Nutritional influences on growth and onset of puberty in Boran and Boran x Friesian bulls in Ethiopia

Twenty-seven Boran and 37 Boran x Friesian crossbred bulls were weaned at 6 months of age and randomly assigned to either a dry season supplementary feed containing 16% crude protein or control groups. Data were collected on body weight, wither height and scrotal circumference (SC) at monthly intervals. Bulls were also challenged with 100 mug of gonadotropin releasing hormone (GnRH) at 2-month intervals and plasma testosterone responses were determined. Semen was collected at monthly intervals by electroejaculation. Post weaning average daily weight gain was significantly (P<0.001) higher in supplemented than in control groups (302 vs 208 g/day). Scrotal circumference growth rates were also significantly (P<0.001) higher in supplemented than in control bulls (0.38 vs 0.31 mm/day). Bulls fed supplemented diets were younger (430 vs 473 days; P<0.001) and heavier (217 vs 203 kg; P<0.05) and had better semen quality at puberty than the control bulls. There was a trend for larger SC at puberty in supplemented than in control bulls (P=0.06). There were no significant differences in wither height or in testosterone response to GnRH at puberty between supplemented and control bulls. Body and SC growth rates to puberty for Boran and Boran x Friesian bulls were 189 and 321 g/day (P<0.001) and 0.27 and 0.42 mm/day (P<0.01), respectively. Boran bulls were older (513 vs 406 days; P<0.01) and lighter (201 vs 215 kg; P<0.05), and had smaller SC (23.9 vs 26 cm; P<0.01) at puberty than Boran x Friesian bulls. Testosterone responses to GnRH increased (P<0.001) with age and were significantly higher (P<0.05) in supplemented and in Boran x Friesian bulls than in control and Boran bulls. Wither height, testosterone response to GnRH and semen quality at puberty did not differ between breeds. Dry season supplementation improved growth rate and enhanced sexual development and maturity in both Boran and Boran x Friesian bulls, and would be a useful management strategy for enhancing fertility in bulls in the tropics.     

Gonadal and extragonadal sperm reserves in Boran and Boran x Friesian bulls raised on two planes of nutrition in the Highlands of Ethiopia

Gonadal and extragonadal sperm reserves were determined in testicular and epididymal tissues obtained from Boran (n=10) and Boran x Friesian (n=12) bulls fed either a high or low plane nutrition diet for a 1-year period. The bulls were 32 months of age at castration. Mean (+/-SEM) daily body weight gains over a 1-year period were 776+/-34 and 264+/-34 g/day (P<0.001) for bulls on high and low nutrition, and their respective body weights at castration were 458+/-17 and 276+/-17 kg (P<0.01). Mean body weights did not differ between Boran and Boran x Friesian bulls. Mean scrotal circumference measurements were 32.1+/-0.6 and 28.8+/-0.6 cm for the high and low planes of nutrition (P<0.01) and 31.8+/-0.7 and 29.2+/-0.6 cm for the Boran and the Boran x Friesian bulls (P<0.05). Paired testes and epididymal weights averaged 432+/-22 and 313+/-22 g (P<0.01) and 46.3+/-2.0 and 32.5+/-2.0 g (P<0.001) for bulls on the high and low planes of nutrition, respectively. Boran x Friesian bulls had significantly heavier (P<0.05) testes, but epididymal weithts did not differ between breeds. Although daily sperm production per gram was not influenced by either plane of nutrition or breed, daily sperm production differed between high (5.3 x 10(9)) and low nutrition (2.9 x 10(9)) bulls (P<0.001) and between Boran (4.6 x 10(9)) and Boran x Friesian (3.5 x 10(9)) bulls (P<0.01). Extragonadal sperm reserves were significantly higher in high than in low nutrition bulls (13.1 x 10(9) vs 6.9 x 10(9); P<0.001) and in Boran than Boran x Friesian bulls (12.9 x 10(9) vs 7.1 x 10(9); P<0.01). The cauda epididymis contributed 50 to 54% to the total epididymal sperm reserves. It was concluded that the plane of nutrition influenced growth rates and testes and epididymal weights, and it improved gonadal and extragonadal sperm reserves in young Boran and Boran x Friesian bulls.     

A quantitative histological study of testicular and epididymal development in Boran and Boran x Friesian bulls in Ethiopia

Quantitative histological techniques were used to characterize the pattern of testicular and epididymal development in 42 Boran and 49 Boran x Friesian bulls aged between 6 and 23 mo. Bulls were divided into five age groups having four-month intervals. Between 6 and 23 mo of age, body weight increased from 124 to 293 kg and 179 to 267 kg (P<0.01) in Boran and Boran x Friesian bulls, respectively. Scrotal circumference measurements increased from 6 to 23 mo by 10.2 and 8.9 cm in Boran and Boran x Friesian bulls. Paired testes weight increased significantly (P<0.001) over the same period from 29 to 304 g and 59 to 291 g in Boran and Boran x Friesian bulls, respectively. Both caput and cauda epididymal segment weights also increased significantly (P<0.001) with age. There were significant (P<0.05) genotype differences in seminiferous tubule diameter, which increased by 137 and 90 mum with increasing age in Boran and Boran x Friesian bulls, respectively. Patent seminiferous tubules were first observed at 206 and 188 d of age in Boran and Boran x Friesian bulls, respectively. The appearance of elongated spermatids and spermatozoa in the seminiferous tubules and epididymal tubules occurred at later ages in Boran than in Boran x Friesian bulls.     

Effect of level of nutrition on onset of puberty and conception rates of zebu heifers

Sixty zebu heifers were divided into three equal groups and reared on isocaloric diets but on different levels of protein. The protein levels were 19.17% (high), 13.37% (medium; NRC recommendations) and 8.3% (low). All animals were examined weekly per rectum for the presence of follicles and corpora lutea and also checked daily for standing heat. The presence of a mature corpus luteum was considered to indicate the attainment of puberty. Body weight and pelvic dimensions were taken at biweekly intervals. Intact bulls were introduced to heifers after they reached puberty and once they reached 200 kg live weight. Pregnancy diagnosis was carried out at 60, 90 and 120 days following introduction of bulls. Mean age at puberty for heifers in the high protein group (570.4 days), medium protein group (640.8 days) and low protein group (704.2 days) differed significantly (P<0.05). body weight at puberty for heifers in the high, medium and low protein groups was 207.1, 187.0 and 161.7 kg, respectively (P<0.05). Pelvic size at puberty was not influenced by the nutritional level. Conception rates of heifers in the three groups were influenced by level of nutrition. Pregnancy rates for the high protein group (58.8%), medium protein group (27.8%), and low protein group (16.7%) by 90-day post-breeding period were significantly different (P<0.05), but body weight at conception between the groups did not differ significantly. The results show that increasing the protein level in the diet is a means of improving the reproductive performance of zebu cattle.     

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 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.     

Influence of age,body weight and body condition score before mating start date on the pubertal rate of maiden Holstein–Friesian heifers and implications for subsequent cow performance and profitability

The aim of this study was to assess the influence of age, body weight (BW) and body condition score (BCS) of maiden Holstein–Friesian heifers before mating start date (MSD) on the rate of puberty, subsequent production and longevity and their implications with regard to farm profitability. Data were available on 871 Holstein–Friesian heifers from 48 herds. BW was recorded electronically and BCS was recorded by a single operator on a scale of 1 to 5. Heifer age was calculated as the number of days from birth to the day of visit. All of the independent variables of interest were grouped into three or four categories. Three age categories (thirtiles), four BW categories (quartiles) and four BCS categories (⩽2.75, 3.00, 3.25 and ⩾3.50) were formed. Heifers with an identifiable corpus lutuem (CL) in the presence or absence of large follicles and peri-ovulatory signs and with a plasma progesterone (P4) concentration ⩾1 ng/ml were classified as pubertal. In addition, heifers without an identifiable CL in the presence or absence of large follicles and peri-ovulatory signs but with a P4 concentration ⩾1 ng/ml were also classified as pubertal. Age, BW and BCS at MSD were all found to be significantly associated with pubertal rate (P < 0.05). Age was shown to have no practical implications on subsequent cow performance. BW at MSD was favourably associated with subsequent calving date (P < 0.05), subsequent cow BW (P < 0.001) and potential (305 days) milk fat plus protein yield (P < 0.001). BCS at MSD was found to be favourably associated with milk fat plus protein yield potential (P < 0.05) and BCS (P < 0.001) during lactation. The economic analysis undertaken indicated that larger, well-grown heifers will be more profitable because of superior production potential, all else being equal. However, because of the finding of poorer reproductive efficiency in heifers grown to more than 343 kg at MSD, heifers at ∼330 kg at MSD are deemed optimal. This will correspond to mature cow BW of ∼550 kg.     

Body composition of beef heifers at puberty

Three trials were conducted to study age, weight, percent body fat and protein content of 131 crossbred and purebred beef heifers at puberty, to investigate relationships among various pubertal measurements and to determine if body fat and protein values could be used in combination with age, weight and shoulder height to predict the onset of puberty. Trials 1 and 2 compared heifers on treatments of high (H), medium (M) and low (L) levels of energy. The rations were formulated at 120, 100 and 80 percent of the National Research Council (NRC) recommendation for energy. The protein level was 100 percent of the NRC recommendation for all three treatments. Each animal was examined every two weeks per rectum for the presence of follicles and corpora lutea. The presence of a mature corpus luteum indicated the attainment of puberty. Trial 3 heifers were fed the same level of nutrition but ovulation data were based on weekly rectal palpations and on the presence of greater than 2.0 ng/ml blood plasma progesterone. Percentage of fat and protein were quantified in all trials using a whole body counter. In Trial 1 there was a significant difference (P<0.01) among energy levels for mean weight and percent fat values at puberty, but no differences in age at puberty. Even though heifers in Trial 2 were also fed different energy levels, there were no differences among treatments for the variables measured. The onset of puberty in Trial 2 appeared to be delayed due to cooler than normal weather during that experimental period. Heifers in Trial 2 tended to be older and reached puberty approximately one month later in the year than heifers in Trials 1 and 3, despite similarities in weight gain among the trials. In all trials, high R(2) values for multiple stepwise regression analyses indicated that body composition estimates were useful in predicting weight at puberty in beef heifers. The results of this study do not support a critical body weight or body composition hypothesis in the beef heifer. It was concluded that these data indicate environmental factors may have more effect than nutrition on the onset of puberty.     

The effect of high and low dose Theileria parva infection on the reproductive function of Boran/Friesian heifers

Two separate experiments were carried out to find the effect of infection with low and high doses of Theileria parva sporozoites on the cyclical status of Boran/Friesian cross heifers. In each experiment, ten heifers were infected and another four heifers acted as controls. Routine monitoring of estrous behavior, determination of serum progesterone concentrations and palpation of the ovaries per rectum were used to assess the cyclical status of each animal. Two and eight animals died in the T . parva low (TpL) and high (TpH) dose experiments, respectively. Five of eight recovered animals in the TpL group cycled regularly postinfection, while three others had extended periods of ovarian dysfunction postinfection. Both infected and recovered animals in the TpH-group similarly had extended periods of ovarian dysfunction postinfection. All controls in both experiments cycled regularly throughout the study period. Differences in cyclical status were not related to the febrile response, parasitological or hematological differences. The animals that continued to cycle throughout lost the least amount of weight. Animals that stopped cycling lost between 16 and 29% of their initial body weights postinfection. In conclusion, this study confirmed previous anecdotal evidence that theileriosis has an adverse effect on reproduction. Results of this study suggested that this was as an indirect result of weight loss associated with infection and not directly attributed to pathology of target organs.     

Pubertal traits and seasonal variation of the sexual activity in Brahman, Hereford and crossbred heifers

Age and weight at puberty and the pattern of ovulatory activity from puberty to 26 mo of age were studied in a total of 55 Brahman (B), Hereford (H), 5/8B-3/8H (B(5)H(3)) and 5/16B-11/16H (B(5)H(11)) heifers. The trial was conducted over two years. Heifers were kept during the whole experimental period on a paddock of native pasture at a stocking rate of 0.5 animals per hectare. Vasectomized bulls were used for estrus detection and blood was collected from the heifers twice weekly to monitor ovulatory activity through progesterone level as determinated by RIA. In addition to age and weight at puberty, the weights and dates at the time of cessation and resumption of ovulatory activity were also considered. There were significant effects (P<0.05 or P<0.01) of genetic group (purebreds vs crossbreds) for age and weight at puberty; the difference being 60 d and 18 kg, respectively, favoring the crossbred groups. After puberty attainment, an anestrous period was detected in all Brahman (118.6 d) and B(5)H(3) (113.4 d) heifers; anestrus was observed in only 14% of B(5)H(11) heifers and for a shorter (43.5 days) period. Hereford heifers did not exhibit interruption of ovulatory activity. In Brahman and B(5)H(3) heifers, the pattern of interruption and resumption of estrus and ovulatory activity correlated closely (0.89 and 0.95 for Brahman and B(5)H(3) heifers, respectively) with the photoperiod curve, suggesting the probable influence of this environmental factor on the regulation of estrous cycle activity in heifers with a higher proportion of Bos indicus genes. Thus, the genetic factor needs be taken into account when establishing programs in reproductive management.     

Effect of supplemental light on growth,prolactin, progesterone and luteinizing hormone in water buffalo (Bubalus bubalis)

Fifty non-pregnant Surti buffalo heifers aged between 17 and 42 months (n=24, <24 months;n=26, >24 months) were randomly assigned to groups subject to either natural daylight +4h supplemental light (n=25) or natural day light (n=25), to study changes in growth, serum prolactin (Prl), progesterone (P₄) and luteinizing hormone (LH) to supplemental lighting. Ambient temperatures (T) and relative humidity (RH) generally were >27° C and <70% during the day-time, respectively. Light-supplemented heifers had 16.2 kg net body weight (BW) gain at 9 weeks compared to 20.8 kg for controls, but higher mean Prl after 6.5 weeks (P<0.01), and higher P₄ (0.41 vs 0.19 ng/ml;P<0.06) than control heifers. Older heifers had 39.7% greater BW (P<0.01), but a net 4.3% BW gain compared to a 10.1% gain for younger heifers at 10 weeks. Older, light-supplemented heifers had higher mean P₄ (0.63 vs 0.19 ng/ml;P<0.07) than the other groups. These weight and hormonal changes suggest that 4 h supplemental light can alter growth and endocrine function in buffaloes under similar planes of nutrition. While light supplementation did not have a positive effect on body wieght during the 10 week study, body weight and endocrine changes due to supplemental light may be important factors for initiation of reproductive cyclicity.     

Induction of LH surges with 17β estradiol in prepuberal beef heifers: An age dependent response

Twenty-four crossbred heifer calves were used to determine the age at which the endocrine mechanisn involving the stimulatory action of estradiol on luteinizing hormone (LH) release becomes competent to function in prepuberal beef heifers.Twelve calves were studied at 3 months of age at an average body weight of 113 kg; and 12 were studied at 5 months of age at an average body weight of 171 kg. Half of the heifers in each age group were injected with 500 μg of estradiol-17β (E₂) in corn oil and half were injected with corn oil (controls). Acute release of LH did not occur in any control heifers of either age nor in any 3-month-old, E₂-treated heifers but did occur in four of the six heifers treated at 5 months of age.The acute release, lasting for 6 to 8 hr, was initiated between 12 and 14 hr after injection of estradiol with LH peaks ranging from 39 to 146 ng/ml. These results suggest that the hypothalamic-hypophyseal mechanism responsible for estradiol-stimulated LH release becomes functional between 3 and 5 months of age in calves that do not ovulate until 12 to 16 months of age.     

Influence of age,weaning, season and body weight on the levels of progesterone,oestradiol-17β and luteinizing hormone in growing buffalo heifers (Bubalus bubalis)

The influence of age, weaning, season of the year and body weight on the peripheral levels of progesterone, oestradiol-17β and luteinizing hormone (LH) were studied during neonatal, perinatal and peripubertal periods in buffalo heifers. The buffalo heifers exhibited oestrus only after 30 months of age and had higher levels of LH and oestradiol-17β and a lower level of progesterone on the day of oestrus. The progesterone concentration was affected significantly (P < 0.01) by different seasons, by weaning (P < 0.05) and varied between pubertal and neonatal periods (P < 0.01), whereas the oestradiol-17β level was affected significantly (P < 0.01) by weaning and varied at different seasons and with body weight. However, the LH concentration was greater during the neonatal period than the pre- and peripubertal periods and changed significantly (P < 0.01) between groups of ages and body weights. The results suggest that increases in the levels of oestradiol-17β and progesterone after 30 months of age are probably indicative of the onset of puberty in buffalo heifers. However, a further increase in oestradiol-17β, LH, and a decrease in progesterone are essential for oestrus and cyclicity to be exhibited in buffalo heifers.     

Influence of season on sexual development in heifers: age at puberty as related to growth and serum concentrations of gonadotropins, prolactin, thyroxine and progesterone

An experiment was done to test the hypothesis that seasonal changes in environment during the first and second 6 months of life influence age at puberty in heifers. Twenty-eight Angus X Holstein heifers, born in March (M) or September (S), were reared under natural conditions until 6 months of age. From 6 to 12 months of age, heifers were reared in environmental chambers programmed to simulate seasonal changes in temperature and photoperiod characteristic of spring, summer and early autumn (Sp-F chamber) or autumn, winter and early spring (F-Sp chamber). S were younger (P less than 0.06) at puberty than M, and Sp-F were younger (P less than 0.08) than F-Sp for both M and S. Mean ages at puberty were 295 for S, Sp-F; 319 for S, F-Sp; 321 for M, Sp-F and 346 days for M, F-Sp. Average daily gain (ADG) between 6 and 9 months of age [1.03 kg/day (S) vs. 0.91 kg/day (M)] and mean concentrations of serum luteinizing hormone (LH) between 6 and 7 months of age [3.45 ng/ml (S) vs. 0.47 ng/ml (M)] were greater (P less than 0.01) for S than M, suggesting an association between these traits and date of birth effects on age at puberty. Differences in these traits did not seem to be involved in the chamber effect on age at puberty, since ADG from 6-9 months of age was greater (P less than 0.05) for F-Sp heifers and chamber did not generally affect LH concentrations. Serum concentrations of follicle-stimulating hormone (FSH) were not significantly influenced by month of birth or chamber, but concentrations tended to decrease with age. Serum concentrations of thyroxine (T4) were higher in M than S at 6 months of age (7.8 micrograms/dl vs. 6.3 micrograms/dl) but not at other times, and chamber did not have a significant affect. Prolactin (Prl) concentrations paralleled patterns of temperature and day length and did not appear to be related to age. Although cattle are not seasonal breeders, these results demonstrate that season of birth and season of attainment of puberty influence age at puberty in heifers. Season may have influenced age at puberty by affecting serum concentrations of LH or Prl, or growth rate.     

Puberty and serum concentrations of ovarian steroids during prepuberal period in Friesian heifers artificially infected with Fasciola hepatica

An experiment was conducted to study the effect of fascioliasis on puberty in 13 Friesian heifers divided into a control group (n = 7) and an infected group (n = 6). At 4 m.o. of age each infected heifer received 600 metacercariae of F. hepatica. Blood samples were taken twice a week, at which time permanent heat mount detectors were checked, from 8 m.o. of age until 2 estruses were detected in all heifers. Serum concentrations of progesterone (P4) and estradiol-17 beta (E2) were assayed by ELISA and RIA, respectively. There was a significant delay in the onset of puberty in infected heifers compared with controls. All animals reached puberty at similar body weights but at different ages. First estrus was delayed by 39 d in infected compared with control animals. Serum concentrations of E2 were significantly higher in the infected group than the control group, while P4 concentrations were lower. Fascioliasis alters the serum concentration of E2, which in turn results in an abnormally low concentration of P4, probably due to underdeveloped or absent corpora lutea.     

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.     

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)     

The effect of Trypanosoma vivax infection on late pregnancy and postpartum return to cyclicity in Boran cattle

A study was designed to examine the effect of infection with Trypanosoma vivax KETRI 2501 on the maintenance of pregnancy and postpartum return to reproductive function in susceptible Galana (n = 6) and trypano-tolerant Orma Boran (n = 6) heifers during the third trimester of pregnancy. Of the 12 study animals, 3 Galana and 3 Orma Boran heifers served as controls. One of 3 Galana heifers calved prematurely with subsequent perinatal loss. Of the 2 heifers that produced live calves, 1 calf died shortly after birth, while the other survived. Two of 3 Orma heifers calved prematurely and all 3 calves died shortly after birth. The 6 control heifers produced live calves at term, all of which survived. Infection with T. vivax during the third trimester of pregnancy delayed the resumption of ovarian activity after calving, with the Ormas taking a significantly (P < 0.05) shorter time from calving to ovulation. There was no clear evidence that premature birth was associated with pathological changes in reproductive organs. Results from this study demonstrated that infection with pathogenic T. vivax during late pregnancy influenced the outcome of pregnancy in both susceptible Galana and trypano-tolerant Orma Boran heifers, resulting in premature births, perinatal loss, retained placentae, low birth weights and a prolonged period to the onset of postpartum ovarian activity.     

Influences of month of birth and age on patterns of luteinizing hormone secretion in prepubertal heifers

An experiment was done to determine if month of birth and age influenced patterns of luteinizing hormone (LH) secretion in prepubertal heifers. Mean concentrations of LH increased linearly (P < .05) in March-born heifers between one and seven months of age. This was partially due to an increase in number of LH pulses. The prepubertal pattern of LH concentrations was quadratic (P < .05) for heifers born in September because concentrations were slightly higher (P = .15) than those in March-born heifers at one month of age. There were no differences between groups during the remainder of the prepubertal period (3 to 7 months). There was a tendency (P = .18) for September-born animals to reach puberty at younger ages than those born in March. September-born heifers also had greater (P = .06) average daily gains, but body weights at puberty were similar for the two groups. These results show that season of birth influenced LH concentrations at one month of age, but did not significantly affect the increase between three and seven months of age.     

Determination of onset of puberty in Zebu bulls under tropical conditions of northern Nigeria

Age at puberty and related phenomena were investigated in White Fulani (Bunaji - WF), Sokoto Gudali (SG) and Friesian X Bunaji (FRXWF) Zebu bulls from 28 weeks to 72 weeks of age. Pubertal traits studied included body weight, heart girth, scrotal circumference and sperm production. Puberty was defined as the age at which an ejaculated semen contained at least 50 x 10(6) spermatozoa with a minimum of 10% motility. Age at puberty was 66.89 +/- 1.0, 73.4 +/- 2.2 and 62.4 +/- 10.7 weeks for WF, SG and FRXWF bulls respectively. The Bunaji bulls were significantly younger than the Sokoto Gudali bulls at production of first motile sperm cell and also at puberty (P<0.01). The SG bulls were significantly heavier (P<0.01) and had larger heart girth (P<0.05) than the FRxWF at production of first motile sperm cells. Body weight and heart girth for all the breeds were not different at puberty (P>0.1). Scrotal circumference of the bulls between the breeds at production of first motile sperm cells and at puberty, did not differ (P 0.>1), despite the variations in age, weight and heart girth at production of first motile sperm cell and at puberty. It is concluded from the data obtained that the indigenous breeds of bulls (Bos indicus ) seem to attain puberty later than exotic breeds (Bos taurus ). The inter-play of genetic, nutritional and environmental factors as a contribution to this delay in attainment of puberty could not be ruled out.