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.

Peripartal changes of estrone, progesterone and prostaglandin in the water buffalo.

The peripheral blood plasma concentration of estrone, progesterone and 15-keto-13, 14-dihydroprostaglandin F2alpha (PGF2alpha metabolite) were determined by radioimmunoassay techniques during the peripartal period in 5 buffalo cows belonging to a river type breed. Estrone levels started to increase from below 200 pg/ml about 15 days prior to parturition, and reached high concentrations (400-750 pg/ml) during the last 5 days of pregnancy. The estrone concentration decreased to baseline levels after delivery. The concentration of progesterone fluctuated between 800 and 2000 pg/ml until 15 days before calving and showed a gradual increase during the last 15 days of pregnancy. The progesterone levels declined abruptly on the day of calving and remained below 100 pg/ml for up to 60 days post-partum. Increased levels of the prostaglandin metabolite were recorded from 15 days prior to parturition with further increases occurring during the last 3 days of pregnancy. PGF2alpha metabolite levels declined gradually after parturition, reaching base line levels 15-20 days after calving.

Early pregnancy diagnosis in buffaloes from plasma progesterone concentration.

Blood samples were collected from 84 buffalo cows 21 days after fixed time artificial insemination following oestrus synchronisation and cloprostenol. Progesterone concentration in plasma was determined by radioimmunoassay. The animals were examined for pregnancy by rectal palpation 60 to 90 days after insemination. Forty-two animals were predicted pregnant on the basis of progesterone concentration (more than 1.0 ng per ml), and 28 (66.7 per cent) of them were subsequently confirmed pregnant by rectal palpation. Thirty-five animals were predicted non-pregnant (progesterone less than 0.7 ng per ml), in 34 (97.1 per cent) this proved to be so. Of the total number, seven (8.3 per cent) were classified as doubtful because their progesterone concentrations were within the range 0.7 to 1.0 ng per ml: two of them were confirmed pregnant and the other five non-pregnant. Out of 31 animals diagnosed pregnant by rectal palpation, 28 (90.3 per cent) had been correctly detected by assay at 21 days. Thirty-four (64.2 per cent) of the 53 animals found non-pregnant had been correctly detected by assay. It was concluded that the determination of plasma progesterone concentration 21 days after insemination was an accurate method of predicting non-pregnancy in buffaloes.