Decreased Milk Yield Research Articles

OUTBREAK PREDICTION METHODS AND MEASURES TO CONTROL THE SPREAD OF BOVINE VIRAL DIARRHEA IN KAZAKHSTAN

Bovine viral diarrhea (BVD) is a contagious, acute disease of cattle that is reported in many countries around the world. BVD is caused by pestiviruses Pestivirus A and Pestivirus B belonging to the genus Pestivirus, family Flaviviridae. The disease causes significant economic damage to livestock breeding, leading to reproductive dysfunction (reduced reproductive capacity, delayed births, early embryonic death, abortion, congenital anomalies) and decreased productivity (morbidity, high calf mortality, decreased milk yield). In recent years, outbreaks of BVD have occurred in several regions of Russia and China bordering Kazakhstan, indicating a high risk of introducing the infection into the country. Although Kazakhstan is officially considered free from BVD, there are numerous indications that this infection is present in many regions of the country, which requires the use of effective control measures in regions at risk for infection. This article provides methods for assessing the epizootological situation and forecasting outbreaks, as well as recommendations for carrying out veterinary measures and monitoring BVD in Kazakhstan, based on the results of a monitoring study of the epizootological situation and an analysis of the risks of the spread of BVD in Kazakhstan in 2021-2023

Nitrogen balance in dairy cows fed low-nitrogen diets based on various proportions of fresh grass and maize silage.

To ensure sustainable and efficient production, dairy farms must reduce their environmental impacts and nitrogen losses, which are sources of pollution, while increasing their feed self-sufficiency. Grass-based dairy systems, frequently combine fresh grass with maize silage when grass is scarce or during dietary transitions. However, the effects of combining fresh grass and maize silage on cow performance and N excretion are poorly known. This study aimed to quantify the effects of increasing the proportion of maize silage in a fresh grass diet on cow N flows and metabolism, in the context of grass-based dairy systems. Four proportions of maize silage in a fresh grass diet (objectives of 0, 17, 34 and 51% DM of maize silage) were investigated. The experiment was performed in a 4×3 Latin square design using eight lactating cows during three 3-week periods. DM intake (DMI), milk yield, faeces and urine outputs, and their N concentrations were measured for each cow. The fresh grass CP concentration was lower than planned (106±13.0g/kg DM). This resulted in very low dietary CP concentration, which decreased from 108 to 86g/kg DM when maize silage in the diet increased from 0 to 51% DM, respectively. DM intake and milk yield both decreased linearly by 3.3kg/day from 0 to 51% DM of maize silage in the diet. Thus, N intake decreased linearly by 100g/day from 0 to 51% DM of maize silage in the diet. The N concentration of milk was highest for the diet with 0% DM of maize silage. Nitrogen excreted in faeces and urine decreased linearly by 29 and 23g/day, respectively, from 0 to 51% DM of maize silage in the diet. The low dietary N concentration resulted in low ruminal NH3-N concentrations (8mg/L, on average) and urinary urea excretion (down to 8% urea N in urinary N). Increasing the proportion of maize silage in an unusually low-N grass diet, without protein-rich concentrates, induced highly N-deficient diets with minimal N losses in faeces and urine but large and unsustainable decreases in DMI and milk yield.

Dietary Neutral Detergent Fiber Levels Impacting Dairy Cows' Feeding Behavior, Rumen Fermentation, and Production Performance during the Period of Peak-Lactation.

This study investigated the impact of dietary neutral detergent fiber (NDF) levels (25.49%, 28.65%, 31.66%, and 34.65%, respectively) on the feeding behavior, rumen fermentation, cellulolytic bacteria, and production performance of dairy cows during peak lactation. A feeding experiment was conducted using four fistulated Holstein dairy cows (600 ± 25 kg) with days in milk (50 ± 15 days), employing a 4 × 4 Latin square design to assign the cows to four groups. The results demonstrated that increasing NDF levels in the diet had the following effects: (1) A linear decrease in dry matter intake (DMI), NDF intake, and physically effective NDF8.0 (peNDF8.0) intake; a linear increase in the average time spent eating and ruminating, as well as the time spent eating and ruminating per kilogram of dry matter (DM); a quadratic response in the time spent ruminating per kilogram of NDF and peNDF8.0. (2) A linear increase in average pH value, acetate concentration, and the proportions of Fibrobacter succinogenes and Ruminococcus flavefaciens among total bacteria; a linear decrease in ammonia nitrogen (NH3-N) concentration, microbial crude protein (MCP), total volatile fatty acid (TVFA), propionate, butyrate, and lactate. (3) A linear decrease in milk yield, milk protein percentage, and nitrogen efficiency of dairy cows; a linear increase in milk fat percentage and milk urea nitrogen (MUN) concentration. Based on the combined results, it was found that diets with 25% and 34% NDF had detrimental effects on the feeding behavior, rumen fermentation, and production performance of dairy cows. However, the diet with 28% NDF showed superior outcomes in production performance compared to the one with 31% NDF. Therefore, it is strongly recommended to include a diet containing 28% NDF during the critical peak lactation period for dairy cows.

The Housing System Contributes to Udder Health and Milk Composition

The aim of this study was to determine the effect of the housing system and somatic cell count (SCC) on the composition and fatty acid profile of milk. A total of 419 milk samples were collected from one herd of 210 cows; 90 cows were kept in the tie-stall system, and 120 cows were kept in the free-stall system. The cows received the same fodder. Samples were collected four times, in winter. Udder health was evaluated based on SCC. The tie-stall system, mainly due to individual care, was superior to the free-stall system. Milk from cows kept in the tie-stall system had lower (p < 0.01) SCC by 72 ths mL−1 cells than milk from cows kept in the free-stall system. An increase in SCC was accompanied by decreases in daily milk yield and lactose concentration. Milk from cows housed in the tie-stall barn had higher polyunsaturated fatty acid (PUFA) contents and a lower n-6/n-3 PUFA ratio. Milk with a higher SCC contained more PUFAs and fewer monounsaturated fatty acids (MUFAs). Tie-stall housing contributed to an increase in the proportions of acids beneficial to the health of consumers. A comparison of two housing systems for cows on one farm showed that the free-stall system was associated with a higher SCC and a less favorable milk composition and fatty acid profile.

The autumn low milk yield syndrome in Brown Swiss cows in continental climates: hypotheses and facts.

Extensive research has been conducted globally on the impact of heat stress (HS) on animal health and milk production in dairy cows. In this article, we examine the possible reasons for the decrease in milk production in Brown Swiss (BS) cows during the autumn season, known as the autumn low milk yield syndrome (ALMYS). This condition has been extensively studied in high-yielding Holstein Friesian (HF) cattle and has also been observed in BS cows with a daily milk yield of around 30kg. Our hypothesis is that the drop in milk yield and the increased prevalence of mastitis in autumn, as found in our recent studies, may be a long-term consequence of summer HS. We re-evaluate our previous findings in light of the possible manifestation of an HS-related form of ALMYS in BS cows. As milk yield, mastitis spread, and reproductive function of cows are interrelated and have seasonal dependence, we examine the consistency of our hypothesis with existing data. The significant drop in milk yield in BS cows in autumn (by 2.0-3.2kg), as well as the threshold of milk yield decrease (temperature-humidity index of 70.7), may point in favour of the manifestation of ALMYS in BS cows, similar to HF cows. Only the percentage effect of seasonal factor (59.4%; p < 0.05) on milk yield of BS cows was significant. HS-related ALMYS provides a robust conceptual framework for diverse sets of productive and animal health data in BS cows, similar to observations in high-yielding HF cattle. However, the limitations associated with the lack of additional data (e.g. immunological indicators) suggest the need for further research to confirm ALMYS in BS breed.

Effects of heat stress abatement on systemic and mammary inflammation in lactating dairy cows

To examine the effects of evaporative cooling on systemic and mammary inflammation of lactating dairy cows, 30 multiparous Holstein cows (parity = 2.4, 156 d in milk) were randomly assigned to 1 of 2 treatments: cooling (CL) with fans and misters or not (NC). The experiment was divided into a 10-d baseline when all cows were cooled, followed by a 36-d environmental challenge when cooling was terminated for NC cows. The onset of environmental challenge was considered as d 1. Temperature-humidity index averaged 78.4 during the environmental challenge. Milk yield and dry matter intake (DMI) were recorded daily. Blood and milk samples were collected from a subset of cows (n = 9/treatment) on d -3, 1, 3, 7, 14, and 28 of the experiment to measure cortisol, interleukin 10 (IL10), tumor necrosis factor-α (TNF-α), haptoglobin, and lipopolysaccharide binding protein (LBP). Mammary biopsies were collected from a second subset of cows (n = 6/treatment) on d -9, 2, 10, and 36 to analyze gene expression of cytokines and haptoglobin. A subset of cows (n = 7/treatment) who were not subjected to mammary biopsy collection received a bolus of lipopolysaccharides (LPS) in the left rear quarter on d 30 of the experiment. Blood was sampled from cows and milk samples from the LPS-infused quarter were collected at -4, 0, 3, 6, 12, 24, 48, and 96 h relative to infusion, for analyses of inflammatory products. Deprivation of cooling decreased milk yield and DMI. Compared with CL cows, plasma cortisol concentration of NC cows was higher on d 1 but lower on d 28 of the experiment (cooling × time). Deprivation of cooling did not affect circulating TNF-α, IL10, haptoglobin, or LBP. Compared with CL cows, NC cows tended to have higher milk IL10 concentrations but did not show effects in TNF-α, haptoglobin, or LBP. No differences were observed in mammary tissue gene expression of TNF-α, IL10, and haptoglobin. Milk yield declined after LPS infusion but was not affected by treatment. Compared with CL cows, NC cows had greater milk somatic cell count following intramammary LPS infusion. Non-cooled cows had lower circulating TNF-α and IL10 concentrations and tended to have lower circulating haptoglobin concentrations than CL cows. Milk IL10 and TNF-⍺ concentrations were higher 3 h after LPS infusion for NC cows compared with CL cows. Additionally, NC cows tended to have higher milk haptoglobin concentration after LPS infusion than CL cows. In conclusion, deprivation of evaporative cooling had minimal effects on lactating cows' basal inflammatory status, but upregulated mammary inflammatory responses after intramammary LPS infusion.

Feeding graded levels of camelina expeller meal up to 20% of dietary dry matter decreases feed intake and milk production but enhances concentration in milk fat of n-3 fatty acids in dairy cows

Eight Holstein cows were used in a replicated 4 × 4 Latin square design study to determine the effects of feeding 0%, 10%, 15%, and 20% camelina expeller meal (CEM) on production and milk fatty acid profiles. Dry matter intake (DMI) and milk fat content decreased linearly, whereas milk yield decreased quadratically, as CEM increased. Concentrations in milk fat of C18:2n-6 and cis-9, trans-11 C18:2 increased linearly, whereas those of C18:3n-3 and trans-10, cis-12 C18:2 increased quadratically as CEM increased. Results show that CEM levels up to 20% decrease DMI and milk yield but increase concentrations in milk fat of desirable n-3 fatty acids.

Association of dry matter intake, milk yield, and days to first ovulation with cytological endometritis in Holstein cows

Dry matter intake (DMI, kg/d) is closely related to the magnitude of negative energy and protein balance during the transition period, and the metabolic adaptations to support lactation in dairy cows. Thus, DMI might affect the development of cytological endometritis in the early postpartum period. Difficulty to adapt to these metabolic changes is related to impaired immune function and increased occurrence of reproductive disorders. We aimed to examine the association of pre- and postpartum DMI, body weight (BW), body condition score, milk yield and milk composition, and days to first ovulation with cytological endometritis at 15 (CYT15) and 30 DIM (CYT30). A second objective was to understand the association of vaginal discharge with CYT15 and CYT30 and performance. We conducted a pooled statistical analysis of 5 studies, including data from 280 multiparous Holstein cows. Based on the cutoffs for the percentage of uterine polymorphonuclear cells (PMN), determined by taking the median value of the data set for 15 and 30 DIM, cows were categorized as follows: LOW15 (PMN % at 15 DIM ≤24%; n = 125), HIGH15 (PMN % at 15 DIM >24%; n = 125), LOW30 (PMN % at 30DIM ≤7%; n = 141); and HIGH30 (PMN % at 30DIM >7%; n = 139). Cows in HIGH15 consumed an average of 1.97 ± 0.5 kg/d less DM than cows in LOW15 during prepartum, and 3.01 ± 0.5 kg/d less DM during postpartum. Dry matter intake (as a percentage of BW) was higher for cows in LOW15 during pre- and postpartum than for cows in HIGH15. Moreover, cows in HIGH15 tended to have lower milk yield than cows in LOW15 from the third until the fifth week postpartum. Although DMI was not associated with CYT30, DMI (as a percentage of BW) was lower for cows in LOW30 pre- and postpartum than for cows in HIGH30. There was no association between CYT30 and milk yield. Cows in LOW15 had greater days to first ovulation than cows in HIGH15, while cows in LOW30 also had greater days to first ovulation than cows in HIGH30. Simple regression analyses demonstrated linear associations of increased DMI, particularly postpartum, with decreased uterine PMN percentage and lower vaginal discharge score. Additionally, increased units of vaginal discharge score and increased percentage units of uterine PMN were linearly associated with decreased milk yield. Corroborating with the notion of the ovarian function being associated with uterine inflammatory status, cows in HIGH15 and HIGH30 ovulated on average 3 d before than cows in LOW15 and LOW30, respectively. Cytological endometritis at 15 DIM was associated with lower DMI from 4 wk before calving until 4 wk postpartum and was associated with lower milk yield. The association of vaginal discharge with cytological endometritis was variable and dependent on the day of evaluation.

Randomized clinical trial evaluating the effects of the administration of acidogenic boluses at dry off on udder health

High milk production at dry off is a risk factor for intramam­mary infections (IMI) postpartum due to milk leakage and im­paired formation of the keratin plug during the dry period. The use of acidifying agents at dry off can induce a temporary feed intake reduction and decrease in milk yield of high-producing dairy cows. Thus, acidogenic boluses are a potential tool to help maintain udder health around the dry period. The study aim was to evaluate the effects of the administration of acidogenic boluses at dry off on udder health.

GENETIC POTENTIAL FOR MILK AND CHARACTERISTICS OF LACTATION ACTIVITY OF COWS OBTAINED BY PUREBRED BREEDING AND CROSSING

GENETIC POTENTIAL FOR MILK AND CHARACTERISTICS OF LACTATION ACTIVITY OF COWS OBTAINED BY PUREBRED BREEDING AND CROSSING

Kilis Keçilerinde Süt Verimi ve Meme Sarkıklığı Arasındaki İlişkiler

Bu çalışma; Kilis keçilerinin süt verimi ile meme sarkıklığı arasında herhangi bir ilişki olup olmadığının belirlenmesi için yapılmıştır. Çalışma, Kilis’in Polateli ilçesinde bir işletmede yetiştirilen 73 baş Kilis keçisi üzerinde yürütülmüştür. Bu amaçla keçilerden Meme Üst Yüksekliği (MÜY), Sarnıç Derinliği (SD), Meme Derinliği (MD), Meme Başları Arası Mesafe (MBAM), Meme Alt Yüksekliği (MAY) ve Meme Başı Yüksekliği (MBY) gibi bazı meme ölçüleri alınmış ve keçilerin bir günlük süt verimleri (GSV) tespit edilmiştir. Bu meme ölçülerine ait en küçük kareler ortalamaları sırasıyla; 47.66±0.36 cm, 21.35±0.58 cm, 15.53±0.47 cm, 21.59±0.57 cm, 26.31±0.59 cm ve 23.67±0.60 cm olarak belirlenmiştir. GSV ise 687.09±32.37 g olarak hesaplanmıştır. Keçinin yaşı bu özelliklerden sadece MÜY üzerine etkiliyken, doğum tipinin ise MÜY ve MD özelliklerini etkilediği belirlenmiştir (P

Temperature-Humidity Index Values and Their Significance on the Daily Production of Dairy Cattle in the North African Arid Region

Climate changes affect the economic viability of livestock. Therefore, this study aimed to characterize the heat stress in Holstein cattle raised in the arid region of Tunisia as well as to evaluate the effect of the temperature-humidity index (THI) on daily milk production and components. For this reason, 76940 monthly individual records collected from 1995 to 2018 from 3056 Holstein cows were used. THI calculated from ambient temperature and relative humidity was used as a measure of heat stress. To study the effect of THI on milk production, a repeated measures linear mixed model was used. Results showed a significant (P<0.01) decrease in daily milk yield, daily protein, and fat content in all cow’s parity classes. For each point increase of the THI values beyond 64, milk yield, fat, and protein contains decreased by 0.32 kg, 0.09, and 0.06 %, respectively. Moreover, when the THI value varied from 64 to 85, fat content decreased by 29 %, protein by 17 %, and milk production by 30 %. Heat stress impact negatively milk production and milk components of dairy cows. These results can be a way to improve the length of productive life for Holstein dairy cattle in the hard climate. Serious management strategies are needed to improve dairy cow productivity and minimize the heat stress impact.

The High Level of RANKL Improves IκB/p65/Cyclin D1 Expression and Decreases p-Stat5 Expression in Firm Udder of Dairy Goats.

Udder traits, influencing udder health and function, are positively correlated with lactation performance. Among them, breast texture influences heritability and impacts on the milk yield of cattle; however, there is a lack of systematic research on its underlying mechanism in dairy goats in particular. Here, we showed the structure of firm udders with developed connective tissue and smaller acini per lobule during lactation and confirmed that there were lower serum levels of estradiol (E2) and progesterone (PROG), and higher mammary expression of estrogen nuclear receptor (ER) α and progesterone receptor (PR), in dairy goats with firm udders. The results of transcriptome sequencing of the mammary gland revealed that the downstream pathway of PR, the receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL) signal, participated in the formation of firm mammary glands. During the culture of goat mammary epithelial cells (GMECs), high RANKL level additions promote the Inhibitor kappaB (IκB)/p65/Cyclin D1 expression related to cell proliferation and decrease the phosphorylated signal transduction and transcription activator 5 (Stat5) expression related to milk-protein synthesis of GMECs, which is consistent with electron microscope results showing that there are fewer lactoprotein particles in the acinar cavity of a firm mammary. Furthermore, co-culturing with adipocyte-like cells for 7 d is beneficial for the acinar structure formation of GMECs, while there is a slightly negative effect of high RANKL level on it. In conclusion, the results of this study revealed the structure of firm udders structure and confirmed the serum hormone levels and their receptor expression in the mammary glands of dairy goats with firm udders. The underlying mechanism leading to firm udders and a decrease in milk yield were explored preliminarily, which provided an important foundation for the prevention and amelioration of firm udders and improving udder health and milk yield.

Case report on an outbreak of theileriosis in a dairy herd: Could it be a co-infection of a virulent strain of Theileria mutans with Theileria parva?

This case report aimed to alert veterinarians of the possibility of simultaneous infections with more than one Theileria species in cattle herds in Zimbabwe. Cows (N=7) and a postmortem specimen from a dairy farm located in Chivhu, Mashonaland East province, Zimbabwe were presented for clinical and postmortem examination, respectively. On history taking, the herd had a decrease in milk yield and high cow mortalities. The presented live animals had a heavy tick burden and were febrile and lethargic. Post-mortem findings revealed strong evidence suggestive of theileriosis. Theileria schizonts and piroplasms were identified in stained lymph node aspirate, impression, and blood smears. The herd was managed using tetracyclines and buparvaquone together with an intensive dipping protocol until deaths had stopped. Both the clinical and postmortem findings were strongly suggestive of the possibility of a simultaneous infection with more than one Theileria species in this herd. Thus, these finding highlight the need to characterise the Theileria species profile in Zimbabwe.

Effect of the DGAT1 K232A mutation and breed on milk traits in cattle populations of Ethiopia

Non-conservative K232A substitution in the diacylglycerol acyl-CoA acyltransferase 1 (DGAT1) gene has been reported to explain variation in milk traits in cattle. The objective of this study was to estimate allele and genotype frequencies and to assess associations between K232A variants and milk yield and composition in cattle populations of Ethiopia. Blood samples for genomic DNA extraction and milk samples for analysis of milk components were collected from 92 randomly selected cattle of five Ethiopian breeds. Gene-specific primers were used to amplify 278 bp of the exon 8 region of DGAT1. Allele and genotype frequencies were calculated using Power Marker, and the GLM function of SAS software was used to assess the associations of detected genetic variation with milk traits. Boran * Holstein Friesian (HF) crosses produced a higher daily milk yield than the other breeds (p&amp;lt; 0.05), whereas the Boran and Begait breeds produced milk with higher fat and protein contents (p&amp;lt; 0.05), and Horro produced milk with a higher content of lactose, than the other breeds studied (p&amp;lt; 0.05). Alleles K and A and genotypes AA, KA, and KK were detected. The frequency of K232 ranged from 0.50 in Boran * HF crosses to 0.97 in the Horro population. The frequency of the KK and KA genotypes in the zebu population ranged from 0.50 to 0.94 and from 0.03 to 0.50, respectively. The AA genotype was associated with higher milk yield in Boran * HF crosses, whereas the KA genotype was associated with higher milk yield in the zebu populations (p&amp;lt; 0.05). The fat and lactose contents of milk produced with the KA genotype were lower than those of milk produced with the KK genotype in all genetic groups (p&amp;lt; 0.05). Substitution of one copy of the K allele led to a significant (p&amp;lt; 0.05) increase in fat content, of up to 0.81%, a decrease in daily milk yield of up to 3 L, and a decrease in lactose content of 0.58% in the sampled populations. The association study confirmed that the DGAT1 K232A marker had significant effects on daily milk yield, milk fat and lactose contents in the investigated cattle. These results suggested that the DGAT1 K232A marker may be utilized to accelerate future molecular breeding of dairy cattle, tropical zebu, their crossbreeds, after validation in a larger population.

Thermal comfort zoning and its impact on dairy production in Rio Grande do Sul state, Southern Brazil

Thermal comfort is one of the main factors that influence the productivity of dairy cattle. The temperature-humidity index (THI) is one of the most used indicators to evaluate thermal comfort levels. This work aimed to evaluate the levels of thermal comfort for bovine dairy production in Rio Grande do Sul state through the THI calculation and its impact on milk production, considering daily yields of 15 kg and 30 kg per cow. The THI values and decrease in milk yield were calculated using data between 1990 and 2021 from the National Institute of Meteorology (INMET). The observed results considering the average temperatures showed that conditions of thermal discomfort occur only in summer, intensifying in January. Milk production was most affected in the western border region of the state, corresponding in parts to the physiographic regions of Alto Uruguai, Missões, and Campanha, which have a warmer climate. The climate classification proposed by Maluf had the best spatial correspondence with the ITU. This classification may be used in the evaluation of places with greater suitability for dairy farming in the state and to indicate places where it is necessary to implement action to mitigate the effects of thermal discomfort in dairy cattle.

Ways to reduce the impact of the external environment in summer on the milk productivity of cows

One of the factors of efficient intensive milk production is the creation of comfortable conditions for keeping cows on a farm or complex. Highly productive cows are quite demanding of the indoor microclimate and conditions of keeping. It is believed that the productivity of animals by 10-30% depends on this. The purpose of the study was to examine the possibility of reducing the influence of high ambient temperature on the milk productivity of cows by different approaches to the organisation of their feeding technology. The paper uses analytical, diagnostic, physicochemical, and statistical research methods. The main climate indicators were monitored during the summer period (June-August). It is established that the decrease in daily milk yield is a consequence of the negative influence of the temperature factor when the daily (from 1100 to 1700) air temperature in June-July is at the level of +26-30°C. At an air temperature of 26.5°C (about 1400), the body temperature of cows rises from 37.5-37.8°C to 38.20-38.46°C. The proof of this is a decrease in the rate of decline in the level of milk productivity of cows of the experimental groups in August when the average daily air temperature dropped to +24-26°C. It is proved that the introduction of 1.5 kg of protein feed additive with protected TEP-mix protein into the diet of highly productive cows increases the productivity of experimental cows (in terms of basic milk) by 15.7% (4.3 kg). Modernisation of the diet of feeding highly productive cows by increasing the content of non-broken down protein in the rumen to normal during temperature stress contributed to better adaptation of animals in terms of productivity and quality indicators of milk: an increase in the mass fraction of fat by 0.67% and the mass fraction of protein by 0.26%, with the content of somatic cells of 285.06±81.0–409.3±134.3 thousand/cm3

Nutritional Modulation of the Somatotropin/Insulin-Like Growth Factor System: Response to Feed Deprivation in Lactating Cows

Mid-lactation Holstein cows (n = 4) were used to evaluate the effects of complete feed deprivation on circulating insulin-like growth factors (IGF) and their binding proteins (IGFBP). Comparisons were made between cows in fed and unfed conditions and included response to a single injection of bovine somatotropin (bST). Two days of feed deprivation decreased milk yield 66%. Concentrations of bST nearly doubled during feed deprivation, whereas glucose and insulin steadily decreased. Circulating concentrations of IGF-I decreased nearly 50%, IGF-II decreased 28% and IGFBP-2 increased 49% during the 2 d of feed deprivation. In contrast, IGFBP-3 was not affected. Eighteen to 24 h after the bST challenge, circulating concentrations of IGF-I rose 100% during the fed period, but there was no response during the unfed period. Blood concentrations of IGF-II decreased 17% after bST challenge in the fed period but were unchanged in the unfed period. More moderate undernutrition (80% of requirements) did not affect circulating IGFBP-2 but did alter the response of IGFBP-2 to bST. A conceptual model was developed that illustrates that nutritional regulation of the ST/IGF system represents a key component signaling the appropriate use of nutrients. Overall, results demonstrate that nutritional modulation of the ST/IGF system plays a key role in animal performance and well-being over a wide range of physiological situations.

Bimodal milk flow and overmilking in dairy cattle: risk factors and consequences.

To maximise the return on capital invested in the milking parlour, the largest number of cows should be milked gently and completely in the shortest possible time. Bimodal milk flow and overmilking negatively influence the efficiency of the milk removal process and teat health. This observational study had the objective of investigating the prevalence of bimodal milk flow and overmilking, determining which individual and farm-related variables are associated with these occurrences, and determining the association of overmilking and bimodal milk flow with milk yield and with short- and long-term teat changes. Twenty-one farms were visited once during the study period, wherein the milking routine was timed, the teat condition was assessed, and dynamic evaluation of the milking vacuum was performed. A total of 606 vacuum graphic records were obtained, with an average of 29±3 records per farm, in order to indirectly evaluate the milk flow and thus determine the occurrence of bimodal milking and overmilking time. The average percentage of bimodality per farm was 41.7%. The median overmilking time was 59 seconds, and on average, 78.3% of the cows in a herd were overmilked longer than 30 seconds. An association was found at cow level between the occurrence of bimodal milk flow and days in milk, the total stimulation time, parity, and the preparation lag time. The increase in the mean total stimulation time and the number of passes during preparation were associated with a decrease in the proportion of bimodality in the herd. Parity, reattachment of the milking unit and milking in manual mode were associated with an increase in overmilking time of an individual cow. The presence of a clogged air bleed hole in the claw and the reduction of the cluster removal milk flow threshold were associated with an increase in the herd's median overmilking time. The average milk flow decreased with the increase in overmilking time and with the occurrence of bimodal milk flow. An association was also found between the occurrence of bimodal milk flow and decreased milk yield. A mean of 78.4% of cows per farm had short-term teat changes in at least one teat, and 33.6% of evaluated cows per farm displayed at least one teat with hyperkeratosis. These results emphasise the association of bimodality and overmilking on milking efficiency and reinforce the importance of the milkers' actions and the functioning of the milking parlour for its prevention.

Effects of different nutrient supply on metabolism and mammary immune response to an LPS challenge in early lactation of dairy cows

Energy and nutrient deficiency in dairy cows in early lactation is considered to contribute to their increased susceptibility to mastitis. We have tested the hypothesis that feeding diets with high contents of either nitrogenic, glucogenic, or lipogenic components in early lactation affects both the endocrine and metabolic status, as well as the mammary immune competence. After calving, cows were fed increasing amounts of concentrate up to 10 kg/d rich in crude protein (nitrogenic, n = 10), glucogenic precursors (glucogenic, n = 11), or lipids (lipogenic, n = 11). In wk 3, one udder quarter was challenged with lipopolysaccharide (LPS) from Escherichia coli. Blood and milk were sampled on the day before LPS challenge (d -1), and on d 0, 1, 2, 3, and 9 after LPS challenge. On the day of LPS challenge additional samples were taken hourly for quarter milk and every 3 h for blood. Urea concentrations were higher in plasma and milk of cows fed the nitrogenic diet. However, plasma concentrations of glucose, cholesterol, triglycerides, β-hydroxybutyrate, nonesterified fatty acids, as well as insulin, glucagon, and insulin-like growth factor-1 were not affected by the different diets. The mammary immune challenge induced a substantial increase of somatic cell count (SCC) in the treated quarter, and a transient decrease of total milk yield and white blood cells similar in all diet groups for one day. The absolute phagocytosis of blood leukocytes was decreased; however, the phagocytosis per cell was increased in glucogenic-fed cows at 6 h after LPS challenge. During mammary inflammation an insulin resistance, shown by increased plasma glucose, insulin, and glucagon, developed similarly in all diet groups. β-hydroxybutyrate and nonesterified fatty acids were decreased at 1 d after LPS challenge in glucogenic-fed cows only. Cholesterol did not change, and triglycerides only decreased significantly in lipogenic-fed cows 6 h after challenge. On d 9 after LPS challenge, SCC and milk yield and metabolic factors were recovered in all groups. In conclusion, the endocrine and metabolic situation, and the immune response to intramammary LPS of dairy cows during early lactation was not substantially influenced by the elevated supply of nitrogenic, glucogenic, or lipogenic components due to the provided feed in this study.