Increasing Pregnancy Rate in Beef Cattle by Clitoral Massage During Artificial Insemination

Clitoral massage (stimulation) at the time of artificial insemination (AI) has been reported to increase pregnancy rate in lactating beef cows, but not to increase pregnancy rate in heifers. These reports have been limited to studies conducted at one location in the U.S. (Miles City, Montana), and the efficacy of clitoral massage on AI pregnancy rates of beef cattle at other geographic locations has not been reported. To our knowledge, there are no reports in the literature indicating a negative effect of clitoral stimulation on pregnancy rate of cows. The following experiment was conducted to test the effects of clitoral massage on pregnancy rate to artificial insemination in beef cattle and to define the effects of age, postpartum interval, and technician on pregnancy responses to clitoral massage performed at the time of artificial inseminatio

Germplasm Utilization in Beef Cattle

Heterosis achieved through continuous crossbreeding can be used to increase weight of calf weaned per cow exposed to breeding by 20%. Comprehensive programs of breed characterization have revealed large differences among breeds for most bioeconomic traits. About 55% of the U.S. beef breeding population involving 93% of the farmers and ranchers who produce beef cattle are in production units of 100 or fewer cows. Optimum crossbreeding systems are difficult to adapt in herds that use fewer than four bulls. Further, fluctuation in breed composition between generations in rotational crossbreeding systems can result in considerable variation among both cows and calves in level of performance for major bioeconomic traits unless breeds used in the rotation are similar in performance characteristics. Use of breeds with similar performance characteristics restricts the use that can be made of breed differences in average genetic merit to meet requirements for specific production - marketing situations. The potential of composite breeds as an alternative to continuous crossbreeding for using heterosis and for using genetic differences among breeds to achieve and maintain a more optimum additive genetic (breed) composition needed to be investigated in a comprehensive experiment. The primary objective of this experiment was to estimate the retention of combined individual and maternal heterosis in advanced generations of inter sè mated composite populations established with contributions from either four or five breeds. Retention of initial (F1) heterozygosity after crossing and subsequent random (inter sè) mating within crosses is proportional to (n-1)/n when n breeds contribute equally to the foundation. When breeds used in the foundation of a composite breed do not contribute equally, percentage of mean F1 heterozygosity retained is proportional to (Equation) where Pi is the fraction of each of n contributing breeds to the foundation of a composite breed. This loss of heterozygosity occurs between the F1 and F2 generations, and if inbreeding is avoided, further loss of heterozygosity in inter sè mated populations does not occur. A primary question in this experiment was the extent to which retention of heterosis in composite populations is proportional to retention of heterozygosity

Correction: Archibong, A.E., et al. Effects of Benzo(a)pyrene on Intra-testicular Function in F-344 Rats

We found some errors in Figure 4 in our paper published in the International journal of Environmental Research and Public Health [1].[...

Sexual Aggressiveness in Beef Bulls

Large differences in conception rate during pasture-mating can exist among beef bulls having semen of acceptable quality. Based on data from artificial insemination, we know also that conception rate increases as the number of inseminations increases, and it is probable that conception rate to natural mating increases as number of matings per cow increases. Sexual aggressiveness (libido) is a behavioral factor that can influence the number of matings a bull can achieve and, thus, may influence the conception rate obtained during natural mating. Accurate evaluation of sexual aggressiveness and its relationship to fertility may provide useful information for selecting young beef bulls with high breeding potential. We conducted the following studies to investigate sexual activity in young beef bulls during a series of libido tests and to evaluate the relationship between libido test activity and fertility during natural mating

Effect of Single-Sire and Multiple-Sire Natural Mating on Pregnancy Rate of Beef Cattle

Although artificial insemination (AI) is widely used in dairy cattle, AI has found only limited application in beef cattle. Use of bulls in natural mating programs accounts for more than 95 percent of the pregnancies achieved each year in the U.S. beef cattle industry. Success of such natural mating programs depends on the reproductive capacity and fertility of the individual herd sires used, but very little research on the natural mating fertility of beef bulls has been conducted. Because of the general lack of information on effective techniques for identifying sires with superior fertility, procedures currently used for selecting herd sires for natural mating are based on factors other than reproductive potential and include factors (such as body wt, growth rate, appearance, etc.) that have little relationship to bull fertility. It is not surprising that a large range in pregnancy rate of beef bulls used in single-sire natural mating has been reported, and commercial cattle producers have resorted to using multiple sires in pasture breeding, assuming that more fertile bulls compensate for less fertile bulls within multiple-sire groups. Conflicting reports exist in the available literature, with some results indicating that pregnancy rate may be higher during multiple-sire breeding. Studies using AI indicate that increasing the number of inseminations per estrous female increases pregnancy rate, and that inseminating mixtures of semen from two or more bulls generally increases pregnancy rate. However, it is unknown if increasing the number of services per female or increasing the number of sires servicing each female results in increased pregnancy rate in natural mating programs. This report presents results of a study conducted to determine the effect of number of services on natural-mating pregnancy rate and to investigate the effect of multiple-sire natural mating on pregnancy rate in beef cattle

Testicular Development and Onset of Puberty in Beef Bulls

Selection and management of young beef bulls have been hampered by a lack of information on reproductive development, growth, and puberty. The use of an increasing number of sire breeds in the beef cattle industry has placed additional emphasis on the importance of defining differences in sexual maturation within and among breeds. We conducted the following studies as part of a program designed to characterize reproductive development and puberty in breeds of beef bulls

Scrotal Thermography as a Tool for Predicting Semen Quality and Natural-Mating Fertility in Young Beef Bulls

The scientific literature offers only sparse information on mechanisms controlling reproductive function in beef bulls and indicates that there are very few consistent relationships between the commonly evaluated male reproductive characteristics and variations in natural-mating fertility of beef bulls. Current techniques for evaluating and predicting reproductive potential of bulls are ineffective, and the beef cattle industry selects breeding males on the basis of appearance, growth rate, size, and other factors of little relationship to reproductive potential. Reproductive merit is five times more important economically than is growth performance and at least ten times more important than product quality for the average cow-calf producer. However, little selection pressure for fertility has been applied to beef sires (bulls) in North America because of the relative inaccuracy of methods available for evaluation and prediction of breeding potential and fertility in beef bulls. For example, detailed semen evaluation in groups of yearling (less than 18 mo of age), physically-sound beef bulls rarely eliminates more than 5% as potential breeding sires, yet single-sire mating using bulls from the 95% that passed semen evaluation still results in dramatic variation in sire fertility. Many producers obtain little or no information on the reproductive status of their bulls prior to use in natural-mating programs, and this is particularly true for the use of young breeding bulls (Le., yearlings) in the beef cattle industry. The lack of effective means for selecting males with superior fertility is due primarily to two factors: 1) the lack of information on basic measurable characteristics of male reproduction that are related to sire fertility, and 2) the cost and difficulty of obtaining accurate fertility data on individual sires. Development of valid knowledge of the limiting mechanisms in male reproduction and establishment of effective, reliable techniques for evaluating the characteristics of male reproduction that are related to fertility are prerequisite to improving the productivity of the livestock industry. It is known that thermoregulation in the testes is essential for sperm production. For normal spermatogenesis in the bull, the testes in the scrotum must be maintained at a temperature approximately 5° to 8°F lower than normal body temperature (101°F). Adverse effects of elevated testicular temperature on sperm production, semen quality, and male fertility have been documented for many species of domestic animals. Recently, other researchers have shown that the surface temperature of the scrotum is highly correlated with deep testicular temperature, and that infrared thermograms (images of radiated heat emission) of the scrotal surface provide accurate information about testicular thermoregulation in domestic species. However, the relationships between scrotal thermography (infrared thermography of the scrotal surface) and various aspects of semen quality and fertility remain unknown in the beef bull. The objectives of the following study were to evaluate the potential usefulness of scrotal thermography as a tool for predicting the natural-mating fertility of yearling beef bulls, and to obtain standard breeding soundness information for comparison to scrotal thermography and bull fertility data

Puberty Occurs at the Same Testis Size in Both \u3ci\u3eBos taurus\u3c/i\u3e and \u3ci\u3eBos indicus\u3c/i\u3e Crossbred Beef Bulls

An increasing number of Bos indicus-blood bulls are being used in crossbreeding programs for commercial beef production in the U.S., but there is little information available on pubertal development, sperm production and semen quality for young bulls of this type. Puberty in young Bos taurus bulls has been defined in a variety of ways (e.g., first ability to serve, first sperm production, first ejaculation of motile sperm, etc.), but all of these criteria are costly and labor-intensive to determine. We have shown previously (Lunstra et al., 1978) that, among young Bos taurus beef bulls of various breeds reared in the same environmental and management conditions, puberty occurs when a scrotal circumference of 28 cm is achieved, regardless of large differences in body wt and age at puberty among and within different breeds of bulls. In that study, puberty was defined as the age at which a bull first produced an ejaculate containing ≥ 50 million sperm with ≥ 10% progressive motility. In addition, we (Lunstra and Echternkamp, 1982) and other researchers have shown that the major characteristics of semen quality improve linearly during the first 12 to 16 wk after reaching this criterion of puberty, and that these improvements in semen quality are highly correlated (r=.44 to .75) with the steady linear increase in scrotal circumference that occurs during this post-pubertal timeframe in Bos taurus beef bulls. Thus, scrotal circumference appears to be an accurate and easily-obtained measurement that provides a relatively reliable predictor of age at puberty in young Bos taurus beef bulls. However, similar studies on Bos indicus-blood bulls are needed before this relationship can be assessed or confirmed in zebu-blood bulls. It is not reasonable to attempt to use young bulls for natural mating or semen processing immediately after reaching this initial criterion of puberty (i.e., first ejaculate containing ≥ 50 million sperm with ≥ 10% progressive motility). It does not become economically feasible to use young beef bulls for collection and processing of semen for artificial insemination until ejaculates containing ≥ 500 million sperm with ≥ 50% progressive motility can be produced, and this is also a reasonable criterion for young bulls to reach before being used for natural mating. However, no studies using this more stringent semen criterion of puberty have been conducted in either Bos taurus or Bos indicus bulls. Because selection and use of superior sires at the youngest possible age is desired for natural mating and artificial insemination, further investigations of the relationships between postpubertal changes in testis size and aspects of semen quality are needed in young Bos taurus and Bos indicus beef bulls. The following study was conducted to determine the age at which young Bos taurus and Bos indicus crossbred beef bulls reach this revised criterion of puberty (i.e., first ejaculate containing ≥ 500 million sperm with ≥ 50% progressive motility), and to evaluate interrelationships between pubertal age, testis size, and body wt in these specietypes of beef bulls

Heritability Estimates and Adjustment Factors for Yearling Testicular Size in Different Breeds of Beef Bulls

Little information is available on breed differences and variation in testicular development of young beef bulls. Larger testis size in young bulls is favorably correlated with sperm output, age at puberty, mature testicular size, and pregnancy rate. If testicular size is to be considered in selection programs for young sires, the breed differences, heritabilities, and relationships of testicular measurements to age and body weight must be established for young beef bulls. The objectives of this study were to measure and define breed differences and variations in testicular size of yearling beef bulls, determine the heritability of yearling testicular size, and to examine the relationships between testicular size and age, growth traits, and age-of-dam effects in yearling beef bulls

Mating and Grazing Behavior of Low and High Serving Capacity Beef Bulls During Average and Heavy Mating Loads at Pasture

Although artificial insemination is widely used in dairy cattle, it has found only limited application in beef cattle. Use of bulls in natural mating programs accounts for over 90% of the pregnancies achieved each year in the U.S. beef cattle industry, and a large percentage of the beef bulls used for natural mating are purchased as yearlings. Many of these yearling bulls undergo a breeding soundness examination prior to sale or the breeding season. This involves visual and manual examination of the genital system as well as assessment of semen, which is usually collected by electroejaculation. However, sex drive and mating ability, which are essential for the delivery of viable spermatozoa and impregnation of females, are not commonly measured. Among beef bulls used for single-sire mating, large ranges in pregnancy rates have been reported, and only low correlations were found between pregnancy rates and semen characteristics. These differences may be potentially explained by differences in the levels of serving capacity (SC) between bulls. Several procedures for testing SC have been used; however, studies investigating the relationship between bulls\u27 SC and herd fertility are inconclusive, with some researchers finding no relationship and other researchers reporting SC test results to be a good predictor of bull fertility. These studies differed in testing procedures used for measuring SC. Thus, differences in the findings may lie in the procedures used for tests or may be due to differences in bull-to-female ratios used when measuring fertility. At present, there is a lack of research relating the SC of yearling beef bulls in a standardized test with their behavior and fertility under pasture mating conditions. The first objective of this study was to evaluate the sexual and grazing behavior of low and high SC yearling bulls when placed with naturally cycling and estrus synchronized cows under pasture mating conditions during bot