Utilization of urea by lactating ewes and growing lambs

Abstract

A study has been carried out on the digestible and metabolizable energy contents in the principal seeds of legurninous plants which, in Spain, are used for
rurninants nutrition: One-flowered tare (Vicia  monanthos, L) Vetch (Vicia sativa, L);
Chickling vetch ( Lathyrus sativus, L), Horse beans (Vicia faba, L. var equina);
Lentil vetch (Vicia ervilia, L), Lentil (Lens esculenta, Moench); Field pea (Pisum arvense, L); Fenugreeks (Trigonellafoenum graecum, L). The digestible and metabolizable energy contents were deterrnined by the difference method, using dried sugar beet pulp as the basal feed; the experimental rations consisted of 50 % of beet pulp and 50 % of one of the lugrninous seeds. The experimental animals were wether lambs of the «Churra breed» from 12 to 18 months old and an average live weight of sorne 40 Kg. The ingestion level ranged, in the various experiments, between 600 and 800 grams of dry matter per animal and per day, that is, 41.64 to 45.98 gr. DM/LW Kg 3/4 per day. Every trial lasted for a month, the collection period being of 10 days.
For the sugar beet pulp the figures found per Kg. dry matter were: Gross energy = 4.156 Kcal.; digestible energy = 3.364 ± 20 Kcal. and metabolizable energy
= 2.870 ± 15 Kcal. The averge figure for the gross energy of the eight seeds was: 4.483 Kcal./Kgr.
dry matter, renging between 4.936 Kcal/Kg. for the fenugreeks and 4.319 Kcall Kgr. for the lentils.
The average digestible energy contents was 3.938 Kcal/Kg. dry matter, varying between a maximum value of 4.168 ± 15 Kcal./Kg. for the chickling vetch
anda mínimum value of 3.750 + 111 Kcal. /Kgr. for the field peas, The digestibility of the gross energy was of 87 .9 % in average, varying between 90.1 % for the oneflowered tare and 81.5 % for the fenugreeks. The average figure for the metabolizable energy contents was 3.230 Kcal /Kg. dry matter, the maximum and the mínimum values being 3.426 ± 46 and. 3.118 ± 80 Kcal./Kg., respectively, for the chickling vetch and for the peas. The metabolizable
energy represents, as average a 82.5 % of the digestible energy anda 72.1 % of the gross energy. A high correlation (r = + 0.914) was found to occur between the digestibility of the gross energy, and the porcentage of this energy becoming
metabolizable. The energy losses in urine represented an average value of 302 Kcal./Kg.
of dry matter ingested, there being a close correlation ( r = + 0.721) between the
protein contents in the leguminous seeds and the amount of energy lost in the urine. A high correlation between the nitrogen contents in the urine and its combustion heat (r = + 0.944) was also observed. A 7 .6 % of the digestible energy or a 6.7 %
of the gross energy of the leguminous seeds is lost through the urine. The energy losses as methane were calculated from the digestibility of the
energy by the equation proposed to such purpose by K. L. BLAXTER and J. L. CLAPPERTON (y = 3,67 + 0.062.D). The values obtained indicate that the energetic losses in this ware about 408 Kcal/Kg. dry matter ingested, which represents the 9.1 %
of the gross energy and 10.3 % of the digestible energy. lt has been shown that the values of digestible energy calculated by means of the prediction equations proposed by K. NEHRING et al. (y = 5.39.Xi + 9.36.X2 + 3.60.X3 + 4.24.X4 + 35) and by D. G. ARMSTR0NG et al. (D. E.··= 1.09 De. 8. 9.) greatly coincide with those experimentally found. The equation proposed by D. G. ARMSTRONG et al. (K. = 0.2 + 0.809.D) to predict the metabolizable energy
from the digestibility of the energy gave satisfactory values too.