Embryonic mortality in buffalo cows

Buffalo species show a tendency to a seasonal reproductive activity and it can be considered a “short day” species. Oestrus cycles occur throughout the year but the frequency of anoestrus and ovarian inactivity is higher and fertility is lower when daylight hours increase. Unfortunately, seasonal reproduction cause an increase of milk availability in autumn winter period while in Italy milk market demand increase in the spring summer period. To avoid market problem, the out of breeding season mating technique is widely applied in Italy and animals are forced to bred mainly in the spring-summer period. Its employment, however, cause longer intercalving periods, a consequent decline in herd fertility and higher culling rate. Also in buffalo, embryo mortality is considered one of the major causes of herd fertility decrease, especially in animals mated when the daylight hours increase. Different trials showed that percentage of embryonic loss in animals mated by artificial insemination (AI) varied between 20% and 40% during seasons characterized by positive photoperiod whereas values of around 7% were recorded in Brazil during decreasing daylight hours. Much of the loss of potential offspring in buffalo seems to occur later than in bovine, between 25 and 40 days from AI and in buffaloes naturally mated its percentage varied between 8.8% and 13.4% respectively at 28-45 days (embryonic mortality) and 46-90 days (foetal mortality) of pregnancy, regardless of conception period. In this trial no differences were found in EM incidence between different conception periods, while a significant high incidence of FM was found in December-March period compared to the April-July period. Embryonic mortality in buffalo species was not affected by age, parity or days in milk and infectious agents explained only about 2-8% of the cases. A reduced capacity to secrete progesterone (P4) seems to explain in part this embryonic mortality but other as yet unidentified factors could contribute between 40-50% to the embryonic losses. Several approaches have been used to increase P4concentration in blood in order to reduce the occurrence of embryonic mortality. Increased P4 plasma levels were achieved either by inducing increased endogenous secretion or by administering exogenous P4. The injection of a GnRH agonist on Day 5 after AI increased milk whey P4 concentrations in 97% of buffaloes subsequently pregnant on Day 40, compared to 68% in the non-pregnant buffaloes (P<0.01). It is however acknowledged that whilst P4 tended to increase on Day 10 in buffaloes treated with buserelin and hCG, its levels were significantly higher than control ones only on Day 15. These findings suggests that hCG and buserelin administration did not act by increasing P4 secretion from the existing corpus luteum but by inducing a new ovulation and the formation of an accessory corpus luteum. A greater (P<0.05) proportion of the buffaloes that ovulated (96.7%), compared to buffalo that did not ovulate (68.4%) recorded a gestational chamber on Day 40 after AI and were judged to be pregnant. Ovulation also increased milk whey P4 levels and reduced embryonic mortality in buffalo cows treated with 1500 I.U. of hCG or 12.6 µg of GnRH agonist on Day 25 after AI.