Elsevier

Theriogenology

Volume 77, Issue 6, 1 April 2012, Pages 1029-1041
Theriogenology

Review
Factors of a noninfectious nature affecting fertility after artificial insemination in lactating dairy cows. A review

https://doi.org/10.1016/j.theriogenology.2011.10.014Get rights and content

Abstract

After 80 years of the commercial application of artificial insemination (AI) in the cow, the method still has numerous benefits over natural insemination including worldwide gene improvement. The efficiency of insemination depends, among many other factors, on the delivery of an appropriate number of normal spermatozoa to the appropriate reproductive tract site at the appropriate time of estrus. The metabolic clearance of steroid hormones and pregnancy associated glycoproteins and the negative effects of different types of stress related to high milk production makes the high-producing dairy cow a good animal model for addressing factors affecting fertility. Nevertheless, extensive studies have shown a positive link between high milk production in an individual cow and high fertility. When a cow becomes pregnant, the effect of pregnancy loss on its reproductive cycle is also a topic of interest. This paper reviews the factors of a noninfectious nature that affect the fertility of lactating dairy cows following AI. Special attention is paid to factors related to the cow and its environment and to estrus confirmation at insemination. Pregnancy maintenance during the late embryonic/early fetal period is discussed as a critical step. Finally, the use of Doppler ultrasonography is described as an available research tool for improving our current understanding of the health of the genital structures and conceptus.

Introduction

Since the beginning of agriculture, cattle among other ruminants have been highly appreciated because they convert vegetable products into highly palatable and nutritious food. In fact, cattle breeding has played an important role in economic development since the Neolithic [1]. The commercial application of cow artificial insemination (AI) is now entering its 80th year and persists as a powerful method of gene dispersal. Artificial insemination has probably been the greatest technological advance in animal breeding. The main reasons for its success have been genetic gain, disease control, and the cost-effectiveness of insemination compared with natural mating [2]. It has also been the most noteworthy example of the successful integration of both research and widespread application [3]. Developments in AI have been sparked by the intensification of milking systems in dairy farms. Artificial insemination offers many advantages and few disadvantages to the dairy farmer, while difficulties in estrus detection limit the use of AI in beef herds. Thus, it has been the dairy industry that has most successfully made use of the technical advances in AI and semen technology [2].

The efficiency of insemination depends among other factors on the deposition of appropriate numbers of normal spermatozoa at the appropriate site in the reproductive tract at the appropriate time of estrus. The metabolic clearance of steroid hormones, such as 17β-estradiol and progesterone [4], pregnancy-associated glycoproteins [5], and the effects of the different types of stress related to high milk production [6] make the high-producing dairy cow a suitable animal model for addressing the factors that affect fertility. This article reviews the factors of a noninfectious nature that affect the fertility of lactating dairy cows in response to AI. The data presented have been mostly obtained by our research group in work conducted on commercial high-producing Holstein-Friesian dairy herds in northeastern Spain. Special attention is paid to factors related to the cow and its environment and to confirming estrus at insemination. The maintenance of pregnancy during the late embryonic/early fetal period is also discussed as a critical step.

Section snippets

Management factors

In the past few decades, infertility has often been linked to the increasing milk yield of high-producing dairy cattle. Milk production and reproductive efficiency are not well correlated genetically [7] and it is difficult to determine which mechanisms are related to the effect of milk production on fertility. Declining fertility has been generally associated with genetic progress and also with the improvements in nutrition and management practices that have led to a continuous increase in

Environmental factors

The impact of environmental conditions on herds of cattle was already noted by ancient civilizations. “On Airs, Waters and Places” documents that Hippocrates in the 5th century BC observed that cattle raised in the near East were more prolific than European cattle because of the temperate climate. The presence of a bull in the herd can positively affect the expression of estrus and therefore the fertility of dairy cattle [21], whereas poor nutrition or the loss of the body reserves (negative

Site of semen deposition

During mating, the bull deposits several billions of spermatozoa into the anterior vagina. However, because the cervix is a major obstacle for sperm transport, the number of spermatozoa that finally reach the uterine body usually does not exceed 1% [38]. In artificial insemination, semen is generally deposited directly into the uterine body, thus bypassing the cervix and permitting the use of a considerably reduced number of sperm [39]. One of the most significant contributions to the

Confirmation of estrus

Man is no match for a bull at detecting estrus in the cow. Incorrect estrus detection is the most common and expensive cause of failure of AI programs. Cows are often falsely identified as being in estrus and inseminated when conception cannot occur [21]. Inseminating the cow is the final, but by no means least important, step in the process of estrus detection. Although professional inseminators palpate the reproductive tract of numerous cows every day, most are not trained to examine the

Pregnancy loss during the late embryonic/early fetal period

Dairy herds are under ever-increasing pressure to improve their efficiency and primary attention is usually directed toward postpartum reproductive disorders and failure to correctly detect estrus. However, it is also of great interest to understand the effects pregnancy loss may have on the reproductive cycle when a cow is pregnant. Records of losses during the early fetal period are not new. Based on monthly records of nonreturn rates, Kidder et al. [60] estimated in 1952 that approximately

Color Doppler ultrasound-based research

The introduction of ultrasonography for use in large farm animals was a technological breakthrough of the 1980s [138]. Nowadays, B-mode ultrasound is common practice in reproductive programs for high-producing dairy herds, especially for pregnancy diagnosis. However, improvements in the equipment used have generated an information cascade. Given the dynamics of changes in ovarian structures, ultrasound examinations are mainly targeted at diagnosing ovarian disorders in nonpregnant cows. The

Conclusions

Fertility in dairy cattle has been declining over the past decades alongside a rise in milk production. The reasons for the decline in fertility are multifactorial and cannot be solely attributed to the increase in milk production. In effect, by improving nutrition and management practices individual milk production can be positively related to high fertility, whereas heat stress, the bull, and inseminator remain as main factors that negatively affect the fertility of a herd. When assessing the

Acknowledgments

The author thanks Ana Burton for assistance with the English translation and Irina Garcia-Ispierto in revising the draft.

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