Au cours des dernières années, la production laitière a été en croissance constante en raison de plusieurs facteurs tels que l’utilisation d’individus plus performants. L’augmentation du nombre d’enregistrements de vaches de la race Jersey confirme l’intérêt économique des producteurs pour cette race en raison de la production élevée de protéines et de gras du lait par rapport aux autres races. Cependant, les embryons de la race Jersey ont montré des difficultés dans le processus de cryopréservation lequel peut aider à une commercialisation massive de matériel génétique de cette race. Il a été observé que la race Jersey présente un faible taux de gestation lors du transfert des embryons après la cryopréservation en comparaison aux embryons de la race Holstein. Nous proposons que cette différence entre les deux races bovines soit due à des caractéristiques spécifiques de la race au niveau du phénotype et du génome. Dans un premier temps, les résultats de cette étude ont mis en évidence des différences au niveau du phénotype et du profil lipidique et génomique de l’embryon Jersey. Celui-ci est caractérisé par un contenu de lipides associé à une faible fonction mitochondriale laquelle déterminera le faible succès à la cryopréservation. Par la suite, nous avons évalué au niveau du phénotype et de la génomique, l’utilisation de la L-carnitine dans le milieu de culture in vitro afin de compenser cette caractéristique des embryons de la race Jersey. Cette étude sur la supplémentation de L-carnitine a permis d'identifier une faible réponse chez les embryons Jersey qui est expliqué par le faible effet de la L-carnitine sur l’activité mitochondriale. Afin de définir l’impact de la fonction mitochondriale sur la viabilité de l’embryon lors de nos études, nous avons mis au point une méthode pour compenser la dysfonction mitochondriale sur le développement embryonnaire chez le bovin. Enfin, l’application de la vitamine K2 dans le milieu de culture in vitro montre un impact positif sur la fonction mitochondriale qui a mené à des changements phénotypiques et génomiques chez les embryons bovins. En conclusion, ce projet a permis de caractériser et d’identifier la race comme un facteur qui limite la cryopréservation des embryons et peut influencer sur le métabolisme embryonnaire au niveau des mitochondries. La fonction mitochondriale est une caractéristique importante sur le développement embryonnaire bovin qui peut ouvrir sur des perspectives d’amélioration de la viabilité embryonnaire. / For the past decades, milk production has been increasing due to several factors such as the use of high genetic merit individuals. In this regard, Jersey cows have been of interest for the producers because of high protein and fat indexes in their milk compared to others breeds. However, there are some challenges associated with Jersey particularly poor results using embryo cryopreservation which could help to massively commercialize the genetic material of this breed. It was observed that the Jersey breed have low pregnancy rates following embryo transfer of cryopreserved Jersey embryos compared to the Holstein breed. Here, we hypothesised that those differences between these two breeds in embryo cryopreservation are due to specific phenotypic and genotypic characteristics at the embryo level. Initially, the results of this study showed differences on the phenotype, lipid profile and genomic differences of Jersey embryo characterized by the higher lipid droplets content associated with low mitochondrial function which will determine the low success with cryopreservation. Subsequently, we assessed the phenotype and genotype of embryos using L-carnitine supplementation in the in vitro embryo culture medium in order to compensate those characteristics in Jersey embryos. The results of this study revealed moderate beneficial effects of L-carnitine supplementation in Jersey embryos through low effect of L-carnitine on mitochondrial activity. To define the impact of mitochondrial function on the embryo viability during our study, we developed a method to compensate the mitochondrial dysfunction during early embryo development in bovine model. To do that, Vitamin K2 supplementation in the in vitro embryo culture medium was applied which showed a positive effect on the mitochondrial function leading to satisfactory phenotypic and genotypic changes in the embryos. In conclusion, this study resulted in identification and characterization of the cattle breeds effects as a critical factor on cryopreservation performance and embryonic metabolism of the mitochondria. Our results emphasized that mitochondrial function is an important feature of embryonic development in cattle, which can provide opportunities to improve embryonic viability.

Telomeres form protective caps at the ends of linear chromosomes. They consist of repetitive DNA nucleotides and associated proteins of the shelterin complex. In vitro telomeres become shorter during cell division and when a critical shortness is reached they trigger a DNA damage response that leads to replicative senescence or apoptosis. Telomere shortening is a recognised hallmark of cellular ageing and seems to be also associated with organismal ageing. Telomere length (TL) and the rate of shortening vary across individuals and several studies have found that short telomeres and fast telomere depletion are associated with poor survival and early onset of age related diseases. However, longitudinal studies are needed to better understand the relationship of TL and TL dynamics with longevity measures. Relevant studies on livestock species are largely missing from the literature. In the dairy industry, farmers are forced to cull a considerable percentage of their heifers and cows at a young age due to fertility problems or diseases. As a consequence many replacement heifers have to be reared to maintain a specific herd size. This results in increased costs, consumption of resources, and damage to the environment. Breeding for an improved productive lifespan is difficult because longevity measures are recorded at the end of life and are known to have a low heritability. Therefore, the expected genetic improvement is generally slow, but could be considerably accelerated if an early life heritable biomarker was identified that is predictive of productive lifespan and could be used for animal selection. The question is if TL could be used as such a biomarker. The objectives of this thesis were to 1) develop robust methods to measure average relative leukocyte TL (RLTL) in cattle, 2) examine RLTL dynamics with age at a population as well as at an individual level, 3) estimate genetic parameters and 4) assess the association of RLTL and RLTL dynamics with productive lifespan. A quantitative polymerase chain reaction (qPCR) based assay developed for human studies was adapted to cattle and delivered robust results (repeatability > 80%, coefficient of variation=0.05). Different DNA extraction methods were tested for their effect on RLTL measurements and it was demonstrated that fast silica based DNA extraction methods are suitable for telomere projects which can improve the sample throughput and enable large-scale projects. Subsequently, RLTL in 1328 whole blood samples of 308 Holstein Friesian dairy cows and additionally in 284 whole blood samples of 38 female calves was measured. Repeatability and random regression models were used for the statistical analysis of telomere data. RLTL decreased considerably within the first year of life, but remained relatively stable afterwards at population level. Animals varied significantly in their amount and direction of telomere change. The genetic correlation between consecutive measurements in the same individual weakened with increasing sample interval from r=1 to r=0.69 which indicates that TL in the beginning of life might be under a different genetic control than TL later in life. For the first time in a livestock species we calculated heritability estimates for RLTL which were high (0.32-0.38) and remained constant over life. Long telomeres at birth were not predictive of better productive lifespan. However, animals with long RLTL at the ages of one and five years had a survival advantage. Also, animals that showed less average RLTL attrition over their lives remained in production for longer. TL dynamics differed among individuals and a considerable subset of individuals demonstrated telomere lengthening between consecutive measurements. On average, telomeres tend to shorten early in life and then remain relatively constant. While TL is a heritable trait throughout lifetime, telomere change is not heritable. Short TL at specific ages and telomere attrition over life were associated with poorer productive lifespan.

Les quantités importantes d’aliments consommés et la proportion élevée de concentrés devant être incorporée aux rations pour soutenir les besoins des vaches hautes-productrices induisent bien souvent des perturbations de l’équilibre ruminal. Ces changements se répercutent sur la biohydrogénation ruminale des acides gras insaturés de la ration, qui entraînent à leur tour une inhibition de la synthèse des matières grasses par le tissu mammaire. Plusieurs stratégies nutritionnelles ont été mises de l’avant pour mieux tirer profit des rations riches en concentrés. Récemment, des études ont montré la capacité du carbonate de potassium (K2CO3) à prévenir la chute de matière grasse associée à des régimes à forte teneur en concentrés. Toutefois, on comprend encore mal l’origine de ces effets. Les travaux de cette thèse visaient donc, dans un premier temps, à départager si les effets observés en ajoutant du K2CO3 aux rations des vaches laitières étaient dus à une augmentation de la différence alimentaire cation anion (DACA), de la teneur en ions K+ ou encore du pouvoir tampon de la ration. Un autre objectif de cette thèse était de déterminer les effets d’un ajout de K2CO3 sur la synthèse de matières grasses du lait lorsque des sources d’acides gras polyinsaturés (AGPI) sont introduites dans l’alimentation de la vache laitière. Enfin, les travaux cherchaient à déterminer l’effet d’un ajout de K2CO3 à la ration sur les populations microbiennes du rumen, particulièrement celles reconnues pour être impliquées dans le métabolisme lipidique. Pour répondre à ces questions, une première expérience a été mise en place, où 35 vaches Holstein en début de lactation ont été distribuées selon un plan en blocs complets aléatoires. La période expérimentale était de 28 jours et précédée d’une collecte de 5 jours (covariable). Les cinq rations expérimentales étaient constituées en vue de départager les effets du K2CO3 (témoin vs K2CO3), de la capacité tampon (K2CO3 vs KHCO3), de la DACA (K2CO3 vs KCl) et du type de cations (K2CO3 vs Na2CO3). Dans cette expérience, et contrairement aux études antérieures, l’ajout de K2CO3 aux rations riches en concentrés n’a pas permis d’augmenter la production de lait ou la matière grasse des vaches en début de lactation. De plus, les résultats suggèrent qu’une augmentation du K alimentaire via l’ajout de K2CO3 pourrait induire un déséquilibre ionique cellulaire qui pourrait affecter le transport des nutriments dans les cellules épithéliales mammaires et ainsi affecter la synthèse du lait. Une seconde expérience a ensuite été menée, où 28 vaches Holstein en début de lactation ont été distribuées selon un plan en blocs complets aléatoires. La période expérimentale était également de 28 jours et précédée d’une collecte de 5 jours (covariable). Les quatre rations expérimentales étaient offertes selon un arrangement factoriel 2 × 2, soit 0 ou 1,5 % K2CO3 et 0 ou 2 % d’huile de soya, comme source d’acides gras polyinsaturés. Les résultats ont montré que l’ajout de K2CO3 peut entraîner une augmentation de la sécrétion des matières grasses laitières chez des animaux recevant de grandes quantités de concentrés. Cette augmentation dépend toutefois de la teneur en lipides de la ration. Cette étude a également permis de mettre en lumière une relation positive entre la production laitière et la teneur en chlore du lait. Lors de cette seconde expérience, des échantillons de contenu ruminal ont également été prélevés chez 24 vaches (n = 6) afin d’étudier l’impact d’un supplément de K2CO3 sur l’environnement et les populations microbiennes du rumen des vaches en début de lactation recevant des rations riches en concentrés avec ou sans huile de soya. Ces travaux ont permis de comprendre que le K2CO3 et l’huile de soya ont des effets distincts sur les populations microbiennes. L’ajout de K2CO3 a stimulé la croissance de Butyrivibrio hungatei, bactérie productrice de 18:1 trans-11. L’ajout d’huile de soya a, quant à elle, réduit la présence de Butyrivibrio/Pseudobutyrivibrio, un groupe de bactéries productrices de 18:1 trans-11, de Fibrobacter succinogenes, une bactérie fibrolytique, de Butyrivibrio proteoclasticus, une bactérie productrice de 18:0, et de Streptococcus bovis, une bactérie amylolytique Les travaux regroupés dans cette thèse apportent un éclairage nouveau sur le rôle de la supplémentation minérale sur les performances de production des vaches laitières / Negative energy balance typically appears in early-lactation dairy cows as a consequence of a reduction of dry matter intake, as well as of an increase in energy demand for milk production. To compensate this energy deficit, cows are fed with high-concentrate diets. However, highly fermentable carbohydrates introduced in diets can result in a decreased milk fat synthesis. Previous studies reported that addition of potassium carbonate (K2CO3) to high-concentrate diets helps to maintain milk fat, although the mechanism is yet to be established. Consequently, the objective of the current thesis was, firstly, to investigate the effects of dietary cation-anion difference (DCAD), cation source, and buffering ability of the mineral supplement on rumen biohydrogenation of fatty acids (FA) and production performance of dairy cows fed a high-concentrate diet. Secondly, this thesis aimed at evaluating the effect of K2CO3 on production performance, biohydrogenation of fatty acids, and mineral composition of milk in early-lactation dairy cows fed a high-concentrate diet with or without soybean oil (SBO), as a source of polyunsaturated fatty acid. A third objective of this thesis was to evaluate the effect of K2CO3 supplementation, in diets containing soybean oil (SBO) on rumen microbial population associated with lipid metabolism. Consequently, a first experiment was set up, where 35 early-lactation Holstein cows were used in a randomized complete block design with 33-d periods, including a 5-d pretreatment collection period used as a covariate. Five different dietary treatments were used to assess the effects of K2CO3 (control vs. K2CO3), buffering ability (K2CO3 vs. KHCO3), DCAD (K2CO3 vs. KCl), and cation type (K2CO3 vs. Na2CO3). In this experiment, and as opposed to previous studies, supplementing high-concentrate diets with K2CO3 did not increase milk or milk fat yield in early-lactation cows. Also, results suggested that increasing dietary K through the addition of K2CO3 could lead to a disequilibrium in cellular ion composition that can impair nutrient transport into and out of the mammary epithelial cells, and consequently affect milk synthesis. A second experiment was conducted where 28 ruminally fistulated Holstein cows were used in a randomized complete block design. The experiment lasted 33 d, including a 5-d pre-treatment collection period used as a covariate. Experimental treatments were arranged as a 2 × 2 factorial with 0 or 1.5% K2CO3 and with 0 or 2% SBO. Results of this experiment revealed that potential effect of K2CO3 on milk fat synthesis is dependent on the levels of dietary polyunsaturated FA. Moreover, a positive relation was established between milk Cl concentration and milk yield, suggesting that the equilibrium of this ion is linked to the efficiency of lactogenesis Finally, rumen samples were collected from the rumen of 24 cows enrolled in the second experiment (n = 6) to assess treatment effects on rumen microbial population associated with lipid metabolism. Feeding K2CO3 and SBO had distinct effects on rumen bacteria. Dietary K2CO3 stimulated the growth of Butyrivibrio hungatei, a bacterium recognized to produce trans-11-18:1 during biohydrogenation. Conversely, feeding SBO reduced the growth of Butyrivibrio/Pseudobutyrivibrio bacterium group, known to produce trans-11-18:1, of Fibrobacter succinogenes, a fibrolytic bacterium, of Butyrivibrio proteoclasticus, a bacterium involved in 18:0 production, and of Streptococcus bovis, an amylolytic bacterium. Overall, the experiments conducted and reported in this thesis provide new insights on the impact of mineral supplementation on milk performance in dairy cows.

<p>Urea kao deo neproteinske frakcije azota mleka, predstavlja krajnji produkt metabolizma proteina u predželucima preživara. Portalnim krvotokom toksični amonijak, nastao mikrobiolo&scaron;kom razgradnjom proteina u rumenu dolazi do jetre gde se transformi&scaron;e u ureu, koja kasnije krvotokom dospeva u mleko. Ishrana, odnosno sadržaj sirovih proteina u obroku ima najveći uticaj na sadržaj uree u mleku. Sadržaj uree sve vi&scaron;e se koristi kao parametar pomoću kojeg je moguće pratiti unos sirovih proteina i energije obrokom kod mlečnih krava. Pored ishrane na sadržaj uree u mleku utiču i drugi faktori, kao &scaron;to su sezona, prinos mleka, stadijum laktacije, paritet i dr.<br />Plodnost krava je veoma važna osobina mlečnih goveda na koju utiče veliki broj faktora. Dosada&scaron;nja istraživanja u ovoj oblasti ukazuju na moguću vezu između plodnosti krava i sadržaja uree u mleku.<br />Određivanje sadržaja uree u mleku primenom infracrvene spektrofotometrije u analizi mleka prilikom redovne mesečne kontrole mlečnosti krava pružilo je nove mogućnosti u praćenju kvaliteta mleka.<br />Cilj ovog istraživanja bio je da se utvrdi:<br />1. variranje sadržaja uree u mleku unutar stada,<br />2. uticaj paragenetskih faktora (farma, sistem proizvodnje, sistem držanja, sezona, redni broj laktacije i stadijum laktacije) na sadržaj uree u mleku,<br />3. korelacija sadržaja uree sa parametrima mlečnosti krava i brojem somatskih ćelija i<br />4. korelacija između sadržaja uree u mleku i dužine servis perioda.</p><p>U okviru ovog istraživanja analizirano je 46.315 uzoraka mleka, u okviru redovne kontrole mlečnosti, sa 11 farmi sa područija Vojvodine. Od kojih je jedna sa organskom, a 10 farmi sa konvencionalnom proizvodnjom. Određivanje sadržaja uree u mleku vr&scaron;eno je na aparatu MilcoScan.<br />Prosečan sadržaj uree u mleku (25,18 mg/dl) bio je u okviru optimalnih vrednosti sadržaja uree u mleku. Koeficijent varijacije za sadržaj uree (34,15%) bio je znatno veći od koeficijenta varijacije za ostale sastojke mleka.<br />Dobijeni rezultati u okviru ove doktorske disertacije ukazuju da najveći uticaj na sadržaj uree u mleku ima menadžment farme. Utvrđen je i statitički značajan uticaj ostalih ispitivanih paragenetskih faktora.<br />Sistem držanja statistički značajno utiče na sadržaj uree u mleku. Niži sadržaj uree u mleku bio je kod krava u slobodnom sistemu držanja.<br />Kao posledica specifičnosti organske proizvodnje konstatovane su statistički značajne razlike između organske i konvencionalne proizvodnje mleka. Razlike se ogledaju u smanjenom sadržaju uree u mleku i prinosu mleka, a povećanom sadržaju mlečne masti i proteina. Broj somatskih ćelija u mleku iz organske proizvodnje je znatno manji u odnosu na broj istih u mleku iz konvencionalne proizvodnje mleka, dok je servis period u posmatranom periodu bio duži kod krava u organskoj proizvodnji u odnosu na krave u konvencionalnoj proizvodnji mleka.<br />Posmatrano po sezonama kontrole najniži sadržaj uree u mleku bio je u jesenjem periodu (22,19 mg/dl), a najveći u letnjem period (27,11 mg/dl). Razlike u sadržaju uree po laktacijama su male, ali statistčki značajne.<br />Konstatovan je statistički značajan uticaj stadijuma laktacije na sadržaj uree u mleku. Najniži sadržaj bio je na početku laktacije (23,05 mg/dl), a maksimalan sadržaj uree u mleku od 26,40 mg/dl, bio je od 121 do 180 dana laktacije.<br />Utvrđene su pozitivne, statistički visoko značajne, korelacije između sadržaja uree i pojedinih sastojaka mleka, kao i između sadržaja uree i prinosa mleka. Korelacija između sadržaja uree i broja somatskih ćelija u mleku je negativna i visoko statistički značajna.<br />U okviru ovog istraživanja utvrđena je pozitivna i statistički visoko značajna korelacija između sadržaja uree u mleku i dužine servis perioda.<br />Dobijeni rezultati, tumačeni u kontekstu drugih istraživanja na ovu temu ukazuju na veliki značaj praćenja sadržaja uree u mleku, koji može doprineti pobolj&scaron;anju menadžmenta ishrane i reprodukcije na farmama mlečnih krava, a sve u cilju smanjenja tro&scaron;kova na farmama, kroz smanjenje tro&scaron;kova ishrane i tro&scaron;kova veterinarskih usluga.</p> / <p>Urea as a part of non-protein fraction of nitrogen in milk represents the final product of protein metabolism in the rumen of ruminants. By portal bloodstream toxic ammonia comes into liver where it is transformed into urea, which comes later into milk by bloodstream. Nutrition and contents of crude proteins in the diet have the greatest influence on the milk urea content. The content of milk urea has been increasingly used as a parameter by which it is possible to monitor balance of energy and crude proteins in the feed of dairy cows.<br />Apart from feeding, milk urea content can be influenced by some other factors as season, milk yield, stage of lactation, parity etc.<br />A great number of factors influence cow&rsquo;s fertility. Previous research in this field has indicated a possible relationship between the fertility of cows and urea content in milk.<br />Determination of urea content in milk, by infrared spectrophotometric, on monthly bases, for milk recording porpoises, offers new opportunities for milk quality monitor.<br />The aim of this study was to determine:<br />1. Variations of milk urea content within the herd,<br />2. The influence of paragenetic factors (a farm, production and housing system, season, parity and stage of lactation) on the milk urea content,<br />3. The correlation with milk urea content and parameters of milk yield as well as the somatic cells count,<br />4. The correlation between the milk urea content and the length of open days.<br />This research includes 46,315 samples of milk which were analysed as regular milk recording samples from 11 farms in Vojvodina. There are 10 farms with</p><p>conventional and only one farm with organic production.<br />Determination of the milk urea contents was carried out by MilkoScan FT+.<br />In the analyzed milk samples the average milk urea content (25.18 mg / dl) was within the optimum values. The coefficient of variation for the milk urea content (34.15%) was significantly higher than the coefficient of variation for the other ingredients in milk.<br />The obtained results in this PhD thesis indicate that the management of a farm has the greatest influence on the content of milk urea. Statistically some significant influence of other examined paragenetic factors was found.<br />According to statistics the housing system significantly influences the milk urea content. Lower milk urea content was found in cow&#39;s milk in free-stall system.<br />As the result of specific organic production some statistically significant differences between organic and conventional milk production were found. The differences shows lower milk urea content and milk yield, as well as higher milk fat and protein content. The somatic cells count in organic milk production is significantly lower than their number in milk from conventional milk production. The open days during observation period were longer in cows from an organic dairy farm then the cows from conventional dairy farms.<br />According to season and stage of lactation an important influence on milk urea was found. The seasonal observation shows the lowest milk urea content in autumn period (22.19 mg / dl) and the highest in summer period (27.11 mg / dl). The lowest content was at the beginning of lactation (23.05 mg / dl) and the maximum milk urea content (26.40 mg /dl) was from 121 to 180 days of lactation. Differences in the milk urea content between lactation were small, but statistically significant.<br />There are positive and statistically significant, correlations between the milk urea content and some ingredients of milk, as well as between milk urea content and milk yield. The correlation between the milk urea content and somatic cells count in milk is negative and high statistically significant.<br />It is shown in this research that high milk urea content has negative impact on the length of open days.<br />Obtained results, interpreted in the context of other studies on the same subject indicate the great importance of the observation of the milk urea content. It can contribute to improving the feeding and reproduction on dairy farms, and lead to reduction of both feeding and veterinary costs.</p>

Imported genetic material of the Holstein-Friesian breed from overseas (OS), mainly from North America, has been used in New Zealand (NZ) since the late 1960's. This has diluted the genetic base of the former NZ Friesian genotype selected under intensive seasonal pasture-based systems. As a result, increased concerns have been raised about the negative influence of these overseas genes on the modern NZ Holstein- Friesian, as it is apparent that the OS Holstein-Friesian has a lower capacity to perform on grazed pasture. The objective of the present thesis was to investigate differences in production performance between three Holstein-Friesian genotypes farmed at different feed allowances (FA) on pasture-based systems; in addition, to investigate differences in the grazing process between strains under contrasting managements and sward conditions, and so to identify animal and pasture factors that affect the herbage intake (DMIH) and performance of the grazing cow. An accurate procedure was also established to estimate DMIH for cows fed forage and maize supplements, grazing in groups. Two modern high breeding worth (BW) Holstein-Friesian strains from NZ (NZ90) or overseas (OS90) origin and a low BW 1970's NZ Friesian genotype (NZ70) were farmed in two field experiments: (1) a long-term 'system' study that compared the yield performance of these genotypes in a range of systems with different feed allowance (FA) per cow, and a (2) a short-term 'component' study that compared the grazing capacity of the strains under contrasting sward conditions but at a common daily herbage allowance. The differences in productive performance between genotypes increased as the study progressed in the system study, with the largest observed in the last season. The mean milksolids (MS) yield per cow and per hectare were higher in NZ90 (395 kg cow-1 and 1,236 k ha-1) than in the NZ70 (336 kg cow-1 and 1,093 kg ha-1) and the OS90 (377 kg cow-1 and 1,154 kg ha-1). The higher production of NZ90 cows was supported by their higher mean daily MS yield than the NZ70 (1.45 vs. 1.21 kg MS cow-1 day-1) and more days in milk than OS90 cows (271 vs. 257 DIM). The lower lactation length of the OS90 strain occurred due to its lower body condition score (BCS) in late lactation, which determined an early dry-off for these cows. The lowest BCS of OS90 at the nadir (irrespective of FA), during lactation and at dry-off indicate these cows mobilised greater amount of body reserves and partitioned most of the energy ingested to yield. Genotype by FA interactions for milk and lactose yields, protein content in the milk and BCS were observed in the second and third seasons of the 'system' study. Milk yield increased as FA increased to a greater extent in OS90 than in the two NZ strains, whereas the content of solids in milk, particularly protein, increased to a greater extent for NZ90 than in both OS90 and NZ70. During lactation DMIH was higher for NZ90, intermediate in OS90 and lower in NZ70 (14.5, 13.9 and 12.6 kg DM cow-1 day-1 respectively for NZ90, OS90 and NZ70, as measured with nalkanes), and declined as lactation progressed, with a smaller difference for the total intake achieved (15.5, 15.2 and 13.1 kg DM cow-1 day-1 respectively) due to the increased supplement consumption. These results indicate that the OS90 needs more feed with a higher proportion of supplement in the diet to improve productive performance on pasture-based systems; the NZ90 would perform better when cow nutrition is mainly supported by grazing pasture, although further increments in performance could be expected from strategic supplementation, but requiring more feed than NZ70. The DMIH per unit of live weight (DMIH/LW) was highest in NZ90 strain in both the 'system' and in the short sward of the 'component' study (31.5 and 31.1 g DM kg-1 DM in NZ90 vs. 28.9 and 28.6 g DM kg-1 DM for OS90 in 'system' and 'component' studies respectively). The higher intake of NZ90 on pasture was sustained by a higher capacity to graze short swards than NZ70 and OS90, and to deal with the herbage of higher bulk density and lower quality present at the base of taller swards. The NZ90 can maintain DMIH in swards with different structures, indicating higher flexibility to perform under different managements and sward conditions. The size of the jaw is smaller in NZ90 than OS90 (88.4 vs. 92.4 mm) with effects on bite area and bite size, and this flexibility to adapt the size of the bite to swards of different structure may improve bite penetration under constraining sward conditions. The reduced ability of the OS90 to adjust ingestive behaviour to different swards would limit the capacity of this strain to perform on pasture. The fact that OS90 cows increased DMIH and DMIH/LW substantially in a leafy and taller sward (up to 21.6 kg cow-1 and 40.8 g DM kg-1Lw vs. 19.2 kg cow-1 and 41.0 g DM kg-1Lw in NZ90 during early lactation) suggests that yield performance can be improved in these cows even on pasture, by fine-tuning pasture management.

A positive phenotypic correlation between milk protein percentage and reproductive performance in dairy cattle, especially during early lactation has been recently reported. The objective of this study was to quantify the relationship between milk protein percentage and different measures of fertility in Irish, seasonal calving, dairy cattle using data from experiments comparing strains of Holstein-Friesian cows under different feeding systems. The relationships between body condition score, milk production and fertility were also investigated. The data used in this study consisted of 584 lactation records over a 5-yr period. Principal component analysis and logistic regression was used to study the relationship between milk protein percentage and fertility performance of the cow. Greater milk protein percentage during the first 60 days post-calving was associated with better reproductive performance. The probability of a cow being submitted in the first 21 days of the breeding season increased with increased milk protein percentage during early lactation. Similarly, the probability of a cow becoming pregnant to its first service or to the whole breeding season also increased. Cows were classified as either high or low milk protein percentage based on their protein percentage over the whole lactation. Cows in the high milk protein group had a 7% greater conception rate compared to cows in the low protein percentage group. In conclusion, cows with higher protein percentage, especially during early lactation are submitted earlier in the breeding season, and have a higher conception rate. Physiologically, the shortage of glucose caused by negative energy balance restricts the synthesis of milk protein in the udder. On the other side, negative energy balance also causes the reduction of IGF-I, LH and oestradiol, which consequently delay the ovarian follicular development and finally reduces fertility. Therefore, there is a biological explanation for the association between milk protein percentage and fertility performance.

Este trabalho foi desenvolvido na Universidade Tecnológica Federal do Paraná, Câmpus Dois Vizinhos, com o objetivo de comparar diferentes modelos matemáticos de base empírica ou mecanicista, quanto à qualidade de ajuste e poder de predição das curvas de lactação, obtidas por meio de dados provenientes do controle leiteiro da APCBRH de rebanhos da região sudoeste do Paraná. Foram obtidos inicialmente 42.281 controles de produções leiteiras referentes aos anos de 2005 a 2011,dos quais foram excluídas as informações de animais que não possuíam a data de secagem e a produção total aos 305 dias, restando 15.142 controles referentes à 2441 vacas da raça holandesa. Os dados utilizados foram classificados de acordo com a ordem de parição das vacas (variando de um a seis), e dentro de cada ordem de parição os animais foram separados em quartis (Q25%, Q50%,Q75% e Q100%) conforme a produção total aos 305 dias. Para cada quartil, dentro de cada ordem de parição foram ajustados quatro modelos matemáticos, dois predominantemente empíricos (modelo de Brody e de Wood) e dois com características mais mecanicistas (modelo de Djikstra e de Pollot) usando o proc nlin do SAS método de Marquardt. O de Wood resultou na melhor qualidade de ajuste aos dados. Entretanto os modelos de Brody e Dijkstra também devem ser considerados para descrever as curvas de lactação de vacas holandesas criadas na região sudoeste do Paraná, por apresentarem desempenho muito semelhante, em que o modelo Dijkistra possui uma descrição biológica dos parâmetros e permite uma conotação fisiológica da curva de lactação. Ressaltando o valor histórico do modelo de Brody como pioneiro em modelagem de curva de lactação. / His work was developed at Federal Technological University of Paraná, Câmpus Dois Vizinhos, aiming to analyze different mathematical models comparing empirical and mechanistic models, as their fit and predictive power of the lactation curves obtained using data from the control of dairy APCBRH herds in the southwest region of Paraná, where the evaluation and analysis of 42.281 controls milk production for the years 2005 to 2011, where information from animals that didn´t have the date of drying and total output to 305 days were excluded from the set of data analysis, leaving 15.142 controls concerning the 2.441 Holstein cows, classifying the data according to the order of calving cows (ranging from one to six) and within each order of calving animals were divided into quartiles (Q25% Q50%, Q75% and Q100%) as the total output to 305 days. For each quartile within each lactation numbers were adjusted four mathematical models, two predominantly empirical model (Brody and Wood) and two with more mechanistic characteristics (model Djikstra and Pollot) using SAS proc nlin Marquardt method. Obtaining the Wood model as a result of best fit to the data. However the use of models and Brody Dijkstra to describe lactation curves of Holstein cows raised in the southwestern region of Paraná, should be considered as an option because they have very similar performance, where the model Dijkistra has a biological description of the parameters and allows a connotation physiological lactation curve. Emphasizing the historical value of the model Brody as a pioneer in modeling lactation curve.

Este trabalho foi desenvolvido na Universidade Tecnológica Federal do Paraná, Câmpus Dois Vizinhos, com o objetivo de comparar diferentes modelos matemáticos de base empírica ou mecanicista, quanto à qualidade de ajuste e poder de predição das curvas de lactação, obtidas por meio de dados provenientes do controle leiteiro da APCBRH de rebanhos da região sudoeste do Paraná. Foram obtidos inicialmente 42.281 controles de produções leiteiras referentes aos anos de 2005 a 2011,dos quais foram excluídas as informações de animais que não possuíam a data de secagem e a produção total aos 305 dias, restando 15.142 controles referentes à 2441 vacas da raça holandesa. Os dados utilizados foram classificados de acordo com a ordem de parição das vacas (variando de um a seis), e dentro de cada ordem de parição os animais foram separados em quartis (Q25%, Q50%,Q75% e Q100%) conforme a produção total aos 305 dias. Para cada quartil, dentro de cada ordem de parição foram ajustados quatro modelos matemáticos, dois predominantemente empíricos (modelo de Brody e de Wood) e dois com características mais mecanicistas (modelo de Djikstra e de Pollot) usando o proc nlin do SAS método de Marquardt. O de Wood resultou na melhor qualidade de ajuste aos dados. Entretanto os modelos de Brody e Dijkstra também devem ser considerados para descrever as curvas de lactação de vacas holandesas criadas na região sudoeste do Paraná, por apresentarem desempenho muito semelhante, em que o modelo Dijkistra possui uma descrição biológica dos parâmetros e permite uma conotação fisiológica da curva de lactação. Ressaltando o valor histórico do modelo de Brody como pioneiro em modelagem de curva de lactação. / His work was developed at Federal Technological University of Paraná, Câmpus Dois Vizinhos, aiming to analyze different mathematical models comparing empirical and mechanistic models, as their fit and predictive power of the lactation curves obtained using data from the control of dairy APCBRH herds in the southwest region of Paraná, where the evaluation and analysis of 42.281 controls milk production for the years 2005 to 2011, where information from animals that didn´t have the date of drying and total output to 305 days were excluded from the set of data analysis, leaving 15.142 controls concerning the 2.441 Holstein cows, classifying the data according to the order of calving cows (ranging from one to six) and within each order of calving animals were divided into quartiles (Q25% Q50%, Q75% and Q100%) as the total output to 305 days. For each quartile within each lactation numbers were adjusted four mathematical models, two predominantly empirical model (Brody and Wood) and two with more mechanistic characteristics (model Djikstra and Pollot) using SAS proc nlin Marquardt method. Obtaining the Wood model as a result of best fit to the data. However the use of models and Brody Dijkstra to describe lactation curves of Holstein cows raised in the southwestern region of Paraná, should be considered as an option because they have very similar performance, where the model Dijkistra has a biological description of the parameters and allows a connotation physiological lactation curve. Emphasizing the historical value of the model Brody as a pioneer in modeling lactation curve.

Department of Animal Science / MSCAGR (Animal Science)

In der Studie wurde untersucht, wie relevant eine durch hohe Milchleistung bedingte höhere Stress- bzw. Stoffwechselbelastung für das Ausbleiben der Fruchtbarkeit bei ansonsten klinisch gesunden Milchkühen ist und inwieweit eine längere freiwillige Wartezeit die Bereitschaft der Kühe für eine wiederholte Trächtigkeit verbessern kann. Die Kühe mit einer freiwilligen Wartezeit von 120 Tagen konnten alle innerhalb von 60 Tagen nach Beendigung der freiwilligen Wartezeit besamt werden, während es in der Vergleichsgruppe nur 92 % waren. Die Trächtigkeitsrate nach der ersten Besamung lag bei 120-tägiger Wartezeit mit 40,7 % um 10,3 % höher als in der Vergleichsgruppe. In der spät besamten Gruppe traten keine embryonalen Fruchtverluste auf, während dieses in der Vergleichsgruppe 8,9 % der Trächtigkeiten betraf. Redaktionsschluss: 26.03.2020