Days To First Service Research Articles

A Survey Study on Management Practices Associated With Voluntary Waiting Period and Its Effects on Reproductive Performance of dairy cows in Iranian Dairy Farms.

Voluntary waiting period (VWP), housing systems and the presence of a veterinarian are effective factors on reproductive performance of a dairy farm. This study aimed to investigate the management practices associated with VWP and its effects on reproductive performance. A total of 136,943 records of 21,756 cows that calved between 1990 and 2013 were used. A questionnaire was also conducted with the farms involved to determine if they adjust the timing of insemination based on the body condition score (BCS) of the cows, postpartum health situation (PPHS) or environmental factors such as heat stress and season. The impact of changing the VWP selectively, the presence of a veterinarian and the type of barn on reproductive outcomes like days open (DO), number of services per conception (NSPC) and days to first service (DFS) was examined using a linear mixed model. This model considered animals and herds as random factors and management practices as fixed factors in the analysis. Among herds that reported altering the VWP based on heat stress, DFS significantly increased (61.68±0.68 vs. 58.4±0.83) while DO (119.70±1.86vs. 126.9±2.29) and NSPC (1.98±0.04vs. 2.48±0.05) reduced compared to herds that did not alter the VWP. Our results showed that farms with a full-time veterinarian had a better reproductive performance than those with part-time care (p < 0.05). Housing system was significantly associated with fertility traits, so that cows in free-stall barns were more fertile than those kept in open-shed barns. The obtained results from this study indicated that management decisions to selectively altering the VWP led to difference in DFS and improved reproductive performance.

Success rate of artificial insemination, reproductive performance and economic impact of failure of first service insemination: a retrospective study

BackgroundA retrospective cohort study using a 10 year artificial insemination (AI) and cow reproductive performance data was conducted to study the success rate of AI; associations between effectiveness of AI and breed, AI season and, number of service per conception, and economic impact of failure of FSC in Dessie town, Dessie zuria and Kutaber districts. A total of 3480 dairy cows’ AI and reproductive performance records which were performed between 2003 and 2013 in the three selected districts of South Wollo were used. The economic losses and costs for cows that failed to conceive at their first AI associated with the larger number of days open were estimated.ResultThe prevalence of conception has a statistically significant difference between breeds of cows (P = 0.019). The non-return rate for first service was 58.54%. The median days to first service (DFS), inter-service interval (ISI) and gestation length (GL) were 126, 30 and 278 days respectively. Whereas, the mean + SD days open, calving interval (CI), number of inseminations (NOI) and number of services per conception (NSPC) were 147.2 ± 60.26, 424.5 ± 60.55, 1.14 ± 0.38 and 1.15 ± 0.39 respectively. Based on AI season there was a significant difference in conception between winter and spring (P = 0.021). There is a 45.04 days extension in the mean calving to conception interval in cows that did not conceive at their first AI but conceived by 2nd and 3rd AI than in cows that did conceive at their first AI. A total of 21,665.3 ETB extra costs was spent on reproductive treatment and other management for cows that failed to conceive at their first AI but conceived by second and third service. In cows that did not conceive totally the owner losses on average 473.7 ETB per cow per day extra costs until the cows will be culled.ConclusionTherefore to increase the conception rate and decrease the economic loss the owners of the dairy cows should supervise the cows regularly and should be trained on how to identify cows on estrous, the AI technicians should be trained to conduct the AI service accurately.

Associations between milk fat, protein and fat-to-protein ratio with some reproductive indices in dairy cows

Postpartum induced lipolysis by negative energy balance (NEB) causing an increase in milk fat, a decrease in milk protein, and as a consequence an increase in milk fat to protein ratio (FPR). The aim of this study was to evaluate the relationship between milk FPR and first service conception risk (FSCR), days to first service (DFS) and calving to conception interval at first service (CCIFS). Therefore, milk and reproduction data of 1,375 primiparous and multiparous Holstein dairy cows from 10 commercial dairy farms located on sub-tropical region were collected on days 30 and 60 of days in milk (DIM) and near the first service. The Pearson correlation test of milk compositions revealed only a significant correlation between milk protein at day 30 DIM and DFS, but in Logistic regression analysis it did not have a constant effect on reproductive indices. On the other hand, the effect of previous dry-off duration and AI season on FSCR were significant. Based on the result of the present study, it is concluded that milk compositions such as fat, protein and FPR had no correlation with the result of the first AI.

The Analysis of Reproduction in Population of the Slovak Spotted Dairy Cows

The aim of study was to analyse the reproduction and factors affecting on reproduction traits of dairy cows in population of Slovak Spotted cattle from 2007 to 2016 the results for 37,274 dairy cows: days to first service (DFS), days open (DO), number of inseminations per conception (NIC), age of first calving (AFC) and calving interval (CI). The basic statistical analysis were analysed using the SAS version 9.3. For the actual computation a linear models with fixed effects was used: For the actual computation a linear models with fixed effects was used: yijklm = μ + HYSi + BTj+ Fk+ Bl +eijklm. The linear model represents coefficients determination R2 = 0.452117% (P &lt; 0.001) for DFS, R2 = 0.377715% (P &lt; 0.001) for DO, R2 = 0.348442% (P &lt; 0.001) for NIC and R2 = 0.317128% (P &lt; 0.001) for CI with all fixed effects. Correlation coefficients among DFS with DO, NIC, AFC and CI were r = 0.37275, r = -0.06881, r = 0.06493 and r = 0.08348. These coefficients were highly statistically significant (P &lt; 0.001).

Genetic aspects of some reproductive, udder health and energy status traits in Holstein cows

The objective of this study was to estimate heritability as well as genetic and environmental relationships between days to first heat (DFH), days to first service (DFS), interval from calving to conception (ICC), calving interval (CI) and number of inseminations per conception (NIS) with mastitis (Mast), number of mastitis occurrence (NumMast), different measures of somatic cell count (SCC) and fat to protein ratio (F:P) in the first lactation of Holstein cows in Iran using linear and threshold animal and sire models. The 33851 first lactation records of Holstein cows from five large dairy herds with calving dates from March 2002 to September 2014 were analyzed with univariate and bivariate linear and threshold animal and sire models using Gibbs sampling methodology. Data from parity one to nine comprising 62483 records were used to conduct repeatability model analysis for reproductive traits. Heritabilities of the reproduction traits varied from 0.067 (for ICC) to 0.105 (for DFH) using linear animal models. Also, the heritabilities of udder health traits varied from 0.005 to 0.102 using different models. The repeatabilities of reproductive traits ranged from 0.110 to 0.307. In general, the genetic correlations (rg) between reproduction traits were positive and high (with the exception of rg between DFH-NIS). The rg between reproduction traits with udder health traits ranged from −0.029 to 0.359 and 0.151 to 0.584 using linear-linear and threshold-linear animal models, respectively. Generally, there was favorable rg between reproduction traits with udder health traits; therefore, selection for one set of these traits would improve the correlated traits. However, due to different (co)variance components and economic weights in each country/region, it can be recommended to investigate inclusion of both sets of these traits in breeding objectives.

Temporal effect of maternal heat stress during gestation on the fertility and anti-Müllerian hormone concentration of offspring in bovine

Ovarian reserve has been suggested as an important contributing factor of reproductive success in bovine. Size of ovarian reserve is determined during fetal period and it could be altered by environmental factors, with which the dam is exposed. Maternal heat stress could impair placental function and fetal development; however, there is limited information on the impact of prenatal heat stress on fertility and ovarian reserve in the offspring. Therefore, a retrospective study was conducted, in which fertility parameters and AMH concentration, as a reliable marker of ovarian reserve in bovine, were studied in the offspring of dams that had been exposed to heat stress during the first (FTE), second (STE) or third (TTE) trimester of gestation and the offspring of dams unexposed to heat stress (US). Additionally, postpartum exposure of offspring with heat stress was considered in the model to adjust the statistical analysis in this regard. Days to first service (DFS) and calving to conception interval (CCI) were prolonged in exposed than unexposed cows (P < 0.05). Days to first service and CCI were also longer in STE compared with FTE cows (P < 0.05). First service conception rate was lower in TTE than UN cows (P < 0.05). The proportion of repeat breeders was higher in exposed compared with unexposed cows (P < 0.05). Service per conception was higher in STE and TTE than UN cows (P < 0.05). Culling rate between different periods of lactation was also higher in exposed than unexposed cows (P < 0.05). Finally, AMH concentration was lower in STE and TTE than UN cows (P < 0.05); moreover, it was lower in STE compared with FTE cows (P < 0.05). In conclusion, the present study revealed detrimental effects of maternal heat stress on fertility, productive longevity and ovarian reserve in the offspring. In this context, the second and third trimesters appeared to be more critical periods.

Inbreeding and crossbreeding parameters for production and fertility traits in Holstein, Montbéliarde, and Normande cows

Breed differences and nonadditive genetic effects for milk production traits, somatic cell score (SCS), conception rate (CR), and days to first service (DFS) were estimated for Holstein × Montbéliarde and Holstein × Normande crossbreds, using an animal model adapted from the French genetic evaluation and extended to across-breed analysis. Inbreeding and breed differences were estimated from all purebred recorded cows. Only records from 1,137 herds with Holstein × Montbéliarde crossbred cows and from 1,033 herds with Holstein × Normande crossbred cows were used to estimate crossbreeding parameters. In these herds, crossbred cows represented about 13% of the total number of recorded animals compared with <1% when all herds were considered. Compared with the Montbéliarde and Normande breeds, the Holstein breed was genetically superior for production [+951kg and +2,444kg for 305-d mature-equivalent (305ME) milk, +40kg and +102kg for 305ME fat, +17kg and +54kg for 305ME protein, respectively] and inferior for fertility traits (−12 and −9% for CR, respectively). Inbreeding depression caused loss of yield for production traits (from −32 to −41kg of 305ME milk, −1.4 to −1.7kg of 305ME fat, and −1.1 to −1.3kg of 305ME protein per inbreeding percentage), a small increase in SCS (+0.001 to 0.006) and DFS (+0.12d), and a decrease in CR (−0.27 to −0.44%). Favorable heterosis effects were found for all traits (+494 to 524kg of 305ME milk, +21 to 22kg of 305ME fat, +15 to 16kg of 305ME protein, −0.05 to −0.04 SCS, +2 to 3% for CR, and −3 to 6d of DFS), to such a point that F1 crossbreds could compete with Holstein cows for milk production while having a better fertility. However, recombination losses suggested that some F1 heterosis was lost for backcross cows.

Influence of non-genetic factors on performance traits in Murrah buffaloes

The study on 522 Murrah buffaloes scattered over 19 years (1993 to 2011) in NDRI Livestock Farm was conducted to reveal the effect of non-genetic factors on performance traits. The fixed linear models were used to estimate the effect of nongenetic factors. The overall least-squares means of Age at First Calving (AFC), Service Period (SP), Days to First Service (DFS), Lactation Length (LL), Test Day 5 Milk Yield (TD 5 MY) and 305 days or less Milk Yield (305 DMY) were obtained as 44.03 ± 0.38 months, 146.28 ± 5.58 days, 89.28 ± 2.23 days, 286.08 ± 2.23 days, 8.13 ± 0.12 kg and 2078.20 ± 31.21 kg, respectively. Season of birth had significant effect (P<0.01) on AFC, autumn was the favourable season of birth for Murrah buffaloes. Season of calving significantly influenced (P<0.01) SP and DFS, where rainy and autumn were observed as favourable for fertility in Murrah buffaloes. Period of calving and parity had significant effect on reproduction traits (P<0.05) and production traits (P<0.01), except lactation length. Age group at first calving significantly influenced SP (P<0.01) and LL (P<0.05). Since, temporary environmental factors play a major role on performance traits, better breeding management should be implemented.

Reaction norm of fertility traits adjusted for protein and fat production level across lactations in Holstein cattle

A total of 304,001 artificial insemination outcomes in up to 7 lactations from 142,389 Holstein cows, daughters of 5,349 sires and 101,433 dams, calving between January 1995 and December 2007 in 1,347 herds were studied by a reaction norm model. The (co)variance components for days to first service (DFS), days open, nonreturn rate in the first service (NRFS), and number of services per conception were estimated by 6 models: 3 Legendre polynomial degrees for the genetic effects and adjustment or not for the level of fat plus protein (FP) production recorded at day closest to DFS. For all traits and type of FP adjustment, a second degree polynomial showed the best fit. The use of the adjusted FP model did not increase the level of genetic (co)variance components except for DFS. The heritability for each of the traits was low in general (0.03–0.10) and increased from the first to fourth calving; nevertheless, very important variability was found for the estimated breeding value (EBV) of the sires. The genetic correlations (rg) were close to unity between adjacent calvings, but decreased for most distant parities, ranging from rg=0.36 (for DFS) to rg=0.63 (for NRFS), confirming the existence of heterogeneous genetic (co)variance components and EBV across lactations. The results of the eigen decomposition of rg shows that the first eigenvalue explained between 82 to 92% and the second between 8 to 14% of the genetic variance for all traits; therefore, a deformation of the overall mean trajectory for reproductive performance across the trajectory of the different calving could be expected if selection favored these eigenfunctions. The results of EBV for the 50 best sires showed a substantial reranking and variation in the shape of response across lactations. The more important aspect to highlight, however, is the difference between the EBV of the same sires in different calvings, a characteristic known as plasticity, which is particularly important for DFS and NRFS. This component of fertility adds another dimension to selection for fertility that can be used to change the negative genetic progress of reproductive performance presented in this population of Holstein cows. The use of a reaction norm model should allow producers to obtain more robust cows for maintenance of fertility levels along the whole productive life of the cows.

Genetic parameters for production, health, fertility and longevity traits in dairy cows

Milk production, fertility, longevity and health records, were extracted from databases of two milk recording organisations in the United Kingdom for the first three lactations of the Holstein–Friesian breed. These included data related to health events (mastitis and lameness), voluntarily recorded on a proportion of farms. The data were analysed to calculate disease incidence levels and to estimate genetic parameters for health traits and their relationships with production and other functional traits. The resulting dataset consisted of 124 793 lactations from 75 137 animals of 1586 sires, recorded in 2434 herds. Incidence of health events increased with parity. The overall incidence of mastitis (MAS) and lameness (LAM), defined as binary traits, were 17% and 16%, respectively. Heritability estimates for MAS and LAM were 0.04 and 0.02, respectively, obtained from repeatability linear sire models. Heritability estimates of mastitis and lameness as count traits were slightly higher, 0.05 and 0.03, respectively. Genetic correlations were obtained by bivariate analyses of all pair-wise combinations between milk 305-day yield (MY), protein 305-day yield (PY), fat 305-day yield (FY), lactation average loge transformed lactation average somatic cell count (SCS), calving interval (CI), days to first service (DFS), non-return at 56 days (NR56), number of inseminations (NINS), mastitis (MAS), number of mastitis episodes (NMAS), lameness (LAM), number of lameness episodes (NLAM) and lifespan score (LS). As expected, MAS was correlated most strongly with SCS (0.69), which supports the use of SCS as an indicator trait for mastitis. Genetic correlations between MAS and yield and fertility traits were of similar magnitude ranging from 0.27 to 0.33. Genetic correlations between MAS with LAM and LS were 0.38 and −0.59, respectively. Not all genetic correlations between LAM and other traits were significant because of fewer numbers of lameness records. LAM had significant genetic correlations with MY (0.38), PY (0.28), CI (0.35), NINS (0.38) and LS (−0.53). The heritability estimates of mastitis and lameness were low; therefore, genetic gain through direct selection alone would be slow, yet still positive and cumulative. Direct selection against mastitis and lameness as additional traits should reduce incidence of both diseases, and simultaneously improve fertility and longevity. However, both health traits had antagonistic relationships with production traits, thus genetic gain in production would be slower.

Genotype by environment interaction for first-lactation female fertility traits in UK dairy cattle

The objective of this study was to examine whether there was genotype by environment interaction (G×E) for female fertility traits for various environmental descriptors used in the United Kingdom. Records on days to first service (DFS), nonreturn rate at 56 d (NR56), calving interval (CI), and number of inseminations (NINS) on approximately 200,000 first-lactation Holstein cows in 3,192 herds and from 1,147 sires were analyzed using both random regression reaction norm models and multiple-trait models. The environmental descriptors were herd averages of DFS, CI, and NR56, and herd production and intensity indices, the latter based on 305-d milk, fat, and protein yields, age at first calving, temperature, and rainfall. No G×E was found for NR56 and NINS. There was an indication of G×E for DFS and CI with respect to the herd average of that trait, but only from the reaction norm model. Genotype by environment interaction existed for DFS and CI with respect to both production and intensity indexes—genetic correlations between top and bottom quartiles ranged from 0.73 to 0.84, with similar results from both models, indicating reranking of bulls. Part of this G×E might be explained by low production and intensity herds also having more concentrated spring calving.

Genetic correlations between body condition scores and fertility in dairy cattle using bivariate random regression models

Genetic correlations between body condition score (BCS) and fertility traits in dairy cattle were estimated using bivariate random regression models. BCS was recorded by the Swiss Holstein Association on 22,075 lactating heifers (primiparous cows) from 856 sires. Fertility data during first lactation were extracted for 40,736 cows. The fertility traits were days to first service (DFS), days between first and last insemination (DFLI), calving interval (CI), number of services per conception (NSPC) and conception rate to first insemination (CRFI). A bivariate model was used to estimate genetic correlations between BCS as a longitudinal trait by random regression components, and daughter's fertility at the sire level as a single lactation measurement. Heritability of BCS was 0.17, and heritabilities for fertility traits were low (0.01-0.08). Genetic correlations between BCS and fertility over the lactation varied from: -0.45 to -0.14 for DFS; -0.75 to 0.03 for DFLI; from -0.59 to -0.02 for CI; from -0.47 to 0.33 for NSPC and from 0.08 to 0.82 for CRFI. These results show (genetic) interactions between fat reserves and reproduction along the lactation trajectory of modern dairy cows, which can be useful in genetic selection as well as in management. Maximum genetic gain in fertility from indirect selection on BCS should be based on measurements taken in mid lactation when the genetic variance for BCS is largest, and the genetic correlations between BCS and fertility is strongest.

International genetic evaluation for fertility traits in dairy cattle

The objective of this study was to review and discuss the results of the first international evaluation for female fertility of Holstein dairy cattle. Fifteen countries, including Italy, provided breeding values of bulls and joined the evaluation. Four trait groups were used to analyze animal’s ability to became pregnant and animal’s abilityto recycle after calving. Italy submitted three traits: days to first service (DTFS), non-return rate at 56 days (NR56) and calving interval (CI). Genetic correlation between Italy and the other countries ranged from 0.72 to 0.94 for DTFS, from 0.25 to 0.90 for NR56 and from 0.67 to 0.87 for CI. Results represent another step forward in the international trade of dairy cattle genetic material.

Selection for Female Fertility Using Censored Fertility Traits and Investigation of the Relationship with Milk Production

Bivariate models (censored linear-linear and censored threshold-linear) were used to estimate genetic parameters for production and fertility traits in the Spanish Holstein population. Records on 71,217 lactations from 41,515 cows were used: 30 and 36% of lactations were censored for days open (DO) and number of inseminations to conception (INS), respectively. Heritability estimates for production traits (milk, fat, protein) ranged between 0.18 and 0.25. Heritability of days to first service (DFS) and DO was 0.05; heritability of INS on the liability scale was 0.04. Genetic correlations between fertility traits were 0.41, 0.71, and 0.87 for DFS–INS, DO–INS, and DO–DFS, respectively. Days open had a larger genetic correlation (ranging from 0.63 to 0.76) with production traits than did DFS (0.47 to 0.59) or INS (0.16 to 0.23). Greater antagonism between production and DO may be due to voluntary management decisions for high-yielding cows, resulting in longer lactation lengths. Inseminations to conception appeared to be less correlated with milk production than were the other 2 female fertility traits. Including INS in a total merit index would be expected to increase genetic gain in terms of profit, but profit would decrease if either DO or DO and DFS were included in the index. Thus, INS is the trait to be preferred when selecting for female fertility. The genetic correlation between actual milk yield and 305-d standardized milk yield was 0.96 in the present study, suggesting that some reranking of sires could occur. Because the target of attaining a 12-mo calving interval, as implied by a 305-d standardized lactation length, is changing in the dairy industry, routine genetic evaluation of actual total lactation milk yield should be considered.

Influence of systematic effects on fertility traits in Swiss Brown cows

Abstract. The study was conducted to investigate the influence of systematic effects on fertility traits in Swiss Brown cows. Days to first service (DFS), days open (DO), calving interval (CI), non-return rate 90 (NRR90), and conception rate to first service (CRFS) were analysed. The data set included records from 82,755 cows out of 1,674 farms in Eastern and Central Switzerland. The observation period lasted from January 1988 to May 2002. Housing system, lactation number, region, zone, calving/insemination season, (all fixed), and 305-day milk yield (covariable) were tested significant at a level of p &lt; 0.05. The random effect of herd*year accounted for between 5.2 and 16.9 % of the total variance. Improved fertility results were consistently investigated in loose housing systems. DFS (67.8 vs. 71.0 days), DO (86.3 vs. 96.0), and CI (378.7 vs. 386.7) were shorter, NRR90 (66 vs. 61 %) and CRFS (52 vs. 44 %) were higher in loose housing systems compared to tie-stall barns. Cows in the first lactation had longer time intervals and lower success rates compared to cows in the second and third lactation. In higher lactation numbers, the reproductive performance consistently decreased. Cows in Eastern Switzerland had the first service 1 day later (69.7 vs. 68.8) compared to animals in Central Switzerland, otherwise the time intervals (DFS –0.9 days; CI –0.8 days) as well as the success rates (NRR90 +3 %; FSCR +4 %) were better. NRR90 and FSCR were highest in the insemination season from April to June (67 and 52 %, resp.). FSCR was lowest from January to March (48 %) and NRR90 had the lowest values from October to December (60 %).

Genetic correlations among body condition score, somatic cell score, milk production, fertility and conformation traits in dairy cows

AbstractGenetic and phenotypic parameters for body condition score (BCS), days to first service (DFS), non-return rate (NRR), somatic cell score (SCS), and 305-day milk, fat and protein yields were estimated, using 38930 multiple lactation records of cows across 1830 herds. The cows were daughters of '243 different sires. Single- and multi-trait repeatability animal models were used to estimate parameters based on restricted maximum likelihood methodology. Fixed effects in the model varied depending on the individual trait. Further, genetic relationships between 27 (linear and descriptive) type traits and functional traits (fertility and SCS) were estimated by regressing daughter type records on their sire's estimated breeding values for functional traits, using the same data set. Estimated regression coefficients were then subsequently used to derive approximate genetic correlations between type and functional traits (DFS, NRR and SCS). Body condition score had a moderate heritability (h2) of 0-26 and fertility traits had a low h2 (0-12 for DFS and 0-06 for NRR). Heritability of SCS and milk production traits was 0-14 and around 0-30, respectively. Ratio of permanent environmental variance to phenotypic variance was higher than h2 for all traits considered and ranged from 0-09 for NRR to 0-45 for milk yield. Body condition score had a favourable genetic correlation (rg) with SCS, but it was not strong (-0-08). Milk production was genetically antagonistic with fertility (rg: range 0-12 to 0-27 with DFS and -0-12 to -0-24 with NRR), with BCS (-0-39 to -0-50), and with SCS (0-10 to 0-15) showing that selecting for milk production alone would lead to decline in genetic merit for these functional traits. Body condition score had favourable genetic correlations with fertility traits (-0-35 with DFS and 0-04 with NRR) suggesting that BCS could be considered in a fertility index. Several type traits (especially 'udder' traits) had a favourable genetic relationship with fertility traits and SCS whereas dairy character had an unfavourable genetic relationship. Results of this study on genetic and phenotypic correlations among several functional, type and production traits could be used to design improved selection indexes for dairy producers.

A comparison of the performance of statistical quality control charts in a dairy production system through stochastic simulation

Statistical quality control charts are plots of observations over time applied to a characteristic of a system to distinguish between normal variation, when the system should be left alone, and unexpected true changes, which should be signaled as soon as possible so the cause of the changes can be corrected. In practice, the performance of control charts (measured as the average time to first signal, either when the system has not changed (causing a false alarm) or for a true change of a certain size) is unknown if the variability of the system is not quantified, such as in a dairy production system. Therefore, a Monte Carlo simulation model of a 1000-cow dairy herd was used to compare the performance of various control chart designs for days to first service (DFS) and estrous detection index (EDI) to signal decreases in estrous detection efficiency (EDE). Shewhart and cumulative sum (cusum) control charts were designed for period lengths of seven days. The observed average time between false alarms, measured in days, on Shewhart charts with 3-sigma control limits and three supplementary runs tests was much shorter than expected. In addition, control charts for the variance of DFS (assuming a normal distribution) or the mean of EDI (assuming a binomial distribution) had high false alarm rates. Control limits were then varied such that the observed average time between false alarms on the control charts were similar to the goal of 400 or 800 days. This allowed for a fair comparison to signal true decreases in EDE as soon as possible. Large decreases in EDE were signaled earlier on most control charts than small decreases. Normal cusum control charts applied to the mean of EDI signaled true decreases in EDE the earliest: it took on average 38 days to signal a decrease to 55% EDE, 15 days to 45% EDE, or 10 days to 35% EDE, when the average time between false alarms was 400 days. Control charts designed for lower false alarm rates and those applied to DFS took longer to signal decreases in EDE. The results suggest that stochastic simulation of complex production systems can provide insight in the performance of control charts in practice. Furthermore, a combination of the Shewhart and cusum control charts based on the normal distribution applied to EDI is a good choice when the goal is to signal a decrease in EDE as soon as possible.

Genotype x environment interaction for grazing vs. confinement. II. Health and reproduction traits.

Continual selection for increased milk yield for more than 40 yr, combined with the antagonistic relationship between increasing yield, somatic cell count, and fertility, have resulted in sires that may not be optimal for producing daughters for grazing systems where seasonal calving is very important. The objective of this study was to investigate the possible existence of a genotype x environment interaction (G x E) in grazing vs. confinement herds within the United States for lactation average somatic cell score (LSCS), days open (DO), days to first service (DFS), and number of services per conception (SPC). Grazing herds were defined as those that utilized grazing for at least 6 mo each year and were enrolled in Dairy Herd Improvement (DHI). Control herds were confinement DHI herds of similar size in the same states. For LSCS, the performance of daughters in grazing and control herds was examined using linear regression of LSCS on the November 2000 USDA-DHIA sire predicted transmitting abilities (PTA) for SCS. Genetic parameters for all traits were estimated using REML in a bivariate animal model that treated the same trait in different environments as different traits. Rank correlations were calculated between sires' estimated breeding values for LSCS, calculated separately for sires in both environments. The coefficient of regression of daughter LSCS on sire PTA was less in grazing herds than in control herds. The coefficient of regression for control herds was closer to expectation. Estimates of heritability were approximately 0.12 for LSCS, and less than 0.05 for the reproduction traits. Heritabilities for DO, DFS, and SPC were slightly higher for control herds. Estimates of genetic correlation for each reproductive trait between the 2 environments were high and not significantly different from unity. Generally, these traits appear to be under similar genetic control, but a lower coefficient of regression of LSCS on sire PTA for SCS in grazing herds suggests differences in daughter performance in grazing herds may be overstated based on current PTA for SCS.

Efficiency of Different Selection Indices for Desired Gain in Reproduction and Production Traits in Hariana Cattle

An investigation was conducted on 729 Hariana cows maintained at Government Livestock Farm, Hisar, from 1973 to 1999, with an objective to compare the efficiency of various selection indices for attaining desired genetic gains in the index traits. The various traits included were age at first calving (AFC), service period (SP), calving interval (CI), days to first service (DFS), number of services per conception (NSPC), lactation milk yield (LY), peak yield (PY), dry period (DP). Except for LY, PY and AFC the heritabilities of all other traits were low. Desirable associations among reproductive traits are supportive of the fact that any one of these traits incorporated in simultaneous selection is expected to cause correlated response in other traits. Production traits (LY and PY) were positively correlated, while DP had low negative genetic correlation with LY, and high genetic correlation with PY. Thus, DP can be taken as additional criteria in selection index for better over all improvement. Almost all production traits except DP had low negative correlation with AFC, SP, DFS and CI meaning that reduction in reproduction traits up to certain level may increase production performance. While, the correlation of NSPC with LY and PY was moderate positive. Among four trait indices I23: incorporating PY, AFC, SP and NSPC and among three trait indices I1: incorporating LY, AFC and SP were the best as these required least number of generations (4.87 and 1.35, respectively) to attain desired goals. Next in order of preference were PY or LY along with DP and SP as the best indices (I20 and I16) of which, index with PY may be preferred instead of LY as it produced considerably high correlated response in LY and reduction in NSPC as well. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 6 : 789-793)