Genetic parameters for endocrine and traditional fertility traits,hyperketonemia and milk yield in dairy cattle

High-yielding cows may suffer from negative energy balance during early lactation, which can lead to ketosis and delayed ability of returning to cyclicity after calving. Fast recovery after calving is essential when breeding for improved fertility. Traditionally used fertility traits, such as the interval from calving to first insemination (CFI), have low heritabilities and are highly influenced by management decisions. Herd Navigator™ management program samples and analyses milk progesterone and β-hydroxybutyrate (BHB) automatically during milking. In this study, the genetic parameters of endocrine fertility traits (measured from milk progesterone) and hyperketonemia (measured from milk BHB) in early lactation were evaluated and compared with traditional fertility traits (CFI, interval from calving to the last insemination and interval from first to last insemination) and the milk yield in red dairy cattle herds in Finland. Data included observations from 14 farms from 2014 to 2017. Data were analyzed with linear animal models using DMU software and analyses were done for first parity cows. Heritability estimates for traditional fertility traits were low and varied between 0.03 and 0.07. Estimated heritabilities for endocrine fertility traits (interval from calving to the first heat (CFH) and commencement of luteal activity (C-LA)) were higher than for traditional fertility traits (0.19 to 0.33). Five slightly different hyperketonemia traits divided into two or three classes were studied. Linear model heritability estimates for hyperketonemia traits were low, however, when the threshold model was used for binary traits the estimates became slightly higher (0.07 to 0.15). Genetic correlation between CFH and C-LA for first parity cows was high (0.97) as expected since traits are quite similar. Moderate genetic correlations (0.47 to 0.52) were found between the endocrine fertility traits and early lactation milk yield. Results suggest that the data on endocrine fertility traits measured by automatic systems is a promising tool for improving fertility, specifically when more data is available. For hyperketonemia traits, dividing values into three classes instead of two seemed to work better. Based on the current study and previous studies, where higher heritabilities have been found for milk BHB traits than for clinical ketosis, milk BHB traits are a promising indicator trait for resistance to ketosis and should be studied more. It is important that this kind of data from automatic devices is made available to recording and breeding organizations in the future.     

Breed of cow and herd productivity affect milk nutrient recovery in curd,and cheese yield,efficiency and daily production

Little is known about cheese-making efficiency at the individual cow level, so our objective was to study the effects of herd productivity, individual herd within productivity class and breed of cow within herd by producing, then analyzing, 508 model cheeses from the milk of 508 cows of six different breeds reared in 41 multi-breed herds classified into two productivity classes (high v. low). For each cow we obtained six milk composition traits; four milk nutrient (fat, protein, solids and energy) recovery traits (REC) in curd; three actual % cheese yield traits (%CY); two theoretical %CYs (fresh cheese and cheese solids) calculated from milk composition; two overall cheese-making efficiencies (% ratio of actual to theoretical %CYs); daily milk yield (dMY); and three actual daily cheese yield traits (dCY). The aforementioned phenotypes were analyzed using a mixed model which included the fixed effects of herd productivity, parity, days in milk (DIM) and breed; the random effects were the water bath, vat, herd and residual. Cows reared in high-productivity herds yielded more milk with higher nutrient contents and more cheese per day, had greater theoretical %CY, and lower cheese-making efficiency than low-productivity herds, but there were no differences between them in terms of REC traits. Individual herd within productivity class was an intermediate source of total variation in REC, %CY and efficiency traits (10.0% to 17.2%), and a major source of variation in milk yield and dCY traits (43.1% to 46.3%). Parity of cows was an important source of variation for productivity traits, whereas DIM affected almost all traits. Breed within herd greatly affected all traits. Holsteins produced more milk, but Brown Swiss cows produced milk with higher actual and theoretical %CYs and cheese-making efficiency, so that the two large-framed breeds had the same dCY. Compared with the two large-framed breeds, the small Jersey cows produced much less milk, but with greater actual and theoretical %CYs, similar efficiencies and a slightly lower dCY. Compared with the average of the specialized dairy breeds, the three dual-purpose breeds (Simmental and the local Rendena and Alpine Grey) had, on average, similar dMY, lower actual and theoretical %CY, similar fat and protein REC, and slightly greater cheese-making efficiency.     

Reproductive disorders in dairy cattle: I. Respective influence of herds, seasons, milk yield and parity

This study was performed in two large dairy units (with 130 and 213 calving cows each) during one year. The objectives were to investigate 1) epidemiological patterns of main post-partum reproductive disorders (metritis, post-partum and post-service anestrus, repeat breeding and embryonic death) and 2) the impact of herd, calving season, milk yield and parity on these patterns. Approximately 20% of the cows in both herds were not affected by any of the disorders. Prevalence of metritis was high (32 to 44%) and appeared influenced by the herds' conditions interacting with calving months and milk yield effects. Cyclic post-partum anestrus incidence was also essentially affected by the herd effect with an added seasonal interaction. Other disorders in both herds were also primarily subjected to the seasonal effect. Individual milk yield and parity only marginally affected the epidemiological patterns. We concluded that even in similar environmental conditions, no general patterns of incidence of reproductive disorders can be drawn and that they are essentially dependent on the characteristics of each herd management.     

Risk factors associated with detailed reproductive phenotypes in dairy and beef cows

The objective of this study was to identify detailed fertility traits in dairy and beef cattle from transrectal ultrasonography records and quantify the associated risk factors. Data were available on 148 947 ultrasound observations of the reproductive tract from 75 949 cows in 843 Irish dairy and beef herds between March 2008 and October 2012. Traits generated included (1) cycling at time of examination, (2) cystic structures, (3) early ovulation, (4) embryo death and (5) uterine score; the latter was measured on a scale of 1 (good) to 4 (poor) characterising the tone of the uterine wall and fluid present in the uterus. After editing, 72 773 records from 44 415 dairy and beef cows in 643 herds remained. Factors associated with the logit of the probability of a positive outcome for each of the binary fertility traits were determined using generalised estimating equations; linear mixed model analysis was used for the analysis of uterine score. The prevalence of cycling, cystic structures, early ovulation and embryo death was 84.75%, 3.87%, 7.47% and 3.84%, respectively. The occurrence of the uterine heath score of 1, 2, 3 and 4 was 70.63%, 19.75%, 8.36% and 1.26%, respectively. Cows in beef herds had a 0.51 odds (95% CI=0.41 to 0.63, P<0.001) of cycling at the time of examination compared with cows in dairy herds; stage of lactation at the time of examination was the same in both herd types. Furthermore, cows in dairy herds had an inferior uterine score (indicating poorer tone and a greater quantity of uterine fluid present) compared with cows in beef herds. The likelihood of cycling at the time of examination increased with parity and stage of lactation, but was reduced in cows that had experienced dystocia in the previous calving. The presence of cystic structures on the ovaries increased with parity and stage of lactation. The likelihood of embryo/foetal death increased with parity and stage of lactation. Dystocia was not associated with the presence of cystic structures or embryo death. Uterine score improved with parity and stage of lactation, while cows that experienced dystocia in the previous calving had an inferior uterine score. Heterosis was the only factor associated with increased likelihood of early ovulation. The fertility traits identified, and the associated risk factors, provide useful information on the reproductive status of dairy and beef cows.     

Comparison of reproductive performance by artificial insemination versus natural service sires in California dairies

This study compared the calving to conception intervals for cows in AI pens with cows exposed to natural service sires, controlling for milk production, mastitis occurrence, parity and calving month effects. Records from 10 western United States dairy herds (mean herd size = 2058 cows) were evaluated retrospectively over an 18-month period. Eight bull breeding analysis cohorts were created (the first cohort 0-50 days in milk and the remaining cohorts at 25 days in milk intervals through 226 days). The cohorts contained non-pregnant cows that were first moved into bullpens during the described cohort period. Equal numbers of non-pregnant cows only exposed to AI during the cohort period were randomly selected from the pool of eligible non-pregnant cows. An AI cow was used only once in the data analysis, but was included in a bull breeding cohort at a later date if she remained non-pregnant and was transferred to a bullpen. Univariate and multivariate survival analysis was used to compare the calving to conception intervals. Cows in AI groups had higher hazard rates for pregnancy across all cohorts. Parity and milk production were significantly associated with risk for pregnancy. In herds that practice a mixture of AI and bull breeding, overall herd reproductive performance might be improved by allowing cows more opportunities at AI prior to moving them into clean-up bullpens.     

Heritability and repeatability of milk lactose and its relationships with traditional milk traits,somatic cell score and freezing point in Holstein cows

Lactose percentage (LP) in milk is currently determined in most herd-testing schemes, and globally, it is usually routinely recorded in the framework of the official milk recording procedures. However, few studies have investigated the phenotypic and genetic variability of this component. Data used in the present paper consisted of 59 811 test-day records from 4355 Holstein cows in 266 herds. Heritabilities of LP and lactose yield (LY) were estimated through single-trait repeatability animal models, whereas genetic and phenotypic correlations of LP and LY with milk composition and production traits, somatic cell score and milk freezing point were estimated using bivariate models. Fixed effects included in the analyses were herd-test-date, season of calving, parity, stage of lactation and the interaction between parity and stage of lactation. Random effects were animal additive genetic, within and across lactation permanent environment and the residual. Lactation curves of LP and LY increased from parturition to the peak of lactation and decreased thereafter, mirroring the typical curve of milk yield. Lactose percentage was greater in first- than later-parity cows. Heritabilities of LP and LY were 0.43±0.03 and 0.14±0.02, respectively, and LP and protein percentage were the most repeatable traits. Genetic correlations (r_a) of LP with somatic cell score, LY and milk freezing point were −0.22±0.08, 0.28±0.08 and −0.46±0.05, respectively. Genetic relationships of LY with milk yield (r_a=0.97±0.00), fat percentage (r_a=−0.71±0.06), protein percentage (r_a=−0.57±0.06) and protein yield (r_a=0.64±0.06) were moderate to strong. Results suggest that milk LP could be considered in breeding strategies to accelerate the gain of correlated low heritable traits. Further research is needed to evaluate the feasibility of including LP in the selection index of Italian Holstein population to address country-specific needs and market demands.     

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.     

Effects of diagnostic low-volume uterine lavage shortly before first service on reproductive performance, culling and milk production

The objective was to evaluate if uterine sampling by low-volume uterine lavage, done shortly before the end of the voluntary waiting period, affected reproductive performance, milk production, or culling. Approximately 20 cows (40 and 60 d postpartum) were sampled in each of 38 herds (total, 752 cows), whereas all remaining cows concurrently between 40 and 60 d were a non-sampled reference cohort (n = 2,252 cows). There was an interaction between parity and sampling for first-service conception, calving to conception interval, and milk production. When stratified by parity, there was a tendency for impaired reproductive performance in sampled primiparous cows compared with non-sampled primiparous cows (Odds Ratio for pregnancy to first-service = 0.78 (95% C.I. 0.58-1.04). The Hazard Ratio for pregnancy in sampled primiparous cows was 0.89 (95% C.I. 0.77-1.04) compared to non-sampled primiparous cows. Sampling did not affect first-service conception rate (Odds Ratio for pregnancy Odds ratio (OR) for pregnancy = 1.03; 95% C.I. 0.80-1.33) or calving-to conception interval in multiparous cows (Hazard Ratio = 1.04; 95% C.I. 0.91-1.18). Sampling did not affect culling risk (Hazard Ratio HR = 0.92; 95% C.I. 0.77-1.11) after accounting for covariates. After stratification by parity, milk production was not affected by sampling except in fourth- and fifth-parity cows where sampled cows produced more milk than non-sampled cows after controlling for first test-day milk production and days-postpartum at first test-day. In conclusion, sampling by low-volume uterine lavage did not have significant detrimental effects on reproduction, culling, or milk production. However, there was a tendency for lower first-service conception in sampled primiparous cows, but the procedure appeared to be benign in multiparous cows.     

Genetic trend for milk yield in Guzerat herds participating in progeny testing and MOET nucleus schemes

Genetic trends for 305-day milk yield (P305) in Brazilian Guzerat herds under selection were compared. Data from 4898 lactations of 3179 purebred and crossbred cows from various regions of Brazil were used. Milk yield was adjusted for mature age and the contemporary groups were defined as herd and calving year. Genetic parameters were estimated using the MTDFREML program. The model included the random effects of animals and permanent environment, and herd-calving year, calving season and genetic composition as fixed effects. Genetic trends were estimated by linear regression of weighted average estimated breeding values as a function of calving year. The average P305 was 2065 +/- 922 kg and the heritability was 0.23 +/- 0.03. The annual genetic trend in estimated breeding values of cows for P305 was 7.09 +/- 0.71 kg between 1987 and 2004, and 6.47 +/- 2.35 kg between 1997 and 2004. For cows born and raised in the multiple ovulation and embryo transfer (MOET) nucleus, this trend was 36.46 +/- 24.54 kg/year between 1997 and 2004, 183.14 +/- 47.94 kg/year between 1997 and 2000, and 9.13 +/- 19.19 kg/year between 2001 and 2004. An average inbreeding coefficient of 0.04 was found for inbred MOET cows in 2004. Increasing the size of the family and introducing new progenies changed reliabilities and predicted transmitting ability estimates of MOET sires. In conclusion, there was a positive genetic trend for milk yield in the MOET nucleus at low inbreeding coefficients due to the increased accuracy and estimated genetic merit, but no changes in the average milk yield were observed.     

Associations between herd size, rate of expansion and production, breeding policy and reproduction in spring-calving dairy herds

Dairy herd size is expected to increase in many European countries, given the recent policy changes within the European Union. Managing more cows may have implications for herd performance in the post-quota era. The objective of this study was to characterise spring-calving herds according to size and rate of expansion, and to determine trends in breeding policy, reproduction and production performance, which will inform industry of the likely implications of herd expansion. Performance data from milk recording herds comprising 775,795 lactations from 2,555 herds for the years 2004 to 2008 inclusive were available from the Irish Cattle Breeding Federation. Herds were classified into Small (average of 37 cows), Medium (average of 54 cows) and Large (average of 87 cows) and separately into herds that were not expanding (Nil expansion), herds expanding on average by three cows per year (Slow expansion) and herds expanding on average by eight cows per year (Rapid expansion). There was no association between rate of expansion and 305-day fat and protein yield. However, 305-day milk yield decreased and milk protein and fat percentage increased with increasing rate of expansion. There were no associations between herd size and milk production except for protein and fat percentage, which increased with increasing herd size. Average parity number of the cows decreased as rate of expansion increased and tended to decrease as herd size increased. In rapidly expanding herds, cow numbers were increased by purchasing more cattle. The proportion of dairy sires relative to beef sires used in the breeding programme of expanding herds increased and there was more dairy crossbreeding, albeit at a low rate. Similarly, large herds were using more dairy sires and fewer beef sires. Expanding herds and large herds had superior reproductive performance relative to non-expanding and small herds. Animals in expanding herds calved for the first time at a younger age, had a shorter calving interval and were submitted for breeding by artificial insemination at a higher rate. The results give confidence to dairy producers likely to undergo significant expansion post-quota such that, despite managing more cows, production and reproductive performance need not decline. The management skills required to achieve these performance levels need investigation.     

Screening for high fertility in high-producing dairy cows

A retrospective study involving 2756 pregnancies from two commercial dairy herds in northeastern Spain determined relationships between management, production and reproductive data, and high fertility (conception before 90 days in milk) in high-producing dairy cows. High fertility was registered in 989 (35.9%) cows. The following data were recorded for each animal: herd, repeated animal (cows included two or more times within the study in which data were obtained from different lactational periods), parity (primiparous versus multiparous), previous twinning, reproductive disorders following calving (retained placenta, primary metritis) and at postpartum gynecological examination (incomplete uterine involution, pyometra and ovarian cysts), days in milk at conception, previous estrous synchronization and season of calving and conception. In order to evaluate the possible effect of high production during the peak milk yield on subsequent fertility, daily milk production at Day 50 postpartum was also recorded and cows were classified as high (> or = 50 kg) and low (< 50 kg) producers. Logistic regression analysis indicated no significant effects of herd, repeated animal, previous twinning, reproductive disorders such as primary metritis, incomplete uterine involution, pyometra and ovarian cysts, previous estrous synchronization and season of calving and insemination. Based on the odds ratio, the likelihood of high fertility increased in high-producer cows by a factor of 6.8. High fertility was less likely for multiparous cows (by a factor of 0.35) and for cows suffering placenta retention (by a factor of 0.65). High fertile cows produced a mean of 49.5 kg milk at Day 50 postpartum, in contrast to that 43.2 kg milk of the remainder cows. These findings question the negative effect of high production on fertility. Our results indicated that high individual cow milk production can be positively related to high fertility.     

Body traits,carcass characteristics and price of cull cows as affected by farm type,breed, age and calving to culling interval

Beef production from cull cows is an additional source of income for dairy farms and greatly contributes to red meat production, but the sources of variation of live animal characteristics and the carcass traits of cull cows have rarely been examined. This study investigated the effects of the farm type, breed, age at slaughter (AGE) and calving to culling interval (Calv_Cull) on the body traits and carcass characteristics of dairy and dual-purpose cull cows. Data from 555 cull cows from 182 herds belonging to five farm types, characterised by a combination of housing and feeding systems, were recorded and analysed. Dairy breeds, such as Holstein Friesian and Brown Swiss, and dual-purpose breeds (Simmental, Rendena) were included in the trait assessments. The day before slaughter, the cows were weighed and scored for body condition (BCS) and fleshiness, and then, their heart girth and wither height were measured. At the slaughterhouse, the carcass weight (CW), dressing percentage (DP), carcass conformation and fatness scores, carcass price per kg and carcass total value were obtained. On average, the cows were slaughtered at nearly 71±27 months of age, 285±187 days after the last calving; 615±95 kg BW; and provided a 257±51 kg CW. Nearly 50% of the cows fell within the BCS range of 2.75 to 3.50, and the carcasses were mostly graded in the lowest class of conformation and fatness scores. Cull cows from free-stall farms had a higher DP, carcass conformation score and price than those from traditional tie-stall farms. The breed influenced the AGE, live animal characteristics and carcass traits. Cows from dairy breeds were younger at slaughter, had a lower BCS and fleshiness, and greater body measurements, but a lower DP and carcass price than those from dual-purpose breeds, although differences between the breeds were found within both groups. The age of the cows at slaughter influenced the Calv_Cull and increased the BW, body measurements and CW, but not the fleshiness and fatness appreciation (both in vivo and postmortem) or carcass price. The increasing Calv_Cull improved the BW, BCS, fleshiness, CW and carcass conformation and fatness. In conclusion, the decision to cull dairy cows should also take into account the factors that affect their carcass value in regards to improving the carcass price of cows.     

Influence of parity on follicular dynamics and resumption of ovarian cycle in postpartum dairy cows

The present study examined ovarian changes preceding the resumption of the ovarian cycle in postpartum dairy cows with different parities under similar body nutritional conditions. In postpartum primi- (n=6), bi- (n=4), and multiparous (n=6) Holstein dairy cows, ovarian ultrasonographic observations starting at 7 days after calving were performed every other day and then daily after the confirmation of clinical signs of oestrus for the detection of postpartum first ovulation. Blood samples were collected at the same time as ultrasonography and analyzed for oestradiol and progesterone to monitor ovarian activity. To evaluate the nutritional condition of the cows, body weight and body condition score (BCS, 1=emaciated to 5=obese) were measured weekly and blood samples for the analysis of glucose, insulin, and non-esterified fatty acid (NEFA) were collected at the same time until postpartum second ovulation. Dominant follicles (>8mm in diameter) of the first follicular wave were detected at 7 days after calving in all cows. The first wave follicle ovulated in five of six multiparous cows, whereas no first wave follicle ovulated in any of the primiparous cows. The days to first ovulation after calving in primiparous cows (31.8+/-8.3 days) were significantly greater (p<0.05) than those in multiparous cows (17.3+/-6.3 days), but were not significantly different from biparous cows (28.8+/-8.6 days). There was a significant relationship between parity and days to first ovulation after calving (p<0.05). BCS was maintained at a level of more than 2.5 during the postpartum period in all cows and there was no influence of parity on postpartum changes in BCS, glucose, insulin, or NEFA throughout the experiment. The present study demonstrated a negative relationship between parity and number of days from calving to first ovulation in dairy cows under similar body nutritional conditions. It is possible that the influence of parity on the resumption of ovarian cycle is modulated by the factors different from the nutrition-related changes during the postpartum period in dairy cows.     

Precalving factors affecting conception risk in Holstein dairy cows in tropical conditions

The objective of this study was to identify precalving nutritional risk factors that may affect variation in first service conception risk in 21 commercial Holstein dairy herds in a tropical environment (Reunion Island). The data set included 473 lactation records in 404 cows. A multivariate logistic-regression model including herd as a random effect was used to analyse the relationship between first service conception risk and energy status (body condition score, plasma glucose, insulin, cholesterol, non-esterified fatty acids and beta-hydroxybutyrate), nitrogen status (urea), hepatic function (gamma-glutamyltransferase, glutamate deshydrogenase, albumin), and mineral deficiencies (calcium, phosphorus, magnesium), adjusting systematically for factors such as breeding, season, parity, previous milk yield and fertility, calving to first service interval and type of oestrus (spontaneous versus induced). The overall mean conception risk was 0.27+/-0.02 (mean+/-S.E.M., n=473). First service conception risk was penalized by calving to 1st service interval shorter than 60 days, synchronized oestrus, previous 305-day milk yield >8000 kg (p<0.05), low blood glucose concentration in high-yielding cows (p<0.05) and combined high urea and beta-hydroxybutyrate concentrations (p<0.01). Precalving energy imbalance, revealed by low prepartum glucose concentration, was a strong nutritional predictor of low first service conception risk in high-yielding cows. Some precalving nutritional disorders potentially associated with consumption of spoiled silage which induces elevated circulating urea and beta-hydroxybutyrate have a delayed detrimental effect on conception, even if the true causes of this effect remain to be elucidated. As a conclusion, our findings should lead the breeders to pay more attention to the feeding of dry cows that is usually neglected in Reunion Island dairy farms.     

Genetic merit for milk production and reproductive success in dairy cows

The effect of genetic merit for milk production traits - fat, protein and milk yield - in dairy cows on milk production, body condition, blood metabolites, reproductive hormones, feed intake and reproductive performance was studied over a period of 2 years. Cows were grouped into two categories, based on calculated pedigree indices using multiple-trait across country evaluation (MACE). Cows of high genetic merit (HGM, n = 48 in year 1 and n = 46 in year 2) had a mean predicted difference +/- standard deviation for milk production of 475 +/- 76kg. The cows of medium genetic merit (MGM, n = 48 in both years) had a mean predicted difference for milk production of 140 +/- 68kg.The cows calved between January and April, and were offered grass silage ad libitum plus 9kg concentrates per cow per day, irrespective genetic merit, from calving to turnout in March, when they were subjected to one of three grazing systems. Cows were available for rebreeding from late April until late July of each year.High genetic merit cows had higher milk production, incurred greater body condition loss between calving and first service and had lower plasma glucose and insulin-like growth factor-1 (IGF-1) concentrations than medium genetic merit cows. Furthermore, HGM cows had lower first and second service and overall conception rates, and required more services per conception than the MGM cows.Cows that did not conceive to first service were retrospectively compared to those that conceived to first service within each genetic merit group. There were no significant differences between the HGM cows that did not conceive to first service and those that conceived to this service in terms of milk production, body condition score change between calving and first service, feed intake at first service, or in plasma concentrations of glucose, non-esterified fatty acids (NEFA) or IGF-1. Medium genetic merit cows that did not conceive to first service lost more body condition between calving and first service than did those that conceived to this service.In the present study, HGM cows had higher milk production and reduced reproductive performance in comparison with MGM cows. However, reproductive performance was not associated with milk production, feed intake or plasma concentrations of glucose, NEFA or IGF-1 between calving and first service, since there were no significant differences in these variates between high or medium genetic merit cows that did not conceive to first service and those that conceived to this service. Therefore, these variates are unlikely to be useful predictors of reproductive performance, under the conditions of the present study.     

Body condition score and live-weight effects on milk production in Irish Holstein-Friesian dairy cows

The objective of the present study was to quantify the relationships among body condition score (BCS; scale 1 to 5), live weight (WT) and milk production in Irish Holstein-Friesian spring calving dairy cows. Data were from 66 commercial dairy herds during the years 1999 and 2000. The data consisted of up to 9886 lactations with records for BCS or WT at least once pre-calving, or at calving, nadir or 60 days post-calving. Change in BCS and WT was also calculated between time periods. Mixed models with cow included as a random effect were used to quantify the effect of BCS and WT, as well as change in each trait, on milk yield, milk fat concentration and milk protein concentration. Significant and sometimes curvilinear associations were observed among BCS at calving or nadir and milk production. Total 305-day milk yield was greatest in cows calving at a BCS of 4.25 units. However, cows calving at a BCS of 3.50 units produced only 68 kg less milk than cows calving at a BCS of 4.25 units while cows calving at 3.25 or 3.00 BCS units produced a further 50 and 114 kg less, respectively. Cows that lost more condition in early lactation produced more milk of greater fat and protein concentration, although the trend reversed in cows that lost large amounts of condition post-calving. Milk yield increased with WT although the marginal effect decreased as cows got heavier. Milk fat and protein concentration in early lactation also increased with WT pre-calving, calving and nadir, although WT did not significantly affect average lactation milk fat concentration.     

Comparison of pure Holsteins to crossbred Holsteins with Norwegian Red cattle in first and second generations

A total of 1922 first generation crossbred cows born between 2005 and 2012 produced by inseminating purebred Israeli Holstein cows with Norwegian Red semen, and 7487 purebred Israeli Holstein cows of the same age in the same 50 herds were analyzed for production, calving traits, fertility, calving diseases, body condition score, abortion rate and survival under intensive commercial management conditions. Holstein cows were higher than crossbreds for 305-day milk, fat and protein production. Differences were 764, 1244, 1231 for kg milk; 23.4, 37.4, 35.6 for kg fat, and 16.7, 29.8, 29.8 for kg protein; for parities 1 through 3. Differences for fat concentration were not significant; while crossbred cows were higher for protein concentration by 0.06% to 0.08%. Differences for somatic cells counts were not significant. Milk production persistency was higher for Holstein cows by 5, 8.3 and 8% in parities 1 through 3. Crossbred cows were higher for conception status by 3.1, 3.6 and 4.7% in parities 1 through 3. Rates of metritis for Holsteins were higher than the crossbred cows by 7.8, 4.6 and 3.4% in parities 1 to 3. Differences for incidence of abortion, dystocia, ketosis and milk fever were not significant. Holstein cows were lower than crossbred cows for body condition score for all three parities, with differences of 0.2 to 0.4 units. Contrary to comparisons in other countries, herd-life was higher for Holsteins by 79 days. A total of 6321 Holstein cows born between 2007 and 2011 were higher than 765 progeny of crossbred cows backcrossed to Israeli Holsteins of the same ages for milk, fat and protein production. Differences were 279, 537, 542 kg milk; 10.5, 17.7, 17.0 kg fat and 6.2, 12.9, 13.2 kg protein for parities 1 through 3. Differences for fat concentration were not significant, while backcross cows were higher for protein percentage by 0.02% to 0.04%. The differences for somatic cell score, conception rate, and calving diseases other than metritis, were not significant. Holstein cows were lower than backcross cows by 1.5% to 2.5% for conception status in parities 1 to 3 and lower for body condition score for parities 1 and 2, with differences in the range of 0.06 to 0.09 units. Culling rates were higher, and herd-life lower for the crossbred cows. The gains obtained in secondary traits for crossbred cows did not compensate for the major reduction in production.     

Relationship between incidence of milk fever and feeding of minerals during the last 3 weeks of gestation

This study evaluated whether differences in milk fever incidence among Swedish dairy herds could be explained partly by differences in mineral feeding during the last weeks of gestation. A case–control study was performed on dietary risk factors for a high incidence of milk fever at the herd level using information regarding feeding and management of the dry cows collected in a written questionnaire distributed by post in spring 2008. The study was conducted from September 2004 to August 2007. Data on the diets fed to dry cows, with an emphasis on the amounts of minerals (Ca, P, Mg and K) fed 3 weeks before calving and at calving, were obtained from 30 herds belonging to the 100 Swedish herds with the highest recorded incidence of veterinary treatment for milk fever (>8.8%) and from 22 herds with no recorded milk fever treatments. Multivariable logistic regression analysis showed that a linear increase in the total amount of K and less than 26 g of Mg/day fed to dry cows 3 weeks before calving was associated with an increased risk of high milk fever incidence. A large increase in the amount of dry matter (DM) fed (>3.1 kg DM extra per day at calving compared with 3 weeks before calving) was associated with a higher incidence of milk fever, but no differences were found for Ca or P intake. Breed composition, herd average milk yield and age composition of the herd did not explain any of the observed differences between the case and the control herds. The results indicate that differences in the frequency of milk fever among herds can be associated with differences in mineral feeding of the dry cows. A high amount of K in the diet may increase the risk of milk fever linearly, whereas Mg should probably be fed at a higher level than the current Nordic recommendation to prevent milk fever.