Some factors related to calf crops of Brahman, Brahman crossbred and Hereford × Shorthorn cows in a stressful tropical environment

Integrated control of the cattle tick, Rhipicephalus australis (Acari: Ixodidae), in New Caledonia through the Pasture and Cattle Management method

Development of the Pasture and Cattle Management (PCM) method is a priority to control the cattle tick, Rhipicephalus australis, in New Caledonia. The PCM method provides the foundation for sustainable integrated tick control because approximately 95% of cattle ticks in infested pastures are off the host in the non-parasitic life stages, and the practice of treating cattle intensely with chemical acaricides is a risk for the emergence of resistance to these active ingredients in commercial acaricidal products available for veterinary use. Here, we report the findings of an assessment survey to document the utility of the PCM method. Analyses of questionnaire data provided by 21 beef cattle producers describing their management of 37 herds informed how to (1) assess the ability of PCM to reduce acaricide use and (2) prioritize best practices and define recommendations to breeders promoting efficient tick control with minimum acaricide use. Boosted regression tree analysis showed a significant (p = 0.002) reduction of ≈33% in the number of acaricide treatments from 7.9 to 5.3 per year by using PCM. Of the 24 factors identified as potentially affecting acaricide use, six factors accounted for ≈86% of the variability in number of acaricide treatments applied annually. The six most influential factors involved farm characteristics as well as pasture and herd management recommendations. These results demonstrated the usefulness of PCM for integrated control of R. australis infestations while reducing acaricide use to improve cattle production in New Caledonia.

A comparison of the growth of Brahman and F1 Senepol × Brahman steers in an Indonesian feedlot

This study compares the performance of F1 Senepol × Brahman steers (F1 SEN) to Brahman (BRAH) steers in an Indonesian feedlot. The focus was to address concerns that crossbred cattle are discriminated against by live export cattle buyers due to a perception that they do not perform as well as Brahmans in Indonesian feedlots. F1 SEN (n = 54) and BRAH (n = 32) steers that had grazed together since weaning at Douglas Daly Research Farm (Northern Territory) were exported to Indonesia and fed for 121 days in a feedlot near Lampung (Sumatra, Indonesia). The average daily gain of the F1 SEN steers over the feeding period was 0.17 kg/day higher (P < 0.001) than the BRAH steers (1.71 vs 1.54 kg/day). As a result the F1 SEN put on an average of 21.6 kg more over the 121-day feeding period and they did not have a higher mortality rate. Consequently, F1 SEN steers performed better than BRAH in an Indonesian feedlot and these results should encourage live export cattle buyers to purchase this type of cattle (Brahman crossed with a tropically adapted Bos taurus breed) with confidence that they can perform at least as well as Brahmans in Indonesian feedlots, although it should be noted that growth rates are usually higher in F1 crosses than in subsequent generations.

Using UHF proximity loggers to quantify male-female interactions: a scoping study of estrous activity in cattle

Reproductive efficiency is an important determinant of profitable cattle breeding systems and the success of assisted reproductive techniques (ART) in wildlife conservation programs. Methods of estrous detection used in intensive beef and dairy cattle systems lack accuracy and remain the single biggest issue for improvement of reproductive rates and such methods are not practical for either large-scale extensive beef cattle enterprises or free-living mammalian species. Recent developments in UHF (ultra high frequency) proximity logger telemetry devices have been used to provide a continuous pair-wise measure of associations between individual animals for both livestock and wildlife. The objective of this study was to explore the potential of using UHF telemetry to identify the reproductive cycle phenotype in terms of intensity and duration of estrus. The study was conducted using Belmont Red (interbred Africander Brahman Hereford-Shorthorn) cattle grazing irrigated pasture on Belmont Research Station, northeastern Australia. The cow-bull associations from three groups of cows each with one bull were recorded over a 7-week breeding season and the stage of estrus was identified using ultrasonography. Telemetry data from bull and cows, collected over 4 8-day logger deployments, were log transformed and analyzed by ANOVA. Both the number and duration of bull-cow affiliations were significantly (P<0.001) greater in estrous cows compared to anestrus cows. These results support the development of the UHF technology as a hands-off and noninvasive means of gathering socio-sexual information on both wildlife and livestock for reproductive management.

Genetics of early and lifetime annual reproductive performance in cows of two tropical beef genotypes in northern Australia

Reproduction records from 2137 cows first mated at 2 years of age and recorded through to 8.5 years of age were used to study the genetics of early and lifetime reproductive performance from two genotypes (1020 Brahman and 1117 Tropical Composite) in tropical Australian production systems. Regular ultrasound scanning of the reproductive tract, coupled with full recording of mating, calving and weaning histories, allowed a comprehensive evaluation of a range of reproductive traits. Results showed components traits of early reproductive performance had moderate to high heritabilities, especially in Brahmans. The heritability of lactation anoestrous interval in 3-year-old cows was 0.51 ± 0.18 and 0.26 ± 0.11 for Brahman and Tropical Composite, respectively. Heritabilities of binary reproductive output traits (conception rate, pregnancy rate, calving rate and weaning rate) from first and second matings were generally moderate to high on the underlying scale. Estimates ranged from 0.15 to 0.69 in Brahman and 0.15 to 0.34 in Tropical Composite, but were considerably lower when expressed on the observed scale, particularly for those traits with high mean levels. Heritabilities of lifetime reproduction traits were low, with estimates of 0.11 ± 0.06 and 0.07 ± 0.06 for lifetime annual weaning rate in Brahman and Tropical Composite, respectively. Significant differences in mean reproductive performance were observed between the two genotypes, especially for traits associated with anoestrus in first-lactation cows. Genetic correlations between early-in-life reproductive measures and lifetime reproduction traits were moderate to high. Genetic correlations between lactation anoestrous interval and lifetime annual weaning rate were –0.62 ± 0.24 in Brahman and –0.87 ± 0.32 in Tropical Composite. The results emphasise the substantial opportunity that exists to genetically improve weaning rates in tropical beef cattle breeds by focusing recording and selection on early-in-life female reproduction traits, particularly in Brahman for traits associated with lactation anoestrus.

Multi-trait assessment of early-in-life female, male and genomic measures for use in genetic selection to improve female reproductive performance of Brahman cattle

Early-in-life female and male measures with potential to be practical genetic indicators were chosen from earlier analyses and examined together with genomic measures for multi-trait use to improve female reproduction of Brahman cattle. Combinations of measures were evaluated on the genetic gains expected from selection of sires and dams for each of age at puberty (AGECL, i.e. first observation of a corpus luteum), lactation anoestrous interval in 3-year-old cows (LAI), and lifetime annual weaning rate (LAWR, i.e. the weaning rate of cows based on the number of annual matings they experienced over six possible matings). Selection was on an index of comparable records for each combination. Selection intensities were less than theoretically possible but assumed a concerted selection effort was able to be made across the Brahman breed. The results suggested that substantial genetic gains could be possible but need to be confirmed in other data. The estimated increase in LAWR in 10 years, for combinations without or with genomic measures, ranged from 8 to 12 calves weaned per 100 cows from selection of sires, and from 12 to 15 calves weaned per 100 cows from selection of sires and dams. Corresponding reductions in LAI were 60–103 days or 94–136 days, and those for AGECL were 95–125 or 141–176 days, respectively. Coat score (a measure of the sleekness or wooliness of the coat) and hip height in females, and preputial eversion and liveweight in males, were measures that may warrant wider recording for Brahman female reproduction genetic evaluation. Pregnancy-test outcomes from Matings 1 and 2 also should be recorded. Percentage normal sperm may be important to record for reducing LAI and scrotal size and serum insulin-like growth factor-I concentration in heifers at 18 months for reducing AGECL. Use of a genomic estimated breeding value (EBV) in combination with other measures added to genetic gains, especially at genomic EBV accuracies of 40%. Accuracies of genomic EBVs needed to approach 60% for the genomic EBV to be the most important contributor to gains in the combinations of measures studied.

Genetic relationships of female reproduction with growth, body composition, maternal weaning weight and tropical adaptation in two tropical beef genotypes

The genetic relationships of female reproduction with growth and body composition, tropical adaptation traits and maternal weaning weight (descriptive of genetic potential milk production) were estimated in 1027 Brahman (BRAH) and 1132 Tropical Composite (TCOMP) females. Female reproduction was evaluated at puberty, as outcomes of the first and second annual mating periods (Mating 1 and Mating 2, which commenced when females averaged 27 and 39 months of age, respectively), as well as annual averages over up to six matings. Traits evaluated included age at puberty, Mating 1 and 2 pregnancy rate, weaning rate and days to calving, and lifetime annual calving and weaning rate. Traits describing growth and body composition (liveweight, hip height, ultrasound-scanned P8 fat depth and eye muscle area, subjective body condition score and blood IGF-I concentration) were measured in the animals as heifers (at ~18 months of age), and again at the start of Mating 2. Traits describing tropical adaptation included coat-length scores in both genotypes and, in BRAH, buffalo fly lesion scores. Previously reported analyses of these data identified heifer IGF-I and coat and buffalo-fly-lesion scores as potential genetic indicators for age at puberty in BRAH. The results of the present study found that exploiting these relationships would have no unfavourable genetic consequences for later female reproduction and, in some cases, may be indicators of female reproduction, when evaluated as outcomes of Matings 1 or 2, or as lifetime annual calving or weaning rates. For BRAH, heifer liveweight was a genetic indicator for Mating 1 weaning rate (rg = 0.70), and, while standard errors were high, there were also positive genetic correlations of heifer hip height, eye muscle area and blood IGF-I concentration with Mating 1 weaning rate (rg = 0.61, 0.58 and 0.43, respectively). For TCOMP, significant genetic relationships of heifer growth, body composition and tropical adaptation traits with female reproduction were virtually absent, suggesting that there is less opportunity to identify earlier in life measures as genetic indicators of reproduction for this genotype. Higher maternal weaning weight was significantly genetically related to lower lifetime annual weaning rate (rg = –0.50) in BRAH, and with lower Mating 2 calving and weaning rate (rg = –0.72 and –0.59, respectively) in TCOMP, which will need to be considered when making selection decisions that affect genetic milk in these genotypes. Importantly, the results presented revealed no strong genetic antagonisms of heifer growth and body composition traits with female reproduction, suggesting that selection could be undertaken to improve these simultaneously.

Evidence of genotype by environment interaction for reproductive and maternal traits in beef cattle

A total of 161 bulls from 11 breeds were used to generate crossbred calves from Angus cows in 1973 to 1977 at each of three diverse New Zealand locations, and from Hereford cows at one of the locations in the same years. The bulls comprised four local breeds, Angus, Friesian, Hereford, and Jersey, and seven recently imported breeds, Blonde d'Aquitaine, Charolais, Chianina, Limousin, Maine Anjou, Simmental and South Devon. This paper reports the reproductive and maternal performance of the straightbred and first-cross cows over the first four calvings, with first mating as yearlings at 14 to 16 months of age. A total of 7575 mating records from 2109 cows were analysed. Location differences were greater for reproduction than for growth traits and resulted in genotype × environment interactions for some components of cow performance and particularly the composite traits, weight of calf weaned per cow joined (productivity) and cow ‘efficiency’ (the ratio of productivity to cow weight). At all locations the Friesian-cross cows weaned the greatest weight of calf per head but were matched or surpassed by the lighter Jersey crosses in terms of efficiency of calf production. Most of the European crosses performed relatively much better in the most favourable environment than in the harsh environment and this was particularly marked for the productivity of Simmental crosses. Heterosis as a proportion of the purebred mean was important for cow performance and particularly pregnancy rate (0·12), productivity (0·21) and the efficiency ratio (0·16). Heritabilities for weight and age at puberty were both 0·34 (s.e. 0·08). Repeatabilities and heritabilities for cow reproductive traits were low (0·0 to 0·10) but higher for calf weights up to weaning as a trait of the cow (0·09 to 0·38). In general, the large European breeds which excelled in growth and carcass production produced female progeny which reached puberty at greater ages, had lower reproductive performance (especially in less favourable environments) and larger mature size. Some breed utilization strategies to achieve trade-offs between these genetic antagonisms are discussed.

Correlated responses to selection for cow fertility in a tropical beef herd

Correlated responses to selection in a tropical beef herd for high (H) and low (L) estimated breeding value for pregnancy rate were measured over three calf crops. The H line calves were proportionately 0·04 lighter at weaning but during the ensuing dry season they lost less weight than L line animals, so that between the ages of 12 and 18 months there were no significant line differences in live weight. It was concluded that selection for cow fertility had not directly altered the progeny's growth rate. Tick resistance and heat tolerance also did not differ between the lines. However, resistance to worms was lower (P < 0·05) in the H line indicating genetic antagonism between cow fertility and worm resistance. Scrotal circumference and scrotal circumference adjusted for live weight were significantly higher in H line bulls between 9 and 18 months of age. Pregnancy rates of heifers in the H line were 0·12 higher than in the L line despite similar average live weights at mating. It is suggested that accelerated sexual maturity in both heifers and bulls has occurred as a result of selection for lifelong cow fertility.

Body condition and suckling as factors influencing the duration of postpartum anestrus in cattle: a review

Prolonged postpartum anestrus is a main factor limiting reproductive efficiency in cattle, particularly in Bos indicus and Bos taurus/Bos indicus cows from tropical regions, because it prevents achievement of a 12 month calving interval. During anestrus, ovulation does not occur despite ovarian follicular development, because growing follicles do not mature. Although many factors affect postpartum anestrus, nutrition and suckling are the major factors influencing the resumption of postpartum ovarian cycles, as they affect hypothalamic, pituitary and ovarian activity and thus inhibit follicular development. Under-nutrition contributes to prolonged postpartum anestrus, particularly among cows dependent upon forages to meet their feed requirements and it apparently interacts with genetic, environmental or management factors to influence the duration of anestrus. The nutritional status or balance of an animal is evaluated through body condition score (BCS), as it reflects the body energy reserves available for metabolism, growth, lactation and activity. There is a converse relationship between energy balance and time to resumption of postpartum ovarian activity; inadequate nutrient intake results in loss of weight and BCS and finally cessation of estrous cycles. Suckling interferes with hypothalamic release of GnRH, provoking a marked suppression in pulsatile LH release, resulting in extended postpartum anestrus. The effects of suckling on regulation of tonic LH release are determined by the ability of the cow to identify a calf as her own or as unrelated. Vision and olfaction play critical roles in the development of the maternal-offspring bond, allowing the cow to identify her own calf, and abolition of both senses attenuates the negative effects of suckling on LH secretion. Thus, the maternal-offspring bond is essential for prolonged postpartum suckling-induced anovulation, and the suppressive influence of suckling is independent of neurosensory pathways within the teat or udder.

Pre-pubertal and postpartum anestrus in tropical Zebu cattle

Bos indicus breeds, commonly known as Zebu cattle, have spread from their center of origin in Western Asia into large areas of Asia (including the Asia-Pacific basin), Africa, South and Central America (including the Caribbean islands). The original Zebu genotype, however, has been modified by planned and unplanned cross-breeding programs involving many native and Bos taurus breeds in their new habitats. Though accurate estimates are not available, more than half of the world's cattle population includes a proportion of B. indicus germ plasma. B. indicus native breeds have developed by natural selection over centuries for their ability to survive in rough, harsh tropical environments. Most of these non-described breeds still exhibit high fertility, in terms of calving rates, and disease resistance but they grow very slowly and take well over 3 years to reach puberty and produce only a few liters of milk over a short lactation period. Selection has been carried out in some areas and distinct Zebu breeds have been developed that have moderately high growth rate and milk production. However, they are slow breeders and have extended pre-pubertal and postpartum anestrous periods, compared to their temperate counterparts exposed to similar environment and management. The reproductive biology of B. indicus is similar to that of B. taurus. Most of the proven management, nutritional, hormonal and biotechnological interventions developed through experimentation with B. taurus breeds are equally applicable to B. indicus and their crosses. Zebu breeds predominate in most tropical countries where the majority of the human population lives. If meat and milk production are to be increased in the tropics, Zebu cow productivity, in terms of number of calves produced per lifetime or per unit area of land, must be increased and the time from birth to slaughter must be reduced. This goal could be achieved either by selection within local Zebu populations or through planned cross-breeding with B. taurus breeds. Because the productive and reproductive potentials of Zebu cattle are relatively low, worthwhile gains could only be achieved by selection over many generations. This would require substantial investment in labor, feed and drugs that may not be economic since the return from such investment is relatively low. However, many studies have shown that cross-breeding with B. taurus, which combines additive, dominance and epistatic effects of the two genotypes, ensures high productive and reproductive performance. Therefore, planned cross-breeding with suitable B. taurus breeds, although demanding additional investment in labor, feed and drugs, will still be economic because the return far exceeds the costs.

Evaluation of beef cattle genotypes and estimation of direct and maternal genetic effects in a tropical environment. 3. Fertility and calf survival traits

Data from a crossbreeding experiment were analysed to compare various breeds in a tropical environment. Data included male fertility [scrotal circumference at yearling age (YSC) and at 18 months of age (FSC)], female fertility [calving success (CS) and days to calving (DTC)], and calf survival [survival of calf up to 1 week after birth (WKS) and up to weaning (PWS)] traits. Male fertility traits were analysed as traits of the progeny generation, whereas female fertility and calf survival traits were analysed as traits of the dam (parental generation). Tropically adapted British breed bulls and taurine crossbreds (British × Sanga) had higher YSC and FSC than Zebu and its crosses when adjusted for their body weights. Large negative direct and maternal additive effects on scrotal circumference for Zebu relative to the British breed also suggested reduced scrotal circumference and fertility in Zebu and Zebu-derived crosses. Direct dominance effects for YSC and FSC were only significant when an adjustment for body weight was not included in the model, emphasising that the heterosis observed was only due to the increased body weight. In general, CS was higher in non-lactating cows and maiden heifers than in lactating cows. The advantage to crossbred genotypes was more pronounced in lactating cows. Among lactating purebreds, CS was significantly (P < 0.05) higher in Belmont Adaptaur (Hereford–Shorthorn, HS) than in Belmont Red (AX), Belmont Brahman cross (BX), and Brahman (Bh). Lactating crossbreds with a common dam breed of HS, AX, BX, and Bh had 19, 33, 21, and 14% greater CS than their respective purebreds. Boran-sired crossbred dams had higher CS than Brahman-sired crossbreds, indicating higher fertility levels of Borans. Significant direct dominance effect for CS in lactating taurine–indicine crosses and in non-lactating taurine–taurine crosses signifies the importance of use of appropriate breed crosses in improving female fertility. Significantly negative (desirable) direct dominance effects for DTC in indicine–indicine and taurine–indicine crosses suggest an advantage from crossbreeding in achieving early calvings. High mortalities were recorded in calves born to HS dams from matings with Brahman bulls due to dystocia. This resulted in low WKS and PWS for HS dam breeds. All additive and dominance effects for calf survival traits were non-significant except for the direct dominance effect in taurine–indicine crosses for PWS. Moderate percentage heterosis estimates in lactating cows for CS and desirable, significant, but low percentage heterosis estimates for DTC were observed. Percentage heterosis estimates for calf survival traits were low and non-significant.

Calving rates in a tropical beef herd after treatment with a synthetic progestagen, norgestomet, or a prostaglandin analogue, cloprostenol

Maiden heifers and lactating cows of known ovarian status and of several breeds were treated with a synthetic prostaglandin, cloprostenol, or a synthetic progestagen, norgestomet, at the start of an artificial insemination (AI) program. Animals in the cloprostenol treatment received 2 injections 10 days apart. Over the next 26 days those animals that showed oestrous behaviour were inseminated. Synchronisation rates and calving rates to insemination over the first 7 days were calculated. Those in the norgestomet treatment received an implant of norgestomet plus an injection of norgestomet and oestradiol valerate. The implant was removed 10 days later and the animals were given an injection of pregnant mare serum gonadotrophin (PMSG). They were inseminated at 48 h (maiden heifers) or 56 h (lactating cows) after implant removal. Calving rates to fixed-time insemination were recorded. After completion of the AI program the animals in both treatments were joined with bulls. Overall calving rates (AI plus bulls) were calculated. By day 7 of the program, 82% of the maiden heifers and 76% of the lactating cows in the cloprostenol treatment had been detected in oestrus. By day 21 the respective figures were 99% and 81%. Norgestomet treatment had an immediate and a prolonged effect on ovarian activity in those females classified as having inactive ovaries at the start of the AI program. Calving rates of those females to fixed-time AI and overall were similar to those of the females with active ovaries in both treatments. Their calving rates to fixed-time insemination, and overall calving rates for the lactating females, were significantly higher than the corresponding values of their contemporaries treated with cloprostenol and inseminated on observed oestrus over 7 days. For those females classified as having active ovaries at the start of the AI program, calving rates to first insemination and overall were similar for both treatments. Overall calving rates of lactating cows of each breed were, with one exception, higher in the norgestomet treatment than in the cloprostenol treatment. Although norgestomet treatment was more expensive than cloprostenol treatment, the advantage in calf crop resulted in an overall monetary advantage to the norgestomet treatment.

Effects of suckling on oestradiol benzoate induced LH release in post-partum, ovariectomised cows

Twelve suckling and 12 non-lactating post-partum cows were treated with a progesterone-releasing pessary for 7 or 14 d followed by an injection of 500 micrograms oestradiol benzoate (ODB) 24 h after pessary removal or no injection. Suckling had no significant effect on plasma progesterone concentrations (plasma P4) or plasma luteinising hormone concentrations (plasma LH) during pessary insertion. After pessary removal plasma LH rose in response to ODB. The extent of the rise was similar in suckling and non-lactating cows treated with progesterone for 14 d but was significantly lower in non-lactating than suckling cows (P less than 0.025) treated for 7 d. These findings indicate that suckling increases the responsiveness of plasma LH in post-partum cows following progesterone and oestrogen treatment compared to non-lactating cows and that extended treatment with progesterone can remove this difference.