Identification of internal control genes for quantitative polymerase chain reaction in mammary tissue of lactating cows receiving lipid supplements

Dietary lipid supplements affect mammary lipid metabolism partly through changes in lipogenic gene expression. Quantitative PCR (qPCR) is a sensitive, reliable, and accurate technique for gene expression analysis. However, variation introduced in qPCR data by analytical or technical errors needs to be accounted for via normalization using appropriate internal control genes (ICG). Objectives were to mine individual bovine mammary microarray data on >13,000 genes across 66 cows from 2 independent studies to identify the most suitable ICG for qPCR normalization. In addition to unsupplemented control diets, cows were fed saturated or unsaturated lipids for 21 d or were infused with supplements (butterfat, conjugated linoleic acid mixture, long-chain fatty acids) into the abomasum to modify milk fat synthesis and fatty acid profiles. We identified 49 genes that did not vary in expression across the 66 samples. Subsequent gene network analysis revealed that 22 of those genes were not co-regulated. Among those COPS7A, CORO1B, DNAJC19, EIF3K, EMD, GOLGA5, MTG1, UXT, MRPL39, GPR175, and MARVELD1 (sample/reference expression ratio = 1 ± 0.1) were selected for PCR analysis upon verification of goodness of BLAT/BLAST sequence and primer design. Relative expression of B2M, GAPDH, and ACTB, previously used as ICG in bovine mammary tissue, was highly variable (0.9 ± 0.6) across studies. Gene stability analysis via geNorm software uncovered MRPL39, GPR175, UXT, and EIF3K as having the most stable expression ratio and, thus, suitable as ICG. Analysis also indicated that use of 3 ICG was most appropriate for calculating a normalization factor. Overall, the geometric average of MRPL39, UXT, and EIF3K is ideal for normalization of mammary qPCR data in studies involving lipid supplementation of dairy cows. These novel ICG could be used for normalization in similar studies as alternatives to the less-reliable ACTB, GAPDH, or B2M.     

Effects of oral administration of acidogenic boluses at dry-off on performance and behavior of dairy cattle

The aim of this study was to evaluate the potential of oral acidogenic mineral boluses (196 g) containing anionic salts to facilitate the transition from lactation to the dry stage by inducing a mild and temporary metabolic acidosis at dry-off. In experiment 1, 84 lactating cows were randomly allocated to 1 of 3 treatment groups consisting of an oral administration of 0, 1, or 2 boluses 5 d before dry-off to evaluate the effects on milk production. In experiment 2, 16 lactating cows were involved in a crossover study to evaluate the effects of the administration of 2 boluses on milk production, feed intake, and urine pH. In experiment 3, 152 lactating cows were allocated to 1 of 2 treatments (control: no treatment; bolus: 2 oral boluses the day before last milking) to evaluate udder pressure, incidence of milk leakage, and lying behavior during the first days following dry-off. Also, milk yield in the subsequent lactation for all enrolled cows was recorded during the first 60 DIM. In experiment 1, cows receiving 2 boluses had the greatest reduction in milk production (?2.56 kg/d of milk) compared with those receiving 1 bolus or no treatment (?1.15 and ?0.23 kg/d, respectively) the second day after bolus application. In experiment 2, the application of oral boluses decreased feed intake of cows during the first 3 d following treatment, and milk production was reduced on d 2 and 3 after bolus application. Reduced urine pH at 8 and 24 h after treatment was observed in bolus cows compared with control cows. In experiment 3, bolus cows had lower udder pressure after drying off, but incidence of milk leakage did not differ between treatments. Bolus cows had an additional 85 min of lying time in the 24 h following dry-off. Serum P and β-OH-butyrate concentrations were lower in bolus cows than in control cows after dry-off, but no other differences in blood parameters between treatments were observed. Also, no differences in milk yield in the subsequent lactation were observed between treatments. It is concluded that oral bolus application diminishes feed intake and milk production, and, if applied at dry-off, it decreases udder pressure and increases lying time during the first 24 h after dry-off.     

Metabolic and production profiles of dairy cows in response to decreased nutrient density to increase physiological imbalance at different stages of lactation

Physiological imbalance (PI) is a situation in which physiological parameters deviate from the normal, and cows consequently have an increased risk of developing production diseases and reduced production or reproduction. Our objectives were to (1) determine the effect of stage of lactation and milk yield on metabolic and production responses of cows during a nutrient restriction period to experimentally increase PI; (2) identify major metabolites that relate to degree of PI; and (3) identify potential biomarkers in milk for on-farm detection of PI throughout lactation. Forty-seven Holstein cows in early [n=14; 49±22 d in milk (DIM); parity=1.6±0.5], mid (n=15; 159±39 DIM; parity=1.5±0.5), and late (n=18; 273±3 DIM; parity=1.3±0.5) lactation were used. Prior to restriction, all cows were fed the same total mixed ration ad libitum. All cows were then nutrient restricted for 4 d by supplementing the ration with 60% wheat straw to induce PI. After restriction, cows returned to full feed. Daily milk yield was recorded and composite milk samples were analyzed for fat, protein, lactose, citrate, somatic cells, uric acid, alkaline phosphatase, β-hydroxybutyrate (BHBA), and milk urea nitrogen. Blood was collected daily and analyzed for metabolites: nonesterified fatty acids (NEFA), BHBA, glucose, plasma urea nitrogen, and insulin. The revised quantitative insulin sensitivity check index (RQUICKI) was calculated for each cow. Liver biopsies collected before and during restriction were analyzed for triglycerides, glycogen, phospholipids, glucose, and total lipid content. A generalized linear mixed model was used to determine the effect of stage of lactation on responses during restriction. Regression analyses were used to examine the effect of pre-restriction levels on changes during restriction. Similar decreases in milk yield among groups indicate that the capacity of individual responses is dependent on milk yield but the coping strategies used are dependent on stage of lactation. Milk yield was a better predictor of feed intake than DIM. Plasma glucose decreased for all cows, and cows in early lactation had increased plasma BHBA, whereas cows in later lactation had increased NEFA during restriction. Milk citrate had the greatest increase (58%) during restriction for all cows. Results reported here identified metabolites (i.e., glucose, NEFA, BHBA, cholesterol) as predictors of PI and identified milk citrate as a promising biomarker for PI on farm.     

Addition of straw to the early-lactation diet: Effects on feed intake,milk yield,and subclinical ketosis in Holstein cows

This study evaluated feed intake, milk yield, and subclinical ketosis in dairy cows in early lactation fed 2 different diets postpartum. Cows are typically offered a high-energy ration immediately after calving. We compared a conventional high-energy total mixed ration (TMR) with a transition ration that contained chopped straw. We predicted that adding chopped straw would increase dry matter intake, milk production, and indicators of energy metabolism during the first 3 wk of lactation compared to cows fed a conventional high-energy TMR. We also predicted that carryover effects would be likely for at least 2 wk after treatment ended. A total of 68 mixed-age Holstein cows were enrolled in the study 3 wk before their expected calving. All cows were managed on a single high-forage diet during the dry period. At calving, cows were allocated to 1 of the 2 diets: half to the conventional high-energy TMR (CTMR; n = 34; net energy for lactation = 1.61 Mcal/kg; neutral detergent fiber = 31.7%), and the other half to a high-forage TMR containing chopped wheat straw, equivalent to 4.27% dry matter (STMR; n = 34; net energy for lactation = 1.59 Mcal/kg; neutral detergent fiber = 33.7%) for 3 wk after calving. Cows on STMR were then shifted to CTMR for the next 2 wk to study short-term residual effects on the performance of cows. Treatments were balanced for parity, body condition score, and body weight. Feed intake was measured daily from 2 wk before to 5 wk after calving using automatic feed bins. Blood was sampled twice weekly from 2 wk before to 5 wk after calving, and β-hydroxybutyrate and glucose were measured in serum samples. Subclinical ketosis was identified using a threshold of β-hydroxybutyrate ≥1.0 mmol/L in wk 1 after calving and ≥1.2 mmol/L in wk 2 to 5 after calving. Cows were milked twice daily, and weekly samples (composite samples of morning and afternoon milkings) were analyzed to determine total solids, fat, protein, lactose, and somatic cell count. Data were analyzed in 2 separate periods: the treatment phase (wk +1, +2, and +3) and the post-treatment phase (wk +4 and +5). The addition of straw to the TMR negatively affected the dry matter intake of STMR cows during wk 2 and 3 of lactation. Daily milk yield during the first 5 wk of lactation was lower in STMR cows than in CTMR cows. Concentrations of β-hydroxybutyrate were higher in CTMR cows than in STMR cows during wk 1, but this effect was reversed during wk 2 and 3 of lactation. By 21 d in milk, STMR cows had a greater risk of developing subclinical ketosis than CTMR cows. Adding chopped wheat straw to the TMR during the first 21 d after calving lowered dry matter intake and provided no metabolic or production benefits to lactating dairy cattle.     

Anti-idiotypic responses of lactating cows immunized with monoclonal antibodies against bovine somatotropin.

The objective of this study was to produce anti-idiotypic antibodies with bovine somatotropin (bST)-like activity by active immunization of lactating cows and to determine their effects on milk yield. Several monoclonal antibodies against bST were evaluated for their interaction with bST in a rat growth bioassay. Two bST-agonist monoclonal antibodies (1 and 2), and two bST-antagonist monoclonal antibodies (3 and 4) were selected. Cows were immunized with immunoglobulin G as a control (n = 12) or with one of the four anti-bST monoclonal antibodies (1, 2, 3, 4; n = 12) on d 3, 24, 45, 66, 87, 108, 129, and 150 of lactation. From wk 3 of lactation, all cows immunized with each of the four anti-bST monoclonal antibodies developed anti-idiotypes until wk 30 of lactation. Total lactation yields were not different among monoclonal antibodies 2, 3, and 4 and control cows (9299, 9321, 9733, and 9415 kg, respectively). However, cows immunized with anti-bST monoclonal antibody 1 had reduced lactation yield compared with cows on other treatments (8136 kg). Daily milk yield of cows immunized with monoclonal antibody 1 was decreased from wk 9 of lactation [36.2 vs. 40.9 kg/d (control)] until the end of lactation, concomitantly with decreased bST concentration from wk 9 of lactation. Cows immunized with anti-bST monoclonal antibody 4 had increased milk yield compared with that of controls during wk 3 to 6 and wk 18 to 21 of lactation. Therefore, anti-idiotypes directed against anti-bST 1 had bST-antagonistic effects on lactation performance; anti-idiotypes against anti-bST 4 transiently increased milk yield.     

The effects of L-type amino acid transporter 1 on milk protein synthesis in mammary glands of dairy cows

The mammary gland requires the uptake of AA for milk protein synthesis during lactation. The L-type amino acid transporter 1 (LAT1, encoded by SLC7A5), found in many different types of mammalian cells, is indispensable as a transporter of essential AA to maintain cell growth and protein synthesis. However, the function of LAT1 in regulating milk protein synthesis in the mammary gland of the dairy cow remains largely unknown. For the current study, we characterized the relationship between LAT1 expression and milk protein synthesis in lactating dairy cows and investigated whether the mammalian target of rapamycin complex 1 (mTORC1) signaling controls the expression of LAT1 in their mammary glands. We found that LAT1 and the heavy chain of its chaperone, 4F2, were expressed in mammary tissues of lactating cows, with the expression levels of LAT1 and the 4F2 heavy chain being significantly greater in lactating mammary tissues with high-milk protein content (milk yield, 33.8 ± 2.1 kg/d; milk protein concentration >3%, wt/vol,; n = 3) than in tissues from cows with low-milk protein content (milk yield, 33.7 ± 0.5 kg/d; milk protein concentration <3%, wt/vol; n = 3). Immunofluorescence staining of sectioned mammary tissues from cows with high and low milk protein content showed that LAT1 was located on the whole plasma membrane of alveolar epithelial cells, suggesting that LAT1 provides essential AA to the mammary gland. In cultured mammary epithelial cells from the dairy cows with high-milk protein content, knockdown of LAT1 expression decreased cell viability and β-casein expression; in contrast, overexpression of LAT1 had the opposite effect. Inhibition of mTORC1 by rapamycin attenuated the phosphorylation of molecules related to mTORC1 signaling and caused a marked decrease in LAT1 expression in the cultured cells; expression of β-casein also decreased significantly. These results suggest that LAT1 is involved in milk protein synthesis in the mammary glands of lactating dairy cows and that the mTORC1 signaling pathway might be a control point for regulation of LAT1 expression, which could ultimately be used to alter milk protein synthesis.     

The effect of dry period length and postpartum level of concentrate on milk production,energy balance,and plasma metabolites of dairy cows across the dry period and in early lactation

Shortening or omitting the dry period (DP) improves energy balance (EB) in early lactation because of a reduction in milk yield. Lower milk yield results in lower energy demands and requires less energy intake. The aim of this study was to evaluate the effects of DP length and concentrate level postpartum on milk yield, feed intake, EB, and plasma metabolites between wk ?4 and 7 relative to calving of cows of second parity or higher. Holstein-Friesian dairy cows (n = 123) were assigned randomly to 1 of 2 DP lengths: 0-d DP (n = 81) or 30-d DP (n = 42). Prepartum, cows with a 0-d DP received a lactation ration based on grass silage and corn silage (6.4 MJ of net energy for lactation/kg of dry matter). Cows with a 30-d DP received a dry cow ration based on grass silage, corn silage, and straw (5.4 MJ of net energy for lactation/kg of dry matter). Postpartum, all cows received the same basal lactation ration as provided to lactating cows prepartum. Cows with a 0-d DP were fed a low level of concentrate up to 6.7 kg/d based on the requirement for their expected milk yield (0-d DP-L; n = 40) or the standard level of concentrate up to 8.5 kg/d (0-d DP-S; n = 41), which was equal to the concentrate level for cows with a 30-d DP (30-d DP-S; n = 42) based on requirements for their expected milk yield. Prepartum dry matter intake, concentrate intake, basal ration intake, energy intake, plasma β-hydroxybutyrate (BHB), and insulin concentrations were greater and plasma free fatty acids (FFA) and glucose concentrations were lower, but EB was not different in cows with a 0-d DP compared with cows with a 30-d DP. During wk 1 to 3 postpartum, milk fat yield and plasma BHB concentration were lower and dry matter intake and concentrate intake were greater in cows with a 0-d DP compared with cows with a 30-d DP. During wk 4 to 7 postpartum, fat- and protein-corrected milk (FPCM), lactose content, and lactose and fat yield were lower in 0-d DP-L or 0-d DP-S cows compared with 30-d DP-S cows. Basal ration intake, EB, body weight, plasma glucose, and insulin and insulin-like growth factor-1 concentrations were greater and plasma FFA and BHB concentrations were lower in 0-d DP-L and 0-d DP-S cows compared with 30-d DP-S cows. Concentrate and energy intake were lower in 0-d DP-L cows than in 0-d DP-S or 30-d DP-S cows. Milk yield and concentrations of plasma metabolites did not differ in wk 4 to 7, although EB was lower in wk 6 and 7 postpartum in 0-d DP-L cows than in 0-d DP-S cows. In conclusion, a 0-d DP reduced milk yield and improved EB and metabolic status of cows in early lactation compared with a 30-d DP. Reducing the postpartum level of concentrate of cows with a 0-d DP did not affect fat- and protein-corrected milk yield or plasma FFA and BHB concentrations in early lactation but did reduce EB in wk 6 and 7 postpartum.     

Cow sensitivity to electricity during milking.

Alternating currents were delivered to lactating cattle through the milk during milking. Electrodes were placed at the top of each short milk tube and jointed for one electrical contact. A metal grid on which the cows' rear hooves stood during milking was the second contact. Constant voltages (0 to 16 V) applied to contacts showed first lactation cows to be more sensitive than multiple lactation cows. First lactation cows kicked milking machines at 8 V (currents greater than 5 mA), and multiple lactation cows kicked at 16 V (currents greater than 8 mA). At lower voltages, there were no consistent significant differences in milking duration, milk yield, or composition for primary or residual milk. Application of constant currents of 5 mA for first lactation cows and 8 mA for multiple lactation cows produced no undesired behaviors but did result in some differences in production variables. Milking duration decreased during application of constant current to first lactation cows. Blood cortisol monitored in the multiple lactation cows during trial 2 showed a significant increase during milking but was equivalent or less during application of current. This study demonstrates that currents of 5 mA or less, delivered through the milk line, did not produce any direct economic effect. To produce this current, voltages on the milk pipe line would have to be in excess of 125 V (obvious human safety hazard) or in excess of 5 V on the claw of the milking cluster.     

Propionibacteria fed to dairy cows: effects on energy balance,plasma metabolites and hormones,and reproduction

To determine the effect of feeding Propionibacteria on energy balance, milk yield, and composition, metabolites and hormones of early-lactating dairy cows, multiparous Holstein cows were individually fed a total mixed ration from -2 to 12 wk postpartum with no addition (control, n = 10) or with an additional 17 g of Propionibacteria culture daily (Treated, n = 9). Daily feed intake and milk production were recorded. Plasma cholesterol, nonesterified fatty acids (NEFA), leptin, insulin, glucose, insulin-like growth factor-I (IGF-I), IGF-binding proteins (IGFBP), and progesterone concentrations were measured up to twice weekly. Cows fed supplemental Propionibacteria had improved energy balance at wk 1 of lactation and had lower DMI per kg of body weight than control cows on wk 3 to 7, 10, and 12. Cows fed Propionibacteria had a greater percentage of milk protein and solids-not-fat and plasma NEFA concentrations than did control cows only at wk 1 of lactation. Treatment did not affect milk production or percentage of milk fat and lactose. Leptin levels were greater in treated than control cows throughout the study. Plasma glucose, insulin, cholesterol, IGFBP-3, and IGF-I concentrations were not affected by feeding Propionibacteria, but those variables increased with week postpartum. Plasma IGFBP-2 and IGFBP-5 levels decreased with week postpartum. Measures of reproductive and ovarian function did not differ between Propionibacteria-treated and control cows. Feeding Propionibacteria culture to transition and early lactating dairy cows may hold potential for improved milk protein production and metabolic efficiency during early lactation, without affecting reproductive function.     

Effects of varying lactation length on milk production capacity of cows in pasture-based dairying systems

The aim of this experiment was to quantify the milk production capacity of cows undergoing extended lactations while fed a pasture-based diet typical of those used in the seasonal-calving dairying systems of Victoria, Australia. One hundred twenty-five Holstein cows were randomly assigned to 1 of 5 groups. Breeding was progressively delayed after calving to enable management of the groups for lactation lengths of 10, 13, 16, 19, and 22 mo (equivalent to calving intervals of 12 to 24 mo). Cows were provided with a daily energy intake of at least 180 MJ of metabolizable energy/cow. This was supplied primarily by grazed pasture with supplementary cereal grain, pasture silage, and hay. Cows were dried off when milk volume fell below 30 kg/wk or when they reached 56 d before their expected calving date. Most cows (>96%) could lactate above this threshold for 16 mo, >80% for 19 mo, and >40% for 22 mo. There were negative relationships between lactation length and annual production of milk and milk solids (milk fat + protein), but losses were small until 16 mo. Annualized yields of milk solids were 497, 498, 495, 474, and 463 kg/cow for the 10, 13, 16, 19, and 22 mo groups, respectively. This reduction in annual production of milk solids with increasing lactation length was relatively less than for milk volume because during extended lactation, cows produced milk with higher concentrations of protein. Cows undergoing extended lactations also finished their lactations having gained more body weight and body condition than cows lactating for only 10 mo. The data showed that many cows on pasture-based diets were capable of lactating longer than the 10 mo that is standard for Victorian herds with seasonally concentrated calving patterns. Further, such extended lactations could be achieved with little penalty in terms of annual milk solids production.     

Holstein-Friesian calves selected for divergence in residual feed intake during growth exhibited significant but reduced residual feed intake divergence in their first lactation

Residual feed intake (RFI), as a measure of feed conversion during growth, was estimated for around 2,000 growing Holstein-Friesian heifer calves aged 6 to 9 mo in New Zealand and Australia, and individuals from the most and least efficient deciles (low and high RFI phenotypes) were retained. These animals (78 New Zealand cows, 105 Australian cows) were reevaluated during their first lactation to determine if divergence for RFI observed during growth was maintained during lactation. Mean daily body weight (BW) gain during assessment as calves had been 0.86 and 1.15 kg for the respective countries, and the divergence in RFI between most and least efficient deciles for growth was 21% (1.39 and 1.42 kg of dry matter, for New Zealand and Australia, respectively). At the commencement of evaluation during lactation, the cows were aged 26 to 29 mo. All were fed alfalfa and grass cubes; it was the sole diet in New Zealand, whereas 6 kg of crushed wheat/d was also fed in Australia. Measurements of RFI during lactation occurred for 34 to 37 d with measurements of milk production (daily), milk composition (2 to 3 times per week), BW and BW change (1 to 3 times per week), as well as body condition score (BCS). Daily milk production averaged 13.8 kg for New Zealand cows and 20.0 kg in Australia. No statistically significant differences were observed between calf RFI decile groups for dry matter intake, milk production, BW change, or BCS; however a significant difference was noted between groups for lactating RFI. Residual feed intake was about 3% lower for lactating cows identified as most efficient as growing calves, and no negative effects on production were observed. These results support the hypothesis that calves divergent for RFI during growth are also divergent for RFI when lactating. The causes for this reduced divergence need to be investigated to ensure that genetic selection programs based on low RFI (better efficiency) are robust.     

Short communication: Repeated mammary tissue collections during lactation do not alter subsequent milk yield or composition

Mammary biopsy collection (MB) is a valuable approach for studying mammary gland biology, but it is unclear if repeated MB impair the performance of lactating dairy cows. The objective of this trial was to examine the effect of repeated MB during lactation on udder health, dry matter intake (DMI), and lactation performance of lactating dairy cows. Sixty-four multiparous, mid-lactation Holstein cows were enrolled in a 29-wk trial, and 32 cows were randomly selected for repeated MB. The MB and non-MB (NMB) cows had similar parity (2.6 ± 0.9) and days in milk (96.5 ± 56.3 d) at enrollment. All animals were housed in the same barn and managed in the same manner. Cows were milked 3 times daily with milk yield recorded at each milking. Milk composition was measured weekly and DMI recorded daily. Three MB were performed per cow: 1 wk after enrollment and at 15 and 24 wk. The first and third MB were performed on the left rear quarter, whereas the second MB was on the right rear quarter. The MB were performed based on previously described procedures using a rotating stainless steel cannula with a retractable blade connected to a cordless drill, with appropriate sedation and antiseptic treatment after each MB. After MB, udder health, surgical wound healing, and presence of blood in milk were visually examined at each milking. Blood was cleared from milk 3.86 ± 2.0 d after MB. During the experiment, 4 rear quarters of MB cows and 5 rear quarters from NMB cows were diagnosed and treated for clinical mastitis. No differences were observed in DMI, milk yield, somatic cell score, or milk concentration and yields of fat, protein, lactose, and solids-not-fat between MB and NMB. In conclusion, lactating cows recover rapidly from MB, and repeated MB have no long-term effects on DMI, milk yield and composition, or udder health of lactating dairy cows.     

Effect of dry period management on mammary gland function and its endocrine regulation in dairy cows

The objective of this study was to evaluate the effect of shortening the dry period on the mammary gland and the hormonal regulation of its functions. Holstein cows (n = 18) were assigned to a short dry period (SDP; 35 d; n = 9) or a conventional dry period (CDP; 65 d; n = 9). All cows were fed the same diets, with the exception that, during the dry period, the SDP cows received only the pre-calving diet for 35 d, whereas the CDP cows were fed a high-fiber diet from 65 to 28 d before calving and then received the same pre-calving diet as the SDP cows. Mammary gland functional capacity was evaluated at 70 days in milk, and mammary biopsies were taken in early and midlactation. Dry period length averaged 64.3 ± 1.1 and 31.9 ± 1.0 d for the CDP and SDP cows, respectively. The SDP cows had a lower milk yield and a lower energy-corrected milk yield compared with the CDP cows. The SDP cows also had a lower dry matter intake from wk 5 to 20 of lactation and tended to have lower plasma concentrations of β-hydroxybutyrate from wk 1 to 4. Prepartum serum progesterone and estradiol concentrations were unaffected by the dry period management. Serum growth hormone concentrations and milking-induced prolactin release were similar in both groups. However, during the period when the CDP cows were dry but the SDP cows were still being milked (wk −9 to −6), serum prolactin concentrations were higher in the SDP cows than in the CDP cows. The SDP cows had a lower milk BSA content than the CDP cows after the dry period and similar milk lactose concentrations, suggesting that their mammary tight junctions were closed following parturition and, therefore, that the later stage of their lactogenesis was not impaired by SDP management. In early and midlactation, mammary cell apoptosis and proliferation rates as well as mammary expression of genes involved in the function of this tissue were unaffected by the dry period management strategy. For cows in their second lactation, mammary gland functional capacity at 70 d in milk tended to be lower in the SDP cows. In conclusion, even though SDP management decreased milk production during the subsequent lactation, it did not affect mammary cell activity. Although direct evidence is still lacking, decreased mammary cell growth during the dry period is likely responsible for this negative effect. The higher prolactin concentrations in lactating cows during late gestation could be involved in this effect. More research is needed to test these hypotheses.     

Prediction of blood metabolites from milk mid-infrared spectra in early-lactation cows

Dairy cows commonly experience an unbalanced energy status in early lactation, and this condition can lead to the onset of several metabolic disorders. Blood metabolic profile testing is a valid tool to monitor and detect the most common early lactation disorders, but blood sampling and analysis are time-consuming and expensive, and the procedure is invasive and stressful for the cows. Mid-infrared (MIR) spectroscopy is routinely used to analyze milk composition, being a cost-effective and nondestructive method. The present study aimed to assess the feasibility of using routine milk MIR spectra for the prediction of main blood metabolites in dairy cows, and to investigate associations between measured blood metabolites and milk traits. Twenty herds of Holstein Friesian, Brown Swiss, or Simmental cows located in Northeast Italy were visited 1 to 4 times between December 2017 and June 2018, and blood and milk samples were collected from all lactating cows within 35 d in milk. Concentrations of main blood metabolites and milk MIR spectra were recorded from 295 blood and milk samples and used to develop prediction models for blood metabolic traits through backward interval partial least squares analysis. Blood β-hydroxybutyrate (BHB), urea, and nonesterified fatty acids were the most predictable traits, with coefficients of determination of 0.63, 0.58, and 0.52, respectively. On the contrary, predictive performance for blood glucose, triglycerides, cholesterol, glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase were not accurate. Associations of blood BHB and urea with their respective contents in milk were moderate to strong, whereas all other correlations were weak. Predicted blood BHB showed an improved performance in detecting cows with hyperketonemia (blood BHB ≥ 1.2 mmol/L), compared with commercial calibration equation for milk BHB. Results highlighted the opportunity of using milk MIR spectra to predict blood metabolites and thus to collect routine information on the metabolic status of early-lactation cows at a population level.     

A note on the lactation performance of twin-bearing cows

Seven pairs of cows were chosen at parturition. In each pair, 1 member had had a twin pregnancy (T) and the other was a comparable cow with a single calf pregnancy (S). All cows were offered the same amount of feed over the first 28 weeks of lactation. In early lactation, intakes were equal; in mid-lactation the T group ate more. The T cows had a lower peak yield of milk than the S cows, but rates of decline in yield in mid-lactation were equal for the 2 groups. Lactose concentrations in the milk were equal throughout lactation, but the fat and protein concentrations were greater for the T group in early lactation. The T group yielded smaller amounts of milk solids. The T group lost less weight in early lactation and gained more weight subsequently. Three of the T group, but only 1 of the S group, did not conceive during the test lactation.     

Presence of viral and bacterial organisms in milk and their association with somatic cell counts

About 20 to 35% of milk samples from cows with intramammary infection or high somatic cell count (SCC) are negative on bacteriological culture analysis. However, little is known about SCC in milk of cows infected with viruses. In the first part of our study, we developed a real-time PCR assay for detection of bovine herpesvirus (BHV) 1, BHV2, and BHV4, and bovine viral diarrhea virus (BVDV) in composite quarter milk samples. A total of 1,479 lactating cows of 1,964 cows in the dairy herd were initially selected because these cows had complete SCC data for at least 3 consecutive test results, of which 139 lactating cows from different lactation age groups were selected randomly and studied extensively. Composite quarter milk samples were collected on 3 alternate days and examined for viruses, SCC, and bacteriological analysis. In total, 10, 28, and 0.7% of the composite quarter milk samples from cows were positive for BHV1, BHV2, and BHV4, respectively; BVDV was not detected in composite quarter milk samples. Bovine herpesvirus was not associated with a particular bacterial species. Our study results indicate that cows positive for BHV in composite quarter milk samples alone are less likely to have elevated SCC compared with cows with bacterial intramammary infection; BHV1, BHV2, and BHV4 are probably not major udder pathogens.     

Staphylococcus aureus strains in primiparous and multiparous cows in six herds with a high prevalence of Staph. aureus intramammary infections

The proportion of different strains of Staphylococcus aureus was tested in four groups of lactating dairy cows in six herds with a high overall prevalence of Staph. aureus using random amplified polymorphic DNA PCR. Group 1 included primiparous cows in early lactation (<50 days in milk, DIM). Group 2 consisted of primiparous cows in late lactation (>250 days in milk). Groups 3 and 4 were multiparous cows in the respective stages of lactation. Eight cows from each group on each farm were tested. Overall quarter prevalence of Staph. aureus ranged from 23.4 to 32.0% in the herds. Of the 130 isolates included in the analysis 86.9% were high prevalence strains (more than three isolates per herd), while 13.1% were strains that were only identified in one or two samples. Low prevalence strains were found in all six herds. The proportion of low prevalence strains was higher in multiparous than in primiparous cows (odds ratio, OR 4.4, 1.2-16.6). It is concluded that low prevalence Staph. aureus strains are common even in herds with a high prevalence of Staph. aureus and that their frequency is lower in primiparous cows than in older cows.