Technical note: Comparative analyses of the quality and yield of genomic DNA from invasive and noninvasive, automated and manual extraction methods

Several new automated methods have recently become available for high-throughput DNA extraction, including the Maxwell 16 System (Promega UK, Southampton, UK). The purpose of this report is to compare automated with manual DNA extraction methods, and invasive with noninvasive sample collection methods, in terms of DNA yield and quality. Milk, blood, and nasal swab samples were taken from 10 cows for DNA extraction. Nasal swabs were also taken from 10 calves and semen samples from 15 bulls for comparative purposes. The Performagene Livestock (DNA Genotek, Kanata, Ontario, Canada) method was compared with similar samples taken from the same animal using manual extraction methods. All samples were analyzed using both the Qubit Quantification Platform (Invitrogen Ltd., Paisley, UK) and NanoDrop spectrophotometer (NanoDrop Technologies, Inc., Wilmington, DE) to accurately assess DNA quality and quantity. In general, the automated Maxwell 16 System performed best, consistently yielding high quantity and quality DNA across the sample range tested. Average yields of 28.7, 10.3, and 19.2 μg of DNA were obtained from 450 μL of blood, 400 μL of milk, and a single straw of semen, respectively. The quality of DNA obtained from buffy coat and from semen was significantly higher with the automated method than with the manual methods (260/280 ratio of 1.9 and 1.8, respectively). Centrifugation of whole blood facilitated the concentration of leukocytes in the buffy coat, which significantly increased DNA yield after manual extraction. The Performagene method also yielded 18.4 and 49.8 μg of high quality (260/280 ratio of 1.8) DNA from the cow and calf nasal samples, respectively. These results show the advantages of noninvasive sample collection and automated methods for high-throughput extraction and biobanking of high quality DNA.     

Factors affecting the lactoferrin concentration in bovine milk

Lactoferrin (LF) concentrations in the milk with different levels of the somatic cell count score were examined using an ELISA to determine whether milk LF concentration is influenced by parity of the cow, stage of lactation, and the somatic cell count. The study animals were 198 Chinese Holstein cows randomly chosen from more than 1,600 cows in 4 dairy farms in the Beijing area. The cows had shown no sign of mastitis for 2 mo. Daily milk production was recorded, and milk samples were taken from individual cow samples. The LF concentration varied between 31.78 and 485.63 μg/mL in milk from normal animals. Lactoferrin was significantly associated with stage of lactation (r = 0.557) and daily milk production (r = −0.472). Nevertheless, there was no significant relationship with parity. Moreover, milk LF concentration tended to be correlated with the somatic cell count score (r = 0.375). This finding suggests that milk LF may be helpful as an indicator for intramammary infection in dairy cows.     

Rapid DNA extraction of pig ear tissues

A single-step DNA isolation procedure from pig tissues was developed and the product used directly for polymerase chain reaction (PCR) amplification, single-strand conformational polymorphism (SSCP) analysis and sequencing. The procedure consists of proteinase K digestion of 2–10 mg of fresh tissue, at 55 °C for 1 h, followed by application of the products of digestion to filter paper. A 1.2 mm-diameter punch of that paper has sufficient DNA to act as a template for PCR amplification. The quality of the genomic DNA appeared to be high as the PCR amplicons produced sharp banding patterns on both agarose gel electrophoresis and on SSCP analysis, and they could be used for DNA sequencing following cloning. The dried genomic DNA on filter paper can be kept at room temperature. The procedure is considered effective as it is simple, fast and inexpensive. It would be useful for large-scale genotyping and could be used to obtain genomic DNA from various tissues.     

Efficacy of Solis, NovasilPlus, and MTB-100 to reduce aflatoxin M1 levels in milk of early to mid lactation dairy cows fed aflatoxin B1

An experiment was conducted to determine the efficacy of 3 adsorbents, Solis (SO; Novus International Inc.), NovasilPlus (NOV; Engelhard Corp.), and MTB-100 (MTB; Alltech), in reducing aflatoxin (AF) M₁ concentrations in milk of dairy cows fed an AF-contaminated diet. Twelve early to mid lactation dairy cows averaging 163 d in milk were used in a 4 × 4 Latin square design with 3 replications. Cows were blocked by parity, body weight, and milk production and were provided ad libitum access to feed and water. Within each replicate, cows were randomly assigned to the 4 dietary treatments for 4 consecutive 7-d periods. Dietary treatments included AF [112 μg of AFB₁/kg of diet dry matter (DM)]; AF + 0.56% SO; AF + 0.56% NOV; and AF + 0.56% MTB. Milk samples were collected on d 6 and 7 of each of the experimental periods. Feed intake, milk production, milk fat percentage, milk protein percentage, and linear somatic cell scores were not affected by dietary treatments and averaged 22.20 kg/d of DM, 33.87 kg/d, 3.78%, 2.95%, and 1.60, respectively, across all treatments. Transfer rates of AF from feed to milk averaged 2.65, 1.48, 1.42, and 2.52% for cows fed AF, AF + SO, AF + NOV, and AF + MTB, respectively. Daily AFM₁ excretion in milk averaged 66, 37, 35, and 63 μg/d for cows fed AF, AF + SO, AF + NOV, and AF + MTB, respectively. The addition of SO and NOV to the AF diet resulted in a significant reduction in milk AFM₁ concentrations (SO, 45%; NOV, 48%) and AFM₁ excretion (SO, 44%; NOV, 46%). In contrast, MTB was not effective in reducing milk AFM₁ concentrations (4%), AFM₁ excretion (5%), or AF transfer from feed to milk (2.52%). Results indicated that SO and NOV at 0.56% of the diet were effective in reducing milk AFM₁ concentrations in cows consuming a total mixed ration containing 112 μg of AFB₁/kg of diet DM.     

Effects of supplementation with a phytobiotics-rich herbal mixture on performance,udder health,and metabolic status of Holstein cows with various levels of milk somatic cell counts

This study evaluated the effects of dietary supplementation of a novel phytobiotics-rich herbal mixture (PRHM) on feed intake, performance, udder health, ruminal fermentation, and plasma metabolites in cows with moderate or high somatic cell counts (SCC) in the milk. Twenty-four Holstein dairy cows (117 ± 26 d in milk and 46.3 ± 4.7 kg of milk/d at the start of the experiment) were blocked by parity and days in milk and split into 2 groups, based on SCC in the milk; 12 cows were with moderate SCC (260,000 < SCC <500,000 cells/mL), whereas 12 other cows had high levels of SCC (>500,000 cells/mL) in the milk. Within each SCC group, cows were blocked by milk yield and parity, and were randomly assigned to 2 different feeding regimens. Half of the cows in each SCC group (n = 6) were supplemented with PRHM (185 g/cow per day, providing 12.4 g of phenolic compounds per day), and the other half (n = 6) were not supplemented in their diets. The experiment lasted 36 d, whereby the first 24 d were used for adaptation to the diets and the last 12 d for sampling. Data showed that supplementation of PRHM decreased somatic cell score in the milk, indicating improved udder health of cows with high initial SCC, but not in cows with moderate SCC. Also, cows supplemented with PRHM consumed more feed DM, produced greater amounts of milk, and showed an improvement of feed utilization efficiency. However, these cows also lost more back-fat thickness during the experiment. Supplementation of PRHM increased fat- and energy-corrected milk yields in cows with high initial SCC, but not in cows with moderate SCC. Supplementation of PRHM decreased milk fat content, whereas other milk components were not affected by PRHM feeding. The PRHM supplementation decreased the acetate-to-propionate ratio in the rumen fluid, but increased β-hydroxybutyrate and cholesterol concentration in the plasma, irrespective of the initial SCC level in the milk. Other plasma metabolites and liver enzymes were not affected by PRHM supplementation. Apparent nutrient digestibility did not differ among treatments. Overall, supplementation of PRHM seems to be an effective strategy to enhance performance and lower SCC, particularly in cows having high SCC levels in the milk. Further research is warranted to evaluate long-term effects of PRHM supplementation, especially with regard to metabolic health status and reproduction.     

Effects of feeding lutein on production performance,antioxidative status,and milk quality of high-yielding dairy cows

This experiment was conducted to determine the influences of supplementing different levels of an additive containing lutein in the diet of Chinese Holstein lactating cows on production performance, antioxidative plasma metabolites, and milk quality. This study was performed on 60 multiparous Holstein dairy cows in peak lactation. The cows were randomly allocated to 1 of 4 homogeneous treatments, with lutein preparation (extracted from marigolds; effective lutein content was 2%) added at levels of 0, 100, 150, and 200 g/d per head, with the actual available amounts being 0, 2, 3, and 4 g of lutein/d per head, respectively. The experiment lasted for 13 wk, with the first week for adaptation. Milk yield and milk compositions were recorded weekly, and milk concentrations of lutein, dry matter intake, and antioxidative blood index were analyzed in the first, fourth, seventh, and thirteenth week of the study. The results showed that adding lutein in the diet had no effect on dry matter intake compared with the control group; however, it slowed down the trend of decline in milk yield, and had a linear incremental effect on milk yield with increasing concentration of lutein. Dietary lutein tended to quadratically increase the percentage of milk fat, and linearly increased milk lactose concentration, with the highest value when treated at 200 g of lutein preparation/d per head, and decreased somatic cell count, with the lowest values when treated with 150 and 200 g of lutein preparation/d per head. The concentration of lutein in milk linearly increased with the incorporation of the additive, with a value of 0.59, 0.70, 1.20, and 1.50 μg/100 mL when treated with 0, 100, 150, and 200 g/d, respectively. Total plasma antioxidant capacity tended to linearly increase in cows fed lutein preparation, whereas plasma superoxide dismutase and glutathione peroxidase activities did not differ significantly. In conclusion, addition of lutein in the diet could improve the production performance and health status of dairy cows.     

Effect of a short dry period on milk yield and content,colostrum quality,fertility, and metabolic status of Holstein cows

We evaluated the effect of shortening the dry period (DP) on milk and energy-corrected milk (ECM) yields, milk components, colostrum quality, metabolic status, and reproductive parameters. Primiparous (n = 372) and multiparous (n = 400) Israeli Holstein cows from 5 commercial dairy herds were subjected to a 60-d or 40-d DP. Cows within each herd were paired according to milk production, age, days in milk, and expected calving. Analysis of the data from all cows, irrespective of age, revealed significant differences in milk and ECM yields that favored the 60-d DP, with a prominent effect in 2 of 5 examined herds. In primiparous cows, milk and ECM yields were similar between groups in 4 of 5 farms. In multiparous cows undergoing a 60-d (vs. 40-d) DP, milk and ECM yields were higher in 3 herds. These differences could not be explained by milk and ECM yields in cows diagnosed with metritis, ketosis, and mastitis (defined by a somatic cell count threshold of 250,000 cell/mL), distribution of infected and noninfected cows, or new infections during DP and after calving. Including the milk and ECM yields from an average of 19.55 d from the previous lactation revealed higher milk and ECM yields for 40-d (vs. 60-d) DP cows in all herds. Analyzing 2 consecutive lactations revealed similar milk and ECM yields between groups in 4 out of 5 herds. In 1 herd, yields were higher in the 40-d compared with the 60-d DP group. One week after calving, the nonesterified fatty acid concentrations of 40-d DP cows were significantly lower than those of 60-d DP cows, indicating better postpartum energy balance. Colostrum quality, measured as IgG concentration, did not differ between the 2 DP groups. Cows assigned to 40-d DP had better reproductive performance, as reflected by fewer days to first insemination, a lower proportion with >90 d to first insemination, and fewer days to pregnancy. With respect to primiparous cows, a short DP increased conception rate after first artificial insemination and decreased the proportion of nonpregnant cows after 150 d in milk. In light of these findings, we suggest that a short DP be applied for its economic and physiological benefits. This is highly relevant to dairy herds located in regions such as Israel, Spain, and Florida that suffer from reduced milk production during the hot season.     

Subclinical hypocalcemia,plasma biochemical parameters,lipid metabolism,postpartum disease,and fertility in postparturient dairy cows

A study was conducted to evaluate the potential association between Ca status at calving and postpartum energy balance, liver lipid infiltration, disease occurrence, milk yield and quality parameters, and fertility in Holstein cows. One hundred cows were assigned to 1 of 2 groups based on whole-blood ionized Ca concentration ([iCa]) on the day of calving [d 0; hypocalcemic [iCa] <1.0 mmol/L (n = 51); normocalcemic [iCa] ≥1.0 mmol/L (n = 49)]. Cows were blocked based on calving date and parity. Blood samples were collected approximately 14 d from expected calving date (d −14), the day of calving (d 0), and on d 3, 7, 14, 21, and 35 postpartum for measurement of plasma nonesterified fatty acid, iCa, total Ca, glucose, and total and direct bilirubin concentrations, and plasma aspartate aminotransferase and gamma glutamyl transferase activities. Liver biopsies were obtained from a subset of cows on d 0, 7, and 35 for quantification of lipid content. Milk samples were collected on d 3, 7, 14, 21, and 35 postpartum for measurement of somatic cell count and percentages of protein, fat, and solids-not-fat. Data for peak test-day milk yield, services per conception, and days open were obtained from Dairy Herd Improvement Association herd records. Disease occurrence was determined based on herd treatment records. Hypocalcemic cows had significantly higher nonesterified fatty acids on d 0. Hypocalcemic cows also had significantly more lipid in hepatocytes on d 7 and 35 postpartum. However, no statistically significant differences were observed between groups for plasma aspartate aminotransferase and gamma glutamyl transferase activities or total and direct bilirubin concentrations. Milk protein percentage was lower in hypocalcemic cows on d 21 and 35. However other milk quality variables (somatic cell count, milk fat percentage, and solids-not-fat) and milk yield variables (peak test-day milk yield and 305-d mature-equivalent 4% fat-corrected milk yield) did not differ between groups. No differences were observed between groups in the occurrence of clinical mastitis, ketosis, displaced abomasum, dystocia, retained placenta, metritis, or fertility measures (percentage cycling at 50–60 d postpartum, services per conception, or days open). These data suggest that early lactation fatty acid metabolism differs between cows with subclinical hypocalcemia and their normocalcemic counterparts.     

磁珠法提取植物蛋白饮料DNA

目的 建立一种快速、高效的植物蛋白饮料基因组DNA提取方法并应用于植物蛋白饮料中植物源性成分的检测。方法 以豆浆、豆奶、芝麻糊、花生牛奶、榛子乳5种植物蛋白饮料为研究对象, 建立利用硅羟基磁珠提取植物蛋白饮料DNA的方法, 通过分析所提取DNA的浓度和纯度, 实时荧光PCR扩增效率, 并与十六烷基三甲基溴化铵法(cetyltrimethylammonium ammonium bromide, CTAB)比较, 综合评价磁珠法提取植物蛋白饮料的效果。结果 大部分样品磁珠法提取的DNA浓度比CTAB法高, ODA260/A280均大于1.70。 结论 磁珠法提取的DNA纯度较高, 杂质少, 能满足植物蛋白饮料源性成分的分析要求, 尤其适用于大豆类蛋白饮料的DNA提取, 为快速、高效获取质量好的植物蛋白饮料基因组DNA提供参考。     

Technical note: Whole-genome amplification of DNA extracted from cattle semen samples

The bovine genome sequence project and the discovery of many thousands of bovine single nucleotide polymorphisms has opened the door for large-scale genotyping studies to identify genes that contribute to economically important traits with relevance to the beef and dairy industries. Large amounts of DNA will be required for these research projects. This study reports the use of the whole-genome amplification (WGA) method to create an unlimited supply of DNA for use in genotyping studies and long-term storage for future gene discovery projects. Two commercial WGA kits (GenomiPhi, Amersham Biosciences, Sydney, Australia, and REPLI-g, Qiagen, Doncaster, Australia) were used to amplify DNA from straws of bull semen, resulting in an average of 7.2 and 67 μg of DNA per reaction, respectively. The comparison of 3.5 kb of sequences from the amplified and unamplified DNA indicated no detectable DNA differences. Similarly, gene marker analysis conducted on genomic DNA and DNA after WGA indicated no difference in marker amplification or clarity and accuracy of scoring for approximately 10,000 single nucleotide polymorphism markers when compared with WGA samples genotyped in duplicate. These results illustrate that WGA is a suitable method for the amplification and recovery of DNA from bull semen samples for routine genomic investigations.     

Effects of dietary vitamin C on neutrophil function and responses to intramammary infusion of lipopolysaccharide in periparturient dairy cows

Neutrophil function and the severity and incidence of mastitis in dairy cows is related to the intake of many antioxidant nutrients. Because vitamin C is the major water-soluble antioxidant in mammals, we examined the effect of dietary vitamin C on neutrophil function and responses to intramammary infusion of lipopolysaccahride (LPS) in periparturient dairy cows. At 2 wk before anticipated calving, Holstein cows were fed diets that provided 0 (16 cows) or 30 (15 cows) g/d of supplemental vitamin C (phosphorylated ascorbic acid). Treatments continued until 7 d after cows received an infusion of 10 μg of LPS into one quarter of the mammary gland (on average, this occurred 32 d postcalving). Supplementation of vitamin C increased plasma concentrations of vitamin C at calving, but no differences were observed in samples taken 24 h postinfusion. Concentrations of vitamin C in milk (24 h postinfusion) and in neutrophils (calving and 24 h postinfusion) were not affected by treatment, but vitamin C concentrations in neutrophils isolated from milk were about 3 times greater than concentrations in blood neutrophils. The LPS infusion did not alter concentrations of vitamin C in plasma or milk, suggesting that the LPS model did not produce the same effects as a bacterial infection of the mammary gland with respect to antioxidant effects. Supplemental vitamin C had no effect on neutrophil phagocytosis or bacterial kill. Dietary vitamin C reduced the milk somatic cell count but did not affect the febrile response or milk production following LPS infusion.     

Residual feed intake of lactating Holstein-Friesian cows predicted from high-density genotypes and phenotyping of growing heifers

A genomic prediction for residual feed intake (RFI) developed in growing dairy heifers (RFI_gro) was used to predict and test breeding values for RFI in lactating cows (RFI_lac) from an independent, industry population. A selection of 3,359 cows, in their third or fourth lactation during the study, of above average genetic merit for milk production, and identified as at least 15/16ths Holstein-Friesian breed, were selected for genotyping from commercial dairy herds. Genotyping was carried out using the bovine SNP50 BeadChip (Illumina Inc., San Diego, CA) on DNA extracted from ear-punch tissue. After quality control criteria were applied, genotypes were imputed to the 624,930 single nucleotide polymorphisms used in the growth study. Using these data, genomically estimated breeding values (GEBV) for RFI_gro were calculated in the selected cow population based on a genomic prediction for RFI_gro estimated in an independent group of growing heifers. Cows were ranked by GEBV and the top and bottom 310 identified for possible purchase. Purchased cows (n = 214) were relocated to research facilities and intake and body weight (BW) measurements were undertaken in 99 “high” and 98 “low” RFI_gro animals in 4 consecutive groups [beginning at d 61 ± 1.0 standard error (SE), 91 ± 0.5 SE, 145 ± 1.3 SE, and 191 ± 1.5 SE d in milk, respectively] to measure RFI during lactation (RFI_lac). Each group of ~50 cows (~25 high and ~25 low RFI_gro) was in a feed intake facility for 35 d, fed pasture-alfalfa cubes ad libitum, milked twice daily, and weighed every 2 to 3 d. Milk composition was determined 3 times weekly. Body weight change and BW at trial mid-point were estimated by regression of pre- and posttrial BW measurements. Residual feed intake in lactating cows was estimated from a linear model including BW, BW change, and milk component yield (as MJ/d); RFI_lac differed consistently between the high and low selection classes, with the overall means for RFI_lac being +0.32 and −0.31 kg of dry matter (DM) per day for the high and low classes, respectively. Further, we found evidence of sire differences for RFI_lac, with one sire, in particular, being highly represented in the low RFI_gro class, having a mean RFI_lac of −0.83 kg of DM per day in 47 daughters. In conclusion, genomic prediction of RFI_gro based on RFI measured during growth will discriminate for RFI_lac in an independent group of lactating cows.     

Lactoperoxidase activity in milk is correlated with somatic cell count in dairy cows

Lactoperoxidase (LPO) is a milk protein with antimicrobial function. The present study was undertaken to examine the correlation between LPO activity and somatic cell count (SCC) in milk to use LPO activity as an indicator of mastitis. Composite milk of 36 cows and quarter milk of 3 cows were collected once per week from 0 to 300 d postpartum and twice per day for 1 wk, respectively. For the measurement of LPO activity, milk was mixed with tetramethylbenzidine solution and incubated at 37°C for 30 min, followed by the measurement of optical density. When only milk with low SCC (132 ± 12 × 10³ cells/mL) was used, a significant decrease in LPO activity was detected in primiparous cows from 0 to 4 mo postpartum. Lactoperoxidase activities of primiparous cows in mo 1, 2, and 3 postpartum were significantly higher than those in multiparous cows. When composite milk was divided based on LPO activity, the SCC was significantly higher in the groups with LPO activity >5 and from 3 to 3.9 U/mL in the second- and fourth-parity cows, respectively, compared with the group with LPO activity <2 U/mL. Extremely high SCC were found in the ≥fifth-parity cows, even in low-LPO activity groups. In the case of quarter milk, higher LPO activity was associated with increased SCC in all 3 cows. The percentage of quarter milk samples with high SCC (4,062 ± 415 × 10³ cells/mL) increased with an increase in the LPO activity. The percentage of quarter milk samples with high SCC was 50.0 to 100% in the milk with LPO activity ≥5 U/mL. These results indicate that the correlation of LPO activity to the SCC in bovine milk may point to the potential use of the former as an indicator of SCC.     

PCR 检测牛乳中大肠杆菌基因组DNA 的提取方法

为获得一种适于牛乳样品大肠杆菌PCR 检测的基因组DNA 提取方法,对饱和酚法、CTAB 法、试剂盒法及溶剂裂解法等4 种提取方法加以比较,通过考察DNA 的纯度、定量分析以及PCR 分析,确定一套有效、快速、适合牛乳中提取大肠杆菌的基因组DNA 方法--溶剂热裂解法。结果显示该方法提取的DNA 模板,适于PCR扩增大肠杆菌DNA,可以用于牛乳中的大肠杆菌检测。     

Effect of lactation number, year, and season of initiation of lactation on milk yield of cows hormonally induced into lactation and treated with recombinant bovine somatotropin

Records representing data from 1,500 barren Holstein cows over an 8-yr period from a large commercial dairy farm in northern Mexico were analyzed to determine the effects of lactation number and season and year of initiation of lactation on milk production of cows induced hormonally into lactation and treated with recombinant bovine somatotropin (rbST) throughout lactation. Peak and 305-d milk yields were also assessed as predictors of total milk yield in cows induced into lactation. A significant quadratic relationship was found between 305-d milk yield and number of lactation [7,607 ± 145 and 9,548 ± 181 kg for first- and ≥6-lactation cows, respectively; mean ± standard error of the mean (SEM)] with the highest production occurring in the fifth lactation. Total milk yields of cows with ≤2 lactations were approximately 4,500 kg less than milk yields of adult cows (the overall average ± standard milk yield was 13,544 ± 5,491 kg per lactation and the average lactation length was 454 ± 154 d). Moreover, 305-d milk production was depressed in cows induced into lactation in spring (8,804 ± 153 kg; mean ± SEM) and summer (8,724 ± 163 kg) than in fall (9,079 ± 151 kg) and winter (9,085 ± 143 kg). Partial regression coefficients for 305-d milk yield and peak milk yield indicated an increment of 157 kg of milk per lactation per 1-kg increase in peak milk yield (r² = 0.69). Neither peak milk yield (r² = 0.18) nor 305-d milk yield (r² = 0.29) was accurate for predicting total milk yield per lactation. Year, parity, and season effects had significant influence on milk yield of cows induced into lactation and treated with rbST throughout lactation, and peak milk yield can assist in the prediction of 305-d milk yield but not total milk yield. This study also showed that hormonal induction of lactation in barren high-yielding cows is a reliable, practical, and affordable technique in countries where rbST treatment and prolonged steroid administration of dairy cows are legally permitted.     

Genetic parameters of milk coagulation properties and their relationships with milk yield and quality traits in Italian Holstein cows

Milk coagulation properties (MCP) are an important aspect in assessing cheese-making ability. Several studies showed that favorable conditions of milk reactivity with rennet, curd formation rate, and curd strength, as well as curd syneresis, have a positive effect on the entire cheese-making process and subsequently on the ripening of cheese. Moreover, MCP were found to be heritable, but little scientific literature is available about their genetic aspects. The aims of this study were to estimate heritability of MCP and genetic correlations among MCP and milk production and quality traits. A total of 1,071 Italian Holstein cows (progeny of 54 sires) reared in 34 herds in Northern Italy were sampled from January to July 2004. Individual milk samples were collected during the morning milking and analyzed for coagulation time (RCT), curd firmness (a₃₀), pH, titratable acidity, fat, protein, and casein contents, and somatic cell count. About 10% of individual milk samples did not coagulate in 31 min, so they were removed from the analyses. Estimates of heritability for RCT and a₃₀ were 0.25 ± 0.04 and 0.15 ± 0.03, respectively. Estimates of genetic correlations between MCP traits and milk production traits were negligible except for a₃₀ with protein and casein contents (0.44 ± 0.10 and 0.53 ± 0.09, respectively). Estimates of genetic correlations between MCP traits and somatic cell score were strong and favorable, as well as those between MCP and pH and titratable acidity. Selecting for high casein content, milk acidity, and low somatic cell count might be an indirect way to improve MCP without reducing milk yield and quality traits.     

Lactation performance and amino acid utilization of cows fed increasing amounts of reduced-fat dried distillers grains with solubles

The use of a solvent-extraction process that removes corn oil from distillers grains produces a reduced-fat co-product (RFDG). To determine the optimal concentration of RFDG in mid-lactation diets, 22 multiparous and 19 primiparous Holstein cows were used in a completely randomized design for 8 wk, including a 2-wk covariate period. The RFDG was included at 0, 10, 20, and 30% of the diet on a dry matter basis, replacing soybean feedstuffs. Increasing RFDG in diets had no effect on dry matter intake (23.1 kg/d) or milk production (35.0 kg/d). Milk fat percentage increased linearly from 3.18 to 3.72% as RFDG increased from 0 to 30% of the diet. Similarly, milk fat yield tended to increase linearly from 1.08 to 1.32 kg/d. Milk protein percentage (2.99, 3.06, 3.13, and 2.99% for diets with RFDG from 0 to 30%) responded quadratically, whereas protein yield was not affected by treatment. Milk urea N decreased linearly from 15.8 to 13.1 mg/dL. The efficiency of N utilization for milk production was not affected by including RFDG (26.1%), whereas the efficiency of milk production (energy-corrected milk divided by dry matter intake) tended to increase linearly with increasing RFDG in the diet. Similarly, concentrations of plasma glucose increased linearly. Arterial Lys decreased linearly from 66.0 to 44.8 μM/L, whereas arterial Met increased linearly from 16.5 to 29.3 μM/L. Arteriovenous difference of Lys decreased linearly from 42.6 to 32.5 μM/L, whereas that of Met was unaffected. The extraction of Lys by the mammary gland increased linearly from 64.3 to 72.2%, whereas that of Met decreased linearly from 71.6 to 42.7%. Feeding up to 30% of RFDG in a mid-lactation diet supported lactation performance similarly to cows fed the soybean protein-based diet (0% RFDG).     

A method to quantify changes in supply of metabolizable methionine to dairy cows using concentrations of selenium in milk

A method that accurately quantifies changes in the supply of metabolizable Met following a dietary change will allow accurate economic comparisons of various Met sources. This paper describes a novel method of estimating the relative supply of metabolizable Met based on changes in the concentration of Se in milk. Selenized yeast (Se-yeast) contains selenomethionine (Se-met) and because Se-met and Met are indistinguishable by cells, Se-met can be used as a tracer of Met. We hypothesized that if the size of the Met pool was increased but intake of Se-met was constant, the concentration of Se in milk relative to milk Met would decrease. To test this hypothesis, 6 Holstein cows were fed a diet that contained 0.3 mg of Se from Se-yeast/kg of diet DM and then in a 2-period crossover experiment, were abomasally infused with water (control) or an aqueous solution that provided 9 g of Met/d. Milk was sampled during the infusion and the specific activity (SA) of milk (Se concentration divided by Met concentration) was calculated for each treatment. The SA in milk from Met-infused cows was divided by SA in milk from control cows to calculate the change in supply of metabolizable Met. As hypothesized, infusing Met reduced the SA of milk (84.7 vs. 72.5 μg of Se/mg of Met). The calculated flow of metabolizable Met was 17% greater when cows were infused with 9 g of Met/d compared with cows infused with water (essentially the same difference was measured using SA calculated with N concentrations of milk). Assuming the infused Met was 100% absorbed, the flow of metabolizable Met for control cows was 9/0.17 = 53 g of Met/d, which agreed well with literature data and estimates derived from common nutritional models.     

Detection of Clinical Mastitis with the Help of a Thermal Camera

Increasing dairy farm size and increase in automation in livestock production require that new methods are used to monitor animal health. In this study, a thermal camera was tested for its capacity to detect clinical mastitis. Mastitis was experimentally induced in 6 cows with 10 μg of Escherichia coli lipopolysaccharide (LPS). The LPS was infused into the left forequarter of each cow, and the right forequarters served as controls. Clinical examination for systemic and local signs and sampling for indicators of inflammation in milk were carried out before morning and evening milking throughout the 5-d experimental period and more frequently on the challenge day. Thermal images of experimental and control quarters were taken at each sampling time from lateral and medial angles. The first signs of clinical mastitis were noted in all cows 2 h postchallenge and included changes in general appearance of the cows and local clinical signs in the affected udder quarter. Rectal temperature, milk somatic cell count, and electrical conductivity were increased 4 h postchallenge and milk N-acetyl-β-D-glucosaminidase activity 8 h postchallenge. The thermal camera was successful in detecting the 1 to 1.5°C temperature change on udder skin associated with clinical mastitis in all cows because temperature of the udder skin of the experimental and control quarters increased in line with the rectal temperature. Yet, local signs on the udder were seen before the rise in udder skin and body temperature. The udder represents a sensitive site for detection of any febrile disease using a noninvasive method. A thermal camera mounted in a milking or feeding parlor could detect temperature changes associated with clinical mastitis or other diseases in a dairy herd.