Sugarcane (Saccharum officinarum) is palatable to ruminants and is commonly used as the only roughage of their basal diet (Gandra et al., 2017; Naves et al., 2015a; Naves et al., 2015b; de Jesus et al., 2012). In Brazil, it is particularly suited for dry season feeding of ruminants (Bernardes et al., 2012). It is often considered an emergency feed (Pate et al., 2002).
Because of its low concentration of crude protein and high fibre content, sugarcane forage is a poor quality roughage that must be complemented with protein rich materials for adequate ration management (Guerra, 2011; Archimède et al., 2008; Preston, 1988). However, in situ DM and OM degradabilities of 6 cultivars (at 5% passage rate) of sugarcane were high, ranging from 74.19 to 86.27% for DM and from 68.22 to 85.41%, suggesting a good potential for ruminant feeding (Arantes, 2014). High and low fibre varieties showed no difference in animal performance (Pate et al., 2002). Whether sugarcane stalks are grazed, used as a soiling crop (entire or chopped) or ensiled, they always require supplementation with protein sources.
In Cuba, a product called "Saccharina" containing 14% crude protein and 90% DM was prepared by adding 15 kg urea and 5 kg minerals to every ton of chopped surgarcane and by drying the mixture (Guerra, 2011).
Principles of sugarcane forage supplementation
Because it is unbalanced for protein, minerals and vitamins, sugarcane-based diets always require supplementation. Correct supplementation of sugarcane forage should aim to:
- satisfy the needs of rumen microbes for fermentable nitrogen (ammonia, urea), trace nutrients (peptides, amino acids, minerals and vitamins) and the physical attributes of an efficient rumen ecosystem (small quantities of readily fermentable fibre);
- provide sources of protein, glucose precursors and long chain fatty acids able to bypass (or escape) the rumen fermentation so that the available nutrients are balanced according to the needs of production;
- obtain feeds and/or chemical substances capable of manipulating rumen fermentation so as to increase propionate relative to other VFAs, and eliminate (or reduce) protozoa in the rumen (Preston, 1988).
Urea and mineral supplementation
Supplementation is often reported to be done with urea (non protein nitrogen, NPN) (Naves et al., 2015a; Naves et al., 2015b). However, some restrictions should be respected as urea has some toxicity. Urea should not be fed at a rate exceeding 2-3% of the concentrate or grain portion of ruminant diets, and should be limited to less than 1% of the total diet. In the French West Indies, it was suggested to have 10 kg urea per ton of fresh sugarcane (Archimède et al., 2008). Additionally, NPN should constitute no more than one-third of the total nitrogen in ruminant diets. Once the decision is made to feed NPN, animals must be slowly adapted to it, and maintained on a consistent dietary NPN content with no significant deviation (Thompson, 2017).
Minerals and vitamins are necessary for the rumen microbes and the physical attributes of a good rumen ecosystem. They could be provided by highly digestible green forages such as sweet potato tops and foliages of forage tree legumes, such as leucaena, at rates of about 600 g DM/100 kg LW (Preston, 1988).
Protein supplementation
Many protein sources have been assessed for the adequate supplementation of sugarcane forage. In most cases, the desirable dietary level of protein was higher than 15% (Naves et al., 2015a; Naves et al., 2015b; Cordeiro et al., 2007).
Rice polishings were reported to be the best sources of by-pass nutrients because of their richness in essential amino acids, starch and lipids. The most economic rate was 0.5-1 kg/d (Preston, 1988). Other supplements such as oilseed cakes or fishmeal also yielded good results (e.g. raw soybean, cottonseed meal, soybean meal, maize/fishmeal concentrates) (Naves et al., 2015a; Naves et al., 2015b; Cordeiro et al., 2007; Preston, 1988).
Combination of urea and protein sources
An important point is that the various types of supplements (urea and other protein sources), which act in the rumen as bypass nutrients, interact. Neither urea nor rice polishings were effective when given alone, yet they had a dramatic effect on animal performance when given together (Preston, 1988). To this respect, the use of foliages from tropical legumes such as gliricidia, leucaena, erythrina, pea, sweet potato, mulberry is very interesting as they provide both non protein nitrogen and by-pass protein (Archimède et al., 2008).
Grazing sugarcane
Sugarcane could be grazed only in emergency situations, and then only once per year and in a manner that completely cleans the grazing area within one week (Pate et al., 2002).
Raw or chopped sugarcane
When sugarcane forage is included in ruminant diets it may represent up to 50-60% of the diet (Lascano et al., 2012; Cordeiro et al., 2007). In small-holder tenure, it was suggested to have green stock of sugarcane for the dry season. In the French West Indies, it is suggested to keep 0.04 ha sugarcane/month of dry spell/ha of grassland. For example, a farmer that has 5 ha of grassland in a place where the dry season is 4 month long should have 0.04*5*4 = 0.8 ha of sugarcane (Archimède et al., 2008).
Dairy cows
When sugarcane forage was used as a basal diet (47% dietary level) for dairy cows, protein supplement was obtained through soybean meal + urea at low level (10 g/kg DM), soybean meal + urea at high level (17 g/kg DM), raw soybean, or corn gluten meal. All protein supplements resulted in the same milk yield but soybean meal + urea at low level (control diet) resulted in the highest protein milk yield (Naves et al., 2015a). In an attempt to reduce the use of costly soybean meal, it was shown that dairy cows in the final third of their lactation could be fed on less CP and higher level of NPN through the use of urea, without affecting DM intake, net energy for lactation or total apparent digestibility. Milk protein yield tended to be lower in cows fed on NPN but no differences were found in milk yield or in cow body condition (de Jesus et al., 2012).
On the contrary, in Cuba, where urea provision may be difficult, it was suggested to use cassava or kenaf foliage in order to replace urea in the supplementation of sugarcane forage/star grass based diets for dairy cows. The foliages could replace urea and yielded more milk than urea supplemented diets (García-López et al., 2016). The use of foliage of sweet potato, erythrina, leucaena and mulberry was also recommended in the French West Indies and it was recommended to avoid urea when these foliages were used (Archimède et al., 2008).
In Brazil, high producing dairy cows were fed on fresh sugarcane in an attempt to replace maize silage. Sugarcane forage decreased DM intake and milk yield and was not recommended for animals at production peak (Corrêa et al., 2003). In India, crossbred cows produced 10-12 kg per day, with an average intake of sugarcane of 20.5 kg per day (Rangnekar, 1988).
Growing and fattening cattle
Because of its low fibre digestibility, sugarcane may limit cattle performance and inclusion levels in the diet of growing cattle may be variable, ranging from 20 to 70%.
Post-weaning crossbred heifers were fed on 70% chopped sugarcane and 30% concentrate with increasing levels of CP (13%, 15%, 19% and 22%). Increasing CP level resulted in higher total apparent digestibility of CP. However, health parameters were found to be better at the lower protein content (13%) (Queiroz et al., 2012).
In Brazil, zebu steers receiving 60% sugarcane forage and 40% concentrate had higher gastrointestinal content at slaughter and their carcass was less compact than those of steers fed on maize silage or bread grass (Brachiaria brizantha) (Macitelli et al., 2005).
In feedlot trials, live weight gain (LWG), feed conversion ratio and meat characteristics declined when chopped sugarcane was above 20-30% dietary level (DM basis), and where concentrates were made out of ground maize, cottonseed meal, citrus pulp and minerals (Pate et al., 2002). In a comparison with cotton seed hulls (20% dietary level) used as basal roughage in growing steers, sugarcane forage (30% dietary level) resulted in lower DM intake, lower LWG, and had poorer feed conversion ratio (Pate et al., 2002).
In Cuba, crossbred Holstein x zebu steers were fed on 73% sugarcane forage molasses-urea (10%) and concentrate (17%). The animals reached 840 g ADG when the concentrate was offered once a day and 950 g when the concentrate was offered twice a day. It was suggested that CP and energy were better utilized when the concentrate was offered twice. It resulted in better feed conversion ratio (9.2 vs. 11) (Rodríguez et al., 2013).
It was shown that cultivars of sugarcane with higher NDF digestibility included at 20 or 40% of the diet could increase DM intake, final body weight and hot carcass yield, and overall profitability in finishing Nellore bulls (Mesquita, 2013).
Sheep
Blackbelly rams fed on sugarcane supplemented with urea had similar OM intake (48 g/kg LW0.75) to rams fed on hay (Dichanthium spp.). Their soluble carbohydrate intake was much higher (22.7 vs. 5.8 g/kg LW0.75) and total tract digestibility of OM was also higher on sugarcane forage (71.2% vs. 64.7% on hay). On the contrary, sheep showed no difference for CP digestibility and had lower NDF digestibility (Archimède et al., 2014). Methane emissions were 34.7 g/kg digestible OM intake in sheep fed on sugarcane compared to 53.7 for sheep fed on hay. These data showed that methane emissions were slightly lower (24 g vs. 34 g) for sheep fed on sugarcane forage (Archimède et al., 2014).
Sugarcane forage raw or treated with 0.5% or 0.9% lime (CaO) were included at 50% dietary level in lamb (22 kg BW) diets. The remainder of the diet was concentrate. Diets were formulated in order to meet animal maintenance demands and gains of 150 g/day. CaO addition neither altered nutrient intake nor improved animal weight gain. It was concluded that CaO could be used a a preservative treatment of sugarcane as it had no adverse effect on the animal performance provided the sugarcane was fed 24h after CaO addition (Freitas et al., 2008).
Ensiled sugarcane
Untreated sugarcane silage
Comparisons between chemical composition and digestion parameters of fresh and ensiled sugarcane have been made. They have shown that ensiled sugarcane was significantly (P<0.05) different for DM, fibre (NDF, ADF and lignin) and ash content. However, conclusions about OM and DM in sacco digestibilities were unclear, and no consistent difference could be found (Reyes-Gutiérrez et al., 2015). Earlier results had suggested some reduction in the nutritive value of ensiled sugarcane with IVDMD reduced from 66,4% to 55,3% when measured in sacco in sheep rumen (Alcantara et al., 1989). Poorer composition parameters have also been reported for MS (20.9 vs. 27.3% ), NDF (54.95 vs. 42.1%), ADF (43.8% vs. 34.9%) and lignin (7.2% vs. 6.8%) for ensiled and raw sugarcane, respectively (Coan et al., 2002). These results advocated for the treatment of sugarcane silage. In comparison to fresh sugarcane, ensiled untreated sugarcane resulted in lower DM intake in cows receiving 60% sugarcane and 40% concentrate (Andrade et al., 2016).
Treated sugarcane silage
It was reported that among 5 sugarcane silages treated with either urea (0.5%), sodium benzoate (0.1%), Lactobacillus plantarum, or Lactobacillus buchneri, no significant changes were observed in terms of in sacco ruminal degradability obtained in Nelore steers between treated and untreated silage (Schmidt et al., 2007).
Dairy cattle
In a trial assessing the effects of sugarcane silage treatments (CaO at 0.5% and 2 types of Lactobacillus spp. addition), ensiled treated sugarcane resulted in lower DM intake in cows receiving 40% sugarcane and 60% concentrate, in comparison to cows receiving fresh sugarcane (Andrade et al., 2016). Milk yield and fat-corrected milk yield were comparable to maize silage for all types of sugarcane products (fresh or ensiled). Cows fed on sugarcane silage tended to have higher milk fat and milk total solids (Andrade et al., 2016).
In Cuba, sugarcane silage made out of sugarcane and cattle faeces was fed to dairy cattle during periods of scarcity and resulted in higher milk yield than a mixture of fresh sugarcane and urea (Carrasco et al., 2004).
Growing cattle
Sugarcane silage was treated with fibrolytic enzyme (20 g enzyme per day) in order to reduce fibre content and it was then fed to heifers during 25 days at 54.9% of the diet. It was compared to untreated sugarcane silage, to untreated maize silage, and to maize silage treated with the same enzyme at the same level, and included at 65.3% of the diet. NDF digestibility of treated forages was increased as well as time spent eating. However, enzyme supply decreased N absorption and heifers had lower microbial protein synthesis than those fed on maize silage (Gandra et al., 2017).
