[en] Poor bovine reproductive efficiency in tropical climates could explain why areas with these conditions account for only 50 and 25% of the world's beef and milk production, respectively. The marked influence of season on reproduction in the tropics is reflected in reduced oestrus detection and calf survival, as well as later onset of ovarian activity during the winter months under range conditions. Lack of knowledge of some of the basic mechanisms that regulate reproductive physiology in farm animals in the tropics has restricted use of techniques such as artificial insemination, thereby limiting genetic progress. From our data we have detected differences in oestrous behaviour, hormonal levels during the oestrous cycle and fertility when comparing our results with the information already available for bovines in temperate areas. (author)

[en] Traditionally, cattle raised under the tropical conditions of the lowland tropics have been dedicated to beef production. However, in the last years, considerable interest has been given to milk production. Hence, the logical step has been the development of dual purpose cattle, thus avoiding losing the income generated by the sale of beef. This concept is particularly important, as the introduction of specialised dairy breeds has mainly proved an unsatisfactory solution to increase milk production in the area. Dual purpose systems, however, have been limited due to poor reproductive performance and are facing considerable dilemmas such as: a) degree of heterosis needed in the cattle for optimal production and adaptability to the tropics; b) suitable management systems, i.e. dual purpose cattle where the main income is beef and milk production is just an added bonus, or conversely, where milk is the main income for the farmer; c) insufficient economical resources of the farmer, those with only subsistence levels as opposed to farmers with certain investment capacity; d) choice of breeding systems, artificial insemination versus natural mating; e) implementation of feeding practices, capacity to implement strategic supplementation in contrast to cattle raised almost exclusively at pasture; and f) adequate marketing of dairy products in the tropics. These considerations related to the strength and weaknesses of dual systems are discussed in this review. (author)

[en] Several researchers have provided sufficient evidence to sustain that the best crossbreeding program to produce milk in the tropics is the direct cross between Bos Taurus and Bos indicus (F1). The problem arises when the farmer faces the challenge to breed the crossbred animal. If the choice is to cross with Bos Taurus the resulting product is quite vulnerable to the harsh environmental conditions in the tropics. If, on the other hand, the selection is to sire with Bos indicus then the offspring will be deficient in milk production. Another alternative is to transfer F1 embryos to F1 dams, hence avoiding the hazards of crossbreeding. Although the technique of embryo transfer (ET) has been available for many years, there are several pitfalls at least under tropical conditions, which need to be considered. Selection of recipients for embryo transfer: The first one is related to the selection of the recipients. These are usually animals displaying spontaneous oestrus or treated with drugs to synchronize their oestrus. The short comings of either of these methods have been experienced by Montiel et al. In short, the use of spontaneous oestrus is time consuming and inaccurate and the response to oestrus with an ensuing ovulation can be as little as 30% if the animals selected are not in reasonable body condition. Embryo transfer programs in small community farms can be tricky because the selection of recipients is restricted to a few animals in the herd and the distance between farms can pose a serious threat to the success of the program. Thus, just because of this constraint, several government programs have ceased to be functional when the subsidy runs out. Production of embryos (F1): The main components of successful embryo production can de divided into three. The quality of the superovulatory response in the donor cow, the ability of the individual to recover as many embryos as possible and the accuracy of the technician to judge the quality of the embryo destined for freezing which has proven to be a difficult task at least under tropical conditions. In relation to the former, figures for embryo production can vary enormously, although some groups demand that the number of good quality embryos cannot be less than eight. However, others have not been so successful. In short, the superovulatory response can be directly related to the follicular dynamics now of treatment. The recovery of embryos can be difficult especially as it has been reported that almost 30% of the donor cows have curved cervices increasing the difficulties in negotiating the catheter. Embryo production can be affected if the conditions are not favourable, in a detailed study, Marquez et al., showed that the number of healthy embryos evaluated by their resistance to freezing and their degree of apoptosis, was affected if the embryos were produced in the spring or the autumn. Economical feasibility of ET among small community farmers: Government organizations in developing countries have launched initiatives to popularize the evident benefits of ET, particularly in enterprises not bigger than 50 cows per unit. These programs have experienced a high degree of acceptance, especially those with a substantial subsidy. However, when the program folds UP, it has proven not to be sustainable for the farmers themselves, thus disappointment is the natural course of events. In a recent study found the estimation of the cost involved in the preparation of the donor and embryo recovery was about US 600.00. The average number of embryos recovered was 3.8. Taking into consideration the cost of gestation, calculated by the percentage of animals pregnant (27%); the cost for preparing the donor, the technique of embryo transfer and the cost of production of the embryo itself, the overall cost per gestation was $1320. Considering a 50-50 ratio of males-females born, the cost for a replacement heifer was 2640 dollars, which surpassed by far the commercial cost of a crossbred heifer (approximately 900 dollars). Considering the difficulties in distributing F1 embryos among farmers in small enterprises, the cost of production and the low success rate found in terms of fertility, for the time being IT does not seem profitable for farmers themselves to sustain a program of this investiture. Government organizations would need to play a more active and systematic role to ensure the reduction of the costs inherent embryo transfer techniques. (author)

[en] Studies designed to evaluate the publication and research trends of Third World countries in areas related to cattle reproduction in the tropics have shown a marked tendency for publication in such forms as national journals, proceedings, annual reports and theses, which are not readily available for evaluation and assimilation by the scientific community in general. This, coupled with the fact that reports are published preferentially in the native language of the country concerned, contributes to the limited impact of these studies at international level. In addition, research is concentrated on topics which require relatively simple methods important for establishing local reproductive parameters. With regard to the publication output of researchers, it was found that the majority publish only one document, with less than 3% producing more than ten, over a 15 year period. On average, researchers publish over a period of less than five years, indicating a lack of continuity in the research effort in this field. A detailed analysis of the research carried out in Mexico revealed a considerable degree of repetition of studies, as well as the publishing of duplicate results. (author). 14 refs, 1 fig., 4 tabs

[en] In order to evaluate the efficacy of oestrus detection procedures and to measure fertility following insemination, monthly visits were made to two Zebu herds to carry out rectal examinations for pregnancy diagnosis and to assess ovarian activity post-partum. During each visit, the percentage of cows inseminated during that month was calculated, on the basis of the number of cows eligible for insemination (i.e. non-pregnant cows >40 days post-partum that had not been inseminated). To evaluate the efficacy of oestrus detection, the percentage of cows inseminated within the next 15 days following the detection of a corpus luteum (CL) was calculated. Oestrus synchronization programmes were carried out in one farm using prostaglandin F₂ or slow releasing progestagen devices. Differences in reproductive response were found between farms; days from calving to the appearance of a palpable CL were 166 and 100 for farms A and B respectively, days from calving to first insemination 167 and 107 respectively, and calving interval 17.1 and 14.8 months respectively (P < 0.01). However, there was no difference in the number of services per conception, the average for the two farms being 1.6. On average, only 17% of those eligible were inseminated and only 39% of the animals detected with a CL were subsequently seen in oestrus. Higher percentages of cows were observed in oestrus during the spring and summer (30 and 33% respectively) than in the winter (21%) and autumn (15%) (P < 0.05). The percentage of cows detected in oestrus increased as the study progressed. No significant differences were found in conception rate following a synchronized oestrus (average 29.7%), regardless of the method used. (author). 21 refs, 3 tabs

[en] A series of experiments were conducted to test the efficacy of drugs used to synchronize oestrus in Zebu cattle. Fertility (conception rates) in adult cows following synchronized (PGF_2α) and non-synchronized oestruses and AI were found to be 22% and 27% respectively; fertility after natural mating (NM) was 47% for cows synchronized with PGF_2α and 41% for control animals. After a 60 day breeding period NM groups were 13% more fertile overall than the AI groups (P<0.05). Fertilized eggs could only be recovered from cows exhibiting signs of oestrus. In a large field trial which involved the use of norgestomet implants, oestrus expression and fertility were significantly less in nursing cows that were not cycling than in those not nursing and not cycling (P<0.05). When norgestomet, a slow progesterone releasing device and PGF_2α were compared in the same herd, no differences in fertility were found, although groups treated with progesterone showed a higher incidence of oestrus than those administered PGF_2α (60 vs. 27%, P<0.01). (author). 22 refs, 1 fig., 6 tabs

[en] Various factors affect reproductive performance in tropical cattle. The time of year when the animal is born, the season when breeding programmes are established, the breed and parity of the animals selected, management decisions and the body condition of the females before breeding are the most common factors that determine the success of farmers in the tropical areas of the world. Examples of these components are reviewed and areas for future research suggested. (author). 29 refs, 3 figs, 2 tabs

[en] Four main aspects of embryo technology are dealt with in this paper. The first analyses the reasons for the poor selection of recipients for embryo transfer, the second relates to inaccurate evaluation of embryos at least under tropical conditions, the third proposes alternative methods to evaluate embryos for selection and freezing, and the fourth analyses the feasibility of establishing this technique as a biotechnology approach for improving production in small community tropical farms. (author)

[en] To evaluate artificial insemination (AI) services and reproductive efficiency in dairy herds in Uruguay two surveys were conducted in 1995 and 1996. The 1995 survey was done in 10 dairy farms of 3 regions on 696 lactating Holstein cows. The 1996 survey was done in 5 dairy farms in one region and included 768 cows. Precision of oestrus detection and efficiency of AI services were determined by milk progesterone samples taken at days 0, 10 and 23 after breeding and by analysis of the records. In 1995 and 1996, the intervals from calving to first service were 123 and 101 days, and to conception were 158 and 134 days, respectively. Parity, body weight and body condition at calving influenced these parameters, but not body weight or body condition at breeding nor milk production. Accuracy of pregnancy diagnosis by milk progesterone was 70.4%. Heat detection rate was 37.5% and pregnancy rate was 15.6%. In 1997 a second study was done to determine the factors affecting reproductive efficiency in a seasonal breeding AI programme in 328 lactating cows on 3 dairy farms. Milk progesterone measurement revealed that 12.5% of the cows were anoestrous at the beginning of the season and remained so during the trial. The category mostly affected were first-calf heifers (82%). Also, 8.5% of the cows cycling were never reported in heat and this was influenced by farm. Oestrus detection efficiency for cows determined to be cycling by progesterone profiles was evaluated in three periods of 21 days and overall efficiency was 46.9%. Main factor affecting it was farm, with an effect of parity (67.8% in mature cows and 33.2% in first-calf heifers) but no effect of days postpartum. Mean interval from the beginning of the breeding season to first service was 27.4 days, again with a strong farm variation but no effect of parity or days postpartum. In an attempt to improve reproductive efficiency in lactating dairy cows, a treatment protocol was designed, where 414 cows in two herds were synchronised with a combination of gonadotrophin releasing hormone (GnRH) + medroxyprogesterone acetate (MAP) on Day 0 and prostaglandin F_2α (PGF) + MAP removal on Day 7, followed by oestrus detection and AI. In Farm A, besides the traditional twice per day (AM/PM) oestrus detection, a third period of observation was included at noon. Progesterone was measured in milk samples to monitor treatment response and to evaluate oestrus detection precision. Interval from PGF to heat was reduced in the farm with three times per day oestrus detection system (6.1 vs. 13.2 days). It was concluded that losses in reproductive efficiency in dairy farms of Uruguay in a seasonal AI programme were mainly due to failure rather than incorrect oestrus detection. More oestrus observation periods improved the response to the synchronisation treatment. (author)