Average daily feed intake (ADFI)
There was a general increase in feed intake across all treatments in the study, this could be attributed to an increase in palatability of the diets [15] which might be probably due to the aromatic characteristics of baobab oil seed cake as reported by [27]. This pattern could also be a reflection of the relative acceptability and palatability as was reported by[28].Similarly, [29] reported that significantly higher concentrate intake in treatment groups fed West African Dwarf goats maybe an indication of the palatability of the concentrate with fermented baobab inclusion(P<0.05). Also, [30] noted that young goats fed diet containing 40 % baobab leaf meal had higher dry matter intake when compared to other leaves as Blighia sapida , Entada africana and Gliricidia sepium. The findings on the increase in ADFI with an increase in time (in week) correspond to that of [31], who observed an increase in feed intake with an increase in age (week) of all broilers fed graded levels of cotton seed meal. This might be a similar case with goats fed graded levels of baobab oil seed cake. Generally, when animals are growing there is a possibility that feed intake also increases due to the fact that feed requirement of an animal is determined by its body weight. The results on sex and treatment effect correspond with that of [32], who reported that dry matter intake was higher in male castrates than in female kids during the interval of 21 to 24 week , and 17 to 32 week of age. These effects could be largely due to differences in body size between male castrates and female kids. Contrary, a study conducted by [33] reported that sex of goats had no significant difference on dry matter intake (P>0.05), this could be attributed to the fact that feed intake on animals is more influence by feed palatability, as well as appetite on an individual animal, which means that either male nor female, any animal that has high appetite is more likely to have higher feed intake, regardless of sex.
Body weight gains (ADG, BWG)
The increase in body weight gains reported in all the treatments is an indication that the goats responded positively to all the dietary treatments and that protein content and dietary energy supply of the experimental diets adequately enhanced growth performance of the goats. There is a general increase in weight gains amongst all treatments, thus implying that the goats were able to convert feed protein into extra muscles. Weekly changes on body weight gains could also be attributed to the adaptability of the animals to dietary treatments. The results obtained in the trial aligns with the report of [34], who observed that there were no significant differences (P>0.05) in body weight gains on rabbits fed 5% and 10% BOSC when compared to those that were placed in the control diet. Regardless of the fact that there were no statistical differences (P>0.05) on body weight gains, goats that were subjected to the diet containing 45% baobab oil seed cake inclusion levels were superior in body weight gains compared to other treatments. This might be attributed to the differences in nutritional composition amongst the dietary treatments. In this study, females had higher ADG values than males. However, [35] reported a contrary results that Boer-cross bucks that were fed Marshall Ryegrass had higher ADG compared with Does. Findings in the current study are different from what was expected, male goats were expected to be more superior on body weight gains than females, due to the presence of growth hormone testoterone. This might be explained by the fact that, males’ goats were castrated 4 weeks before the commencement of the feeding trial, thus it might happen that some of them were not yet healed, hence growth rate was delayed by castration stress. As shown in table 2, incorporation of baobab oil seed cake in the diet and sex significantly increased (P<0.05) body weight gain, with female’s notable having higher BWG than males at 0, 15, and 45% BOSC, while only males fed on diet with 30% BOSC have higher BWG than females. The inconsistency found in the current study could be attributed to the above-mentioned reason that male goats that were used in the study were castrated 4 weeks before commencement of the study, hence it could happen that some males had not yet recovered, hence castration stress had negatively affected body weight gains in males.
Feed Conversion ratio (FCR)
There are limited studies to support or dispute results, on weekly changes of feed intake and growth performance parameters. Several studies focus more on treatment effects, but generally, feed conversion ratio is negatively correlated with body weight. Increase in body weight leads to a decrease in FCR. Nevertheless, lower FCR means that animals were able to utilize feed efficiently. The results on FCR can be supported by similar trend that was observed on ADFI, ADG, BWG, this concludes that as the goats were growing on weekly basis, feed intake and growth rate was also increasing, thus goats were able to convert feed into muscle. The results in this study are different from [36] who reported lower FCR in diet with 10% BBSM inclusion level and higher FCR at 15% BBSM inclusion level. This increase in FCR was associated with increase in anti-nutrient content of the diet with increase in BBSM inclusion level.
Effect of Baobab oil seed cake on enteric methane emission.
The results in the current study show that animals that consumed more feed, emitted significantly more methane gas compared to those that consumed less feed, dry mater intake being the major determinant [37]. Also, previous findings reported that approximately 95% of methane that is emitted during enteric fermentation is lost to the atmosphere via nose, while only 2-3% is lost via rectal emissions [38].
Nevertheless, the CH4 emission varies largely, depending on various factors, with dry mater intake (DMI), digestibility and diet composition being the most important determinants of methane production [38]. [39] reported that there is an inverse relationship between gross energy intake and methane production. In the current study, methane output depletes as the level of baobab oil seed cake increases. This could be attributed to the presence of tannins in baobab seeds. The Baobab oil cake contains 2-12% tannin [40,41]. The decline in enteric methane emissions with increase in inclusion of tannins in ruminant diet was similarly reported by several authors [42,43]. Also,[44] reported that tannins may modulate ruminal fermentation favourably, thereby decreasing protein degradation in the rumen, preventing bloat, as well hindering of methanogenesis. Tannins-containing forages have been an evidence that tannins reduce methane emissions both in vivo and in vitro [16]. Similarly,[45] reported that tannins have a potential to degrade enteric CH4 production in ruminants as a result of decrease in fibre digestibility.
In general, tannins could reduce methanogenesis through reductions of numbers of protozoa, methanogens and depressed fibre degradation depending upon the chemical structure of tannins and methanogen species[46]. In its simplest form, propionate is considered to reduce nitrogen. This means it reduces the amount of H2 available for methogens, thus methane production declines. The three main VFAs are generally produced relatively to each other at a ratio of 70: 20: 10 for acetate: propionate: butyrate. Nevertheless, these portions can be altered by dietary manipulation to reduce the ratio of acetate to propionate in particular to less than 0.5 [47]. This will help to avoid access of H2, which might increase methane production. Nevertheless, if hydrogen produced is not used correctly, ethanol or lactate can be formed, hence inhibiting microbial growth, and further production of VFAs. Enteric methane emission is reduced if the flow of hydrogen shifts towards alternative electron acceptors [37].
In the current study, the results show that female goats exhibited more methane gas output than male goats. However, there is limited literature to support or dispute the effects of baobab oil seed cake on enteric methane emissions. The results in the current study could be ascribed to the fact that, female goats generally consumed more feed than male goats; hence DMI was higher in females than in males, as a result of that, male goats emitted less methane gas than female gas. Findings in the current study contradict that of [37], who reported that male goats produced more methane gas than female goats. This could be possible due to the fact that males animals normally, are the ones that usually consume more feed (higher DMI) than female animals, thus that was the case with [37]. The result in figure 1, 2, 3 and 4 show that methane production was not consistent with time. Generally, from week 1 to week 4, animals emitted more methane with time; however, there were lots of fluctuations from week 5 onwards. This could be explained by the fact that animals were adapting to the dietary treatments with time, hence they were consuming more feed thus methane gas production was increased.