Issues and special features of animal health research

In the rapidly changing context of research on animal health, INRA launched a collective discussion on the challenges facing the field, its distinguishing features, and synergies with biomedical research. As has been declared forcibly by the heads of WHO, FAO and OIE, the challenges facing animal health, beyond diseases transmissible to humans, are critically important and involve food security, agriculture economics, and the ensemble of economic activities associated with agriculture. There are in addition issues related to public health (zoonoses, xenobiotics, antimicrobial resistance), the environment, and animal welfare.Animal health research is distinguished by particular methodologies and scientific questions that stem from the specific biological features of domestic species and from animal husbandry practices. It generally does not explore the same scientific questions as research on human biology, even when the same pathogens are being studied, and the discipline is rooted in a very specific agricultural and economic context.Generic and methodological synergies nevertheless exist with biomedical research, particularly with regard to tools and biological models. Certain domestic species furthermore present more functional similarities with humans than laboratory rodents.The singularity of animal health research in relation to biomedical research should be taken into account in the organization, evaluation, and funding of the field through a policy that clearly recognizes the specific issues at stake. At the same time, the One Health approach should facilitate closer collaboration between biomedical and animal health research at the level of research teams and programmes.

Influence of Grass-Based Diets on Milk Fatty Acid Composition and Milk Lipolytic System in Tarentaise and Montbéliarde Cow Breeds

Two experiments were conducted to evaluate the effects of nature of forage on fatty acid composition and lipolytic system in cow milk to increase the nutritional quality of dairy products. Each experiment was divided into a 4-wk preexperimental and 6- or 8-wk experimental period. During the 2 preexperimental periods, 56 midlactating Montbéliarde or Tarentaise cows received a diet based on corn silage. Subsequently, in Experiment 1,40 cows were allocated into 5 groups (4 Montbéliarde and 4 Tarentaise cows per group) and assigned to dietary treatments: corn silage (87% of dry matter intake), grass silage (86%), ryegrass hay (90%), mountain natural grassland hay (87%), or a diet rich in concentrate (CONC, 65/35% concentrate/hay). In Experiment 2, 16 cows divided into 2 groups were fed during 3 or 6 wk mountain natural pasture (100%) or mountain natural grassland hay (87%). Principal component analysis was applied to describe the relationships among dairy performances, milk fatty acids (FA), and lipolytic system. The milk 18:0, cis-9-18:1, trans-11-18:1, and cis-9, trans-11-18:2 percentages were closely associated with 3-wk mountain natural pasture diet, whereas short- and medium-chain (mostly saturated) FA were associated with the CONC diet. Tarentaise milk fat contained a lower proportion (-3 to 4 g/100 g) of 16:0 and higher proportions of stearic acid and fewer markedly polyunsaturated FA than Montbéliarde milk fat. Milk lipolysis was lowest for CONC and corn silage groups. Milk from Tarentaise cows presented lower initial free FA and postmilking lipolysis. Diets given to cows, especially young grass, modified the milk content of FA with a putative nutritional effect on human health.

An individual modelling tool for within and between lactation consecutive cases of clinical mastitis in the dairy cow: an approach based on a survival model

Clinical mastitis in dairy cows has for many years been the subject of numerous epidemiological surveys to determine the main risk factors. In most cases this data has been analysed using a standard Poisson model without taking into consideration possible dependence between consecutive pathological events. These analyses have brought to light a great many potential risk factors without making it possible to clarify a certain amount of confusion surrounding the effects. The extension of an individual within a lactation model, considering dependence between clinical cases of mastitis within lactation so as to take into account inter-lactation dependence (which has already been published) is presented in the form of mixed distributions within the same survival model framework. By introducing new parameters, infection rate at calving and the identification of a higher exogenous infection rate indoors than at pasture, it is possible to take into consideration what had previously appeared to be a lactation stage factor, a calving month factor or even part of a parity factor. By considering these two types of dependence within the same model, it appears to be possible to obtain a simpler model in terms of the factors to be taken into account, and one that is based on generally acknowledged and easily understandable biological considerations. Lastly, a possible way of extending the model is to consider the dry period before calving and this is presented. This would make it possible to envisage developing a complete model of the animal's lifetime in the not-too-distant future. It is still necessary, however, to determine the farming system factors in the general sense of the term, which specifically affect one or the other of the different model parameters, before one can draw conclusions as to the potential extension of this type of model. A national survey is currently being carried out on approximately 600 French breeding farms that will help meet this last objective.

Effect of genetic potential and level of feeding on milk protein composition

Two groups of 15 multiparous cows in mid-lactation were used in a Latin square design experiment with 4-week experimental periods. The genetic milk protein concentration level was high in the first group and low in the second. Each group of cows was given in a random order three feeding levels that covered 85, 100 and 115% of energy requirements and 90, 110 and 125% of nitrogen requirements, respeetively. In both groups, increasing level of feeding induced a significant increase in milk yield (+ 2.4 kg/d between lowest and highest levels) and in protein concentration (+ 1.7 g/kg). The proportion of paracasein in total proteins was not altered by either genetics or nutrition. The proportion of casein in total proteins was slightly increased by 0.5 percentage points (P < 0.05) with the intermediate level of feeding. Plasmin and plasminogen activities were not significantly modified by the genetic milk concentration level. Plasmin activity significantly increased with nutrient supplementation, but only in animals of low genetic potential (+ 21% between low and high levels, P < 0.01). Casein composition was not significantly altered by the genetics or level of nutrition. Over the whole range of individual measurements taken (n = 90), the relationships between casein or paracasein and total protein concentrations were linear and very narrow (R2 = 0.92 and 0.95, respectively). The proportion of casein or paracasein in total proteins significantly decreased as plasmin activity increased.

An individual modelling tool for consecutive clinical mastitis during the same lactation in dairy cows: a method based on a survival model

The high number of clinical mastitis recurring within the same lactation in dairy cows constitutes one of the factors of overdispersion in standard Poisson models. Our method, based on biological parameters, i.e., recurrence hazard in relation to udder exogenous infection (Rex) or recurrence hazard and rate in relation to endogenous infection (Ren), produced a model capable of integrating a possible change of state in the udder after clinical mastitis. This model was based on a study of the time intervals between successive clinical episodes, both types of risk being considered in the form of a distribution mixture in the survival model. The modelling tool allowed to determine the factors that specifically act on either one of the potential risks and estimated the distribution of the number of clinical mastitis per lactation, as well as the distribution of when mastitis occurs. Estimation results obtained by this method in an experimental herd were compared with those from more classical models with or without random individual effects. The distribution of the number of mastitis per lactation estimated by our method was well-fitted to the data and the method identified variation factors which were relatively standard in this type of study: lactation number, lactation stage and calving month. Prediction results obtained in another experimental herd with more recent data without parameter re-estimation demonstrated the adequacy of the model in fitting observed data. This modelling method based on biological parameters in a mixture of survival distributions was interesting to model clinical mastitis recurring within the same lactation. However in the future it will also be important to integrate the possible relationship between successive lactations and to apply this model to other types of farming systems.

Factors contributing to variation in the proportion of casein in cows' milk true protein: a review of recent INRA experiments

The aim of this study was to identify and rank the various factors, in particular those involving feeding, that affect the proportion of caseins in milk true protein. Twenty-nine feeding trials involving 821 lactations were assessed, and lactoprotein genetic variants were known for 551 of these. The main factor affecting the casein: protein ratio was the genetic variant of beta-lactoglobulin: once corrected for other factors, the milk of BB type animals had a ratio nearly 30 g/kg total protein higher than AA animals. kappa-Casein variant B also had a positive effect (+12 g/kg in favour of BB relative to AA animals). Except in the last weeks of pregnancy and the first weeks of lactation, the casein: protein ratio varied little during lactation. It was significantly reduced when milk cell count exceeded 200,000 cells/ml, even in the absence of clinical mastitis. It also decreased slightly with parity. Among the various dietary factors studied (level and type of nitrogen and energy supplies, forage type and preservation method), none had any significant effect on the milk casein: protein ratio, except in drastic dietary situations. That ratio increased very slightly in parallel with the animals' milk yield and milk protein content. In practice, measuring the milk protein content in animals free from clinical mastitis remains a very precise predictor of casein content, accounting for 93% of its variation.

Effect of lactation stage on the cheesemaking properties of milk and the quality of Saint-Nectaire-type cheese

Two groups of eight multiparous cows with different calving periods (November or February) were managed in the same way during lactation. During four 4 week experimental periods distributed over 12 months, the cows were fed on a diet composed of hay and concentrate (70:30) in a restricted and controlled amount which varied according to their lactation stage, so as to cover the animals' requirements correctly. The animals' average lactation stage varied according to period from 26 to 298 d. Milk from each group was processed on two occasions during each period to make Saint-Nectaire-type cheese; the cheesemaking conditions were the same throughout. Lactation stage had an important effect on milk fat, protein and calcium contents but not on the casein: protein ratio or phosphorus content. The milk pH and the urea content were higher in late lactation. The calcium concentration of milk was higher in late lactation but the soluble fraction was higher in early lactation. Despite higher protein contents, the maximal firmness of the coagulum of late-lactation milk was not different from that of early or mid-lactation milks. pH was higher in cheeses from late-lactation milks compared with those from early and mid-lactation milks. Cheeses from early lactation milks were more yellow than the others and had a lower dry matter fat content. In sensory analysis the odour of cheeses from early and late-lactation milks was less pleasant than that of those from mid-lactation milks. Cheeses from late-lactation milks were more melting and less firm than those from early or mid-lactation milks. Their taste was more intense and more persistent. At tasting, they were less appreciated than the others. These differences were linked to increased proteolysis in the cheeses made with late-lactation milks.

Effect of extreme walking conditions for dairy cows on milk yield, chemical composition, and somatic cell count

Thirty-two cows (16 Montbeliardes and 16 Tarentaises) in midlactation were used in an experiment utilizing a 2 x 2 factorial arrangement of treatments. Throughout the trial, cows received first-cutting cocksfoot hay for ad libitum intake supplemented with a fixed amount of concentrate that was individually adapted to the milk yield of each cow. During a 23-d experimental period, one group of cows walked 9.6 km/d; the other group of cows remained in the barn. Cows that walked daily ate less hay (-1.3 and -2.1 kg/d of dry matter for Tarentaise and Montbeliarde cows, respectively) and yielded less milk (-1.7 and -2.5 kg/d for Tarentaise and Montbeliarde cows, respectively) than did cows that did not walk daily. A residual effect of walking on milk yield was observed during the 10 d following the experimental period. For both breeds, fat content and, to a lesser extent, protein content were higher (+6.4 and +1.0 g/kg, respectively) for cows that walked. Somatic cell count was also higher for cows that walked (+115,000 cells/ml). This difference was more marked in cows that were initially infected by a minor or major pathogen (+185,000 cells/ml) than in uninfected cows (+47,000 cells/ml) and on the 1st d of walking when walking was linked to increases in pH, bovine serum albumin, and immunoglobulin G1 contents of milk (+0.08 unit, +0.16 g/L, and +0.19 g/L, respectively). Throughout the experimental period, walking induced a rise in body temperature (+1 degree C) and in plasma nonesterified fatty acids (+0.63 mM/L). On the 1st d of walking, plasma glucose, lactic acid, and cortisol contents were significantly higher for cows that walked (+0.25 g/L, +0.64 g/L, and +28.8 ng/ml, respectively).

Comparison of the National Research Council energy system for lactating cows with four European systems

The structure, prediction steps, and accuracy of the US (NRC), United Kingdom (ARC), Dutch (VEM), French (UFL), and German (NEL) systems for feeding high producing cows were compared. Simulations were made using 15 feeds ranging from hays to cereals. Agreement was satisfactory among European systems for the prediction of metabolizable energy and net energy for lactation (NEL) contents of feeds and the quantities of feeds in balanced diets necessary to meet the energy requirements of lactating cows. The metabolizable energy and NEL contents of feeds seemed overestimated by the US system compared with results using the European systems, and the ratio of NEL to total digestible nutrients was almost constant, unlike the other systems. Estimating the NEL content of feeds for a level three times maintenance intake allowed satisfactory rationing for the production of 20 to 25 kg of fat-corrected milk/d. However, feed allowances seemed underestimated for higher milk production, especially with diets based on hay, probably because of the overestimation of feed NEL content, the underestimation of level of feeding, and the effects associated with feeding levels > 3 and high concentrate diets.

Effect of forage conservation (hay or silage) and cow breed on the coagulation properties of milks and on the characteristics of ripened cheeses

Forty-two multiparous dairy cows of three different breeds (Holstein, Montbéliarde and Tarentaise) were fed on the same type of forage (natural grassland) preserved in the form of either hay (H) or silage (GS), according to a changeover design (two 4 week periods). The proportion of concentrate in the diet and the energy and nitrogen contents were similar in both treatments. The milk produced by these cows was used for the manufacture of Saint-Nectaire type cheeses, under controlled and identical cheesemaking technological conditions. More cheese was produced with the H treatment milk. The cheeses made with the GS treatment milk were more yellow and tended to be more bitter. The other chemical and sensory characteristics did not differ much between the two treatments. Of the 51 volatile compounds identified, four were in significantly higher proportion in the GS than in the H cheeses. Cheeses produced from Tarentaise cows' milk were more yellow and their pH was higher than those made with the milk of Holstein or Montbéliarde cows. The cheeses from Montbéliarde and Tarentaise cows' milk were firmer, more melting and tastier than those made with the milk of Holstein cows. Although some trends were apparent, there were no significant differences in cheese volatile compounds for different breeds.

Effect of foot lesions on milk production by dairy cows

Individual curves for milk production of 428 cows affected by foot lesions were compared with control curves drawn from data of healthy lactating cows. First, differences were classified into patterns of milk loss, and their distribution was analyzed among the patterns with regard to breed, season, parity, stage of lactation, and milk production. Then, individual milk losses were estimated and analyzed according to the same factors. During early lactation, as during mid to late lactation, no marked modifications of the lactation curves occurred for about one-half of the cases. In 25% of the cases, milk production was affected for an expanded period (medians were 17 wk for early lactation and 12 wk for mid to late lactation). Corresponding median milk losses were 440 and 270 kg, respectively. Summer foot lesions were more severe than winter lesions, regardless of stage of lactation. Milk production at foot lesion onset was a determining factor of the amount and pattern of milk loss only for cases occurring during mid to late lactation.

Predictive model of mastitis occurrence in the dairy cow

Mastitis occurrence within a lactation and times of mastitis onset were studied for about 1000 cows. The number of mastitis cases within a lactation was modeled through overdispersed Poisson regression with individual and herd covariants. The results emphasized the role of the herd variable. Increased production potential increased the number of cases per lactation at a rate of 1.4/10 kg. Calving month also played an important role. The incidence of mastitis was greater when calving took place in early autumn or winter, which led to an expanded housing period. The interval from calving to the first case of mastitis and the intervals between successive cases were modeled for cases occurring during lactation through random selections from fitted gamma distributions, these distributions being truncated to consider the lactation length. The results of both steps can be used to simulate mastitis occurrence in different conditions.

Effects of feeding practices on milk fat concentration for dairy cows

Thirty-seven dairy farms, using high producing (7500 kg/yr per cow on average) Montbéliarde cows that were fed hay-based rations, were included in a detailed survey involving the structure of the farm and the herd, the quality of forage, the feeding practices in winter and summer, and genetic characteristics of the cows (breeding values and herd effects). These data were used to analyze variation in milk fat concentration among farms, particularly variation linked to environmental factors, as assessed by the herd effect. When farms were ranked according to herd effect of fat concentration, farms with the highest herd effects fed concentrate to cows in rolled form, distributed forage before or with the concentrate, and provided hay in the trough in summer. The effects of such practices on digestive phenomena in the rumen are discussed. This study supported the use of herd effects to identify factors related to variation in dairy cow performance.

Modeling the impact of mastitis on milk production by dairy cows

Individual milk production curves of 542 cows with 722 cases of mastitis were compared with control curves drawn from healthy lactating cows. First, differences were classified into patterns of milk loss, and their distribution was analyzed among the patterns with regard to breed, season, lactation number, stage of lactation, and milk production. Then, individual milk losses were estimated and analyzed according to the same factors. In early lactation, almost 7% of mastitis cases necessitated culling or drying off. For 36% of the cases of mastitis occurring in early lactation, milk production was affected for an extended period, and the milk loss induced was 911 kg on average over the entire lactation. Fifty-two percent of the mastitis cases occurring after lactation peak was not accompanied by marked modifications of the lactation curves. For 38% of cases of mastitis occurring from mid to late lactation, milk production was affected for an extended period. When milk production was the most affected (26% of total cases), the average loss was 850 kg over the entire lactation. For cases in early or mid to late lactation, the production at mastitis onset was a determining factor of the amount and pattern of milk production loss induced. Results were applied in a simulation over two simulated groups of cows.

Effect of nature of forage on spontaneous lipolysis in milk from cows in late lactation

Levels of free fatty acids (FFA) were determined in milk from cows after 7 months of lactation and 4 months of pregnancy immediately after milking (initial FFA) and after 22 h storage at 4 degrees C (FFA-22). During the pre-experimental period, cows were at pasture. When housed indoors (experimental period) they were fed hay or grass silage for 3 weeks. Then all cows received grass silage for 3 weeks (post-experimental period). Feeding hay did not increase FFA-22 content in milk compared with pasture, but grass silage feeding enhanced FFA-22 content in milk compared with pasture (+130%) or hay (+93%). Increased lipolysis with grass silage was not due to underfeeding of the cows because grass silage and hay were both of high nutritive value. As pasture, hay and grass silage were of the same type (native mountain grassland), the high level of lipolysis occurring with grass silage probably resulted from the method of forage conservation.