The effects of maternal calving date and calving interval on growth performance of beef calves

This study was undertaken to investigate the growth performance of calves born to dams with different calving dates and calving intervals. Early calving dams produced calves with the lowest birth weights, the highest actual weaning weights and the highest pre-breeding heifer weights. The higher weaning weights of early calvers were due to higher pre-weaning average daily gains and the older age of their calves at weaning. Corrected weaning weights of calves born to dams calving at different times during the calving season were not significantly different. A one-day increase in calving interval resulted in a decrease of 0.29 ± 0.01 kg for weaning weight and a decrease of 0.54 ± 0.01 kg for heifer pre-breeding weight. It is recommended that date of calving and actual weaning weight of calves should be considered when evaluating the reproductive and productive performance of breeding cows. (South African Journal of Animal Science: 2000, 30(1): 70-76

Bromide: A potential risk to livestock production in South Africa

No Abstract Keywords: animals, groundwater, halides, toxicity, water qualit

Survival and development of embryos of Gallus gallus domesticus treated with inorganic bromide

The range of bromide (Br-) in groundwater sources surveyed in South Africa is 0 - 18.4 mg/L. The research aimed to establish chicken embryo sensitivity to a range of Br- treatments (mg/L) injected into fertilised Ross-308 eggs in three phases: (1) five eggs injected with 10 mg Br-/L; (2) 45 eggs divided into groups and injected with 0, 1 and 5 mg Br-/L; (3) 148 eggs divided into groups injected with 0, 0.01, 0.05, 0.5, and 1 mg Br-/L. Incubation was at standard conditions. Breakout analysis was done at various stages of incubation. The mass of the embryo and of the heart, liver and brain was measured at Day 20. Statistical analysis used Statistical Analyses System® software FREQ procedure to determine the chi-square goodness-of-fit test for percentages of live or dead embryos within and between treatments. The GLM procedure was applied to test for differences in relative organ mass (g) between treatments using F-test. The results showed: (1) 10 mg Br-/L is toxic; (2) Br- is lethal to embryos at concentrations >1 mg/L and toxic at 1 mg/L; and (3) embryo survival was significantly negatively correlated (R2 = -0.92) with increasing Br- concentrations. Concentrations >0.5 mg Br-/L showed greater risk on differential development. Concentrations >0.01 mg Br-/L showed potentially severe effects on developing embryos. The heart showed the greatest relative growth response followed by the brain. The no observed adverse effect level target water quality range (NOAEL-TWQR) in developing chicken embryos was 0 - 0.01 mg/L.Keywords: Bromine, embryo model, halogens, maximum residue level, toxicity, water qualit

Productive performance of naked neck, frizzle and dwarf laying hens under various natural climates and two nutritional treatments

The productive performance of major genes for feather reduction (naked neck and frizzle) and body size reduction (dwarf) in a dual-purpose layer strain was evaluated in the subtropical coastal region of southeast Africa (Maputo, Mozambique). The experimental material consisted of ight different genetic groups, two diets (14.4 and 16.2% crude protein) and two climatic seasons. Birds were caged individually in a laying house with natural light and ventilation. Traits measured were: temperature and relative humidity, body weight, age at first egg, egg number and weight, feed intake and mortality. The following were calculated: persistence, egg mass, feed efficiency, feed conversion, biological efficiency (EMD/BW 0.75) and productivity (EN/BW 0.75). The main results show that: (1) none of the feather-reducing genes significantly improved egg production or feed efficiency, although the naked neck (Na) excelled in terms of biological efficiency and productivity; (2) the dwarf gene (dw) was associated with delayed sexual maturity, production of fewer and lighter eggs, higher persistence, better feed conversion and higher survivability; (3) elevated temperatures restrained voluntary feed intake, egg number and weight, and body weight gain; (4) the lower dietary protein content resulted in decreased body weight. It was concluded that the genes were not equally responsive to the environments, which offers the opportunity for selective breeding. South African Journal of Animal Science, Vol 31, Issue 3, Oct – Dec (2001): pp.174-180Key Words Temperature, Poultry, Naked neck, Frizzle, Dwarf, Egg production, Laying hen

The influence of geochemistry on health risks to animals and humans in geographically localised livestock production systems

(South African J of Animal Science, 2000, 30, Supplement 1: 82-84

An evaluation of the use of blood metabolite concentrations as indicators of nutritional status in free-ranging indigenous goats

The aim of this study was to determine whether blood metabolite concentrations in free-ranging indigenous goats are sensitive to expected variations in nutrient supply, and whether they could be used to evaluate different kidding seasons at two locations subject to similar seasonal variations in terms of nutrient supply. Monthly blood samples were taken over a period of one year. At Delftzyl farm, where a winter kidding season (June) was practised, glucose concentrations decreased from February onwards and reached their lowest levels just prior to the kidding season. Plasma glucose concentrations increased sharply after parturition and subsequently decreased until the end of lactation. Glucose concentrations were lower in lactating does than in non-lactating does during the first two months of lactation. In contrast, glucose concentrations during lactation in does at Loskop farm, where kidding took place during spring (October), did not differ from those recorded during the four months following weaning, and neither were there differences between lactating and non-lactating does. Glucose concentrations during lactation at Loskop farm were also higher than at Delftzyl farm. The different responses can be attributed to the fact that lactation at Loskop farm coincided with peak nutrient availability during the summer period of vegetative growth, whereas lactation at Delftzyl farm coincided with low nutrient availability and quality during the winter period of plant dormancy. Plasma urea concentrations were also elevated during the last month of pregnancy and the first two months of lactation at this location, and were higher during lactation than those recorded at the summer kidding site, indicating that body protein reserves may have been catabolized to support gluconeogenesis in these animals. Plasma cholesterol concentrations were higher in lactating goats than in non-lactating goats at Delftzyl farm but not at Loskop farm. Cholesterol concentrations during lactation were also higher at Delftzyl than at Loskop. This suggests that body adipose tissue reserves were catabolized during the winter lactation at Delftzyl farm. These results indicate that lactating does at Delftzyl farm were unable to maintain glucose homeostasis during pregnancy and lactation without significant catabolism of body reserves, and suggests that the winter kidding practised there was inappropriate in relation to the available nutrient supply. It was concluded that the plasma concentrations of all the blood metabolites studied were sensitive to seasonal changes in nutrient supply, and that they could be of use as a management tool in free-ranging farming systems in which conventional methods of nutritional assessment are difficult to apply. (South African Journal of Animal Science, 2000, 30(2): 115-120

A review of diagnostic and functional imaging in headache

The neuroimaging of headache patients has revolutionised our understanding of the pathophysiology of primary headaches and provided unique insights into these syndromes. Modern imaging studies point, together with the clinical picture, towards a central triggering cause. The early functional imaging work using positron emission tomography shed light on the genesis of some syndromes, and has recently been refined, implying that the observed activation in migraine (brainstem) and in several trigeminal-autonomic headaches (hypothalamic grey) is involved in the pain process in either a permissive or triggering manner rather than simply as a response to first-division nociception per se. Using the advanced method of voxel-based morphometry, it has been suggested that there is a correlation between the brain area activated specifically in acute cluster headache — the posterior hypothalamic grey matter — and an increase in grey matter in the same region. No structural changes have been found for migraine and medication overuse headache, whereas patients with chronic tension-type headache demonstrated a significant grey matter decrease in regions known to be involved in pain processing. Modern neuroimaging thus clearly suggests that most primary headache syndromes are predominantly driven from the brain, activating the trigeminovascular reflex and needing therapeutics that act on both sides: centrally and peripherally