa do not only derive income from livestock farming but they also use them as a source of savings (Stroebel et al., 2011). Most small-scale sheep farmers in South Africa, like their commercial counterparts, fatten their lambs in a quest to fetch good prices for their animals on the market. Stroebel (2004) has noted that it is becoming a common practice for small-scale sheep farmers in South Africa to fatten their animals before selling them. Feed accounts for 70-80% of the total production costs in ruminant feeding (Hanning, 1999), so cheaper feed materials ought to be sought to enable profitable and sustainable livestock production by small-scale farmers. The most expensive constituents of feedlot rations are energy and protein sources (Mustafa and Alamin, 2012). Conventional protein supplements such as soyabean meal are extensively used in feedlots in South Africa but are usually too expensive and often not readily available to small-scale farmers (Nkosi et al., 2011). The problem of feed shortages can be addressed by the use of unconventional feedstuffs provided they can be easily sourced, are nutritious and affordable (Skenjana, 2006). Acheampong-Boateng (2008) argued that the problem of shortage of protein sources and their high costs can be mitigated through the use of locally produced good quality alternative non-conventional feed materials.

Limpopo Province, particularly Vhembe district, is one of the three main macadamia (Macadamia integrifolia) producing provinces of South Africa and is also known to be the home of baobab (Adansoniadigitate) trees (Venter and Witkowski, 2013). Plant oil is produced by mechanical pressing of Macadamia nuts and Baobab seeds and the resultant residues are called Macadamia oil cake (MOC) and Baobab seed cake (BSC) respectively. Resource poor farmers (small scale) in and around Vhembe district can use locally produced Macadamia oil cake and Baobab seed cake as protein supplements for ruminants. Macadamia oil residues have a potential to be used as protein supplement in the diets of ruminants (Skenjana et al., 2006). Research conducted in South Africa show that inclusion of 10% MOC in diets for fattening sheep and cattle can substitute soyabean meal as a protein supplement without compromising on the growth performance of these animals (Acheampong-Boateng et al., 2017; Acheampong-Boateng et al., 2008). However, there is lack of information on the studies to compare the response of animals given MOC or BSC as protein supplements. Therefore, the aim of this study was to compare the performance of fattening lambs given diets constituted with BSC or MOC as protein supplements.

Experimental site
 
In 2016 an experiment was conducted at Grey and Grey farm, South Africa (S 26 38971; E 29 47 468. Elevation: 1639 m).
 
Experimental design
 
A complete randomized block design arranged as a 2x2 factorial was used in this experiment.
 
Animal management
 
Five to six months old (16 males and 16 females) South African Mutton Merino lambs weighing on average±30 kg were housed individually in metabolism cages.  Eight lambs consisting of four males and four females were randomly allocated to each of four experimental diets (10% BSC diet, 15% BSC diet, 10% MOC diet, and 15% MOC diet). Feed and water were provided for the lambs daily ad libitum. The lambs received feed every day at 9 am. At the beginning of the trial the lambs were vaccinated for pulpy kidney and drenched for internal parasites.
 
Diets
 
Four iso-nitrogenous and iso-energetic diets were formulated to contain 10% or 15% of either Baobab seed cake or Macadamia oil cake (Table 1). The diets were formulated to contain 15-16% crude protein and 12 MJ ME/kg required by growing lambs.


 
Growth measurements
 
This experiment was conducted over 67 days with the first fourteen days being an adaptation period preceding commencement of data collection. Feed remaining (feed refusals) in the troughs was removed and weighed every day before feeding. The animals were weighed at the beginning of the trial and thereafter every Friday morning between 00:00 and 00:00. The weight of the feed refusals was subtracted from the amount of feed offered to each lamb to determine the average daily feed intake. The weights of the animals taken weekly were used to calculate the weekly weight gains which were in turn used to compute the average daily gain (ADG). Feed conversion ratio (FCR) was calculated for each animal by dividing feed intake by average daily gain. At the end of the trial the animals were weighed and then transported to a local commercial abattoir. At the abattoir, the animals were stunned by means of a captive bolt pistol, their throats cut immediately and the skin, head, offal and the feet were removed. Each carcass was weighed (hot dressed mass) before the carcasses were transferred to the cold room where they were kept for twenty four hours.

The following day the carcasses were weighed to determine the cold carcass mass. After the weighing of the carcasses, the tails were removed at their bases and the carcasses were split along the midline. The left side was further cut horizontally between the 12^th and the 13^th rib to expose the ribeye area which was then traced on a tracing paper for the determination of the ribeye area. The back fat thickness was measured on the 13^th rib using a digital caliper. Carcass length was measured using a flexible plastic tape measure.
 
Statistical analysis
 
Data collected in the study was subjected to analysis of variance using the General Linear Model of Minitab software version 17 (2014).

Growth performance of South African Mutton Merino lambs
 
Table 2 presents the results on average daily feed intake (ADFI), average daily gain (ADG) and feed conversion ratio (FCR). Significant (P<0.05) protein supplement source´level of inclusion interactions was detected for: ADFI and ADG. The ADFI for lambs fed diets supplemented with 10% BSC, 15% BSC, and 10% MOC were similar (P>0.05). However, lambs fed 15% BSC and 10% MOC supplemented diets consumed significantly more (P<0.05) feed than lambs on the 15% MOC supplemented diet. Feed consumption by lambs fed the 10% BSC supplemented diet was similar (P>0.05) to that of lambs on the 15% MOC supplemented diet.

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The differences in ADFI in this study may be due to the difference in ether extracts content of the four diets (Table 1). The higher ether extracts content of feed negatively affect daily feed intake in Awassi lambs (Haddad and Younis, 2004). Contrary to the findings of the current study, Acheampong- Boateng et al., (2008) reported that the inclusion level of MOC in diets of feedlot cattle did not affect daily feed intake of the cattle. The differences could be attributed to species differences.

Contrary to the findings of the current study on BSC inclusion in lamb diets, Madzimure et al., (2011) reported that BSC inclusion beyond 5% in the diets of lactating dairy cows reduced daily feed intake. Similar findings were reported by Belewu and Ibikunle (2009).

The ADG of lambs in this study mirrored the feed consumption patterns as reported in Table 2. The differences in ADG in the present study may be attributed to the differences in ADFI. Feed intake is positively related to body weight gain (McDonald et al., 2011). The lambs on BSC diets and those on 10% MOC diets performed much better than those on 15% MOC. Least performance by lambs associated on the 15% MOC diet may be attributed to low ADFI of these animals. However, contrary to our findings, Acheampong-Boateng et al., (2017) reported that MOC inclusion in lamb diets do not affect ADG.

Similar findings to those of the current study were reported by Ilori et al., (2013) who indicated that inclusion of whole Baobab seed meal in WAD goat diets did not affect ADG. However, Belewu and Ibikunle (2009) observed reduced ADG as the content of BSC was increased in lamb diets. Madzimure et al., (2011) reported a reduction on milk production when BSC was increased in dairy cows diet.

The non- significant differences in FCR in the present study was consistent with the findings of several researchers (Souza et al., 2013; Beken and Sahin, 2011; Nkosi et al., 2011; Belewu and Ibikunle, 2009; Koyuncu, 2008) who reported that FCR was not affected by diets.

Contrary to the results of this study on MOC, in a similar study, Acheampong-Boateng et al., (2008/2017) reported a significant difference in FCR values among the treatments. Similar findings were reported by Shirima et al., (2014).

Inclusion levels for both MOC and BSC did not have any significant effect on ADFI, ADG and FCR values. The better growth performance of male lambs compared to their female compatriots in the current study is in agreement with the findings of Sen et al., (2011) and Kashani and Bahari (2017) who found that male lambs out-perform their female counterparts in terms of growth.
 
Carcass characteristics of South African mutton merino lambs
 
Table 3 presents results for carcass characteristics of lambs. The significant (P<0.05) diet x inclusion level interaction for warm and cold carcass traits can be explained by a differences in response by the two traits to increased levels of the two protein sources. When BSC was increased in the diet carcass mass increased whereas an increase in MOC resulted in a decrease in carcass mass.

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The results on carcass characteristics show that lambs fed with 10% BSC, 15% BSC and 15% MOC supplemented diets had similar (P>0.05) warm and cold carcass mass (WCM and CCM respectively). Lambs fed with 15% BSC and 10% MOC supplemented diets had similar (P>0.05) WCM and CCM. However, lambs fed with 10% MOC supplemented diet had significantly (P<0.05) heavier WCM and CCM than the lambs fed 15% MOC and 10% BSC supplemented diets. Acheampong-Boateng et al., (2017/2008) reported similar findings when MOC was included in lamb and cattle diets. Similar findings were also reported by Shirima et al., (2014) and Mioc et al., (2007).

Diets did not significantly affect (P>0.05) dressing percentage (DP), carcass length (CL), fat thickness (FT) and rib eye area (REA). Similar findings on DP were reported by Acheampong-Boateng et al., (2008), Koyuncu (2008) and Ustuner et al., (2012). However, contrary to his earlier findings (Acheampong-Boateng et al., 2008) and those of the current study, Acheampong-Boateng et al., (2017) working with South African Mutton Merino lambs reported that DP was significantly influenced by the addition of MOC in lambs’ diets. The non-significant differences in carcass length found in this study were similar to the report of Macome et al., (2011). Results on CL contradicted the findings of Acheampong-Boateng et al., (2017). The results on fat thickness of this study were similar to the findings of Flakemore et al., (2015). The non-significant differences in the rib eye area in the present study are similar to the findings of Flakemore et al., (2015), Ustuner et al., (2012) and Koyuncu (2008). Acheampong- Boateng et al., (2017) reported significant difference in rib eye area of the carcass which was contrary to the current findings.

The results of the carcass characteristics of lambs in the current study indicated that carcasses from male lambs had heavier (P<0.05) WCM, CCM and CL, than carcasses from their female counterparts. The carcasses of female lambs had thicker (P<0.05) FT than the carcasses of male lambs. Sex did not significantly affect DP and REA of the carcasses (P>0.05). The superior carcass characteristics of male lambs in the current study over their female counterparts agree with the findings of Sen et al., (2011).

It was concluded that 10% MOC and 15% BSC can be incorporated in diets for fattening of growing South African Mutton Merino lambs without compromising growth performance and carcass characteristics.

The University of Venda’s Research and Publication Committee as well as Capacity Development Grant financed the current research project.