Reproduction, Events and Management | Mating Management: Fertility

Mating Management: Fertility M G Diskin, Teagasc, Animal & Grassland Research and Innovation Centre, Mellows Campus, County Galway, Ireland ª 2011 Elsevier Ltd. All rights reserved.

Introduction In dairy cows, reproduction has two major functions: to induce the onset of lactation and to provide replacement animals for the current generation of cows. Consequently, reproductive efficiency is a major factor affecting production and economic efficiency. Over the past four decades, milk yield per cow has increased significantly through genetic selection and improved management. Not withstanding these improvements, there has been a steady decline in reproductive performance of dairy cows coincident with the improvement in yield. The focus of this article is to review the components that determine reproductive efficiency of dairy cows, and to investigate how best to use the new information that has emerged over the last few decades to improve the reproductive management of a herd and consequently its production efficiency.

Reproductive Targets Although it is frequently argued that milk production efficiency is at its highest when cows reproduce once every 365 days, the optimal reproduction function that maximizes profit is dependent on numerous factors, including production system, level of milk production, milk prices, and feed cost, among others. Consequently, it is impossible to give a set of specific targets applicable to all systems of production. However, the three measures presented in the following section (see also Table 1) are useful as initial measures of reproductive performance in seasonal and all-year-round calving herds. Using only one measure of reproductive efficiency can be misleading and can mask other important inefficiencies.

Components of Reproductive Efficiency Even though there are numerous factors that affect the reproductive performance of individual cows and consequently herd reproductive performance, these factors can be categorized under the following three broad headings: 1. The interval from calving to resumption of ovulation and regular estrous cycles 2. Estrous detection efficiency and submission rate 3. Conception rate following service

The Interval from Calving to Resumption of Ovulation and Regular Estrous Cycles Generally, about 80% of dairy cows will have ovulated within 28 days of calving and about 10% of cows will not have commenced ovulation by 42 days postcalving. In dairy cows, the main cause of anestrum is prolonged negative energy balance (NEB), which results in low LH pulse frequency, decreased concentration of insulinlike growth factor-I (IGF-I), low estradiol production, and ultimately the failure of the dominant follicle (DF) to ovulate. The number of ovulatory estrous cycles preceding insemination has been shown to beneficially influence subsequent conception rate. Consequently, it is desirable that dairy cows resume ovulation in the first 4 weeks after calving. Following delivery of the calf and fetal membranes, there is a decline in the plasma concentrations of progesterone and estradiol and a corresponding removal of the negative feedback effects of these steroids, particularly estradiol, on gonadotropin synthesis and secretion. Follicle-stimulating hormone (FSH) secretion commences during the first week postpartum, and this stimulates the commencement of ovarian follicle growth and the appearance of a DF on the ovary at about days 12–16 postpartum. The fate of this follicle in terms of whether it ovulates or undergoes atresia appears to be related to whether it produces estradiol, which in turn appears to be associated with exposure to an adequate LH pulse frequency and concentration of IGF-I. NEB in early lactation does not affect the follicle population or the timing of recommencement of DF growth but does affect the ovulatory fate of the first DF. However, energy balance (EB) in early lactation, rather than milk yield per se, appears to be the more important factor affecting resumption of ovulation postcalving, and dry matter intake (DMI) is a more important determinant of EB than milk yield. Positive association between EB in early lactation and the interval from calving to resumption of estrous cycles has been recorded. There is increasing evidence that IGF-I is a potential mediator of nutritional effects on fertility. Increased plasma concentrations of IGF-I during the first 2 weeks postpartum are associated with early resumption of ovulation. It has been demonstrated that feeding dairy cows an insulin-promoting diet increases plasma concentrations of insulin and also shortens the interval from calving to first postpartum

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476 Reproduction, Events and Management | Mating Management: Fertility Table 1 Targets for seasonal and all-year-round calving herds Variable

Seasonal calving herds

All-year-round calving herds

Calving interval Culling for infertility Compactness of calving

365 days <5% 80% calved in 60 days

<420 <10% NA

hasten the onset of estrous cycles postcalving but also to increase conception rates (see later) and shorten calvingto-conception intervals. Increasing dietary intake is restricted by the requirement for inclusion of fiber in the diet to maintain rumen function as well as by the variability in voluntary feed intake by cows during this period.

ovulation in both high- and low-genetic merit dairy cows. Insulin is a potent stimulator of follicle differentiation and steroidogenesis, promotes DF differentiation, and enhances responsiveness to LH and in turn increases estradiol secretion leading to a preovulatory LH surge and ultimately the ovulation of the DF. NEB also causes a decrease in circulating concentrations of IGF-binding proteins (IGFBPs). Because the IGFBPs transport and increase the half-life of IGFs, low blood concentrations of IGFBPs brought about by NEB would therefore limit the availability of IGFs to target cells in the follicle and hence limit their ability to synergize with pituitary gonadotropins to stimulate cell proliferation and steroidogenesis and ultimately ovulation (Figure 1). An objective with dairy cows in early lactation is to achieve a high DMI, as this would be expected not only to

Improving Heat Detection The single most important factor affecting heat detection efficiency is the ability of those responsible for checking for heat to fully understand the signs of heat and their commitment to heat detection for as long as is planned to use artificial insemination (AI). About 10% of the reasons for failure to detect heats can be attributed to cow problems, and 90%, to ‘management’ problems. The latter

Brain NPY and EOP Hypothalamus N GnRH U

Glucose

T Anterior pituitary GH

R Liver

FSH

I

Insulin

LH

T Steroid and protein negative feedback

IGF-I Pancreas DF

I O N

Autocrine and paracrine factors

Figure 1 Possible mechanisms by which nutrition could affect ovarian follicular function. EOP, endogenous opioid peptides; NPY, neuropeptide Y. Reproduced with permission from Diskin MG, Mackey DR, Roche JF, and Sreenan JM (2003) Effects of nutrition and metabolic status on circulating hormones and ovarian follicle development in cattle. Animal Reproduction Science 78: 345–370.

Reproduction, Events and Management | Mating Management: Fertility

would include too few observations per day for checking for heat activity, too little time spent observing the cows, and/or observing the cows at the wrong time or in the wrong place, such as feeding time or in the collecting yard at milking time. Another major reason for failure to detect heat is that those involved in heat detection do not understand the signs of heat. Records

Individual animal records are an essential part of good breeding management. All animals must be clearly and permanently identified by one of several methods, such as plastic ear tags, neckbands, or freeze branding. Whichever system is preferred, it is essential that the animal number be clearly legible from a reasonable distance. Breeding records should include (1) animal number, (2) calving date, and other information relevant to calving, (3) prebreeding heat dates, (4) first and repeat service dates, sire used on each date, and inseminator code, (5) date and result of pregnancy diagnosis, and (6) date of expected calving. Good records are not only part of good farm management practice, but also the first essential step in all infertility investigations. Monitoring submission rate

Submission rate is calculated as the proportion of cows calved at the beginning of the breeding season that are intended for rebreeding and submitted for insemination. A submission rate of at least 80% of the eligible cows during a 21-day period is desirable. Submission rate, which is easily calculated, is an excellent measure of heat detection rate and should be calculated at the end of the first 21-day period of the breeding season. A submission rate of less than 80% indicates a problem with heat detection, and diagnosis of this problem at an early stage allows corrective action to be taken before much of the breeding period has elapsed. Technological Aids to Improve Heat Detection The low to moderate heat detection efficiencies achieved on most farms reflect the difficulty of detecting heat in cows. Consequently, it has been and is the goal of many animal science programs to develop more objective systems to overcome some of the problems of heat detection. An ideal system for detecting estrus should have the following characteristics: (1) continuous surveillance of the cow; (2) accurate and automatic identification of the cow in estrus; (3) operation for the productive lifetime of the cow; (4) minimal labor requirements; and (5) high accuracy and efficiency (95%) for identifying the appropriate physiological events that correlate with estrus or ovulation or both. A number of aids and technologies, inexpensive or expensive, are available to meet some, but not all, of these criteria. In any case, use of the various

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technologies to identify the symptoms associated with estrus, ovulation, or both will require the judgment of the herd management, based on common husbandry experience, to verify whether or not the cow seems to be in estrus. Tail-painting

Research from a number of laboratories has shown that applying paint or chalk to the tailhead of cows is effective in indicating standing activity. When such tail-painted cows are mounted from the rear some or all of the chalk or paint is rubbed off indicating that the painted cows possibly stood in estrus while being mounted by a herd mate. When combined with early-morning and late-evening observations, checks for paint loss at milking times should result in a heat detection rate of close to 90%. Vasectomized bulls with chin ball marking harness

Active vasectomized teaser or detector bulls are useful in identifying cows either coming into or on heat. Vasectomy should be carried out 40–60 days prior to introduction to the herd. Many small- to medium-size dairy herds in Ireland are now finding that teaser bulls are particularly useful after the first 3 weeks of the breeding season when fewer cows are in heat each day and when the level of heat-related activity in the herd is reduced as more cows become pregnant. However, considerable variation in libido exists among bulls, and they require the same management as full bulls without conferring any of the advantages. As an alternative to vasectomized bulls, cows or heifers treated with testosterone or estradiol can be useful in detecting cows in estrus. Pressure-activated heat mount detectors

These devices, including the ones marketed as Kamars, Bovine Beacon, and Mate Master, are affixed to the tailhead of the cow and change color when pressure is applied by the weight of the mounting animal. Reported efficiencies of heat detection using such heat mount detectors vary from 56 to 94%, whereas the accuracy of heat detection is reported to vary from 36 to 80%. The relatively low accuracy of heat detection, combined with the difficulties in keeping the devices affixed to the tailhead, limits the potential of this approach. Pedometers

Estrus in cattle is accompanied by increased physical activity. Cows in heat do 2–4 times more walking than a nonestrous cow. Pedometers can be attached to the leg of the cow to measure the amount of her activity over a unit time-span. Early pedometer-aided heat detection systems operated with a reported heat detection efficiency of 60–100% and with an accuracy in the range of 22–100%. The low level of accuracy was related to a

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high proportion of false-positives and to technical problems that led to breakage, malfunction, or loss of the pedometers. New improved pedometric technology has now led to improved information storage systems; improved analytical capabilities to allow comparison of current with previous physical activity; incorporation of internal power supply to operate the electronics; and the development of self-contained devices to interrogate the pedometers in milking parlor and relay and store the information in a personal computer. Some systems have an inbuilt alert system, such as a bleeper or flashing light, which alerts the farmer when a cow is deemed to be in heat. A number of pedometric systems are commercially available in the United States and Europe. Even though scientific information on their operating efficiencies is not yet available, these systems would appear to have significant commercial potential particularly when cows are housed. Radiotelemetric devices

The primary sign of heat is standing to be mounted. A number of research laboratories have attempted to develop pressure-sensitive devices that measure such standing activity. Such a system (HeatWatch II; CowChips Manalapan, NJ, USA) is currently commercially available in the United States and in a number of other countries. This system involves the location of a pressure-sensitive battery-powered transmitter on the cow’s tailhead, which, when activated by the mounting cow, emits a radio signal, which is picked up by either a receiver or a repeater and relayed to a buffer and ultimately to a personal computer where the information is digitized and stored. The time, date, and duration of each mount along with the identity of each cow are recorded. From this information, the time of heat onset is calculated. The HeatWatch software generates management reports and individual cow reports that can be viewed or printed. HeatWatch classifies a standing heat as a cow having three standing events in a 4-h period. A cow with fewer standing events is recorded as a ‘suspect heat’, and such a cow should be checked for secondary signs of heat prior to deciding to inseminate her. Periodically during the day, the farmer checks the computer for a listing of the cows in heat. The data available suggest that HeatWatch operates with both an efficiency and an accuracy of almost 100% in detecting cows in heat. Heat detection patches

Recently, a number of scratch card type patches have come on the market, including Estrus Alert and ESTROTECTTM. These are affixed to the cow’s tailhead. Friction from mounting activity rubs off the silver coating to reveal a bright-colored patch underneath. These devices show significant potential to improve submission rates in dairy herds.

The consistent drawbacks with all of these systems that require the fixing of a device such as a kamar, beacon, or transponder to the tailhead of a cow are the significant amount of effort required to maintain the devices on the cows and the high loss rates. Similarly, tail-paint or chalking must be reapplied to cows at 7–10 day intervals – again requiring handling and time. Conception Rate This is the third major factor affecting reproductive efficiency. The main factors implicated in causing conception failure or embryo death are normally categorized as those of genetic, physiological, endocrine, and environmental origin. Fertilization rate and early embryo loss rates in Cattle

Based on published data, there is little evidence to suggest that fertilization rates are likely to be different in the modern high-producing cow as compared with lowerproducing cows or heifers particularly under temperate climatic conditions. When adequate numbers of spermatozoa are used from bulls of high fertility and cows are correctly inseminated during or shortly after the end of standing estrus, fertilization rates approaching 90% should be expected. Although fertilization rate is apparently similar in high- and moderate-producing cows and is unlikely to be affected by whether the cows are on pasture or high-input total mixed ration (TMR) diets, the average calving rate to a single service, nevertheless, is significantly lower in high-producing cows than in either low-producing cows or heifers. An embryonic and fetal mortality rate (excluding fertilization failure) of 40% is calculated for moderate-producing cows based on a fertilization rate of 90% and an average calving rate of 55%, with an estimated 70–80% of the loss being sustained between day 8 and 16 after insemination. The comparative figure for high-producing dairy cows, based on a fertilization rate of 90% and a calving rate of 40%, would be 56%. Pattern of early embryo loss

Based on published literature, there is some evidence that the pattern of early embryo death in the modern highproducing cow may be different from that observed in heifers and lower-yielding dairy cows. The extent of early embryo loss appears to be larger in the modern highproducing dairy cows, with a much higher proportion of the embryos dying before day 7 following insemination. The expected outcome of 100 inseminations of BritishFriesian and Holstein-Friesian cows is summarized in Figure 2. Because fertilization rate is close to 100%, conception failure is almost synonymous with embryo and fetal loss.

Reproduction, Events and Management | Mating Management: Fertility British Friesian 1980

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Holstein Friesian 2009 Late embryo mortality

7%

Calving 55%

7% Early embryo death 28%

Early embryo death 43%

10% %%

Calving 40%

10% Fertilization failure

With the advent of ultrasound scanning, it has been comparatively easier to accurately establish the extent and timing of late embryo/fetal mortality. A recent study by the Teagasc laboratory, Galway, Ireland, quantified the extent and pattern of embryo/fetal loss from days 28 to 84 of gestation in 1046 lactating dairy cows and 162 dairy heifers managed on pasturebased systems of milk production. The overall embryo/fetal loss rates between days 28 and 84 of gestation were similar for cows (7.2%) producing on average 7247 kg of milk and heifers (6.1%), and the pattern of loss over this period was also similar for cows and heifers. Almost half (47.5%) of the total recorded loss occurred between days 28 and 42 of gestation. There was no significant association between the level of milk production or milk energy output measured up to day 120 of lactation, milk fat concentration, milk protein concentration, or milk lactose concentration and the late embryo/fetal loss rate. The extent and pattern of embryo/fetal loss were not related to either the cow’s or the cow sire’s genetic merit. The author does acknowledge that the extent of late embryo/fetal mortality recorded in the Irish pasture-based studies is much lower than that reported for some US-based studies. However, a clear explanation for the reported differences is not apparent but may be related to the level of milk production, ambient temperature, and/or the breeding of cows following various Ovsynch-based protocols in the United States. Progesterone during the cycle immediately prior to insemination and embryo survival rate

Data from a recent study conducted by the Teagasc laboratory, Galway, Ireland, clearly show that there is a positive linear association between the concentrations of progesterone on the day of PGF-2-induced luteolysis and the subsequent embryo survival rate (Figure 3). Following a literature review, it was concluded that the most probable effect of low concentrations of

Probability of embryo survival

Figure 2 Reproductive outcomes in British-Friesian vs. Holstein-Friesian cows.

1 0.8 0.6 0.4 0.2 0 1

2 3 4 5 6 Plasma progesterone (ng ml–1)

7

Figure 3 Relationship between plasma concentrations of progesterone on day of induced luteolysis and subsequent embryo survival rate.

progesterone in the cycle preceding estrus on subsequent embryo survival rate is preterm oocyte maturation, which subsequently compromises its ability to continue normal embryo development after its fertilization. Post insemination progesterone and embryo survival rate

Recent studies by the Teagasc laboratory, Galway, Ireland, that have employed logistic regression techniques to model the relationship between the binomially distributed dependent variable (conception/embryo survival rate; yes or no) and the continuously distributed independent variable (progesterone) have established a relationship between circulating progesterone and embryo survival rate. In a study by Stronge et al. (Figure 4) there was a positive linear relationship between milk concentrations of progesterone on days 5, 6, and 7 post insemination and the embryo survival rate, and a quadratic relationship between the rate of change in concentrations of progesterone between days 4 and 7 and the embryo survival rate. Further analysis of this data set reveals that 75, 72, and 56% of dairy cows had concentrations of progesterone that were optimal for conception on days 5, 6, and 7 post insemination, respectively. There is evidence that progesterone supplementation of dairy cows having low endogenous

17–18

15–16

13–14

9–10

7–8

5–6

3–4

11–12

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 >8

7–8

6–7

5–6

4–5

3–4

2–3

1–2

Δ Day 4–7

(∩) Probability of embryo survival

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

Day66 Day

<2

100 90 80 70 60 50 40 30 20 10 0

21–22

19–20

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

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10–11 17–18

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7–8

Day77 Day

5–6

100 90 80 70 60 50 40 30 20 10 0

0–1

100 90 80 70 60 50 40 30 20 10 0

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0–1

Day55 Day

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

<0

100 90 80 70 60 50 40 30 20 10 0

<4

(

) Embryo survival (%)

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Milk progesterone concentration (ng ml–1) Figure 4 Relationship between milk concentrations of progesterone on day 5, 6, and 7 after AI and subsequent embryo survival rate in lactating dairy cows. Reproduced with permission from Stronge AJH, Sreenan JM, Diskin MG, Mee JF, Kenny DA, and Morris DG (2005) Post-insemination milk progesterone concentration and embryo survival in dairy cows. Theriogenology 64: 1212–1224.

concentrations of progesterone, and consequently at risk of suffering embryo death, will have improved embryo survival rates. A series of studies with dairy cows at the University of Wisconsin have shown that peripheral concentrations of both progesterone and estradiol are lowered by increased plane of feed intake owing to increased metabolic clearance rate (MCR) of the steroids, which is related to liver blood flow (LBF). From these studies, it would appear that LBF is elevated in high-producing lactating dairy cows and this in turn would result in a lowering of peripheral concentrations of progesterone thus increasing the risk of embryo death. The reduced progesterone effect may retard the growth and development rate of the embryo by hampering uterine secretion of proteins and growth factors essential for early embryo development. Interferon-, the embryonic signal required for the maintenance of the corpus luteum and the estalishment of pregnancy, has also been shown to be positively correlated with progesterone. Uterine expression of the mRNA for progesterone receptor and estradiol receptor and of the retinol-binding protein mRNA are all sensitive to changes in peripheral concentrations of progesterone during the first week after AI.

Nutrition–Energy Balance Over the past three decades, intensive genetic selection for milk yield has increased the differences between feed intake potential and milk yield potential. This has resulted in dairy cows that have a greater predisposition for mobilizing body reserves and for NEB. It is also clear that even under optimal grazing conditions total DMI is lower than when cows are fed maize-based TMR diets. A pasture DMI of 3.4–3.6% of body weight has been recorded for early-lactation cows grazing high-quality pasture compared to 3.9–4.2% of body weight for cows fed a nutritionally balanced TMR. From this, it is clear that under optimal grazing conditions the actual DMI of cows is significantly lower than the cows’ potential intake, and this is likely to have implications for EB status and subsequent fertility in early lactation, particularly for cows with a high genetic potential for milk production. Energy balance during the early postpartum period and subsequent conception rate

The relationships between EB, DMI, and peripheral concentrations of IGF-I measured during the first 28 days of lactation and subsequent conception rate have recently been explored in a number of Teagasc studies. All three variables were positively associated with first-service

(a)

Probability of conception to 1st service

Reproduction, Events and Management | Mating Management: Fertility

1.0

Intake

0.8 0.6 0.4 0.2 0.0

Probability of conception to 1st service

10

(b)

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1.0

12

14 16 18 20 Average daily UFL intake

22

Energy balance

0.8 0.6 0.4 0.2 0.0

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(c)

2 –8 –6 –4 –2 0 Average daily energy balance UFLs per day 1.0

4

IGF-I

0.8 0.6 0.4 0.2 0.0 2

4

6 8 10 12 14 Plasma concentration of IGF-I

16

18

Figure 5 Relationships between (a) average daily intake (UFL day1), (b) average daily EB (UFL day1), and (c) plasma concentration of IGF-I during the first 28 days of lactation and probability of conception rate to first service in dairy cows. Reproduced with permission from Patton J, Kenny DA, Mee JF, et al. (2006) Effect of milking frequency and diet on milk production, energy balance, and reproduction in dairy cows. Journal of Dairy Science 89: 1478–1487.

conception rate, and the results are presented in Figure 5. This is a particularly interesting observation and suggests that there may be long-term carryover effects of nutrition/EB on conception rate. It has also been hypothesized that follicles exposed to adverse conditions such as a negative EB during their initial stages of growth would have impaired development resulting in the production of inferior quality oocytes and dysfunctional corpora lutea. The results of this study strongly emphasize the importance of maximizing feed intake and minimizing NEB in the immediate postcalving period. Energy balance at around the time of insemination and subsequent conception rate

It is clear that DMI is lower for cows grazing pastures than for cows fed maize-based TMR diets. Supplementation of dairy cows at pasture with concentrates increases the total DMI, but its effects on conception rate are equivocal. Following a review of a

number of experiments that examined the effects of supplementation on conception rate, Diskin et al. (2008) concluded that supplementation had little effect on conception rate but that withdrawal of the supplementation during the breeding period may be counterproductive to conception rate. Only a small proportion of the additional feed intake achieved by concentrate supplementation is partitioned toward an improvement in EB, with >80% supporting increased milk production. This clearly highlights the difficulty that improving the EB of the modern dairy cow presents at this stage of lactation when grazed grass is the predominant component of the diet. Based on the Wisconsin study, it is reasonable to hypothesize that the increased milk production resulting from concentrate supplementation may well be associated with a further increase in hepatic blood flow resulting in increased metabolism of progesterone and consequently in lowering of the peripheral concentrations of progesterone, thus predisposing cows to greater risk of embryo death.

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Effect of sudden reductions in feed intake on conception rate

Studies by the Teagasc laboratory, Galway, Ireland, show that sudden reductions in DMI at around the time of insemination adversely affect embryo survival in heifers. When energy intake was reduced from a high level of twice their maintenance requirement to 0.8 times maintenance for 2 weeks immediately after AI, embryo survival rate in heifers was consistently <40%. When heifers were either provided with a constant level of feed intake or changed from a low to a higher level of feed intake, embryo survival was consistently high at 65–71%. In one study where heifers were used, there was no indication of any association between energy intake and systemic progesterone concentration. Unlike the situation in sheep and pigs, there was no change in systemic progesterone following either an increase or a reduction in energy intake. Changes in progesterone metabolism may have been balanced by changes in progesterone production.

of insemination site and inseminator on conception rate. For some inseminators, there was a significant increase (up to þ percentage points) on conception rates following cornual insemination, whereas for others there was no effect. A retrospective analysis of all the data showed that there was an inverse relationship between the improvement in conception rate and conception rate following uterine body insemination. The largest improvements in conception rates were recorded by inseminators with the lowest conception rate following body insemination. These results suggest that conception rates could be improved for individual inseminators by adopting the practice of placing half of the inseminate beyond the curvature of each uterine horn as opposed to body insemination, which is the normal practice. It is clear from many studies that placement of the inseminate in the cervix results in significantly lower conception rates. Therefore, it is critical to at least ensure that the inseminate is placed in uterine body, and for skilled and experienced inseminators, it would appear beneficial to place half of the inseminate in each uterine horn.

Protein nutrition and conception rate

Dairy cows at pasture frequently ingest high quantities of protein, often with a high proportion of the ingested protein being rapidly degradable in the rumen. The effects of high intakes of crude protein on conception rate are equivocal. For example, US data have shown that high-protein intake reduces uterine pH, which has been hypothesized to have a detrimental effect on either the gametes or the developing embryo. High-protein diets elevate plasma urea nitrogen (PUN) levels. PUN in excess of 19 mg dl1 has been associated with a 20% depression in conception rate in dairy cows. However, in an extensive range of studies by the Teagasc laboratory, Galway, Ireland, using beef heifers in positive EB, no effect of a high crude-protein intake on conception in heifers was recorded, irrespective of whether the crude protein was derived from highly nitrogen-fertilized grazed grass or from added urea to a silage-based diet. Furthermore, a retrospective analysis of the data failed to record any association between peripheral concentrations of urea and embryo survival, notwithstanding peripheral concentrations of urea having been elevated up to 25 mmol l1. It is concluded that elevated peripheral concentrations of urea per se are not detrimental to embryo survival. However, it needs to be clarified whether the observed adverse effects of urea on embryo survival are dependent on the energy status of the animal. Insemination technique

The reported effects of the site of placement of semen within the uterus on conception rate are equivocal. In a recent study by the Teagasc laboratory, Galway, Ireland, involving 3546 dairy cows in 51 herds and 8 inseminators, Diskin et al. (2005) recorded a significant effect (P < 0.02)

Time of insemination

Results from a recent large-scale study that utilized the HeatWatch system to detect the onset of standing heat concluded that conception rates were optimum when dairy cows were inseminated 4–16 h after heat onset. Insemination later than 16 h after heat onset results in significantly lower conception rates. However, in most instances the time of heat onset is not accurately determined, and in such situations once-daily AI for cows observed in standing heat is equally effective as inseminating cows in accordance with the long-established a.m.–p.m. guidelines. Calving difficulty

Calving difficulty, besides affecting calf and cow mortality and the milk yield, also decreases cow rebreeding performance. Teagasc data clearly show that as the severity of calving difficulty increases, conception rate to the first and to all services combined also decreases (Figure 6). This reduction in conception rate is owing to the abnormalities directly arising from calving difficulty, including delayed uterine involution and increased uterine infection, damage to the reproductive tract, and the development of uterine and ovarian adhesions. Furthermore, the interval to first heat is often extended after a difficult calving. For optimal reproductive performance, calving difficulty must be minimized. Two factors that greatly influence the incidence of calving difficulty are the age of the cow and the breed of the sire. The incidence of calving difficulty is 4–8 times higher in first-calving heifers than in mature cows and about twice as high in second calvers as in mature cows. The breed of the sire and indeed the individual sire within a breed should be carefully selected for use on

Reproduction, Events and Management | Mating Management: Fertility

Conception rate (%)

100

CR to 1st service CR to all services

80 60 40 20 0 1

3 4 2 Calving difficulty score

483

improvement in conception rate often arises following the introduction of a bull. This apparent improvement is likely to be because of cows being mated at a longer postpartum interval and/or because of inaccuracies in heat detection being eliminated. Where heat detection is accurate, and when insemination is timed and carried out correctly, conception rate is similar following either AI or natural service.

5

Figure 6 Relationship between calving difficulty score and conception rate to first services and to all services combined. Difficulty ranges from score 1 (unassisted birth) to score 5 (severe difficulty requiring mechanical extraction of the calf).

heifers and on young cows to minimize the risk of calving difficulty and therefore of subsequent infertility. In some countries, there is a practice of breeding latecalving dairy cows to beef sires. The combined effect of the longer gestation and the increased incidence of calving difficulty makes it even more difficult to achieve a 365-day calving interval in such cows. The wisdom of this practice, especially if the objective is to optimize reproductive performance, is therefore questionable. Bull fertility

Bull reproductive performance is influenced by several factors including testicular development, semen quality, libido, mating ability, and physical soundness. On farms using natural service, the level of bull fertility can have a major impact on pregnancy rate and calving spread. Published data suggest that up to 5% of bulls in natural service may be completely infertile and that a further 30% may be subfertile. Unfortunately, if a bull is infertile, it is not usually discovered until at least one repeat interval has elapsed since joining the herd. Although a veterinary examination combined with a semen evaluation 1 month before the start of the breeding season will help to identify the majority of infertile bulls, it will not identify subfertile bulls. Furthermore, it should be realized that a bull may not remain fertile for all of his working life or even throughout a single mating season. For example, a bull that is ill with a raised temperature for a number of days may have a period of temporary infertility 40–60 days later. Similarly, injury to the penis, sheath, or prepuce, though not necessarily affecting mounting behavior, can prevent mating. Therefore, the bull should be observed regularly for serving ability, and all mating dates recorded. Such recording will help identify infertile or subfertile bulls at an early stage. AI versus natural service

AI is often criticized on the grounds that conception rate is lower than when following natural service. Apparent

Relative Importance of Heat Detection Efficiency and Conception Rate Once estrous cycles have resumed postcalving, then it is the product of heat detection efficiency and conception rate that determines the overall herd reproductive efficiency (Table 2). The clear message from Table 2 is that low or relatively low conception rates can be compensated for by improving heat detection efficiency. Practical and easily adoptable technologies are available to improved heat detection efficiency.

Conclusion It is well established that reproductive performance is critically important, particularly in seasonally calving herds, to maintain compact calving close to the onset of the grazing season. Even though the modern high-genetic merit Holstein-type dairy cow selected solely for milk production is biologically more efficient at converting forage, irrespective of source, to milk, their sustainability in predominately pasture-based systems of production is questionable given their low fertility. Therefore, it is important to develop appropriate supplementation strategies, probably beginning before parturition, to improve fertility in dairy cows on pasture-based systems of production. In the medium to long term it should be possible to develop more balanced breeding strategies with greater emphasis on fertility- and feed intake-related traits, which are critically important to pasture-based systems of milk Table 2 The effect of different heat detection (submission) and conception rates on the percentage of the herd that is pregnant at 90 days after onset of breeding season Conception rate (%)

Heat detection rate (%)

90 70 50 40

60

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484 Reproduction, Events and Management | Mating Management: Fertility

production. It is clear that sufficient genetic variability exists within the Holstein breed for important fertility and feed intake traits. Alternatively, strains of cows derived from more balanced breeding objectives, such as the New Zealand Friesian, or alternative dairy breeds such as the Jersey or Norwegian Red could also be utilized in such production systems. It is now becoming increasingly clear that EB during the immediate postcalving period affects both the onset of estrous cycles postcalving and the subsequent conception rates. Development of feeding strategies that increase intake without proportionally increasing milk yield, thereby improving EB, is important. Paying more attention to other factors that are predominately under management control, particularly heat detection, can significantly offset some consequences of inherently low fertility traits that exist with the modern dairy cow. Improving heat detection efficiency by 12–15% has the equivalent effect of increasing conception rate by 10 percentage points. Based on numerous published reports, it can be concluded that there is scope in most herds to improve heat detection efficiency by at least 15 percentage points by adopting well-described practices. Conception rate is affected by a range of both cow and management-related factors. Producers should ensure that cows presented for insemination are in heat and are properly inseminated with high-fertility semen. Sudden reductions in feed intake during the breeding season should be avoided.

Further Reading Beam SW and Butler WR (1999) Effects of energy balance on follicular development and first ovulation in postpartum dairy cows. Journal of Reproduction and Fertility Supplement 54: 411–424. Butler WR (1998) Review, effect of protein nutrition on ovarian and uterine physiology in dairy cattle. Journal of Dairy Science 81: 2533–2539. Diskin MG, Kenny DA, Dunne L, and Sreenan JM (2002) Systemic progesterone pre and post AI and early embryo survival in cattle. Proceedings of the Agricultural Research Forum, p. 27. Tullamore, Ireland.

Diskin MG, Mackey DR, Roche JF, and Sreenan JM (2003) Effects of nutrition and metabolic status on circulating hormones and ovarian follicle development in cattle. Animal Reproduction Science 78: 345–370. Diskin MG and Morris DG (2008) Embryonic and early foetal losses in cattle and other ruminants. Reproduction in Domestic Animals 43(2): 260–267. Diskin MG, Murphy JJ, and Sreenan JM (2006) Embryo survival in dairy cows managed under pastoral conditions. Animal Reproduction Science 96: 297–311. Diskin MG, Pursley R, Kenny DA, Mee JF, Corridan D, and Sreenan JM (2005) The effect of deep intrauterine placement of semen on conception rates in dairy cows. Proceedings of the Agricultural Research Forum, p. 29. Tullamore, Ireland. Diskin MG and Sreenan JM (2000) Expression and detection of oestrus in cattle. Reproduction Nutrition Development 40: 481–491. Dunne LD, Diskin MG, Boland MP, O’Farrell KJ, and Sreenan JM (1999) The effects of pre-and post-insemination plane of nutrition on embryo survival in beef heifers. Animal Science 69: 411–417. Gong JG, Lee WJ, Garnsworthy PC, and Webb R (2002) Effect of dietary-induced increases in circulating insulin concentrations during the early postpartum period on reproductive function in dairy cows. Reproduction 123: 419–427. Macmillan KL and Curnow RJ (1977) Tail painting – A simple form of oestrus detection in New Zealand dairy herds. New Zealand Journal of Experimental Agriculture 5: 357–361. McNeill RE, Sreenan JM, Diskin MG, et al. (2006) Effect of progesterone concentration on the expression of progesterone-responsive genes in the bovine endometrium during the early luteal phase. Reproduction, Fertility and Development 18: 573–583. Nebel RL, Walker WL, Kosek CL, and Pandolfi SM (1995) Integration of an electronic pressure sensing system for the detection of estrus into daily reproductive management. Journal of Dairy Science 78(1): 225 (Abstract). Patton J, Kenny DA, Mee JF, et al. (2006) Effect of milking frequency and diet on milk production, energy balance, and reproduction in dairy cows. Journal of Dairy Science 89: 1478–1487. Sangsritavong S, Combs DK, Sartori RF, Armentano LE, and Wiltbank MC (2002) High feed intake increases liver blood flow and metabolism of progesterone and estradiol 17 in dairy cattle. Journal of Dairy Science 85: 2831–2842. Silke V, Diskin MG, Kenny DA, et al. (2001) Extent, pattern and factors associated with late embryonic loss in dairy cows. Animal Reproduction Science 15: 1–12. Stevenson JS (2001) A review of oestrous behaviour and detection in dairy cows. In: Diskin MG (ed.) Proceedings of the BSAS Occasional Publication No. 26. Fertility in the High-Producing Dairy Cow, Vol. 1, pp. 43–62. Galway, Ireland. Stronge AJH, Sreenan JM, Diskin MG, Mee JF, Kenny DA, and Morris DG (2005) Post-insemination milk progesterone concentration and embryo survival in dairy cows. Theriogenology 64: 1212–1224.