Environmental factors affecting the conception rates of nulliparous and primiparous dairy cattle

Dairy cattle must allocate energy to milk production and reproduction. Therefore, understanding the environmental factors that affect conception rates in nulliparous and primiparous cows is helpful in appropriate feeding management strategies before and after calving. Accordingly, the aim of this study was to investigate the influence of environmental factors before and after the first calving on the conception rate, representing the starting point of milk production. The records of the first artificial insemination (AI) from Holstein nulliparous cows (n = 533,672) and primiparous cows (n = 516,710) in Hokkaido, Japan, were analyzed using separate multivariable logistic regression models. The mean conception rates for nulliparous and primiparous cows from 2012 to 2018 were 55.2 and 39.2%, respectively. In both nulliparous and primiparous cows, the conception rate of crossbreeding using Japanese Black (JB) semen was significantly higher than that for purebred Holstein breeding. The conception rate using sexed semen decreased in the warmer months only in nulliparous cows. Moreover, we grouped primiparous cows according to milk yield during peak lactation (PY; < 25, 25–30, 30–35, ≥35 kg) and the interval from calving to first insemination (CFI; < 60, 60–79, 80–99, ≥100 d), and evaluated their combined effect on the conception rate. Both PY and CFI strongly affected the conception rate in primiparous cows, which decreased with an increase in PY, even for the group with CFI ≥100 d; however, the conception rate increased for a CFI ≥60 d regardless of PY. Taken together, this study demonstrates the long-term effect of PY and an independent effect of CFI on the conception rate of cows. These results provide guidance for management to execute appropriate AI implementation strategies before and after lactation.     

Effects of an injectable trace mineral supplement on first-service conception rate of dairy cows

A total of 825 dairy cows from a commercial dairy farm in central California were used to evaluate effects of one or 2 doses of an injectable trace mineral supplement containing 20 mg/mL of zinc, 20 mg/mL of manganese, 5 mg/mL of selenium, and 10 mg/mL of copper on first-service conception rate. Cows were randomly allocated into treatment or control group to either a single dose (experiment 1) or a double dose (experiment 2) of injected supplement. Allocation was based on days in lactation for experiment 1 and the length of gestation periods for experiment 2. In experiment 1, cows 38 to 45 d in lactation (n = 190) received a single dose of 5 mL of injected supplement. Similar cows were used as controls (n = 227). In experiment 2, cows and pregnant heifers received an initial injection of 5 mL of the mineral supplement from 2 to 3 wk precalving (n = 186). An equal dose was repeated 38 to 45 d in lactation. A similar group of cows and pregnant heifers served as controls for experiment 2 (n = 222). Health and reproductive events postcalving were recorded. In experiment 1, the odds of first-service conception were not significantly different for cows receiving a one-dose regimen of minerals compared with untreated control cows; conception rates were 26.8 and 27.5% for experiment 1 treatment and control groups, respectively. In experiment 1, the odds of first-service conception were significantly lower (odds ratio = 0.66) for cows and heifers given the 2-dose regimen of minerals compared with untreated controls; overall conception rates were 21.5 and 31.5% for experiment 2 treatment and control groups, respectively. In this intensively managed dairy herd, a single dose of injected trace minerals before breeding had no beneficial effects on first-service conception rate. However, dairy cows receiving a dose of trace minerals before calving and another dose before breeding had lower conception at first service.     

Effects of seasonal climatic conditions on the diagnosis of Mycobacterium avium subspecies paratuberculosis in dairy cattle

Validity of Johne's disease programs and control protocols that rely on established cut points [e.g., specified sample-to-positive (S/P) ratios] for ELISA serological tests depends on interpreted results that are not susceptible to variable test accuracy. It was hypothesized that seasonal variability exists in serological response to Mycobacterium avium subsp. paratuberculosis (MAP) infection. Further, a reciprocal response may occur, resulting in greater risk of fecal shedding in subclinically infected animals. A testing regimen was invoked that included multiple testing of individual adult cows during the 4 seasons. Serum was collected on a cyclic, monthly basis from 3 randomly selected cohorts of dairy cows, and fecal samples were collected from the 20% of cows with the greatest ELISA test S/P ratios. Staggered, quarterly sampling was continued for 1 yr, and at the conclusion, serum was analyzed en masse. The ELISA outcome values (i.e., S/P ratio) were treated both as categorical and continuous variables. The potential lagged effects of temperature-related seasonality on S/P ratio, as well as the potential for a change in test result caused by temperature were assessed. Results for fecal culture were analyzed on a categorical scale and compared with the ELISA results to explore the possibility of reciprocal fecal shedding. No significant seasonal effects on either S/P ratios or the proportion of cows seropositive to MAP were observed. Furthermore, no evidence was found linking temperature-related seasonality to a reciprocal increase in the risk of fecal culture positivity for MAP.     

Effects of gonadotropin-releasing hormone and human chorionic gonadotropin on pregnancy rate in dairy cattle

This study was to determine if gonadotropin-releasing hormone, human chorionic gonadotropin, or their interaction would affect pregnancy rate or milk progesterone profiles in dairy cattle. Cows and heifers eligible for first, second, and third services were assigned to four treatments: 1) saline i.m. within 5 min after AI (d 0) and saline 15 d after AI (n = 222 AI); 2) gonadotropin-releasing hormone (100 micrograms) i.m. within 5 min after AI and saline on d 15 (n = 223); 3) saline after AI and human chorionic gonadotropin (3500 IU) i.m. on d 15 (n = 196); 4) gonadotropin-releasing hormone at AI and human chorionic gonadotropin on d 15 (n = 195). Progesterone was quantified in milk samples collected twice weekly for 5 wk from all cows. Neither gonadotropin-releasing hormone, human chorionic gonadotropin, gonadotropin-releasing hormone x human chorionic gonadotropin interaction, age, nor service number affected pregnancy rate, which averaged 46.2%. Pregnancy and human chorionic gonadotropin affected milk progesterone profiles. Pregnancy maintained progesterone concentrations and human chorionic gonadotropin on d 15 increased them. This study does not support the general use of gonadotropin-releasing hormone at AI or human chorionic gonadotropin 15 d after AI as methods for enhancing pregnancy rates of dairy cattle.     

Effects of milk urea nitrogen and other factors on probability of conception of dairy cows

The objective of this study was to evaluate the relationships between milk urea nitrogen (MUN) and other factors and the probability of conception in dairy cows. Data were retrieved from the Lancaster Dairy Herd Improvement Association (DHIA). A total of 713 dairy herds and 10,271 dairy cows were included in the study. Logistic regression was used to determine the within-herd effects of MUN, milk production, lactation number, and breeding season on the probability of conception for each of 3 services. Within herds, MUN displayed a slight negative association with probability of conception at first service. For example, there was a 2- to 4-percentage unit decrease in conception rate at first service with a 10-mg/dL increase in MUN. In among-herd regression analysis, there was no effect of MUN on probability of conception. These results suggest that MUN may be related to conditions affecting reproduction of individual cows within a herd. Diet formulation usually would affect MUN equally among all cows at a similar stage of lactation in a herd. Because there was no effect of MUN among herds, diet formulation did not appear to affect conception rate.     

Effect of simultaneous thawing of multiple 0.5-mL straws of semen and sequence of insemination on conception rate in dairy cattle

The objectives of this study were to determine 1) the effect of simultaneous thawing of multiple 0.5-mL straws of semen and sequence of insemination (first, second, third, or fourth) on conception rates in dairy cattle, 2) whether the conception rates achieved following AI by professional AI (PAI) technicians and herdsman-inseminators (HI) differed, and 3) the effect of elapsed time from initiation of thawing straws of semen to seminal deposition on conception rates in dairy cattle. Four dairies with PAI and four with HI participated in the study. Initial data recorded included beginning thaw time, cow identification number, and time of seminal deposition. Herd records were retrieved following pregnancy diagnosis. Conception rates of dairy cows (n = 1025) were not affected by sequence of insemination (first, second, third, or fourth). Conception rates for herds using PAI were 40, 47, 41, and 50%. Conception rates for herds using HI were 24, 20, 33, and 30%. Average conception rates of dairy cows differed between PAI and HI (45 vs. 27%, respectively). The difference in mean conception rate achieved by PAI and HI was not attributable to milk production, parity, service number or stage of lactation. The elapsed time from initial thaw to completion of fourth AI was shorter for PAI than for HI, 7.6 vs. 10.9 min, respectively. Although the average conception rate differed between PAI and HI, elapsed time from initial thaw to completion of fourth AI and sequence of insemination (first, second, third, or fourth) had no effect on conception rate within inseminator group.     

Genetic analysis of dairy cattle production traits in a management intensive rotational grazing environment

Management intensive rotational grazing is a low input form of dairy herd management that is practiced by an increasing number of US dairy producers. However, concerns exist regarding the predictability of progeny performance in a grazing environment because most US dairy sires are progeny tested under conventional conditions of herd management. Lactation data from 27 Wisconsin dairy herds that have practiced management intensive rotational grazing for at least 4 yr were analyzed, as were data from three randomly chosen groups of control herds. Coefficients of regression of progeny milk, fat, and protein yields on USDA sire PTA values were 0.99, 0.76, and 0.96, respectively, from the grazing herds. In the control herds, regression coefficients for milk, fat, and protein yields averaged 0.95, 0.98, and 0.88, respectively. Therefore, progeny performance of grazing herds was predicted adequately by national sire PTA values that were derived primarily from conventionally managed herds. Heritability estimates for milk, fat, and protein yields were 0.23, 0.17, and 0.26, respectively, in the grazing herds and 0.24, 0.27, and 0.27, respectively, in a pooled data set containing all control herds. Estimated genetic correlations between production traits in the grazing environment and in the control environment were 0.92, 0.88, and 0.99 for milk, fat, and protein yields, respectively. These correlations, as well as the regression coefficients, indicate that interaction of genotype by environment is not important for these management systems, and nearly optimal genetic progress can be achieved by selecting AI sires progeny tested under traditional management conditions.     

Effects of heat-stress on production in dairy cattle

The southeastern United States is characterized as humid subtropical and is subject to extended periods of high ambient temperature and relative humidity. Because the primary nonevaporative means of cooling for the cow (radiation, conduction, convection) become less effective with rising ambient temperature, the cow becomes increasingly reliant upon evaporative cooling in the form of sweating and panting. High relative humidity compromises evaporative cooling, so that under hot, humid conditions common to the Southeast in summer the dairy cow cannot dissipate sufficient body heat to prevent a rise in body temperature. Increasing air temperature, temperature-humidity index and rising rectal temperature above critical thresholds are related to decreased dry matter intake (DMI) and milk yield and to reduced efficiency of milk yield. Modifications including shade, barns which enhance passive ventilation, and the addition of fans and sprinklers increase body heat loss, lowering body temperature and improving DMI. New technologies including tunnel ventilation are being investigated to determine if they offer cooling advantages. Genetic selection for heat tolerance may be possible, but continued selection for greater performance in the absence of consideration for heat tolerance will result in greater susceptibility to heat stress. The nutritional needs of the cow change during heat stress, and ration reformulation to account for decreased DMI, the need to increase nutrient density, changing nutrient requirements, avoiding nutrient excesses and maintenance of normal rumen function is necessary. Maintaining cow performance in hot, humid climatic conditions in the future will likely require improved cooling capability, continued advances in nutritional formulation, and the need for genetic advancement which includes selection for heat tolerance or the identification of genetic traits which enhance heat tolerance.     

Effect of herd environment on the genetic and phenotypic relationships among milk yield, conception rate, and somatic cell score in Holstein cattle

A total of 248,230 primiparous records of Holstein cows calving from 1987 to 1994 (daughters of 588 sires in 3042 herds) was used to evaluate potential genotype by environment interactions among mature equivalent milk yield, lactation mean somatic cell score, and conception rate at first service. Herds were classified into low and high environmental groups using three different criteria: standard deviation of herd mature equivalent milk yield, a combination of herd mature equivalent milk yield mean and standard deviation, and the herd mean of body weight at first calving divided by age at first calving. Genetic parameters were modeled by using multiple-trait linear mixed models and were fitted using the multiple-trait derivative-free software. Heritabilities for mature equivalent milk yield, lactation mean somatic cell score, and conception rate at first service were 0.221, 0.106, and 0.015 in low environment herds and 0.300, 0.093, and 0.009 in high environment herds, respectively. Genetic (and phenotypic) correlations between mature equivalent milk yield and lactation mean somatic cell score, mature equivalent milk yield and conception rate at first service, and lactation mean somatic cell score and conception rate at first service were 0.277, -0.417, and -0.209, (-0.049, -0.180, and -0.040) and 0.173, -0.318, and -0.144, (-0.087, -0.166, and -0.035) in low and high environment herds, respectively. The genetic correlations between pairs of traits were consistently smaller in high environment herds, suggesting that differences in management between the two environment levels lessened the antagonistic genetic association between the traits studied. A long-range plan for low environment herds should focus on improving the level of management, which would greatly reduce the unfavorable correlated changes in lactation mean somatic cell score and conception rate at first service associated with the genetic improvement of mature equivalent milk yield.     

Short-term administration of bovine somatotropin to lactating dairy cows in a subtropical environment

Our objective was to evaluate response of lactating dairy cows to daily injections of bovine somatotropin during a subtropical summer. Ten Holstein cows, averaging 196 d in lactation, were used in a 30-d study. No treatment was imposed during d 1 to 10 (period 1) and d 21 to 30 (period 3). During d 11 to 20 (period 2), cows were injected daily with either 0 or 59 IU of pituitary-derived bovine somatotropin in 30 ml solution. Dry matter intake and milk yield and composition were measured daily. Jugular blood samples, taken on d 10, 15, 20, and 30, were analyzed for insulin, nonesterified fatty acids, urea nitrogen, and insulin-like growth factor-1. Body temperatures and respiration rates were measured at 1400 h on 4 or 5 d during each 10-d period. Data were analyzed using orthogonal contrasts. Contrast of period 1 plus period 3 vs. period 2 for treatment X days interaction was significant for milk yield, respiration rate, serum nonesterified fatty acids, and insulin-like growth factor-1. Under heat stress, cows injected with bovine somatotropin for 10 d produced 9.3% more milk than control cows with no change in feed intake. This increased production was accompanied by higher respiration rates (6%) and higher concentrations of serum nonesterified fatty acids (150%) and insulin-like growth factor-1 (222%).     

Effects of pathogen-specific clinical mastitis on probability of conception in Holstein dairy cows

The objective of this study was to estimate the effects of pathogen-specific clinical mastitis (CM), occurring in different weekly intervals before or after artificial insemination (AI), on the probability of conception in Holstein cows. Clinical mastitis occurring in weekly intervals from 6 wk before until 6 wk after AI was modeled. The first 4 AI in a cow’s lactation were included. The following categories of pathogens were studied: Streptococcus spp. (comprising Streptococcus dysgalactiae, Streptococcus uberis, and other Streptococcus spp.); Staphylococcus aureus; coagulase-negative staphylococci (CNS); Escherichia coli; Klebsiella spp.; cases with CM signs but no bacterial growth (above the level that can be detected from our microbiological procedures) observed in the culture sample and cases with contamination (≥3 pathogens in the sample); and other pathogens [including Citrobacter, yeasts, Trueperella pyogenes, gram-negative bacilli (i.e., gram-negative organisms other than E. coli, Klebsiella spp., Enterobacter, and Citrobacter), Corynebacterium bovis, Corynebacterium spp., Pasteurella, Enterococcus, Pseudomonas, Mycoplasma, Prototheca, and others]. Other factors included in the model were parity (1, 2, 3, 4 and higher), season of AI (winter, spring, summer, autumn), day in lactation of first AI, farm, and other non-CM diseases (retained placenta, metritis, ketosis, displaced abomasum). Data from 90,271 AI in 39,361 lactations in 20,328 cows collected from 2003/2004 to 2011 from 5 New York State dairy farms were analyzed in a generalized linear mixed model with a Poisson distribution. The largest reductions in probability of conception were associated with CM occurring in the week before AI or in the 2 wk following AI. Escherichia coli and Klebsiella spp. had the greatest adverse effects on probability of conception. The probability of conception for a cow with any combination of characteristics may be calculated based on the parameter estimates. These findings may be helpful to farmers in assessing reproduction in their dairy cows for more effective cow management.     

Effect of genetic merit and concentrate feeding on reproduction of grazing dairy cows in a subtropical environment

This study was conducted to determine the effects of genetic merit for milk production and concentrate feeding on the intervals to the onset of postpartum cyclic ovarian activity, first insemination, and establishment of pregnancy. Other factors considered included biochemical measures of energy balance, liveweight, and measures of production. A farmlet study was conducted with two lines of cattle that differed in Australian Breeding Value by 735 L milk and 47 kg of fat plus protein that were fed 300 or 2000 kg of concentrate per cow per year in a subtropical grazing system based on ryegrass, clover, and kikuyu pasture. Milk yield was higher in cows fed 2000 kg of concentrate per cow per year (23.6 L/d) than those fed 300 kg/cow per year (18.2 L/d), and cows of medium genetic merit (19.6 L/d) produced less milk than those of high genetic merit (22.2 L/d). Plasma glucose concentration was lower in the cows of high genetic merit (3.11 mmol/L), than in the cows of medium genetic merit (3.39 mmol/L). The cumulative probabilities of ovulation, insemination, and establishment of pregnancy by any day postpartum were determined by a Weibull distribution. Medium genetic merit cows in winter were more likely to ovulate by any day postpartum than in summer and more likely than high genetic merit cows in either summer or winter. The cumulative probability of insemination was lower in primipara than multipara and in summer than in winter. Primiparous cattle had a lower cumulative probability of pregnancy by any day postpartum.     

Altered vocalization rate during the estrous cycle in dairy cattle

Correct detection of estrus is a problem in dairy herds. In practice, several procedures exist for detection of estrus besides conventional visual observation by humans. These procedures deliver very different results regarding detection of estrus. It is known that the calls of female mammals can contain information about reproductive status. It is also suspected that the vocalizations of cattle contain information about age, sex, dominance status, and stage in the estrous cycle. In the present study, a methodology for the continuous automatic recording of vocalization of heifers during the periestrous period is presented. It was shown in 10 tethered heifers that the estrous climax results in an increase in vocalization rate. Vocalization rate of heifers increased approximately 84% from d −2 to 0 (related to observed estrus) and approximately 59% from d −1 to d 0. After d 0, vocalization rate decreased about 79%. Increased vocalization was correlated with the visual observation of estrus by humans. We also found 2 different structures in the vocalization of heifers. The harmonic structure showed regular frequency bands, whereas the nonharmonic structure was noisy. The hypothesis that the disharmonic structure increases near the estrous climax was confirmed. Hence, it seems possible to get information about stage of the estrous cycle of dairy cattle by means of monitoring vocalization. The presented method of automatically detecting the rate of cattle vocalization (patent pending) could be used solely or in combination with other automated systems for detecting estrus and could considerably increase current estrus detection rates once its applicability can be demonstrated in nontethered cattle.     

Effects of breed and production system on lameness parameters in dairy cattle

The aim of the present study was to assess the effects of Holstein-Friesian (HF) and Norwegian (N) dairy cattle genotypes on lameness parameters in dairy cattle within different production systems over the first 2 lactations. Following calving, HF (n = 39) and N (n = 45) heifers were allocated to 1 of 3 systems of production (high level of concentrate, low level of concentrate, and grass-based). High- and low-concentrate animals were continuously housed indoors on a rotational system so that they spent similar amounts of time on slatted and solid concrete floors. Animals on the grass treatment grazed from spring to autumn in both years of the study, so that most animals on this treatment grazed from around peak to late lactation. Claw health was recorded in both hind claws of each animal at 4 observation periods during each lactation as follows: 1) −8 to 70 d postcalving, 2) 71 to 150 d postcalving, 3) 151 to 225 d postcalving, and 4) 226 to 364 d postcalving. Sole lesions, heel erosion, axial wall deviation, sole length of the right lateral hind claw (claw length), right heel width, and right lateral hind heel height were recorded as well as the presence of digital dermatitis. The N cows had lower (better) white line and total lesion scores than HF cows. Cows on the high- and low-concentrate treatments had better sole and total lesion scores than cows on the grass treatment. The HF cows had better locomotion scores than N cows. Breed and production system differences were observed with respect to claw conformation, including claw length, heel width, and heel height. Digital dermatitis was associated with worse sole lesion scores and interacted with production system to influence white line lesion scores and maximum heel erosion scores. This study shows that genetic, environmental, and infectious factors are associated with hoof pathologies in dairy cows.