Intensive beef production on cultivated pastures in a sub-tropical environment.
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Date
1984
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Abstract
The comparative performance of spring-calving beef
cowherds comprising either Dual Purpose (Simmentaler) or
British-cross (Hereford x Africaner) cows and calves was
investigated at stocking rates of 3,0, 4,12, 5,34 and 6,74
cows and calves/ha on Kikuyu pasture over three seasons. An
increase in stocking rate was associated with a decrease in
the length of the grazing period, an increase in the mass and
condition loss of cows, a decrease in calf livemass gains, a
decrease in milk production, an increase in the production of
beef per hectare and a decrease in margins over feed costs
per cow. Stocking rate did not influence reconception rates,
which averaged 65% over the three seasons. Simmentaler cows
produced calves approximately 2 kg heavier at birth and 24 kg
heavier at weaning, approximately 1,4 litres of milk more per
day, lost more condition and attained higher margins over
feed costs per cow and per hectare than Hereford-cross cows.
Season influenced the length of the grazing season, birth
mass, livemass gains in calves and mass changes in cows. Milk
production accounted for 40% of the variation in calf gains
on pasture. The conversion of milk to calf gain was
influenced by milk yield, stocking rate, breed and calf sex.
Ovarian and endocrinological responses associated with
normal and restricted suckling for a 15-day period at two
postpartum stages (Days 35 to 50 and 60 to 75) were examined
in Bos taurus and Bos indicus cows. All cows received
progestagen therapy, followed by GnRh administration during
the periods of variable suckling intensity. Restricted
suckling exerted little influence in Bos taurus cows, but
tended to improve the ovulatory response, to decrease the
incidence of "short" cycles and to increase reconception
rates in Bos indicus cows. Treatment exerted no influence on
calf growth and on tonic LH and oestrogen secretion. Bos
indicus cows suckled normally released more LH in response to
GnRh than Bos taurus cows. Bos indicus cows suckled once
daily secreted less LH in response to GnRh than those suckled
normally.
Seasonal effects on tonic LH, and progesterone secretion
were studied in cycling Friesland cows. Mean tonic LH levels
during autumn were significantly higher than those during
summer and spring. Season. exerted no influence on
progesterone secretion.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.
Keywords
Pastures--KwaZulu-Natal., Kikuyu grass., Beef cattle--Reproduction., Beef cattle--Feeding and feeds., Theses--Animal and poultry science.