Physiological and genetic differences between low and high index dairy cows

Relationship between Milk Yield and Reproductive Parameters on Three Hungarian Dairy Farms

It is postulated that there is negative correlation between milk yield and reproductive performance. However, some studies definitely doubt this causality. The aim of our study was to investigate the relationship between milk production and fertility on three dairy farms. The production parameter was the milk yield (in kg), and fertility was expressed by the number of inseminations per conception (AI index), as well as by the length of the service period (in days). A total of 13 012 lactations from cows with their first three lactations completed were analysed. The number of inseminations was significantly correlated with the milk yield and with the studied farm (p < 0.0001), but its correlation with the lactation number was not significant (p = 0.9477). A similar relationship was found after evaluating the length of the service period. A multiplicative model showed that a 2000 kg milk increase extended the service period by 9% and increased the AI index by 13%. Thereafter, using quartiles of the cows, the service period of the highest-producing group rose by 41.5 days, and the AI index by almost 1, compared to the lowest quartile. Our results indicate a definitive decline in reproductive indicators parallel to an increase in milk production but did not prove an inevitable correlation.

Plasma progesterone concentration after first service is associated with individual genetic traits, postpartum phenotypes, and likelihood of conception in seasonal-calving pasture-based dairy cows

The aims of this study were to (1) evaluate postpartum phenotypes, cow factors, and genetic traits associated with plasma progesterone (P4) concentrations after first artificial insemination (AI); (2) determine variation in daily plasma P4 concentrations between d 7 and 13 after first AI; and (3) evaluate associations between plasma P4 concentrations and pregnancy success after first AI. First and second parity (n = 2,797) spring-calving lactating dairy cows from 35 dairy herds were enrolled. Farm visits were performed every 2 wk during the postpartum period as follows: cows that were at wk 3 (range: 14-27 d in milk) and wk 7 (range: 42-55 d in milk) postpartum were examined. Farm visits were performed weekly during the breeding season, and cows that were between 7 and 13 d after the first AI were examined. Body condition score (BCS) was measured at each visit using a 1 to 5 scale [low (≤2.75), target (≥3.0)]. Transrectal ultrasound examinations were conducted at wk 3 and wk 7 postpartum visits to determine presence or absence of a corpus luteum (CL) and uterine tract score [scale of G₁ (best)-G₄ (worst)]. Blood samples were collected at each visit, and plasma concentrations of glucose, β-hydroxybutyrate, and fatty acids were analyzed. On the day of the weekly farm visit during the breeding season, blood samples for P4 determination were collected from all cows that were between 7 and 13 d after first AI during the breeding period. Cows that had a CL present and a G₁ uterine score at wk 7 postpartum had greater plasma P4 concentration after first AI (+0.67 ng/mL and +0.4 ng/mL, respectively) compared with cows with no CL present and with a uterine score ≥G₃. Cows with low BCS at wk 7 postpartum had lesser plasma P4 concentration after first AI than cows with target BCS. Each unit increase in plasma fatty acids and β-hydroxybutyrate concentration at AI was associated with 0.45 ± 0.33 ng/mL (estimate ± standard error) and 0.07 ± 0.04 ng/mL greater plasma P4 concentration after first AI, respectively. Regarding genetic merit traits, each unit increase in fertility subindex was associated with 0.005 ± 0.003 ng/mL greater P4 concentration. In addition, for every 1 ng/mL increase in plasma P4 concentration, the odds of estimated probability of pregnancy per AI increased by 3% (odds ratio = 1.03; 95% confidence interval = 1.00, 1.05). In conclusion, cows with superior genetic merit for fertility traits and milk production traits, favorable fertility phenotypes at wk 7 postpartum, (e.g., presence of a CL, a G₁ uterine score, and target BCS), and blood parameters indicative of better metabolic status at AI were all associated with greater plasma P4 concentration after AI. In turn, greater plasma P4 concentrations were associated with greater odds of successful pregnancy establishment. This study underlines the important associations between early postpartum fertility phenotypes (CL presence, uterine health status) and subsequent plasma P4 concentrations after first AI, and hence provides additional evidence of the mechanisms through which selection for fertility traits improves phenotypic fertility performance.

Endometrium On-a-Chip Reveals Insulin- and Glucose-induced Alterations in the Transcriptome and Proteomic Secretome

The molecular interactions between the maternal environment and the developing embryo are key for early pregnancy success and are influenced by factors such as maternal metabolic status. Our understanding of the mechanism(s) through which these individual nutritional stressors alter endometrial function and the in utero environment for early pregnancy success is, however, limited. Here we report, for the first time, the use of an endometrium-on-a-chip microfluidics approach to produce a multicellular endometrium in vitro. Isolated endometrial cells (epithelial and stromal) from the uteri of nonpregnant cows in the early luteal phase (Days 4-7) were seeded in the upper chamber of the device (epithelial cells; 4-6 × 104 cells/mL) and stromal cells seeded in the lower chamber (1.5-2 × 104 cells/mL). Exposure of cells to different concentrations of glucose (0.5, 5.0, or 50 mM) or insulin (Vehicle, 1 or 10 ng/mL) was performed at a flow rate of 1 µL/minute for 72 hours. Quantitative differences in the cellular transcriptome and the secreted proteome of in vitro-derived uterine luminal fluid were determined by RNA-sequencing and tandem mass tagging mass spectrometry, respectively. High glucose concentrations altered 21 and 191 protein-coding genes in epithelial and stromal cells, respectively (P < .05), with a dose-dependent quantitative change in the protein secretome (1 and 23 proteins). Altering insulin concentrations resulted in limited transcriptional changes including transcripts for insulin-like binding proteins that were cell specific but altered the quantitative secretion of 196 proteins. These findings highlight 1 potential mechanism by which changes to maternal glucose and insulin alter uterine function.

Feed supplementation prevents post-conception decline in milk progesterone concentrations associated with production stress in dairy buffaloes (Bubalus bubalis)

The onset of pregnancy may be associated with hormonal changes and decline in milk yield of buffaloes. To investigate this, forty lactating buffaloes from 1st to 23rd weeks post-conception were selected. The animals were assigned to three treatments: PRT, PRS, NPRT and three milk yielding groups HMY, 66 to 75 l/week, n = 12; MMY, 56 to 65 l/week, n = 16; LMY, 46 to 55 l/week, n = 12). Milk samples were collected on alternate weeks and analyzed with ultrasonic milk analyzer. EIA was used for milk progesterone concentrations. Group means were compared and correlation analysis was conducted. Progesterone concentrations increased in almost similar pattern with the advancing weeks post-conception. The high and low yielder showed greater progesterone concentrations in the supplemented than the animals on traditional ration (P < 0.001). Progesterone concentrations correlated positively with fat (%), negatively with milk yield, protein (%) and lactose (%). Decline in milk yield became drastic when progesterone concentrations rose above 6.44 ng/ml. The pregnant animals on traditional ration exhibited a sharper decline in milk yield with the increasing progesterone concentrations as compared to pregnant animals with supplemented ration. It is concluded that concentrates supplementation induced a raise in progesterone levels. Progesterone concentrations and milk yield showed an inverse relationship.

Genetic and environmental factors influencing first service conception rate and late embryonic/foetal mortality in low fertility dairy herds

The objective of this study was to identify factors affecting variation in conception rate to first artificial inseminations (AI) (CR: number of pregnant cows on D80-100/inseminated cows) and the incidence of embryonic/foetal loss (LEM) between 21 and 80 days of pregnancy (number of cows non-pregnant on D80-100/pregnant on D21) in 44 low fertility dairy herds of the west-central region of France. Reproductive status was assessed using progesterone milk concentration on D0 = Day of AI and D21-24, plasma PSPB concentration on D30-35, rectal palpation on D80-100 and observed return to oestrous. The final data set contained 1285 Prim'Holstein cows, 5.0% (64/1285) were inseminated in the luteal phase (progesterone > or = 3 ng/ml on D0), 61.3% (787/1285) were pregnant on D21-24 (progesterone < 3 ng/ml on D0 and > or = 5 ng/ml on D21-24), 15.4% lost their embryo/foetus between D21-24 and D80-100 (198/1285) and 45.8% (589/1285) were pregnant on D80-100. The incidence of late embryonic/foetal loss (LEM) was 25.2% (198/787). Multivariate logistic regression models including the random herd effect were used to analyse the relationship between AI centre, AI sire, cow's sire, parity, interval between calving and AI, milk production, milk protein content, body condition score (BCS) on D0, season of calving, season of AI, estimated genetic index on CR and LEM incidence. CR was significantly related to parity (p < 0.05), milk production after calving (p < 0.05) and estimated genetic value (p < 0.01). A significant difference in CR was observed for calving to AI interval > or = 70 days versus > or = 90 days, but the overall effect of the interval was not significant (p = 0.11). LEM incidence was affected by period of AI (p < 0.05), milk production (p < 0.05) and BCS (p < 0.05), but was not related to estimated genetic index. In conclusion, in these low fertility herds, the incidence of LEM was high and 25% of the cows lost their embryo after 21 days of pregnancy. LEM was affected by specific factors (season, BCS), which were not related to CR. The absence of a relationship between estimated genetic index and LEM in spite of its effect on CR indicates that estimated genetic merit has a greater effect on early embryonic loss or fertilisation failure than on later stages of embryo development.

Metabolic variables and plasma leptin concentrations in dairy cows exhibiting reproductive cycle abnormalities identified through milk progesterone monitoring during the post partum period

We have used milk progesterone analysis to monitor reproductive function in lactating dairy cows and have then related this reproductive function to a variety of metabolic variables. Monitoring of cows (n = 41) during the period of onset of luteal function (first milk progesterone reading>5 ng/ml) revealed that delayed onset was associated with increased milk yield and greater loss of body weight and body condition but was not related to plasma metabolite or leptin concentrations. Further monitoring of reproductive function in these 41 cows and an additional 33 cows (total n = 74) during the mating period (from weeks 6 to 14 post partum) identified reproductive cycle abnormalities in 29 (39.2% of animals). The occurrence of cycle abnormalities was associated with increased milk yield (P < 0.05), elevated plasma beta hydroxybutyrate (P < 0.05) and reduced plasma leptin (P < 0.01) concentrations as well as a lower (P < 0.05) rate of gain of body weight and condition score but was not associated with plasma urea or glucose concentrations. Furthermore, cows exhibiting cycle abnormalities had a longer (P < 0.01) interval to first service and a smaller percentage had conceived by 100 days post partum (34.5% versus 66.7%; P < 0.01). These results provide further evidence that impaired reproductive function during the post partum period in dairy cows is caused by a poor energy status and not elevated urea concentrations. Reduced plasma leptin concentrations in animals suffering reproductive dysfunction further supports this view.

Seasonality of Days Open in US Holsteins

The objectives of this study were to establish a pattern for the seasonality of days open (DO) by state and region within the United States and to present statistics on regional trends for DO. Data included 8,676,915 records on DO for Holsteins from 1997 to 2002 covering all regions of the United States. Fixed effects in the model included herd, parity, milk-class, state x month of calving (MOC), year of calving x MOC, and parity x MOC. Least squares means of DO were highest for calvings in March and lowest for calvings in September. The highest mean DO of 155 d was recorded in the Southeast, while the mean DO for the Midwest, Northeast, Northwest, and Southwest were 142, 141, 140, and 137 d, respectively. Variation in monthly averages of DO was highest in Southeast with a range of 51 d, and less than 25 d in all the other regions. Seasonality of calving was defined as the ratio of the fewest to the most calvings in months. The SOC was > or = 60% in Southeast and < or = 23% in the other regions. Selected states: Texas, Oklahoma, and Arizona in the Southwest and Missouri, Kansas, and Kentucky in the Midwest showed patterns of variation in monthly averages and seasonality of calving similar to those of Southeast. Distributions of DO were bimodal for some months of calving due to postponed breeding during the hot season or depressed fertility as a result of thermal stress; the second mode at > 200 d was highest in the Southeast but also could be observed in Texas, Wisconsin, and California. High level of heat stress for DO exists in the Southeast and in selected states of the Midwest and the Southwest; these regions contribute less than 10% of national records. A methodology for analyzing DO especially under heat stress needs to consider effects of intentionally delayed breeding--by using a model that accounts for bimodality, for example.