Liquid Feeds - Research Findings - Dairy, Beef, Sheep, Pigs, Poultry
The use of molasses in livestock and poultry feeds dates back to the nineteenth century. At that time, the properties of molasses as a source of dietary energy and as a dust eliminator were already known. This dust prevention is extremely important, since animals, are prone to bronchial diseases caused by dust. Dust is also a problem for the people feeding livestock and legislation has attempted to minimise personal exposure to dust. Dust may also result in feed wastage. Literature reports have shown that 10% molasses practically eliminated all dust and 30% eliminated fine particles.
Molasses may be fed to livestock in several ways such as molassed meal, molasses blocks, and liquid form to provide energy directly or be used as a carrier for non-protein nitrogen, vitamins and minerals as well as medicinal compounds.
Microbial protein supply to the duodenum should be maximised for efficient use of feed protein and energy (Firkins, 1996). Matching the rates at which energy and nitrogen from the basal forage and concentrate become available to the microbial population – synchrony, is seen as a method of enhancing rumen microbial protein synthesis (Dewhurst, 1999).
Post-ensiling, sugars in grass are fermented to much lower energy yielding sources and consequently animal performance is lower on grass silage than fresh grass. This is attributed to a limited energy supply to the rumen microbes resulting in a much lower level of microbial protein synthesis.
Asynchronous release of energy and nitrogenous components is often proposed as the reason for the low efficiency of microbial protein synthesis on grass silage diets (Van Vuuren et al., 1995) due to the rapid release of ammonia from the large amount of non-protein nitrogen compounds present (Chamberlain and Choung, 1995). While there is no convincing evidence of a need for close synchronisation, as microbes appear to withstand transient periods of asynchronous nutrient supply in many cases, severe mismatching of energy and nitrogen release may be detrimental (Chamberlain and Choung, 1995; Firkins, 1996). In the literature, confounding results are often a problem because of the difficulty in separating the effects of synchrony from different dietary ingredients.
Chamberlain et al. (1993) concluded that sugars, particularly sucrose are clearly superior to starch as an energy source for the microbial fixation of nitrogen in the rumen. Sucrose gives a greater microbial protein synthesis than starch (Table 1). Supplementing grass silage with molasses or sucrose significantly reduces ruminal ammonia N concentrations compared to other carbohydrate sources such as starch (Chamberlain et al., 1985; Moloney et al., 1994; Keady and Murphy, 1997; Moloney, 1997; Y-G Oh et al., 1999).
High rumen ammonia levels are associated with poor reproductive performance in dairy cows (Butler, 1998).
|Silage alone||Added Sucrose*||Added Starch||Added Xylose||Added Lactose||Added Fructose|
|Rumen Ammonia Concentration (mg/l)||255||157||213||180||158||164|
|Microbial Protein Synthesis (g/d)||64||93||74||82||89||86|
|Silage alone||Added Sucrose*||Added Starch|
|Rumen Ammonia Concentration (mg/l)||255||157||213|
|Microbial Protein Synthesis (g/d)||64||93||74|
|Added Xylose||Added Lactose||Added Fructose|
|Rumen Ammonia Concentration (mg/l)||180||158||164|
|Microbial Protein Synthesis (g/d)||82||89||86|
Source: Chamberlain et al. 1993; Chamberlain and Choung, 1995
Grass, especially when well fertilised with nitrogen, contains a high level of crude protein and relatively low levels of water-soluble carbohydrates particularly in the spring and autumn. Because of a shortage of fermentable organic matter, large quantities of grass nitrogen are not converted into microbial protein but rapidly degraded into NH3 (De Visser et al., 1997). Thus, there is a potential benefit to supplementing grass with a rapidly degradable energy source. Supplementation of a grass diet with an energy source (O’Mara et al., 1997) or synchronisation of the ruminal release of supplemental carbohydrate with pasture nitrogen (Kolver et al., 1998) appears to improve the capture of ruminal N and increase the efficiency of microbial synthesis.
Molasses supplies the rumen with rapidly fermentable energy in the form of sugars.
Inclusion of molasses (complete diet form) in grass silage/concentrate diets at up to 23% (Casssidy et al., 1997), 31% (Yan and Roberts, 1997) or 26% (Murphy and Younge, 1996; Murphy, 1999) (i.e. ~ >4.0kgDM) of the total DM significantly increased milk yield, milk protein concentration and yield, casein concentration and total DMI. In the studies of Yan et al. (1997) increasing the molasses concentration up to 47% of the total DMI did not significantly increase milk yield and resulted in some scouring in a proportion of the cows.
The increase in milk protein concentration with molasses or sucrose inclusion in silage diets (Keady and Murphy, 1998; Murphy, 1999; Phipps et al., 1999) is attributed to an increased microbial protein synthesis, thus amino acid production. Murphy (1999) reported a significant linear decline in milk fat concentration and milk non-protein nitrogen with increasing molasses inclusion.
McKendrick et al. (1996) found that the partial replacement of concentrate with cane molasses (1.8kg DM) significantly increased total DMI, milk yield (by 1 kg/day) and milk protein content and reduced milk fat content of cows on a grass silage based diet. Cassidy et al. (1997) concluded that cow DMI and performance was similar between diets containing 4kg DM of molasses, barley or unmolassed beet pulp when fed as part of an isonitrogenous supplement to a grass silage diet. Similarly, Phipps et al. (1999) showed that 7% molasses could replace a selection of energy and protein ingredients without affecting DMI or milk yield of cows on a maize silage based diet.
Thus, results show that up to 25-31% molasses inclusion in the total dietary DM of dairy cows increases milk yield and protein yield without any adverse effects on cow performance. In addition, molasses can effectively replace moderate levels of common energy sources.
Evidence also suggests that there is a greater response to an increase in dietary UDP when lactating cows are fed high levels of molasses.
In a series of experiments carried out at Grange, Drennan (1985) feeding isoenergetic and isonitrogenous supplements (barley v. cane molasses/soyabean) to finishing steers or bulls on grass silage obtained similar animal performance between diets when molasses was included at 21% of the DMI (2.3-2.9 kg fresh weight/day). However unlike barley, increasing the level of molasses to 33% or 37% of DMI (3.6-5.7kg fresh weight/day) did not significantly increase animal performance. In other words, cane molasses is used more efficiently at the lower ration inclusion rates where its feeding value is similar with that of barley dry matter.
Moloney et al. (1993a) found no difference in the intake or performance of steers offered isoenergetic and isonitrogenous barley based or molasses based (17% of dietary DM–2.2kg fresh weight/day) supplements with grass silage. Chapple et al. (1996) concluded that the replacement of barley with molasses did not affect liveweight gain of finishing bulls.
However, Drennan et al. (1994) working with bulls on grass silage based diets indicated that performance from cane molasses supplementation (40% of concentrate – 18% of total DM) was better at high concentrate protein intakes than low concentrate protein intakes partly due to the low protein digestibility of molasses.
The relative poorer utilisation of molasses at higher dietary inclusion levels is attributed to alterations in the end products of rumen fermentation (i.e. lower ammonia and L lactate concentrations, proportionately lower acetate and higher butyrate concentrations) resulting in a possible reduction in fibre digestibility and possible differences in the site of digestion (Moloney et al., 1993b; Moloney et al., 1994).
Butler (1974) reported that at dietary feeding levels of 15-40%, a substitution rate of 1.4kg sugarcane molasses for 1.0kg of barley was valid. Similarly Drennan et al. (1994) concluded that at dietary inclusion levels of greater than 0.1 to 0.2, cane molasses DM has ME and NE values relative to barley of approximately 0.8 and 0.7 respectively.
Thus, the literature suggests that a relatively high energy value is attained for molasses (with adequate protein supplementation) at up to 20% dietary DM inclusion in beef cattle diets.
Yan et al. (1996) reported that sheep can be given up to 25% molasses with grass silage/barley straw based diets without any health problems.
Fitzgerald (1987) found that the performance of finishing lambs on a grass silage-based diet offered a molasses/soyabean meal (6:1) supplement (34-47% of the total DMI) was similar to that of lambs fed on a barley supplement. It was calculated that in terms of carcass gain that the response was 4% better for molasses/soyabean DM then barley DM (or the replacement value of barley DM was 0.96 that of molasses/soyabean DM) when fed as supplements with grass silage fed ad libitum.
O’Doherty and Crosby (1992) concluded that stepped supplementation of a hay or silage diet offered to twin and triplet bearing ewes, with fortified (i.e. including 10% high UDP) molasses over the last 47 days of pregnancy and an additional 150g soyabean in the last 10 days, was successful in terms of both ewe and lamb performance. Molasses formed 35-40% of the dietary DMI in the last week of pregnancy.
Thus, molasses is an effective supplement at up to 40% inclusion in total sheep diets.
With both pigs and poultry the level of molasses inclusion in the diet is usually limited because of the risk of soft faeces or diarrhoea thought to be due to the risk of high levels of potassium and sodium rather than simply the level of sugar (Harland, 1995). Sugar cane molasses reduces faecal dry matter in pigs due to potassium, magnesium and impurities (Diaz and Ly, 1991).
There is an abundance of literature on feeding sugar cane molasses to pigs in countries such as Cuba and Mexico where there is surplus molasses but reported production/feeding systems and pig performance are different to here. Very high dietary levels of molasses are fed e.g. up to 60% in the diet of gilts and sows, and up to 25-30% for growing pigs/finishing pigs. The energy value of molasses decreases with increased inclusion level. With increasing molasses inclusion the performance of finishing pigs is associated with increased intakes and growth rates but reduced feed efficiency associated with a higher rate of passage. Unlike fattening pigs, growing pigs are unable to adapt as well to high inclusions of molasses. These data also suggest that when sugarcane molasses is fed at levels above 25% it has a laxative effect.
Other studies have concluded that sugar beet molasses may be included up to 20 and 40% in the diets of growing and fattening pigs respectively (Karamitros, 1987).
Mavromichalis et al. (1998) concluded that lactose can be replaced by cane molasses in the diets of nursery pigs.
Walker (1985) concluded that fatteners can tolerate about 15% and pregnant sows about 37% molasses in the diet. Harland (1995) reported studies suggesting that a safe level of inclusion is 5% in growing pigs and 10% in finishing pig diets.
Evidence in the literature suggests that the addition of molasses to sow lactation diets subsequently resulted in a larger litter size and a more rapid return to service after weaning.
Maximum dietary inclusion is 5% for growing pigs, 10-15% for finishing pigs and 35% for pregnant sows.
Harland (1995) concluded that 10% molasses could be included in growing rations and 20% in laying hen diets. However, a problem with molasses is its high potassium content, which has a laxative effect on birds. While most birds perform well on balanced diets containing up to 20% molasses, inclusion levels much above 4% will likely result in increased water intake and manure wetness (Leeson and Summers, 1997). According to Leeson and Summers (1997) maximum dietary inclusion level for young birds 0-4 weeks is 1% and other categories is 5%.