The high dry matter yield, protein and calcium content of alfalfa make it a suitable forage for all classes of ruminants. It is often a major component of cattle diets: in the USA where 70-75 % of alfalfa was grown for dairy cattle in 2008 (Summers et al., 2008); 62 % of dairy cattle were fed alfalfa in 1995 (Mowrey et al., 1999). Alfalfa can be grazed, fed as green forage, offered as hay and silage or dehydrated. Cattle highly relish it though there are palatability differences among cultivars that could result from different patterns of protein fractionation (Summers et al., 2008; Frame, 2005; Cook et al., 2005; Mauriès, 2003).
Ruminants benefit from two major characteristics of alfalfa. Firstly, its high protein content is readily digestible (protein digestibility varies from 81 % to 73 % in green alfalfa during the first cycle) and this digestibility surpasses that of competing forages. Secondly, alfafa fibre is very valuable as it is rapidly digested in the rumen, which is beneficial to rumen activity due to its buffering effect (INRA, 2007; Cook et al., 2005; Robinson, 1998). Ruminants fed on alfalfa have higher nutrient intake and digestibility than when fed on other forages (Frame, 2005; Martin et al., 2005; Journet, 1993). Alfalfa may supply more than 30 % of the total digestible nutrients supplied by the same quantity of maize grain (Bruce et al., 2008). The beta-carotene content of alfalfa is much higher than in other forages and it has beneficial effects on the reproductive performance of dairy cows, as it increases calf weight at birth and reduces the interval between mating and calving. It also has a stimulatory effect on milk yield (Mauriès, 2003).
Organic matter digestibility ranges from 55 % to 77 % and depends on growth stage, cut number (leaf:stem ratio), and cutting frequency, harvesting conditions and processing (INRA, 2007).
Stage of growth
When alfalfa matures, cell wall content increases while OM digestibility and metabolizable energy decrease. From the vegetative stage to flowering, OM digestibility decreases from 77 to 60 % and ME diminishes by 2.6 MJ/kg DM (INRA, 2007). The decrease is least in leaves and higher in lower stem fractions than in upper ones (Buxton, 2003). The decrease in leaf:stem ratio associated to a decrease in digestibility of the stem parts (that become more fibrous) results in a general decline in digestibility (Veronesi et al., 2010). However, alfalfa digestibility declines more slowly than warm-season perennial grasses (Jennings, 2010).
Cut and cutting frequency
The highest digestibility is obtained during the first vegetation cycle. After the second cut, regrowths become more leafy with a higher leaf:stem ratio, resulting in an increase in OM digestibility (68 % to 71 % between the 2nd and 4th cut harvested when harvested at 5 week intervals) (Mauriès, 2003; INRA, 2007).
Effect of growth conditions, harvest conditions and preservation methods
High temperatures during growth decrease the digestibility of most forages. In this respect, alfalfa is particularly valuable since it loses only 2.6 percentage points of OM digestibility when other forages grown under high temperatures lose between 6.6 and 12.4 percentage points (Wilson et al., 1991). Harvesting alfalfa in moist conditions is detrimental to the quality of alfalfa hay, as losses of cell contents results in a higher proportion of cell walls (an increase in fibre) and thus in lower digestibility (Mauriès, 2003).
Preservation methods play also an important role in the nutritive value of alfafa: correctly made silages have a higher ME and OM digestibility than hay, and almost the same nutritive value as green alfalfa (INRA, 2007).
Green alfalfa can be grazed or pen-fed. In grazing systems, stocking rates should be high enough to remove the herbage within 7-10 days. The rest period between grazing should be long enough (about 4-5 weeks) to let alfalfa reach the bud-to-early-flower stage before the next grazing (Lacefield et al., 2005). Alfalfa grazing should not be done in areas where the soil is too moist as alfalfa cannot withstand trampling (Meisser et al., 2005). Since wet conditions favour bloat, cattle should be removed from the alfalfa stands when the weather becomes rainy (Meisser et al., 2005; Mauriès, 2003). Green alfalfa cut and carried to cattle gives higher productivity per unit of area as cattle cannot select the most palatable parts of the plant (Mauriès, 2003).
Lactating dairy cows and ewes
In the USA, several trials reported that grazing cows could consume 20 kg/d DM from alfalfa pasture and yield about 25 kg/d milk without supplementation (Mauriès, 2003). In Brazil, alfalfa stands could sustain 20 kg milk/d at stocking rates of 3 head/ha without affecting animal health or reproductive performance (Vilela, 2001). Cows grazing tropical pasture increased their milk yield from 10-12 L/d to 14-12 L/d and up to 20 L/d when they were supplemented with green alfalfa alone or green alfalfa and grain, respectively (Cook et al., 2005). When alfalfa is pen-fed in combination with maize silage, at an inclusion level of 50 % of the diet, an overall increase in DM intake is obtained. Green alfalfa inclusion also saves about 1 kg soybean meal of the daily ration, as alfalfa provides up to 20 % protein, and fat milk yield decreases (Mauriès, 2003).
Green alfalfa, used as sole feed provided enough digestible nutrients for dry and pregnant ewes but required supplemention in lactating ewes (Brand et al., 1999). Rotational grazing yielded higher animal performances in ewes (Thomas et al., 1995).
Growing and fattening cattle
Alfalfa is less commonly used for beef cattle than for dairy cows, as its lower energy availability does not allow it to sustain the same average daily gains as grass forages (Summers et al., 2008). In cow-calf production systems, alfalfa can sustain 0.8-1 kg daily weight gain in cows without supplementation (Mauriès, 2003). Irrigated lucerne can carry a beef cow and a calf on 0.5 to 1 ha on a year-round basis. Green alfalfa fed to beef cattle sustains daily live-weight gains of about 0.7 kg/head/day, which is lower than 1 kg/head/day obtained with diets based on the association of oats with improved or native tropical pasture. However, in areas where alfalfa grows throughout the year, supplementing native pasture with alfalfa over the full year can increase gains from 0.5 to 0.7 kg/head/day at double the stocking rate (Cook et al., 2005).
Under favourable conditions, with store steers (181-272 kg) average daily gains may be as high as 1.4-1.5 kg/head/day, and meat production ranging from 107 kg/ha (in rainfed swards) to 1946 kg/ha (under irrigation) (Summers et al., 2008; Popp et al., 1999). Limiting utilization of alfalfa-based pasture to less than 70 % may be more important for maximizing gain per head than managing herbage quality (Popp et al., 1999).
Alfalfa is valuable in mixed pastures. Steers grazing stands of alfalfa (38 % of biomass) and tall fescue (Festuca arundinacea) had greater average daily gains (300 vs 240 g/d) and gains per ha (17.6 vs 8.7 kg/ha) than those grazing tall fescue pastures only. The fatty acid composition of meat was not affected by the presence of alfalfa even though the fatty acid composition of the mixed pasture was different from that of grass alone (Dierking et al., 2010).
Growing and fattening sheep and goats
Sheep numbers can be increased from 6 to 15/ha by supplementing native pasture with alfalfa. In Australia, irrigated alfalfa can carry more than 80 dry sheep equivalents/ha from October to May (Cook et al., 2005). In Spain, alfalfa pasture grazed rotationally in 5-day periods can sustain up to 60 ewes/ha (Mauriès, 2003). Lambs grazing alfalfa pasture as sole feed during winter in the Sonora desert (California) gained 4.5-5.4 kg per month (Summers et al., 2008). In Australia and New-Zealand extensive systems based on alfalfa pastures are used for finishing lambs (Mauriès, 2003).
Mixed pastures of alfalfa and grass are possible. However, if the grass is over 50 % of the sward lambs have lower feed intakes and lower weight gains. Alfalfa-based diets can be supplemented with cereal grains, unless it is too expensive and unprofitable (Mauriès, 2003).
Goats fed on Sudan grass (Sorghum × drummondii) supplemented with alfalfa had greater (+ 82.3 g/day) average daily gain than goats supplemented with other legumes such as Lablab purpureus and Desmanthus bicornutus (Cook et al., 2005).
The high content of structural fibre in alfalfa hay fibre that is rapidly digested by rumen microbia is particularly valuable in ruminants because it enhances DM intake. Alfalfa fibre helps to prevent acidosis due to its intrinsic buffering effect and to the stimulation of ruminative chewing and salivation which results in rumen buffering (Robinson, 1998). Alfalfa hay may be finely chopped, or coarse with long fibre.
Alfalfa hay is used in lactating cows and heifers. Depending on the stage of growth at harvesting, alfalfa hay may be more or less rich in protein and fibre. Young alfalfa at pre-bud to bud stage yields high protein and low fibre. This harvesting stage may be suitable for high milk yield because protein is the most limiting factor of milk production during early lactation (Robinson, 1998; Dubé, 1978). An important proportion (25-35 %) of this crude protein is rumen undegradable and readily available for milk production. Feeding alfalfa hay alone can yield up to 27 kg milk/cow/d. In high-yielding dairy cows whose milk yield is higher than 45 kg/d, supplementary protein and energy (i.e. soybean meal and cereal grains) must be offered to sustain milk production but alfalfa hay already provides 50 to 60 % of total requirements (Dubé, 1978). Feeding dairy cows with alfalfa hay-based diets helps to reduce the purchase of costly rumen-undegradable proteins (Robinson, 1998; Dubé, 1978). Alfalfa hay can be the sole constituent of the roughage diets of lactating dairy cows or it can be mixed with maize silage at 1:1 ratio (Rouillé et al., 2010; Dubé, 1978). Offering alfalfa hay cut at bud stage is a good way to preserve daily weight gains in cows during early lactation but it is also possible to provide concentrates in order to prevent weight losses during lactation (Mauriès, 2003).
Dry cows are sensitive to excess protein and calcium and they should not be offered alfalfa. It might result in milk fever, downer cows, loss of appetite and poorer resistance to stress (Dubé, 1978).
Dairy ewes and goats
Alfalfa hay is valuable fodder for lactating dairy ewes as it results in satisfactory milk yield and animal weight gain. In goats, alfalfa hay is readily accepted and results in only 15 % refusals. Alfalfa hay has a stimulating effect on feed intake in goats (Summers et al., 2008). Alfalfa hay results in high voluntary intakes (91.3 g/kg W0.75) in lactating goats (Giger et al., 1987). A good quality alfalfa hay may sustain 2.8 kg/d milk yield. Milk yield can also be enhanced by maize silage supplementation (Mauriès, 2003).
Growing and fattening animals
Alfalfa hay can be used as sole feed in cow-calf production systems. Long fibre alfalfa should be preferred because it increases retention time in the rumen and nutrient utilization. Alfalfa hay may be mixed with maize silage and partially replace urea or soybean meal. Inclusion levels range from 12 % to 50-60 %, depending on the desired performance. Diets based on alfalfa and maize silage give better results than diets based on maize silage and urea, but result in lower animal performance than diets based on soybean meal and maize silage (Mauriès, 2003).
Alfalfa hay provides high amounts of minerals and vitamin A, the latter element being the main deficiency in cow-calf production systems. Feeding beef cows with alfalfa hay only requires salt and P supplementation (Mauriès, 2003).
In the USA, alfalfa hay is a good source of protein and energy for over-wintering beef cows. Alfalfa is an important transition feed for creep-fed calves. It is then offered with cereal grains at a ratio of 40:60 and sustains daily weight gains of about 1.4-1.5 kg/d. During the finishing period, diets may contain 15 % alfalfa hay and up to 85 % cereals, with average daily gains of 1.3-1.4 kg/d (Mauriès, 2003). During hot summers, alfalfa hay is mainly used as a fibre source in feedlots (Summers et al., 2008).
Dehydrated alfalfa is the best way to preserve the quality of fresh alfalfa. Dehydration has a preservative effect on the energy value and improves the protein value through protein protection. The protein of dehydrated alfalfa is less rumen-degradable and can produce more total amino acids to be absorbed by the small intestine per unit of protein than does soybean meal (Price et al., 1985). Dehydrated alfalfa partially replacing concentrates in dairy cow diets increased DM intake, milk yield and milk acidification rate (Calamari et al., 2007). Providing 3 kg of dehydrated alfalfa to cows fed on grass silage, maize silage, barley grain and soybean meal, resulted in similar animal performance, higher feed intake (+2.5 kg DM/day), higher milk protein yield (+1 point) and lower soybean inclusion (-350 g/day) (Thénard et al., 2002).
Traditional alfalfa silage
Alfalfa silage is a valuable feed: properly managed, ensiling preserves the nutritive value of alfalfa to a greater extent than hay-making. Also, alfalfa can be ensiled under harsher conditions than hay.
Lactating dairy cows, ewes and goats
When alfalfa silage is fed to high-yielding lactating dairy cows, it should be harvested at bud stage since yield of milk yield produced from alfalfa silage decreases by 4 kg/day between bud stage and flower stage. However, alfalfa silage contains high amounts of non-protein N, which results in poor utilization of crude protein and excessive N excretion. Lowering protein breakdown into non-protein N in the silo can improve utilization of alfalfa protein (Broderick, 2001). Additives are necessary if silage (whatever its moisture content) is offered to lactating dairy cows: they improve DM intake and total usable protein content which is of utmost importance for high milk yields. Concentrates can be added to silage: this practice had a depressive effect on silage consumption but a positive effect on overall diet intake and animal performance (Mauriès, 2003). Alfalfa silage could replace 50 % of maize silage in diets of lactating dairy cows with no decrease in milk yield and milk quality parameters (Rouillé et al., 2010)
A meta-analysis of trials compared the effects of various legume silages on milk production. Dry matter intake tended to be higher (+0.8 kg/d) with alfalfa silage than with red clover silage (Trifolium pratense). While milk yield was not affected, cows fed on alfalfa silage produced milk richer in protein (+0.7 g/kg) and, therefore, yielded more milk protein than those fed on red clover silage (Steinshamn, 2010).
Growing and fattening cattle and sheep
Alfalfa silage can be fed to beef cattle. Cattle fed with alfalfa haylage achieved daily gains of 1.1 kg/d and up to 1.8 kg/d when supplemented with maize grain or dry corn gluten feed (Hannah et al., 1990). Additives may not be useful in drier silages (above 35% DM) as they do not improve animal performance. Protein content has to be monitored since it is the main determinant of animal performance. Alfalfa silage containing less than 20 % protein does not compete favourably with maize silage for cattle fattening. Adding concentrates to a diet based on alfalfa silage has a positive effect on animal performance and is a prerequisite to obtain as good results as with grass silages in growing cattle (Mauriès, 2003).
Alfalfa silage may also be fed to growing sheep and results in higher DM intake than alfalfa hay (74 g DM/ kg W0.75 vs 65 g/kg DM/kg W0.75). However, protein efficiency is not as high as in alfalfa hay due to the higher protein breakdown in silage (Peccatte et al., 1998).
Wrapped baled silage
Making wrapped baled silage has advantages over traditional hay-making. It has a more flexible harvest date, less weather dependency, and it offers greater flexibility in diet formulation (Savoie et al., 2003). Baled silage should be pre-wilted (2-3 day drying) so that baled silage contains more than 40 % DM (Demarquilly et al., 1998). Baled silage enhances feed intake in cattle in comparison to hay. In lactating dairy cows, baled silage did not increase milk production and other dairy parameters as well as alfalfa hay but over-wintering heifers fed on baled silage had higher weight gains than heifers fed on silage or hay (Demarquilly et al., 1998).