Nutrient intake and digestibility
The nutrient intake and digestibility of our study are compatible with Lee et al. (2019), Shain et al. (1993) and Jenkins et al. (1989), who found that increasing lysophospholipid tended to decrease intake and apparent digestibility of DM, OM and NDF. Sontakke et al. (2014b) observed no significant difference in nutrients intake and digestibility, however, significantly higher EE digestibility due to RBLPL inclusion. Contrary to present findings, Huo et al. (2019) found that LPL supplementation increased DM and CP digestibility but large decrease in NDF and ADF digestibility. The RBCL contains higher amount of unsaturated fatty acids and it is well established that unsaturated fatty acids are toxic for rumen microbes therefore decrease the fibre digestion. Sabiha (2009) stated that the lysophospholipids (lecithin) enhance the nutrient digestion and absorption by their ability to form comparatively smaller micelles and by increasing the flux rate of different digested nutrients across the cell membrane by improving permeability. Wettstein et al. (2000a) noticed that raw canola lecithin and deoiled soy lecithin improved the apparent digestibilities of dry matter and organic matter. Yoon et al. (1986) found an increase in fibre digestibility in sheep with the addition of 3.4% soy lecithin/kg total dry matter. Abel-Caines et al. (1998) found a higher NDF digestibility with a mixture of soy lecithin, soybean soapstock and soy hay (SLSSSH). The inconsistent results of nutrient intake and digestibility may be due to the duration of experiments, source of lecithin, method of manufacturing, dose, degradation in the rumen and rumen bypass of lecithin. Zampiga et al. (2016) and Polycarpo et al. (2016) reported that LPL supplementation on nonruminant animals increased of apparent nutrient digestibility, thereby improving feed efficiency.
Nitrogen and Energy balance
Wettstein et al. (2000a) reported that at a similar nitrogen intake, faecal nitrogen voided was numerically lowest with the raw canola lecithin diet and overall nitrogen balance was positive in all diets. It has been well established that the N utilization efficiency can be improved through synchronously supply of adequate fermentable energy and N for maximum microbial growth in the rumen and capture ammonia for protein synthesis (Dijkstra et al., 2011). The nitrogen utilization efficiency is not improved due to inadequate fermentable energy for rumen microbes in present experiment, which supports the reduction in ADG. The metabolizability values obtained in this study were 0.51-0.52 and these were in the normal range (0.40-0.64) proposed in several reports (ARC, 1980; Kamalzade et al., 2004). The ME:DE values were above the generalized value 0.82, suggested by Blaxter (1962) and ARC (1965). The results of present findings are in conformity with Huo et al. (2019), suggested that the status of nitrogen and energy in the body has not been improved, which supports the outcome of no or a slight difference in ADG. Contrary to present finding, Lee et al. (2019) found decrease in urinary N excretion with increasing LPL in diet, however Shain et al. (1993) reported that cows fed the high SLS diet had the highest positive energy balance. The lower methane energy loss in rice bran supplemented groups could be related to lower methane production due to either bio-hydrogenation of unsaturated fatty acids or low acetate production in the rumen. The low HI is associated with lower DMI along with the higher level of RBCL in ration of experimental calves. The net energy available for growth and maintenance is only 5 % higher in RBCL-4 group and equal in RBCL-6 group in comparison to RBCL-0 group.
Ca and P balance
Because of limited information about lecithin in ruminants, studies with nonruminant animals fed lecithin is discussed. In the support, Overland et al. (1994) noticed that lecithin had no impact on the retention of total P and Ca in pigs while contrary Huang et al. (2007) observed that lecithin at 2% level significantly improved the Ca and P utilization in broilers. In current study, the higher faecal Ca might be attributed to the formation of insoluble calcium soap from by reaction of Ca with free long chain fatty acids (LCFAs) present in RBCL. While RBCL is a good source of phosphorus but the phosphorus absorption is inversely proportional to the intake, might be possible explanation behind less phosphorus retention. The lower Ca and P retention is also correlated with the reduction in ADG in experimental calves.
Growth performance and methanogenesis
In the conformity of present findings, Shain et al. (1993) reported that daily gain and feed efficiency were not affected by SLS replaced corn grain in beef calves. Lee et al. (2019) stated that any improvements in animal performance by LPL, if existent, would come from increased utilization efficiency of feed ingested rather than more nutrients supplied. Contrary to our results, Huo et al. (2019) and Li et al. (2016) reported increased ADG in LPL treatment but difference did not reach the level of significance. The inconsistent results of animal performance may be due to the trial period, , method of manufacturing, dose, and source of lecithin, degradation in the rumen and rumen bypass of lecithin. Lysophospholipids as a feed additive have been examined mostly with nonruminant animals, where increased growth rates and feed efficiency have been observed by feeding LPL to chicken and pigs (Zhao et al., 2015, 2017; Zampiga et al., 2016).
In the concurrence of present findings, Sontakke et al. (2014a) and Wettstein et al. (2000b) reported lower methane production with supplementation of RBLPL and soy lecithin. The results are also in agreement with Benchaar et al. (2001), Hart et al. (2009), Yan et al. (2010) and Lima et al. (2013), who reported a decrease in CH4 production (kcal/d) with decreased DMI in cattle. PUFA also has an inhibitory effect on methane production through direct use of hydrogen by saturation in the rumen (Rasmussen and Harrison, 2011). Inhibitory effects of unsaturated fatty acids can be expected for methanogens and, maybe to a lesser degree, for Gram-positive cellulolytic bacteria (Nagaraja et al., 1997) and ciliates (McAllister et al., 1996) which provide hydrogen as a substrate for the methanogens. The lower reduction of methane release with lecithin than with canola oil indicates that phospholipids were either not hydrolysed to the same extent or slower as triglycerides (Jenkins et al., 1989). In current study the lower methane production may be attributed to lower DMI and presence of PUFAs.
Metabolic profile
In present study, the higher serum urea and cholesterol level in RBCL-12 group may be attributed to the insufficient utilization of ammonia by ruminal microbes due to lower soluble carbohydrate and supplementation of higher amount of fat in the diet. Plasma glucose, NEFA and BHBA are considered as principle circulating blood metabolite to assess the energy status of the animals (Muwel, 2016). The positive balance of Ca and i-P is clearly reflected by the serum levels. The results of our study are in conformity with the finding of Li et al. (2016), who observed that soy lecithin in the diet did not affect concentrations of serum glucose, albumin, total protein and calcium while increased the serum concentration of triglyceride, total cholesterol and HDL-cholesterol in steers. Huo et al. (2019) found that glucose, total protein, albumin, globulin, blood urea and total cholesterol did not alter with the supplementation of LPL in lambs. Lough et al. (1991) showed that feeding soy lecithin to lambs increased cholesterol. Jenkins (1990) reported lecithin had no effects on plasma non-esterified fatty acids and glucose concentrations. Contrary, Jenkins et al. (1989) observed lecithin increased serum NEFA but had no effect on concentrations of glucose, triglyceride or total cholesterol. The results of our study is in the compatible with the Yildiz et al. (2003) and Cha and Jone (1998), who found that fat feeding increases plasma leptin concentration, however, Becú-Villalobos et al. (2007) found lower leptin level in fat supplementation Researches demonstrated that the plane of nutrition directly influences the circulating level of IGF-1 and IGF-1 along with insulin are reported to indicate the nutritional status of the animals (Ciccioli et al., 2003; Lents et al., 2005). It has been well established that both dietary energy and protein are the principal nutritional determinant for basal circulating plasma concentration of IGF-1 (Elsasser et al., 1989).
Rumen profile
In the accordance of present study, Sontakke et al. (2014a) observed that the production of acetate, propionate and butyrate was similar upto 10% level of RBLPL inclusion in the ration. Wettstein et al. (2000b) reported that lecithin increased propionate proportion along with total VFA concentration but reduced the apparent ruminal protein degradation. Bacteria counts were reduced by the inhibitory effect of fatty acids on fibre degrading bacteria (McAllister et al., 1996) and also by the generally lower supply of fermentable matter because a part of the carbohydrates was replaced by lipids. On the other hand, ciliates numbers were higher in all lecithin diets with increasing dispersibility in water which may be the reason for the lower bacteria counts found with the lecithins (Jouany and Ushida, 1999). Kim et al. (2020) observed that LPL supplementation increased the proportion of butyrate, valerate, and iso-valerate but tended to decrease propionate. Considering that glycerol which is one of the main products in lipid metabolism could be fermented into propionate, butyrate, valerate, and isovalerate rather than acetate. Total bacteria increased in a linear manner. Cilliate protozoa unaffected but fungi, F. succinogenes and R. albus were significantly decreased in a linear manner by LPL supplementation. Huo et al. (2019) found 37% higher ammonia-N concentration and 61% higher total SCFA concentration in lecithin group in lambs. Lee et al. (2019) observed reduced proportion of acetate in total VFA with no differences in propionate proportion, resulting in a tendency for decreasing the ratio of acetate to propionate. Contrary, Cho et al. (2013) noticed that ammonia nitrogen (ammonia-N), TVFA, acetate, propionate, butyrate and valerate production increased in LPLs treatments compared with control for whole incubation times, however, A:P ratio decreased. Abel–Cains (1996) found similar ratio of acetate to propionate, while higher total, cellulolytic, carboxy-methylcellulose degrading bacterial and protozoal counts in TMR containing soy lecithin, soy soap stock and soy hay (SLSSSH) compare to control. Yoon et al. (1986) also observed no change in butyrate proportion on 8% lecithin supplementation in the diet of sheep. Jenkins et al. (1989) reported decreased acetate and increased propionate proportions but the proportion of butyrate was not influenced by phospholipids in sheep. Jenkins (1990) found a decrease in acetate proportion and increased butyrate when lecithin was added in combination with hydrogenated fat to steer diet. Paul (1994) observed a decrease in butyrate production during in-vitro study when pure phospholipids were used in comparison to free fatty acid and triglycerides.