EVALUATION OF MODELS FOR LACTATION CURVES FOR BUNAJI, FRIESIAN AND FRIESIAN-BUNAJI CROSSBRED COWS IN NIGERIA
EVALUATION OF MODELS FOR LACTATION CURVES FOR BUNAJI, FRIESIAN AND FRIESIAN-BUNAJI CROSSBRED COWS IN NIGERIA
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Date
1991-12
Authors
OLORUNJU, STEVE AJAYI SHADE
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Abstract
This study investigated the suitability of the available
models in representing the pattern of milk production of
Bunaji, Friesian and Friesian-Bunaji crossbred cows in
Nigeria. The models evaluated were Gamma, Modified Gamma and
the Inverse Polynomial functions.
Five hundred and eighty-four lactations were used. These
comprised of 205, 111 and 268 records from Bunaji, Friesian
and Friesian-Bunaji crossbreds. The lactation records covered
a period of 18 years and the records were from cows in the
first five parities. Each lactation was fitted to each of the
models. The curve and production indicators namely initial
week average daily production (initprd), peak week (pwk),
peak production (Mxprod), persistency (s) and total
production per lactation (Tprod) were obtained for each
model. These parameters were subjected to least squares
analysis considering parity, lactation length, season and
year of calving as factors. A combined analysis was also
undertaken for the breeds incorporated as additional factor
to evaluate the effects of the curve and production
parameters.
Multiplicative factors were developed for estimating 44 week
(305-day) production for each breed.
Results showed the average lactation lengths for Bunaji,
Friesian and Friesian-Bunaji crossbreds were 32, 50 and 36
weeks, respectively. The average milk production per
lactation varied between 928-1010 kg for Bunaji, 3800-4300 kg
for Friesians and 1860-2000 kg for Friesian-Bunaji
crossbreds. The average initial week daily productions were
4.69, 8.39 and 8.69 kg while the corresponding peak
productions were 6.4, 18.9 and 11.4 kg, respectively.
The observation showed that Gamma function was the most
suitable when compared to other functions. The function had
the least deviations comparing the observed with the
estimated for each breed. Also, the function estimated the
production parameters with a higher precision compared to
others. The Co-efficient of determination (R2) was highest
under the Gamma function. The values were 84% for Bunaji, 74%
for Friesian-Bunaji and 68% for Friesian cows. The values
obtained using the Inverse polynomial functions were 70% for
Bunaji, 61% for Friesian-Bunaji and 52% for Friesians. Values
under the Modified Gamma function were relatively closer to
those of Gamma function. Multiplicative factors obtained
using the Gamma function were found to be more precise than
those based on the other two functions.
Bunaji and Friesian-Bunaji crossbred cows had
significantly (P<0.05) higher persistency than the Friesian
cows. This is due to the higher adaptability to the
environment by the two relatively more indegenous breeds.
Some factors were found to have effects on the
production pattern of the cattle in Nigeria. These included
breed, parity, lactation length,season and year of calving of
the cows. Furthermore, all the factors enumerated above had
effects on the persistency of milk production.
Prom this study, the phenotypic correlation between the
curve and the production parameters showed that the initial
week average daily production and the peak production
correlated very highly (P<0.001) with the total production.
This therefore could be a useful and readily available tool
to be used in culling low milk producing animal from the
herd.
Finally, as a result of the relatively short lactation
length observed in Bunaji and Friesian-Bunaji crossbred cows,
it is possible and practicable to embark on early re-breeding
of these breeds of cattle to boost the milk production as
well as increasing the herd size provided there is a
corresponding improvement in the management.
Description
A Thesis
Submitted to the Postgraduate School
Ahmadu Bello University
In partial fulfillment of the Requirements for the degree
of Doctor of Philosophy
Department of Animal Science,
Faculty of Agriculture,
Ahmadu Bello University,
Zaria.
DECEMBER, 1991
Keywords
EVALUATION,, MODELS,, LACTATION,, CURVES,, BUNAJI,, FRIESIAN,, RIESIAN-BUNAJI,, CROSSBRED COWS