Effect of urea-ammoniation of dietary roughage and concentrate ratio on ruminal microbial activity in Jersey cows.

Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

The effect of untreated roughages on digestibility and rumen fill of the gut was reviewed as physical mechanism influencing the regulation of roughage intake. The review of literature also focused on identifying factors that affect the way in which urea-ammoniation alters the roughage intake, digestibility and performance of ruminant animals. Trials were carried out with fistulated cows to address to what extent concentrate proportion and urea-ammoniation affected microbial colonization and degradation of roughage diets in the rumen. One interest of this study was to develop a model that would help to predict the benefit associated with urea-treatment of roughages. The first trial (Chapter 3) investigated the effect of urea-ammoniation of roughage and concentrate proportion of the diet on degradation of roughages, and the benefit associated with the treatment of roughages. Four rumen-fistulated Jersey cows were fed on a basal diet composed of either urea treated (3 kg of urea per 100 kg of straw) or untreated Eragrostis curvula hay. These basal diets were supplemented with concentrate composed of maize meal (78%) and cotton seed cake (22%). The concentrate contributed 0, 25, 50 and 75% of the total ration and hay the rest. The experiment consisted of 6 periods. Each period lasted 19 days, comprising 12 days of adaptation to the experimental diet followed by 6 days degradability measurements and 1-day rumen fluid collection. During each period the 4 Jersey cows were randomly allocated to 4 of the 8 dietary treatments, ensuring that each diet was fed to 3 animals during the entire experimental period. The experimental roughages used in this trial were wheat (Triticum sativum) straw, barley (Hordeum Vulgare) straw, coastcross (k11) (Cynodon hybrid) hay, veld hay (natural grass), oat (Avena sativa) straw, oat (Avena sativa) hay, maize (Zea mays) stover, kikuyu (Pennisetum clandestinum) grass, weeping love grass (Eragrostsis curvula) and Italian rye (Lolium multiflorum) grass. Each roughage (sample) was subdivided into two equal portions, one of which was then treated with urea. The urea solution was prepared by dissolving 30 g of urea in 0.4 liter of water. The solution was fully distributed over I kg of roughage. Treated roughages were sealed tightly and stored at room temperature for 5 weeks in plastic bags. Immediately after opening, the different roughages, including the untreated ones, were sun dried, chopped fine by hand and ground through a 2-mm screen in a laboratory mill. About 3 g of each sample was weighed into labeled nylon bags. The bags were tied to a stainless steel disc with 10 evenly spaced small holes drilled through the periphery of the disc serving as anchor points. The bags were incubated (in duplicate per time interval) in the rumen for 120, 96, 72, 48, 24, 12, 6 and 3 h, sequentially. The treated samples were incubated in animals fed treated hay, while untreated samples were incubated in animals given untreated hay. Immediately after removal from the rumen, the bags, including the 0 hour ones, which had not been incubated but soaked in warm water for I hour, were washed in 6 cycles (each lasting 4 minutes) in a semi-automatic washing machine. The washed bags were then dried in a forced draught oven at 60 degrees C for 48 hours, cooled in a desicator and weighed. The pH of the rumen fluid ranged between 6.5 and 6.8 for all diets. Rumen ammonia concentration was higher (P<0.002) when the basal diet consisted of urea treated hay. Increasing the concentrate proportion in the diet had the desired effect of increasing rumen ammonia concentration without severely affecting pH. Urea-ammoniation increased (P<O.OOO1) the slowly degradable fraction (B), potential degradability (PD), effective degradability (ED) of dry matter and neutral detergent fiber (NDF), decreased (P>0.05) lag time (LT) but had no effect on the rate of degradation (c) of dry matter. Concentrate proportions affected (P<0.05) the slowly degradable fraction, potential degradability, lag time and effective degradability but had no effect (P>0.05) on the rate of degradation of dry matter (DM). Maximum and minimum values of the slowly degradable fraction, potential degradability and effective degradability of DM and NDF were obtained at the 25 and 75% concentrate levels, respectively. Within urea-ammoniation, roughage type affected (P<O.OO1) the B-fraction, PO and EO of OM and NDF degradation. Rate of degradation of DM of untreated roughages varied from 0.022 h(-1) in wheat straw to 0.087 h(-1) in rye grass, while for urea treated roughages it varied from 0.022 h(-1) in oat straw to 0.082 h(-1) in rye grass. Rye grass degraded almost three to four times faster than urea treated oat or untreated wheat straw. Urea-ammoniation was less effective in increasing DM and cell wall degradation rates (c) of rye grass compared to wheat straw. The results showed that low quality roughages such as wheat straw benefited relatively the most from urea-ammoniation. The effect of urea-ammoniation and dietary manipulation on microbial colonization (Chapter 4) of fiber particles in the rumen of animals was also investigated in two experiments. In Experiment 1, the cows were fed on rations comprising either urea-ammoniated or untreated Eragrostis curvula hay supplemented with concentrate at hay to concentrate ratio of 100:0, 75:25, 50:50, 25:75, resulting in eight different rumen environments. The experiment consisted of two periods. Each period lasted 12 days of adaptation to the experimental diet followed by one-day incubation of urea-ammoniated and untreated barley straw. Experiment 2 consisted of two urea-ammoniated (7.5 kg of urea per 100 kg of hay) hay levels (20 and 40% of the total ration) and concentrate levels (60 and 80%). Fistulated Jersey cows were adapted for 12 days after assigning to the dietary treatment. Feed was given at the rate of 9.0 kg day(-1) per animal portioned into equal meals of 4.50 kg each and offered at 08:00 and 16:00 every day. About 3 g of urea-ammoniated or untreated barley (Hordeum vulgare) straw, ground through a 2-mm screen, was weighed into a labelled nylon bag and incubated for 3, 6 or 12 h in the rumen of the fistulated cows. Microbes adhering to incubated fiber particles were examined under the Environmental Scanning Electron Microscopy (ESEM) and analysed on the image analyser. Depending on morphology , the microbes were divided into three groups: bacilli (rod), cocci (round) and others (spiral, fimbrea and cluster ; not specifically defined or undefined microbes). Urea-ammoniation of dietary roughage decreased (P<O.OO1) bacilli counts and total bacteria count but had no effect on count of the undefined group of microbes on fiber particles in the rumen of cows (Experiment 1). Concentrate proportions had no effect (P>0.05) on bacilli, cocci and total bacterial count on fiber particles. However, the results from electron micrograph observations revealed that the total bacterial count tended to decrease as the concentrate level increased in the diet of cows. Bacilli, cocci, undefined group of microbes and total count of microbes increased (P<0.05) as length of incubation increased. In Experiment 2, incubated feed, concentrate proportion and time of incubation had no effect (P>O.05) on bacilli , others (undefined group of microbes) and total count of fiber-adhering microbes in the rumen of cows. However, increasing concentrate in the diet of cows tended to decrease (P<O.07) the count of fiber-adhering cocci. The total count of microbes on fiber particles was higher in animals fed 80% concentrate as compared to 60% concentrate. The benefit derived from urea treatment in terms of B-fraction, effective degradability and potential degradability of DM and fiber of roughages increased with increasing the NDF content. Therefore, the important conclusions drawn from the results of the present study is that urea-ammoniation of roughages should be done strategically and that high quality roughages may give little return per unit of cost of ammoniation. This means that the benefit associated with urea-ammoniation would be justified for poor quality roughages only.