At Home in Nature

  (Agate, Colorado)
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Are tree leaves nutritious for animals?

We are currently testing the nutrient levels in the blood of our animals as we feed them tree leaves, and while tree leaves may seem unusual, they are common foods for animals in most other places.  The TDN, RFV, and mineral content varies considerably from forage to forage, even two different fields of grass will be significantly different in most respects depending on species of grass, or variety of alfalfa.  The FAO and many foresters agree, trees are no different.  However, studies (FAO: 4.1 The Nutritive Value of Tree Legumes, Dr.B.W. Norton indicate that there is little difference between tree leaves and most standard hays.
Many people supplement based on a belief of what they are feeding their animals.  Often, they are wrong in their assumptions, and attempts to perfectly balance diet are futile unless you are working with laboratory formulated feeds, such as those which are manufactured by Purina and other vendors.
Leaves are excellent food for not only ruminants (it is the food of choice throughout most of the world, though in the Americas, we are just discovering this), but also animals with simpler stomachs.  Even people eat quantities of tree leaves without harm.  Some tree leaves are poisonous in small quantities, others are poisonous in large quantities; others are wholesome and healthsome in even minute quantities.  Many trees have medicinal properties. 
The answer for those who supplement to overcome deficiencies in diet when using conventional grass and alfalfa feeds is the same for those who supplement to overcome deficiencies in tree leaf diets: hedge on the side of too much rather than too little.  Few nutrients cause disease when overfed in moderate amounts.  In Colorado, selenium deficiency is common because the soil is so poor in selenium. Most leaves have about 10% crude protein, with about 60% digestibility, and while oaks may have up to 15% mean taninnic acid equivalent, most trees typically have much less than half that and 15% is not bad, if the oaks are diluted with other feed ("Nutritive Value of Tree Leaves in the Kansas Flint Hills," JR Forwood and CE Owensby: Journal of Range Management 38(1), January 1985).  I, myself, enjoy the linden leaves best.  They make an excellent salad. 

Nutrition increases wool production

Nourishment is important to many kinds of farm production, but also for wool production.  Texas A&M University has known through the efforts of James Addison Carey III (Effects of Range Management Practices on Wool Production, 1984) that even rotation of grazing pastures can result in a significant difference in fleece weights (3.35kg vs 3.04 kg) because undernourishment results in a temporary reduction in the number of active follicles which are associated with fiber shedding. 

Mr. Carey explains, “if the wool data for lactating ewes and non lactating ewes had been analyzed together, no significant differences would have been found between any of the grazing management treatments. When the physiological state of the ewes was considered, a reduction (P<.05) of 10% ingrease fleece weight was noted in the lactating ewes (3.14 kg) compared to non lactating ewes (3.52 kg). This agrees with the 10 to 14% reduction in annual grease fleece due to full cycle reproduction found by other studies (Doney, 1958; Brown et al., 1966; Seebeck and Tribe, 1963; Slen and Whiting, 1956). Brown et al. (1966) concluded that about one-third of the reduction in wool growth by Merinos during pregnancy and lactation stems from a decrease in fiber numbers and two-thirds from a decrease in fiber volume.  Observations on the number of fibers per unit area of skin by Brown et al. (1966) indicated there may be a greater decrease during pregnancy than during lactation, although this change was evident in both phases of reproduction in the study by Slen and Whiting (1956). These results indicate that ewes producing lambs are more sensitive to grazing treatments than non producing ewes. Therefore, when wool production is used for an endpoint and treatment differences are expected to be small, only ewes that wean lambs should be used as experimental units in grazing studies to detect these small differences.”

The reason, of course, is that ewes which are also producing milk or lambs have more need for food. 

Mr. Carey also explains that if you are maximizing fleece production, you should stock many sheep per hectare, but if you are trying to maximize lamb production, you should ensure each ewe has as much food as possible.  The reason is that fleece production responds less than lamb production to shortages of food.  “Stocking rates had no significant effect on grease fleece weights per ewe, and grease fleece weights per hectare increased with increased stocking rates. Fiber diameter decreased significantly (P<.05) as the stocking rate increased. These findings would suggest that a six ewe per hectare stocking rate would be optimal; however, lamb production data on these same ewes indicate that a stocking rate of six ewes per hectare severely depressed lamb production.  There was no difference (P>.17) in grease fleece weights between the two ewe, four ewe and six ewe stocking rates; however, there was a significant (P<.05) linear effect in fiber diameter (25.5, 24.5 and 24.1 microns, respectively), as stocking rate increased.  These results tend to agree with the findings of McManus et al., (1964) and George and Pearse (1978) that stocking rates had little influence on wool quality and that increased production per hectare would more than offset the decreased production per ewe. Wool production per hectare was higher as stocking rates increased; however, at the higher six ewe per hectare stocking rate, lamb production was severely depressed in the second year of the study. The percent of ewes weaning lambs in the six ewe per hectare treatment dropped from 90% in the first year to 29% in the second year, compared to 90% for the two ewe and four ewe per hectare stocking rates in the second year (Bryant et al., 1984).”

That said, an improvement of 10% in wool production is not only significant, but worthwhile.  Especially when lambs are brought into the equation: lambs are worth much more than fleeces.  Supplementing feed on small pastures makes sense.

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