Intact Bulls Research Articles

Use of beef steers for profitable management of biologically valuable semi-natural pastures in Sweden

Cessation of grazing is an increasing threat to the biodiversity rich semi-natural pastures in Sweden due to a decreased number of grazing livestock despite environmental payments for management of these pastures. The aim of this study is to compare the profitability of raising beef breed calves as intact bulls kept indoors after weaning and slaughtered at 15 months to raising them as steers grazing semi-natural pastures and slaughtered at 20, 25 or 30 months of age. The 20 and 25 month steers graze one summer and the 30 month steers two summers post-weaning. Profitability is calculated as gross margin to cover fixed costs of the farm and background data is obtained from an animal experiment and official Swedish standard budgets. The comparisons include alternatives with holdings situated in one out of two districts (plain or forest) and with one out of six types of semi-natural pasture (low- or high-yielding pasture, pasture with payment on a base level only or with extra payment for special values, 100% semi-natural pasture or 50% semi-natural pasture with 50% complementary ley pasture). The result suggests that the 30 month steer is the most profitable production system in most of the studied alternatives provided that the present environmental payments, single farm payment and support for less favoured areas are maintained. Bulls are more profitable than 30 month steers only if the semi-natural pasture is both high-yielding and entitled payment on a base level only. The 20 and 25 month steers have no economical competitiveness in any of the alternatives studied. Steers with two post-weaning grazing seasons seem to be a cost-efficient way to preserve the grazing dependent biodiversity in Sweden and other parts of Europe with increasing shortage of calves.

Physical composition, primary cuts and meat cuts of carcasses from Zebu and Bos taurus X Bos indicus crossbred cattle

Data on hot carcass weight, hot carcass yield, hindquarter weights and physical components, forequarter and spare ribs, and the weights of the main commercial cuts from the hindquarters of twenty young intact bulls were assessed. The animals, belonging to four genetic groups (Nellore, ½ Guzerath + ½ Nellore (½ G + ½ N), ½ Red Angus + ½ Nellore (½ R + ½ N) and ½ Marchigiana + ½ Nellore (½ M + ½ N)), were raised on pastures, finished in dry lot and slaughtered at live weights ranging from 445 to 517 kg, and at ages ranging from 679 to 863 days. During the dry lot period, which lasted 114 days, animals were fed sorghum silage offered ad libitum, and a concentrate (13.5 MJ of ME, 18% CP in the DM) at 1% live weight per day. Genetic group influenced hot carcass weight, forequarter weight, meat weight in the spare ribs, as well as meat and bone weights in the forequarter. Animals in the ½ M + ½ N group were superior both to those in the Nellore and in the ½ G + ½ N groups for hot carcass weight, forequarter weight and meat weight in the spare ribs. The ½ M + ½ N group also differed from the ½ R + ½ N and from the ½ G + ½ N groups in terms of forequarter weight and meat weight in the forequarter, respectively. Conversely, forequarter bone weight of ½ M + ½ N animals was higher than in animals from the Nellore and the ½ R + ½ N groups, respectively. There was no effect of genetic group on hindquarter cuts, except for higher shank and knuckle weights in the ½ M + ½ N group compared to the ½ G + ½ N and Nellore groups, respectively.

Proximate chemical composition and fatty acid profiles of <i>Longissimus Proximate chemical composition and fatty acid profiles of Longissimus thoracis </i>from pasture fed LHRH immunocastrated, castrated and intact<i> Bos indicus </i>bulls

This study was carried out to evaluate the effect of a luteinizing hormone-releasing hormone (LHRH) fusion protein vaccine vs. surgical castration on the chemical composition and fatty acid profile of beef cattle (Bos indicus) slaughtered at three years of age. Thirty bulls (Nellore-cross) were divided into three groups: immunized against LHRH fusion protein, castrated or left intact (control). These animals were 24 months old at the initiation of the study and ranged on Brachiaria grass in Mato Grosso, Brazil. Meat of intact bulls presented a lower fat content compared to castrated or surgically castrated animals. For the immunized and surgically castrated animals there were differences in fat and cholesterol concentrations. Although the fatty acid profiles of the three treatments were similar in composition, there were differences in the concentrations of some fatty acids (miristic, C14:0; stearic, C18:0; linolenic, C18:3n-3; and eicosapentaenoic, C22:5n-3). Meat samples of surgically castrated animals had less polyunsaturated (PUFA) and monounsaturated (MUFA) fatty acids (8.2 and 37.7%, respectively), higher saturated (SFA) fatty acids (52.2%) and a lower PUFA/SFA ratio (0.16) and were different compared to intact and immunized bulls. The PUFA/SFA ratio increased as the fat content decreased. On the other hand, surgically castrated bulls had a higher lipid and lower cholesterol contents. It is concluded that immunization against LHRH using new recombinant LHRH fusion proteins could be an alternative to physical castration to improve carcass quality in cattle production.

A longitudinal study of LH, gonadal and adrenal steroids in four intact Asian bull elephants ( Elephas maximus) and one castrate African bull ( Loxodonta africana) during musth and non-musth periods

During their annual musth cycle, adult African and Asian bull elephants have increased gonadal androgens (testosterone [T], dihydrotestosterone [DHT], androstenedione [A4]). Because musth is a physiologically and psychologically stressful time, this study was conducted to investigate whether the adrenal glands (stimulated by stress) increase production of both glucocorticoids and androgens during musth. Weekly serum samples were taken for 11–15 months from four intact adult Asian bull elephants, and from a castrate African bull elephant who exhibits musth. Testosterone, androstenediol (A5), A4, luteinizing hormone (LH), cortisol, and dehydroepiandrosterone (DHEA) were measured in each sample. In three of the four intact bulls, all hormones measured increased during musth. Adrenal androgens were strongly correlated with LH and testicular androgens, though not to cortisol. None of the hormones measured in the castrate bull increased during his musth cycles. While the significance of adrenal activity in the elephant during musth has yet to be determined, this study provides evidence that the adrenal gland actively produces both glucocorticoids and androgens during musth in the Asian elephant.

Effects of Method and Timing of Castration and the Use of an Estrogenic Growth Stimulant on Weight Gain of Bull Calves

Two experiments were conducted to determine the effects of method and timing of castration on performance of bull calves. In Exp. 1, 2- to 3-mo-old bulls (n = 168) were left intact or were castrated either surgically or with rubber bands, and all calves were implanted with 36mg of zeranol. Intact bulls were castrated at weaning (7 to 8 mo) with large rubber bands and all calves were re-implanted with 36mg of zeranol. In Exp. 2, 139 bulls were assigned at birth to the following treatments: banded, banded and implanted (36mg zeranol), or left intact. Four weeks before weaning, intact bulls were castrated with large rubber bands and all animals were implanted. In Exp. 1, ADG from 2 mo to weaning was not different for implanted bulls compared with bulls castrated and implanted. The ADG of implanted bulls that were banded at weaning was less (P < 0.05) during the following 50 d compared with bulls castrated and implanted at 2 to 3 mo of age. In Exp. 2, intact bulls had similar BW 30 d before weaning compared with bulls that were castrated at birth or castrated and given an implant at birth. The BW of bulls that were banded 30 d before weaning was reduced (P < 0.01) at weaning compared with bulls banded at birth. It is concluded that intact bulls do not have an advantage in pre-weaning growth compared with bulls castrated and implanted at less than 3 mo of age. Castrating bulls at greater than 6 mo of age with large rubber bands decreased BW gains during the next 30 d.

Composition and estimation of intramuscular and subcutaneous fatty acid composition in Spanish young bulls

Sixty Pirenaica yearling intact bulls were raised and slaughtered at 519 ± 50 kg live weight and 371 ± 18 days of age. Fatty acid composition of intramuscular lipids in longissimus dorsi muscle and subcutaneous fat were determined by capillary gas chromatography. Carcass conformation and fatness, carcass weight, ether extractable intramuscular fat percentage, marbling, dorsal fat thickness, and ultrasonic parameters were recorded to study the relationship between these traits and fatty acid profile. Lipids of subcutaneous adipose tissue had higher monounsaturated fatty acids (MUFA) percentage (49% vs. 33%) but lower saturated fatty acids (SFA) (51% vs. 46%) and polyunsaturated fatty acids (PUFA) (16% vs. 5%) percentages than intramuscular fat depots ( p < 0.001). Fatter carcasses had higher MUFA percentage and lower PUFA percentage ( p < 0.01) in intramuscular fat. Carcass weight and conformation would contribute to explain the fatty acid profile of subcutaneous fat ( p < 0.05). Ultrasound readings reflected the effect of fatness on fat composition.

Reproductive characteristics of grass-fed, luteinizing hormone-releasing hormone-immunocastrated Bos indicus bulls1

Two field trials were conducted in Brazil to evaluate LHRH immunocastration of Bos indicus bulls (d 0 = 2 yr of age). In Study I, 72 bulls were assigned randomly to one of three treatment groups: LHRH0-immunized, castrated, and intact. Immunized animals (n = 25) received a primary and two booster injections of ovalbumin-LHRH-7 and thioredoxin-LHRH-7 fusion proteins on d 0, 141, and 287. Twenty-three bulls were surgically castrated on d 141, and 24 served as intact controls. All animals were slaughtered on d 385, at approximately 3 yr of age. In Study II, 216 bulls were assigned randomly to the same three treatments as in Study I; however, because of a drought in the area, bulls were kept on pasture an additional year, and a fourth treatment was added, in which one-half the LHRH-immunized bulls received an additional booster on d 639 (fourth immunization). All animals in Study II were slaughtered on d 741 (4 yr of age). Luteinizing hormone-releasing hormone antibodies increased following each immunization for immunized bulls, but they were not detectable in castrate or intact animals in either study. Consequently, scrotal circumference was suppressed in immunized bulls compared with intact controls in both studies. By d 287, serum concentrations of testosterone in LHRH-immunized bulls were decreased compared with intact controls (P < 0.01). In both studies, testes and epididymal weights at slaughter were greater (P < 0.01) for intact (500 +/- 17 and 60 +/- 2 g, respectively) than for immunized bulls (173 +/- 22 and 26 +/- 2 g, respectively) and fourth immunization bulls (78 +/- 23 and 20 +/- 2 g, respectively; Study II). At the end of each study, BW was greater (P < 0.01) for intact bulls than for castrated and LHRH-immunized animals. In these two studies, the efficacy of the LHRH fusion proteins to induce an effect similar to that of surgical castration was considered 92 and 93%, respectively. These data support the concept that immunocastration of bulls at 2 yr of age was successful and that it has practical application as a tool for producing grass-fattened bulls in Brazil.

Growth and carcass characteristics of pasture fed LHRH immunocastrated, castrated and intact Bos indicus bulls

The effectiveness of a luteinizing hormone-releasing hormone (LHRH) fusion protein vaccine or surgical castration, at two years of age, on growth and carcass characteristics of Bos indicus bulls was evaluated. Seventy Nelore-cross bulls were divided into three groups: (1) immunized, (2) castrated and (3) intact control. At slaughter (three years of age), intact bulls had higher body weights, ADG, carcass weights, and muscle percentage compared to immunized and surgically castrated animals. Both castrated and immunized animals had greater marbling and percent carcass fat than the intact bulls. Average tenderness scores were inferior for intact bulls compared to immunized and castrated animals, but these differences were not significant ( P>0.05). Juiciness, flavor, thawing, nor cooking losses differed significantly among the three groups. Immunocastration was effective in producing carcass traits similar to that of surgical castration. Therefore, immunization with LHRH fusion proteins appears to have practical utility in the management and castration of grazing bulls.

Les antagonistes de la GnRH

The objective of this study was to evaluate the effect of the GnRH vaccine on the performance and meat quality of Holstein bulls fed high concentrate diets. A total of 493 approximately 7 month old bulls (initial BW 298 ± 1.2 kg) were allocated into 3 treatment groups, intact bulls (n = 164), animals surgically castrated at 15 to 17 d of the study (n = 164), and animals vaccinated on 0 and 28 d of the study with the GnRH vaccine (n = 165). Animals were slaughtered between 131 and 133 d and carcass quality was evaluated. Hot carcass weight, dressing percentage, fat classification and meat quality parameters did not differ significantly between surgically castrated and vaccinated animals but differed (P < 0.05) from intact bulls. Carcass classification, pH at 26 h, and fat color were not affected by treatment.

MRNA of insulin-like growth factor (IGF) quantification and presence of IGF binding proteins, and receptors for growth hormone, IGF-I and insulin, determined by reverse transcribed polymerase chain reaction, in the liver of growing and mature male cattle

Plasma insulin-like growth factor-I (IGF-I) concentrations were related to hepatic levels of IGF-I mRNA measured by competitive reverse transcription polymerase chain reaction (PCR) (RT-PCR) in neonatal (8 d old) calves, veal calves, fattened castrated bulls and mature intact bulls. Furthermore, the presence of mRNAs of IGF-II and of receptors for IGF-I (IGF-IR), growth hormone (GHR) and insulin (IR), as well as mRNAs of IGF binding proteins (IGFBP-1, -2 and -3) were assessed by RT-PCR. Hepatic IGF-I mRNA levels and plasma IGF-I concentrations in veal calves, fattened castrated bulls and in intact bulls were 4 to 8 times higher than in 8-d old calves and were 2 to 3 times higher in calves fed colostrum than in calves fed only milk replacer. Hepatic IGF-I mRNA concentrations were closely correlated (r = 0.92) with plasma IGF-I concentrations, suggesting that hepatic IGF-I production largely determines plasma IGF-I levels. The presence of IGF II, IGF-IR, GHR, IR and IGFBP-1, -2 and -3 mRNA was confirmed in the liver of 8-d old calves and older cattle as well, and among newborn calves their presence was independent of differences in nutrition. In conclusion, the major hepatic components of the GH-IGF axis were present in neonatal calves, but the IGF-I expression and therefore also plasma IGF-I levels were relatively low.

Plasma fatty acids, prostaglandin F2alpha metabolite, and reproductive response in postpartum heifers fed rumen bypass fat.

An experiment was conducted to determine whether feeding rumen-protected fatty acids (FA) to postpartum heifers would increase plasma concentrations of linoleic acid and PGF2, metabolite (PGFM), shorten the interval from calving to first increase in plasma concentrations of progesterone (P4), and increase pregnancy rate relative to controls. Hereford x Angus heifers (346 kg) were assigned randomly to treatments containing either lipid or barley supplemented diets for the first 30 d postpartum. Lipid was .23 kg.heifer(-1).d(-1) of calcium salts of FA (CSFA; n = 20), and an isocaloric amount of barley served as the control (n = 19). Supplements, with .23 kg of barley as a vehicle, and a basal diet of meadow and alfalfa hays were pen fed to heifers (5/pen). Heifers were bled on alternate days (d1 to 30) and twice weekly (d 30 to 2 wk after first estrus) for RIA of plasma PGFM and P4, respectively. Weight percentage of major FA in plasma on d1 and 7 was determined with gas chromatography. First behavioral estrus was detected by use of intact bulls and confirmed by an increase in plasma P4. On d 7, but not d 1, plasma from heifers fed CSFA had altered proportions of major FA (P < .01), including an increase in linoleic acid compared with those of controls (29.1 vs 25.6% of total FA; SE = .75; P < .01). Analysis of variance of contrast variables revealed an effect of treatment on direction of change in PGFM from d 3 to 5 (P < .01). By d 7 and on d 9, plasma concentrations of PGFM were greater in heifers fed CSFA than in controls (P = .02 and P = .06, respectively). There was no difference in plasma concentration of PGFM between treatments on d 1, 3, 5, 11, 13, and 15 postpartum (P = .80, .17, .52, .82, .46, and .77, respectively). Days to first estrus with ovulation, pregnancy rate, and calving interval were not affected by treatments (P = .58, .52, and .24, respectively). Although supplemental lipid fed to primiparous beef heifers increased plasma levels of linoleic acid and production of PGFM in the early postpartum period, it did not improve the fertility of these heifers in the subsequent breeding season.

The effect of prepubertal immunization against gonadotropin-releasing hormone on the development of sexual and social behavior of bulls.

To determine the effect of prepubertal immunization against GnRH on the development of sexual and social behavior of Friesian bulls, 90 calves were randomly assigned to five treatments: 1) I2, immunized against GnRH at 2 and boosted at 2.5, 4, and 7.5 mo of age, n = 2 x 10; 2) I4, immunized against GnRH at 4 and boosted at 4.5 and 7.5 mo of age, n = 2 x 10; 3) I7.5, immunized against GnRH at 7.5 and boosted at 8 mo of age n = 2 x 10; 4) S, steers castrated at 2 mo of age, n = 10; and 5) B, intact bulls, n = 2 x 10. Blood samples were collected initially every 2, then every 3 wk. Plasma was analyzed for anti-GnRH titers and plasma testosterone concentration. Sexual and agonistic behavior, male-male mounting, and damage to paddocks was assessed throughout the experiment. All immunized calves developed antibodies against GnRH (32.3 +/- 2.0% bound at a 1:10 plasma:PBS-BSA dilution, 14 d after first boost). Plasma testosterone concentrations were < 1 ng/mL for all immunized animals until 11 mo of age, when they increased to levels found in intact bulls at 14 mo of age. At slaughter, testes and seminal vesicle weights were 38.3 and 31.6% lighter, respectively, for all immunized treatments compared to B. There were no significant differences between I2, I4, and I7.5 in any of the sexual or agonistic behavior tests. Bulls scored higher than steers in all sexual behavior tests. Immunized bulls scored lower than bulls in sexual behavior tests from 10 to 17 mo of age. The proportion of immunized animals that serviced an estrous cow was lower than the proportion of intact bulls at 10, 12.5, 14, and 17 mo of age. Immunized animals scored lower than bulls in bull challenge tests at 8.5, 11.5, 13, 14.5, and 17 mo of age. Paddock damage by animals on the three immunization treatments was lower than that by bulls from 7 to 14.5 mo of age, as were leg were scores (an indicator of male-male mounting behavior) from 9 to 14 mo of age. There was no difference in sexual behavior between immunized bulls (I2, I4, and I7.5) and bulls while held in lairage pens for 16 h before slaughter, but all treatment groups scored higher than steers. There was a similar trend for agonistic behavior, although I4 bulls were no different from steers. Prepubertal immunization against GnRH at 2, 4, and 7.5 mo of age impaired testes function and affected the development of social and sexual behavior of young bulls.

Epidemiological investigation of the buller steer syndrome (riding behaviour) in a western Canadian feedlot.

To describe the buller steer syndrome in a Western Canadian feedlot. a retrospective study. 78,445 male cattle that entered a 24,00-head feedlot in western Canada from 1991 to 1993. All cattle were given a hormonal growth promotant containing 20 mg oestradiol benzoate and 20 mg progesterone within 24 h of arrival at the feedlot. A 'buller' was a steer that was observed at daily pen checking to be ridden persistently by pen mates or had evidence of having been persistently ridden by pen mates. At the completion of the feeding period, animal health records for bullers were collected and analysed. The prevalence of bullers in the total population was 2,139/78,445 (2.7%, range per pen 0 to 11.2%). The prevalence of bullers increased with increasing weight and age. The relapse risk after first treatment (three days in the feedlot hospital plus treatment for concurrent disease) was 30% on average (27 to 35%). Individual records from 9,734 yearling steers that entered the feedlot in 1991 and 1992 showed that bullers were significantly (P < 0.05) heavier at processing than non-bullers. Bullers occurred as a point source epidemic with a cause occurring soon after cattle arrived at the feedlot and were mingled into pen grous. This gave a 'days on feed' distribution. The peak incidence of bullers occurred much sooner after arrival and dropped off much quicker in older cattle. The daily incidence of bullers was temporal, but was not related to season of the year, weather condition of any other feedlot management practice. It was related to the seasonal arrival of cattle at the feedlot, their age at entry to the feedlot and the post arrival occurrence of bullers. Reimplantation with hormonal growth promotants and castration of intact bulls did not produce an epidemic of bullers. The findings of this study support the theory that bullers are the result of agonistic interactions, which occur concurrent with the establishment and maintenance of a social hierarchy with pens of feedlot cattle.

Relationship between circulating progesterone and conception at the first postpartum estrus in young primiparous beef cows.

The objective of this study was to determine whether patterns of change in concentration of progesterone in circulation of primiparous beef cows were related to conception rates at the first postpartum estrus. Data were collected over 2 yr from crossbred primiparous 2-yr-old cows (n = 77). Cows were artificially inseminated when estrus was detected between 3 and 20 (yr 1) or 3 and 23 (yr 2) wk after parturition. Cows were exposed to intact bulls for 32 (yr 1) or 21 d (yr 2) after the periods of AI, and estrus detection also occurred during the period when natural mating occurred. After parturition, blood samples were collected twice weekly to determine time of transient (less than 1 wk) and sustained increases (more than 1 wk) in progesterone of more than 1 ng/mL of serum. Mean times from parturition to transient increase in progesterone, first estrus, conception, and sustained increase in progesterone were 91, 100, 108, and 105 d, respectively. Sixty-four percent of the cows conceived as a result of AI at the first estrus that was detected after parturition, 32% conceived at a subsequent estrus, and 4% failed to conceive. In 31.1% of the cows, a transient increase in progesterone was not detected before the first estrus after calving. Conception as a result of AI at the first estrus after calving was less if a transient increase in progesterone did not precede estrus (76 vs 41%; P < .01). These data indicate that the majority of cows have increases in progesterone before the first postpartum estrus. If the transient pre-estrus increase in progesterone occurs in postpartum cows, there seems to be an enhanced conception rate as compared with cows without the increase in progesterone before their first estrus following parturition.

Calving intervals in beef cows at 2, 3, and 4 years of age when breeding is not restricted after calving.

The objective of this study was to evaluate calving intervals and repeatability of calving intervals of young beef cows when breeding seasons were initiated immediately after calving. Average calving date at 2, 3, and 4 yr of age was recorded, and duration of calving interval between the first and second and second and third parities was compared in 178 crossbred beef cows calving between 1981 and 1988. Cows were placed in paddocks with intact bulls immediately after calving so they had the opportunity to conceive at the estrus associated with the initial estrous cycles after calving. Average Gregorian date of calving for cows was progressively earlier with older age (March 9, March 5, and February 14 at 2, 3, and 4) yr of age, respectively). Repeatability of calving intervals within individual cows was also evaluated. There was an interaction between year and parity on calving interval between 2 and 3 (P < .001) and 3 and 4 (P < .004) yr of age. Repeatability of calving interval was low and negative during 5 of the 6 yr. In young beef cows, year and parity interact to influence calving interval, and this average interval is less than 365 d when initiation of the breeding season is not restricted after calving.

Evaluation of the bloodless castration procedure for feedlot bulls

Studies were undertaken to evaluate bloodless castration (B) based on growth and carcass traits. During the first 28 d, bloodless and surgical (S) castrates showed a 51–53% and 68–73% reduction in average daily gain, respectively, compared with intact bulls (I) (P &lt; 0.05) in two trials. Bulls grew faster than steers overall. Carcass traits and grade were similar for B, S and I (P &gt; 0.05). Key words: Bloodless, surgical, castration, growth, carcass traits

Plasma progesterone and blood metabolite profiles in post-partum small east African zebu cows.

Plasma progesterone profiles were used to monitor post-partum reproductive activity in 12 Small East African zebu (Bos indicus) cows allocated to either supplementary or no supplementary feeding (control) with continuous or restricted (twice daily) suckling regimes. Intact bulls were used for breeding. Blood samples were collected 3 times a week for 33 weeks to determine plasma progesterone levels. Weekly blood samples were also used to determine blood metabolite concentrations. Plasma progesterone levels remained below 1 ng/ml in all cows until week 12 post-partum. Only 5 cows showed ovarian activity over the 33 week period. Cows that cycled expressed irregular and short-lived progesterone rises (> 1 ng/ml) lasting 8 to 12 days prior to establishment of normal patterns of progesterone secretion where progesterone levels ranged from 8 to 10 ng/ml in cows with normal cycles. Plasma total protein, albumin, globulin, blood urea nitrogen and glucose levels varied over time without consistent trends, and were not influenced by either supplementary feeding of suckling regimes, nor differed between cyclic and acyclic cows. It was concluded that extended post-partum anoestrus, conception failure and early embryonic mortality were responsible for lowered reproductive efficiency in zebu cows. Blood metabolite concentrations were not good indicators of nutritional status and were not related to post-partum ovarian activity.

Bulk and trace elements in the accessory glands of buffalo bulls

Little is known of the importance of mineral levels in buffalo semen or the relationship of the level of various elements to spermatozoan activity. To establish a basis upon which further studies could be conducted, the accessory glands (seminal vesicles, prostate and bulbo-urethrals) of 43 buffalo bulls (2–4 years old) with intact testes and eight steers (3–4 years old) were analysed for their content of bulk and trace elements. The ash obtained from known weights of various accessory glands was used to determine the concentrations of Na and K using emission flame photometry. P was determined chemically, whereas Ca, Mg, Cu, Fe and Zn were assayed by atomic absorption spectrophotometry. The accessory glands of intact bulls varied significantly in the concentration of all elements except Fe. Ca and Cu were relatively more concentrated in the seminal vesicles. The prostate had the highest concentration of Zn, while the highest concentrations of Na, K, Mg and P were found in the bulbo-urethral glands. Age of the bulls had no marked effect on any of the elements studied except Cu which appeared to decrease significantly in older bulls. Seasonal variation was significant for the levels of K, Ca and Zn. Castration appeared to result in a highly significant reduction of Zn concentration in all accessory glands.

Effects of supplementary feeding and suckling intensity on postpartum reproductive performance of small East African Zebu cows

Small East African Zebu cows (n = 120) which calved during the dry season were used to determine the effects of postpartum nutritional supplementation and suckling intensity on body weight, body condition score, reproductive performance and on calf mortality and preweaning growth performance. Cows were allocated based on calving body weight to either receive a supplementary feed of molasses blocks containing 10% urea or to serve as controls and to be grazed only. Within nutritional groups, cows were further assigned either to continuous suckling or to restricted suckling twice daily. Intact bulls were introduced 21 days after the first cow had calved, and data were collected for 8 months. Calving body weight and body condition score of dams ranged from 186 to 192 kg and from 3.8 to 4.2 and did not differ among the treatment groups. Supplementary feeding significantly (P<0.05) reduced calf mortality from 40 to 20%, while restricted suckling reduced mortality by 13% from 36 to 23%. Body weight and body condition score did not vary between groups during the supplementation period. Over the 8-month period, 65% of supplemented and 53% of control cows exhibited estrus (P>0.05). A significantly (P<0.05) karger percentage of restricted suckled cows showed estrus than of continuously suckled cows (74 vs 42%). The postpartum estrus interval was shorter by 54 days in supplemented than in control cows and by 13 days in restricted than in continuously suckled cows. The pregnancy rate was higher in supplemented than in control cows (37 vs 33%; P>0.05) and in restricted than in continuously suckled (46 vs 22%; P>0.05) cows.

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

Shortly after weaning at 8 months of age, 43 Boran and 46 Boran × 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 × Friesian heifers.