Effect of selenium and vitamin E supplementation during the late pregnancy on reproductive indices and milk production in heifers

A trial was performed to determine the effects of supplementation of selenium (Se) and vitamin E (VE) on reproductive indices and milk production in Holstein heifers. Sixty heifers at the late stage of gestation were randomly assigned into three groups. Heifers were balanced for age, weight and time of calving. Four and 2 weeks before expected calving the heifers were injected 0 ml (C), 20 ml (T1), and 40 ml (T2) Se and VE supplements. Each ml contained 0.5mg Se and 50 IU of D, L-alpha-tocopheryl acetate. Blood samples were collected from heifers 4 weeks before expected calving and at calving day. Se concentrations in serum and colostrums were measured. The reproductive parameters were recorded. The effects of Se and VE supplements on somatic cell count (SCC) and milk yield also were measured. Supplementation of Se increased the level of Se in serum of treated heifers at calving day (P<0.05). Se concentration of colostrums were affected by the treatments (P<0.05). Concerning reproductive performance of treated heifers; gestation length was similar among groups but in comparison with controls, T1 and T2 had no incidence of retained fetal membrane (i.e., beyond 12h.). In addition, open days were fewer in T1 and T2 heifers and the number of services per conception was fewer in T2 compared with controls (P>0.05). Daily milk production at 8 weeks lactation was significantly increased in T2 compared with controls (P<0.05). Likewise, the milk SCC decreased in treated heifers compared with controls (P<0.05).     

Associations between bovine IGFBP2 polymorphisms with fertility, milk production, and metabolic status in UK dairy cows

Insulin-like growth factor binding protein-2 (IGFBP2) is a key regulator of IGF activity that has been associated with insulin resistance and obesity. In cows, IGFBP2 mRNA expression is differentially regulated according to nutritional status in different tissues including the liver, reproductive tract, and mammary gland. This study investigated associations between single nucleotide polymorphisms (SNPs) in bovine IGFBP2 with fertility, milk production, and metabolic traits in Holstein-Friesian dairy cows. Fertility was assessed in heifers by measuring age at first service, age at first conception, and age at first calving. During the first and second lactation, the number of postpartum days for commencement of luteal activity (based on milk progesterone profiles), days to first service, days to conception, average milk production per day, 305-day milk yield, total milk yield, and total days in milk were recorded. Blood samples were taken at -1, +1, and +8 weeks relative to first and second calving for assessment of metabolic status (IGF1, insulin, beta-hydroxybutyrate, and glucose). Five novel SNPs were identified in IGFBP2, two of which had significant associations with fertility (age at conception in heifers and commencement of luteal activity) and 305-day milk yield in lactation 1. Trends of association were also observed with the peripartum metabolic status, in particular the glucose, insulin, and beta-hydroxybutyrate concentrations around second calving. These results indicate that IGFBP2 SNPs may influence tissue mobilization in dairy cows and may thus be of interest for marker assisted selection.     

Season of birth is associated with first-lactation milk yield in Holstein Friesian cattle

The aim of the present research was to assess factors associated with first-lactation milk yield in dairy heifers, including maternal and environmental factors, factors related to the development of the heifer and factors related to its offspring such as gender of the calf. In addition, the potential underlying mechanism, in particular metabolic adaptations, was further explored. Data on body growth, reproduction and milk yield of 74 Holstein Friesian heifers on three herds in Flanders (Belgium) were collected. At birth, body measurements of the heifers were recorded and blood samples were taken (in order) to determine basal glucose and insulin concentrations. Body measurements were assessed every 3 months until first calving, and gender and weight of their first calf were recorded. Information on fertility and milk yield of the heifer and its dam were collected from the herd databases. Daily temperature and photoperiod were recorded from the database of the Belgian Royal Meteorological Institute. Linear mixed models were run with herd as a random factor, to account for differences in herd management. Heifers grew 867±80.7 g/day during their first year of life and were inseminated at 14.8±1.34 months. First calving took place at 24.5±1.93 months, at a weight of 642±61.5 kg and heifers produced 8506±1064 kg energy corrected milk during their first 305-day lactation. Regression models revealed that none of the maternal factors such as milk yield and parity, nor the growth of the heifer during the 1^st year of life were associated with milk yield during first lactation. Age, and to a lesser extent BW at first parturition were positively associated with first-lactation milk yield. In addition, the season of birth, but not calving, had a significant influence on milk yield, with winter-born heifers producing less than heifers born in any other season. The lower yielding winter-born heifers had higher insulin concentrations at birth, whereas glucose concentrations were similar, the latter being suggestive for lower insulin sensitivity of the peripheral tissues. Furthermore, environmental temperature at the end of gestation was negatively correlated with neonatal insulin concentrations. In conclusion, results of the present study suggest heifers born during the hotter months are born with a higher peripheral insulin sensitivity, finally leading to a higher first-lactation milk yield.     

The effects of bovine necrotic vulvo-vaginitis on reproductive and production performance of Israeli 1st calf heifers

Bovine necrotic vulvovaginitis (BNVV) is a syndrome unique to Israel characterized by necrotic lesion in the caudal vagina mainly in first calf heifers after calving, associated with Porphyromonas levii. The objectives of this study were to analyze the impact of BNVV on reproductive performance, milk production and survival in the heard of first calf dairy heifers in affected farms, and to verify if the effects of BNVV are severity-dependent. For assessment of the severity level a scale of 4 degrees was formed, and cows were scored 4 to 6 d after calving. Data were obtained from two dairy farms during 2006-07, consisting of 603 lactations. The incidence and the severity of BNVV declined between 2006 and 2007, and severe BNVV tended to be more prevalent in the summer. The odds to conceive in the first artificial insemination of BNVV cow tended to be lower than healthy cows (OR = 0.676, P = 0.052). Cows with BNVV had longer empty period (145.8 d vs. 135.1 d of healthy cows, P = 0.031), but only severe BNVV had a negative effect on the odds of the cow to be empty at 150 d in milk (DIM) (OR = 2.05, P = 0.052). Severe BNVV also affected the mean survival time to conception (155.9 d vs. 142.3 d, P = 0.042). All BNVV severity degrees had a negative effect on milk production. The effect on milk production was not limited only to the beginning of the lactation, cows with BNVV produced 338.1 kg milk less than healthy cows (P = 0.016) in 305 d corrected lactation. The effect on milk production was not severity depended. No effect on survival time in the herd was demonstrated.     

A combination of nutrition and genetics is able to reduce age at puberty in Nelore heifers to below 18 months

Nelore heifers usually begin their reproductive life at ⩾24 months of age mainly due to suboptimal nutritional conditions and genetics. This study aimed to determine the effect of expected progeny difference (EPD) for age at first calving and average daily gain (ADG) on puberty in Nelore (Bos taurus indicus) heifers. A total of 58 weaned heifers (initial BW=174±6 kg; age=9±1 months) were allocated into 28 feedlot pens. Heifers were born from four sires, of which two had low EPD for age at first calving (L; n=33) and two had high EPD for age at first calving (H; n=25). Then, heifers of each EPD were randomly assigned to high ADG (HG; 0.7 kg) or low ADG (LG; 0.3 kg), resulting in four treatments: heifers from L sires were submitted to either HG (LHG; n=17) or LG (LLG; n=16), and heifers from H sires were submitted to either HG (HHG; n=12), or LG (HLG; n=13). The HG heifers were fed a 75% grain diet, whereas the LG heifers received 93% of forage in their diet. Blood samples were collected at 9, 14, 18, 24 and 28 months of age for IGF1 and leptin determination. There was a treatment effect (P<0.01) on the proportion of heifers that attained puberty by 18 (62%, 0%, 0% and 0%), 24 (100%, 6%, 54% and 0%) or 36 (100%, 100%, 100% and 38%) months of age for LHG, LLG, HHG and HLG treatments, respectively. In addition, mean age at puberty was different across treatments (P<0.01). Heifers from the LHG achieved puberty at the earliest age when compared with cohorts from other treatments (18.1, 28.9, 23.9 and 34.5 months for LHG, LLG, HHG and HLG, respectively). Serum IGF1 concentrations were higher for L heifers compared with H cohorts at 9, 14, 18, 24 and 28 months of age (P<0.01; treatment×age interaction), whereas circulating leptin concentrations were higher (P<0.01; age effect) as heifers became older, regardless of the treatments. In conclusion, only Nelore heifers with favorable genetic merit for age at first calving were able to attain puberty by 18 months of age. In heifers with unfavorable genetic merit for age at first calving, supplementary feeding to achieve high ADG was unable to shift the age at puberty below 24 months.     

The effect of dairy heifer pre-breeding growth rate on first lactation milk yield in spring-calving,pasture-based herds

Optimising heifer growth rate may offer an opportunity to improve lifetime milk yield per cow, enhancing the environmental and economic efficiency of dairy farming operations. The effect of dairy heifer pre-breeding average daily weight gain (ADG_PB) on first lactation milk yield was investigated. This observational study employed a data set comprising 265 Holstein-Friesian, or Holstein-Friesian-cross-Jersey heifers from seven commercial, spring-calving, pasture-based dairy herds, where the major component of the diet was grazed grass. These were weighed at birth and prior to breeding and ADG_PB was calculated. Milk recordings were performed throughout the heifers' first lactation and 305-day yield figures calculated from these records. Yields were corrected to 4% fat and 3.1% protein to create standardised 305-day milk yield (SMY), which was the outcome of interest. Median ADG_PB was 0.72 kg/day. Median 305-day yield was 5 967 kg. Linear regression was used to investigate the effect of weight and genetic, age and first calving factors on SMY. Pre-breeding average daily weight gain, age at first calving and predicted transmitting abilities for milk protein production and calving interval were all significant in the final model, which also included the random effects of farm and month of calving within year. ADG_PB was quadratically related to first lactation SMY, with an ADG_PB of 0.82 kg/day corresponding to the maximum predicted SMY. The model predicted that a heifer growing at 0.82 kg/day would produce 1 120 kg more SMY than a heifer growing at 0.55 kg/day, 218 kg more than a heifer growing at 0.7 kg/day and 103 kg more than a heifer growing at 0.90 kg/day. Manipulation of heifer growth rate may offer a viable method of increasing first lactation milk yield.     

Influence of age,body weight and body condition score before mating start date on the pubertal rate of maiden Holstein–Friesian heifers and implications for subsequent cow performance and profitability

The aim of this study was to assess the influence of age, body weight (BW) and body condition score (BCS) of maiden Holstein–Friesian heifers before mating start date (MSD) on the rate of puberty, subsequent production and longevity and their implications with regard to farm profitability. Data were available on 871 Holstein–Friesian heifers from 48 herds. BW was recorded electronically and BCS was recorded by a single operator on a scale of 1 to 5. Heifer age was calculated as the number of days from birth to the day of visit. All of the independent variables of interest were grouped into three or four categories. Three age categories (thirtiles), four BW categories (quartiles) and four BCS categories (⩽2.75, 3.00, 3.25 and ⩾3.50) were formed. Heifers with an identifiable corpus lutuem (CL) in the presence or absence of large follicles and peri-ovulatory signs and with a plasma progesterone (P4) concentration ⩾1 ng/ml were classified as pubertal. In addition, heifers without an identifiable CL in the presence or absence of large follicles and peri-ovulatory signs but with a P4 concentration ⩾1 ng/ml were also classified as pubertal. Age, BW and BCS at MSD were all found to be significantly associated with pubertal rate (P < 0.05). Age was shown to have no practical implications on subsequent cow performance. BW at MSD was favourably associated with subsequent calving date (P < 0.05), subsequent cow BW (P < 0.001) and potential (305 days) milk fat plus protein yield (P < 0.001). BCS at MSD was found to be favourably associated with milk fat plus protein yield potential (P < 0.05) and BCS (P < 0.001) during lactation. The economic analysis undertaken indicated that larger, well-grown heifers will be more profitable because of superior production potential, all else being equal. However, because of the finding of poorer reproductive efficiency in heifers grown to more than 343 kg at MSD, heifers at ∼330 kg at MSD are deemed optimal. This will correspond to mature cow BW of ∼550 kg.     

Comparison of reproductive performance in Belgian dairy and beef cattle

A computerized program was written to collect, evaluate and compare reproductive performance data of 2004 beef (Belgian Blue breed) and 1649 dairy (Friesian Holstein and German Red) cattle in 35 Belgian herds (6 suckler beef herds, 9 milked beef herds and 20 dairy herds). Reproduction data were collected at monthly herd health visits. No difference in age at first calving was observed. Significant differences were observed among the 3 kinds of herds, and the best results were obtained in dairy herds for the calving interval, interval from calving to the first estrus, interval from calving to the first service and average number of days open. Concerning these parameters, first calvers had lower results than multiparous cows, mainly in suckler and milked beef herds. Significant differences were noted in the number of services per pregnancy. Heifers that had never calved presented the highest fertility. Primiparous beef cows had higher fertility than pluriparous cows. In dairy herds, pluriparous cows had higher fertility than primiparous cows. Estrus detection was better in milked beef herds than in suckled beef and dairy herds. Suckled beef herds had the lowest incidence of metritis and ovarian cysts of the three types of herds. Rates of abortion, overall culling and retained fetal membranes were similar in all the herds. The percentage of animals removed for infertility was highest in milked beef herds and lowest in dairy herds. Because 90% of the 1159 calvings recorded in the beef herds required a caesarean section, the reproductive performance of beef cattle represent results after caesarean section.     

Housing, Feeding and Management of Calves and Replacement Heifers in Swedish Dairy Herds

A questionnaire was sent to 1500 randomly selected dairy herds in Sweden, asking for general information about the herds, including routines from birth to first calving and also routines at breeding, calving and during the grazing period. Fifty-eight percent of the questionnaires were returned. The preweaned calves were kept in individual calf pens in 68% and in group housing systems in 28% of the herds. Pens with slatted floors were the main housing system for replacement heifers from weaning to breeding, and tie stalls from breeding to first calving. Whole milk was used in 44% and milk replacements in 42% of the herds. The calves received, as a median, 2.5 litres of milk per meal and 2 meals per day. The median age at weaning was 8 weeks. Age was the single most common criteria used for deciding both weaning and breeding time. The median age when the heifers were first turned out to pasture was 6 months. Prophylactic anthelmintic treatment was used by 65% of the herds. The most common diet for replacement heifers before calving was a combination of grain, hay and silage.     

Growth rates of contract-reared versus home-reared replacement dairy heifers

Successful heifer rearing is dependent on achieving optimal average daily gain (ADG) targets to calve for the first time at 24 months. Whilst dairy farmers internationally have traditionally managed their heifers on-farm to achieve these targets, recent dairy herd expansion within Europe has resulted in increased demand for labour-saving heifer-rearing strategies, such as off-farm contractrearing. However, loss of direct influence on the day-to-day management decisions affecting the ability of heifers to grow adequately to achieve this age of first calving may represent a potential barrier to uptake. Hence, the aim of this longitudinal observational study was to compare the growth rates of contract- vs home-reared heifers. Approximately 6 500 heifers from 120 commercial Irish dairy farms were enrolled in a 3-year study. For 65 of these farms, heifers were reared at a contract-rearing facility. For the remaining 55 farms, heifers were reared on their home farm. Over the course of 20 months from birth until precalving, heifers were examined and weighed at four farm visits. The relationship between several independent variables (farm type, herd size, heifer breed, economic breeding index (EBI) and health events) and ADG at different time points was investigated and analysed utilising linear mixed models. Overall ADG for heifers throughout the rearing period was 0.71 kg/day. There was a significant association between farm type and ADG for all five linear ADG models; home-reared heifers grew, on average, 0.025, 0.039, 0.11 and 0.059 kg/day more than contract-reared heifers between visit 1 and visit 4 (overall ADG), visit 1 and visit 2, visit 2 and visit 3 and visit 1 and visit 3, respectively. The occurrence of diarrhoea during farm visit 2 (median age 8.5 months) was associated with a significant reduction in ADG between visit 3 and visit 4. Calf-hood disease (diarrhoea, respiratory disease or navel ill) was not associated with the growth rate during any of the subsequent visit periods. While home-reared heifers had greater ADG during four of the five periods studied, median heifer ADG in both cohorts exceeded the minimum published target weight gains at each developmental stage required for heifers to reach puberty, conceive at 15 months and calve for the first time at 24 months. Importantly, there was wide variation both within enterprises and between farms. It was concluded that while the absolute difference in daily growth rates of home- and contract-reared heifers was minimal, when considered in the context of the entire heifer-rearing period, these growth rate differences have the potential to impact the future reproductive and milk production performance of heifers.     

Rearing strategy and optimizing first-calving targets in dairy heifers: a review

Much research has been carried out and published on dairy replacement management, in order to rear heifers as efficiently as possible, from both a technical and economical point of view. In most cases, the aim is to rear the heifers at the lowest cost possible without any deleterious effects on future performances. However, the importance of dairy heifer husbandry is not sufficiently well recognized and probably mishandled by most farmers. The present review aims to give an actual overview of rearing procedures in dairy heifers and possible ways to achieve optimal goals. For many years, it has been well known that rapid rearing lowers the age of sexual maturity and consequently may be an efficient way to reduce the non-producing period prior to conception. But this may impair mammary development and consequently future milk production, at least during first lactation. In addition, a growth rate that is too low may not only be costly but also result in animals that are too fat at first calving, creating problems such as calving difficulties, dystocia, etc. Genetic considerations must also be factored, i.e. frame, size, body weight, etc. have changed during the last 20 years and there are differences between breeds. As a result, some time-honoured recommendations may not be appropriate. The present paper reviews factors and management practices that may affect rearing and subsequent performance of dairy heifers.     

The effect of sire predicted transmitting ability for production traits on fertility,survivability, and health of Holstein dairy cows

The major objective of this study was to evaluate, using survival analysis and multivariable regression models, the relationship of sire predicted transmitting ability (PTA) for production traits with their daughters' milk production, fat, and protein percentage (PROPCT), reproductive performance, postpartum disease incidence, and survivability. Data were collected from six large commercial dairy farms, and data analysis included 22,205 cows. Information regarding each sire's genetic evaluation included the following: PTA for fat yield (FAT), fat percentage (FATPCT), milk yield (MILK), protein yield, and PROPCT. Sire PTA was categorized into quartiles to facilitate data analysis and interpretation. Retained placenta, metritis, displaced abomasum, and clinical mastitis were diagnosed and treated by farm personnel. The overall average daily milk production, milk fat and PROPCT during the first 10 months of lactation was higher for the cows in the highest quartile of sire PTA, and cows in the lowest quartile had lower averages. There was no significant association between sire PTA for production traits and first test day fat to protein ratio or the incidence of postpartum disease. Sire PTA for MILK, FATPCT, and PROPCT were significantly associated with the hazard of pregnancy. The median days from calving to conception were 159, 155, 170, and 181 days for cows in the sire PTA for MILK quartiles 1, 2, 3, and 4, respectively. Sire PTA for PROPCT and FATPCT were also significantly associated with the hazard of pregnancy. The median days from calving to conception were 175, 189, 152, and 145 for cows in the sire PTA for PROPCT groups 1, 2, 3, and 4, respectively. Additionally, cows in the highest quartile for sire PTA for FATPCT had the lowest median days from calving to conception (144 days) and cows in lowest quartile had the highest median interval (177 days). Sire PTA for FAT was the only sire PTA significantly associated with the hazard of death/culling. When compared with the cows in the highest sire PTA for FAT quartile cows in the first, second, and third quartiles were at 1.51, 1.30, and 1.13 times higher hazard of death/culling, respectively. In conclusion, this study shows that high sire PTA for MILK and low sire PTA for milk fat and PROPCT are associated with decreased daughters' reproductive performance. Sire PTA for production traits were not found to be associated with postpartum disease incidence.     

Effect of Prepartum Supplementation of Selenium and Vitamin E on Serum Se, IgG Concentrations and Colostrum of Heifers and on Hematology, Passive Immunity and Se Status of Their Offspring

Forty heifers at the late stage of gestation were randomly assigned into five groups. Heifers were balanced for age, weight, and time of calving in each group. Four and 2?weeks before expected time of calving, the heifers were injected with 0?ml (C), 10?ml (T1), 20?ml (T2), 30?ml (T3), and 40?ml (T4) Se and VE supplements, respectively. Each milliliter of the supplement contained of 0.5?mg Se as sodium selenite and 50?IU of dl-alpha-tocopheryl acetate. Blood samples were collected from the heifers 4?weeks before expected calving and at calving day and from the calves at birth and 7?days of age. The serum Se and immunoglobulin G (IgG) concentrations, white blood cell and differential leukocyte counts were measured. The Se concentrations in the sera of the heifers before the injections of Se and VE supplements were the same among the groups (P?>?0.05), but after calving were significantly increased in the treated heifers (P??0.05). The white blood cell counts were higher in calves of heifers in groups T3 and T4 compared with the control group at 7?days of age (P?相似文献   

Factors influencing heifer survival and fertility on commercial dairy farms

The average dairy cow survives only three lactations, reducing the availability of replacement heifers. Prenatal losses occur due to early embryonic mortality (about 40%), later embryo loss (up to 20% in high-yielding herds) or abortion (about 5%). A recent survey of 19 UK herds showed that 7.9% of calves were born dead and 3.4% died within 1 month. During the rearing phase, 6.7% of animals were lost before reaching first service at 15 months due to disease or accident and another 2.3% failed to conceive. Many potential replacements therefore never enter the milking herd. This severely limits opportunities for on-farm selection of breeding cows in addition to presenting a welfare issue and causing economic loss. The most profitable animals once lactation is reached combine good milk production with a regular calving pattern. Some aspects of performance are related to age at first calving (AFC), which in turn is influenced by heifer growth rates. Poorly growing animals required more services to conceive, calved later and subsequently performed badly. Optimum fertility and maximum yield in the first lactation were associated with an AFC of 24 to 25 months. However, heifers calving at 22 to 23 months performed best in terms of total milk yield and survival over the first 5 years, partly because good heifer fertility was associated with better fertility later. We have investigated some possible juvenile predictors of future performance. Low-birth-weight calves were more likely to come from either primiparous mothers or older dams (3+ lactations) with higher peak milk yields, suggesting that the uterine environment may limit prenatal calf growth due to competition for nutrients with maternal growth or milk production. Linear trait classification scores for frame size show genetic correlations with longevity. The skeletal measures of height and crown rump length in 1-month-old calves was correlated to subsequent stature, and frame size was correlated to weight at 15 months. It may thus be possible to predict performance from simple size measurements as juveniles. Neither endogenous nor stimulated growth hormone (GH) release in 6-month-old calves were related to milk yield in the first three lactations, but size of a stimulated GH peak was positively related to milk energy values in the first lactation. Cows with delayed ovulation (>45 days) in the first lactation had a higher GH pulse amplitude and lower IGF-I as a juvenile. Cows that partition excess energy into milk in their first lactation may suffer reduced longevity.     

Effect of prepartum somatotropin injection in late-pregnant Holstein heifers on metabolism, milk production and postpartum resumption of ovulation

The aim of this study was to determine the effect of prepartum somatotropin injection in late-pregnant Holstein heifers on metabolism, milk production and resumption of postpartum ovulation. For this study, 31 late-pregnant Holstein heifers were used. The heifers were assigned randomly into two treatments: (1) 500 mg sc injections of somatotropin (somatotropin treatment, n = 15) at -35 and -21 days, and, if pertinent, at -7 days from expected calving date and (2) no treatment (control group, n = 16). Blood samples were collected weekly from -5 to 7 weeks after calving. Heifers with progesterone concentrations in plasma above 1 ng/ml in two consecutive postpartum samples were considered as having resumed ovarian activity. A higher proportion (P = 0.04) of heifers treated with somatotropin resumed ovarian activity in the first 7 weeks post partum (73.3%; 11/15) compared with the control group (37.5%; 6/16). A higher number (P = 0.02) of heifers in the somatotropin treatment group also ovulated during the first postpartum follicular wave (53.3%; 8/15) compared with the control group (12.5%; 2/16), as indicated by the number of heifers ovulating in the first 3 weeks post partum. Pregnancy rate was not affected by treatments (P > 0.10) and averaged 40.0% (6/15) in somatotropin-treated and 25.0% (4/16) in control heifers when evaluated up to 150 days in milk. Somatotropin treatment increased the average daily milk production by 2.8 kg/cow per day (P < 0.0001) and reduced the somatic cell count (P = 0.009). Plasma IGF-I was higher (P < 0.05) for somatotropin-treated heifers in the prepartum period. Insulin and body condition score were higher (P < 0.05) and non-esterified fatty acids were lower (P < 0.05) for somatotropin-treated cows in the early postpartum period. In conclusion, somatotropin injection during the prepartum period in late-pregnant Holstein heifers was able to increase the proportion of heifers resuming ovarian activity early post partum, inspite of higher milk production.     

Evaluating the success of sex-sorted semen in US dairy herds from on farm records

These data summarize on-farm records of dairy herds (n = 211) using sexed semen. Sexed semen was predominantly used at first and second service in virgin heifers, which is reflected in younger ages at AI and at calving. Conception rates at first service averaged 47% for Holstein heifers and 53% for Jersey heifers, which were ∼80% of that achieved with conventional semen. Analysis of inter-estrus intervals provides no evidence that cycle lengths are extended by use of sexed semen. Among singleton births, 89% were reported as female offspring and this rises to 90% for gestation lengths within a normal 265-295 d range. Age at calving appeared to interact with calf sex and semen type to influence the incidence of stillbirths. Semen type had no effect on the incidence of stillbirths among heifers delivering female calves. However, the incidence of stillbirths among heifers delivering male calves was greater for those conceived from sexed semen and was only partially explained by age at calving. Because the incidence of male calves from sexed semen is only 10%, the total incidence of stillbirths was not affected by semen type. In conclusion, failure to differentiate sexed from conventional semen in data recording and preferential bias in use of sexed semen in younger, more fertile females makes legitimate comparisons of sexed and conventional semen in the commercial setting difficult. When used in Holstein heifers, the average first service conception rate achieved with sex-sorted semen was 47%, which appeared to ∼80% of that achieved with conventional semen in the same herds. The percentage of female calves (89%) was consistent with expectations. After adjusting for age at calving, sexed semen had no affect on the total incidence of stillbirths, however the source for an apparent increased incidence of stillbirth among male calves born from X-sorted sperm populations requires further investigation.     

Mortality in Holstein-Friesian calves and replacement heifers, in relation to body weight and IGF-I concentration, on 19 farms in England

The incidence of mortality and culling in Holstein-Friesian heifers from birth through first calving was determined on 19 dairy farms selected from across southern England. The outcome of 1097 calvings was determined. Size (BW, heart girth, crown-rump length and height at withers) and insulin-like growth factor-I concentration of live heifer calves were measured at a mean age of 26 ± 0.7 days (n = 506). Associations between the heifer-level variables and mortality were determined using clustered binary logistic regression. Perinatal mortality (stillbirths and mortality within the first 24 h of birth) of male and female calves was 7.9%. This figure was significantly higher in cases where calving assistance was required (19.1% v. 5.6%, P < 0.001) and in twin births (18.5% v. 7.0%, P < 0.05), and was lower in pluriparous v. primiparous dams (5.6% v. 12.1%, P < 0.01). On average, 6.8% of heifers died or were culled between 1 day and 6 months of age. Low BW at 1 month was associated with reduced subsequent survival up to 6 months. Between 6 months and first calving, a further 7.7% of heifers either died (42%) or were culled (58%); accidents and infectious disease accounted for the majority of calf deaths between 6 and 15 months, whereas infertility (16/450 animals served, 3.5%) was the main reason for culling following the start of the first breeding period. In total, 11 heifers (2.2%) were culled as freemartins; eight at birth and three around service. Overall, 14.5% of liveborn potential replacement heifers died or were culled before first calving.     

Managing the dominant follicle in lactating dairy cows

Reproductive efficiency is not optimal in high-producing dairy cows. Although many aspects of ovarian follicular growth in cows are similar to those observed in heifers, there are numerous specific differences in follicular development that may be linked with changes in reproductive physiology in high-producing lactating dairy cows. These include: 1) reduced circulating estradiol (E2) concentrations near estrus, 2) ovulation of follicles that are larger than the optimal size, 3) increased double ovulation and twinning, and 4) increased incidence of anovulation with a distinctive pattern of follicle growth in anovular dairy cows. The first three changes become more dramatic as milk production increases, although anovulation has not generally been associated with level of milk production. To overcome reproductive inefficiencies in dairy cows, reproductive management programs have been developed to synchronize ovulation and enable the use of timed AI in lactating dairy cows. Effective regulation of the CL, follicles, and hormonal environment during each part of the protocol is critical for optimizing these programs. This review discusses the distinct aspects of follicular development in lactating dairy cows and the methodologies that have been utilized in the past two decades in order to manage the dominant follicle during synchronization of ovulation and timed AI programs.     

Managing the dominant follicle in lactating dairy cows

Reproductive efficiency is not optimal in high-producing dairy cows. Although many aspects of ovarian follicular growth in cows are similar to those observed in heifers, there are numerous specific differences in follicular development that may be linked with changes in reproductive physiology in high-producing lactating dairy cows. These include: 1) reduced circulating estradiol (E2) concentrations near estrus, 2) ovulation of follicles that are larger than the optimal size, 3) increased double ovulation and twinning, and 4) increased incidence of anovulation with a distinctive pattern of follicle growth in anovular dairy cows. The first three changes become more dramatic as milk production increases, although anovulation has not generally been associated with level of milk production. To overcome reproductive inefficiencies in dairy cows, reproductive management programs have been developed to synchronize ovulation and enable the use of timed AI in lactating dairy cows. Effective regulation of the CL, follicles, and hormonal environment during each part of the protocol is critical for optimizing these programs. This review discusses the distinct aspects of follicular development in lactating dairy cows and the methodologies that have been utilized in the past two decades in order to manage the dominant follicle during synchronization of ovulation and timed AI programs.