11 Effect of breed type on production of bovine embryos: Experience in Paraguay

Abstract

One of the parameters that has the most influence on invitro embryo production programs is the number of oocytes obtained in each follicular aspiration session (ovum pickup; OPU). A significant impact of the breed of the donor on this parameter has been reported. The objective of this work was to compare the parameters of an invitro embryo production program of cows of different breeds in Paraguay. A total of 4811 OPU sessions were performed between 2016 and 2019 in cows classified according to breed and type. Beef-type breeds: Nelore (Bos indicus): n=1569; Aberdeen Angus (Bos taurus): n=1276; and Brangus (Cross): n=182 OPU, and Gyr (Bos indicus): n=1086; dairy breeds: Holstein (Bos taurus): n=401, and Girolando (Cross): n=297. The oocytes were aspirated and transported to the same laboratory located in Asunción, Paraguay. The invitro embryo production protocol was similar in all types. Bull semen tested for IVF was used. The number of oocytes, percentage viability, and percentage embryo production were evaluated. Additionally, the mean and standard deviation of the variables were calculated to show the efficiency of the processes, according to the production aptitude of the donors (meat or milk) and the breed type (Bos indicus, Bos taurus, or crosses). Continuous data were analysed with ANOVA and Tukey’s post hoc comparisons. Categorical data were analysed using Chi-squared at a significance level of 0.05. In this work, the production aptitude had no significant effect over the studied variables. However, some significant differences were found considering the breed type of the oocyte donor cow, as shown in Table 1. When crosses with the pure breeds are compared with their crosses, we found that Brangus produced more pregnancies and a greater number of oocytes/OPU compared with Angus (P<0.05). When the same comparison was made between Girolando and Holstein, no significant differences were found. The results show that Bos indicus breeds and their crosses have a greater capacity to produce more oocytes and embryos and that Bos indicus and crossbreeds were more efficient in producing pregnancies (2-fold) per OPU session than Bos taurus breeds. Additionally, crossing with meat indicus breeds generates better quality embryos and increases efficiency in the system of embryo production. Table 1. Comparison of embryo production parameters Item Breed type Bos indicus Cross Bos taurus Oocytes/OPU (mean±SD) 29.8±2.7a 26.3±7.8a 14.6±1.4b Viable oocytes, % 64.7±3a 64.6±3.4a 60.1±3.1a Embryo produced/OPU, % 35.2±4.7a 32.8±9.4a 26.2±4a Embryo/OPU 6.9±1.7a 5.4±1.7a 2.3±0.4b Pregnancy rate, % 29.6±5.5a 33.1±6.3a 25.3±5a Pregnancies/OPU 2.1±0.9a 1.9±1a 0.6±0.2b a,bValues within a row different letters differ (P<0.05).