Intake, digestion and rumen parameters of goats fed mature veld hay ground with deep litter poultry manure and supplemented with graded levels of poorly managed groundnut hay
Lindela R Ndlovu(1) and Lewis Hove(2)
(1) Department of Animal Science, University of Zimbabwe, P O Box MP167,
Mount Pleasant, Harare, Zimbabwe
(2) Makoholi Research Station, Private Bag 9182, Masvingo, Zimbabwe
Ten mature Small East African does weighing 26 "3.2 kg were allocated to two latin squares to investigate the potential of weather-damaged groundnut hay as a supplement in a diet for goats. The basal diet offered at 900 g/d/goat consisted of mature veld hay ground with dried poultry litter and the daily supplements were 0, 135, 270, 405 and 900 g of groundnut hay. Inclusion of groundnut hay resulted in a decrease in intake of the basal diet at the rate of 37 g for every 100 g of groundnut hay eaten but total dry matter intake was increased. The levels of ammonia-nitrogen and volatile fatty acids in the rumens of the goats were lower than those needed for high ruminant productivity (2-8 mg NH3 - N and 31 - 73 mmole/l). Rumen degradability of the basal diet was not affected by the amount of groundnut hay offered or eaten but in vivo dry matter digestibilities were 37, 42, 45, 50 and 55% (sed 1.9) for diets in which 0, 135, 270, 405 and 900 g of groundnut hay were offered. It was concluded that weather damaged groundnut hay does not act as a supplement but rather as a substitute for mature veld hay diets given to mature goats, despite its palatability and content of readily degradable cell wall.
KEY WORDS: Goats, groundnut hay, veld hay, poultry manure, supplementation
Voluntary feed intake is a major determinant of livestock productivity; limited voluntary feed intake is a primary constraint to productivity in animals fed forage diets. Voluntary feed intake of such diets can be improved by grinding and pelleting the forages but this is often costly and impracticable in African small scale farming systems. There is therefore a need to find alternative ways of improving intake of forage diets in these farming systems. This is particularly important since forages are the main sources of nutrients available to ruminant livestock in most African small scale farming systems.
Supplementation with cereal and/or legume grains has resulted in increased intakes in intensive livestock production systems and has been the subject of several excellent reviews including those by Doyle (1987) and Lawrence (1988). However the use of grains to feed ruminants is undesirable in small scale farming systems as this puts ruminants into direct competition for food with the human population. Moreover in some areas the production of these grains is insufficient to support the human population and therefore the grains would not be available to feed ruminants. Consequently other systems of supplementation need to be investigated.
Use of forages as supplements has been suggested as an alternative to using grains (Ndlovu and Buchanan-Smith 1987). Legume forages have readily degradable walls (Van Soest 1982) which would increase substrates available to cellulolytic microbes with a consequent increase in the population of these microorganisms, if other nutrients are not limiting. One of the constraints to degradation of forage diets is the small population of cellulolytic microbes in the rumen ecosystem (Mackie and White 1990). In addition legume forages supply nitrogen, an essential nutrient for most rumen microbes and minerals.
In Zimbabwe, an abundant source of legume hay is groundnut tops; 71,000 tonnes are produced annually in the small scale farming systems (Central Statistics Office 1989). However, the groundnut tops are gathered when mature and the storage facilities are such that the resultant feed is low in nitrogen but very palatable. The experiments described here were aimed at investigating the potential of poorly managed groundnut hay as a supplement in goat diets. Goats are important sources of ready cash and meat to most small scale farmers in Zimbabwe.
Materials and methods
Animals and design
Ten mature (3 years old) non-pregnant non-lactating does weighing 26"2.8 kg were used in two 5 (treatments) x 5 (periods) latin squares. The 5 does used in square 1 were fitted with permanent rumen cannulae. In square 1, the periods were 28 days long - 14 days to allow the animals to adjust to the treatments and 14 days for data collection. In square 2, the periods were 17 days long - 10 days for the animals to adjust and 7 days for measurement of intake and digestibility.
Mature veld hay was mixed with dried deep litter poultry manure from a poultry enterprise that used veld hay as bedding. The mixture, consisting of 75 parts mature veld hay and 25 parts dried deep litter poultry manure (w/w), was ground in a hammer-mill to pass through a 20 mm screen to reduce selection and used as the basal diet in all the trials. The poultry manure was included to increase the nitrogen content of the basal diet which was offered at 900 g per goat per day. Treatments consisted of groundnut (Arachis hypogea) hay, which had been weather-damaged by rain and sun, offered at 135, 270, 405 and 900 g per goat per day in addition to the control with no supplementation.
The chemical composition of mature veld hay, the basal diet and groundnut hay offered to the goats is shown in Table 1.
|Table 1: Chemical composition of the main ingredients of the diets offered to the goats|
|Veld Hay||Basal diet*||Hay|
|Dry Matter (%)||88.0||89.0||89.0|
|As % of DM:|
|N x 6.25||3.4||6.4||7.4|
* Basal diet consisted of mature veld hay and dried poultry manure mixed in proportions of 75:25 (w/w) and milled together such that they were inseparable.
Intake and digestibility
The animals were offered both the basal diet and the supplement at 0800 h and any feed remaining in the troughs was removed before fresh feed was added. The residual feed was weighed, sub-sampled and stored for chemical analysis. Residual groundnut hay, mainly stems, was physically separated from veld hay weighed and stored separately. Digestibility was measured in square 2 using goats in metabolism crates which allowed for separate collection of faeces and urine.
Rates and extent of fibre degradation
Rumen degradability was measured by incubating nylon bags containing 4 g of the basal diet, ground by a hammer-mill to pass through a 2 mm screen, in the rumen of fistulated goats. The bags were removed serially at 3, 6, 9, 12, 24, 48, 60 and 72h post incubation and washed under clean running tap water until the water obtained by squeezing the bags was clear. The bags were then oven dried at 60 °C.
Rates of passage
On day 8 of the experimental period in square 1 the goats were dosed with feed marked with Yb169 at the rate of 1% of dry matter intake. The marker was prepared by soaking overnight 60 g of the basal diet in 100 ml of distilled water in which 0.15 ml of a 1 micro Curie Yb169 solution had been added and drying at 60 °C in an oven. Faecal grab samples were collected at 4, 8, 12, 16, 20, 24, 36, 48, 60, 72, 84, 96, 108, and 120h post dosing. The faeces were oven-dried at 105 °C and then assayed for gamma emission (counts/g/min) on a Packard Tricarb Scintillation Spectrometer.
Rumen fluid was sampled at 0, 4, 8, 12, 16 and 24 h post feeding at the end of each period in square 1. The pH of the fluid was measured within 2 minutes of collection and the fluid was stored at -20 °C for analysis of concentrations of rumen ammonia nitrogen (NH3-N) and types and concentrations of volatile fatty acids (VFAs).
Feed, residual feed and faeces were analyzed for dry matter (DM) and neutral detergent fibre (NDF); additionally feed was analyzed for organic matter (OM) and nitrogen using AOAC (1975) recommended methods. Rumen NH3 - N was measured using the method of Novazamsky et al (1974) while individual concentrations of VFA were determined using gas liquid chromatography. Total VFA concentration was calculated as the sum of the concentration of individual VFAs and molar proportions of individual VFAs were calculated as percentages mol/100 mol of total VFA concentration.
Data on intake and digestibility were analyzed using regression techniques and ANOVA procedures for a 5 x 5 latin square in the MINITAB package which accounted for diet, animal and period effects.
Rates of digestion were obtained by fitting data on DM and NDF loss from nylon bags to the non-linear model of Orskov and MacDonald (1979). The equation used was p = a+b(1-e-ct) where "p" = amount lost at time "t" and "a" is the readily available fraction, "b" is potentially degradable fraction whilst "c" is the rate of degradation of the "b" fraction. The constants "a", "b", and "c" from the above equation derived for each animal in each period were tested for diet, animal and period effect using ANOVA procedures for a 5 x 5 latin square in the MINITAB package.
Rates of passage from the rumen were obtained by fitting data on faecal counts per g per min to the non-linear model of Grovum and William (1973)
y = Ae -k1(t-TT) - Ae -k2(t-TT)
where k1 is the rate of passage from the rumen, k2 is the rate of passage from the post-ruminal compartment, TT is transit time and "y" is counts per gram per minute at time t. The k1 values obtained were then analyzed for diet, animal and period effect as described for other data.
For rumen parameters, the data were meaned across the sampling times in each period for each diet per animal. The 24 h means were then tested for diet, period and animal effect using 5 x 5 latin square ANOVA as described above.
|Table 2: Effects of groundnut hay offered on intake of basal diet dry matter (DM), groundnut hay dry matter, total dry matter, total organic matter (OM) and total neutral detergent fibre (NDF) and digestibility of DM and OM|
|Level of Groundnut hay offered|
|Basal diet DM||407||297||293||229||134||27.3|
|Total diet DM||407||414||522||561||802||27.3|
Basal diet dry matter was offered at 801 g/d;
SEdiff: Standard Error of difference
|Table 3: Effect of groundnut hay offered on rumen degradability of dry matter (DM) and neutral detergent fibre (NDF), and ruminal rates of passage*|
|Level of groundnut hay offered, g/day|
|a DM (%)||15.9||14.1||14.1||14.0||14.4||1.17|
|b DM (%)||54.0||49.3||43.3||47.6||37.3||5.33|
|c DM (%/h)||1.9||2.46||3.18||3.47||2.78||1.44|
|a NDF (%)||13.2||12.4||11.2||6.7||10.9||1.37|
|b NDF (%)||39.4||37.1||36.7||37.1||35.4||2.01|
|c NDF (%/h)||1.8||2.5||4.1||4.4||2.9||1.07|
SEdiff: Standard error of difference
a,b,c: from equation of Orskov and MacDonald (1979) p=a+b(1-e-ct)
k1: Rumen rates of passage were derived from the equation of Grovum and Williams (1973). y = Ae -k1(t-TT) - Ae k2(t-TT)
|Table 4: Effect of groundnut hay offered on daily mean rumen pH, ammonia-nitrogen (NH3-N) concentration (mg/100 ml), total volatile fatty acid (VFA) concentration (mmoles/litre) and molar proportions of Acetate, Propionate, Butyrate, Isobutyrate, Valerate and Isovalerate (mol/100 mol)|
|Level of Groundnut hay offered|
SEdiff: Standard Error of difference
Intake and digestibility
Total dry matter intake increased linearly with increasing level of groundnut hay offered (Table 2). The relationship is described by the equation: total dry matter intake (g) = 385 + 0.485 groundnut hay offered (P= 0.05, r = 0.66). Not all the groundnut hay offered was consumed (Table 2); groundnut hay intake increased by 0.75 g for every g increase in groundnut hay offered (groundnut hay intake (g) = 16.24 + 0.75 groundnut hay offered, r = 0.47). On the other hand as groundnut hay offered increased, the amount of basal diet consumed decreased (Table 2). For every g of groundnut hay consumed the consumption of the basal diet decreased by 0.37g (basal diet intake (g) = 374 - 0.37 groundnut hay intake, r = 0.47). However level of groundnut hay offered did not affect (P>0.05) amount of NDF consumed except at the 900 g level where amount consumed was increased by 38% over the mean of the other treatments.
Digestibility of dry matter and organic matter increased linearly with increase of groundnut hay offered (Table 2) with slopes of 0.37 and 0.34 (r = 0.72 and 0.69), respectively.
Rates and extent of digestion and rates of passage
Level of groundnut hay offered did not affect (P>0.05) the readily degradable fraction, extent of digestion and rate of digestion of the basal diet (Table 3). Rate of passage was increased (P<0.005) by 94 and 161% over the control when groundnut hay was offered at 405 and 900g/d, respectively. The other levels of offer did not significantly (P>0.05) affect the rate of passage (Table 3).
Though the data were collected at 4h intervals over a 24h period, the results are presented as means for a 24h period since the animals had food available all the time and feeding occurred intermittently throughout the 24h period.
The pH levels were generally high for all diets (mean 6.6, Table 4) with groundnut level offer of 405 g resulting in the highest pH. Rumen ammonia levels were low (mean 4.22 mg/100 ml Table 4). Only goats offered groundnut hay at 405 g/d had ruminal ammonia concentrations that differed significantly (P<0.05) from those of the control diet (Table 4).
Concentration of VFA was not affected (P>0.05) by level of groundnut hay offered except at the 900 g level (Table 4). Acetate: Propionate ratios based on molar proportions (Table 4) were: 7.90, 6.98; 4.95; 6.35 and 5.60 for 0, 135, 270, 405 and 900 g of groundnut hay offered, respectively. Higher chain VFA made up approximately 20% of the total VFAs for all diets (Table 4).
A supplement is a feed that will increase total intake whilst maintaining or increasing intake of the basal diet (Kempton 1977). Recommendations for supplementation of poor quality roughages have emphasized nitrogen supply (Preston and Leng 1984) but there is evidence that a source of readily degradable fibre can result in increased intakes of poor quality roughage diets (Ndlovu and Buchanan-Smith 1987). In our experiment, the intake of the basal diet decreased by 37 g with every 100 g increase in intake of groundnut hay. Thus groundnut hay served as substitute food rather than a supplement. The preference of goats for the groundnut hay was probably due to a readily degradable cell wall of the groundnut hay compared to that in the basal diet. The crude protein content of the two feeds was not sufficiently different to account for the preference (Table 1). Substitution of basal diet by legume crop residues has been found by other workers working with cereal crop residues as basal diets (Mosi and Butterworth 1983; McMeniman et al 1988; Adu et al 1992; Ngwa and Tawa 1992). Digestibility of dry matter, cell wall and organic matter increased with increasing level of groundnut hay consumed (Table 2). This increase was probably due to the fact that cell walls of leguminous forages are more degradable than cell walls of grasses (Van Soest 1982).
Assuming a value of 15.6 MJ of ME/kg digestible OM (ARC 1984), the ME available from the diets consumed by the goats was 2.25, 2.62, 3.39, 4.02 and 7.08, MJ/d respectively for groundnut hay offered at 0, 135, 270, 405 and 900 g. The intakes were therefore below the maintenance requirements of mature does based on a value of 0.48 MJ/d/kg0.75 (Hatendi et al 1990) except for the highest level of groundnut hay offered. This occurred even though the basal diet was offered in large amounts that allowed for maximum refusal (refusal rates of basal diet ranged from 49% with no groundnut hay offered to 83% with 900 g groundnut hay on offer).
The low total DM intakes (1.36 - 1.87% of liveweight) of the diets when groundnut hay was offered at 0, 135, 270, and 405 g/d are probably due to the low rumen ammonia-nitrogen levels. A minimum NH3-N level of 2 - 5 mg/100 ml rumen fluid has been suggested to maximize rumen microbial synthesis (Salter and Slytter 1974) and 15 mg/100 ml rumen fluid to maximize fibre digestion and 20 mg/100 ml rumen fluid to maximize intake (Preston and Leng 1987).
The mean ruminal NH3-N levels obtained in our study were, in the main, low. It is possible that the goats selected against the poultry litter. Unfortunately the crude protein content of the refusals was not measured. Nonetheless, the rumen NH3-N levels obtained in our study were similar to those obtained by Gelaye et al (1990) and Gelaye and Amoah (1991) when diets containing peanut hay were fed to goats. Ruminal pH was within the optimal range of 6.0 - 7.0 for cellulolytic bacterial activity (Hespell and Bryant 1979) while total volatile fatty acid concentrations (Table 4) were low except at the highest level of groundnut hay offered. This was consistent with data on intake and digestibility (Table 2). The molar proportions of acetate were higher than those obtained by Gelaye et al (1990) and Gelaye and Amoah (1991) using peanut hay diets. The proportions of propionate in the rumen liquid were low compared to the results of Gelaye and coworkers. This low propionate in the products of digestion of our diets could constrain goat productivity as propionate has been shown to be the major glycogenic fatty acid in ruminants (Preston and Leng 1987). However, the diets used in our experiment resulted in higher proportions of branched chain volatile fatty acids than has been obtained by other workers using low quality roughages (Chiema et al 1991). The cause of these high levels was not determined but could be linked to ruminal lysis of microbes and fermentation of microbial cells.
The degradation values obtained in this study were within the range reported for similar feeds by Abate and Kiflewalid (1992) and are typical of fibrous feeds. It is noteworthy that the parameters were not affected by increases in groundnut hay intake. On the other hand, in vivo apparent dry matter digestibility was affected by level of groundnut hay intake. This fact further buttresses arguments against using nylon bag degradation values for predicting in vivo digestibility of low quality diets (Orskov 1989).
At high levels of offer, poorly managed groundnut hay and mature veld hay were consumed in quantities sufficient to meet maintenance energy requirements of adult Small East African goats. This, however, was achieved by substituting for the basal diet and not by supplementing it. Digestibility of total dietary nutrients improved with increasing levels of groundnut hay consumed but degradation kinetic parameters were not affected.
This work was funded by the Southern African Coordination Conference on Agricultural Research (SACCAR) Small Research Grant Number SRG-22 and the University of Zimbabwe Research Board.
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(Received 1 October 1994)