Influence of dietary neutral detergent fiber on feed intake and nutrient digestibility of crossbred Black Angus cattle

The objective of this experiment was to evaluate different neutral detergent fiber (NDF) levels affected on the feed intake and nutrient digestibility of crossbred beef cattle. Four male F 1 (Black Angus x Zebu cross) cattle at 20.5±1.21 (Mean±SD) months of age with average body weight of 299±12.1 kg were used in a 4x4 Latin square design (fourteen days per each period). The treatments were 47% (NDF47), 51% (NDF51), 55% (NDF55), and 59% (NDF59) NDF in diets. The results showed that the dry matter (DM), organic matter (OM), and crude protein (CP) intake were not different (P>0.05) among treatments. However, both NDF and acid detergent fiber (ADF) consumption were lower for NDF 47 than NDF59 treatments (P<0.05), while metabolizable energy was highest for NDF47 compare with NDF59 treatment (P<0.05). The DM digestibility was higher (P<0.05) for the NDF47 (65.3%) compared with NDF59 (57.5%), while NDF47 was similar (P>0.05) to NDF51 (62.4%), and NDF55 (59.4%) treatments. The data for CP, NDF, and ADF digestibility were similar (P>0.05) among treatments. However, there was tended to be lower in NDF59 than NDF47 treatments. The daily weight gain was 866, 821, 786, and 686 g/animal/day for treatments of NDF47, NDF51, NDF55, and NDF59, respectively. While, feed conversion ratio was lower for NDF47 and higher for NDF59 treatments (P>0.05). The conclusion in the present study was 55% NDF in diet could be properly recommended for farmers’ practice in terms of feed utilization.


Introduction
Crossbred beef cattle were produced by artificial insemination between Zebu crossbred with sire breeds such as Angus, Charolais, Wagyu, etc. (Vu et al., 2021); and the crossbred cattle had higher growth performance than Zebu crossbred (Truong, 2021).However, ruminant animals can use locally available forage, as rumen microorganisms can break fibrous materials into simple chemical compounds which are either used by microbes or absorbed into the body (Dong and Thu, 2020).However, crossbred beef cattle fed traditionally by the local people would not be suitable for high-produced beef cattle.Forage contained with a high level of the cell wall or neutral detergent fiber were digested slowly and promoted low voluntary feed intake reported by Tham and Udén (2013).According to Rahman et al. (2009), the digestibility of NDF in diet improved and as result, live weight gain was increased.In Vietnam, studies on NDF levels in the diets of crossbred beef cattle are still limited.In a previous in vitro study, Truong and Thu (2020) reported that there was a negative relationship between increasing the levels of dietary NDF from 35 to 65% and digestibility of OM and NDF; and the level from 47 to 59% NDF content in diets could reasonably be tested for the upcoming study of in vivo and growth performance.However, the nutrient requirements of beef cattle were different for each period of the age.This is the reason that the experiment was conducted to test the hypothesis.The aims of the experiment were to determine the daily feed intake and apparent digestibility of nutrients of different levels of NDF on Black Angus crossbred from 21 to 23 months old.

Location and time
The study was conducted in Viet Nam at Sau Duc cattle farm, which was located in Tri Ton district of An Giang province (10°29'33.6"N104°49'05.4"E),and samples were analyzed at the laboratory E205 of the Department of Animal Science, College of Agriculture, Can Tho University from May to August 2021.

Experimental design
Four crossbred male F1 (Black Angus x Zebu crossbred) cattle at 20.5±1.21 months of old (Mean±SD) with average body weight of 299±12.1 kg.The experiment followed a Latin Square design with four treatments (NDF levels) and elaborate four periods (14 days/period).The different levels of NDF in the diet including 47, 51, 55, and 59% corresponding to NDF47, NDF51, NDF55, and NDF59 treatments based on the study results of Truong and Thu (2020).The dietary CP content was calculated by the suggestion of Thu and Dong (2015) and the nutrient requirements of ruminants in developing countries by Kearl (1982).The composition of feeds used in the present study showed in Table 1; ingredient proportion and chemical composition of the experimental diets presented in Table 2. Feed ingredients used for diets formulation were elephant grass was planted in the cattle farm, rice straw and O. turpethum vines were bought in the farmers' surrounding the farm.While the concentrate was formulated (% in DM basis) from rice bran (51.7), broken rice (20.8), soybean meal (24.7), dicalcium phosphate (1.14), salt (1.14), premix vitamins, and minerals (0.57).Urea and extra soybean meal were used to fix the dietary CP content of 11.4 %.The fixed quantities of feed supplements were daily offered to the animals two times at 7:00 am and 1:00 pm.Elephant grass and O. turpethum vines were supplied at a level in diets at 8:00 am and 2:00 pm, ad libitum rice straw.The crossbred beef cattle were individually penned, and water was available at all times.Before the start of this study, each animal was treated for external and internal parasites (Ivermectin and given Albendazole, respectively).

Measurements taken Feeds, nutrient and energy intakes
Samples of feed, refusal, and feces were analyzed for dry matter (DM), organic matter (OM), crude protein (CP), and ash following the standard method of AOAC (1990).Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed following the methods of Van Soest et al. (1991).Determination of metabolizable energy (ME) in the diets was calculated by the method of Bruinenberg et al. (2002), in which ME (MJ/head/day) = 15.1*DOM(with DOM/DCP>7.0;where: DOM is digestible organic matter and DCP is digestible crude protein).

Apparent nutrient digestibility
Apparent DM, OM, CP, NDF, and ADF digestibility were employed with the animal feces collected and weighed daily according to McDonald et al. (2010).In this study, each experiment period was 14 days.The first seven days were for adaptation to the experimental diets and the last seven days were for collecting and dissecting samples.

Daily weight gains (DWG) and feed conversion ratio (FCR)
Cattle were weighed for 3 consecutive days in the early morning before feedings at the beginning and the end of each experimental period by an electronic scale (Model TPSDH, YAOHUA, Taiwan).The feed conversion ratio was calculated by dividing the average DM intake by the DWG of each crossbred cattle.

Results and Discussion
Feed, nutrient, and ME intakes of experimental beef cattle.Feeds, nutrients and metabolizable energy intakes of crossbred beef cattle in different treatments are shown in Table 3.The results in Table 3 showed that the nutrient intake was not different (P>0.05)among treatments but NDF, ADF and ME were different (P<0.05) between NDF groups.The DM intake was not different (P>0.05)among treatments and ranged 6.45-6.57kg/animal/day.It was similar to the results on crossbred beef cattle of Kearl (1982) which reported that 6.0-7.0 kg DM for 0.50-0.75kg average weight gain.The CP intake of crossbred beef in this experiment was similar (P>0.05)among NDF groups and ranged from 0.710 to 0.723 kg/animal/day.Peng et al. (2018) reported that the CP was intermediate for genotype expression and muscle formation for the breed, it is necessary to respond to enough protein in the diet to improve growth performance.The CP in this study was similar to the results of Kearl (1982) who reported 0.705-0.780kg for 0.50-0.75kg daily weight gain.The NDF consumption (kg/animal/day) was higher (P<0.05) for NDF59 treatment (3.80 kg) than NDF47 treatment (3.11 kg).Similarly, the ADF intake was different (P<0.05)among treatments, the highest value for NDF59 treatment (2.28 kg) and the lowest value for NDF47 treatment (2.09 kg).The NDF intake in this study was similar to the findings of Porsch et al. ( 2018) who reported that the daily NDF consumption of crossbred cattle (312 kg) was about 2.92 to 3.38 kg.The ME intake in this study was different (P<0.05)among treatments.It was 58.0, 55.1, 52.7 and 49.7 MJ/animal/day corresponding to NDF47, NDF51, NDF55 and NDF59 treatments, respectively.While, NDF47 and NDF55 were not different (P>0.05) in this study.The ME in this present study was lower than the result of ME intake which ranged from 56.1 to 62.6 MJ/crossbred cattle/day reported by Kearl (1982).However, It was similar to the finding of Kongphitee et al. (2018), who reported that ME consumption was decreased by increasing levels of NDF in the diets from 45.2 to 63.2%.Although, increasing the level of NDF from 47 to 59% in diets did not affect CP intake per 100 kg body weight (0.224-0.225 kg) but the proportion of DM intake per 100 kg body weight tended to be higher (P>0.05) in NDF47 than in NDF59 treatments (2.06 and 2.01%, respectively).When the NDF content of diets increases and feed intake was reduced.The result of this study suggests that the main factor of feed intake regulation was NDF (Tham and Udén, 2013).Moreover, Brandao and Faciola (2019) reported that highly productive animals maybe require less than 58% NDF in diets.In short, Table 3 showed that the NDF intake of NDF59 treatment was higher than NDF47 treatment (P<0.05).Moreover, the increasing NDF levels have not a better ME intake of beef cattle and DM/BW.

Nutrient digestibility and digestible nutrient of experimental cattle
The nutrient digestibility and digestible nutrients of experimental crossbred beef cattle are shown in Table 4.Both digestibility and digestible value (DM and OM) were different (P<0.05)among treatments but no difference (P>0.05) was observed for NDF, ADF, and CP.The DM digestibility of NDF47 treatment (65.3%) was higher than NDF59 (57.5%), but it was not different compared with NDF51 (62.4%) and NDF55 treatments (59.4%).Konka et al. (2015) observed that increasing NDF from 55.4 to 66.2% in the diets, reduced DM digestibility from 57.8% to 55.5%.Besides, the OM digestibility was different (P<0.05)among treatments.It was 65.6, 62.5, 59.6 and 57.6 % corresponding to NDF47, NDF51, NDF55 and NDF59 treatments.In this study, OM digestion was a major component to reflect on nutrient digestibility of diets, which is in agreement with Truong and Thu (2020) who demonstrated that NDF levels in diets are the main limit for OM digestibility from NDF different sources.Although digestibility of DM and OM decreased with decreasing levels of O. turpethum vines.However, no differences were found in NDF47, NDF51, and NDF55 treatments during the experimental period.
Nguyen Binh Truong, Tran Trung Tuan The CP digestibility was not affected (P>0.05) by the treatments and ranged from 65.3 to 68.5%.An increasing level of NDF in the diets from 47 to 59% did not affect (P>0.05)NDF and ADF digestibility.However, both NDF and ADF digestibility tended to be lower in NDF59 (57.4 & 49.6%) than NDF47 treatments (63.6 & 56.0%,respectively).In another study by Konka et al. (2015), due to increasing levels of NDF in the diets from 55.4% to 66.2% and as a result, NDF digestibility (%) was decreased from 54.2 to 53.2%.In the current study, the DM digestible value (kg/animal/day) tended to be lower (P=0.057) in NDF59 (3.71 kg) treatment than NDF47 (4.28 kg) treatments, however, there were not different (P>0.05)among NDF47, NDF51 (4.09 kg) and NDF55 (3.92 kg) treatments.The digestible OM of treatment (kg/animal/day) decreased from the NDF47 (3.84 kg) to NDF59 (3.29 kg) and were significantly different (P<0.05)among the treatments but NDF47, NDF51 (3.65 kg), and NDF55 (3.49 kg) were not different in this study.The above results explained that NDF47 had higher ME consumption than NDF59 treatment from a calculator by Bruinenberg et al. (2002).Based on rumen fermentation characteristics, the digestibility of treatments was decreased by increasing NDF levels in the diets.Increasing NDF levels in the cattle diets led to reducing DM and OM digestibility (P<0.05);however, NDF55 treatment was not different (P>0.05) with NDF47 and NDF51 treatments.

Daily weight gain and feed conversion ratio
The daily weight gain and feed conversion ratio of NDF levels are presented in Table 5. Daily weight gain (DWG) of crossbred beef cattle in this study was similar (P>0.05)among treatments.However, the DWG (g/animal/day) decreased slightly from the NDF47 (866 g) to NDF51 (821 g), NDF55 (786 g), and NDF59 treatments (686 g).Subepang et al. (2019) reported that the DWG of male crossbred beef cattle was 0.80 kg/animal/day in the 51.9% NDF diet.

Table-5. Daily weight gain and feed conversion ratio of cattle in different treatments
The DM conversion ratio of NDF47 treatment (7.92 kg) was lower than (P>0.05)NDF51 (10.3 kg), NDF55 (10.2 kg) and NDF59 treatments (10.8 kg).In another study, Truong and Preston (2021) reported that the feed conversion ratio of crossbred beef cattle was around 7.98-13.6kgDM.The NDF conversion ratio was similar (P>0.05)among treatments.It was 3.76, 5.29, 5.60, and 6.37 kg NDF/kg DWG corresponding to NDF47, NDF51, NDF55, and NDF59 treatments.In short, daily weight gain was reduced from NDF47 to NDF51, NDF55, and NDF59 treatments.The feed conversion ratio at NDF59 treatments was higher than NDF47 treatment.Overall, the DM/BW (%) of the NDF59 treatment was lower than other treatments.The daily ME of NDF47 treatment was higher than NDF59 treatment but NDF47, NDF51 and NDF55 treatments were not different in this study.The difference NDF in the diets affected nutrient digestibility and digestible value in crossbred Black Angus cattle.In detail, DM and OM digestibility decreased (P<0.05) from NDF47 to NDF59 treatments.Nutritionally, highly productive animals probably needed diets containing NDF lower than 58% (Brandao and Faciola, 2019).According to Harper and McNeill (2015), the higher NDF content in the diet can be considered a more feasible target in the tropical cattle system.In tropical developing countries, the high fiber diets are usually applied for cattle due to the utilization of locally available forages with low feed costs.

Conclusion
An increase in dietary NDF from 47% to 59% reduced intake, ruminal digestibility of DM and OM.The dietary NDF level of 55% was recommended for crossbred Black Angus cattle from 21 to 23 months of old.