Effect of a controlled-release urea supplementation on feed intake, digestibility, nitrogen balance and ruminal kinetics of sheep fed low quality tropical forage.

Four ruminally cannulated crossbred sheep (25+/-3.4kg BW) were divided into a 4x4 Latin square design to measure the effects of controlled-release urea supplement (CRUS). The basal diet consisted of 60% sugar cane tops (Saccharum officinarum), 30% full plant corn stubble (Zea mays), and 10% King grass (Pennisetum purpureum). Feed intake, digestibility, N balance and in situ ruminal kinetics were studied with four diets, D1 (control), D2, D3 and D4, which included the ratios of 100:0%, 90:10%, 80:20% or 70:30% of basal diet with CRUS. Results showed DMI differences (P<0.05) for D4 (822g per day) versus D1, D2 and D3 (580, 659 and 700g per day, respectively). N retention increased (P<0.05) for D4 (35.69g per day) versus D1, D2 and D3 (9.29, 6.85 and 19.10g per day, respectively). In vivo N digestibility was greater (P<0.05) in D4 (79.63%) than in D1 (57.57%). In vivo digestibility of DM, OM, GE, cellulose and hemicellulose was similar among the four groups. Digestibility of cell walls in D4 was higher (P<0.05) at 74.06% versus 67.78% in D1. In situ DM digestibility showed differences (P<0.05) among all diets at 9, 12, 24 and 48h of incubation. Potentially digestible fiber, 52.61%, was higher (P<0.05) in D4 versus 31.00% in D1. Indigestible fiber, 35.29%, was lowest (P<0.05) in D4 compared to 81.51% in D1. Digestion rate constant (k(d)) was different (P<0.05) between the experimental diets and control. Passage constant (k(p)) was different (P<0.05) between all diets (0.036/h in D4 to 0.081/h in D1). True digestibility was higher (P<0.05) in D4 (44.64%) compared to D1 (19.55%), but in D2 (24.54%) and D3 (28.22%) there was no difference. Cellulose in situ digestion rate, the potentially digestible fiber, was higher (P<0.05) in D3 (42.74%) as compared to D1 (22.50%). Time of disappearance of cellulose in D4 (14.79h) was less (P<0.05) than in D1 (24.03h), however there was no difference between D1 and D2. Hemicellulose in situ digestion was different (P<0.05) between D3 (45.48%) and D1 (23.61%). Digestion rate was higher (P<0.05) between D3 and D4 as compared to D1. Passage rate was different (P<0.05) between D4 (0.033/h) and D1 (0.018/h). True digestibility in D3 (34.84%) and D4 (34.62%) was higher (P<0.05) than that in D1 (20.06%) and D2 (25.86%). Half-time disappearance (t(1/2)) for hemicellulose was higher (P<0.05) in D1 (62.36h) than in D3 (28.00h) and D4 (20.64h). This study demonstrated that low quality forages at 70% of the total diet can be efficiently utilized by sheep when controlled-release urea supplementation is 30% of the feeding regime.

Effect of a controlled-release urea supplement on rumen fermentation in sheep fed a diet of sugar cane tops (Saccharum officinarum), corn stubble (Zea mays) and King grass (Pennisetum purpureum).

Four cannulated sheep were used to study ruminal fermentation of a diet consisting of 60% sugar cane tops (Saccharum officinarum), 30% corn stubble (Zea mays), 10% King grass (Pennisetum purpureum) and 0% (control), 10, 20 or 30% controlled-release urea supplement (CRUS) (diets 1, 2, 3 and 4, respectively). Average ruminal pH did not differ among diets (P>0.05), but during the first 6h of sampling tended to be higher for CRUS diets. Ammonia concentrations were higher (P<0.01) in all treatments over controls, indicating microbial protein generation. Acetic acid production (mM/1) decreased (P<0.05), propionic acid increased (P<0.05), while butyric acid production did not differ among CRUS diets and controls (P>0.05). Total amounts of ruminal VFA were lowest (P<0.01) in controls, while CRUS diets produced more of these energy sources. Supplementation of the high fiber diets with 10, 20 or 30% CRUS increasingly improved rumen fermentation, ammonia supply and VFA production. The results show that low quality forages (up to 70% DMI) can be used efficiently by sheep when conditions for ruminal microorganism are improved with a controlled-release urea supplement.

Seasonal variation of macro and trace mineral contents in 14 browse species that grow in northeastern Mexico.

Leaves and twigs from shrub species consumed by range goats: Acacia berlandieri, Acacia farnesiana, Acacia greggii, Acacia rigidula, Celtis pallida, Cercidium macrum, Condalia obovata, Cordia boissieri, Desmanthus virgathus, Leucaena leucocephala, Leucophyllum texanum, Opuntia lindehimieri, Porlieria angustifolia, Prosopis glandulosa, and Ziziphus obtusifolia were evaluated for comparative seasonal contents of Ca, P, Mg K, Zn, Mn, Cu and Fe. Plants were collected in summer (September 12, 1992), fall (November 20, 1992), winter (February 20, 1993) and spring (May 22, 1993) in Marín, County, Nuevo Leon, Mexico. During spring and summer mineral concentrations were higher in general. Only Ca, Mg, K, and Fe were in substantial amounts in all seasons to meet adult goat requirements. With the exception of spring, shrubs had extremely low P concentrations. Manganese, Cu and Zn in most plants had low marginal levels to meet adult goat requirements. Moreover, potential intake of P, Mn, Cu and Zn in shrub species by goats weighing 50kg BW consuming 2.0kg per day DM was low. However, plants such as D. virgathus, L. texanum, P. glandulosa, L. leucocephala and C. macrum can be considered prominent components in diets of range goats because of their high mineral concentrations. It appears that ration formulations for range goats in northeastern Mexico should include P, Mn, Cu and Zn in all seasons of the year.