Second-lactation Cows Research Articles

Fertility of lactating dairy cows treated with gonadotropin-releasing hormone at AI, 5 days after AI, or both, during summer heat stress

Objectives of this experiment were to evaluate pregnancy per AI (P/AI) and progesterone (P4) concentrations after AI of lactating dairy cows under heat stress conditions treated with 100 μg gonadotropin-releasing hormone (GnRH) at AI, 5 d after AI, or both. Lactating Holstein cows from two herds were enrolled in the study during summer. Cows detected in estrus based on tail paint removal were allocated to four treatments: (1) control (CON = 722); (2) GnRH treatment at AI (G0 = 739); (3) GnRH treatment 5 d post-AI (G5 = 697); or (4) GnRH treatment at AI and 5 d post-AI (G0+G5 = 697). Blood samples were collected from a subgroup of cows at AI (study d 0), study d 5 and 12 to determine P4 concentrations. Pregnancy diagnosis was conducted at study d 36 and 94. Temperature and relative humidity were collected from a meteorological station nearest the herds and temperature-humidity index (THI) was calculated. Average THI during study enrollment was 83.8 ± 0.1 and THI at study d 0 tended (P = 0.09) to be associated with P/AI at study d 36, but it was not (P = 0.33) associated with P/AI at study d 94. Treatment with GnRH at AI, 5 d after AI, or both, did not affect (P ≥ 0.64) P/AI at study d 36 or 94. An interaction, however, was detected (P = 0.06) between treatment and lactation number. Such an interaction was observed because, among ≥ third-lactation cows, P/AI was greater for G0+G5 (28.6%) and G5 (25.3%) than CON cows (17.3%) at study d 36. Pregnancy per AI of ≥ third-lactation G0 cows did not (P ≥ 0.11) differ from CON, G5, and G0+G5 cows. No differences in P/AI were detected among treatments in first- and second-lactation cows. Overall, treatments with GnRH at AI, 5 d after AI, or both were not (P = 0.94) associated with P4 concentrations on study d 0, 5 or 12. Among cows diagnosed pregnant at study d 36, progesterone concentration on d 5 was not affected (P ≥ 0.24) by treatments with GnRH at AI, 5 d after AI, or both, but progesterone concentration on d 12 was greater for cows treated with GnRH at AI and 5 d after AI compared with G0 cows. Lactating dairy cows in their third or greater lactation exposed to heat stress conditions with compromised fertility may have increased P/AI after treatment with GnRH 5 d after AI or the combined treatment of GnRH at AI and 5 d after AI because of reduced early embryonic loss.

Agentes etiológicos em diferentes fases de lactação em vacas produtoras de leite para consumo humano na região de Imperatriz – MA

This study aimed to record the predominant etiologic agents of microorganism sensitivity to bovine mastitis in farm animals producing milk for human consumption and the different stages of infection from it. Milk samples were collected at the first milking and before it was done in each quarter of the rapid test California Mastitis Test, after which his result was taken for the new sample lactocultura and sensitivity testing to antibiotics. The samples were conditioned in a thermal box and led the multidisciplinary laboratory animal biology at the State University of Maranhão. Sample of milk was 0.5 mL and added to test tubes with 4.5 mL of Brain Heart Infusion (BHI) for dilutions up to 10 ³. Then they were placed in the incubator for 24 hours at 37 ° C. After 24 hours of emissions, the serial dilution 10 ³ milk in BHI (1mL) was transferred to Petri dishes containing agar specific for the growth of Staphylococcus sp, and the plates were placed in the incubator for 24 hours at 37° C for growth of colonies, microorganisms were isolated in specific agar and identified by means of differential staining of Gram and catalase production, performed in a slide, adding to a colony, 0.2 mL of H2O2 (hydrogen peroxide) 3%. The proof of the sensitivity strains of Staphylococcus spp isolated from milk samples were performed by using disks impregnated with antibiotics. The strains were grown in test tubes containing BHI and incubated at 37 ° C for 24 hours. After incubation, a swab moistened in broth was cultivated and sown in Petri dishes containing Mueller-Hinton agar. The antibiotics used in the tests were: Penicillin G (PEN 10), Chloramphenicol (CLO 30), cephalothin (CFL 30) and amikacin (AMI 30), which showed greater sensitivity to cephalothin active principle with an inhibition halo of 3.4 cm in diameter on average followed by Chloramphenicol at 3.0 cm in diameter, the Amikacin with 2.0 cm and finally diameter penicillin G with a halo of bacterial inhibition of only 1.6 cm in diameter. Cows in second lactation had a high rate of contamination was detected and clinical mastitis in 73% of cows tested and index of bacterial resistance to penicillin G.

Effects of heat stress on production, somatic cell score and conception rate in Holsteins.

We examined the effects of heat stress (HS) on production traits, somatic cell score (SCS) and conception rate at first insemination (CR) in Holsteins in Japan. We used a total of 228 242 records of milk, fat and protein yields, and SCS for the first three lactations, as well as of CR in heifers and in first- and second-lactation cows that had calved for the first time between 2000 and 2012. Records from 47 prefectural weather stations throughout Japan were used to calculate the temperature-humidity index (THI); areas were categorized into three regional groups: no HS (THI < 72), mild HS (72 ≤ THI < 79), and moderate HS (THI ≥ 79). Trait records from the three HS-region groups were treated as three different traits and trivariate animal models were used. The genetic correlations between milk yields from different HS groups were very high (0.91 to 0.99). Summer calving caused the greatest increase in SCS, and in the first and second lactations this increase became greater as THI increased. In cows, CR was affected by the interaction between HS group and insemination month: with summer and early autumn insemination, there was a reduction in CR, and it was much larger in the mild- and moderate-HS groups than in the no-HS group.

Milk Yield, Somatic Cell Count, and Udder Measurements in Holstein Cows at Different Lactation Number and Months

The aim of this study was to investigate the effect of lactation number and months on milk yield, somatic cell count (SCC) and udder measurements in Holstein cows. In the study, 30 first lactation and 49 second lactation, totally 79 Holstein cows housing in a farm located in Nigde province (Turkey) were used. Somatic cell count and udder measurements were determined at each visit of the farm per months, while lactation milk yield of each animal was calculated using Test Interval Method. It was observed that the effect of lactation number on lactation milk yield (P<0.01) and SCC (P<0.05) was increased significantly. The effect of lactation number on udder measurements was significant (P<0.01) except front teat length (FTD). Influence of lactation months on milk yield and SCC was increased and statistically significant (P<0.01). The effect of lactation months on distance between front teats (DFT), distance between rear teats (DRT), front teat diameter (FTD), rear teat diameter (RTD) was significant (P<0.01). A negative correlation was found between SCC and milk yield, front teat clearance from ground (FTC) and rear teat clearance from ground (RTC). On the other hand, a positive correlation was also evident between RTD and distance between front and rear teats. Furthermore, there were positive correlation between milk yield and DFT, DFR, DRT, and FTD, whereas a negative correlation was observed between milk yield and FTC. In conclusion, cows in second lactation showed importantly increased milk yield and SCC as compared to cows in first lactation, whereas FTC and RTC decreased and other udder measurements increased. Key words: Holstein cow, lactation, milk yield, somatic cell count, udder measurement

Effect of Somatic Cell Count on Milk Yield and Composition of First and Second Lactation Dairy Cows

This study was carried out to investigate the effect of somatic cell count (SCC) on milk yield and milk composition in first and second lactation Holstein dairy cows. Thirty cows in first lactation and 49 cows in second lactation were used in the study. Animals were 15±9.87 days in milk. Individual milk samples were collected monthly from June 2009 to March 2010, and somatic cell counts, milk protein, milk fat, lactose and milk urea-N were determined. Four SCC groups were formed for determining effect of SCC on milk yield and composition. These groups were as follows: ≤200, 201-500, 501-999, and ≥1.000×103 cell/mL. It was observed that SCC had a high significant effect on milk yield, milk protein, milk lactose (P<0.01), total solids and milk urea-N (P<0.05), however, the effect of SCC on milk fat was not significant (P>0.05). This study indicates that high SCC negatively affects not only milk yield but also milk composition and quality.

Profile and genetic parameters of dairy cattle locomotion score and lameness across lactation

This study investigated the profile of locomotion score and lameness before the first calving and throughout the first (n=237) and second (n=66) lactation of 303 Holstein cows raised on a commercial farm. Weekly heritability estimates of locomotion score and lameness, and their genetic and phenotypic correlations with milk yield, body condition score, BW and reproduction traits were derived. Daughter future locomotion score and lameness predictions from their sires’ breeding values for conformation traits were also calculated. First-lactation cows were monitored weekly from 6 weeks before calving to the end of lactation. Second-lactation cows were monitored weekly throughout lactation. Cows were locomotion scored on a scale from one (sound) to five (severely lame); a score greater than or equal to two defined presence of lameness. Cows’ weekly body condition score and BW was also recorded. These records were matched to corresponding milk yield records, where the latter were 7-day averages on the week of inspection. The total number of repeated records amounted to 12 221. Data were also matched to the farm’s reproduction database, from which five traits were derived. Statistical analyses were based on uni- and bivariate random regression models. The profile analysis showed that locomotion and lameness problems in first lactation were fewer before and immediately after calving, and increased as lactation progressed. The profile of the two traits remained relatively constant across the second lactation. Highest heritability estimates were observed in the weeks before first calving (0.66 for locomotion score and 0.54 for lameness). Statistically significant genetic correlations were found for first lactation weekly locomotion score and lameness with body condition score, ranging from −0.31 to −0.65 and from −0.44 to −0.76, respectively, suggesting that cows genetically pre-disposed for high body condition score have fewer locomotion and lameness issues. Negative (favourable) phenotypic correlations between first lactation weekly locomotion score/lameness and milk yield averaged −0.27 and −0.17, respectively, and were attributed to management factors. Also a phenotypic correlation between lameness and conception rate of −0.19 indicated that lame cows were associated with lower success at conceiving. First-lactation daughter locomotion score and/or lameness predictions from sires’ estimated breeding values for conformation traits revealed a significant linear effect of rear leg side view, rear leg rear view, overall conformation, body condition score and locomotion, and a quadratic effect of foot angle.

Relationships between conception rate in Holstein heifers and cows and milk yield at various stages of lactation

We investigated the relationships between conception rates (CRs) at first service in Japanese Holstein heifers (i.e. animals that had not yet had their first calf) and cows and their test-day (TD) milk yields. Data included records of artificial insemination (AI) for heifers and cows that had calved for the first time between 2000 and 2008 and their TD milk yields at 6 through 305 days in milk (DIM) from first through third lactations. CR was defined as a binary trait for which first AI was a failure or success. A threshold-linear animal model was applied to estimate genetic correlations between CRs of heifers or cows and TD milk yield at various lactation stages. Two-trait genetic analyses were performed for every combination of CR and TD milk yield by using the Bayesian method with Gibbs sampling. The posterior means of the heritabilities of CR were 0.031 for heifers, 0.034 for first-lactation cows and 0.028 for second-lactation cows. Heritabilities for TD milk yield increased from 0.324 to 0.433 with increasing DIM but decreased slightly after 210 DIM during first lactation. These heritabilities from the second and third lactations were higher during late stages of lactation than during early stages. Posterior means of the genetic correlations between heifer CR and all TD yields were positive (range, 0.082 to 0.287), but those between CR of cows and milk yields during first or second lactation were negative (range, −0.121 to −0.250). Therefore, during every stage of lactation, selection in the direction of increasing milk yield may reduce CR in cows. The genetic relationships between CR and lactation curve shape were quite weak, because the genetic correlations between CR and TD milk yield were constant during the lactation period.

Incidence of metabolic disorders and reproductive performance following a short (35-d) or conventional (60-d) dry period management in commercial Holstein herds

A total of 850 Holstein cows from 13 commercial dairy herds were involved in the present study to compare the effects of 2 different dry period (DP) management strategies on health and reproductive parameters. Cows were assigned to either a short (SDP; 35-d) or a conventional (CDP; 60-d) DP management within each herd, based on previous 305-d milk yield, parity (414 primiparous and 436 multiparous), and estimated calving interval. Cows assigned to CDP were fed a dry cow ration from dry-off until 21 d prepartum, and were then switched to a precalving ration. Cows assigned to SDP were fed the precalving ration throughout their DP. Rations were specific to each herd. A significant treatment × parity interaction was found for culling rate. Dry period management did not affect culling rate for second-lactation cows but a significantly higher culling rate occurred in multiparous CDP cows compared with SDP (42.6 vs. 31.6% ± 3.7 for CDP and SDP, respectively). Management used in the DP did not affect incidence of severe ketosis, displaced abomasum, milk fever, and mastitis, although incidence of these metabolic disorders were lower in second-lactation than third- or greater-lactation cows. The incidence of mild ketosis (evaluated by milk ketone concentration) was lower following SDP, probably as a result of better energy balance. On the other hand, the incidence of retained placenta was higher in multiparous cows assigned to SDP, but the reason for this increase remains unclear. Nevertheless, this did not lead to increased incidence of metritis. Moreover, DP management did not influence reproductive measures, including days in milk at first breeding, number of breedings per conception, as well as conception rates at first and second services. Regarding days open, overall, all 13 herds were not significantly affected by treatment, but 1 herd clearly showed opposite results to the 12 others. Our results indicate that a short DP management strategy could facilitate transition from one lactation to the next by decreasing the incidence of mild ketosis, with no major negative effects on other health parameters and reproduction. The variation in results observed among herds suggests that other management practices influence the response observed following a short or conventional DP, emphasizing the need for other field studies.

Associations between paratuberculosis milk ELISA result, milk production, and breed in Canadian dairy cows

The 3 objectives of this study were (1) to quantify milk production differences among cows with different paratuberculosis (ParaTB) milk ELISA results; (2) to determine if production differences existed in lactations preceding the test among cows with different ParaTB milk ELISA results; and (3) to assess whether Channel Island breeds were more likely to test positive with the ParaTB milk ELISA than other dairy breeds. Current and completed lactation records from 35,591 dairy cows in Ontario and western Canada that had been tested with a commercial ParaTB milk ELISA were included in the analysis. The first occurrence of the highest categorical test result was used to classify the cow. Cows were then grouped by the lactation in which the first high-positive (HTP), low-positive, or negative milk ELISA occurred, and comparisons were made within lactation groups. High test-positive cows were defined as those that had an optical density ≥1.0 on at least 1 ParaTB milk ELISA. The associations between ParaTB milk ELISA status and milk production, as measured by the 305-d milk yield, were assessed with a series of linear mixed models. The effect of breed on the likelihood of testing positive with the milk ELISA was assessed using a logistic mixed model for the lactation in which the first negative or positive ParaTB milk ELISA occurred. Test-positive cows produced on average 2.9 to 6.8% less milk than negative herdmates in the lactation in which they were tested. The HTP cows produced on average 466, 514, and 598kg less milk than low-positive herdmates in lactations 1, 2, and 4, respectively. Cows testing low-positive in their second lactation had, on average, a 218-kg higher milk yield in their first lactation than their test-negative herdmates. Otherwise, no association was found between test result and milk production in preceding lactations. Differences in milk production among negative, test-positive, and HTP cows increased with increasing parity. Cows of the Channel Island breeds had 1.4 to 8.3 times the odds to test positive compared with other dairy breeds. The findings of this study are consistent with previous studies that have reported that milk production is lower in test-positive animals. The differences in milk production increased with increasing ELISA optical density scores and parity in which the animal tested positive. However, with the exception of second-lactation cows, no differences in milk production were observed in tests preceding lactations. The differences in milk ELISA status among dairy breeds support the need for further studies investigating the genetic component of ParaTB susceptibility.

Effects of sodium salicylate on productivityof postpartum dairy cows (2011)

Inflammation has been proposed as a contributor to metabolic disorders in transition dairy cows. The purpose of this experiment was to determine whether a non-steroidal anti-inflammatory drug, sodium salicylate (SS), benefits transition cows. At calving, 78 cows (primiparous, n = 39; second lactation, n = 28; ≥3 lactations, n = 11) were assigned alternately to either a control (CON) or SS treatment for 7 days and remained on study until 21 days postpartum. Treatment was administered via individual water bowls at a concentration of 2.5 g/L, delivering a mean of 183 ± 8.5 g/day SS during the 7 days of treatment. Milk yields were collected daily and milk samples were collected twice weekly. Data were analyzed using mixed models with repeated measures over time. No treatment effects were detected for daily feed or water intake. Milk yield for third or greater lactation cows tended to increase (P < 0.10) with SS at the end of the trial (days 19 to 20). Milk protein content increased (P < 0.05) with SS in first- and second-lactation cows during week 1 and milk urea nitrogen (MUN) decreased (P < 0.01) with SS. Milk fat content increased (P < 0.05) with SS in weeks 2 and 3 postpartum. A 10% increase (P < 0.05) in energy-corrected milk (ECM) was observed for SS cows during week 3. Metritis incidence increased (P < 0.01) with SS in third or greater lactation cows, but no other effects on disease incidence were detected. In contrast to our hypothesis that SS treatment would decrease transition disorder incidences, SS treatment seemed to promote increased milk fat content and milk energy output during early lactation with no effect on total disorder incidence.; Dairy Day, 2011, Kansas State University, Manhattan, KS, 2011; Dairy Research, 2011 is known as Dairy Day, 2011

25 EFFECT OF REPRODUCTIVE TRACT SIZE ON CONCEPTION RATES IN LACTATING DAIRY COWS UTILIZING A REPRODUCTIVE TRACT SCORING SYSTEM

Reproductive tract scoring (RTS) systems have been effective in evaluating fertility of heifers. A similar RTS system has not been reported in lactating dairy cows pertaining to conception rates following artificial insemination. Objectives of this study include development of a RTS system for lactating dairy cows and determining if RTS had an effect on artificial insemination (AI) success with various types of semen [conventional (CS), sexed (SS)]. During pre-breeding examinations (typically 30–60 DIM) by trained personnel, cows were assigned a RTS (1, 2, or 3) based on size and length of the cervix and uterine horns, but not including status of the ovaries. Tracts for RTS 1 were small, compact uterine horns resting within the pelvic cavity, RTS 2 were intermediate in size with uterine horns resting partially outside the pelvic cavity, and RTS 3 were large, deep tracts resting entirely outside the pelvis into the abdominal cavity. Additionally, cows were evaluated for RTS at a local abattoir before harvest, and tracts collected for volume and length measurements. Volume measurements were collected using Foley catheters and measuring water displaced in the uterine horns at a constant pressure. Length of the vagina, cervix, and uterine horns were measured using a flexible tape. Insemination data analysis was performed using mixed model analysis of variance in Glimmix SAS 9.2 (SAS Institute Inc., Cary, NC, USA). Insemination data included 613, 308, and 572 scores in first, second, and third+ lactation cows, respectively. First-lactation cows had 65.25% with RTS 1, 30.02% RTS 2, and 4.73% RTS 3. Second-lactation cows had 53.25% RTS 1, 39.29% RTS 2, and 7.47% RTS 3. Cows with 3+ lactations had 43.18% RTS 1, 43.88% RTS 2, and 12.94% RTS 3. Cows were artificially inseminated (n = 2401 inseminations) with either CS (n = 1981) or SS (n = 420). Conception rates for CS were 38.65%, 34.26%, and 24.41% for RTS 1, 2, and 3, respectively (P = 0.0154 for RTS 1 v. 3). Conception rates for CS (38.65%, RTS 1; 34.26%, RTS 2) were higher compared to SS (21.37%, RTS 1 (P = 0.0001); 20.72%, RTS 2 (P = 0.0186)). No differences were detected between CS (24.40%) and SS (22.35%) within RTS 3; however, observations were limited for SS inseminations with RTS 3. Preliminary data regarding total length (vagina, cervix, and uterine horns; RTS 1, 2, 3 = 103.1 cm, 114.9 cm, 134 cm, respectively) and volume (RTS 1, 2, 3 = 102 mL, 131 mL, 133.3 mL, respectively) suggest both increase as RTS increases but limited observations prevent conclusions at this time. Conception rates indicate smaller reproductive tracts have improved fertility in lactating dairy cows when using CS. Identification of larger reproductive tracts will allow for more economically efficient AI programs by utilising inexpensive, high fertility semen.

MILKABILITY IN HOLSTEIN COWS

The aim of this work was evaluation of milkability in Holstein cows. We collected a total 63 milk flow curves, using electronic mobile milk flow meter – lactocorder. The measuring was carried out in cows from 5 to 305 days in milk. The average milk yield per milking was 15.63 kg, with average milk flow rate 2.84 kg.min-1 and average maximum milk flow rate of 4.49 kg.min-1. The average duration of incline phase was 1.09 min., duration of plateau phase was 1.82. min, and duration of decline phase was 2.26 min. Percentage of bimodal milk flow curves was 52 %, on average. The highest average milk flow rate (3.01 kg.min-1) and the highest average peak milk flow rate (4.96 kg.min-1) were found in cows in second lactation, in comparison with primiparous cows (2.87 kg.min-1, and 4.37 kg.min-1) and cows in another lactation (2.7 kg.min-1, and 4.3 kg.min-1).

Differences in udder health and immune response traits of Holstein-Friesians, Norwegian Reds, and their crosses in second lactation

The objective of this study was to investigate potential differences in udder health and immune response traits among Holstein-Friesian (HF), Norwegian Red (NR), and NR×HF (NRX) cows on 30 commercial Irish dairy farms. A total of 648 second-lactation cows (HF n=274, NR n=207, and NRX n=167) were immunized with hen egg white lysozyme (HEWL) to induce antibody-mediated immune response (AMIR). Candida albicans was used to induce a cell-mediated immune response, with in vivo delayed-type hypersensitivity used as the indicator. Antibody response to HEWL was measured by ELISA. Udder health defined as mean somatic cell score (SCS) over the lactation, mean SCS within 30 d of the beginning of the immunization, peak SCS for each individual cow during lactation, and incidence of mastitis were statistically superior for the NR. The NR had a greater primary AMIR, producing greater concentrations of anti-HEWL immunoglobulin G on d 14 compared with HF and NRX. No difference was observed among the breed groups in the magnitude of secondary AMIR (d 21 post-immunization) or cell-mediated immune response. The proportion of high and low responders was similar across breed groups. Cows with high AMIR and high cell-mediated immune response had significantly lower mean SCS within 30 d of the start of the immunization, but greater occurrence of clinical mastitis, recorded as a binary trait over the course of the lactation. Otherwise, no significant difference in udder health was evident between cows designated as high and low responders. Although differences in mean breed group SCS values were in line with group mean AMIR values, no association was found among the traits when correlated on an individual cow basis. Results highlight the superiority of the NR with regard to udder health and suggest that improvements to udder health may result from crossbreeding with the NR. However, the immune response traits investigated proved to be inconsistent indicators of udder health.

Milking-to-Milking Variability for Milk Yield, Fat and Protein Percentage, and Somatic Cell Count

The main objectives were to analyze milking-to-milking variability in milk yield, fat and protein percentages, and somatic cell count (SCC). Additional objectives were to investigate the factors that affect variation in milk fat percentage and to study the seasonal variations in milk, fat, and protein yields and SCC. A total of 16 farms (14 milked 2× and 2 milked 3×) across Canada participated in a 5-d milk-sampling study, with 27,328 milk samples collected and analyzed for fat and protein yields and SCC. Descriptive statistics for both 2× and 3× herds for milk yield and fat and protein percentages followed a typical pattern throughout lactation, and the somatic cell linear scores were higher in early lactation for first-lactation cows (4.7 vs. 3.8) but were higher at the end of lactation for cows in second lactation or greater (5.1 vs. 4.9). The 2× herds had higher milk yields in the morning (∼17 vs. ∼14kg), whereas the 3× herds had the lowest milk yields in the morning, and yields peaked at the evening milking (∼9 vs. ∼11.2kg). A herd management questionnaire was distributed to participating producers to investigate the relationship between management variables and variations in milk fat percentage over the 5-d sampling period. Data from the questionnaire determined that milking period had a significant effect on milk fat in 2× herds, with fat percentage 1.11% lower in the morning compared with the evening milking period. Seasonal differences in milk, fat, and protein yields were investigated in 910 cows on 3 farms, with 5,517 fat and 5,534 protein samples. The seasonal differences in fat yield [summer = 1.02±1.05kg/d (SEM); winter = 1.19±1.05kg/d] and protein yield (summer = 0.85±1.05kg/d; winter = 0.96±1.05kg/d) were significant only for first lactation. Understanding the variability in milk yield, fat and protein percentages, and SCC is important when making management decisions and in milk-recording programs.

Pregnancy Incidence in Norwegian Red Cows Using Nonreturn to Estrus, Rectal Palpation, Pregnancy-Associated Glycoproteins, and Progesterone

The objectives of the study were to estimate pregnancy incidence and calving rate after first artificial insemination (AI) in Norwegian Red cows undergoing spontaneous estrus, to assess the relationship between pregnancy and management factors at herd or cow level, to evaluate differences between 60-d nonreturn rate (NRR60d) and pregnancy incidence, and to compare the accuracy of pregnancy diagnosis by rectal palpation and plasma pregnancy-associated glycoproteins (PAG) analysis supported by progesterone measurements. In total, 829 animals (n = 229 heifers, 234 first-lactation, 173 second-lactation, and 193 >second-lactation cows) were included. Milk samples for progesterone analysis were collected both at AI and 3wk later. Cows with progesterone concentrations <3 ng/mL at AI were considered in estrus or having nonactive ovaries, whereas cows with progesterone concentrations >7 ng/ mL 3wk later were considered pregnant. Blood sampling for PAG analysis and pregnancy diagnosis by rectal palpation were conducted 57.6±0.92 d after AI. Pregnancy-associated glycoprotein concentrations equal to 2.5 ng/mL gave the greatest sensitivity (94.3%) and specificity (94.6%) in the assessment of pregnancy. The number of days from calving to first AI was 85.3±1.71. Overall NRR60d after first AI was 72.5%. The corresponding values for heifers, first-lactation, second-lactation, and >second-lactation cows were 76.9, 67.1, 69.9, and 76.2%. Overall pregnancy incidence after first AI was 63.7%. The corresponding values for heifers, first-lactation, second-lactation, and >second-lactation cows were 70.0, 58.2, 61.6, and 64.9%. Overall calving rate to first AI was 57.2%. The corresponding values for heifers, first-lactation, second-lactation, and >second-lactation cows were 64.9, 54.3, 54.7, and 53.9%. The overall difference between NRR60d and pregnancy incidence was 8.8%, whereas the parity-specific differences were 6.9, 8.9, 8.3, and 11.3% for heifers, first-lactation, second-lactation, and >second-lactation cows, respectively. Eight animals with PAG <2.5ng/mL and classified as pregnant by rectal palpation calved, whereas 5 animals with PAG ≥2.5 ng/mL and classified as non-pregnant by rectal palpation also calved. The study showed that Norwegian Red cows have relatively high reproductive performance. Breeding for fertility traits over 35 yr is probably an important reason for such high fertility.

Blood Mineral, Hormone, and Osteocalcin Responses of Multiparous Jersey Cows to an Oral Dose of 25-Hydroxyvitamin D3 or Vitamin D3 Before Parturition

Twenty-seven multiparous Jersey cows were randomly assigned to receive an oral bolus containing corn starch (control, CON), corn starch plus 15mg of 25-hydroxyvitamin D3 (25-OH), or 15mg of cholecalciferol (D3) at 6 d before expected parturition. Cows were maintained in individual box stalls from 20 d before expected parturition and fed a common diet. Jugular blood samples were collected at −14, −13, −5, −4, −3, −2, −1 d before expected calving, at calving, and at 1, 3, 5, 7, 9, 11, 13, 28, 56, and 84 d postcalving. After calving, cows were housed in 1 pen in a free-stall barn and consumed a common diet. Colorimetric assays were used to analyze Ca, P, and Mg concentrations in serum. Serum concentrations of osteocalcin (OC), an indicator of bone formation, serum 25-hydroxyvitamin D3, and parathyroid hormone (PTH) were determined in samples obtained from d −5 through d 13. The 9 control multiparous cows and 5 untreated primiparous cows were used to evaluate the effect of parity on the variables that were measured. There was no effect of parity on Ca, PTH, or 25-OH concentration. Compared with second-lactation cows and older cows (>2 lactations), first-lactation cows had greater serum OC (22.3, 32.0, and 48.3ng/mL, respectively), indicating that younger animals were forming more bone. Blood Ca, P, and Mg decreased near the time of calving and then increased over time. Serum 25-hydroxyvitamin D3 was greater for cows dosed with 25-OH (119.0ng/mL) compared with those dosed with D3 (77.5ng/mL) or CON (69.3ng/mL). Cows dosed with 25-OH tended to have lower serum PTH concentration, but treatments did not affect serum Ca, P, or Mg. Serum OC was greater in second-lactation cows compared with cows entering their third or fourth lactation but OC was unaffected by treatment. Although results indicated a 60% increase in serum 25-hydroxyvitamin D3 due to a single oral dose of 25-OH before calving, the amount administered in this study apparently was not sufficient for initiation of any improvement in Ca homeostasis at parturition.

Effect of continuous milking and prostaglandin E2 on milk production and mammary epithelial cell turnover, ultrastructure, and gene expression1

Mammary epithelial cell (MEC) growth is reduced in continuously milked (CM) mammary glands, and administration of a mammogenic compound such as prostaglandin E(2) (PGE(2)) at parturition might improve MEC growth in CM tissue. The objectives were to 1) compare MEC turnover, ultrastructure, and gene expression in CM and involuting mammary tissue, and 2) evaluate the effects of CM and intramammary infusion of PGE(2) on early lactation MEC turnover, ultrastructure, mammary gene expression, milk yield, and composition. First- and second-lactation cows (n = 8) were used in a half-udder model, in which one-half was dry for 60 d (CTL) and the other was CM. Udder halves (n = 16) were assigned to a postpartum (PP) treatment of PGE(2) (+PGE(2); 875 mug/10 mL of medium-chain triglyceride oil) or no PGE(2) (-PGE(2)) treatment at parturition and at 72 h PP. Biopsies of CM and CTL quarters were obtained during milk stasis (MS) of the CTL half at 3 and 7 d after dry-off of the CTL half (3d-MS; 7d-MS) and postpartum (PP) at 2 and 4 d (2d-PP; 4d-PP). Milk yield was reduced (P < 0.01) in CM udder halves compared with CTL halves (13.2 vs. 22.1 kg/d), but reductions were less in second-lactation cows. The apoptotic index was greater (P < 0.05) in CTL glands than in CM glands (3d-MS, 0.52 vs. 0.11% and 7d-MS, 0.24 vs. 0.12, respectively). Proliferation of MEC was unchanged at 3d-MS, but was increased (P = 0.01) in CTL halves at 7d-MS compared with CM halves (3.10 vs. 0.93%). At 2d-PP, MEC proliferation was increased (P = 0.05) in CM halves compared with CTL halves (1.3 vs. 0.6%), but was unaffected by PGE(2) (P > 0.2). Apoptosis was elevated in early lactation regardless of treatment. Ultrastructure was unchanged by dry period length or PGE(2). In prepartum tissue, involution in CTL halves increased (P < 0.05) the expression of the proapoptotic genes Bcl-2-associated x protein (bax) and IGFBP5 and decreased (P < 0.05) alpha-lactalbumin expression compared with CM tissue. In PP mammary tissue, CTL halves expressed greater (P < 0.05) levels of ATP-binding cassette 1 (ABC1) and IGFBP5. Treatment with PGE(2) did not alter (P > 0.1) gene expression. The results confirm that CM reduced milk yield of cows with a mammary growth requirement. Reduced MEC turnover and milk yield were not alleviated by IMI of PGE(2), which indicates that peripartum PGE(2) concentrations in CM glands are not limiting mammary growth or milk synthesis.

Comparison of J5 Vaccinates and Controls for Incidence, Etiologic Agent, Clinical Severity, and Survival in the Herd Following Naturally Occurring Cases of Clinical Mastitis

Holstein dairy cattle in 3 commercial herds were randomly allocated to J5 vaccination (n=251) or untreated control (n=306) groups. There were 221 new cases of clinical mastitis (CM) affecting 120 cows. Coliform mastitis cases had a higher percentage of severe quarter swelling or signs of systemic illness among control cows but not among J5 vaccinates, in comparison to noncoliform cases. Culling or death from CM affected 13 controls (4.3%) and 4 vaccinates (1.6%), with losses occurring earlier in lactation among controls, a higher hazard (probability of a cow dying on each day of lactation) for controls than vaccinates. The J5 vaccination was significantly associated with protection from culling for mastitis among the 15 Klebsiella cases; 2 out of 10 (20%) Klebsiella-infected controls were culled and 0 out of 5 vaccinates were culled. Cows in second lactation were at reduced hazard of culling for mastitis compared with older animals, even when adjusting for effects of J5 vaccination. When all CM cases (including subsequent new cases during the same lactation and multiple quarters or pathogens within the same cow on the same day) were evaluated, for the 221 cases of CM, the rate was significantly higher among vaccinates than controls (0.10 and 0.07 cases/30 d in milk, respectively). This was because J5 vaccinates had more subsequent new cases of CM in the same cow than controls. Pathogens isolated, which included mainly environmental bacteria, were not different among J5 vaccinates and controls. Immunization with J5 was associated with protection against severe clinical coliform mastitis signs, culling, and death loss from CM but not with any reduction in overall CM.

Use of Flavored Drinking Water in Calves and Lactating Dairy Cattle

Experiments were conducted to investigate the use of added flavor in drinking water of Holstein calves and lactating dairy cattle to determine effects on dry feed intake. Nine calves were used in a replicated 3×3 Latin square design, and water offered was unflavored or flavored with orange or vanilla. All calves were offered commercial starter. Feed intake of the dry starter was increased in calves offered the orange flavor treatment compared with the control or the vanilla treatment. The increased dry feed intake agreed with the significant increase in weight gain measured in calves on the orange treatment. Further experiments were performed with 4 second-lactation cows using the addition of another orange flavor to the water compared with unflavored water under conditions of free access or time-restricted water access. No significant changes were found for dry matter intake, water consumption, or milk yield. These findings demonstrate an important finding that flavoring agents need not be added only to the starter feed for calves, but flavor can stimulate dry feed intake and BW gain when used in drinking water.

Direct-Fed Microbial Supplementation and Health and Performance of Pre- and Postpartum Dairy Cattle: A Field Trial

A double-blind field trial was conducted on a commercial dairy to study the effects of feeding a direct-fed microbial (DFM) product consisting of 2 strains of Enterococcus faecium plus Saccharomyces cerevisiae yeast on prepartum and postpartum performance of Holstein cows. Treatments consisted of the normal pre- and post-fresh TMR supplemented with the DFM (2 g/cow per d) or a placebo. Treatments started approximately 10 d prepartum and continued until about 23 d in milk (DIM). A total of 366 Holstein cows were enrolled in 1 of 2 placebo groups or 2 DFM-supplemented groups. Groups were enrolled consecutively, starting with the placebo treatment. Sample size was limited to 4 groups because the cooperating dairy prematurely terminated the study due to increased health problems in one of the groups. Blood samples were taken during the prefresh period between 2 and 10 d prior to calving and at weekly intervals from 3 to 23 DIM. Blood concentrations of nonesterified fatty acids before calving and β-hydroxy-butyrate after calving were not affected by treatment. Supplementation with the DFM product increased milk fat percentage for the first lactation cows and increased milk protein percentage for the second and greater lactation cows during the first 85 DIM. Second-lactation cows fed the DFM product received fewer antibiotic treatments before 85 DIM than cows receiving the placebo. This validated the dairy producer's concern that cows consuming one of the diets (revealed to be the placebo diet after the study was completed) were experiencing more health problems. Most measures of milk yield were numerically increased by supplementation with the DFM product. However, differences in milk yield were not significant. Key covariates for main study outcomes included milk yield in the previous (first) lactation, body condition score prior to calving, days spent in the maternity pen, and stocking density of the pre-fresh pen.