Zootechnical performance of cloned cattle and offspring: preliminary results

This paper presents information on the evolution of sets of cloned heifers of Holstein breed in comparison to that of control heifers derived from artificial insemination (AI) in the same farm, as well as data on a set of cloned bulls and their semen characteristics. Preliminary observations on a group of calves sired by a cloned bull and offspring of cloned females are reported. Mean birth weight in the clone group (50 females) was statistically higher than that of 68 contemporary female controls obtained by AI (49.27 +/- 10.98 vs. 40.57 +/- 5.55 kg, respectively, p < 0.05). Growth rate was within normal values for Holstein heifers (from 0.7 to 0.8 kg/day) and daily gain was not influenced by the high or low birth weight of clones. Within animals of the same clone, variability of daily gain was reduced compared to their control counterparts. Semen production from three cloned bulls was within the parameters expected for young bull of the same age. A direct comparison of morphological analysis was made between the frozen thawed semen of the donor bull and of his three clones collected at the same age. The overall semen picture appeared within acceptable limits and the clones presented similar percentages of sperm abnormalities (80% of morphologically normal spermatozoa) as the donor. These preliminary results suggest no deleterious effect of cloning on the semen picture of cloned sires. Frozen semen from one clone bull was used for an AI trial, resulting in 65% pregnancies, 25 live calves were naturally delivered. Concerning the offspring of both female and male clones, the phenotypical and clinical observation of the calves in the first week of age did not reveal any clinical abnormality, suggesting that the deviations observed in clones are not transmitted to the progeny.     

Heifers sired by bulls with either high or low expected progeny differences (EPDs) for marbling do not differ in age at puberty

Selection for carcass traits such as deposition of intramuscular fat (marbling), which is a primary trait used as an indicator of meat quality, may incur additional effects such as younger age at puberty. Therefore, a trial was conducted for 2 years to determine age of puberty for two groups of crossbred heifers (n = 124) sired by purebred Angus bulls selected for either low (Low, n = 6) or high (High, n = 6) expected progeny differences (EPDs) for marbling. Our working hypothesis was that age at puberty would be reduced in heifers sired by bulls with high EPDs for marbling in comparison to those heifers sired by bulls with low EPDs for marbling. Puberty was determined by collecting weekly blood samples and assaying for concentrations of progesterone. Mean age at puberty for heifers during the study did not differ (392 ± 5 and 387 ± 5 days, Low and High respectively). Of the 124 heifers, 79% reached puberty within the 145 days allotted for the study. We conclude that use of sires that produce daughters with increased ability to marble does not result in decreased age at puberty.     

Telomere length status of somatic cell sheep clones and their offspring

This study was carried out to determine the telomere length status of sheep clones and their offspring, and to examine telomere dynamics and chromosomal abnormalities in culture propagated donor cells. Skin samples were collected from somatic cell nuclear transfer-derived sheep clones, and three of their progeny generated by natural mating. Samples were collected from control animals (n = 35), spanning in age from 1 month to 36 months of age. Genomic DNA was extracted from cell/tissue samples and their telomere lengths were assessed by terminal restriction fragment (TRF) analysis. Results revealed: that (a) sheep clones derived from cultured somatic cells have shortened telomere lengths compared to age-matched controls; (b) the offspring derived from natural mating between clones had normal telomere lengths compared to their age-matched counterparts; and donor cell cultures beyond 20 population doublings had significantly (P < 0.05) shortened telomeres and exhibited a higher numerical and structural chromosomal abnormalities.     

The relationship between secretory patterns of gonadotrophic hormones and the attainment of puberty in bull and heifer calves born early or late during the spring calving season

It was suggested that an early increase in gonadotrophin secretion in calves aged between 6 and 24 weeks might be critical for initiating developmental changes culminating in puberty. An early rise in luteinizing hormone (LH) release appears to be caused by an increase in LH pulse frequency in bull calves and by an increase in LH pulse amplitude in heifer calves. Previously we have found differences in the characteristics of the LH rise between prepubertal beef calves born in spring or fall; however, age at puberty was not affected by season of birth. Here we report the LH/FSH secretory patterns in prepubertal bull and heifer calves (Hereford x Charolais), born in March or April, respectively (i.e., early or late during the spring calving season; six animals of each sex born at each time). The bull calves of both groups reached puberty (defined as an attainment of scrotal circumference of >or=28 cm) at 43.2+/-1.3 weeks of age (P>0.05). Age at puberty for March- and April-born heifer calves (defined as the age at which serum progesterone concentrations first exceeded 0.4 ng/ml) averaged 56.0+/-1.4 weeks (P>0.05). Based on blood samples taken weekly from birth to 26 weeks of age, and then every other week until puberty, bull calves born in March exceeded April-born bull calves in mean serum LH concentrations at 6, 10 and 12 weeks of age (P<0.05). Mean FSH concentrations were greater (P<0.05) in March-born compared to April-born bull calves from 34 to 32 weeks before puberty. Mean serum LH (at 40, 42 and 56 weeks) and FSH concentrations (at 2, 10, 20, 22-26, 30 and 56 weeks of age) were greater (P<0.05) in heifer calves born in April than March. On the basis of frequent blood sampling (every 12 min for 10 h), heifer calves born in April exceeded March-born animals in mean LH and FSH concentrations, at 5 and 25 weeks, and LH pulse frequency, at 5, 10 and 25 weeks of age (P<0.05). None of the parameters of LH secretion (i.e., mean concentrations of LH, LH pulse frequency and amplitude based on frequent blood collection) differed between March- and April-born bull calves in this study (P>0.05). In summary, March-born bull calves had greater mean serum LH and FSH concentrations prior to 24 weeks of age than April-born calves. April-born heifer calves had greater mean serum concentrations of LH and FSH but this difference was not confined to the early postnatal period. Although there were significant differences in absolute amounts of LH secreted, there were no differences in the frequency of LH secretory pulses amongst March- and April-born bull calves and no differences in LH pulse amplitude in heifer calves born in March or April. As these particular parameters of LH secretion, as well as age at puberty, are not affected by the time or season of birth, they may be primary hormonal cues governing sexual development in bulls and heifers, respectively.     

Effect of dietary energy and protein density on body composition,attainment of puberty,and ovarian follicular dynamics in dairy heifers

The objectives were to examine the effects of dietary energy and protein density on age and body composition at puberty, and on ovarian follicular dynamics during the pre- and peripubertal periods in Holstein heifers. In Phase 1, heifers were randomly allotted (n=10 per diet) at 100 kg body weight (BW) to diets with either low (P1L), medium (P1M) or high (P1H) energy and protein formulated for an average daily gain (ADG) of 0.5, 0.8 or 1.1 kg per day, respectively. During Phase 2 (P2), all heifers were fed ad libitum a common diet formulated for an ADG of 0.8 kg per day. Half the animals within the high (n=5) and low groups (n=5) entered P2 either at 12 months of age (P2H-12; P2L-12) or at 330 kg BW (P2H-330; P2L-330). Heifers fed P1H, P1M, P1L, and P2L-12 diets attained puberty at approximately 9, 11, 16, and 14 months of age, respectively (P<0.01). Urea space estimates of body fat and protein percent, and back-fat thickness, were lower in P1L heifers compared to P1H or P1M heifers at similar chronological ages (P<0.05) but did not differ at puberty (P>0.10). Compared to P1L heifers, P1H heifers had high amplitude LH pulses at 8 months, and high frequency low amplitude LH pulses at 10 months of age (P<0.05). The mean diameter (mm) of the dominant follicle was smaller (P<0.05) in P1L heifers (10.6) compared to P1H (12.8) or P1M (12.2) heifers at 8 months. Maximum size and growth rate of the nonovulatory dominant follicle increased with age (P<0.05) but did not differ between P1H and P1M heifers at puberty. The diameter (mm) of the nonovulatory dominant follicle, and the first and second ovulatory follicles were larger in P2L-12 heifers (14.0, 14.7, and 14.9) compared to P1M heifers (13.1, 12.5, and 11.9), while the peak progesterone levels and CL growth were lower (P<0.05) in the first cycle. In conclusion, dairy heifers attained puberty at a constant body weight and body composition independent of dietary manipulation, the size of dominant follicles increased with age in association with increased LH support, and heifers realimented from a low energy diet developed larger first ovulatory follicles and smaller CL with lower peak progesterone concentrations in the first cycle.     

Effects of oestradiol, zeranol or trenbolone acetate implants on puberty, reproduction and fertility in heifers

The effects of anabolic agents on reproduction in beef heifers were determined by using 300 mg trenbolone acetate (TBA), 36 mg zeranol and 19 mg oestradiol-17 beta in a biodegradable pellet (1E: American Cyanamid, USA), or two such pellets (2E). On Day 1 of experiment, 81 Hereford x Friesian heifers (mean age = 84 +/- 1.2 days) were allocated at random to the following treatments: (1) controls (N = 15); (2) TBA (N = 15); (3) 1E (N = 12); (4) 2E (N = 15); (5) zeranol (N = 13); (6) TBA + 2E (N = 11). The 1 (1E), or 2 (2E) oestradiol implants were administered on Day 1 of the experiment only. Heifers assigned to receive TBA and zeranol were implanted on Days 1, 84, 168 and 252. Blood progesterone concentrations and oestrous activity were monitored from Days 137 and 200 respectively. Mean age (days) and weight (kg) at puberty (first ovulation), for heifers that reached puberty in Groups 1-6 respectively were 352 and 308, 419 and 356, 373 and 325, 381 and 331, 400 and 353, 423 and 383 [residual standard deviation (r.s.d.) = 43.8 and 39.4 for age and weight respectively]. Heifers in Group 4 were older (P less than 0.05), but not heavier (P greater than 0.05), while those in Groups 2 and 5 were both older (P less than 0.005) and heavier (P less than 0.005) than the controls at puberty. Age and weight at puberty were not different in heifers assigned to Groups 3 and 4, or to Groups 2 and 6. The proportion of heifers showing oestrus before puberty (prepubertal oestrus) were 3/15, 12/15, 6/12, 7/15, 10/13 and 11/11 in Groups 1-6 respectively. Heifers in Groups 2 and 5 had higher incidences of prepubertal oestrus than controls, while those in other treatment groups were not different. There was no treatment effect on the incidence of silent ovulations, but the incidence of non-ovulatory oestrus, after puberty, was increased from 4/48 in Group 1 to 26/40 (P less than 0.001), 15/56 (P less than 0.05) and 34/57 (P less than 0.001) in Groups 2, 4 and 5, respectively. Heifers in Group 6 had a higher incidence of non-ovulatory oestrus (P less than 0.05), but not of prepubertal oestrus, than did those in Group 2.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of bull exposure and body growth on onset of puberty in Bunaji and Friesian x Bunaji heifers

A total of ninety seven pre-pubertal Bunaji (BJ) and Friesian-Bunaji (FR x BJ) heifers were allotted randomly to two treatments groups for a period of 15 months. The treatment groups consisted of the followings: Mature Bull Exposure (MBE) and No Bull Exposure (NBE). Heifers were body condition scored and their live weights recorded on 28 days consecutive intervals. A heifer tactile stimulation in bull bio-stimulation. was considered to have attained puberty if she displayed oestrus, had a palpable corpus luteum with an associated P4 concentration > 1 ng x mL(-1). The onset of puberty was significantly earlier in MBE heifers (23.1 +/- 0.4 months) than NBE heifers (26.4 +/- 0.4 months). The mean ages at puberty for MBE-BJ, NBE-BJ, MBE-FR x BJ, NBE-FR x BJ were 24.3, 27.8, 22.1 and 25.0 months respectively. More MBE heifers (70.8%) attained puberty between 17 and 24 months of age than NBE heifers (18.3%) and on the same ages, more FR x BJ heifers (62.0%) than BJ heifers (25.5%). The mean live weight of MBE heifers at puberty (224.4 +/- 4.2 kg) was significantly lower than that of the NBE heifers (255.8 +/- 4.2 kg). The FR x BJ heifers attained puberty at a significantly higher live weight (270.2 +/- 4.2 kg) than the BJ heifers (228.6 +/- 4.2 kg). The use of a vasectomised bull especially in some elite farms that rely on artificial insemination services may be an effective management tool that can decrease age at puberty. More work is required to determine the relative contribution of visual, auditory, olfactory, pheromonal and tactile stimulation in bull biostimulation.     

Effects of season of birth on the prepubertal pattern of gonadotropin secretion and age at puberty in beef heifers

There is an early transient rise in gonadotropin secretion in spring-born prepubertal heifers and there is an indication that this pattern is different in autumn-born heifers. The effect of season of birth on age and weight at puberty is equivocal. This study was designed to compare the temporal patterns of LH and FSH secretion between spring- and autumn-born heifers and to determine the effects of season of birth on age and weight at puberty. Blood samples from 2 groups of heifer calves born in spring (last week of March, n = 5) or autumn (last week of October, n = 5) were collected every other week from birth to puberty and every 15 min for 10 h at 6, 12, 18, 24 and 32 wk of age. Timing of puberty was determined by measuring progesterone in plasma samples collected every 2 to 3 d starting at 42 wk of age. Age and weight at onset of puberty did not differ between the 2 groups of heifers (P > 0.05); however, the autumn-born heifers tended to mature in a wider range of ages and weights. Based on the 10-h sampling periods, mean serum concentrations of LH and LH pulse frequency and amplitude were higher in spring-born heifers at 18 wk of age than in autumn-born heifers (P < 0.05). In spring-born heifers, LH pulse frequency increased over time to 32 wk of age, and LH pulse amplitude was higher at 12 and 18 wk than at 32 wk of age (P < 0.05). Autumn-born heifers had higher LH pulse frequency at 6 wk and showed a decrease in mean concentrations of LH at 12 and 18 wk of age (P < 0.05). The FSH pulse frequency of spring-born heifers was higher at 12 wk of age than in autumn-born heifers (P < 0.05), FSH pulse amplitude in autumn-born heifers decreased from 6 to 32 wk of age. It was concluded that although the mean age and weight at puberty did not differ between spring- and autumn-born heifers, the range in age and weight at puberty was wider in the autumn-born heifers. The patterns of LH secretion differed between spring- and autumn-born prepubertal heifers, with spring-born calves exhibiting an early rise in LH secretion, while mean serum concentrations of LH decreased during this period in autumn-born heifers.     

A possible dominant white gene in Jersey cattle

A white heifer ("Snow") was born in 1991 from coloured registered Jersey parents. She produced six calves sired by coloured Jersey bulls: three white bull calves, two white heifer calves, and one coloured bull calf. One of the white bull calves was mated with 40 Hereford × Friesian yearling heifers (white face, predominantly black body with some white patches). The 38 resulting calves included 16 white and 22 coloured calves. Twelve of the 16 white calves were heifers and four were bulls. Red or black spotting was recorded on some white calves. The results are consistent with an autosomal dominant mutant causing the white phenotype. The mutation appears to have arisen spontaneously in Snow, then passing to her white progeny and white grand-progeny. The white individuals varied from entirely white in a few cases, to most having some residual small areas of red or black pigmentation in patterns not typical of other reported white spotting patterns of cattle.     

Effect of electrical stimulation or presence of a bull on puberty in beef heifers

Three experiments were conducted to determine if electrical stimulation or the presence of a bull would hasten puberty in Angus and Hereford heifers. In experiment I, electrical stimulation of the genital tract per rectum given once on day 0 of the experiment failed to hasten puberty and did not alter the size of large follicles. The presence of a teaser bull, for a period of three weeks, did not hasten puberty in a group of prepuberal heifers in experiment II. Experiment III was designed to determine whether a response to bulls could be discerned if heifers were treated with 12 mg progesterone daily for nine days. Introduction of teaser bulls to progesterone-treated heifers did not influence the percentage of heifers that reached puberty in either of two 30-day trials of this experiment. Progesterone alone did not significantly increase the percentage of heifers that reached puberty, but it appeared to synchronize estrus in heifers that reached puberty after treatment.     

Ovarian hypoplasia in heifers due to germ cell weakness

Ovarian hypoplasia due to germ cell weakness was found in 18 heifers of the Swedish Red and White breed simultaneously with a sharp increase of the same syndrome in bulls of the same breed. The heifers were examined because they had not shown estrus or had not become pregnant after several months on pasture together with a fertile bull. After palpation of the ovaries per rectum they were classified as normal, partially hypoplastic or totally hypoplastic. The heifers were slaughtered and the numbers of primordial follicles were counted in the serially sectioned ovaries. The average numbers of follicles per ovary in the 3 diagnostic groups were 18716, 6617 and 4761, respectively. The numbers of primordial follicles in hypoplastic ovaries were significantly lower than in normal ovaries but were still within normal limits for heifers. However, the hypoplastic ovaries were very small, and the totally hypoplastic ones weighed only 1 g or less. The growth of the primordial follicles was disturbed and very few developed into Graafian follicles. There were also many empty cortical cords and anovular follicles. The heifers had all been sired by bulls belonging to breeding lines where germ cell weakness had occurred.     

Response to biostimulation in peri-puberal beef heifers: influence of male-female proximity and heifer's initial body weight

The objectives were to determine if exposure of 12 mo old peri-puberal beef heifers to androgenized steers for 35 d hastened puberty, and if the response was related to the physical proximity between males and females and to heifer's initial body weight. Hereford x Aberdeen Angus heifers (n = 131), 12 mo old, were assigned to two treatments: 1) Exposed group, exposed to androgenized steers from Day 0 to Day 35 (E, n = 66); or 2) Control group, isolated from the steers and other males (C, n = 65). Cyclic activity was determined through estrous behavior detection (twice daily) and weekly ultrasound imaging to detect a CL. For each Exposed heifer, an association index (with males) was determined thrice weekly, based on the distance to androgenized steers every 10 min for 4 h (until cyclic activity began). Data were analyzed according to heifer's initial body weight, which was categorized into three ranges (low, medium, and high, designated LW, MW, and HW, respectively). The cumulative proportion of cyclic heifers was greater for Exposed than Control heifers as of Day 21. By the end of the exposure period, more Exposed than Control heifers had attained puberty (16/66 vs. 2/65; P < 0.001). Within the HW classification, more Exposed than Control heifers became puberal (11/20 vs. 2/21; P = 0.002). However, there were no differences between MW and LW in the proportions of heifers that reached puberty. Association index in Exposed heifers was greater in HW than in MW and LW (0.10 ± 0.09 vs. 0.06 ± 0.03 and 0.06 ± 0.04; P < 0.05), and in heifers that began cyclic activity compared to those that did not in the MW heifers (0.09 ± 0.05 vs. 0.05 ± 0.02; P = 0.01) and tended to be different in the HW treatment (0.12 ± 0.10 vs. 0.06 ± 0.02; P = 0.09). In conclusion, exposure of peri-puberal beef heifers to androgenized steers for 35 d advanced puberty in heavier heifers; an earlier response occurred in heifers with greater proximity to androgenized steers.     

Modulation of luteinizing hormone and follicle-stimulating hormone in circulation by interactions between endogenous opioids and oestradiol during the peripubertal period of heifers.

The aim of this study was to determine whether the decline in oestradiol inhibition of circulating luteinizing hormone (LH) and follicle-stimulating hormone (FSH) during the peripubertal period of heifers is associated with a change in opioid modulation of LH and FSH secretion. Opioid inhibition of LH secretion was determined by response to administration of the opioid antagonist naloxone. Prepubertal heifers (403 days old) were left as intact controls, ovariectomized or ovariectomized and chronically administered oestradiol. Control heifers were used to determine time of puberty. Three weeks after ovariectomy, four doses of naloxone (0.13-0.75 mg kg-1 body weight) or saline were administered to heifers in the treatment groups in a latin square design (one dose per day). Blood samples were collected at intervals of 10 min for 2 h before and 2 h after administration of naloxone. This procedure was repeated four times at intervals of 3 weeks during the time intact control heifers were attaining puberty. All doses of naloxone induced a similar increase in concentration of serum LH within a bleeding period. During the initial bleeding period (before puberty in control heifers), administration of naloxone induced an increase in LH concentration, but the response was greater for heifers in the ovariectomized and oestradiol treated than in the ovariectomized group. At the end of the study when control heifers had attained puberty (high concentrations of progesterone indicated corpus luteum function), only heifers in the ovariectomized and oestradiol treated group responded to naloxone. Opioid inhibition of LH appeared to decline in heifers during the time control heifers were attaining puberty. Heifers in the ovariectomized group responded to naloxone at the time of administration with an increase in FSH, but FSH did not respond to naloxone at any other time. Administration of naloxone did not alter secretion of FSH in ovariectomized heifers. These results suggest that opioid neuropeptides and oestradiol are involved in regulating circulating concentrations of LH and possibly FSH during the peripubertal period. Opioid inhibition of gonadotrophin secretion appeared to decline during the peripubertal period but was still present in ovariectomized heifers treated with oestradiol after the time when age-matched control heifers had attained puberty. We conclude that opioid inhibition is important in regulating LH and FSH in circulation in heifers during the peripubertal period. However, opioids continue to be involved in regulation of circulating concentrations of LH after puberty.     

Serum thyroid hormone concentrations during growth and puberty in Carora dairy heifers of Venezuela

The aim of this study was to characterize changes in serum concentrations of triiodothyronine (T(3)) and thyroxine (T(4)) in relation to growth and the onset of puberty in Carora heifers, a Venezuelan dairy breed. Heifers aged 7 to 16 months were grouped retrospectively according to puberty status into 4 groups: Pubertal (control group; n = 12) and nonpubertal (n = 8) contemporary (born during the same week) heifers, pubertal (n = 7.) and nonpubertal (n = 7) noncontemporary (born in different months) heifers. A split-plot model with repeated measures over Months 7 to 16 of age was used. Control heifers attained puberty at 290 +/- 5 kg body weight (BW) between 13 and 14 months of age. Significant (P < 0.01) interactions of birth time of year and puberty status were detected in BW and serum concentrations of T(3), but only interaction of birth time of year was found in T(4). A transient but significant (P < 0.05) decrease in T(3) secretion was seen in pubertal contemporary and noncontemporary (101 +/- 4 and 113 +/- 4 ng/d1, respectively) heifers at Month 12 of age, a change which could be critical to the onset of puberty. Significant (P < 0.05) positive correlation was found between BW and T(3). In summary, thyroid hormone secretion changed across the months of growing and around the onset of puberty in Carora heifers.     

The relationship between breeding soundness evaluation and fertility of beef bulls under group mating at pasture

The relationships between natural service fertility of beef bulls and the components of breeding soundness evaluation, age, preweaning average daily gain, yearling weight and scores of two libido tests were studied in two seedstock herds. In one of the herds (YBH), 15 yearling bulls were rotated during six-week breeding season so that each group of five bulls served the cows for a period of one week and rested for two weeks before the next exposure. Five older bulls (one 3-year old and four 2-year old) were assigned to the other herd (MBH) during the entire breeding season (six weeks). The progeny of each bull were identified by blood typing.Calf crop was 6.4% higher (P=0.14) in the MBH compared with that in the YBH. There were large differences in fertility between the bulls in the MBH. The 3-year old bull sired 40.9% of the calves, presumably due to his high social dominance order. The third group of yearling bulls, which served the herd during the third and sixth weeks of breeding, sired the highest number of calves (49.4%) compared with the other two groups (28.4% and 22.2%). In each of the groups one and two of the yearling bulls, one bull did not produce any progeny, while another one sired 44% of the calves. The correlation coefficients between fertility of the bulls and the traits used to predict their fertilizing capacity were generally small and inconsistent in different groups, when the effect of age in the mixed age group was removed. The correlation coefficients of bull fertility with scrotal circumference and reproductive system score were higher and more consistent in different groups as compared with the other traits studied.     

Growth hormone-releasing factor (GRF) induced growth hormone advances puberty in female buffaloes

Exogenous bovine growth hormone-releasing factor (bGRF) at the dose rate of 10 microg/100 kg body weight was administered intravenously (i.v.) to six Murrah buffalo heifers as treatment group, while another six buffalo heifers served as control group which received the vehicle (0.9% NaCl solution) at an interval of 15 days for a period of 9 months to study the effect of bGRF on puberty onset associated with temporal hormonal changes in peri-pubertal buffalo heifers. Blood samples were collected at 3-day interval from all the animals during the experimental period and plasma harvested was assayed for growth hormonal (GH), luteinizing hormone (LH) and progesterone. The day that plasma progesterone was greater than 1.0 ng/ml for three consecutive sampling days was defined as the day of puberty. Exogenous bGRF administration increased (P = 0.02) plasma GH concentration in treatment group over control group during the treatment of bGRF as well as during the peri-pubertal period. Plasma progesterone concentrations increased transiently earlier (P = 0.05) by 58.5 days in bGRF-treated buffaloes than that in the control group. However, plasma LH concentrations were unaffected by the treatment of bGRF (P = 0.48). Both plasma GH and LH in the buffalo heifers increased (P < 0.01) over time preceding puberty and the higher hormonal concentrations were maintained during the onset of puberty, and thereafter, the concentrations of both the hormones declined (P < 0.05) after puberty. GH and LH were positively correlated both before puberty (r = +0.59 and +0.63; P < 0.05 for control and treatment group, respectively) and after puberty (r = +0.42 and +0.46; P < 0.05 for control and treatment group, respectively) indicating the interaction and/or close relationship of GH and LH in the mechanism of puberty in buffalo species.     

Reproductive characteristics of cloned heifers derived from adult somatic cells.

This study examined the onset of puberty, follicular dynamics, reproductive hormone profiles, and ability to maintain pregnancy in cloned heifers produced by somatic cell nuclear transfer. Four adult somatic cell-cloned heifers, derived from a 13-yr-old Holstein cow, were compared to 4 individual age- and weight-matched heifers produced by artificial insemination (AI). From 7 to 9 mo of age, jugular venous blood samples were collected twice weekly, and from 10 to 11 or 12 mo of age, blood sampling was carried out every other day. After the heifers reached puberty (defined as the first of 3 consecutive blood samples with peripheral plasma progesterone concentrations of >1 ng/ml), ultrasound examination of ovaries and jugular plasma sample collection were carried out daily for 1 estrous cycle. Cloned heifers reached puberty later than controls (mean +/- SEM, 314.7 +/- 9.6 vs. 272 +/- 4.4 days and 336.7 +/- 13 vs. 302.8 +/- 4.5 kg for clones and controls, respectively; P < 0.05). However, cloned and control heifers were not different in estrous cycle length, ovulatory follicle diameter, number of follicular waves, or profiles of hormonal changes (LH, FSH, estradiol, and progesterone). Three of the 4 clones and all 4 control heifers became pregnant after AI. These results demonstrate that clones from an aged adult have normal reproductive development.     

Estradiol influences on pattern of gonadotropin secretion in bovine males during the period of changed responses to estradiol feedback in age-matched females

When ovaries are removed prior to puberty, administration of exogenous 17 beta-estradiol (E2) decreases concentrations of luteinizing hormone (LH) below that of ovariectomized heifers receiving no E2. Subsequent to the time age-matched intact heifers reach puberty, exogenous E2 increases secretion of LH in ovariectomized heifers above that of ovariectomized heifers receiving no E2. The hypothesis that E2 would inhibit gonadotropin secretion in bovine males during the time E2 no longer inhibited gonadotropin secretion in age-matched bovine females was tested. Males (n = 12) and females (n = 12) were gonadectomized at 241 +/- 3 days of age, and half of each sex (6 males and 6 females) were administered a 27-cm E2 implant. An additional group of males (n = 6) and females (n = 6) remained intact and served as controls. Blood samples were collected (to quantify LH and follicle-stimulating hormone [FSH]) from all animals at 15-min intervals for 24 h at 1, 7, 13, 17, 21, 25, 29, 33, 37, and 43 wk after gonadectomy. Additional blood samples were collected twice weekly from control females to monitor progesterone and onset of corpus luteum function (451 days of age). E2 inhibited frequency of pulses of LH (p less than 0.01) and decreased mean concentration of LH and FSH (p less than 0.01) at Week 1 in gonadectomized males treated with E2 compared to gonadectomized males not administered E2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exposure of beef females to the biostimulatory effects of bulls with or without deposition of seminal plasma prior to AI

The objective of this experiment was to evaluate the biostimulatory effect of bull exposure, with or without the deposition of seminal plasma, on expression of estrus and pregnancy rate to AI in cattle. Beef heifers (n=86) and cows (n=193) were allocated to one of three treatments: (1) no bull exposure (CON; n=95), (2) exposure to a bull with a surgically-deviated penis for 21 d prior to AI (DB; n=88), or (3) exposure to a vasectomized bull for 21 d prior to AI (VB; n=96). The DB treatment provided the physical presence of a bull but prevented intromission, whereas the VB treatment allowed for intromission and deposition of seminal plasma but not spermatozoa. The estrous cycles of all females were synchronized using the Select Synch+CIDR protocol (GnRH+CIDR-7d-CIDR removal+PGF(2α), detection of estrus+AI 12h later for 84 h-clean-up TAI+GnRH). Pregnancy was detected via transrectal ultrasonography on d 35 post-AI. At the onset of the experiment, 75.7% of heifers and 86.1% of cows were estrous cycling. The percentages of females that displayed estrus were similar (P>0.05) among treatments (71.4%, 76.8%, and 74.4% for CON, DB, and VB, respectively). Pregnancy rates tended to be greater (P=0.06) in females in the DB treatment (60.5%) compared to females in the VB treatment (42.2%), with the control group intermediate (49.5%). In conclusion, biostimulation did not affect the expression of estrus but females exposed to the DB treatment tended to have an increased pregnancy rate.     

Effects of dry season nutritional supplementation on growth, onset of puberty and subsequent fertility in Boran and Boran x Friesian heifers in Ethiopia

Shortly after weaning at 8 months of age, 43 Boran and 46 Boran x Friesian crossbred heifers were randomly divided to either receive a supplementary feed containing 16% crude protein during the dry season or to serve as controls. Heifers were examined monthly, and data on body weight, wither height and body condition score were recorded. Ovarian size and structures were determined per rectum and heifers were kept under continuous observation for standing estrus. Blood samples were collected at 10-day intervals every month for determination of plasma progesterone levels. All heifers were exposed to intact bulls for 4 months after they attained 18 months of age. Average daily weight gain to puberty was significantly (P<0.01) higher in heifers given supplementation than in the controls (360 vs 326 g/day). The average daily weight gain in Boran heifers (296 g/day) was significantly (P<0.01) lower than in crossbred (392 g/day) heifers. Mean age at puberty differed significantly (P<0.001) between heifers given supplementation (573 days) and the controls (627 days). Boran heifers attained puberty at a significantly later age (660 vs 540 days; P<0.001) than crossbred heifers. Body weight at puberty did not differ between supplemented and control heifers (226 vs 222 kg); while the difference between Boran and crossbred heifers was significant (216 vs 232 kg; P<0.01). Pelvic size and body condition score were not influenced by supplementation but differed significantly between genotypes. Pregnancy rate after 4 months of breeding was higher in supplemented (79%) than in control (64%) heifers. Boran heifers had a significantly (P<0.001) lower pregnancy rate than crossbred heifers (52 vs 91%). Mean age and body weight at conception were not affected by supplementation but differed significantly (P<0.05) between genotypes. The results indicate that prepubertal supplementary feeding during the dry season increased growth rate, reduced age at puberty and improved fertility in both Boran and Boran x Friesian heifers.