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Fluctuations of Bovine Milk Chemical
Composition in Cows Fed on Legume Stover and
Feed Grade Urea Fertilizer Nitrogen-Based Feeds
Chisowa DM1* and M PofuI DT2
1Southern University, School of Agriculture, Department of Animal Science, Zambia
2Chinhoyi University of Technology, School of Agricultural Sciences and Technology, Department of Animal Production and Technology, Zimbabwe
Submission: November 7,2020;Published: December 08, 2020
*Corresponding author: Chisowa DM, Southern University, School of Agriculture, Department of Animal Science, P. O Box 60293, Livingstone, Zambia
How to cite this article: Chisowa D, M PofuI D. Fluctuations of Bovine Milk Chemical Composition in Cows Fed on Legume Stover and Feed Grade Urea Fertilizer Nitrogen-Based Feeds. JOJ Wildl Biodivers. 2020: 3(2): 555608 DOI: 10.19080/JOJWB.2020.03.555608
This study evaluated the weekly fluctuations of bovine milk quality from cows fed Legume Stover (LS) and feed grade urea fertilizer (UET). The study involved feeding Maize Stover (MS) improved using UET, Chopped Groundnut Stover (CGS), Chopped Soybean Stover (CSS), Mineralized Groundnut Stover Solution (MGS) and Mineralized Soybean Stover Solution (MSS) to lactating dairy cows. The feeding trial involved twelve (12) dairy cows in their second parity. Effect of supplementation with MS improved with UET, cGS, cSS, mGS and mSS on milk quality was evaluated following on-station feeding trials. The study involved 22 factorial experiments within a Completely Randomised Design (CRD). Milk samples were analysed for protein, lactose, fat and solid not fat (SNF) and milk density.
Mean milk protein levels ranged from 3.52mg/ml to 3,73mg/ml (s.e=0.03) for milk from cows fed on MS improved using cGS and mGS respectively. Protein and Lactose were observed to be the least variable (3.64g/ml ±0.12, and 5.24g ±0.24 respectively). Average milk fat content was highest (4.78%, se=0.52) in milk from cows fed on UET treated MS and lowest (3.43%, se=0.52) in milk from cows fed on gGS protein-based MS. Within legume type milk fat was higher (4.75%±1.99) in milk from cows fed on MS blended with mGS than that in milk from cows fed on MS improved with cGS (3.43%±1.99). Similar result was observed in milk fat from cows fed on MS improved with the use of soybean. Lactose in milk from cows fed on UET treated MS was highest (5.51g, se=0.061) and lowest (5.10g, se=0.061) in milk from cows fed on MS blended with cGS. Milk from cows fed on MS improved with mGS was higher (9.61p/cwt, se=0.14) in SNF and lowest (8.88p/cwt, se=0.14) in milk from cows fed on MS with cGS. The milk density values ranged from 32.65sg, se=0.53 for milk from cows fed on UET treated MS to 30.42sg, se=0.053 for milk from cows fed on MS blended with cGS. Milk components were higher when cows were fed on MS improved using mineralized legume stover solutions. Results of the current study have indicated that milk composition is clearly influenced by diet, and period of lactation. In the current study it was observed that milk fat was the most variable component not only among feed types but also over the feeding period.
The nutritional value of livestock products has been acknowledged in human nutrition. For example,  stated the following with regard to the use of animal products in human diet: “As diet becomes richer and more diverse, the high-value protein that the livestock sector offers improves the nutrition of the vast majority of the world. Livestock products not only provide high-value protein but are also important sources of a wide range of essential micronutrients such as iron and zinc, and vitamins such as vitamin A. For the large majority of people in the world, particularly in developing countries, livestock remains a desired food for nutritional value and taste.” This statement is
particularly true for Zambia where the per capita consumption of meat is only 2.4 kg per annum . In the advent of the HIV/AIDS pandemic, livestock has even become critical in that animal products provide specific nutrients that directly demobilize the progression of HIV to the AIDS condition. This is because these nutrients are associated with maintenance or enhancement of the immune system of the human body. Meat is a good source of high-quality protein, micronutrients such as zinc, magnesium, selenium, iron and vitamins A, E, and B-complex [3,4]. Work by , revealed that milk is the most complete of all foods, containing all the constituents of nutritional importance to human beings.
Eggs make a useful contribution to the daily intake of vitamin D,
retinal, riboflavin, iodine, iron and protein. Thus, a combination of
red meat, eggs and milk provides a complete diet to take care of
all the necessary nutrients that would mitigate or keep the HIV at
low levels and keeping a person healthy. Clearly, the importance
of livestock from a nutritional point of view and the well-being of
human beings cannot be overemphasized.
Many factors can influence milk composition. This is an
important point to remember when evaluating the potential to
improve a herd’s milk composition and component yields. The
major components of milk are water, fat, protein, lactose and
minerals. Factors that influence composition are genetics and
environment, level of milk production, stage of lactation, disease
(mastitis), season and age of the cow. Farms that used genetic
information (EBV) and phenotypes when selecting sires were
higher (p<0.05) for milk fat percentage than farms that used
only phenotypes and personal opinion [5,6]. reported that, with
increase in feeding of concentrate, there is also a reciprocating
increase in milk protein components up to a point where if dry
matter in the diet is more than 50% concentrate, the increase in
starches shows a decrease in milk fat percentage. Feeding strategies
that optimize rumen function also maximize milk production and
milk component percentages and yield . Dairy breeds mostly
used by dairy farmers show variations in fat, protein, lactose and
ash. This shows the influence of breed on milk quality . Work
by , indicated that the composition of milk varied for some
components. There was seasonal variation (p<0.05) on calcium.
Total solids (TS) and soluble nitrogen fats (SNF) were significant
(p<0.05) as affected by season. Parity and season had no effect on
cholesterol, magnesium and phosphorus. A study by , indicated
that parity, year of calving, days in milk and age of calving affect
yield and composition of milk of Red Dane cows in Zimbabwe. It
was reported by , that milk protein and SNF were found to
be higher during rainy season than in the summer and winter
seasons. Proper feeding significantly increased milk yield and to a
certain extent, could alleviate the decline in milk components. Air
temperature above 25oC and humidity below 65% has effect on
changes in milk fat, protein and lactose content. Milk yield, protein
and lactose content are affected by the kind of supplemented
green feed . Feed quality and quantity have been observed to
show seasonal fluctuation, a trend which affects animal nutrition
and performance. Dry seasons in Zambia and many other
tropical countries are marked with periods of feed shortages
resulting in general retardation in animal growth and production
. A systematic critical appraisal of the establishment and
management methods of improved pasture and fodder species
is probably relevant in the promotion of better development and
utilization of the crop by dairy cattle in the small-scale farming
systems . Milk composition is influenced by season, storage
conditions, lactation period and regional location. This is due
to changes in temperature and feed availability during different
seasons. Development of different feeding systems according to
season and region is needed to produce high quality and satiable
milk production [14,15] observed that milking period affects milk
fat, making the fat percentage lower in the morning compared
with the evening milking period. Seasonal differences in milk fat,
protein and somatic cell count were significant.
It is against this background that a research project was carried
out at the Batoka Livestock Research Centre in Choma district of
the southern province of Zambia with an objective of assessing the
effect of inclusion of legume stover on milk quality and nutritive
value. The study specifically compared the nutritional composition
of milk from cows fed on groundnut and soybean nitrogen based
maize stover as well as the effect of stover processing methods on
The research was conducted in Southern Province of Zambia.
The province lies at an altitude range of 400- 1400 m above sea
level. It has a mean annual temperature ranging from 14°C to 28°C.
It receives an annual rainfall of 700 mm to 1000 mm. The soil type
ranges from clay to sandy loam .
Treatment with urea
Dry maize stover was chopped using a stover shredder and
treated using the Urea-Ensiling Technique (UET) before being
offered to the cows. The standard method of urea treatment
used in other developing countries which involves the making
of a solution of urea using four (4) kg urea fertilizer feed grade
(46%N) into sixty (60) litres of water and mixing this with one
hundred (100) kg of stover was used. Pits were dug on raised
ground for the purpose of the UET. The stover was chopped into
3-5 cm pieces, mixed with the urea solution using a watering can
and buried into the pit, ensuring an air-tight environment using
polythene plastic sheets and compacting. The stover and straw
were ready for feeding in 21 days (3 weeks urea incubation
period). Three kilograms (3 kg) of the feed was given to each cow
per day in a 22-factorial experiment in a Complete Randomised
Design (CRD). UET was taken as novel therapy or positive control
and compared with the test therapies.
Treatment with legume stover
The quality of maize stover was improved using mineralized
and chopped legume stover [Groundnuts (Arachis hypogea) and
Soybean (Glycine max)]. These feeds constituted test therapies.
The feed ingredients (maize and legume stover) were all procured
from local farmers. Three kilograms (3 kg) of the feed was given
to each cow per day in a 22-factorial experiment in a Complete
Randomised Design (CRD). Four rations were prepared on the
basis of cereal type, legume type, source of nitrogen and method
of processing of legumes as follows:
a. Maize stover + mineralized Groundnut stover solution
b. Maize stover + chopped Groundnut stover
c. Maize stover + mineralized Soybean stover solution
d. Maize stover + chopped Soybean stover
A similar number of animals fed on a commercial diet (dairy
meal) were used as a positive control. Additionally, another
similar number of animals that just grazed normally (no
supplementation) were used as a negative control. Test diets were
formulated such that they were iso – nitrogenous (same CP) and
iso – energetic (same GE or ME). To ensure that the diets were
iso-nitrogenous and iso-energetic, samples of cereal stover and
legume stover were analysed for their GE and nitrogen content
respectively before rations were compounded. Quantities of cereal
and legumes (maize, groundnut and soybean stover) used were
computed by simple proportion to equate the energy and nitrogen
content in each feed based on the results of the proximate analysis.
This was important for the data to be valid and reliable hence the
conclusions and recommendations.
Mineralization of legume stover
Dry groundnut and soybean stover were tied into bundles
each weighing 5 kg. Three (3) bundles of groundnut stover were
completely immersed in 100 litres of water in a plastic drum of
210 litre capacity. The drum was covered with a tight lid. Another
three (3) bundles of soybean stover were treated in a similar
manner in another drum. The set up was left for five days to allow
for mineralization to take place. A preliminary proximate analysis
of samples revealed that a period of five (5) days was the optimum
for mineralization to be effective.
Rations were prepared using the BLP 88 computer program
[17,18] to meet the nutrient requirements of dairy animals (NRC,
2001) . Amounts generated from the ration formulation
program were measured using a scale. These were mixed by
rolling and turning several times on polythene plastics spread on
concrete floor using a garden fork in order to ensure consistence
in the composition.
Two (2) types of rations were compounded: one comprising
chopped cereal and legume stover. The other comprised chopped
cereal stover and mineralized legume stover solutions. The
mineralized legume stover solutions were sprayed on the measured
quantities of chopped maize stover using a watering can and then
turned several times using a garden fork on a concrete floor. To
help bind the chopped (ground) legume stover to maize stover, as
well as to improve palatability, molasses solution was sprinkled
and mixed with all types of ingredients at compounding. All other
ingredients were the same for the rations but only differed in the
source of protein and processing method used. Feeds were then
packed in 25 kg plastic bags in readiness for delivery to the feeding
or milking parlor site where feeding was carried out.
The feeding trials involved twelve (12) lactating dairy cows
in their second parity arranged in a 22-factorial experiment
within a Complete Randomized Design (CRD). The experimental
units (dairy cows) were randomly selected using simple random
numbers from the herd available at Batoka Livestock Trust
Research Centre (BLTRC). Treatments (rations) were randomly
allocated to experimental units (dairy cows) by picking lots using
animal identities (Ear-tags and feed type) written on pieces of
paper and placed in two separate urns (boxes). An adaptation
period of five (5) days was allowed for each feed before data was
The feeding trial commenced by determining the optimum
quantity of feed to be given to each animal. Quantities of fourkilogram
(4 kg), three kilograms (3 kg), two kilograms (2 kg)
and one-kilogram (1 kg) were tried over a period of seven (7)
days. During the trial one kilogram (1 kg) of feed was found
to be the appropriate quantity of feeding to appetite during
supplementation since rejected quantities were much less.
The experimental cows were allowed to graze from seven (7)
to twelve (12) hours and then brought to the milking parlor for
milking each day. Each animal was offered one (1 kg) of the rations
being administered at a given time (control or test therapy). The
control or test treatments were supplements to the free grazing
during times of feed shortage. The parameters used to test the
effect of the treatments was feed intake. An adaptation period of
seven (7) days was allowed for each feed before data was recorded.
Data pertaining to feed intake was taken as the difference between
feed offered and feed left in the feeding trough. Data was for each
experimental unit were recorded on score sheets.
Yij=μ +Ri + Wj + (RW)ij + b(x) + εi
Where Yij= observed milk quality on individual cow of a given
ith legume type and jth week.
Ri=effect of the ith legume type
Wj=effect of jth week
(RW)ij = effect of two-way interaction of ration and week
b(x)=b is the regression coefficient for initial milk quality
used as a covariate
εij=random error component
Research design and data collection
The twelve (12) dairy cows were arranged in a 22-factorial
experiment in a Complete Randomized Design (CRD). Daily feed
intake was recorded on individual score cards identified by animal
identity numbers from June 12, 2017 through November 09, 2017.
Data was analysed using the Statistical Analysis System on the
General Linear Model computer. Treatment means were compared
using the F-test.
Mean milk protein levels ranged from 3.52 mg/ml to 3,73
mg/ml (s.e=0.03) for milk from cows fed on maize stover whose
quality was improved using chopped groundnut stover and
that from milk for cows fed on maize stover whose quality was
improved using solution from mineralized groundnut stover
respectively. However, though the means differed numerically the
differences were not significant (p>0.05). Results presented in
(Table 1) (Figure 1) show a general increase in protein level with
a period of lactation within each feed type. Mean milk protein
levels increased gradually from week 1 to week 3 in milk from
cows fed on chopped legume stover based feeds. Conversely, mean
milk protein increased between week 1 and week 2 but gradually
dropped between week 2 and week 3 in milk from cows fed on
mineralized legume stover solution and urea-based feeds (Figure
1). The variance estimate for milk protein for feeds was 0.0144
mg/ml. (Tables 2 & 3). The total (crude) protein content of milk
is determined by analyzing milk for nitrogen and multiplying by
a factor of 6.38. The total protein percentage of milk is generally
considered to be about 3.5, of which 94 to 95 percent is in the form
of true protein [19,20].
Across feed type the highest average milk fat content
(4.78%, se=0.52) was recorded in milk from cows fed on urea
ensilage treated maize stover while the lowest (3.43%, se=0.52)
was observed in milk from cows fed on maize stover that were
improved using chopped groundnut stover (Table 3). Similarly, the
differences were not significant (p>0.05) (Table 4). The variance
estimate for milk fat for feeds was 3.960%.
Within legume type the milk fat was higher(4.75%±1.99) in
milk from cows fed on maize stover blended with mineralized
groundnut stover solution than that in milk from cows fed on maize
stover improved with chopped groundnut stover (3.43%±1.99)
(Table 3). A similar picture was observed in milk fat from cows fed
on maize stover improved with the use of soybean (Table 3). There
was a general decrease in milk fat with increase in days among all
the samples from cows fed on the different feeds. The decline in
fat content was more pronounced between week 1 and week 2.
Between week 2 and week 3 the curve started levelling (Figure 2).
(Tables 5 & 6) show comparisons of levels of lactose content
in the five (5) treatments used in the study. Milk from cows fed on
urea ensilage treated maize stover reflected the highest (5.51 g,
se=0.061) content of lactose, while milk from cows fed on maize
stover blended with chopped groundnut stover was observed
to contain the lowest (5.10 g, se=0.061) quantity of lactose. It
was observed that the means for lactose content for the five (5)
treatments did not differ significantly (p>0.05). When evaluated
within each feed type results show a general increase in lactose
content with period. Lactose content consistently increased from
week 1 to week 3 in milk from cows fed urea and chopped legume
stover based feeds. Lactose content in milk from cows fed on
mineralized legume stover based feeds declined between week 2
and week 3 (Figure 3). The variance estimate for lactose content
was 0.056 g.
Solid-Not-Fat (SNF) content
Results of the study indicated higher (9.61 p/cwt, se=0.14)
Solid-not-fat levels in milk from cows fed on maize stover improved
by blending with mineralized groundnut stover solution. The
study further showed that milk from cows fed on maize stover
mixed with chopped groundnut stover had the lowest (8.88 p/
cwt, se=0.14) Solid-not-fat (Table 7). Milk from cows fed on
the five feeds showed a similar trend in SNF content during the
feeding period. There was a gradual increase in SNF content in
milk between week 1 and 2, followed by a gradual decrease in SNF
content in milk between weeks 2 and 3 (Figure 4). Levels among
all the five (5) treatments did not differ significantly (p>0.05)
Results of the current study revealed numerical differences in
density ranging from 32.65 sg, se=0.53 for milk from cows fed on
urea ensilage treated maize stover to 30.42 sg, se=0.053 for milk
from cows fed on maize stover blended with chopped groundnut
stover (Table 9). Despite these differences there were no significant
(p>0.05) differences among the effects of treatments (Table 10).
Milk density from cows fed on the five feeds showed a similar
trend over the feeding period. Milk samples collected between
week 1 and week 2 reflected a gradual increase in density after
which milk density in all the samples showed little or no change
Milk Freezing Point
An evaluation of the effect of feed type on Freezing Point (PF)
of milk showed lowest (59.95oC, se=0.42) in milk from cows
fed on maize stover treated with chopped groundnut stover and
highest (64.15oC, se=0.42) Freezing Point in milk from cows fed
on maize stover treated with urea by urea ensilage. Generally
Freezing point for milk from cows fed urea, chopped soybean and
chopped groundnut stover increased with increase in lactation
period (i.e from week 1 to week 3). Milk freezing point in milk
samples from cows fed on mineralized legume stover based
feeds (i.e mineralized soybean and groundnut stover) increased
between week 1 and week 2 and showed a decline thereafter
(Figure 6) (Tables 11 & 12).
Milk quality differences recorded among the effect of
treatments were certainly related to the diets’ nutrient contents,
in particular the protein content which was higher in groundnutbased
diets and UET and lower in soybean based diets (Table
1, Figures 1 & 2). We can also explain this difference by several
factors such as the biological variations among experimental
units. The overall mean values of fat and SNF 4.528 and 8.754
percent observed by , were in consonance with results of
today’s study. Similarly,  reported variations in milk quality
on the basis of type of legume forage used. Cows on Red Clover
diets yielded milk with lower milk fat and protein contents than
cows fed on grasses and other legumes.
Results of the current study are in agreement with those of
, who reported previous studies in Thailand showing milk
fat percentage levels for crossbred cattle ≥75% Holstein having
milk fat values of 3.77%, with a protein content of 3.17 g/ml.
This low level in fat content is a result of high temperatures and
humid climate characteristic of tropical regions. This study used
the Batoka crossbreed resulting from cross breeding of local
cattle and the Holstein Friesian dairy breeds. This implies that the
experimental units used in the current study had some percentage
of Bos indicus influence which affects milk fat. Results of the study
by , who used Sahiwal and Red Sindhi showed higher milk
fat values (4.3-5.2% and 4.5-5.2%, respectively) than the values
observed in today’s study.
In the current study it was observed that milk fat was the
most variable component (4.24% ±1.99) not only among feed
types but also over time (Feeding period) (Table 3, Figure 3).
However, despite the observed numerical variations, levels of fat
content did not differ significantly (p>0.05) among treatments
or sources of nitrogen. Factors contributing to variations in milk
composition include species, differences between individuals
within strain and differences in conditions affecting individuals.
On all milk components, milk fat is the most influenced by
dietary manipulation. Most changes in milk composition due to
dietary manipulation are related to changes in ruminal-acetatepropionate
ratio. Among the notable factors that influence milk
composition are plane of nutrition, forage to concentrate ratio,
forage quality (e.g particle size), level and type of dietary fat.
Outcomes of this work agree with those of , who indicated
that milk fat depression can be alleviated within 7 to 21 days by
changing the diet. Milk protein changes may take 3 to 6 weeks or
longer if the problem has been going on for a prolonged period.
Protein and Lactose were observed to be the least variable (3.64
g/ml ±0.12, and 5.24 g ±0.24 respectively). This lower difference
in protein and lactose among treatments is indicative of suitability
of groundnut and soybean stover as possible alternatives to the
use of conventional sources of Nitrogen in dairy rations.
When evaluated across legume type fat, protein, SNF, FP and
lactose contents were numerically higher in milk from dairy cows
fed on groundnut stover based diets. However, there were no
significant (p>0.05) differences among the treatments. In contrast
density was numerically higher in milk from cows fed on soybean
stover based diets. Similarly, no significant (p>0.05) differences
were observed among the treatments. These results may be due to
the differences in nutritive value of the materials used to improve
the quality of maize stover.
Effect of processing method on milk quality
The outcomes of the study have shown a general common
trend in protein level, fat percentage, lactose level, SNF, Milk
Density and Milk Freezing point (FP). When evaluated within
feed type, milk components were higher in milk from cows fed
on maize stover treated with mineralized legume stover solutions
than in that in milk from cows fed on maize stover treated with
chopped legume stover.
In an evaluation of milk components between feed types,
the study has revealed that milk from cows fed on maize stover
treated with chopped soybean stover was higher in almost all milk
components than that from cows fed maize stover treated with
chopped groundnut stover.
Conversely, milk components in milk from cows fed maize
stover treated with mineralized groundnut stover solution were
higher than milk components from cows fed on maize stover
treated with mineralized soybean stover solution.
The study has revealed that milk protein, fat, lactose and
solid-not-fat components were generally higher in milk from
cows fed on maize stover improved using groundnut stover than
milk from cows fed on soybean-based rations. When evaluated
across processing method today’s study has indicated that milk
from cows fed on maize stover improved with mineralized legume
stover solution was superior in protein, fat, lactose and solid-notfat
components than that from cows fed on maize stover improved
with chopped legume stover. Results of the current study have
indicated that milk composition is clearly influenced by diet, and
period of lactation. This study has revealed differences in the effect
of legume type on milk composition. Milk from cows fed on Urea
based diet was superior in all milk components than that from
both soybean and groundnut-based diets. In the current study it
was observed that milk fat was the most variable component not
only among feed types but also over the feeding period. Though
milk components differed numerically these differences were not
significant (p>0.05). Results of this study indicate that soybean and
groundnut stover can be used interchangeably without adversely
affecting milk composition. Smallholder farmers and animal
nutritionists can positively influence the composition (nutritive
value) of milk by improving the quality of maize stover with cheap
and locally available legume stover in formulating dairy rations.
Additionally, the study has shown that improving the quality of
maize stover using mineralized legume solutions is more effective
in altering the milk quality on smallholder dairy farms. Finally, the
potential of other legume stover other than those of groundnut
and soybean should be evaluated.
The authors of this article are thankful to Batoka Livestock
Centre for availing their facilities during the research. We are
grateful to Professor Pandey of the veterinary school at the
University of Zambia for facilitating the laboratory sample
analysis. Authors are grateful to smallholder dairy farmers who
provided important information during the trials.
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