Livestock Research for Rural Development 4 (2) 1992

Citation of this paper

Influence of fish meal and dehydrated brewers grains on intake, live-weight gain and rumen digestion of growing cattle consuming fresh cut forage

Arelys Reaño, A Meléndez, J Márquez and J Combellas

Facultad de Agronomía, Universidad Central de Venezuela, Apartado 4579, Maracay, Venezuela


Two feeding trials were carried out to evaluate the influence of by-pass protein on the intake and live-weight gain (LWG) of growing cattle consuming a basal diet of fresh cut forage. A third trial was carried out with rumen fistulated dry cows to evaluate the effect of these supplements on some characteristics of rumen fermentation. The use of fish meal as a source of by-pass protein resulted in moderate increments in LWG without effects on forage consumption when substituting urea in a supplement based mainly on maize meal. The use of urea increased the rumen ammonia N concentration but did not affect the degradation of forage in nylon bags. The use of a supplement based exclusively on sources of by- pass protein, such as fish meal and dehydrated brewers grains resulted in small non-significant (P>0.05) increases in LWG compared with equal amounts of a supplement which is highly degradable in the rumen.

KEY WORDS: By-pass protein, forage, cattle, rumen degradation


Large responses in live-weight gain (LWG) and intake have been observed when low quality fibrous feeds are supplemented with by- pass protein (Preston and Leng 1987; Leng 1990). These resources have been defined by Leng (1990) as those with a dry matter digestibility (DMD) lower than 45% and a crude protein (CP) content below 8%. Cattle production in Tropical America is mainly sustained in pastures with DMD and CP values below those found in temperate regions (Minson 1981) but in a range above the limits defined by Leng. The information available on the use of by-pass protein sources as supplements for this category of feeds is less abundant.

The results of two feeding trials comparing the responses in LWG and intake to supplements containing by-pass protein or nitrogen (N) degradable sources in growing animals consuming a basal diet of cut fresh forage are presented. Some characteristics of rumen digestion were evaluated in a third trial with rumen fistulated animals.

Materials and methods

The feeding trials (Experiments 1 & 2) and digestion trial (Experiment 3) were carried out in Maracay, which has a range in monthly average temperatures from 23.4 to 26.5 °C and a mean rainfall of 989 mm during the last 10 years.

Experiments 1 & 2

Completely randomized designs were used to compare three treatments in each trial, consisting of supplements containing feed sources of high (H) and low (L) rumen degradable N or a mixture of both (HL) in Experiment 1, and supplements containing urea (U), fish meal (F) or urea and fish meal (UF) as sources of N in Experim. 2 (Table 1).


Table 1: Concentrate formulations (%)
  Experiment 1 Experiment 2 & 3
Maize meal by-product 73.3 - 36.7 88.8 77.0 72.8
Sesame meal 20.0 - 10.0 - - -
Urea 2.0 - 1.0 3.8 - 3.8
Fish meal - 20.0 10.0 - 21.0 21.0
Dehydrated brewers grains - 78.5 39.3 - - -
Sulphur 0.2 - 0.1 0.4 - 0.4
Mineral mixture 3.0 - 1.5 5.0 - -
Salt 1.5 1.5 1.5 2.0 2.0 2.0


Eighteen animals, 14 Brahman x Holstein and 4 Brown Swiss, were used in each trial. Equal numbers of each sex were included in Experiment 1 and 12 males and 6 females were used in Experiment 2. The animals were housed in partially covered individual pens of 2 x 5 m with concrete floors. Two feeding troughs were available, one for the forage and the other for the supplements. Water was permanently available in plastic buckets of 50 litres.

Fresh forage was offered daily between 07:30 and 09:30h allowing approximately 15% refusals. The forage had variable but similar amounts of elephant (Pennisetum purpureum), para (Brachiaria mutica) and star (Cynodon plectostachyus) grasses. The concentrate was offered between 07:00 and 08:00h, 1.5 kg/day in Experiment 1 and 2.0 kg/day in Experiment 2 during the 84 days of duration of each trial.

Samples of forage offered and refused were taken daily, dried for 48h at 65 °C and dry matter (DM) intake determined daily. Subsamples were accumulated for four week periods to be analyzed for N and ash (AOAC 1984), calcium (Fick et al 1979) and phosphorous (Harris and Popat 1954). Samples of concentrate were taken from each mixing batch and were also analyzed for those fractions. In vitro organic matter digestibility (IVOMD, Alexander and McGowan 1967) was determined in concentrate samples. The animals were weighed weekly before the morning feeding and the LWG estimated as the slope of the simple regression of weights on time.

Experiment 3

A Latin square 3 x 3 was used with 17 day periods and three rumen fistulated cows. The concentrates U, F and UF described in Experiment 2 were compared fixing the proportion of concentrate in each diet at 25% on a DM basis. The supplement to be offered to each animal was calculated daily according to forage consumption the day before. Feed and animal management was similar to the first two trials. This experiment was conducted simultaneously with Experiment 2 and the same forage was offered.

Rate of digestion of silage, maize meal and fish meal dry matter were estimated using the nylon bag technique (Orskov et al 1980) collecting two samples of each feed at 6, 12, 24, 48 and 72h during the last three days of each period. A sample of the forage offered was oven dried at 65 °C for 48h, ground through a 3 mm screen and 5 g introduced into each bag. The rate of digestion was calculated as the half time (T2) using the procedure described by Kempton (1980). Rumen liquid samples were taken just before feeding, every hour after feeding for 6h and every 2h during the following 12h of day 15 in each period and filtered through cheese cloth. pH was measured and two samples of 30 ml acidified with eight drops of 97% sulphuric acid and stored in a freezer. The samples were analyzed for volatile fatty acids (VFA) and ammonia N following the methodology described by FAO (1986).

The DMD of the diets was determined with 9 adult sheep, 3 per treatment, with total collection of faeces. The animals received the rations for 24 days and the measurements were carried out during the last seven.


The chemical composition of forages and feeds used is shown in Table 2. Concentrates in Experiment 1 had a similar content of CP, calcium and phosphorous, but the IVOMD of concentrate L was almost 30 percentage units lower than concentrate H, and concentrate HL was intermediate. CP content of concentrate UF in Experiment 2 was as expected higher than the others, and concentrate U was slightly higher than F. IVOMD was somewhat lower in concentrates with fish meal.

The forage consumption in Experiment 1 was similar in all treatments (Table 3) and LWG were slightly, though not significantly (P>0.05), higher in treatments with by-pass protein.


Table 2: Chemical composition of forages an concentrates

Chemical fraction (% of DM)

          IVOMD (%)
  CP Ash Ca P  
Experiment 1          
Concentrate H 27.9 10.5 1.0 1.2 85.7
Concentrate L 32.6 10.0 1.6 1.3 57.4
Concentrate HL 29.6 9.6 1.2 1.3 67.6
Forage offered 8.0 10.9 0.4 0.3  
Experiments 2&3          
Concentrate U 27.7 11.0 1.6 1.1 82.5
Concentrate F 23.9 11.2 1.7 1.7 81.9
Concentrate UF 34.2 11.5 1.8 1.7 77.9
Forage offered 6.9 10.4 0.3 0.2  


Table 3: Intake and live-weight (LW) gain of growing cattle offered supplements with sources of high (H) and/or low (L) rumen degradable N in Experiment 1


  H L HL    
Forage DM daily intake          
(kg) 3.57 3.50 3.66 0.26  
(g/kg LW) 19.2 17.8 19.1 0.82  
Total DM daily intake          
(kg) 4.94 4.90 5.07 0.26  
(g/kg LW) 26.5 25.0 26.5 0.81  
LW gain (kg/day) 0.62 0.69 0.67 0.043  


No differences in forage intake were observed between treatments in Experiment 2, but LWG were higher (P<0.05) in animals receiving concentrates with fish meal (Table 4). The addition of urea to the concentrate with fish meal did not increase LWG.

The results of Experiment 3 are shown in Table 5. The intake per unit body weight was lower than in Experiment 2 and again no differences were observed between treatments. The values of pH were similar in all treatments with mean values per hour varying from 6.5 to 7.0. Ammonia N concentrations per day were higher in treatments with urea, reaching a peak of about 330 mg/litre two hours after feeding against 170 mg/litre in treatment F. These values decreased to about 80 mg/litre ten hours after feeding in all treatments and remained at this level for the rest of the day. Molar proportions of acetic, propionic and butyric acids were similar in all treatments. The rate of digestion of forage estimated by T2 was similar in the three treatments. The T2 of maize meal was about 20h and for fish meal it was 113h. The DMD of the diets determined with sheep were 63.3, 62.8 and 63.2% for U, F and UF, respectively (P>0.05).


Table 4: Intake and live-weight (LW) gain of growing cattle offered a concentrate with urea (U) and/or fish meal (F) in Experiment 2


  U F UF  
Forage DM daily intake        
(kg) 2.62 2.80 2.59 0.131
(g/kg LW) 16.7 16.9 15.6 0.65
Total DM daily intake        
(kg) 4.41 4.61 4.42 0.137
(g/kg LW) 28.0 27.9 26.7 0.90
LW gain (kg/day) 0.65 0.80 0.81 0.049*


Table 5: Rumen fermentation indices and intake of dry cows offered a concentrate with urea (U) and/or fish meal (F) in Experiment 3


  U F UF  
Rumen pH 6.7 6.8 6.7 0.02
Ammonia N (mg/lire) 148 90 178 12.8*
Molar proportions of VFA        
Acetic 76.0 72.3 73.7 0.35
Propionic 15.7 18.2 17.2 0.42
Butyric 8.3 9.5 9.2 0.25
Rate of DM digestion (T2,h) 85.4 84.1 84.2 0.25
Total DM daily intake        
(kg) 7.73 7.97 7.92 0.521
(g/kg LW) 16.7 17.2 17.1 1.12




The LWG response to a supplement based exclusively on sources with a high proportion of by-pass protein and low digestibility was low when compared to a concentrate high in degradable N and degradable organic matter (Table 3). A large proportion of the concentrate L was dehydrated brewers grains (DBG, Table 2), which has a low digestibility, decreasing the level of energy supplementation compared with concentrate H. DBG also has a low rate and extent of DM disappearance in the rumen (Parra et al 1984), decreasing the amount of organic matter available for microbial protein synthesis. Both effects tended to out weigh the benefits of this supplement as a source of by-pass protein and resulted in the small increases in LWG which were obtained.

The addition of fish meal as a source of by-pass protein to a concentrate based on maize meal resulted in moderate and significant responses in LWG compared with urea as a source of degradable N, but without effects on forage consumption. Similar results have been obtained in other trials carried out in Tropical America using forages and silages as the base of the diets (Combellas 1991). Higher responses in LWG and increases in roughage consumption have been observed when by-pass protein is supplemented to diets poor in N, but this was not the case because the control diet (Treatment U) was supplemented with a concentrate high in degradable N (Table 2). The addition of urea to the concentrate with fish meal (Treatment UF) had no effects on animal response (Table 4) indicating that the small proportion of degradable N of fish meal complemented other sources of this nutrient in the diet and was enough to fulfil the requirements of microorganisms. The urea in treatments U and UF increased the level of ammonia N in the rumen (Experiment 3, Table 4), but did not improve the rate of digestion of forage in nylon bags. Probably, as was suggested by Leng (1990) for low quality fibrous diets, the concentration of ammonia N required in this type of diet to optimize intake and forage utilization probably decreases when by-pass protein is offered.

The results of Experiment 2 have shown, as was observed in previous trials (Combellas 1991), that the supplementation with by-pass protein in diets based in tropical forages and silages with adequate amounts of degradable N result in moderate increases in LWG without raising forage consumption. However, the substitution of high rumen degradable supplements by sources of by-pass protein of low digestibility (Experiment 1) decreases the LWG responses in growing cattle.


This research was partially sponsored by the International Atomic Energy Agency, Project N? VEN/5/013.


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(Received 17 July 1992)