1. Introduction
It has become necessary to look for non-traditional feed ingredients in order to be able to provide the large amounts required for livestock [
1]. The agri-food industry produces a large amount of waste and by-products characterized by high nutritional and economic value [
2]. In Egypt, about 600,000 feddans (feddan = 4200 m
2) were cultivated with sugar beet in 2018/2019, which produced about 715,600 tons of dried sugar beet pulp (DSBP). DSBP contributes 644,038 tons of dry matter (DM), 467,155 tons of total digestible nutrients (TDN), and 27,695 tons of digestible crude protein (DCP) [
3] to the local nutrient supply. Fresh sugar beet pulp is dried using pulp dryer until it possesses approximately 10% moisture, and then it is pelleted to facilitate storage and transportation [
4]. When sugar beets are processed into sugar, they produce sugar beet pulp as a by-product, which is used as feed for various livestock, either as dried flakes or as compressed pellets. Extracted grounded sugar beet pulp is used as ruminant feed and fed as fresh, dried, or silage (fermented beet pulp). Sugar beet pulp could be a highly palatable feed with moderate energy levels. It is low in sugar and different non-structural carbohydrates contents, containing fiber that is highly digestible, and necessary for ruminants to maintain rumen condition and increase acetate production [
5].
Sugar beet pulp (SBP) is the solid substance produced during the extraction of sugar from sugar beets, representing about 6% of the DM of beet root weight [
6]. Sugar beet pulp has a high crude fiber content (17–22%) and low crude protein content (8–11%) [
7]. Despite this fact, it possesses excessive fiber, and its digestion is acceptable due to its low lignin content [
8]. Consequently, SBP is considered to be an essential energy source in complete rations of dairy cattle and sheep [
9].
An alternative of high-energy grains with such other feedstuffs as SBP is one means of lowering using excessive grains component in diets of ruminants [
10]. Feeding Holstein cows on DSBP mid-lactation had a considerable effect on milk yield of about 10% (3–4 kg of milk) compared to the control group [
11]. The high NDF content in SBP has a beneficial effect on milk yield and fat content [
12]. Replacing 50% of energy ingredients (yellow corn, wheat bran, and rice bran) with DSBP in the rations of growing lambs improved their performance with respect to digestibility, rumen fermentation, and blood parameters, while increasing feed conversion and economic efficiency [
13].
This work aimed to study the effect of partial (25 and 50%) replacement of yellow corn grains with DSBP on feed intake, digestibility, rumen fermentation, plasma parameters, milk yield, composition, and feed conversion in dairy Holstein cows.
4. Discussion
The comparison of chemical composition between yellow corn grains (YCG) and dry sugar beet pulp (DSBP) revealed higher DM, OM, EE, and NFE contents and lower CP, CF, and ash contents in YCG than DSBP. With respect to experimental ration, DM, OM, EE, and NFE contents decreased slightly; however, CP, CF, and ash increased slightly with increasing replacement level of YCG with DSBP. Similar results were obtained by Mahmoud and El-Bordeny [
22] and Ali et al. [
13]. The results of the fiber fraction revealed that the contents of NDF, ADF, ADL, cellulose, and hemicellulose were higher in DSBP than in YCG and increased in the rations with increased DSBP. On the other hand, non-fiber carbohydrate (NFC) was lower in DSBP than in YCG and decreased in the experimental rations with increasing DSBP. Similar findings were obtained by Mahmoud and El-Bordeny [
22], who indicated that NDF, ADF, and ADL contents increased, but NFC decreased linearly with an increasing ratio of SBP in the rations.
The CF digestibility was significantly higher with the introduction of DSBP in DSBP
25 and DSBP
50 than in YCG. Similar results were obtained by Ali et al. [
13], who found that the CF of beet pulp was highly digestible. Moreover, the degradability of the fiber fractions increased significantly with 10% DSBP supplementation in Italian ryegrass hay used for feeding fistulated goats [
23]. Meanwhile, the digestibility of OM, NFE, and CP did not show any significant difference among the three rations containing 0, 17.13, and 34.25% DSBP. With respect to feeding values, the results showed that the TDN and DCP of the different rations were not significantly affected by replacing YCG with DSBP, and were nearly the same. Similar findings were reported by El-Badawi et al. [
9], who found that TDN and DCP values differed insignificantly among rations when SBP replaced YC at 50 and 100% in lamb rations. Omer et al. [
24] found that dietary treatments based mainly on concentrate feed mixture (CFM) composed especially of grains or primarily based on 90% DSBP plus 10% soybean meal as a fibrous concentrate did not affect TDN and DCP values. The nutritional value of DSBP could be fairly compared with that of excessive energy grains like corn, barley, or oats. The TDN value of DSBP was in the range of 68–74% [
10].
The palatability and the bulkiness of dry sugar beet pulp can lend these characteristics to heavy concentrate mixtures, thus not affecting the feed intake [
25,
26]. Sugar beet pulp is high in rumen fermented energy (FME) in palatable shape [
27]. Eweedah [
28] showed that replacing YC with DSBP did not affect total feed intake by lambs. Abd-El Galil et al. [
29] fed sheep on rations containing 70% CFM that contained 50% YC or SBP, and found no differences in total DM and CP intake between the experimental rations. Feed intake as dry matter, TDN, DCP, and DE was nearly the same for the control and DSBP rations [
11].
Ruminal pH value was significantly lower in DSBP
25 and DSBP
50 than YCG. Additionally, ruminal NH
3-N concentration was significantly lower in DSBP
50 compared to YCG, while DSBP
25 was intermediate, demonstrating insignificant differences. However, ruminal TVFA’s concentration was substantially higher in the rations containing DSBP (DSBP
25 and DSBP
50) in comparison to the control one (YCG). Total concentration of VFAs increased significantly with increasing proportion of DSBP in the ration [
30]. A linear negative effect on ruminal pH and ammonia nitrogen concentrations with SBP rations has been reported compared with the control ration [
22]. Rations containing DSBP have been reported to lead to substantially higher concentrations of TVFAs in the rumen fluid of lambs [
13].
Introducing DSBP into the rations of dairy Holstein cows revealed significant improvements in blood plasma biochemistry. Plasma total protein and globulin concentrations were significantly higher in DSBP
25 and DSBP
50 than in YCG. However, plasma albumin was significantly higher in YCG compared to DSBP
50, with no significant differences being recorded for DSBP
25. In this respect, the groups fed DSBP had higher total protein and globulin values in serum than the control group in buffaloes and lambs [
13].
Concentrations of glucose, total lipids, triglyceride, and cholesterol were almost comparable for the different groups and were not significantly affected by DSBP. Belibasakis and Tsirgogianni [
31] reported no significant differences in the serum concentrations of glucose, triglycerides, and cholesterol when DSBP was added into the rations of Holstein cows, replacing and an equal proportion of YC.
Introducing DSBP into the rations of dairy cows led to a markedly low liver enzyme activity (AST and ALT). The values of AST and ALT were much higher in the plasma of YCG compared to that of DSBP
50, with insignificant differences for DSBP
25. The enzymatic activity of ALT and AST in the serum of cows in the control group was higher than the groups fed DSBP. The activity of ALT and AST was much better in the control group, while at the same time, both DSBP groups exhibited decreased values [
13].
The investigation of yield revealed that the yield of actual milk was significantly higher for cows fed DSBP rations (DSBP
25 and DSBP
50) than the control group (YCG). At the same time, 4% FCM yield changed greatly for DSBP
50, followed by DSBP
25, but YCG had a decrease yield. Actual milk yield increased by 1.55 and 3.05 kg/day, or by 5.06 and 9.95% for DSBP
25 and DSBP
50 compared to YCG, respectively. The 4% FCM yield values were 5.70 and 10.98 kg/day or by 19.73 and 38.27%, respectively. The fact that the improvements in 4% FCM yield were greater than those in the actual milk yield might be attributed to the improvements in the fat content of the milk. The present results are in agreement with the findings of El-Badawi et al. [
32], who found that daily milk yield increased significantly in cows fed the concentrate mixtures containing 25 and 40% DSBP compared to the control ration. Additionally, El-Fouly et al. [
33] reported that daily milk yield was significantly increased in ewes fed the concentrate mixtures containing 27 and 54% DSBP compared to those fed the control ration. Petit and Tremblay [
34] and Petit and Tremblay [
35] fed Holstein cows on grass silage with ad libitum intake with a concentrated supplement containing soybean meal fed with corn (SBCO) or SBBP and reported that 4% FCM was higher by 3.5 kg/d for cows fed SBBP than those given SBCO-supplemented feed. El-Badawi et al. [
32] found that the average daily yield of 4% FCM increased by 7.15% and 11.90% for cows fed concentrate mixtures containing 25 and 40% DSBP, respectively. El-Ashry et al. [
8] stated that 7% FCM yield (kg/d) tended to increase with the increase of DSBP in buffalo rations.
The contents of fat, protein, SNF, and TS in cows’ milk increased significantly with feeding rations containing DSBP, in addition to increasing the level of DSBP. At the same time, lactose and ash contents were not significantly affected by DSBP. The improvements in milk composition when fed DSBP may be attributed to the higher CF, NDF, ADF, cellulose, and hemicellulose content of DSBP compared to YCG. Additionally, the improvements in milk composition detected in our study were directly attributed to the increase of fiber intake by cows and increased TVFA with increasing DSBP levels. Consistent with this observation, the fat content of milk increased for cows fed DSBP because of higher fiber intake and greater acetate concentrations in the rumen [
36], and acetate is directly correlated with milk fat [
37]. El-Fouly et al. [
33] reported that milk fat content was significantly increased in ewes fed the concentrate mixtures containing 27 and 54% DSBP compared to the control ration. Preissinger et al. [
38] stated that dairy cows fed DSBP had higher milk fat content. Mansfield et al. [
39] found that milk fat percentage increased by 4.7% when beet pulp replaced corn in the ration of Holstein cows. Petit and Tremblay [
34] and Petit and Tremblay [
35] fed Holstein cows on grass silage ad libitum with a concentrated supplement containing soybean meal fed with corn (SBCO) or soybean meal fed with beet pulp (SBBP) and found that milk protein was higher with SBBP than SBCO. O’Mara et al. [
40] found that milk protein was higher when feeding cows on concentrate based on beet pulp when using a concentrate based on corn or wheat. Mousa [
41] reported that SNF yield in the milk of does fed a fodder containing beet roots was appreciably better than for those fed the control ration. El-Ashry et al. [
8] found an increase in the total milk solids of buffalo fed DSBP compared to the control.
Feed conversion ratio showed that cows fed the high degree of DSBP (DSBP
50) recorded lower quantities of DM, TDN, and DCP per one kg 4% FCM, followed by those fed the low level of DSBP (DSBP
25); however, higher amounts were detected with the control ration (YCG). The improvements in feed conversion with the introduction of DSBP in the ration of dairy cows may be attributed to the increase of 4% FCM. Comparable results were obtained by Mansfield et al. [
39], who found that efficiency of feed utilization was markedly improved in cows fed beet pulp compared with cows given corn. El-Badawi et al. [
32] reported that feed conversion, either as DM or TDN/kg gain, was significantly improved with the ration containing 50% USBP compared to the control, but feed conversion deteriorated significantly when they were fed concentrate ration of 100% USBP. Talha et al. [
6] stated that DM, TDN, or DCP/kg gain were better for lambs fed rations containing 50 or 75% DSBP than for those fed the control ration. The addition of 3% urea-treated sugar beet pulp to replace 50% of the common concentrate mixture is usually recommended in rations for growing sheep, and could provide a safe carbohydrate source with a more extended passage rate and, therefore, better utilization of dietary energy [
42]. The incorporation of dried sugar beet pulp in the rations of growing lambs greatly improved feed conversion, with the lambs that were fed the control ration showing higher DM, TDN, DCP, and DE required per one kg live weight than those fed a ration containing DSBT [
13].
The improved economic efficiency of feeding with DSBP is in agreement with the findings of Omer et al. [
24], who found that the use of sheep ration using SBP supplemented with 10% SBM, replacing CFM, led to a decrease in the feeding price and improved the daily profit above the feeding price and feed cost LE/kg gain with respect to the control ration. Additionally, introducing SBP in the ration of sheep resulted in the formulation of a cheap ration, therefore reducing the feeding cost. Beet pulp is appropriate for use as a supplement for gestating or lactating cows, an ingredient in ideal diets, or as a replacement for roughage in finishing diets [
41]. Feeding lambs on rations containing DSBP notably decreased the daily feed cost and feed cost per one kg weight gain, as well as increasing daily weight gain, net revenue, and economic efficiency compared with the control ration [
11].