Impacts of reproductive technologies on beef production in South America.

The majority of beef cow herds in South America are constituted by Bos indicus females, which have particular reproductive features that contribute to reduced reproductive efficiency compared with that of B. taurus cohorts. Hence, several alternatives to enhance reproductive efficiency of B. indicus heifers and cows have been developed to address their inherent reproductive shortcomings. These research-based technologies are being described in detail within this chapter and have already made an impact on South American B. indicus-based production systems. These include the following: (a) hormonal protocols to induce puberty in nulliparous heifers or estrous cyclicity in postpartum cows to maximize their reproductive performance during the subsequent breeding season, (b) hormonal protocols to synchronize estrus and/or ovulation in B. indicus females to exploit their reproductive responses to artificial insemination, and (c) genetic and environmental factors that influence reproductive success in beef herds, including reproductive diseases and excitable temperament of B. indicus females, that have been investigated to support/promote the development of appropriate mitigation technologies.

Treatments to Optimize the Use of Artificial Insemination and Reproductive Efficiency in Beef Cattle under Tropical Environments.

Bos indicus cattle, the preferred genetic group in tropical climates, are characterized by having a lower reproductive efficiency than Bos taurus. The reasons for the poorer reproductive efficiency of the Bos indicus cows include longer lengths of gestation and postpartum anestrus, a short length of estrous behavior with a high incidence of estrus occurring during the dark hours, and puberty at older age and at a higher percentage of body weight relative to mature body weight. Moreover, geography, environment, economics, and social traditions are factors contributing for a lower use of reproductive biotechnologies in tropical environments. Hormonal protocols have been developed to resolve some of the reproductive challenges of the Bos indicus cattle and allow artificial insemination, which is the main strategy to hasten genetic improvement in commercial beef ranches. Most of these treatments use exogenous sources of progesterone associated with strategies to improve the final maturation of the dominant follicle, such as temporary weaning and exogenous gonadotropins. These treatments have caused large impacts on reproductive performance of beef cattle reared under tropical areas.

Intravaginal progesterone device and/or temporary weaning on reproductive performance of anestrous crossbred Angus x Nelore cows.

UNLABELLED: The objective of this experiment was to evaluate effects of treatments with intravaginal progesterone (P4) device and/or 48h temporary weaning (TW) on reproductive performance of postpartum anestrous crossbred AngusxNelore cows, throughout the breeding season (BS). Anestrous cows (n=286; 53+/-5 DPP, body condition score between 2.5 and 3.5, on a 1-5 scale) were assigned randomly to four treatments (2x2 factorial design): (1) CONTROL Group (no treatment; n=73); (2) TW Group (48h TW beginning on day 0 of BS; n=70); (3) P4 Group (Intravaginal P4 device between days -7 and 0 of BS; n=73); and (4) P4+TW Group (Intravaginal P4 device between days -7 and 0 of BS followed by 48h TW; n=70). On day 0 of BS (when P4 devices were removed and TW was initiated), cows had their ovaries evaluated by ultrasonography aiming to evaluate size of the largest follicle. Signs of behavioral estrus were observed twice a day (morning and evening), between days 0 and 25 of BS, and cows observed in estrus were inseminated 12h later. Between days 26 and 80 of BS, cows were submitted to natural service. Pregnancy diagnosis was conducted by transrectal ultrasonography on days 32 and 53 (pregnancies by AI) and 114 (pregnancies by natural service). Rates of detection of estrus during the first 3 days and within 25 days of BS were greater in cows receiving TW (45.0% compared with 9.6% and 50.0% compared with 29.5%, respectively; P<0.01). Conception rate in cows inseminated in the first 3 days of BS was greater in cows treated with P4 (54.8% compared with 11.1%; P<0.01). Combining P4+TW increased pregnancy rate in the first 3 days ( CONTROL: 1.4%, TW: 4.3%, P4: 8.2% and P4+TW: 24.3%; P<0.01) and in 25 days of BS (CONTROL: 10.9%, TW: 7.1%, P4: 13.7% and P4+TW: 28.6%; P<0.05). Pregnancy rate at the end of BS did not differ among treatment groups. In conclusion, TW alone increased estrous behavior whereas P4 alone benefited conception. Combining P4 with TW improved pregnancy rate with direct benefits to behavioral estrus and conception.

Effect of progesterone and/or estradiol treatments prior to induction of ovulation on subsequent luteal lifespan in anestrous Nelore cows.

Three experiments evaluated effects of estradiol (E(2)) and/or progesterone (P(4)) prior to induction of ovulation with GnRH on subsequent luteal lifespan in anestrous Nelore cows. In Experiment 1, cows (25-65 days post-partum [DPP]; n=114) were assigned randomly to receive a 6-day treatment with an intravaginal P(4) device (CIDR) and/or 1mg i.m. injection of 17beta-E(2) (4 groups; 2x2 factorial design) prior to ovulation. Blood samples were collected on days 0, 5, 7, 9, 12, 15 and 19 for evaluation of luteal function. Pre-treatment with P(4) reduced occurrence of premature luteolysis (PL; 79.2% in non-treated vs. 13.5% in treated cows; P<0.01), but there was no effect of treatment with 17beta-E(2) on percentage of PL. In Experiment 2, cows (30-40 DPP; n=35) were assigned randomly to receive either 0.5mL i.m. injection of cottonseed oil (placebo) or 1mg i.m. injection of E(2) cypionate. Blood samples were collected on days 0, 5, 9 and 15 for evaluation of luteal function. Incidence of PL (83.0% in Control Group vs. 75.0% in ECP Group; P>0.1) and mean serum P(4) did not differ between treatment groups. In Experiment 3, cows (30-60 DPP; n=109) were randomly assigned to receive either a 6-day (6-d Group) or a 3-day (3-d Group) treatment with CIDR. Blood samples were collected on days 0, 5, 7 and 9 for luteal function evaluation. Incidence of PL (5.5% in 6-day vs. 5.5% in 3-day groups; P>0.1) and mean serum P(4) did not differ between treatment groups. In conclusion, both 3- and 6-day treatments with P(4) prior to induction of ovulation in anestrous Nelore cows increased percentage of normal luteal lifespan, while administration of 1mg of 17beta-E(2) or E(2) cypionate failed to prevent occurrence of PL.