Doctoral Degrees (Animal and Poultry Science)

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The effect of stocking rate on the performance of beef cows and their progeny in the highland sourveld areas of Natal.
(1988) Van Niekerk, Alvin.; Lishman, Arthur William.
In three separate. but related studies, the performance of weaner/replacement heifers, dry pregnant cows, and first calvers and mature cows and their progeny, at different stocking rates in the Highland Sourveld, was investigated. The study area was located in Bioclimatic region 4e in the Province of Natal, Republic of South Africa. In the first study, carried out over four seasons, the effect of winter and summer nutritional levels on the performance of replacement heifers, bred at two years of age, was investigated. The results of this study indicated that compensatory growth was a potentially important factor in reducing feed costs, but the degree of compensation was highly dependent upon stocking rate and the condition of the veld. The most economical regime for rearing heifers up to the mating stage was a low growth rate (0 - 0,25 kg/day) during the first winter (post weaning) followed by a low stocking rate (0,75 AU/ha) on summer veld. Treatment did not generally affect the number of heifers attaining puberty, nor their conception rates. Pregnancy rates as high as 96% were achieved. Treatment also had no apparent effect on subsequent calving rates. In the second series of experiments, the role of condition scoring as a management tool in the Highland Sourveld was studied. The condition score of the cow was shown to be an important factor determining conception rate and time of conception. Only 8% of the cows mated at a condition score of 1,5, conceived, whereas 80% conception rates were achieved when the cows were mated at a condition score of 3,0 - 3,5. The cost of improving a cow's condition from 1,5 to 3,0 was R108, whereas the cost of improving a cow's condition from 2,0 to 3,0 was R54. In the third study, carried out over nine consecutive seasons, the effect of stocking rate and lick supplementation on the performance of iactating cows and first calvers was investigated. Four stocking rates were applied - 0,83, 1,0, 1,25 and 1,67 cows plus calves per hectare. The very high stocking rate was terminated after four seasons because of a significant decline in both cow and calf performance, and the severe deterioration of the natural pasture. There was no benefit to either the cows or calves with access to a urea-based lick at the very high stocking rate, but at the low stocking rate (1,0 cow + calf/ha) the cows were in such a condition that the grazing season could have been extended, thereby saving on winter feed costs. First calvers produced weaners as heavy as those of the mature cows and were in similar body condition at the end of the grazing season. The excellent performance of the first calvers was attributed largely to the fact that they calved 3 - 4 weeks prior to the mature cows. The grazing behaviour of the first calvers and the mature cows, at the different stocking rates, was observed in the fourth study which was carried out over two consecutive seasons. There were no significant differences in the grazing time between the first calvers and the mature cows at any of the stocking rates. In all the treatments, the first calvers appeared to establish the grazing patterns, with the mature cows adopting a followership role. Alloparental behaviour was noted in the early part of both grazing seasons.
Estimation of carcass composition of beef cattle by the urea dilution technique.
(1977) Kock, Schalk Willem.; Stielau, Werner Johannes.
No abstract available.
The importance of age at first calving, relationship between body mass and fertility and feeding systems on production in the beef female.
(1978) Meaker, Helgaard Johannes.; Lishman, Arthur William.
No abstract available.
The influence of energy density on the performance of feedlot cattle.
(2002) Dominy, Neil John.; Nsahlai, Ignatius Verla.; Lishman, Arthur William.
This study examined the interaction of diets differing in their energy densities and heat increments of feeding on the feed intake patterns, physiological measurements, empty body composition, and animal performance of steers in a feedlot environment. The energy densities of the diets ranged from 7.97 to 11.83 MJ ME and 6.50 to 9.53 MJ Effective Energy (BE) and the ratio of EE to ME ranged from 0.79 to 0.84. The feed intake pattern of steers was not affected by differences in the diets energy densities but was affected by diets that differed in their heat increments of feeding. The physiological measurements, rectal temperatures measured at 9.00 am and 2.00 pm (TR 9.00 am and 2.00 pm) and respiration rates of steers in the feedlot were compared to control steers kept on pasture. Steers in the feedlot registered significantly (P < 0.001) higher physiological measurements than the controls and the accepted norms for cattle not under heat stress. A relationship exists between the pattern of physiological measurements over time and feed intake pattens over time. Physiological measurements peak and dip during the same weeks as the feed intakes peak and fall. Peaks and the immediate dips thereafter are related to points of acute response resulting in a chronic response and acclimatisation. All feedlotted steers experienced heat stress within the first week of feeding. Steers feedlotted in summer took 28 days to achieve their peak feed intake whereas steers feedlotted in winter required 42 days to reach their peak feed intake. Steers that required 42 days in which to reach their peak intakes had greater increases in their daily intakes than those that required 28 days to reach their peak intakes. Steers feedlotted in winter lost their winter coat between weeks three and six. Differences in peak feed intakes were recorded for animals of a heavier starting live weight (late versus early maturing and long yearling versus weaners). Peak feed intake increased in line with increasing live weight at the start of feedlotting. These differences were attributed to their greater surface area and hence greater heat loss capacity. Comparison of steers tissue deposition rates of steers on diets differing in their ratio of EE to ME revealed non significant differences in the growth rates of protein and lipid. The proportional use of energy intake was significantly different with significantly (P < 0.1) more of the daily energy intake being utilised for lipid deposition in diets with a higher heat load. Animals suffering from differing heat loads were inhibited in depositing protein but were able to deposit lipid due to the associated lower heat production. This enforced deposition of lipid results in animals reaching slaughter condition after similar lengths of time but at lower ADG and lower carcass weights. The economic consequences are that the returns are higher due to higher carcass gains for steers fed diets with a higher ratio of EE to ME.
Intensive beef production on cultivated pastures in a sub-tropical environment.
(1984) Louw, Brian Peringuey.; Lishman, Arthur William.
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.

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Browsing Doctoral Degrees (Animal and Poultry Science) by Subject "Beef cattle--Feeding and feeds."