Heritability estimate and genetic correlations of reproductive features in Nellore bulls, offspring of super precocious, precocious and normal cows under extensive farming conditions

The present work aimed to estimate heritability and genetic correlations of reproductive features of Nellore bulls, offspring of mothers classified as superprecocious (M1), precocious (M2) and normal (M3). Twenty one thousand hundred and eighty-six animals with average age of 21.29 months were used, evaluated through the breeding soundness evaluation from 1999 to 2008. The breeding soundness features included physical semen evaluation (progressive sperm motility and sperm vigour), semen morphology (major, minor and total sperm defects), scrotal circumference (SC), testicular volume (TV) and SC at 18 months of age (SC18). The components of variance, heritability and genetic correlations for and between the features were estimated simultaneously by restricted maximum likelihood, with the use of the vce software system vs 6. The heritability estimates were high for SC18, SC and TV (0.43, 0.63 and 0.54; 0.45, 0.45 and 0.44; 0.42, 0.45 and 0.41, respectively for the categories of mothers M1, M2 and M3) and low for physical and morphological semen aspects. The genetic correlations between SC18 and SC were high, as well as between these variables with TV. High and positive genetic correlations were recorded among SC18, SC and TV with the physical aspects of the semen, although no favourable association was verified with the morphological aspects, for the three categories of mothers. It can be concluded that the mother's sexual precocity did not affect the heritability of their offspring reproduction features.     

Breeding Soundness Evaluation and Semen Analysis for Predicting Bull Fertility

Bull fertility is influenced by numerous factors. Although 20–40% of bulls in an unselected population may have reduced fertility, few are completely sterile. Breeding soundness refers to a bull's ability to get cows pregnant. A standard breeding soundness evaluation identifies bulls with substantial deficits in fertility, but does not consistently identify sub-fertile bulls. In this regard, the use of frozen-thawed semen (from bulls in commercial AI centres) that meets minimum quality standards can result in pregnancy rates that differ by 20–25 percentage points. Although no single diagnostic test can accurately predict variations in fertility among bulls that are producing apparently normal semen, recent studies suggested that a combination of laboratory tests were predictive of fertility. This review is focused on recent developments in prediction of bull fertility, based on assessments at the molecular, cellular and whole-animal levels.     

Associations between sperm abnormalities, breed, age, and scrotal circumference in beef bulls

The objectives of this study were to determine the associations of breed, age, and scrotal circumference (SC), and their interaction, on the prevalence of sperm abnormalities in beef bulls in Alberta, Canada, and the percentage of satisfactory potential breeders identified during breeding soundness examination solely due to normal sperm morphology. Eosin-nigrosin stained semen smears and evaluation reports of 1642 bull breeding soundness evaluations were procured from 6 veterinary clinics in Alberta. Sperm morphology was determined for at least 100 sperm per bull. The most common defects were detached head [4.86% ± 5.71%; mean ± standard deviation (s)], distal midpiece reflex (6.19% ± 9.13%), and bent tail (1.01% ± 1.54%). Although breed, age, and SC did not significantly affect the prevalence of head or midpiece defects, morphologically normal or abnormal sperm, tail defects were more prevalent in Angus and Hereford bulls compared with other breeds. Overall, solely on the basis of sperm morphology, 1363 (83.0%) bulls were classified as satisfactory potential breeders and the remainder 279 (17.0%) as unsatisfactory (> 30% abnormal sperm, > 20% defective heads, or both). Although not significantly different, the breed with the highest percentage of satisfactory potential breeders was Limousin (90.6%) and the lowest was Hereford (78.8%). That 17% of bulls subjected to breeding soundness evaluation were designated as unsatisfactory solely on the basis of sperm morphology highlights its importance.     

Seminal Leucocytary Profile in Beef Bulls

Despite evidences that seminal leucocytes could affect semen quality, references for the frequency and concentration of these cells in bulls are not available. The aim of this study was to determine the normal concentration of leucocytes in beef bulls and to correlate this characteristic with semen quality. First, 57 bulls from artificial insemination centres were evaluated to obtain the normal leucocytary profile values. Next, 382 bulls were subjected to breeding soundness evaluation. The average concentration of leucocytes in bovine semen was 4.73 × 10⁶/ml. Unsatisfactory bulls showed a higher number of leucocytes/field than that in the satisfactory ones. Logistic regression analysis revealed that the unsatisfactory bulls showed 6.5‐fold more chances of having higher leucocyte counts than satisfactory ones. Values of up to 1 leucocyte/field in the bull ejaculate are considered physiologically normal, whereas >5 leucocytes/field is associated with poor semen quality.     

Mycoplasma mycoides subsp. mycoides SC identification by PCR in sperm of seminal vesiculitis-affected bulls.

In this study, by using the polymerase chain reaction (PCR) diagnosis for the detection and identification of Mycoplasma, we investigated mycoplasmas contaminating the semen of yearling bulls affected by seminal vesiculitis. The bulls presented neither subclinical nor clinical contagious bovine pleuropneumonia signs and the complement fixation test for specific antibodies was negative. Furthermore, we have investigated mycoplasmas isolated from semen of healthy breeding bulls of several breeds and origins, which routinely underwent breeding soundness examinations and presented no clinical signs of seminal vesiculitis. We were able to demonstrate mycoplasma infection in all tested samples by i) growth on mycoplasma-specific media and ii) a PCR-based method using a mycoplasma-specific MGSO/GPO1 primer set to amplify the 16S fragment rDNA. In addition, the identification of Mycoplasma species was made by PCR using the MSC1/MSC2 primer set that specifically amplifies M. mycoides subsp. mycoides SC or the MM450/MM451 primer set followed by AsnI digestion analysis in order to identify M. mycoides subsp. mycoides LC. The data presented herein clearly show that M. mycoides subsp. mycoides SC infection was associated with seminal vesiculitis while M. mycoides subsp. mycoides LC was only found in bull semen from healthy control animals. Our findings confirm that the M. mycoides subsp. mycoides SC is shed in the sperm making the ejaculate a valuable biological sample for the isolation of these bacteria from serologically negative animals. Although the pathogenic role of M. bovigenitalium in bull seminal vesiculitis has been established, our clinical findings, semen characteristics, microbiological and bacterial genomic analysis strongly suggest that M. mycoides subsp. mycoides SC may contribute to induce vesicular adenitis in the bull.     

The fertility of bulls born twin to freemartins: a review.

Evidence for the existence of XX germ cells in the testes of bulls born twin to females is reviewed. It is concluded that there is probably no shift in the sex ratio of the offspring in favour of females. Reports on the fertility of such bulls are reviewed. It is suggested that, provided the semen is normal, there is no reason why such a bull should not be used for breeding purposes.     

夏南横交种公牛生产性能研究

通过对8头采精夏南横交种公牛和18头本交夏南横交种公牛生产情况调查,夏南横交种公牛具有早熟性,无论是生产冻精还是本交,18月龄的种公牛均可投入生产,夏南横交种公牛生产性能良好,本交年均配种量可达264头,可制冻精细管20 175剂,配种数量、冻精产量、首配准胎率具有明显季节性,以春季最高,夏季最低。     

Artificial insemination outcomes in beef females using bovine sperm with a detectable fertility-associated antigen

In this study, semen samples from 25 bulls that had passed a breeding soundness evaluation were analyzed for the presence or absence of a 31-kDa protein, known as fertility-associated antigen (FAA), on spermatozoal membranes. Eighteen bulls had FAA on sperm (FAA-positive) and seven were devoid of FAA on sperm (FAA-negative). A single ejaculate from each bull was extended and frozen with 25 to 30 x 10(6) sperm in .5-mL straws. Crossbred replacement heifers (n = 865) were estrus-synchronized and artificially inseminated either at timed AI or 12 h after they were detected in estrus. Mature cows (n = 285) were inseminated 12 h after they were detected in estrus during a 45-d AI period. Pregnancy rates (pooled) to first AI service for females (n = 764) inseminated with FAA-positive sperm were 65.6% and were 49.7% for females (n = 386) inseminated with FAA-negative sperm (P < .005). Among the estrus-synchronized replacement heifers, pregnancy rates to synchronized AI service for heifers (n = 550) inseminated with FAA-positive sperm were 62% and were 45.7% for heifers (n = 315) inseminated with FAA-negative sperm (P < .005). These data indicate that pregnancy rates to first AI service at spontaneous and synchronized estrus are higher when using semen from bulls with detectable FAA on spermatozoal membranes compared to semen from bulls devoid of FAA on membranes. Fertility-associated antigen is an important determinant for fertility potential of sperm from bulls to be used in AI breeding programs.     

法系夏洛来牛的引进繁育(上)

1986年后我站相继从国内、外引进法国夏洛来牛9头,在4头母牛基础上开始纯繁自育发展牛群。截至2003年6月,繁殖犊牛87头,存栏62头,其中成年公、母牛45头。4岁龄纯繁公、母牛平均体尺体重与同龄原种牛比,均有所提高。纯繁公牛20月龄采精调教,平均利用年限为61.73月龄,生产冻精71 074剂,淘汰年龄平均为84.6月龄。母牛平均初孕年龄为25.16月龄,平均淘汰年龄为95.71月龄,终生产犊4.8头。为社会创造巨大经济效益。     

Distribution of Mycobacterium avium subsp. paratuberculosis in organs of naturally infected bull-calves and breeding bulls

Paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis, has particular importance in cattle due to the resulting chronic diarrhoea, weight loss, decreased production, infertility and eventual death. While faecal oral route of infection is generally recognised, reports about semen-derived infection are rare. The objective of this work was to assess whether M.a. paratuberculosis may disseminate from the gastrointestinal tract to reproductive organs, and compare this event between naturally infected bull-calves and breeding bulls. Ten bull-calves, aged 6-28 weeks and four breeding bulls were tested by serology, faecal and tissue culture, IS900 PCR and RFLP. In seven bull-calves M.a. paratuberculosis was isolated predominantly from mesenteric lymph nodes (75%); isolates from mucosa of the intestine constituted 25%. In three breeding bulls, M.a. paratuberculosis was isolated both from intestinal mucosa and mesenteric lymph nodes. Head and mediastinal lymph nodes, liver, spleen and semen of bull no. 1 (Holstein-Friesian); testes and epididymis of bull no. 2 (Piemonte); testes, epididymides and seminal vesicle of bull No. 3 (Hereford); and seminal vesicle of bull No. 4 (Simmental) tested positive by culture. Hot-start PCR revealed M.a. paratuberculosis in semen, seminal vesicle and intestinal tissue where culture isolation was difficult. Isolates from bull-calves and breeding bulls were of RFLP types B-C9 and B-C1, respectively. Bull-calves born in infected herd can be sources of infection when later used for natural mating or artificial insemination. Sub-clinically infected bulls release M.a. paratuberculosis into semen, consequently infecting the uterine environment of cows.     

Breeding soundness of beef bulls after circumcision: 33 cases (1980-1986)

Case records of 33 beef bulls that had preputial prolapses and underwent circumcisions were reviewed. Data retrieved included age, breed, duration of preoperative medical treatment, complications of surgery, length of time from surgery to first breeding, ability of bull to copulate, duration of active breeding, and complications resulting in breeding unsoundness. The mean age of all bulls was 3.5 years (1 to 7 years). Breeds represented included Santa Gertrudis (n = 13), Beefmaster (n = 8), Brangus (n = 7), Brahman (n = 4), and Angus (n = 1). The mean duration of medical treatment before surgery for all bulls was 16.4 days (2 to 38 days). There was no statistically significant difference between the mean duration of medical treatment before surgery between bulls that became breeding sound (16 days), compared with those that were breeding unsound (19 days). However, bulls requiring more than 14 days of medical treatment before surgery were approximately 3 times (relative risk, 2.8) more likely to develop postoperative complications than those bulls requiring 14 days of treatment or less. Eleven bulls (33%) developed one or more postoperative complications. The complications resolved in 4 bulls, but 7 were never able to breed. Of these 7 bulls, 4 had problems directly related to the circumcision, 2 had extensive fibrosis of the prepuce already present at surgery, and 1 was discharged from the hospital with no apparent complications but was never able to breed. Twenty-five of the 33 bulls (76%) were breeding sound for 1 or more years after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hereditary defects in cattle in relation to chromosome analysis

In the cytogenetic study of karyotypes of breeding bulls and cows aimed at their health and at the hereditary defects in offspring the lymphocytes from the peripheral blood from the jugular vein were employed. On the basis of the percentual evaluation of numerical and structural deviations in karyotypes the following criteria were established: the animals with deviations up to 10%--Ist class, with deviations from 10 to 20%--IInd class, with deviations over 20%--IIIrd class. From 17 breeding bulls of the first group two were included in the Ist class, twelve in the IInd class and three in the IIIrd class. From the second group, two sires belonged to the IInd class and four to the IIIrd class. Both dairy cows (mothers) that delivered calves with lethal factors, as well as the leukosis-suffering mother with daughter, were included in the IIIrd class. The chromosome analyses are given in tables.     

Putative urinary pheromone of bulls involved with breeding performance of primiparous beef cows in a progestin-based estrous synchronization protocol

The objective of this study was to determine if factors associated with the biostimulatory effect of bulls alter breeding performance of primiparous, suckled beef cows using a progestin-based estrous synchronization protocol. We tested the hypotheses that the estrous synchronization response and AI pregnancy rates differ among cows exposed to bulls, continuously exposed to bull urine, and exposed to fence-line contact with bulls or cows not exposed to bulls or bull urine. Data were collected from 3 experiments performed over consecutive years. Cows were assigned to the following treatments: bull exposure (BE; n = 26) or no bull exposure (NB; n = 25) in Exp. 1, bull urine exposure (BUE; n = 19) or steer urine exposure (SUE; n = 19) in Exp. 2, and fence-line contact with bulls (BFL; n = 26) or no bull exposure (NB; n = 26) in Exp. 3. Synchronization protocols in each experiment included the use of a controlled internal drug release device (d -10), PGF(2alpha) (d -3), and GnRH and fixed-time AI (TAI; d 0). Cows that were observed in estrus by 60 h after PGF(2alpha) were inseminated 12 h later. Cows not observed in estrus by 60 h after PGF(2alpha) were TAI at 72 h and given GnRH (100 mug). Pregnancy was determined by ultrasonography 35 d after TAI. In Exp. 1, 2, and 3, cows were exposed directly to bulls, bull urine, or bull fence-line contact for 35, 64, and 42 d, respectively. Data were analyzed between treatments within each experiment. The proportion of estrous cycling cows did not differ between treatments at the beginning of each experiment; however, more (P < 0.05) BE and BFL cows were estrous cycling at the beginning of the estrous synchronization protocol than NB cows in Exp. 1 and 3. The proportion of cows that showed estrus and interval to estrus after PGF(2alpha) did not differ between treatments in Exp. 1 and 3. However, in Exp. 2, more BUE cows tended (P = 0.09) to have shorter intervals to estrus and to exhibit estrus after PGF(2alpha) than SUE cows. Overall, AI pregnancy rates were greater (P < 0.05) for BE and BUE cows than for NB and SUE cows in Exp. 1 and 2, respectively. There was no difference in AI pregnancy rates between BFL and NB cows in Exp. 3. The presence of bulls and exposure to bull urine appeared to improve breeding performance of primiparous beef cows using a progestin-based estrous synchronization protocol, whereas fence-line bull exposure was insufficient to cause this biostimulatory effect. We propose that a novel urinary pheromone of bulls may be responsible for the enhancement of fertility in the primiparous, postpartum cow.     

Efficacy of methods used to test fertility of beef bulls used for multiple-sire breeding under range conditions

A study was conducted during the 1982, 1983 and 1984 breeding seasons with 277 crossbred bulls, 1 to 3 yr of age, that were evaluated for physical soundness, testicular development, seminal quality, and both sexual and social behavior immediately before exposure to crossbred cow herds ranging in size from 89 to 329 cows. Crossbred cow herds were exposed to 4 to 24 bulls per breeding group (mean of 14) at a mean female: male ratio of 21.2 +/- .6:1 under extensive range conditions for 31 to 62 d (mean 46.6 d). All resulting calves were blood-typed to determine the number of calves sired by each bull as an estimate of his fertility. The mean number of calves sired by 1- (n = 116), 2- (n = 126) and 3-yr-old (n = 35) bulls was 4.7 +/- .1, 8.2 +/- .1 and 10.5 +/- .1, respectively. A regression model for predicting bull fertility under multiple-sire, range breeding conditions was selected that accounted for 29% of the total variance in fertility. Similar models accounted for a greater proportion of variance in fertility of 1-yr-old (37%) than of 2-yr-old bulls (22%). Due to the large amount of unexplained variation, the model could not predict individual bull fertility precisely. However, this study demonstrated that selection of herd sires with large scrotal circumference, low backfat thickness, low levels of primary sperm defects, and a low number of mounts in combination with a moderate number of services during libido testing would be expected to improve fertility of beef bulls used under extensive range conditions.     

Effects of crossbreed pregnancies on the abortion risk of Neospora caninum-infected dairy cows

Previous studies have shown that the use of beef bull semen significantly reduces the rate of abortions due to Neospora caninum in artificially inseminated (AI) seropositive dairy cows. In addition, certain beef breeds could be more resistant to N. caninum infection and abortion than others. The aim of the present study was to determine whether different crossbreed pregnancies, those derived from Limousin, Charolais, Piedmontese or Belgian Blue semen, carry different risks of abortion in Neospora-infected dairy cows. The effects of possible interactions between maternal levels of N. caninum antibodies and the different breed crosses were also evaluated. The study was performed on five commercial Holstein–Friesian dairy herds in Northeast Spain with previously confirmed diagnoses of N. caninum infection in aborted foetuses. The study population was comprised of 1115 pregnancies: 633 pregnancies recorded after AI using Holstein–Friesian semen from 18 bulls and 482 after AI using beef semen from 27 bulls (304 inseminations using semen from Limousin bulls, 191 from Belgian Blue bulls, 89 from Piedmontese bulls and 49 from Charolais bulls). Abortion rates were 32.2% (155/482) and 15.2% (96/633) for seropositive cows inseminated with Holstein–Friesian and beef breed semen, respectively. Logistic regression analysis revealed the herd and the interaction between maternal N. caninum antibody titre and the different crossbreeds as significant factors affecting the abortion rate. Lowest abortion rates, similar to that shown by seronegative animals in the analysed herds (3.2%, 239/7432), were observed in dams AI using Limousin semen that had low (<30 relative index (RI) units) N. caninum antibody titres (2.1% abortion, 3/145) and these cows were used as reference. Compared to the cows used as reference, cows with low N. caninum antibody titres (<30 RI units) showed a similar risk of abortion when inseminated with Piedmontese or Charolais bull semen, but higher risk of abortion when inseminated with Holstein (17.9 times) or Belgian Blue (7.2 times) bull semen. All cows with high N. caninum antibody titres (≥30 RI units) had a higher risk of abortion, ranging from 8.9 times (cows inseminated with Limousine semen) to 37.8 times (cows inseminated with Piedmontese semen), compared to the cows used as reference. In conclusion, different crossbreed pregnancies carried different abortion risks in Neospora-infected dairy cows. The use of beef bull semen dramatically reduced the risk of abortion in dairy cows, especially if Limousin breed semen was used. Moreover, this reduction was found to be dependent on the N. caninum antibody titre such that the lowest incidence of abortions was recorded in Limousin semen inseminated cows with low antibody titres. Insemination of Neospora-seropositive cows with beef bull semen could both reduce the risk of abortion and avoid breeding replacements for infected cattle.     

The effect of amount of body fat and loss of fat on breeding soundness classification of beef bulls.

Two hundred and fifty-one Aberdeen Angus, Horned Hereford, Polled Hereford, and Charolais bulls were examined at the time of sale (sale) and again from 10 to 85 days later (test) to determine the effect of amount of body fat and loss of fat on semen quality. Sale and test measurements included body weight, backfat depth, and scrotal circumference. Breeding soundness evaluations were done at test. For all bulls, over all years, the positive correlations of body weight loss vs. backfat loss, weight loss vs. scrotal circumference loss, and backfat loss vs. scrotal circumference loss were highly significant. Aberdeen Angus, Horned Hereford, Polled Hereford, and Charolais bulls lost weight at a mean rate of 1.77, 2.19, 1.94, 1.16 kg per day, respectively, in the interval from sale to test. Bulls classified as unsatisfactory lost significantly more weight than satisfactory bulls. However, bulls classified as unsatisfactory did not differ significantly from satisfactory bulls in the amount of backfat at sale and test and in the amount of backfat lost. No significant relationship could be demonstrated between increments of backfat and classifications of breeding soundness evaluations. Bulls with satisfactory semen quality had significantly larger scrotal circumference measurements than those with questionable or unsatisfactory classifications. Backfat data at bull sales may be helpful in selecting bulls with desirable growth characteristics, as well as reducing the risk of purchasing bulls with poor semen quality due to excessive body fat.     

An investigation into the causes of low calving percentage in communally grazed cattle in Jericho, North West Province

The communal grazing system is generally understood to have a low input, low output type of management. However, the actual inputs and outputs of the farmers are not well known and the farmers are often unaware of their problems. Although the causes of low calving percentage are well understood in commercial beef farming enterprises in South Africa, the same is not true for communal farming systems. The aim of this study was to determine the reproductive performance of beef cattle on a communal farming system in Jericho, North West Province. Ten farmers from five villages with a total of 265 cows and 13 bulls were purposively selected. The selection criteria were that each farmer had to have a minimum of 10 breeding cows and a bull and be willing to participate in the study. This was followed by a 12-month longitudinal study with monthly herd visits where cows were examined rectally and bulls (n = 13) were subjected to a single breeding soundness evaluation. The calving percentage was found to be 37.7%. This is lower than the recorded percentages for commercial beef cattle on extensive grazing. The factors playing a role in low calving percentage were ranked using field data. From this it appeared that failure of cows to become pregnant was the main cause of poor calving percentage as opposed of loss of calves through abortion or resorption. Sub-fertility of the bulls was found to be of great significance and it is proposed that this be included in extension messages and that bulls be fertility tested routinely. Poor body condition score of cows, mainly caused by poor management, was also considered to play a major role in reducing pregnancy rates. Infectious diseases like trichomonosis, campylobacteriosis and brucellosis played a much leser role than anticipated.     

Calm Temperament Improves Reproductive Performance of Beef Cows

Profitability of a beef operation is determined by the proportion of cows attaining pregnancy early in the breeding season and those that are pregnant at the end of breeding season. Many factors, including temperament, contribute to those reproductive parameters. The objective of this study was to evaluate effects of temperament on reproductive performance of beef cows. In Experiment 1, Angus and Angus‐cross beef cows (n = 1546) from eight locations were assigned a body condition score (BCS; 1 = emaciated; 9 = obese) and chute exit and gait score (1 = slow exit, walk; calm temperament; 2 = jump, trot or run; excitable temperament). Cows were grouped with bulls (1 : 25 to 1 : 30; with satisfactory breeding potential and free of venereal disease) for an 85‐day breeding season. Pregnancy status and stage of gestation were determined (transrectal palpation) 35 days after the end of the breeding season. Controlling for BCS (p < 0.01) and handling facility (p < 0.0001) and handling facility by temperament score interaction (p < 0.001), breeding season pregnancy rate was lower in excited versus calm cows [88.6% (798/901) vs 94.1% (607/645); p < 0.001]. Cows with an excitable temperament took 24 more days to become pregnant compared to calm cows (median days to pregnancy, 35 vs 59 days; p < 0.0001). In Experiment 2, Angus and Angus‐cross beef cows (n = 1407) from 8 locations were assigned scores for body condition and chute exit and gait (as described in Experiment 1) and assigned to bulls (breeding sound and free of venereal disease; 1 : 25 to 1 : 30) for 85 days. Pregnancy status was determined by transrectal palpation at 2 and 6 months after the onset of the breeding season. Controlling for BCS (p < 0.05), pregnancy loss was higher in excited versus calm cows [5.5% (36/651) vs 3.2% (20/623), p < 0.0001]. In conclusion, beef cows with an excitable temperament had significantly lower reproductive performance than calmer cows. The modified two‐point chute exit–gait scoring method was repeatable and identified cattle with an excitable temperament.     

Prevalence of Tritrichomonas fetus in a bull population and effect on production in a large cow-calf enterprise

OBJECTIVE: To determine prevalence of infection with tritrichomonas fetus in a bull population; assess influence of age, breed, and grouping; assess effects on measures of cow performance (pregnancy rate, weaning percentage, weaning weight); and estimate test sensitivity. DESIGN: Epidemiologic study. ANIMALS: 1,383 bulls and records for 28,471 cows bred by these bulls in the immediate past breeding season. PROCEDURE: Bulls in 11 cattle units on a large ranch were tested for T fetus colonization by vigorous preputial scraping and protozoologic culture until no newly infected bulls were identified. Bull infection prevalence within units was calculated and correlated to production measurements reported for each cattle unit. RESULTS: Mean prevalence of T fetus-infected bulls was 11.9% (range, 0 to 35.9%). Significant difference was detected between mean age of infected bulls (5.5 years) and noninfected bulls (3.9 years). Difference in prevalence among breeds was found, although other factors may have influenced this finding. Cow performance measurements (weaning percentage, mean weaning weight, and adjusted mean weaning weight/exposed cow) for cows exposed by breeding to bull groups with the highest prevalence of infection (35.9%) were significantly different from mean values for the entire study population. Test sensitivity for this study (73%) was less than that reported in other studies. CLINICAL IMPLICATIONS: T fetus infection in a natural service beef herd has an adverse impact on several production measures: Severity of impact is related to prevalence of infection in the bull population, where prevalence is bull age and population dependent.     

Genetic and economic evaluation of a basic breeding programme for Kenya Boran cattle

The objective of this study is to describe the present organisational structure of Boran cattle breeding and develop a model breeding programme using a deterministic approach under the current structure of the Boran Cattle Breeders Society. A breeding unit of 13,000 cows supplying bulls to a commercial population of 39,000 cows was assumed. Selection criteria used were growth and reproduction traits while breeding objective traits targeted were growth, carcass, reproduction, survival, milk yield and feed intake traits. Higher selection intensity was possible for breeding sires resulting in higher genetic gains compared to dams even though selection accuracies were generally low. Annual genetic gains were positive except for dressing percentage, cow survival rate, and age at first calving. However, a reduction of age at first calving by 9.5 days obtained a return of Ksh 49.76. The overall monetary genetic gain obtained was Ksh 84.89 with a profit per cow per year of Ksh 377.98. The basic breeding programme could be expanded to accommodate a larger population of Boran cattle. The implications of the results are also discussed.