Effect of heat stress on conception in a dairy herd model under South African conditions.

Three regression models are proposed for predicting reproduction in a model dairy herd under South African conditions. Conception rate (CR%) was related to mean monthly temperature-humidity index (THI) by; CR% = 31.15 THI - 0.25 THI(2) - 890.2, and first service conception rate (FSCR%) to THI by; FSCR% = 173.45 - 1.79 THI. Conception rate was related to numerical month of the year (M) by; CR% = 11.86 M - 0.82 M(2) + 26.36. The relation between mean monthly THI values and the conception rate of dairy cattle is significant. Further investigations to test the proposed regression models under various dairy herd conditions and to improve reproduction in South African dairy herds are needed.

Heat stress in dairy cattle and other livestock under southern African conditions. III. Monthly temperature-humidity index mean values and their significance in the performance of dairy cattle.

Temperature-humidity index (THI) values applicable to South Africa and Namibia have been established during this investigation for each month of the year by means of computerized modelling and mapping techniques. The data indicate that each year heat stress risk areas (HSRA's) expand from August to January and retract from February to July. The THI values classified according to the Livestock Weather Safety Index (LWSI) for lactating dairy cattle (LDC), suggest that, especially during November to March there is the risk of moderate to advanced heat stress in most South African dairy cows. This has important implications for their general health, udder health, production and reproduction. Careful planning of facilities and highly adaptable herd management are required to protect dairy cattle from heat stress.

Salmonella isolated from feeds and feed ingredients during the period 1982-1988: animal and public health implications.

The prevalence of Salmonella in southern Africa in farm feeds and by-products of animal origin during 1982-1988 was determined. Salmonella occurred in 5.18% of the farm feed samples and in 9.54% of the by-product samples. Different serovars were isolated, some only once. The findings underestimate the true prevalence of Salmonella in farm feeds and by-products, and is representative of only the most severely contaminated products. The epidemiology of salmonellosis is discussed with special reference to the importance of multiple resistance to antibiotics, the increase in the number of cases of salmonellosis worldwide and "Salmonella free" feeds and foods. More detailed research on the role of farm feeds in the epidemiology of salmonellosis is required. Efforts should be made to increase awareness of the problem, to improve quality management at farm feed production plants and to develop efficient systems to monitor the hygienic safety of feeds and foods.

Heat stress in dairy cattle under southern African conditions. II. Identification of areas of potential heat stress during summer by means of observed true and predicted temperature-humidity index values.

November-March are the hottest months of the year with the highest monthly mean "temperature-humidity index" (THI) in South Africa and Namibia. These 5 months are associated with severe heat stress in dairy cattle, are of critical importance for their performance and may have great economic implications for the owner as well as for the dairy industry. Firstly, compared with the existing Livestock Weather Safety index (LWSI), more relevant meteorological data can be generated when mapping South Africa and Namibia according to the LWSI modified for lactating dairy cattle (LDC). Secondly, compared with the observed true THI values alone, more relevant data on heat stress and its deleterious effects on dairy cattle performance, become available when mapping South Africa and Namibia according to the combined observed true and predicted THI values. Minimum precautions against heat stress in dairy cattle are recommended depending on THI values as classified by the LWSI for LDC.

Udder health implications of premature bovine mammary regression. I. Clinical, subclinical and reducing-sugar changes in milk during 168 hours of suspended milking in mid-lactation.

The investigation involved 4 mastitis-free cows, exposed to 168 h of suspended milking to induce prolonged milk stasis and premature mammary regression during mid-lactation. After 48 h the milk stasis elicited mastitis-like changes in the clinical, somatic cell count (SCC), bovine serum albumin (BSA) and beta-N-acetyl-D-glucosaminidase (NAG) characteristics of the udder secretions. Such changes in secretions from non-mastitic regressive mammary glands raise doubts about the present knowledge, definition, and diagnosis of so-called non-specific or aseptic mastitis. Determinations of fluctuating lacteal concentrations of lactose, galactose, mannose and glucose suggest that the secretory epithelium altered its metabolism and integrity in response to the intramammary perturbation by following a certain pattern of regressive adjustments which: (i) were apparently triggered during the initial 24 h of perturbation by disturbed Na-K-ATPase activities, followed by a cascade of changes in ion regulation, carbohydrate metabolism and increased formation of lactic acid as a metabolic end-product; (ii) advanced in a stepwise fashion during 0-24, 24-72 and 72-168 h of perturbation from recognition response to alarm reactions and manifestation of regression respectively; (iii) showed that markedly decreased carbohydrate levels preceded major increases of the SCC, BSA and NAG values; (iv) indicated that after 72 h of milk stasis leucocytic infiltrations sharply increased the SCC to more than 500,000 per ml and accelerated the manifestation of regression. The results of this study imply that extensive premature regression of healthy, and especially, pre-irritated udders could have significant implications for the development of different types of bovine mastitis during lactation and should be further investigated.

Udder health implications of premature bovine mammary regression. II. Collateral intramammary reactions in quarters milked normally during 168-hour milk stasis in opposite quarters.

This investigation has shown that collateral intramammary reactions (CIR's) occur when secretory disturbances in one quarter lead to corresponding changes in one or more of the other, unperturbed, quarters of the same udder. Compared with normal baseline values, the mean values and variations of bovine serum albumin (BSA), beta-N-acetyl-D-glucosaminidase (NAG), mannose (MAN), galactose (GAL) and glucose (GLU) showed slight increases under CIR conditions. Fluctuations of the carbohydrates preceded changes of somatic cell counts (SCC), BSA and NAG in milk. SCC and NAG showed significant negative correlations with MAN, GAL and GLU, the latter being the only parameter significantly correlated with each of the other parameters. The data suggest that the cow's stress control system responded to the milk stasis in the unmilked quarters, by initiating a form of general stress that affected the whole udder. This aggravated regressive conditions in the unmilked quarters and provoked CIR's in the normally-milked quarters. The CIR's amounted to a transient, regressive, compensatory re-adjustment of lactational homeostasis under conditions of acute general stress. CIR's similar to those investigated could also occur in close association with other local and general stressful conditions, disturb the natural defence of the udder and account for fluctuating mammary resistance to bacterial infection.

Heat stress in dairy cattle and other livestock under southern African conditions. I. Temperature-humidity index mean values during the four main seasons.

The Livestock Weather Safety Index (LWSI) indicates that in large areas of South Africa and South West Africa/Namibia and for prolonged periods of the year warm conditions are causing heat stress in food-producing animals, especially dairy cattle, thereby hampering their performance. South Africa and South West Africa/Namibia have been mapped according to a modified LWSI, which includes the critical "temperature-humidity index" value for milk production. The importance of heat stress in dairy cattle is discussed relative to such areas.

A high performance liquid chromatographic method for the fluorimetric determination of lactose, galactose and glucose in normal and abnormal milk of cows.

A high performance, liquid chromatographic, gradient method with post-column derivatization and highly sensitive fluorescence detection has been developed for the determination of reducing sugars, such as lactose, galactose and glucose, in normal and abnormal milk of cows. The method requires little sample preparation, is applicable to a fully automated HPLC system and has been found suitable for the processing of hundreds of samples. Peaks of minor constituent components of samples showed retention times identical with those of ribose, cellobiose, fucose, mannose and xylose. Further research with the HPLC technique, supplemented with modern gas chromatography and mass spectrometry, is considered necessary for elucidating the role of minor carbohydrates in the physiology and physiopathology of the bovine udder.

Pathogenesis of subclinical bovine mastitis: a comparison of the dynamic balances of various subclinical udder health states monitored by means of single-, double- and triple-parameter laboratory techniques.

This comparison of results from parallel investigations, conducted on the small herd model already discussed, has made it abundantly clear that during lactation, udder health as such depends on the 3 major determinants of intramammary epithelial integrity, somatic cellular defence and bacterial challenge. Different subclinical health states and related dynamic fluctuations indicate that each of these conditions and changes depends on the type of major determinant of udder health as well as on the nature and magnitude of factors challenging that determinant, either singly or in combination with another of the main determinants. Because of the involvement of 3 important determinants, diagnostic techniques must of necessity facilitate the concurrent monitoring of each of the determinants and the integrated interpretation of results generated. Such an approach to investigations into subclinical mastitis is not feasible by means of either single- or double-parameter techniques. In contrast, triple-parameter determinations capable of monitoring each of the 3 major determinants of udder health and performed during this investigation by means of the IDF/BSA (International Dairy Federation/bovine serum albumin) criteria, clearly have facilitated the interpretation of results at unprecedented levels of diagnostic differentiations. In the light of this clearer insight into a comparatively extensive range of udder health states at the subclinical level and corresponding dynamic balances and pathogenetic developments, it is apparent that appropriately designed and standardized triple-parameter techniques of high diagnostic sensitivity and reliability, would make the diagnosis of udder health states far more specific, and the control and prevention of subclinical mastitis far more cost-effective, than generally thought possible under present conditions. Further progress in research and practical work on subclinical mastitis may well depend on efficient triple-parameter techniques for determinations on persisting, deteriorating and improving states of bovine udder health.

Pathogenesis of subclinical bovine mastitis: diagnostic and dynamic characteristics of various subclinical udder conditions monitored by means of the International Dairy Federation criteria.

This investigation, conducted on a small herd milked by machine without disinfectant teat dipping, shows that a limited population of 21 normally lactating dairy cows regularly examined at 24 h intervals during 22 consecutive days, may be used for monitoring dynamic fluctuations of udder conditions. From the results it is apparent that, on subclinical levels, udder health of dairy cows depends in principle on a variety of conditions, variability in dynamic fluctuations and the balance between persistent, deteriorating and improving health states. As health states, especially active and intermediate to the mastitic and normal condition at the opposing extremes of udder health, aseptic mastitis (AM) and latent infection (LI) cross-reacting with each other and with each of the other health states, are of particular practical interest. From the dynamic fluctuations of AM and LI it seems conceivable that the strategy of mastitis control proposed by several workers and found lacking in several respects during this investigation, may promote the shifting of abnormal udder conditions from those associated with mastitogenic infections to others of a non-bacterial, i.e. unspecific nature. In general, the data suggest that further work on the dynamics of different health states is necessary, and that it may be advantageous also to use the small herd model described for determinations on representative populations of cows selected at random from large dairy herds otherwise unsuitable for investigations on daily and other dynamic changes of udder health.

Pathogenesis of subclinical bovine mastitis: persistence, deterioration and improvement of various subclinical conditions monitored by means of the International Dairy Federation/Bovine Serum Albumin criteria.

From this investigation, it is apparent that owing to the superior diagnostic differentiating of udder conditions by means of the IDF/BSA criteria, a range of detailed data has become available which facilitates an unprecedented insight in the dynamic balancing during normal lactation of several health states determinable at subclinical levels. The findings therefore from different points of view augment the corresponding results generated during the preceding investigation by means of the IDF criteria of acknowledged diagnostic limitations. In general, the data suggests that regardless of the diagnostic technique used for determinations during normal lactation on bovine udder conditions, udder health as such depends on 3 major determinants, namely intramammary epithelial integrity, intramammary somatic cellular defence and intramammary bacterial challenge. Subclinical septic mastitis, clearly, develops through different types of gradually escalating deteriorations of health states which depend on several pathways of pathogenetic development. These are subject on the one hand to the 3 major determinants of udder health, and on the other hand to the nature and magnitude of their single and combined challenging. The deterioration of udder health in some quarters is opposed by the improvement of that in others which in the light of data on the rather transient persistence of health states implies, that deterioration of condition is at all levels of its development opposed directly but, possibly, somewhat delayed by the cow's efforts at restoring udder health as such to its completely normal level.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of stress on udder health of dairy cows.

The appropriate literature has been reviewed for the purpose of defining the phenomenon of stress in lactating dairy cattle, establishing a baseline concept of lactation stress and emphasizing the most significant aspects of the natural mammary defence mechanisms. Data on the general adaptation syndrome (GAS) make it clear that stress is essentially the rate of wear and tear of the biological system affected by a stressor either eliciting stress of the organism as a whole or partly so. Owing to the variety of stressors which may affect the dairy cow at physiological and pathological levels, a definition of stress in the broad sense is indicated. This is essential from the point of view of the anti-homeostatic effects (metabolic and immunological) of lactation stress, aggravated by anti-homeostatic effects elicited by superimposed other types of stress (e.g. heat stress). The lactating cow, as a ruminant in a state of sustained stress, requires a special profile of hormonal mediators. In high yielding cows, for example, acute and sustained heat stress promotes increased activities of prolactin, progesterone and catecholamines. Compared with the mainly glycogenic/glycogenolytic metabolism of non-ruminant mammals, the lipogenic/lipolytic and glycogenic/glycogenolytic metabolism of the dairy cow depends on hormonal mediators which differ from those of the former not so much in their nature but in their magnitude and ratios. Stressors induce the development of GAS reactions in the dairy cow. These enable the cow to create and maintain homeostasis of its integrated 3 main physio-pathological systems and thus to endure the stressor(s). The cow's compensating adjustments to a stressor are therefore the effects of stress. This means that natural lactation is the effect of the lactation stress induced by the cow's progeny (i.e. the natural lactation stressor). Artificial lactation stressors (e.g. removal of milk by hand and machine) may affect the lactation stress in magnitude but not necessarily in nature. Likewise, a range of behavioural, physiological, lactational and lacteal changes related to other stressors are the effects of different types of stress. Lactation stress, like other types of stress, shows 3 stages of development, i.e., an overcompensating alarm phase (= lactogenesis), resistance phase (= galactopoiesis) and exhaustion phase (= regression). They facilitate adjustments of the cow's homeostasis from the level of involutional homeostasis (= no lactational activity) to that of lactational homeostasis. Like other tissues in a state of stress, the lactating mammary epithelium requires a greatly increased supply of glucose.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacteriological findings regarding the hygienic safety of poultry litter intended as an ingredient of feeds for ruminants.

An investigation of poultry litter intended for use in farm feeds showed that 0,37%, 0,49%, 0,25% and 12,3% of the 813 samples tested were contaminated with Clostridium spp., haemolytic Escherichia coli, Staphylococcus aureus and 21 different species of Salmonella. The findings clearly underline the hygienically dangerous nature of crude poultry litter. The practical implications of the results are briefly discussed, particularly in view of current regulations.

Plasminogen activator activity in secretions from clinically normal, mastitic, lactating and dried-off udders of dairy cows.

Using the composite fibrin plates method, plasminogen activator (PA) activity was found in secretions from clinically normal, mastitic, lactating and dried-off udders of dairy cows. The possible involvement of the fibrinolytic system in the physiology and pathology of the bovine mammary gland is discussed.

[Tissue reactions and residues in slaughter cattle after administration of long-acting oxytetracycline formulations]. / Binnespierse weefselreaksie en residue in slagbeeste na toediening van langwerkende oksitetrasiklien formulasies.

Samples from 40 slaughter cattle were investigated over 10 weeks for determining macroscopic tissue reaction following intramuscular administration of Liquamycin/LA (Pfizers) into the thigh and Terramycin/LA (Pfizers) G 333 into the neck respectively. Antibiotic residues in the lesions were assessed under ultra violet light and by microbiological means. Antibiotic residues were still detected after 7 weeks in the thigh and 5 weeks in the neck. One week old lesions in the thigh consisted mainly of a local necrotic centre, up to 120 mm in diameter, with a haemorrhagic zone and surrounded by oedema and petechia in adjacent muscle. This was gradually replaced by mainly fibrotic tissue as the weeks went by and eventually by local abscess formation still apparent 10 weeks later. Much the same pattern was seen in the neck but of milder degree and shorter duration - 6 weeks. Alarming is the fact that only in one case out of 40, a lesion could be detected in the carcass on the slaughter line, the others could have passed fit for human consumption in an abattoir. Because the manufacturer suggests a 28 day withholding period before slaughter and after administration of the product, results of this investigation raise several questions on format, completeness and contents of such directions for use and their implications for meat inspection, meat hygiene and public health.

Electron microscopic observations on the luminal surface of teat cup liners of milking machines used under South African conditions.

An investigation undertaken with the aid of scanning electron microscopy (SEM) on new and used teat cup liners revealed the generally poor quality of luminal surfaces. Even those of the brand-new distributor controls showed significant faults in the evenness and continuity of the liner surface. A hundred and 500 milkings apparently tend to aggravate faults like cracks, pores, grooves and pits, because of the general brittleness of some of the teat cup liners. The poor quality of the liners investigated raises various questions about the method of distribution of teat cup liners and serious concern about the role they play in predisposing bovine udders to mastitogenic infections, spreading mastitis, affecting the production and quality of milk, increasing the cost of milk production and reducing profits of dairy farming.

Fluctuations in the glucose level of cow's milk from normal and subclinically diseased udders.

Individual quarter samples from some 19 cows on average were investigated monthly over 12 months for determining the udder health status of cows and the glucose concentrations of foremilk and strippings. Foremilk showed a mean 0,1311 mM concentration of glucose which remained fairly stable during the period of investigation and lactation. A fluctuating mean value of 0,2037 mM was determined in strippings in which glucose levels were consistently and appreciably higher than those of foremilk. Foremilk from completely normal quarters and others affected by non-specific cellular reaction, relevant or irrelevant teat canal infection and aseptic or septic subclinical mastitis, showed mean glucose concentrations of 0,1410; 0,1392; 0,1337; 0,1417; 0,1262 and 0,1248 mM, respectively. Strippings from the same quarters showed corresponding values of 0,2056; 0,2861; 0,2100; 0,1733; 0,1661 and 0,1617 mM glucose.

Levels of glucose, serum albumin and somatic cells before and during early stages of acute clinical mastitis artificially induced in cows by means of human strains of group-B streptococci (GBS) administered intracisternally.

The investigation was performed on 3 cows, sampled repeatedly before and during the initial 48 h of artificially induced, acute, clinical mastitis. The results of the investigation both augment and support those of earlier work on the levels and significant correlations of glucose, serum albumin and somatic cells in normal and abnormal secretions monitored before and after the usual milking of healthy lactating cows had been suspended. During acute mastitis, udder secretions from artificially infected quarters showed highly significant escalations of somatic cell counts which coincided with equally significant increases of a high and intermediate level of serum albumin values in both the infected and non-infected quarters. Corresponding glucose values fluctuated from 0,07-0, 22 and 0,18-0, 32 mM in the former and latter quarters respectively. The selective and elevated transfer of serum albumin in otherwise unaffected quarters of acutely mastitic udders suggests rather specific collateral vascular and epithelial changes of unknown nature and magnitude. The data indicate that marked fluctuations of glucose may occur within and between quarters of individual and different cows respectively. Such variations could significantly affect phagocytosis and killing of bacteria challenging the intramammary leucocytic udder barrier before and particularly during manifestation of mastitis. Hence, udder health, although dependent on specific natural defence mechanisms such as the leucocytes and related systems in milk, may depend even more significantly on the supplies of glucose to and within the bovine mammary gland.

Experimental induction of bovine mastitis with human strains of group B streptococci (streptococcus agalactiae).

Intrapapillary deposition of 5-30 CFU of 6 separate human strains of Group B streptococci into 7 lactating quarters of 6 cows resulted in clinical mastitis in all. Identical streptococci were subsequently recovered from 6 of the affected quarters. Details of milk somatic cell counts, bacterial isolations and clinical findings are tabulated. The role of GBS in human medicine and the implications of proof that the bovine udder is susceptible to small numbers of GBS from human sources, are discussed.

Therapy of bovine mastitis: the intramammary tissue compatibility of mastitis remedies administered intracisternally to cows.

Eight different mastitis remedies were administered intracisternally on a rotational basis to the 48 quarters of 12 mastitis negative cows. The resulting intramammary reactions were monitored by determining the Somatic Cell Count (SCC) and Bovine Serum Albumin (BSA) levels in milk. The reactions observed indicate that the intramammary cellular reactions frequently elicited by the local treatments in the treated and sometimes even in the untreated quarters of the treated udders are not necessarily inflammatory in nature. Evaluation of the intramammary tissue compatibility of a mastitis remedy mainly in terms of SCC values therefore seems unreliable. Moreover, it may do injustice to a product unless the SCC values are augmented by BSA or other determinations providing a more accurate indication of truly mastitic reactions. The investigation also implies that the patterns of cellular reactions related to individual mastitis remedies require further elucidation before they can be used as indications of an advantageous or disadvantageous intramammary tissue compatibility of a product. Intramammary tissue compatibility, as such, of mastitis remedies and comparable agents requires definition. It seems more expedient, however, that such a definition and the necessary standardization of mastitis remedies in terms of their intramammary tissue compatibility be attempted by the International Dairy Federation (IDF).