173 Pregnancy rates in suckled beef cows synchronised with progesterone/oestradiol-based protocol and inseminated with conventional or sexed-sorted semen
Authors: Huguenine E. , de la Mata J. , Menchaca A. , de Carneiro R. L. R. , Bo G. A. 
Published: December 2019

An experiment was designed to evaluate pregnancy rates per AI (P/AI) in suckled beef cows synchronised with a progesterone (P4)/oestradiol-based protocol and AI with non-sexed (conventional) semen and with a sexed-sorted semen with 65% X-bearing sperm and 35% Y-bearing sperm that was named SuperConventionalTM. Angus and Hereford suckled cows (n=558), 60-90 days postpartum, with a body condition score of 2 to 3.5 (1-to-5 scale) and 48% (269/558) with a corpus luteum, were randomly allocated to be AI with non-sexed (conventional) or SuperConventional semen. The experiment was performed on 3 farms using straws with sexed-sorted SuperConventional semen containing 6 or 8 million sperm and non-sorted conventional semen with 25 million sperm per straw. Semen was from split ejaculates from two Angus bulls. All cows received a P4 device with 0.6g of P4 (Pluselar, Calier) and 2mg of oestradiol benzoate (Calier) on Day 0. All P4 devices were removed on Day 8, and all cows received 400IU of equine chorionic gonadotrophin (Vetegon, Calier), 150µg of d+cloprostenol (Veteglan, Calier), and 1mg of oestradiol cipionate (Calier) at the same time. All cows were also tail-painted and observed for signs of oestrus. Cows with &gt;30% of the tail paint rubbed off by 48-50h after P4 device removal were AI at that time with either SuperConventional or conventional semen. Those not showing oestrus by 48-50h received 10µg of buserelin (Pluserelina, Calier) at that time and were AI with either SuperConventional or conventional semen 50-52h after P4 device removal. Pregnancy was diagnosed using ultrasonography 60 days after AI, and all pregnancies were sexed to determine the proportion of female pregnancies. Data were analysed using GLM for binary data. The P/AI were different between cows showing or not showing oestrus (P&lt;0.01) but did not differ among the three types of semen used (Table 1). The percentage of cows pregnant with female fetuses was 51% (50/98) for cows AI with conventional semen and 65.5% (55/84) and 65.3% (51/78) for those AI with SuperConventional semen with 8 million or 6 million sperm per straw, respectively. In conclusion, sexed-sorted semen with 65% of X-bearing sperm and 6 or 8 million sperm per straw can be successfully used to inseminate suckled beef cows. Furthermore, results confirm those of previous studies that cows in oestrus at the time of fixed-time AI have higher pregnancy rates than cows not in oestrus in P4/oestradiol-based synchronisation programmes.

Table 1.Effect of semen type and oestrus expression on pregnancy rates per AI in suckled beef cows synchronised with a progesterone/oestradiol-based protocol

Semen type
In oestrus,% (n)
Not in oestrus,% (n)
Total,% (n)

Conventional (25 million sperm)
59.8 (82/137)a

32.0 (16/50)b

52.4 (98/187)

SuperConventional (8 million sperm)
53.7 (73/136)a

20.0 (10/50)b

44.6 (83/186)

SuperConventional (6 million sperm)
50.4 (63/125)a

26.7 (16/60)b

42.7 (79/185)

Total
54.8 (218/398)a

26.3 (42/160)b

a,bDifferent superscripts denote differences in pregnancy rates per AI between cows in oestrus and not in oestrus by the time of fixed-time AI (P&lt;0.01).

Research was supported by Fondo Nacional de Ciencia y Tecnología (FONCYT PICT 2017-4550) and UNVM.