Effects of Replacing Maize Silage with Silage Sweet Sorghum on Milk Production and Blood Biochemical Indexes of Dairy Cows

Siwei WANG Kuiying LI Shaoqing SHI Feng ZHANG Kun WANG

Abstract In order to study the effects of replacing different proportions of silage maize with silage sweet sorghum treated by different fermentation methods on the production performance and blood biochemical indexes of dairy cows， 25 Chinese Holstein lactating cows were randomly divided into 5 groups， 5 in each group. The control check （CK） was fed the basal diet; for the experimental group 1 and the experimental group 2， 50% of the silage maize in the basal diet was replaced with the additive silage sweet sorghum and the conventional silage sweet sorghum， respectively; and as to the experimental group 3 and the experimental group 4， all the silage maize in the basal diet was replaced with additive silage sweet sorghum and conventional silage sweet sorghum， respectively. The preliminary trial period was 7 d， and the trial period was 35 d. The results showed that the experimental group 1 and the experimental group 3 had the dry matter intake significantly higher than that of the experimental group 2， the experimental group 4 and the CK （P<0.05）. The daily milk yields of the experimental group 1 and the experimental group 2 were significantly lower than that of the CK （P<0.05）， and the experimental group 3 and the experimental group 4 were significantly lower than the experimental group 1 and the experimental group 2 （P<0.05）. The milk protein percentage of the experimental group 2 was extremely significantly higher than that of the experimental group 4 （P<0.01）. The experimental group 1， the experimental group 2 and the experimental group 3 showed the blood glucose levels extremely significantly higher than that in the CK （P<0.01）. The blood urea nitrogen contents in the experimental group 2 and the experimental group 4 were significantly higher than those in the experimental group 1 and the CK （P<0.01）. There were no significant differences in other blood biochemical indexes between various groups  （P>0.05）.  It is feasible to use silage sweet sorghum to feed dairy cows， but the proportion should not be too large， and attention should be paid to the energy and nitrogen balance of the diet.

Key words Silage sweet sorghum; Silage maize; Additive; Production performance; Blood biochemical index; Holstein cow

Roughage is an important part of dairy cow diet. In recent years， the scale and intensification of dairy cow breeding in China have been continuously improved. However， due to the shortage of high quality roughage， poor quality and low feed conversion efficiency in China， it is forced to use high concentrate diet for a long term in milk cow production， resulting in low yield of dairy cows， poor milk quality， and multiple nutritional metabolic diseases in dairy cows. With the advancement of the structural reform of the agricultural supply side， the adjustment of the planting structure and the implementation of planting food crops into feed crops and combining crop farming and breeding industry， the development of high quality roughage resources for dairy cows has become an urgent problem to be solved. Sweet sorghum （Sorghum bicolor （L.） Moench） is an annual herb in Sorghum of Gramineae， a variant of sorghum， and a high efficiency plant with strong drought resistance， good salt and alkali tolerance and good adaptability. It can be grown in most parts of China[1-2]. Sweet sorghum stalks are fresh， rich in sugar， soft in leaves and good in palatability， and thus serve as an excellent green fodder[3]. Forage sweet sorghum as a quality feed crop only second to forage maize has shown significant economic benefits in dairy industry in the United States， Australia and other countries. It is now receiving more and more attention in Chinas dairy production. However， there are few studies on the utilization of silage sorghum in dairy cow production and its impact on dairy cow performance. The research on the feeding effect of silage sweet sorghum substituting for silage maize in different proportions and different treatment methods in dairy cow production has been rarely reported. In this study， silage sweet sorghum treated with different fermentation methods was used to replace different proportions of silage maize in the diet， and its effects on dairy cow performance and blood biochemical indexes were investigated， with an attempt to provide a theoretical basis for the application of sweet sorghum in dairy cow diet.

Materials and Methods

Experimental animals

Twenty five healthy Chinese Holstein lactating cows were provided by the dairy farm of Institute of Cereal and Oil Crops， Hebei Academy of Agricultural and Forestry Sciences.

Preparation of silage sweet sorghum

Sweet sorghum （Juneng Liangwang 2） was planted in the Dishang station of Institute of Cereal and Oil Crops， Hebei Academy of Agricultural and Forestry Sciences. Sweet sorghum was harvested at the end of the milky stage， crushed and cut to 2-3 cm. One part of the sweet sorghum was directly wrapped and silaged. The other part was added with lactic acid bacteria additive according to the instruction （lactic acid bacteria ≥1×10 11  cfu/g， provided by some Biotechnology Co.， Ltd. in Nanjing） after mixing， and the mixture was then wrapped and silaged for 45 d of fermentation.

Experimental design

Using a two factor experimental design， 25 healthy Chinese Holstein lactating cows were selected and divided into 5 groups according to the principle of similar age， body condition， parity， lactation days， milk production and feed intake， with 5 individuals in each group. The control check （CK） was fed the basal diet; for the experimental group 1 and the experimental group 2， 50% of the silage maize in the basal diet was replaced with the additive silage sweet sorghum and the conventional silage sweet sorghum， respectively; and as to the experimental group 3 and the experimental group 4， all the silage maize in the basal diet was replaced with the additive silage sweet sorghum and conventional silage sweet sorghum， respectively. The preliminary trial period was 7 d， and the trial period was 35 d. The composition and nutritional level of the experimental diet are shown in Table 1.

Feeding and management

The test herd was fed TMR twice a day （08： 00， 17：00）， free to eat and drink， and milked 3 times a day （08： 00， 15： 00， 22： 00）. The milk yield was recorded.

Sample collection and treatment

Determination of TMR composition

TMR samples were collected from various groups once a week during the experiment， and dried and pulverized at 65 ℃ in an oven， for the determination of the main nutritional ingredients， including crude protein， crude fat， crude ash， neutral detergent fiber， acid detergent fiber， calcium and phosphorus.

Determination of production performance

The feeding  amount，  the remaining amount and the daily milk yield in each group were recorded every day， and the dry matter intake was calculated. Milk samples were collected every 7 d during the experiment， mixed at the ratio of 4∶3∶3 （the morning， noon and night）， and then immediately stored in a refrigerator at 4 ℃. The collected milk samples were sent to the Fine Livestock Breeding Workstation of Hebei Province for the determination of milk fat percentage， milk protein rate， lactose， milk urea nitrogen and somatic cell count.

Determination of blood biochemical indexes

On the last day of the experiment， 9 ml vacuum blood collection tubes were used for jugular vein blood collection before morning feeding. After standing at room temperature for 30 min， it was stored in a refrigerator at 4 ℃ overnight， and then centrifuged at 4 ℃ at 3 000×g for 15 min. A micropipette was used to pipette the supernatant to prepare serum， which was frozen in a refrigerator at -20 ℃. The serum biochemical indexes were determined with an automatic biochemical analyzer （HITACH17080）， including albumin （ALB）， total protein （TP）， globulin （GLO）， glucose， urea nitrogen （BUN）， cholesterol （CHOL）， alanine aminotransferase （ALT）， total bilirubin （TBIL） and alkaline phosphatase （ALP）.

Statistical analysis of data

The original data of the experiment were initially prepared using Excel 2010， and then subjected to statistical analysis using SPSS 19.0 software. Duncans multiple comparisons were performed between groups， and the data were expressed as "mean±standard deviation".

Results and Analysis

Effect of replacing silage maize with silage sweet sorghum on TMR Nutritional Composition

The results are shown in Table 2.

Table 2 shows that the crude protein content of TMR was higher in the four experimental groups than in the CK. The contents of neutral detergent fiber and acid detergent fiber in the experimental group 1 and the experimental group 2 were lower than other groups; and the diet nutrition of the experimental group 1 and the experimental group 2 was slightly better than the other groups， without significant differences （P>0.05）. It indicated that partial replacement or complete replacement of silage maize in the basal diet with silage sweet sorghum had no significant effect on the main nutritional components of TMR.

Effect of replacing silage maize with silage sweet sorghum on production performance of dairy cows

The results are shown in Table 3.

It can be seen from Table 3 that the dry matter intake of the experimental group 1 and the experimental group 3 was significantly higher than that of the experimental group 2， the experimental group 4 and the CK （P<0.05）， while the CK was not significantly different from the experimental group 2 and the experimental group 4  （P>0.05） . The daily milk yields of the experimental group 1 and the experimental group 2 were significantly lower than that of the CK （P<0.05）， and the experimental group 3 and the experimental group 4 were significantly lower than the experimental group 1， the experimental group 2 and the CK （P<0.05）. The milk protein percentage of the experimental group 2 was extremely significantly higher than that of the experimental group 4 （P<0.01）， and significantly higher than those of the CK and the experimental group 3  （P<0.05）.  The lactose content of the CK was significantly higher than that of the experimental group 1  （P<0.05） ， but had no significant differences from those of other three groups （P>0.05）. The milk urea nitrogen content of the CK was extremely significantly lower than those of the experimental group 3 and the experimental group 4 （P<0.01）， and significantly lower than that of the experimental group 1 and the experimental group 2 （P<0.05）， and the experimental group 4 was significantly higher than the experimental group 1 and the experimental group 2 （P<0.05）. There were no significant differences in milk fat percentage and somatic cell count between various groups （P>0.05）. It indicated that the use of the additive silage sweet sorghum instead of silage maize can increase the dry matter intake of dairy cows; the daily milk yield of dairy cows decreased with the increase of the proportion of silage sweet sorghum; the appropriate addition of silage sweet sorghum can increase the milk protein percentage of dairy cows; and the urea nitrogen content in the milk increased with the increase of the proportion of silage sweet sorghum.

Effect of replacing silage maize with silage sweet sorghum on serum biochemical indexes of dairy cows

The results are shown in Table 4.

It can be seen from Table 4 that the glucose contents of the experimental group 1， the experimental group 2 and the experimental group 3 were extremely significantly higher than that of the CK （P<0.01）， and significantly higher than the experimental group 4 （P<0.05）， while there was no significant difference between the experimental group 4 and the CK （P>0.05）. The urea nitrogen contents of the experimental group 2 and the experimental group 4 were extremely significantly higher than those of the CK and the experimental group 1 （P<0.01）， while the experimental group 1 and the experimental group 3 were not significantly different from the CK （P>0.05）. There were no significant differences in other indexes between various groups （P>0.05）. It indicated that the additive silage sweet sorghum could increase the glucose content in the serum of cows; the blood urea nitrogen content increased with the increase of the proportion of silage sweet sorghum in the diet， and the increasing trend was more obvious with the use of conventional silage sweet sorghum; and adding silage sweet sorghum did not have a significant effect on cows.

Discussion

Effect of replacing silage maize with silage sweet sorghum on production performance of dairy cows

Researchers at home generally believe that sorghum silage has a soft texture and good palatability， containing the nutritional ingredients equivalent to or better than that of forage maize， and the utilization rate after eaten by dairy cows is higher. Compared with silage maize， it can increase the milk yield of dairy cows based on the increase of silage yield， thus having high economic benefits[4-7]. The study results of Wang et al.[5] and Li et al.[7] have shown that the use of silage sorghum to feed dairy cows compared with silage maize increases milk yield without changing milk quality. Duan et al.[6] compared the effects of silage sweet sorghum and silage maize stalks on dairy cows， and found that the feed intake and milk yield of dairy cows fed silage sweet sorghum increased. However， some foreign studies suggest that although silage sweet sorghum can replace silage maize for feeding cows， it may not be better than feeding silage corn. Colombini et al.[8] found that there were no significant changes in milk yield， 4% corrected milk， milk protein percentage and fat percentage when replacing maize silage with sorghum silage， but the urea nitrogen level of dairy cows fed silage maize was lower. Amer et al.[9] found that the use of silage sweet sorghum instead of silage alfalfa reduced the milk yield of dairy cows， and simultaneously reduced lactose and the urea nitrogen content in milk， but increased milk fat percentage.

The results of this study indicated that the addition of conventional silage sweet sorghum to the diet had no significant effect on the dry matter intake of dairy cows （P>0.05）， but the addition of additive silage sweet sorghum to the diet could significantly improve the dry matter intake of dairy cows （P<0.05）， indicating that the additive treatment could significantly improve the palatability of silage sweet sorghum. However， with the increase of the addition proportion of silage sweet sorghum， the daily milk yield of dairy cows also decreased significantly （P<0.05）， which might be because silage sweet sorghum has a lower starch content than silage maize， and the equal replacement of silage maize results in a decrease in energy in the diet. The milk protein percentage significantly increased when the conventional silage sweet sorghum was used to replace 50% of silage maize （P<0.05）， but the complete replacement of silage maize did not significantly changed the milk protein percentage （P>0.05）. It showed that the use of silage sweet sorghum to replace silage maize had a little effect on the production performance of dairy cows.

Effect of replacing silage maize with silage sweet sorghum on serum biochemical indexes of dairy cows

Serum biochemical indexes can not only reflect the physiological state and immune level of the animal body， but also reflect the metabolism of dietary nutritive substances in animals. Therefore， monitoring animal serum biochemical indexes can provide a basis for further improvement of animal feeding management[10]. Glucose is the most basic nutritive substance in the body tissues， and the change in blood sugar content is a reflection of the dynamic  equilibrium  of the bodys absorption， activities and metabolism. In general， blood sugar level is commonly used to reflect carbohydrate and energy intake， which is an important indicator of the energy and nutrition status[11]. In this study， the blood glucose levels of the experimental groups with the addition of silage sweet sorghum were higher than that of the CK， indicating that feeding silage sweet sorghum had obvious advantages in the bodys sugar metabolism， and the use of additive silage sweet sorghum to replace 50% of silage maize resulted in a blood sugar content higher than the use of conventional silage sweet sorghum to replace 50% silage maize， which mean that the use of the additive helped to improve the digestion and absorption of silage sweet sorghum. The level of urea nitrogen in the blood is an important indicator reflecting the bodys nitrogen metabolism， as well as an indicator reflecting the nutritional status and kidney function. Wilson et al.[12] showed that serum urea nitrogen content is inversely proportional to the nitrogen use efficiency of feeds. The results of Chikhou et al.[13] showed that blood urea nitrogen level can reflect animal protein metabolism and can be used as an indicator of protein deposition in the body. When the level of urea nitrogen is elevated， it often means an increase in the bodys protein decomposition or an increase in the degree of liver urea  recirculation.  Studies have shown that the increase in serum urea nitrogen level is often accompanied by a decrease in nitrogen deposition in animal bodies[14]. In this study， the blood urea nitrogen level of dairy cows increased with the increase of the addition of  silage  sweet sorghum， indicating that silage sweet sorghum was not conducive to the utilization of feed nitrogen by dairy cows compared with silage maize， which would reduce the protein metabolism level of dairy cows. In addition， studies have shown that there is a strong linear correlation between urea nitrogen content and serum urea  nitrogen  content in dairy cows[15-16]. In this study， the milk urea nitrogen content of each experimental group was extremely significantly or significantly higher than that of the CK （P< 0.05  or  P<0.01 ）， similar to the results of blood urea nitrogen， consistent with previous studies.

Conclusions

In this study， silage sweet sorghum with different fermentation treatments was used to replace different proportions of silage maize in dairy cow diet， and the feasibility of feeding dairy cows with silage sweet sorghum was analyzed by measuring production performance and serum biochemical indexes. The results showed that the experimental group 1 and the experimental group 3 had the dry matter intake significantly higher than that of the experimental group 2， the experimental group 4 and the CK （P<0.05）. The daily milk yields of the experimental group 1 and the experimental group 2 were significantly lower than that of the CK （P<0.05）， and the experimental group 3 and the experimental group 4 were significantly lower than the experimental group 1 and the experimental group 2 （P<0.05）. The milk protein percentage of the experimental group 2 was extremely significantly higher than that of the experimental group 4 （P<0.01）. The experimental group 1， the experimental group 2 and the experimental group 3 showed the blood glucose levels extremely significantly higher than that in the CK （P<0.01）. The blood urea nitrogen contents in the experimental group 2 and the experimental group 4 were significantly higher than those in the experimental group 1 and the CK （P< 0.01） . It is feasible to use silage sweet sorghum to feed dairy cows， but the proportion should not be too large， and attention should be paid to the energy and nitrogen balance of the diet.

References

[1] LI CH， ZHANG PT， GUO WQ， et al. Status and prospects of research and utilization of sweet sorghum silage[J]. Jiangsu Agricultural Sciences， 2014， 42（3）： 150-152.

[2] LI SS， LI F， BAI YF， et al. Utilization technology of sweet sorghum [J]. Pratacultural Science， 2017， 34（4）： 831-845.

[3] ZHANG SJ， DONG ZG， YANG JB. Cultivation and utilization of forage sorghum[J]. Journal of Animal and Veterinary Sciences， 2000， 19（2）： 31-33.

[4] GUO YP， YU Z， GU XY， et al. Effects of different additives on the quality of forage sorghum[J]. Acta Agrestia Sinica， 2010， 18（6）：  875-879.

[5] WANG YH， CHEN JP， ZHANG PT， et al. Study on the silage quality of sweet sorghum and maize and their feeding effects on dairy cattle[J]. Journal of Anhui Agricultural Sciences， 2015， 43（14）： 127-128.

[6] DUAN JH， YU TM， WANG JC， et al. Feeding test on forage sorghum in dairy cattle[J]. China Dairy Cattle， 2014， 14： 51-52.

[7] LI CX， FENG HS， LI YS， et al. Comparative of feeding cows and sheep and milk quality of silage sweet sorghum and silage maize[J]. Science and Technology of Qinghai Agriculture and Forestry， 2014 （2）： 8-11. （in Chinese）

[8] COLOMBINI S， RAPETTI L， COLOMBO D， et al. Brown midribforage sorghum silage for the dairy cow： nutritive value and comparison with corn silage in the diet[J]. Ital J Anim Sci， 2010， 9（3）： 273-277. （in  Chinese）

[9] AMER， SUN P， ZHANG YX. Effect of feeding sweet sorghum silage on milk production of lactating dairy cows[J]. China Animal Husbandry and Veterinary Medicine， 2012， 39（9）： 113. （in Chinese）

[10] ZHAO XW， YANG YX， HUANG DW， et al. Effect of supplementing Ligustrum lucidum Ait on production performance and serum biochemical indexes of lactating dairy cows[J]. China Animal Husbandry and Veterinary Medicine， 2015， 42（7）： 1732-1737. （in Chinese）

[11] SONG P. The determination and analysis of dairy cows blood biochemical indexes under different rearing conditions[D]. Harbin： Northeast Agricultural University， 2007. （in Chinese）

[12] WILSON AD， STOKES CR， BOURNE FJ. Effect of age on ab sorption and immune responses to weaning or introduction of noveldietary antigens in pigs[J]. Res Vet Sci， 1989， 46（2）： 180-186.

[13] CHIKHOU F H， MOLONEY A P， ALLEN P， et al. Long termeffects of cimaterol in friesian steers： i. growth， feed efficiency， andselected carcass traits[J]. J Anim Sci， 1993， 71（4）： 906-913.

[14] WANG M， WANG JQ， ZHANG JY， et al. Effects of sugar beet pulp substituted for ground corn on the performance and blood metabolite of dairy cows[J]. China Animal Husbandry and Veterinary Medicine， 2011， 38（1）： 18-22. （in Chinese）

[15] AN PP. Effects of different diet types on metabolism of milk protein precursor in lactating dairy cows[D]. Lanzhou： Gansu Agricultural University， 2012. （in Chinese）

[16] CHAVEIRO A， ANDRADE M， ANDRADE M， et al. Association between plasma and milk urea on the insemination day and pregnancy rate in early lactation dairy cows[J]. Iran J App Anim Sci， 2011， 1（2） ：  9-14.