To save this undefined to your undefined account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your undefined account.
Find out more about saving content to .
To save this article to your Kindle, first ensure email@example.com is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
In this paper we discuss the likely future milk production scenarios and breeding and management strategies in the EU in general, and in Britain and Ireland in particular. EU markets for most dairy products are stagnant in volume terms. There is, however, scope for value growth which would emphasise quality and added value, not price. The background scenario is therefore one of sharp commercial focus heavily influenced by consumer demands for quality, not only in physical terms but also in ethical, welfare and aesthetic ones. Future systems of production will need to be in tune with future markets. Perhaps three main sectors can be identified: intensive high output, pasture based systems and niche systems (e.g. organic systems). In each of these options the same questions arise: (i) What kind of cow/breeding strategy is suitable for the sector?, and (ii) What are the management guidelines which will secure efficient, sustainable productivity? In the past, the majority of dairy cattle improvement programmes have focused primarily on improving returns by increasing milk or milk solids yields. Future breeding programmes are likely to pay much greater attention to reducing costs than they have in the past. In pasture-based systems, or niche markets, this may lead to renewed interest in cross breeding to reduce health, re-breeding and replacement costs. In all systems there is likely to be much greater emphasis on traits other than production in selection indexes. Customised indexes will help producers to tailor their selection decisions to their particular markets and production systems. If the differences between future production systems are extreme, it may be cost effective to produce bull evaluations for each of the main systems. New molecular techniques are beginning to assist conventional selection programmes. In the longer term the transfer of genes between strains, breeds or species may be used for agricultural applications. However, it is questionable whether or not this would be acceptable to consumers in the EU. Management issues which will be important in future are exactly the same as they have ever been, dealing with feeding, fertility, health, housing, milking practice, hygiene and pasture management. Nearly all of these interrelate with each other and with breeding strategy. Particular issues in future may include management of robotic milking, loose housing, deliberately extended lactations, organic production systems and extended grazing. Future ‘feeding’ challenges will include optimizing concentrate use for cows of different genetic merit, and finding alternatives to conserved grass. Direct genetic modification of grass and other forages to improve their qualities both as grazed and as conserved material would also be useful. There is also likely to be increased emphasis on feeding cows to improve control of nutrient partition, and on improved feeding of animals in the transition between lactations. Tailoring feeding and management policies to the genetic merit of cows will be a continuing challenge.
Causes of variation amongst cattle within a herd in their ability to initiate and maintain pregnancy are largely unknown. An experimental animal resource has recently been established to understand the biology of early reproductive performance. This paper summarises the results achieved during the establishment phase and from several experiments aimed at determining the physiological basis of the difference between sub-herds of contrasting pregnancy rates on Day 60. Each of 155 contemporary yearling heifers received 2 in vitro-produced embryos on 6 separate occasions during a 26-month period. Sixty days after transfer, pregnancy and twinning rates were determined ultrasonically, pregnancies terminated and the process repeated. The interval between successive transfers was greater than 100 days. Heifers were ranked on their aggregate pregnancy rate performance after 6 rounds of transfer, and the highest (High) and lowest (Low) 25 were retained. Differences in reproductive performance during the establishment phase of the herd are reported. In addition, several subsequent experiments examined ovarian follicle turnover and progesterone levels during an oestrous cycle, early embryo development after either AI or embryo transfer, and protein, interferon tau and ubiquitin-cross-reactive protein levels in uterine luminal flushings.Pregnancy rates were 7-folder higher in the High sub-herd (76 vs. 11%), with much of this difference apparent by Day 25. The proportion of heifers observed in standing oestrus prior to embryo transfer and the interval from the end of synchronisation treatment to the onset of oestrus were similar in the sub-herds. Oestrous cycle length, ovarian follicular dynamics and progesterone profiles during the oestrous cycle were also similar. More conceptuses had elongated by Day 14 in the High sub-herd (67 vs. 14%, P<0.05), which also tended to have a higher pregnancy rate after artificial insemination (52 vs. 29, P<0.1). Total protein in flushings from the uterus was similar in the sub-herds on Day 14 and Day 17. Conceptuses in the High sub-herd were longer on Day 17 following embryo transfer (6.5 vs. 4.8, P<0.05). Interferon-tau levels were higher in the High sub-herd (25.9 vs. 16.1, P<0.01), although ubiquitin cross-reactive protein levels were also higher in the High sub-herd, but this difference just failed to reach significance. We conclude that: 1. Most of the difference in sub-herd pregnancy rate occurs within 3 weeks of ET; 2. Ovarian factors are unlikely to contribute to the difference; 3. Major differences occur after blastocyst hatching and probably depend upon a differing endometrial environment before Day 14; 4. Differences in the ability of the uterine milieu to stimulate the expression of interferon-tau may be responsible for the differences in pregnancy rate; 5. The two sub-herds are a unique experimental resource for understanding early pregnancy in cattle following either AI or ET.
The financial implications of delays in conception at different stages of lactation in the average and the high yielding dairy cows were investigated. Variables included in the calculations were net loss in annual yield, lost income from a calf, cost of extended dry period, cost of slipping in calving pattern, cost of extra veterinary treatments and AI services, benefit of a delay in calving for reduced risk of production diseases, potential benefit of delay in conception on milk yield from the current lactation, and the value of quota leasing. For the average yielding cow, the net cost of one day of delay in conception was calculated at £2.41 when conception is delayed from 85 to 100 days post-calving, increasing to £5.02 per day if conception occurred at 146 to 175 days post-calving. After taking value of quota leasing into account, the net cost of a lost day was calculated at £1.73 and £3.55 per day for the two delay intervals respectively. For the high yielding cow, the net cost of one day of delay in conception was calculated at £2.48 when conception is delayed from 85 to 115 days post-calving, increasing to £6.52 per day if conception occurred between 206 and 235 days post-calving. The net costs after quota leasing being considered were calculated at £1.68 and £4.08 per day for the two delay intervals respectively. On the basis of the above estimations, and after considering the cost of culling for poor fertility, it was concluded that it is a cost-effective option to keep trying to get the typical average cow in calf until 266 days post-calving, whereas the breakeven point for the high yielding cow is at 290 days post-calving.
In the cow, the embryo during the first three weeks of pregnancy is free living in the uterine lumen and is dependent on the maternal glandular secretions for its nutritional support. If the environment is appropriate, the embryo will develop sufficiently to prevent luteolysis. The aim of this study was to investigate the regulation of factors involved in embryonic-endometrial interactions during early pregnancy. Uterine horn sections were collected from 17 pregnant (PREG), 9 inseminated but no embryo present and 10 uninseminated cyclic control cows on days 12, 14, 16 and 18 after natural oestrus. The latter two groups were combined to form a single non-pregnant (NP) group. Trophoblast sections were also collected from the day 14, 16 and 18 embryos. The mRNA for interferon tau (IFNτ), oxytocin receptor (OTR), oestrogen receptor a (ER), prostaglandin G/H synthase -2 (PGHS-2), insulin-like growth factor (IGF) -I and IGF binding protein -1 (IGFBP-1) was determined by in situ hybridisation using 45 mer oligonucleotide probes end-labelled with35 S. The optical density (OD) readings were measured from the resulting autoradiographs. The expression of IFNτ mRNA in the trophodectoderm did not vary with embryo age. The expression of OTR mRNA in the luminal epithelium was first detectable on day 14 in 2 out of 5 NP cows and increased thereafter. Conversely, OTR mRNA was undetectable in all PREG cows except for one day 18 cow. In the NP cows, the first significant increase in ER mRNA concentrations in the luminal epithelium was observed on day 16. The pregnancy had no effect on ER mRNA concentrations in the luminal epithelium on days 12 and 14, but was significantly reduced on day 16 and was undetectable by day 18. On day 18, PGHS-2 mRNA was detectable in the luminal epithelium of all cows, but was unaffected by pregnancy status. The expression of IGF-I mRNA in the subepithelial stroma was maintained from days 12 to 18, but was reduced in the day 18 NP cows. IGFBP-1 mRNA concentrations in the luminal epithelium peaked on day 14 in both NP and PREG cows. Thereafter, concentrations declined in the NP group but were maintained in the PREG animals. In conclusion, the suppression of OTR mRNA expression by the embryo does not appear to require the prior suppression of ER mRNA. The continued expression of IGF-I and IGFBP-1 mRNA is likely to play an important role in the establishment of early pregnancy in the cow.
The objective of this study was to estimate the effects of genetic merit for milk yield on energy balance (EB), dry matter intake (DMI), and fertility for cows managed on three different grass based feeding systems, and to estimate possible interactions between genetic merit and feeding system. Individual animal intake estimates were obtained at pasture on 11 occasions across three grazing seasons. The data set contained 96 first lactation animals in 1995, 96 second lactation animals in 1996, and 72 third lactation animals in 1997. Half of these animals were of high (HG), and half of medium genetic merit (MG) for milk solids production. Genetic effects for the traits of interest were estimated as the contrast between the two genetic groups, and by the genetic regression of phenotypic performance on the estimated breeding value for fat and protein yield, based on pedigree information alone (PI). Significant effects of feeding system were observed on yields, DMI and EB, whereas there was no effect on live weight, condition score or reproductive performance. The interaction between genetic merit and feeding system was not significantly different from zero for any of the traits. Yields, grass DMI, and total DMI were all higher for HG than for MG, and also positively correlated (P<0.001) with PI. Furthermore, condition score, conception to first and second service, and pregnancy rate were significantly negatively correlated with PI. While at pasture, EB was positively (P<0.01) correlated with PI, although the contrast between HG and MG was not significantly different from zero. Condition score changes during very early lactation, demonstrated that HG had a more negative EB than MG. The results clearly illustrate the production potential of HG cows on grass based systems, however the reduced reproductive performance questions their suitability for seasonal calving systems.
Following parturition, there is an early resumption of sequential but transient FSH increases of 2-3 days duration in dairy and beef cows. The first increase results in the emergence of the first postpartum follicle wave and the decline in FSH results in selection of a dominant follicle (DF). The ovulatory fate of this DF is dependent on LH pulse frequency and IGF-I concentrations. The energy status of the cows affects the degree of anoestrus. High yielding cows in prolonged negative energy balance (NEB) have a greater incidence of anoestrous, where the DF is smaller and fails to produce sufficient oestradiol to induce ovulation. Thus, there are sequential follicle waves in anoestrus prior to first ovulation. A small percent of DFs in dairy cows fail to ovulate and they continue to grow due to high LH pulse frequency and form follicular cysts. These cysts produce oestradiol for a variable period and then become physiologically defunct, despite their morphological presence for variable periods before final regression. During their physiological active state, new follicle wave emergence and ovulation are suppressed. A further problem in high yielding cows is the increased incidence of abnormal ovarian cycles after ovulation, and specifically, the high incidence of maintained corpora lutea (CL), probably related to uterine problems in the peri-parturient period. The ovulation of smaller DFs and the high liver metabolic rate may adversely affect oestradiol and progesterone concentrations. The long-term effects of prolonged NEB on oocyte competence, DF physiology and follicular and luteal steroidogenesis all may have detrimental effects on conception rates to AI. Hormonal methods to induce ovulation should be carried out in conjunction with corrective management problems, once diagnosed The pre-treatment of anoestrous cows with progesterone for 5-9 days is a prerequisite for the concomitant expression of oestrus at first ovulation, but whether or not further hormonal therapy is necessary to ensure the ovulation of the DF, is dependent on energy status, body condition score and postpartum interval, which regulate LH pulse frequency.
A number of measurable physiological events characteristically occur and cause changes during the perioestrual period including the classical, diagnostic sign of standing behaviour. The onset of oestrus coincides with peak titres of oestradiol-17β that subsequently induce the preovulatory surge of LH within 1 to 3 h and ovulation of a mature follicle some 24 to 32 h after the onset of oestrus. Although detection efficiencies are consistently greater in higher producing herds, oestrus-detection efficiency generally has declined in recent years as herd size and milk production have increased. New technologies have introduced some needed assistance for detecting cows in oestrus. These include various in expensive heat mount detectors to more sophisticated electronic gadgetry, such aspedometry and radiotelemetric sensors that detect temperature, tissue impedance, and pressure. Oestrus detection aids are usually more efficient but not necessarily more accurate than visual observation. Differences in housing and environmental conditions, in addition to labor inputs, costs, and efficacies, result in variable acceptance of such technologies. Detection efficiency and accuracy can be improved by simultaneous use of synergistic technologies; those that compliment each other and monitor different indicators of oestrus. Combining technologies for simultaneous measurements of several physiological events associated specifically with the onset of oestrus and their radiotelemetrically signaling to a central computer for subsequent analysis should provide greater efficiency ofoestrus detection with fewer false positives. The ultimate goal of determining the onset of oestrus or ovulation is to predict the optimal timing for insemination. Ultimately, herd personnel must interpret information gathered by these technologies and judge whether or not and when to inseminate cows based on their visual inspection of identified cows.
The National Dairy Herd Fertility Project (renamed the InCalf Project) consists of two large, prospective observational studies conducted in commercial dairy herds from 4 Australian states. The project aims to identify factors associated with variation in reproductive performance between cows and herds. The larger of the two studies included over 33,000 cows and 168 herds. The database has undergone extensive error checking and correction resulting in high quality data. Large variations in reproductive performance were observed between cows and herds, indicating that there are important risk factors for reproductive performance and that cows and herds are exposed to varying combinations of these risk factors. Models for several reproductive outcomes were constructed using multivariable stepwise logistic regression. No significant associations were detected between any measures of cow genetic merit and 6 week in-calf rate. Neither milk volume nor protein yield were significantly associated with 6 week in-calf rate. A weak negative association was detected between fat yield in the first 120 days of lactation and 6 week in-calf rate. However, differences in estimated 6-week in-calf rate between moderate and high producing groups (2 to 5 percentage points) were small when contrasted against the 63 percentage point range in performance observed between herds (23% to 86%).
The study compared the impact of feeding different energy supplements (barley, molassed sugar beet and fat) prior to calving and the effects of feeding supplemental fat post-partum, on subsequent production and reproductive efficiency of dairy cows. Forty-eight multiparous Holstein-Friesian dairy cows were assigned to one of two groups, six weeks prior to expected calving date and fed a grass based total mixed ration according to ME requirements for late gestation. Group 1 was supplemented with barley (B) or molassed sugar beet feed (SB) prior to calving and was then given a high starch lactation ration. Group 2 was supplemented with either fat (F) or no supplement (C) pre partum, and was then given a similar lactation ration as Group 1 but supplemented with fat. Lactation rations were fed through to week-20 post partum and the cows were monitored during this period. Milk yield (P<0.002) and milkfat (P<0.02) production were higher and milk protein concentration (P<0.001) was lower in Group 2. The number of days to first rise in progesterone following parturition was greater (P<0.01) in Group 2. Due to the design of the study, effects of prepartum supplementation were only evaluated within each lactation ration group. Conception rate to first service was higher (P<0.001) for B than SB supplemented cows in Group 1 and higher (P<0.02) for F than C supplemented cows in Group 2. Services per conception were lower (P=0.06) for B than SB supplemented cows in Group 1 and lower (P<0.05) for F than C supplemented cows in Group 2. Overall pregnancy rates and days open were not significantly different between the groups. The data shows that pre-partum nutrition had an important role in determining subsequent fertility. Despite having negative effects early post partum, supplementing with fat did not affect overall reproductive performance but it did improve milk production.
The abnormalities of the puerperium can be arbitrarily divided into two broad categories. Those which arise following a difficult calving or retained placenta are referred to as “common”, while abnormalities such as sub- and anoestrus, irregular cycles, cystic follicles, absence of ovarian activity, repeat breeding and increased number of inseminations per pregnancy are described as “special”. Since the “common” abnormalities are well understood, this paper deals in greater detail with the “special” abnormalities of the puerperium. Based on the axiom that many facets of the “special” abnormalities can be caused by dysfunction of the liver (as in the case of fatty liver), information is presented based on experiments conducted with the over-conditioned dairy cow model (AM) which suffers from both a severe negative energy balance (NEB) and fatty liver syndrome during early lactation. This cow model guarantees a severe NEB, with body weight loss and clear changes in the body condition score (BCS), lower milk production, a higher milk fat concentration, temporary decline in blood insulin and glucose concentrations, elevated blood concentrations of non esterified fatty acids (NEFAs) and beta-hydroxybutyrate (BHB) as well as elevated liver concentrations of tri-acyl-glycerol (TAG) during the first weeks post partum. Additionally, this model leads to a higher incidence of metabolic and infectious diseases. Particular attention was paid to LH pulse frequency and to its value in predicting the occurrence of first post partum ovulation would occur, to oestrous behaviour and to oocytes quality. Cows with fatty liver (> 50 mg TAG/g liver tissue) had longer intervals between parturition and 1st ovulation and showed fewer standing heats within the first 100 days post partum, but the proportion of detected heats, compared to endocrinological “heats” was higher in confirmed AM-cows. Moreover, when AM cows come in heat, their heats lasted longer and had a higher pregnancy rate following AI. However, the developmental capacity of oocytes in AM cows, and in particular oocytes that were destined to ovulate between 80 and 120 days pp, was adversely affected. We conclude that the fatty liver condition is a trigger for many problems, including metabolic and infectious diseases, and also of reduced fertility. Prevention of over fatness at calving (BCS>3.5) is the best guarantee for a normal puerperium.
Poor reproductive performance is a major problem on dairy farms across Northern Ireland and the United Kingdom (UK) as a whole, and recent studies suggest that the problem is increasing. In order to identify the key factors influencing reproductive performance at farm level, a major research initiative was established in 1998 with the objective of collating a comprehensive database on reproductive performance from 20 herds, representing over 2000 dairy cows, across Northern Ireland. Preliminary results for five herds from the first year of the study indicate a high heat detection rate (84%) across all farms. The mean intervals to first observed heat and to first service for cows calved within 19 days of the start of the breeding season were similar between herds (42.8 ± 14.0 days and 50.0 ± 11.0 days respectively). In contrast, the interval to first service for all recorded services was 89.8 ± 66.3 days and varied considerably between farms (69.9 to 112.7 days). Investigation of progesterone profiles indicates that 62.3% of cows had resumed normal cyclic activity by 40 days post calving. Of the cows with atypical ovarian patterns, 19.4% were classified as prolonged post-partum anoestrus with a further 12% exhibiting at least one post-partum prolonged luteal phase.
A series of in vitro and in vivo experiments were conducted to characterise the dialogue between embryo and maternal units relative to the mechanisms controlling embryo survival in dairy cattle. Endometrial explants from pregnant cows had an attenuated PGF2α secretory response following treatment with melittin (stimulator of PLA2) and phorbol 12, 13 dibutyrate (PDBu). Thus previous exposure to the conceptus appears to regulate the endometrial synthetic pathway at a point coincident with or distal to PLA2 as well as inhibit PKC or PKC mediated events. Endometrial explants collected from cows receiving intrauterine infusions of rblFN-τ had a reduced secretory response following stimulation with PDBu indicating attenuation in PKC activity. Based upon tyrosine-phosphorylation of STAT-proteins and their translocation to the nucleus after treatment with rbIFN-τ, the JAK-STAT pathway is functional in immortalised bovine endometrial cells (BEND cells). Bend cells, exposed to rblFN-τ, reduced PDBu induction of PGF2α secretion and also decreased protein expression of Cox-2 and PLA. RblFN-τ clearly reduced PKC mediated events leading to an antiluteolytic response in endometrial cells. Feeding diets containing 2.6, 5.2 and 7.8% Menhaden fish meal to lactating dairy cows reduced uterine secretion of PGF2α following sequential injections of oestradiol and oxytocin. Thus antiluteolytic effects in early pregnancy may be amplified by feeding by-pass fats. Pregnancy rate to a timed insemination at first service post-partum is increased in association with injection of bST(500 mg; sc) given at insemination. Furthermore injection of bST at time of insemination in superovulated donor cows increased the number of blastocysts and reduced number of unfertilised embryos. Prospects of integrating novel strategies to improve embryo development and survival into reproductive management systems appear to be attainable in high producing dairy cows.
Previous studies have shown that 35 — 40 % ofmodern dairy cows experience ovarian disturbances during early lactation. Even though negative energy balance (NEB) has been implicated as a regulator of ovarian function, the exact metabolite(s) or hormone(s), which mediate this effect is still not clear. In this study, we investigated the relationship between blood metabolites (NEFA, BHB and glucose) and plasma insulin like growth factor-I (IGF-I) and ovarian dysfunction. Thirty three Holstein-Friesian cows were fed a lactational ration ad libtium and were inseminated at observed oestrus starting from 56 days post calving. Three times weekly milk samples and weekly blood samples were collected from cows from calving until confirmed pregnant. Cows were placed into “NORMAL” or “ABNORMAL” categories of ovarian activity based on their milk progesterone profiles. The days to first service were 71 ± 2 in “NORMAL” and 78 ± 6 in “ABNORMAL” animals. The calving to conception interval (days open) was shorter in the “NORMAL “ than the “ABNORMAL” group (90 ± 8.7 vs 119 ± 15.2 days). IGF-I levels were significantly lower in the “ABNORMAL” group from 2 until 7 weeks after calving (P<0.02) and NEFA concentrations were higher in the “ABNORMAL” cows in the early postpartum period (P<0.03). There was no significant difference in either plasma BHB or glucose. This study confirms that elevated plasma NEFA concentrations are associated with “ABNORMAL” ovarian activity. The most significant difference was in plasma IGF-I concentrations, which stayed lower for nearly 2 months in the “ABNORMAL” animals.
Over the past 30-40 years genetic improvement and better nutrition of dairy cows have led to a significant increase in milk production per cow but this is associated with an increase in cow reproductive wastage. Reproductive wastage in the dairy herd particularly in a seasonal calving system, results in a serious financial loss. Early embryo death accounts for a significant portion of cow reproductive wastage and information is becoming available on the extent and timing of early embryo loss and on aspects of embryo growth, development, metabolism and viability. Such information is necessary to facilitate objective investigation of factors that contribute to early embryo death. For heifers and moderate yielding dairy cows published estimates of fertilisation rate of about 90%, and of average calving rates of about 55% indicate an embryonic and foetal mortality rate of about 40%. Of this total loss, 70 to 80% is sustained between days 8 and 16 after insemination, a further 10% between days 16 and 42 and a further 5-8% between day 42 and term. In high yielding cows there is some evidence of a higher increment of late embryo loss. During the period of greatest embryo loss, between days 8 and 16 after fertilisation, there is a dramatic increase in the growth rate and protein content of embryos, particularly from day 13 to day 16 when the increase is exponential. There is evidence that from day 13 to 15 cattle embryos undergo time and developmental stage-dependent changes in the rate of de-novo protein synthesis and protein phosphorylation. It seems that by the time cattle embryos have elongated they have passed their maximal synthetic activity in terms of protein synthesis and phosphorylation, which seems to occur at day 13 or earlier. While there is little published information on the causes of embryo loss it is clear that even a short-term reduction in energy intake near the time of insemination can significantly reduce embryo survival rate. Abo and low post-ovulatory systemic progesterone has been associated with increased embryo loss. Recent evidence shows that elevated systemic concentrations of ammonia and urea per se do not reduce embryo survival rate but there may be other modifying factors, such as negative energy balance, operating in the high yielding dairy cow that lead to reduced fertility when the systemic concentrations of urea and or, ammonia are high.
Decreasing levels of fertility of dairy cows are occurring, associated with increased average annual milk yields, increased herd size and a decreased labour investment per animal. To-date, there has been no positive genetic selection in the UK for improved female fertility due to the lack of reliable recording of fertility traits. Selection is further limited by the low heritabilities of traditional fertility measures, which are subject to environmental influences and management decisions and biological restraints such as age and sex. Assessment of the hormone patterns of fertile cows and determination of the atypical patterns exhibited by subfertile animals provides an objective method of identifying the causes and assessing the impact of subfertility and for the development of remedial treatment strategies. This knowledge can then be used to identify potential physiological parameters associated with high fertility which, in future, may be used for sire breeding value estimations to select for more fertile offspring. Regular assessment of the progesterone concentrations in milk provides a non invasive method of determining progesterone patterns. The results of two studies of milk progesterone levels in cows taken between 1975/82 and 1995/98 involving over 3200 lactations have been analysed and compared. They indicate a major increase over this period in the proportion of animals showing atypical milk progesterone patterns before mating from 32 to 44% (P<0.001) associated with less animals inseminated, delays to conception and lower conception rates. There was a significant decrease (P<0.01) over this period in animals calving to first postpartum insemination from 57% to less than 40% a decrease of approximately l%per annum. This may indicate an increase in the level of early embryo mortality. An early post ovulatory progesterone rise to adequate luteal phase levels has been shown essential for normal embryo development with low post ovulatory levels occurring in some cows resulting in lower calving rates. Milk progesterone analysis provides a robust and reliable method of measuring progesterone patterns for identifying subfertile animals, for targeting remedial treatments to improve fertility and for investigations into heritable fertility parameters for future selection programmes.
The relationship between body condition at calving, uterine tone and discharge, time to first oestrus and changes in concentration of serum calcium and magnesium in early post partum was examined in 209 multiparous dairy cows located in four herds in the San Joaquin Valley of California. Body condition score (BCS) was graded from 0 to 5 and BCS at calving was estimated from BCS in the late dry period (LDBCS). Uterine tone and discharge were graded from l(best) to 3(worst) after rectal palpation at two weeks post partum. Concentrations of blood metabolites and levels of progesterone were determined from blood samples taken at selected stages of lactation from the late dry period to ten weeks post partum. Abnormal uterine discharges were strongly correlated with uterine tone. Uterine tone and discharge scores were significantly lower in cows that calved with body condition scores of 2.5 and 3.0 than in those which calved with body condition scores of < 2.5 and ≥ 3.5. Serum calcium and magnesium concentrations were higher at two weeks post partum in cows with scores of 2.5 and 3 than in cows with higher or lower scores. Serum calcium and magnesium concentrations appeared to be higher with decrease in grades of uterine discharge and tone but this was significant only in the case of serum calcium and uterine discharge. The number of days to first oestrus was significantly associated with uterine discharge and tone (P < 0.05) but not significantly associated with LDBCS. The number of days to second oestrus was not significantly associated with uterine discharge and tone but was significantly less in cows with LDBCS 3 (17.28 days) than cows with lower or higher LDBCS (P < 0.05). It is concluded that body condition at calving is associated with serum micromineral balance and subsequent uterine and ovarian health. Based on these measurable indicators, cows calving with body condition scores of 2.5 and 3 appeared to be in optimum condition for post partum reproductive performance.