Factors affecting retention of early pregnancy in dairy cattle

Potential factors affecting retention of pregnancy during weeks 5-9 of gestation were studied in dairy cows and heifers (N = 211) on two farms. Cows were examined by ultrasonography for presence of a viable embryo, and sizes of the corpus luteum (CL) and of follicles > or = 5mm were recorded. Blood samples were taken at each examination and assayed for progesterone and estradiol. Overall pregnancy loss was 11.4%. Cows with two CL did not have greater concentrations of progesterone than cows with one CL and they retained fewer pregnancies (P < 0.01; 73% versus 91%). Pregnancy retention was associated positively with concentrations of progesterone and estradiol during week 5 (P < 0.05). Embryos that were lost apparently died before CL regression. Retention of pregnancy declined in cows with high body condition and as age of the cow increased. Pregnancy retention was lower in cows bred to one of four frequently-used service sires (P < 0.05). Days postpartum, milk production, parity, service number, inseminator, synchronization of estrus, diameter of follicles and size of CL did not affect pregnancy retention. In conclusion, retention of pregnancy during placentation varied with concentrations of progesterone and estradiol, age of cow, body condition and service sire.     

Risk factors for clinical endometritis in postpartum dairy cattle

Bacterial contamination of the uterine lumen after parturition occurs in most dairy cattle. The presence of clinical endometritis beyond three weeks post partum depends on the balance between microbes, host immunity, and other environmental or animal factors. The present study tested the hypothesis that clinical endometritis is associated with animal factors, such as retained fetal membranes, assisted calving and twins, as well as fecal contamination of the environment. The association between selected risk factors and the lactational incidence risk of clinical endometritis was examined in 293 animals from four dairy herds. Multivariate analysis was used to identify risk factors and quantify their relative risk (RR) and population attributable fraction (PAF) based on the proportion of cows exposed to each factor. The lactational incidence of clinical endometritis was 27% and significant risk factors for clinical endometritis were retained fetal membranes (RR = 3.6), assisted calving (RR = 1.7), stillbirth (RR = 3.1), vulval angle (RR = 1.3), primparity (RR = 1.8), and male offspring (RR = 1.5) but not the cleanliness of the environment or the animal. The highest PAF was associated with male offspring (0.6) so the use of sexed semen has the greatest potential to reduce the incidence of clinical endometritis. The dominant association between retained fetal membranes and clinical endometritis was supported by an expert panel of clinicians. The risk factors for clinical endometritis appear to be associated with trauma of the female genital tract and disruption of the physical barriers to infection rather than fecal contamination.     

Relationship of declines in grain consumption and milk yield to estrus in dairy cattle

A retrospective study was done to determine if a reduction in daily grain consumption or decline in daily milk yield were accurate indicators of estrus in 25 Holstein cows. A computer automatically identified all cows that left more than 10% of their daily grain allocation in the feed stall or that gave less than 85% of their most current 7-d daily average milk yeild. By retrospectively analyzing breeding records, grain refusal and milk declines were identified as either occurring in conjunction with estrus or nonestrus. Declines in grain consumption and milk yield were frequently associated with estrus, but many cows in estrus did not exhibit such declines. While such declines hold promise as estrous detection aids, it was concluded that refusals of daily grain allocation or declines in daily milk yield were not sufficiently accurate to supplant other methods of estrous detection in dairy cattle.     

Influence of management factors on pregnancy attrition in dairy cattle

The present study was conducted to determine the influence of management factors on pregnancy attrition in dairy cattle. Data from 3162 diagnosed pregnancies in parous cows and 1050 in heifers at 9 commercial dairy herds in northeastern Spain were used. Pregnancy diagnosis by palpation per rectum was performed from 30 to 70 d post insemination. Pregnancy attrition was registered when pregnancy diagnosis resulted negative in a second palpation carried out between 120 and 150 d following insemination. Overall proportion of pregnancy losses was 7.9% (9.6% in parous cows and 2.8% in heifers). Data analysis was performed by multiple logistic regression methods. For all animals, effect of time of pregnancy diagnosis was shown (Odds ratio = 0.97 for 1 d increase; P = 0.0042). Conceptus loss in heifers was lower than in parous cows (Odds ratio = 0.28; P = 0.0001), and a higher proportion of pregnancy attritions was detected in animals inseminated in spring, summer and winter, compared to those inseminated in autumn (P < 0.04). Herd effect on pregnancy attrition was also significant. Similar results were observed in the subanalysis for parous cows and, furthermore, no effect of lactation number and of interval from previous calving to pregnancy was shown in this group. In heifers, no effect of time of pregnancy diagnosis and of insemination season on pregnancy attrition was shown, and only a herd effect was observed. Our data suggest that the influence of parity status (heifer vs cow) could affect the proportion of pregnancy attrition rather than early diagnosis, and, in pregnant cows, adaptation to seasonal changes associated with temperature decreases seem more efficient.     

Risk factors associated with cystic ovarian disease in Norwegian dairy cattle

Background  

The aims of this study were to establish the incidence of cystic ovarian disease (COD) and its geographical and seasonal variation in Norway, investigate the effect of COD on culling rates, and describe the effects of COD on subsequent reproductive performance and its association to twins.     

Twinning in dairy cattle: A study of risk factors and effects

Twin calvings on Dutch dairy farms were studied using data collected through a routine herd health and production management program. Over a period of 6.5 yr, 381 twin calvings (762 calves) of a total of 11,951 calvings were recorded on 33 farms. The 381 twin calvings were compared with a referent group of 1,536 calvings that was randomly selected from the orginal 11,951 calvings. Risk factors for twin calvings were parity, season, herd and previous twinning. High cumulative milk production was associated with cows conceiving twins. Treatment for infertility in the preceding lactation was an equivocal risk factor. Twin calvings increased the risk of abortion, retained placenta, fertility-related treatment, as well as the number of days open and the number of inseminations per conception. Although twin calvings resulted in more calves born per dam, the number of available replacement heifers did not increase. After twin calving, cows produced slightly less milk and were culled more often than single calving cows. To adapt appropriate management practices for cows carrying twins, an early and reliable method for detecting twin pregnancies is needed.     

Spatial and management factors associated with exposure of smallholder dairy cattle in Tanzania to tick-borne pathogens

A cross-sectional study of serum antibody responses of cattle to tick-borne pathogens (Theileria parva, Theileria mutans,Anaplasma marginale, Babesia bigemina and Babesia bovis) was conducted on smallholder dairy farms in Tanga and Iringa Regions of Tanzania. Seroprevalence was highest for T. parva (48% in Iringa and 23% in Tanga) and B. bigemina (43% in Iringa and 27% in Tanga) and lowest for B. bovis (12% in Iringa and 6% in Tanga). We use spatial and non-spatial models, fitted using classical and Bayesian methods, to explore risk factors associated with seroprevalence. These include both fixed effects (age, grazing history and breeding status) and random effects (farm and local spatial effects). In both regions, seroprevalence for all tick-borne pathogens increased significantly with age. Animals pasture grazed in the 3 months prior to the start of the sampling period were significantly more likely to be seropositive for Theileria spp. and Babesia spp. Pasture grazed animals were more likely to be seropositive than zero-grazed animals for A. marginale, but the relationship was weaker than that observed for the other four pathogens. This study did not detect any significant differences in seroprevalence associated with other management-related variables, including the method or frequency of acaricide application. After adjusting for age, there was weak evidence of localised (<5 km) spatial correlation in exposure to some of the tick borne diseases. However, this was small compared with the 'farm-effect', suggesting that risk factors specific to the farm were more important than those common to the local neighbourhood. Many animals were seropositive for more than one pathogen and the correlation between exposure to the different pathogens remained after adjusting for the identified risk factors. Identifying the determinants of exposure to multiple tick-borne pathogens and characterizing local variation in risk will assist in the development of more effective control strategies for smallholder dairy farms.     

Relationship among estradiol, cortisol and intensity of estrous behavior in dairy cattle

Economic profitability of a dairy farm is based, in part, on the calving interval of the cows. The optimal interval is 365 d. To achieve this, the cow needs to be pregnant within 85 d post partum. The first and most problematic step in this process is the determination of the optimal time for insemination, which is based on estrous behavior. The expression of estrous behavior, however, is at a low level in modem dairy herds, resulting in low detection rates and longer calving intervals. In the present study, a point scale was used to monitor postpartum, nonpregnant cows for estrous symptoms. Frequent blood samples were taken around estrus, and the cows were fit with pedometers to measure their activity. Correlations between the occurrence of symptoms of estrus and levels of estradiol and cortisol were then analyzed. Standing heat, the standard symptom of estrus, was observed in only 53% of the cows. A high correlation of 0.7 was found between estradiol concentration and estrous behavior. This was empasized by the fact that the estradiol level reached its highest level of 7.76 + 2.39 (SD) pg/mL at the same time as the highest behavior score. The highest pedometer readout lagged 8 h behind this moment. Cortisol levels did not exceed the physiological levels in rest situations but showed an increase at the time estrous behavior was at its maximum. The present study showed that standing heat is not the primary symptom for detecting estrus in cows. Pedometers are a useful aid but they have to be read several times a day. The high correlation between the visual symptoms of estrus and estradiol concentrations indicates that visual estrus detection is an efficient, reliable way to determine the right time for insemination.     

Postpartum anestrus in dairy cattle

Fertility of the postpartum period is negatively influenced by the incidence of anestrus. The latter condition is characterized by the absence of estrous behavior, which may be an indication of suboptimal conditions (e.g., inadequate peripartum nutrition) or pathologic conditions (e.g., chronic debilitating diseases or uterine and ovarian diseases). Although initiation of ovarian follicular growth in the postpartum period is generally not affected, subsequent development (deviation) and the fate of the dominant follicle are the primary factors that affect reestablishment of ovarian cyclicity. Anestrus can be classified based on the three functional states of follicular development; that is, follicle emergence, deviation, and ovulation. Prevention of anestrus is preferable to treatment and can be achieved in part by maintaining a healthy periparturient period. To better understand the etiology of anestrus and its prevention, research is urgently needed in the following three areas: the role of peripartum disease conditions that influence reproduction, genes involved in ovulation, and the influence of proteins (e.g., leptin) that appear to be important links between metabolic signals and the neuroendocrine axis.     

Exploitation of genetic and physiological determinants of embryonic resistance to elevated temperature to improve embryonic survival in dairy cattle during heat stress

Heat stress causes large reductions in fertility in lactating dairy cows. The magnitude and geographical extent of this problem is increasing because improvements in milk yield have made it more difficult for cows to regulate body temperature during warm weather. There have been efforts to improve fertility during heat stress by exploiting determinants of oocyte and embryonic responses to elevated temperature. Among these determinants are genotype, stage of development, and presence of cytoprotective molecules in the reproductive tract. One effective strategy for increasing pregnancy rate during heat stress is to use embryo transfer to bypass effects of elevated temperature on the oocyte and early embryo. Pregnancy success to embryo transfer in the summer can be further improved by exposure of embryos to insulin-like growth factor-I during culture before transfer. Among the cytoprotective molecules that have been examined for enhancing fertility during heat stress are bovine somatotropin and various antioxidants. To date, an effective method for delivery of these molecules to increase fertility during heat stress has not been identified. Genes in cattle exist for regulation of body temperature and for cellular resistance to elevated temperature. Although largely unidentified, the existence of these genes offers the possibility for their incorporation into dairy breeds through crossbreeding or on an individual-gene basis. In summary, physiological or genetic manipulation of the cow to improve embryonic resistance to elevated temperature is a promising approach for enhancing fertility of lactating dairy cows.     

Risk factors for perinatal mortality in dairy cattle: Cow and foetal factors, calving process

It was the aim of this study to identify risk factors of perinatal mortality (PM) on a large dairy farm in Germany. Four hundred and sixty-three cows were observed continuously around calving. Data such as the lactation number, body condition score, pelvic measurements, duration of second stage of labour (SSL), degree of abdominal press (AP), presentation/position/posture of the calf, calving classification, various measurements of the calves and every action of the barn staff were documented. Calves born dead and those that died within 24 h were classified as cases of PM. Logistic regression was performed to identify risk factors for the dependent variables PM, SSL and AP. 9.7% of all calves born (n = 483) were classified as PM. In the logistic regression model, only SSL and presentation/position/posture of the foetus remained as significant effects for PM. The odds ratio for PM was 0.20, when SSL was ≤120 min, and 0.33, when the calves were born in anterior presentation, upper position and normal posture. With regard to SSL, primipara, insufficient AP, assisted calvings and as a trend, work shift changeover, these were risk factors for a prolonged SSL beyond 120 min. The risk for insufficient AP was lower when the calves were born spontaneously, in anterior presentation and as single calves. In conclusion, the duration of SSL and presentation/position/posture of the calf seemed to be key risk factors for PM. Interventions should be considered when SSL lasts longer than 2 h. Insufficient monitoring around parturition had a negative effect on the duration of SSL and thereby, indirectly on PM.     

Ovulation failure and double ovulation in dairy cattle: risk factors and effects

Ovulation failure and double ovulation rates were examined in 1917 inseminations performed in high-yielding dairy cows under standard commercial conditions. The ovulation rate was determined 11 days post-insemination by ultrasound detection of at least one corpus luteum in the ovaries. Analyzing the double ovulation and pregnancy rates, the study population consisted only of ovulated cows (n = 1792). Data were analyzed using logistic regression methods. A failure to ovulate was recorded in 125/1917 (6.5%) services: 82/663 (12.4%) during the warm and 43/1254 (3.4%) during the cool period. Based on the odds ratios, the risk of ovulation failure was 3.9 times higher for inseminations performed during the warm period. No significant effects of estrous synchronization, milk production and days in milk at AI, and service and lactation number on ovulation failure were found. Double ovulation was recorded in 277/1792 (15.5%) services: 146 (52.7%) unilateral double ovulations (42.5% left versus 57.5% right); 115 (41.5%) bilateral double ovulations; and 16 (5.8%) triple ovulations. Double ovulation was recorded in 72 (12.4%) and 205 (16.9%) AI during the warm and the cool period, respectively. The percentages of double ovulation for first, second and third or more lactations were 6.7, 16.6 and 25%, respectively. Double ovulation rates for early (less than 90 days), mid- (90-150 days) and late (more than 150 days) lactation periods were 13, 20.7 and 14.2%, respectively. Reaching estrus during the warm period decreased the likelihood of double ovulation by a factor of 0.86; the risk of double ovulation was lower in cows with higher milk production (a 1 kg increase in milk yield led to a 0.97-fold reduced risk of double ovulation); cows in their second and in their third or more lactations showed a likelihood of double ovulation (using the first lactation as reference) increased by factors of 3.4 and 5.6, respectively; and reaching estrus during the early and late lactation period was related to a decreased probability of double ovulation (using the mid-lactation period as reference) by factors of 0.56 and 0.84, respectively. No significant effects of synchronization and service number on the double ovulation rate were found. Pregnancy was recorded in 914/1792 (51%) services: rates of 53.5% (811/1515) were recorded for single ovulations; 37.2% (103/277) for double ovulations: 28.8% (42/146) for unilateral double ovulations; 45.2% (52/115) for bilateral double ovulations; and 56.3% (9/16) for triple ovulations. The likelihood of pregnancy diminished in cows: inseminated during the warm period (by a factor of 0.5); inseminated by one particular bull (by a factor of 0.33); with higher milk production (a 1 kg increase in milk yield decreased the probability of pregnancy by a factor of 0.98); or undergoing unilateral (by a factor of 0.31) and bilateral (by a factor of 0.64) double ovulation. Logistic regression analysis indicated no significant effects of synchronization, days in milk, lactation number and service number on pregnancy rate. Collectively, our results indicate that cows showing estrus in conditions of heat stress had a high risk of ovulation failure. The effect of milk production on double ovulation was negative, whereas lactation number was positively correlated with this factor; the highest incidence of double ovulation occurring during the mid-lactation period.     

Relationship between progesterone concentrations in milk and blood and time of ovulation in dairy cattle

The objective of this study was to investigate whether monitoring progesterone concentrations in milk and blood plasma can be used to predict time of ovulation in dairy cattle. Whole milk was sampled twice daily and blood samples were collected once a day before the morning milking. Ovulation was assessed by trans-rectal ultrasonography at 4h intervals beginning from the end of estrus. For a parameter to be useful as predictor for time of ovulation, it should be precise (i.e. variation between animals should not exceed 12h). In milk, progesterone concentration dropped <15 ng/ml at 97.7+/-17.8h (range: 54-126 h) before ovulation, to <5 ng/ml at 79.7+/-11.2h (range: 54-98) before ovulation to decline further to <2n g/ml at 70.7+/-16.8h (range: 38-90 h) before ovulation (n=20). In plasma, progesterone concentration dropped to <4ng/ml 90.5+/-19.6h (range: 66-138 h) before ovulation and to <2 ng/ml at 75.0+/-12.2 h (range: 50-98) before ovulation. These intervals were not influenced by parity, milk production or days in milk. In conclusion, monitoring of progesterone alone is not sufficient to predict ovulation because of the large variation in timing of decrease of progesterone concentrations relative to ovulation between animals. At best the range is about 2 days.     

Hoof overgrowth in Holstein--Friesian dairy cattle

The genetic etiology of hoof overgrowth, a widespread problem in Holstein-Friesian cattle, was examined. Although all four feet are affected, the hind feet usually have a greater degree of overgrowth. There is a distinct age tendency for the trait; the younger cows' hooves grow faster than those of the older cows, but the overgrowth in older cows reaches greater proportions. Analysis of variance of chi-square frequency tests showed that there is a component of heritability involved in the expression of the trait, but that it follows a more complex model than a simple autosomal recessive gene would show.     

Plasma progesterone profiles and factors affecting embryo-fetal mortality following embryo transfer in dairy cattle

The relationship between plasma progesterone (P4) levels and embryo survival, and the value of P4 profiles for the selection of cattle embryo transfer recipients is still a matter of controversy. This study reports a comparison between lactating cows and heifers (n = 407) from a single dairy herd, after transfer of either fresh or frozen-thawed good quality embryos, of their ability to sustain embryo-fetal development to term. Plasma P4 concentrations on the day of estrus (Day 0 = D0), Day 4, Day 7 and on Day 21 were measured and related to embryo survival. Plasma P4 levels on Days 0, 4 and 7 were similar in recipients later found pregnant or open. Plasma P4 levels on Day 7 were significantly higher (P < 0.01) in heifers than in cows, but they were similar in pregnant and nonpregnant heifers and in pregnant and nonpregnant cows. Pregnancy rates for fresh and frozen-thawed embryos were higher in heifers than in cows, but the differences did not reach significance. However, the overall late embryonic mortality was significantly higher (P < 0.01) and the calving rate for frozen-thawed embryos was significantly lower (P < 0.05) in cows than in heifers. As expected, plasma P4 on Day 21 was significantly higher (P < 0.001) in pregnant than in nonpregnant recipients, but there was no difference between pregnant cows and pregnant heifers. Plasma P4 levels on Day 7 of recipients presumed pregnant on Day 21 and later found pregnant or nonpregnant were similar, but plasma P4 levels on Day 21 were significantly higher (P < 0.001) in pregnant than in nonpregnant recipients. The results of this study suggest that plasma P4 levels until the day of transfer, except for the rejection of recipients with abnormal luteal function, are of limited practical use for embryo transfer recipient selection. However, in lactating cows low plasma P4 values on Day 7 might negatively affect embryo survival, while in heifers this effect is not noticeable. Lactating cows are more prone to embryo loss than heifers, especially in the case of frozen-thawed embryos; this is associated with a lower competence of the corpus luteum at Day 7.     

Inheritance of UMP synthase in dairy cattle

The inheritance of uridine-5'-monophosphate (UMP) synthase in dairy cattle was consistent with a two-allele, single-autosomal-locus model. Two phenotypes were associated with different levels of the enzyme in bovine erythrocytes. The predominant phenotype (assumed normal) had twice the concentration of UMP synthase as the second phenotype (deficient). A one-to-one correspondence between enzyme level and genotype identified one homozygote as normal, the heterozygote as deficient, and the other homozygote as unobserved. Three alternative hypotheses were rejected. The deficiency as homozygous recessive was rejected because 20 matings between assumed normal males and deficient females resulted in 10 normal and 10 deficient offspring. The hypothesis that the deficiency was homozygous dominant was rejected because the 95 percent confidence interval about the observed gene frequency, 0.0024 to 0.0146, did not contain the estimated gene frequency for equilibrium between an average 10(-5) mutation rate and selection against the deficiency as homozygous dominant. Analyses of female relatives implicated one bull as deficient (96 percent probability), as he had, independently, 2 deficient daughters, 5 deficient granddaughters from untested dams, and 3 deficient great-granddaughters from untested ancestors. The hypothesis that the deficiency was sex-linked was rejected because 3 of 9 tested sons of the putative deficient bull were deficient. Calf mortality is expected in 25 percent of matings between deficient animals.     

Evaluation of different shades to improve dairy cattle well-being in Argentina

 Two tree shades (TS1 and TS2) and an artificial shade structure (AS) were evaluated using black globe temperatures (BGTs) to assess their effectiveness in reducing heat load. The artificial structure consisted of a black woven polypropylene cloth providing 80% shade, mounted on 2.5-m-high eucalyptus posts. The work was carried out at Rafaela Experimental Station, Argentina, during the summer (January and February) 1994. BGTs and floor temperatures were measured in concrete floor holding pens with and without artifical shade. The results showed no difference between TS1, TS2 and AS, their average BGTs being 30.2 (SD 0.58), 29.0 (SD 0.70) and 30.2 (SD 0.74)°C, respectively. BGTs under all three shades were significantly lower (P<0.01) than the average BGT recorded outside: 35.5 (SD 1.12)°C. Average BGTs in holding pens were 32.4 (SD 1.38) and 39.9 (SD 1.91)°C for shaded and non-shaded areas (P<0.01). The corresponding average floor temperatures were 27.8 (SD 0.68)°C and 47.7 (SD 2.13)°C (P<0.01). To assess the effects of shade on animal well-being, afternoon rectal temperatures (RT) and respiratory rate (respirations per minute, RR) of lactating cows were recorded twice a week. Rectal temperatures were significantly higher for non-shaded cows (P<0.01), mean RT being 40.1 (SD 0.65)°C vs 39.3 (SD 0.42)°C for the shaded animals. Corresponding RRs were 78.9 (SD 18.0) and 60.7 (SD 10.6) (P<0.05). It was concluded that: (1) tree and artificial shades produced similar effects, (2) shading the holding pen with an 80% shading cloth was effective in reducing heat load and floor temperatures, and (3) access to shade in our pasture-based system improved animal well-being. Received: 9 September 1996 / Revised: 10 March 1997 / Accepted: 2 July 1997